2.6 results of technologies screening and … · ards but will reduce the likelihood of present or...

Off-site disposal will contain similar items, but. includethe transporteition and off-site disposal costs. Both tech-nologies involve very high capital costs.

2.6 RESULTS OF TECHNOLOGIES SCREENING AND REMEDIAL ACTIONALTERNATIVES DEVELOPMENT

The screening of the remedial action technologies performedin the previous sections is summarized in Table 2-3. Thetechnologies that have been retained after screening arelisted below:

- JP-No Remedial Action - Monitoring only **•Low Permeability Soil CapMultilayered CapRegradingr Diversion Ditches, & Revegetation (SiteManagement)Gas Interception and VentingDowngradient PumpingUpgradient Controls-Pumping or Interception TrenchGravity SettlingLime Treatment SystemActivated CarbonFiltrationChlorinationOn-Site IncinerationOff-Site Treatment - Local WWTPComplete Removal - RefusePartial Removal - RefuseOn-Site Disposal - Landfilling of the Western Partof the Landfill on the Eastern Part

• Off-Site Disposal - New Landfill

The technologies listed above will be combined in the devel-opment of the alternatives. The remedial action alter-natives are formulated to address the site environmentalissues and containment pathways through the . screenedtechnologies, and to meet both the alternative screeningcriteria and the site-specific remedial action objectives.

The process of remedial action alternative developmentfollows the steps outlined below:

2-67

Alternative development begins with thetechnologies that have been retained afterscreening.

Technologies are combined that are complementaryand interrelated; for example:

o Surface Capping - Site Regra$Hng and SurfaceWater Diversion - Gas Venting **

o Groundwater Controls that involve pumping -Treatment of Discharge - Monitoring

o Partial Removal - On-Site Disposal - Regrading,-- Backfilling and Surface Water Diversion -Surface Capping - Gas Venting

The alternatives are then formulated from thegrouped technologies and determining which arebest suited to the site and address the siteproblems and containment pathways identified inTable 2-4.

Alternatives are to address the Remedial ActionAlternative objectives listed below:

o Maintain public health and safety

o Protect and restore the quality of New CastleCounty's water resources

o Provide private, industrial, and municipalusers with potable water.

o Ensure technical feasibility, publicacceptability, and cost effectiveness of the

• remedial actions.

Not all the alternatives formulated will meet allthe objectives or be as effective in addressingpart or all the site problems and contaminantpathways.

As part of the Feasibility Study at least onealternative for each of the following categoriesmust at a minimum, be evaluated.

(a) Alternatives for treatment or disposal at anoff-site facility approved by EPA (including

2-68 SR30

TABLE 2-4

SITE ENVIRONMENTAL ISSUES GROUPED SCREENEDAND CONTAINMENT PATHWAYS TECHNOLOGIES

- •*• Residential well located 900 ft. - No Aoifrion - Monitoringfrom the Landfill became con- - Community Water Treatmenttaminated by leachate generatedby the; Landfill.

• Leachate contaminated groundwater - Downgradient Pumping -began migrating down gradient to Treatment - Monitoringa well field providing water forlocal communities.

• Water enters the landfill site intwo waiys:

Direct precipitation infiltration - Surface Capping - Regrad-through the landfill. The ing, Diversion Ditches,present landfill soil cover is Revegetation - Gas ventinga granular, very permeablematerial. Differential settle-ment has created depressionswhich act as collection areas,and

Lateral movement of groundwater - Upgradient Pumping - Treat-into the bottom of the landfill ment - Monitoringfrom the Columbia Formation on - Partial removal - Disposalthe western side of the landfill. on-site - Surface cappingThis groundwater can then enterthe Potomac Formation where thePotomac clay layer was removed oris naturally thin.

• Discharge of recovered groundwater - Physical - Chemical treat-should address treatment needs ment on-site (Gravity settl-

ing, Lime Treatment System,Activated Carbon, Filtrationand Chlorination).Off-Site Treatment, LocalWWTP

2-69

RCRA, CWA, CAA, MPRSA, and SDWA approvedfacilities), as appropriate;

(b) Alternatives which attain applicable andrelevant Federal public health or environment-al standards;

(c) As appropriate, alternatives which exceedapplicable and relevant %&blic health orenvironmental standards?

(d) Alternatives which do not attain applicable orrelevant public health or environmental stand-ards but will reduce the likelihood of presentor future threat from the hazardous sub-stances . This must include an alternativewhich closely approaches the level of protec-tion provided by the applicable or relevantstandards and meets CERCLA's objective ofadequately protecting public health, welfare,and environment.

(e) A No Action Alternative.

6. The following criteria is then used in thescreening and evaluation of the developedalternatives:

Initial Screening

- Environmental and Public Health- Cost Factors

Analysis

Non-Cost Analysis^ Technical Feasibility- Environmental Evaluation- Institutional Requirements- Public Health Evaluation Cost Analysis

In summary, the cost-effective alternative is defined as thelowest cost alternative that is technologically feasible andreliable, effectively mitigates or minimizes damage, andprovides adequate protection of public health, welfare, andthe environment (NCP, 19855. Alternatives were developed fayapplying the technologies to the site singly or in combina-tion, based on the previously developed remedial objectives.

AR300S92

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The NCP specifies that remedial alternatives, besides fill-ing each of the categories, should be classified either assource control (40 CPR 300.68(e)(2)) or off-site (managementof migration) remedial actions (40 CFR 300.68(e)(3)).Source control remedial actions address situations in whichhazardous substances remain at or near the areas in whichthey were originally located and are not adequately con-tained to prevent migration into the environment. Manage-ment of migration remedial actions address ij -tuations inwhich the hazardous substances have largely migrated fromtheir original locations. Alternatives developed may fallsolely in either classification or may involve a combinationof source control and management of migration measures, asdetermined by the specific site problems addressed. Table2-5 displays the source control and management of migrationalternative that have been developed for the Army CreekLandfill site.

2.6.1 Treatment of Contaminated Groundwater -A Separate Analysis

The treatment of groundwater pumped by the recovery wellswill be evaluated as a separate analysis from the altern-ative evaluation. All of the source control alternativesinclude downgradient pumping to address the priority require-ment of preventing the contaminant plume from migrating todowngradient production wells. Whether the recovery wellsare to be operated during the initial phases of an alterna-tive or for a longer term, discharge from these wells willrequire some form of treatment. Several treatment schemesand different levels of treatment may be appropriate at theArmy Creek Landfill site. Several permutations to eachalternative would then be possible. This is better handledin a separate analysis.

The status of site discharge permits and the treatment needsof the adjacent Delaware Sand & Gravel Site will not befully resolved before this study is completed. This is anadditional reason for evaluating treatment schemes separatefrom the developed remedial action technologies.

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TABLE 2-5

DEVELOPED REMEDIAL ACTION ALTERNATIVES

SOURCE CONTROL - *

1. No ActionMonitoring Only

2. Downgradient Pumping* Monitoring•~ Discharge to appropriate treatment

3. Landfill Capping• Site Regrading and Surface Water Diversion• Gas Collection and Venting

Downgradient Pumping* Monitoring• Discharge to appropriate treatment

4. a) Phased ApproachPhase 1:

Landfill Capping• Site Regradincj and Surface Water Diversion• Gas Collection and Venting

Downgradient Pumping• Monitoring• Discharge to appropriate treatment

• fPhase 2:

Upgradient Pumping• Monitoring• Discharge to appropriate treatment

b) Same as Alternative 4(a) but is a non-phasedapproach i.e. everything is implemented at the sametime.

5. Partial Removal and Disposal On-Site• Regrading, Backfilling, Surface Water

Diversion

Landfill Capping - Multilayer __Cap• Gas Collection and Venting

Downgradient Pumping flji300* Monitoring• Discharge to appropriate treatment

2-72

TABLE 2-5 (continued)

DEVELOPED REMEDIAL ACTION ALTERNATIVES

On-Site Incineration - Refuse Treatment• Complete Removal• Dewatering of Refuse by Upgradient Pumping

*- MDowngradient Pumping• Monitoring• Discharge to appropriate treatment

Off-Site Disposal by Landfilling on Approved Site• Complete Removal of Landfill• Dewatering of Saturated Refuse by Upgradient

Pumping

Downgradient Pumping• Monitoring* Discharge to appropriate treatment

II. MANAGEMENT OF MIGRATION

8. Treatment of Community Wells

Landfill Capping• Regrading & Surface Water Diversion• Gas Collection & Venting

2-73

SECTION 3

DISCUSSION OF THE REMEDIAL ACTION ALTERNATIVES

3.1 INTRODUCTION

The following sections present a discussion of each of thealternatives developed in Section 2.6 . Ar^gumnary of thetasks completed to date as a result of the Round TableConference will also be presented at the end of thissection. Section 4 involves the screening of remedialalternatives based on environmental and public healthcriteria, followed by an "order of magnitude" costscreening. This two-step screening permits an initialassessment of the applicability of each alternative relativeto the others.

3.2 DISCUSSION OF ALTERNATIVES

3.2.1 Source Control Alternatives

The following discussion of source control alternativesaddresses only the Army Creek Landfill as the source ofcontamination. Various other sources (including theDelaware Sand and Gravel Landfills) exist in the immediatearea of the Army Creek Landfill and these other sources maybe introducing contamination to the environment.

3.2.1.1 Alternative 1 - No Action - Monitoring Only

The purpose of presenting a No Action Alternative is toprovide a basis for comparison of existing conditions withthe other proposed remedial alternatives. Under the NoAction Alternative, no additional remedial activities willbe taken and any current activities will be terminated atthe Army Creek Landfill site. This would mean that thepresent hydrologic divide between the ground watercontaminant plume and the Artesian Water Companies' wells,maintained by the recovery well system, would be eliminated.

This alternative includes a long-term monitoring program toprovide information concerning contaminant presence andconcentration. Ground water monitoring will be performedbetween the landfill and Artesian Water Company wells andwithin the wellfield. Figure 3-1 illustrates the site

G

3-1

environmental issues and conditions associated with the NoAction Alternative.

3.2.1.2 Alternative 2 - Downgradient Pumping

• Monitoring* Discharge to Appropriate Treatment

This alternative consists of continuing the^downgradientground water recovery program with discbjfcrge of therecovered contaminated ground water to an appropriatetreatment system. A long-term ground water monitoringprogram will also be included in this alternative.

Alternative 2 basically continues the present remedialactions. A RCRA-type cap is not addressed in thisalternative. This alternative therefore, does not attainall applicable or relevant public health or environmentalstandards for an NPL site, but does reduce the likelihood ofpresent or future threats to drinking water supplies fromthe contaminated ground water. Figure 3-2 illustrates thisalternative.

3.2.1.3 Alternative 3 - Landfill Capping and DowngradientPumping

Landfill Capping - Low Permeability Soil Cap

• Installation of a Low Permeability Soil Cap• Site Regrading and Surface Water Diversion• Gas Interception and Venting

Downgradient Pumping

• Monitoring• Discharge to Appropriate Treatment

This alternative consists of capping the landfill with a lowpermeability soil cap and continuing the downgradientpumping and monitoring program. Capping the landfill with alow pearmeability soil cap will significantly reduce thewater entering the landfill by precipitation infiltration.Capping includes site regrading and placement of cleanbackfill which will eliminate surface depressions, flattensteep unstable slopes, and create drainage ditches andswales to divert surface water away from the site. A gas

R3

3-3

tI

3-4

interception and venting system will be installed as part ofthe capping program 'to prevent methane gas migrationoff-site.

The downgradient punping system will be continued tomaintain the ground water divide. Discharge of therecovered ground water will be to appropriate treatment. Along-term monitoring program is included with thisalternative* With the possible exception of the impacts ofground water entering the northwest corner /bottom of thelandfill, this alternative could attain appli ble andrelevant Federal public health and environmental standards.Figure 3-3 illustrates this alternative.

3.2.1.4 Alternative 4a And 4b - Capping and GroundwaterPumping

4a) Phased Approach

Phase 1: Landfill Capping

• Placement of a Surface Cap• Site Regrading and Surface Water

Diversions• Gas Collection and Venting



Phase 2: Upgradient Pumping


Two approaches to Alternative 4 are proposed. The first isa phased approach consisting of two phases. Phase 1includes the capping of the landfill with a surface cap tosignificantly reduce the rainfall infiltration. The sitewill be regraded and clean backfill placed to eliminatesurface depressions. Drainage ditches to divert surfacewater away from the landfill will be constructed. A gasinterception and venting system will be installed along withthe installation of the cap. Phase 1 also includes thecontinuation of the downgradient punping system which issuccessfully containing the contaminant plume.

fiRSOOSOO3-5

The relative amount of contaminants being contributed viaground water movement through the northwest corner of thelandfill is not known. Consequently, the effectiveness ofreducing ground water movement through the landfill viawater table drawdown is not known. Monitoring of thedischarge and water levels of the recovery wells and samplesfrom existing monitoring wells will initiate or eliminatePhase II, Contaminant levels and ground^ water levelsmonitored over a reasonable period of time will ndicate the^effectiveness of the surface cap and will help assess theneed to install an upgradient controls. The Upgradientcontrols will draw down the water table and reduce theground water entering the site on the northwestern side ofthe landfill, thereby reducing leachate generation. Thisalternative will attain applicable and relevant Federalpublic health and environmental standards*

4b) Non-Phased Approach

This alternative differs from Alternative 4a only in itsapproach. In Alternative 4b all activities will beinitiated at relatively the same time. Cost analysis willdistinguish this alternative from 4a. Figure 3-4illustrates these two approaches.

3.2.1.5 Alternative 5 - On-Site Disposal and Downgradientpumping

Partial Removal and Disposal On-Site

• Excavation of waste from the western part of thelandfill.

• Deposition of the excavated waste on the easternpart of the landfill.

• Regrading, backfilling, surface water diversion

• Dewatering of western landfill by upgradientpunning Jrandfj;fc3r* Capping.

--• Placement of a surface cap over the eastern part ofthe landfill. .

• Gas collection and venting Downgradient Puirping

• Monitoring

• Discharge to Appropriate Treatment

3_7 AR300602

Alternative 5 consists of complete removal of waste in thewestern part of the landfill, disposing of the wastematerial on the eastern side, and then capping the easternlandfill. The removal of the western part of the landfillwill eliminate a possible source of leachate generation fromground water infiltrating the northwestern border/landfillbottom and coming in contact with the refuse. Precipitationinfiltration through the landfill is addresae€ by placing asurface cap on the eastern landfill. AlternatWfe 5 includesthe continuation of the downgradient pumping program withmonitoring of ground water quality. By removing the wastefrom contact with the ground water and infiltration,leachate generation could be significantly reduced. Asground water quality improves, downgradient punping may begradually phased out over the long-term.

Before the saturated material in the western landfill iscompletely removed, the bottom portion will requiredewatering. A system of upgradient well points can beinstalled to perform the dewatering. The excavated refusemust be properly compacted when placed on the eastern sideto avoid the settling problem that characterizes theexisting landfill. The site will be regraded and the westside backfilled. Drainage ditches and swales will divertsurface water away from the landfill.

This alternative is expected to eventually exceed applicableand relevant Federal public health and environmentalstandards. Significant odor problems can be expected aspart of the excavation activities. Figure 3-5 illustratesthis alternative.

3.2.1.6 Alternative 6 - On-Site Incineration andDowngradient Pumping

Incineration - On-Site Refuse Treatment

• Complete Removal• Construction of on-site incineration facility

---• Incineration of excavated waste.• Backfill of incineration ash on-site.

Downgradient Punping

• Downgradient of excavated waste• Monitoring• Discharge to Appropriate Treatment

3-9

COWU.TJIKI3

Thisv alternative consists of the construction of anincinerator and power generator facility adjacent to thesubject site, and then excavating and incinerating thewaste, and backfilling the ash residue on-site. In orderfor this alternative to be feasible, the excavated landfillwastes at the site must be mixed with raw-solid waste fromnearby communities to produce a combustible mixture.Otherwise, the fuel requirements for burning'j he wet wastewill be~ "very excessive. Excavation of the saturatedmaterial in contact with the water table on the western sideof the landfill will require dewatering. This can beachieved by upgradient pumping. The discharge from thedewatering operation may require treatment.

This alternative includes continued downgradient pumping toassure that contaminated ground water does not reach theArtesian Water Company wellfield. A long-term ground watermonitoring program will determine when the downgradientrecovery system can be phased out after the landfill hasbeen removed and incinerated. Discharge from the recoverywells will be directed to an appropriate treatment system.This alternative is expected to eventually exceed applicableand relevant public health and environmental standards.

3.2.1.7 Alternative 7 - Off-Site Disposal and DowngradientPumping

Off-Site Disposal by Landfilling on Approved Site

• Complete removal of waste from the landfill• Hauli ng of the excavat ed waste to a permi tted

off-site disposal facility.• Backfilling of the excavation.


• Monitoring• Discharge to appropriate treatment

This alternative consists of completely removing the land-filled waste by standard excavation methods and disposing ofthe waste in an off-site approved facility. Upgradientpumping has been included for anticipated dewatering forexcavation of the saturated material in the bottom of the

R300606

3-11

western part of the landfill. The landfill area would bebackfilled, following complete excavation of the wastematerial. This alternative eliminates a source of leachategeneration (refuse) and thus eliminates toe addition ofcontaminants to the ground water.

This alternative includes a downgradient pumping programwith discharge to an appropriate treatment system.Monitoring of the recovery system will dete'rlftne when thesystem can be phased out after complete removal of thelandfill. This alternative is expected to eventually exceedapplicable and relevant public health and environmentalstandards.

3.2 DISCUSSION OF THE TASKS COMPLETED TO DATE ASRROBBJBSB8ar~SY THE ROUND TABLE CONFERENCE

Beginning in 1972 with the belief that all of the groundwater contamination problem discovered in late 1971 wasemanating from the Army Creek Landfill, New Castle Countyrecognized the need to correct the situation. The initialstep towards correction was installation of a recovery wellsystem to intercept the contaminated ground water andcontrol the contaminant plume. Figure 1-14 shows thecontaminant plume and Figure 5-1 shows the piezometricsurface of the upper Potomac Aquifer prior to installationof any recovery wells.

The following wells were installed to intercept and controlthe contaminants, creating the original recovery wellsystem: 27, 28, 29, 31, 53, RW-1, RW-2, RW-3, RW-4, RW-5 andRW-6, The punping of these recovery wells, in concert witha decrease "in punping at the Artesian Water Company well-field, created a ground water divide between the recoverywells and the production wells (Figure 1-15 and 1-16).

With the initial control (the recovery wells) in place andoperative by 1973, the County and WESTON began to evaluatevarious options for "elimination" of the landfill .and itsassociated problems. These options ranged from excavatingthe refuse and transporting to another existing or newlybuilt location in Delaware or Pennsylvania, to taking noaction at all.

ftR3006073-12

In order to ensure a technically feasible and cost-effectivesolution to the problems associated with the landfill, theCounty Council in 1977 directed the New Castle CountyAreawide Waste Treatment Management Program (NCCAWTMP) toconvene a committee to recommend a solution to the Council.The NCCAWTMP received a grant from the U.S. EPA to conduct atechnical Round Table Conference. Its purpose was to obtaininput and opinions from nationally and internationallyrecognized workers in landfill and ground-water remediation.The attendees were provided with all available informationon the Army Creek Landfill in order for them to evaluatealternatives previously proposed to the County, and todevelop a technically feasible and cost-effective solutionto the problem.

The Round Table Conference was held on 17 - 18 November1977. Twelve authorities on the subject of landfill andleachate control and management from the United States andCanada were present at the conference. Representatives ofthe U.S. EPA, Delaware Department of Natural Resources andEnvironmental Control, Delaware Geological Survey, and theNew .Castle County Department of Public Works alsoparticipated. Table 3-1 lists the Round Table participantsand observers.

The hydrogeology and history of the landfill were presentedto the conference attendees and the data available deemedadequate for determining a remedial action alternative.Various remedial alternatives were discussed and are brieflysummarized below:

1. Attenuation - This is essentially a no actionalternative whereby the soil capacity for removingcontaminants and dilution with clean water arerelied upon to render the water safe at the pointof withdrawal. Since this alternative was the leastcostly and appeared to have technical merit, it wasdiscussed extensively.

2. Remove the Source - Several alternatives of this" ••" solution were considered, including removing the

landfill to another site, and incineration. Movingthe landfill was considered to be little more thanmoving the problem, with the associated additionalcosts of excavation, transportation and re-land-filling, and the possibility of causing new pro-blems rather than solving the existing problem was

3-13

Table 3-1

ARMY CREEK LANDFILL ROUND TABLE INVITED PARTICIPANTSNovember 17 and 18, 1977

1. Dr. Graham Farquhar - jfDepartment of Civil Engineering r«University of WaterlooWaterloo, Ontario

2. Mr. John NunanHydrology Consultants, Ltd.Mississauga, Ontario

3. Dr. Bob K. HamDepartment of Civil and Environmental EngineeringUniversity of WisconsinMadison, Wisconsin

4. Mr. Keros CartwrightIllinois State Geological SurveyUrbana, Illinois

5. Mr. Frank A. RoversConestoga-Rovers and AssociatesWaterloo, Ontario

6. Mr, John G. PaceyEmcon AssociatesSan Jose, California

7, Mr. George HughesMinistry of the Environment (MDE)Toronto Ontario

8. Mr. Hans MooijWaste Management BranchEnvironmental Protection ServiceFisheries and Environment, CanadaOttawa, Ontario

9. Mr. Gary MerrittPennsylvania Department of Environmental ResourcesHarrisburg, Pennsylvania

10. Mr. Ron LandonRoy F. WestonWest Chester, Pennsylvania

AR300609

3-14

Table 3-1 (Continued)

ARM* CREEK LANDFILL ROUND TABLE INVITED PARTICIPANTSNovember 17 and 18, 1977

11. Mr. Water LeisRoy F. Weston - jf

... West Chester, Pennsylvania _ '-*•

12. Dr. Don L. WarnerDepartment of Geological EngineeringUniversity of MissouriRcilla, Missouri

13. Mr. N. C. VasukiDelaware Solid Waste AuthorityDover, Delaware

14. Ma:. Donald SanningEnvironmental Protection AgencyCincinnati LaboratoryCincinnati, Ohio

15. Mar. Dirk BrunnerEnvironmental Protection AgencyCincinnati LaboratoryCincinnati, Ohio

16 . Mr. Mike ApgarDelaware Department of Natural REsources and Environ-

mental ControlDover, Delaware

17. Mr. Ken WoodruffDelaware Geological SurveyNewark, Delaware

18. Mr. Warren O1 SullivanAssistant County EngineerNew Castle CountyNewark, Delaware

19. Ms. Merna KurdWaste Treatment Management Program AdministratorNew Castle CountyNewark, Delaware

o n A €1 I AJ U U b 1 U

3-15

Table 3-1 (Continued)

ARM? CREEK LANDFILL ROUND TABLE INVITED PARTICIPANTSNovember 17 and 18, 1977

20. Mr. David C. ClarkProject ManagerNew Castle CountyNewark, Delaware

21. Mr. Bruce KraeuterPlanning AgencyNewark, Delaware

3-16

ftRSOOSIj

Table 3-1(Continued)

ARMY CREEK LANDFILL ROUND TABLE

INVITED OBSERVERS

1. Mary Jqrnlin County Executive

2. Henry Folsom County Council President

3. Joe Toner County Councilman

4. Al Madpra Director of Public Works

5. Pierre Olney Secretary, Department ofNatural Resources and

" , ---- - - - • - • srivironment;al_ Control

6. Bob Alien EPA, Philadelphia

7. John Humphreys EPA, Philadelphia

8. Al Montague EPA, Philadelphia

9. Ray Lee EPA, Philadelphia

10. Toby Goodrich EPA, WashingtonRepresentative Research and Development Solid

Wastes, Water

11. Abraham Thomas Roy F. Weston, Inc.

12. Representatives from13. Congressional Delegation14. and Staff

Special I jfited Guests: Region III, EPA Administrator,&*- Deputy Administrative

Assistant, Solid Waste

3-17

considered to be very real. Incineration was con-sidered to be probably the ultimate technical solu-tion, but did not conform with the State's SolidWaste Management Plan.

3. Promote In-Place Decomposition - Severalalternatives of this solution were considered,including the recycling of leachate through thelandfill and annelidic decomposition. Theannelidic decomposition alternative (wherebyearthworms consume the biodegradable fraction ofthe refuse) was considered viable only to theextent that it would address the biodegradablematerials. More than 90% of the landfill masswould still have to be re-landfilled at anothersite.

4. Hydrogeologic Control - This solution was made upof several steps where leachate production could besignificantly reduced and the remaining leachatecollected in a concentrated form within thelandfill boundaries. It was considered importantto reduce the leachate production by reducing oreliminating water entry into the landfill by (1)applying a relatively impermeable cover to thelandfill surface, regrade the surface to promoterunoff, and revegetate, and (2) divert ground wateraroundthe landfill. The second step discussed was therelocation of recovery wells so as to collectconcentrated leachate from beneath the landfill.This would reduce the volume of clean water to bepumped to maintain the divide between the ArtesianWater Company wellfield and the recovery wellfield.This was the alternative ultimately recommended bythe Round Table.

Shortly after the Round Table Conference, a workshop washeld on & December 1977 before the New Castle County Councilto relat the findings and recommendations. The Council andCounty Administration then directed the New Castle CountyDepartment of Public Works to proceed with development of ascope of work and other steps necessary to finance andaccomplish the recommended corrective measures for the ArmyCreek Landfill. The County's multi-year program wasdeveloped with the following six items included toaccomplish the goals of the program:

AH3006I3

3-18

1. Redesign the recovery well network by relocatingselected wells to allow pumping of contaminatedwaters closer to and within the landfill. This

; would allow the downgradient aquifer to receivegreater amounts of fresh water recharge.

2. Systematically monitor the ground water quality inthe aquifer to include both the existing wells aswell as new pumping and observation wells.

3. Determine a water budget and the safe yield of thePotomac aquifer in the vicinity of Army CreekLandfill to enable ground water recovery pumping tobe at a minimum effective volume.

4. Minimize surface infiltration into the old landfillto reduce the volume of leachate that is producedand transferred into the Potomac aquifer.

5. Maintain the redesigned wellfield until such timeas the reduced leachate production and improvedground water quality would allow a gradual phaseoutof the entire recovery wellfield to eventually relyon natural renovation within the aquifer.

6. Present cost estimates associated with ground waterrecovery discharge and monitoring, as well as sitemodification.

A 3-phase approach was developed to accomplish the abovegoals in an orderly fashion. These phases and associatesubtasks are as follows:

Phase I

Redesign the recovery well system by well relocation andselected existing well phase-out.

Step 1 - Assess the potential well interferences within thelandfill and in the adjoining area immediately southoft'the landfill, based upon available data.

Step 2 - Locate and test drill wells within the Army CreekLandfill and conduct pump tests to evaluate wellinterference between these and the existing recoverywells. These wells would then be completed forground water recovery pumping.

ftR3006Il*3-19 .:•>,.:.;

Step 3 - Locate/ test drill and test pump wells in theexisting line of recovery wells between RW-4 and 31,and complete them for ground water recovery pumping.

Step 4 - Drill and outfit approximately ten new observationwells within the new pumping network.

Step 5 - Survey elevations of the new wells and tie into theexisting well network.

Step 6 - Initiate pumping at these new wells and closelymonitor until optimum pumping rates are achieved.

Step 7 - "Fine tune" the entire recovery network to concen-trate the bulk of pumping near the landfill.

Step 8 - Conduct systematic sampling of the new wells andanalyze on a monthly basis for the first six monthsto determine baseline contaminant quality in the newwellfield.

Step 9 - Determine the safe yield of the Potomac aquifer asit should affect pumpage in the vicinity of the ArmyCreek Landfill.

Step 10- Install approximately 12 gas monitoring pointsaround the periphery of the landfill with particularattention given to the northwest corner of thelandfill where construction and urban activities aremore common.

Step 11- Terminate pumping in the recovery wells which arelocated farthest from the landfill.

Phase II

Within a six month period after the redesigned system is onlina, evaluate the effectiveness of the relocated recoverywellii©ld nd/or any additional remedial steps.

Step 1 - Assess the quantitative and qualitative aspects ofthe relocated ground water recovery wells todetermine the need for additional pumping and/orobservation wells for optimum ground watermanagement.

AR3006I5

3-20

Step 2 - Determine the actual rate of infiltration ofprecipitation through the landfill and the rate ofground water underflow to determine the hydrologic/ground water flux.

Step 3 - Rehabilitate the new and existing recovery wells asnecessary.

Step 4 - Reduce the pumping rate of the line of recoverywells adjacent to Army Creek and terminate, ifpossible, pumping from those wells located furtherdown gradient.

Step 5 - Assess the alternatives for ground water discharge/treatment by: improvement of Army Pond, dischargeto the proposed sewer line or construction of anon-site treatment plant.

Phase III

Within a three to five year period after the redesignedsystem is on line, long term ground water control measuresand a site management program would be developed.

Step 1 - Conduct a systematic monitoring, sampling andanalysis program on a selected basis to ensure thatcontaminated ground water emanating from thelandfill is fully contained.

Step 2 - Continue decreasing the pumping rate from thecontaminant recovery wells to determine wheneventual shutdown is feasible.

Step 3 - Top-grade and cover the landfill as necessary tominimize infiltration. •>

New Castle County approved the above phases and tasks of themulti-year program in a modified format. The chronology ofevents in the implementation of Phase I of the program arelisted below. With the completion of this phase in May 1982(constructflfe-n of the modified wellfield) the multi-yearprogram be an.

R

3-21

COOJUMTC

Chronology of Initiation of Multi-Year Program

Date Program Activity

17-18 November 1977 ARMY CREEK LANDFILL TECHNICAL ROUNDTABLE

6 December 1977 COUNTY COUNCIL WORKSHOP - Synopsis offindings and recommendations fromtechnical Round Table.

13 April 1978 ROY. F. WESTON SUBMITS SCOPE OF WORKFOR CORRECTIVE ACTION TO NEW CASTLECOUNTY.

30 May 1978 COUNTY COUNCIL WORKSHOP - WESTONpresents work scope.

8 June 1978 MEMO TO JACK KIRK FROM HENRY FOLSOM -outlining workshop conclusions.Administration request to proceedwith solution presented.

20 July 1978 MEETING - County and DNREC re: rolesand responsibilities of County andDNREC.

9 August 1978 LETTER TO JOHN KIRK FROM AUSTIN OLNEYoffering State assistance and

encouraging County to proceed withcorrective actions.

7 September 1978 MEETING - EPA, DNREC, and County re:funding opportunities for correctiveactivities.

11 September 1978 MEETING - EPA and County, re: Federalgrant funding for corrective

**, activit ies.j r - • • - . . .

January 1979 New Castle County approves work scopefor modified Phase I Multi-year planto be funded by NCCO capital budget.

February-May 1979 Aquifer analyses and location ofproposed new recovery wells.

30 March 1979 LETTER TO RICHARD AURICH FROM ALMADORA - notification of£ fJLgtfile for construction grant.

3-22

May 1979 Selected location of new wells.

25 May 1979 DRAFT R & D PROPOSAL CIRCULATED FORREVIEW

11 June 1979 MEETING - EPA, DNREC and County, re:Construction grant and R & D funding

14 June 1979 LETTER TO GREENE JONES FROM AUSTINOLNEY AND JOHN KIRK - requestingdetermination of construction granteligibility

June - November 1979 Developed specification and biddocuments for new recovery wells.

July 1979 R & D PROPOSAL REVISED AND CIRCULATEDFOR REVIEW

7 September 1979 LETTER TO GREENE JONES FROM JOHN KIRK- again requesting determination ofgrant eligibility.

7 December 1979 SUBMISSION OF R & D PROPOSAL TO EPA

February 1980 Well construction request for bids... , _ released by NCC.

March 1980 Request for proposal for pretreatmentand discharge of ground water toState Road interceptor.

April-October 1980 Construction of 5 recovery wells and11 new monitor wells.

January-May 1981 Development of specifications andbids for electrical service, pumpinstallation and discharge pipingfrom each new recovery well.

16 March 1<*8JL LETTER TO ALBERT MADORA FROM DONALD* " HILL - declining to fund R & D

proposal.

July 1981 Proposal prepared for feasibilitystudy for control of contaminants atthe Army Creek Landfill.

AR3006183-23

I. '- '

July 1981 Request for bids for above serviceand equipment released by NCC

October 1981 Notice to proceed for constructionactivity.

March 1982 Completion of inspection of aboveservices.

May 1982 New recovery wells placed on line.

March 1983 EPA Grant offer withdrawn.

1982-1983 Well field rehabilitation, routinemonitoring, assessment of relocatedwell field.

New Castle County's initial contaminant control programevolved into an ongoing site management program. Therecommendations by the Round Table Conference have resultedin a phased approach (the multi-year program) to remedialaction. To date, a number of evaluation tasks have beencompleted.

Phase I tasks included modification of the recovery wellnetwork as recommended by the Round Table Conference. Thesemodifications involved relocating the recovery wells closerto tha landfill and phasing out recovery wells locatedfarthest from the landfill. Recovery wells RW-10, RW-11,RW-12, RW-13 and RW-14 were installed as part of thesemodifications. The locations of these wells can be found onFigure 1-2. By May 1982 these new recovery wells wereoperational and evaluation of the recovery well network wascompleted in August 1983.

The present recovery well network utilizes Wells 27, 28, 29,31, SW-lr RW-4, RW-9, RW-10, RW-11, RW-12, RW-13 and RW-14.Tha pumping of these wells has maintained the ground waterdivide nfcessary to intercept any contaminants (Figure 5-9).Tha monitoring presently being conducted includes weeklywater level and discharge measurements, monthly sampling androutine wall rehabilitation to maintain the efficiency ofthe recovery wells.

&R3006I3

3-24

SECTION 4

SCREENING OF REMEDIALACTION ALTERNATIVES

4.1 INTRODUCTION

This section involves a screening of remedial alternativesbased on environmental and public health criteria, followedby an "order of magnitude" cost screening. This two-stepscreening permits an initial assessment of the applicabilityof each alternative relative to the others.

This process eliminates alternatives that do not provideadequate protection of public health, welfare, and theenvironment, and those that are much more costly than otherswithout providing significantly greater protection.

The treatment of contaminated ground water will be evaluatedin subsection 5.7.

4.2 E'NVIRONMENTAL AND PUBLIC HEALTH SCREENING

4.2.1 ALTERNATIVE 1 - No Action - Monitoring Only

Implementation of a No Action Alternative at the Army CreekLandfill would include discontinuing the pumping at therecovery wells.

Without ground water controls and/or reduction of leachatebeing generated, the contaminant plume will continue tomigrate downgradient. The continued production of leachaterepresents an environmental impact on ground water whichwould not be controlled.

The contamination that remains would then begin to migratein response to the changes in the ground water flow system.The new flflw*_direction would be toward and influenced bypumping at" the Artesian Water Company's LlangollenWellfield. This would create a situation where contaminantsfrom two distinct landfills, Army Creek and Delaware Sandand Gravel, would begin to move toward the LlangollenWellfield. The proximity of the two landfills, the mixingof contaminants, makes it difficult to distinguishcontaminant sources. Since the Llangollen Wellfield is usedfor public water supply it is necessary to assess the

AD on f £.H JUUo

4-1

potential for contamination of these wells under the NoAction Alternative. This evaluation will consider onlycontaminant concentrations from wells sampled at the ArmyCreek Landfill.

One way to estimate the potential impact of contaminantmigration is to develop a solute transport model based ontha information available regarding the local groundwaterflow system. Since there are widely varying degrees ofprecision available within the realm of groundwater models,clearly defined goals must be established before proceedingwith a model. Without these goals it is possible to selecta model which is entirely inappropriate or to misinterprettha results. Because of the lack of specific data coveringthe study area, the goal for chemical concentrationpredictions must be relatively general. Therefore, the goalof this modeling study is to provide a prediction ofapproximate future chemical distribution in the groundwaterif tha current recovery pumping is terminated. It is nottha intent to prov ide pr ec i s e determi nations ofconcentrations that will occur downgradient, but rather toestimate the magnitude of reduction in concentrations thatwill likely occur.

The first step in the modeling exercise is to collect orestimate all of the necessary input data. These data can begrouped into two general categories. First is the datarelating to the groundwater flow, such as hydraulic conduc-tivity, effective porosity, saturated aquifer thickness, andhydraulic gradient. The other group includes parameterswhich have more bearing on contaminant transport, such ashorizontal and transverse dispersivities, initial chemicalconcentration, and chemical adsorption coefficients. Valuesfor each of the parameters must be either measured or estima-ted before a model can be applied. Development of thesegroups of data will also result in an important under-standing of the availability and reliability of spatiallydistributed data. This is an important factor whens-elactrng an appropriate model for contaminant transportpredicfH.on.

jr -Using the pumping test data reported in Appendix M, alongwith logs of observation wells, an estimate of hydraulicconductivity can be developed for the Army Creek area. Themean transmissivity from the pump test data is approximately51000 gpd/ft, and the average aquifer thickness from theobservation well logs is approximately 65 feet. Thesevalues are consistent with data reported by others (Martin1984; Martin and Denver, 1982; Miller, 1982; Sundstrom andPickatt, 1971; and DeWalle and Chian, 1981). * n o n n C O 1AHaUUOcI

4-2

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The following relationship is used to calculate an averagehydraulic conductivity of approximately 100 ft/day.

T = Kb

where: T = transmissivityK = hydraulic conductivityb = aquifer thickness

A specific discharge can be calculated once a hydraulicconductivity is estimated. Using a procedure outlined byWalton (1962), the drawdown at various distances from apumping well can be estimated for leaky artesian aquifers(See Appendix R). Using a pumping rate of 2 mgd for theArtesian wellfield, and assuming that the entire volume isremoved from one well, an average hydraulic gradient of0.011 is calculated. The one well withdrawal of 2 mgd is aconservative assumption with respect to this analysis sincea concentrated withdrawal creates a maximum drawdown effect.Based on Darcy's Law and the estimated hydraulicconductivity and hydraulic gradient established above, thespecific discharge is calculated as approximately 1 ft/dayby the following relationship:

q = KI

where: q » specific dischargeK = hydraulic conductivityI = hydraulic gradient

Using 1 ft/day as the specific discharge and an effectiveporosity of 0.2, which is estimated from the literature, anaverage velocity of 5 ft/day is calculated using the follow-ing formula:

V = q/ne

where: V = average velocity.—""q = specific discharge^b- — effective porosity*• e ^

The second set of data needed are those values related tomass transport in the groundwater. Those parameters includelateral and transverse dispersivity, initial chemicalconcentrations, and chemical adsorption coefficients.

3' F O:fl f\ f* 3 Ait38Q6224-3

Calculation of dispersivity coefficients requires eitherdata from a type of aquifer test which is not routinelyperformed, or a very complete record of groundwater qualitycovering the entire life of the source. Since neither ofthose is available for the Army Creek Landfill, an estimateof dispersivity must be made based on reported values .

Several investigators report lateral dispersivity values forfield scale problems on the order to 10 to 100 meters(Freeze, et al, 1979? Newsom, 1985). For the purposes ofthis model, a value of 30 feet was used for longitudinaldispersivity; 10 feet for horizontal transversedispersivity; and 3 feet for vertical transversedisparsivity estimated from these reported values .

The next input parameter which must be estimated is theinitial chemical concentration. A review of groundwaterquality data from wells located in the Army Creek Landfillindicates many contaminants with highly variable concentra-tions ,(see Tables 4-1 and 4-2). In order not tounnecessarily complicate the modeling effort, ""a standardizedconcentration of 1.0 mg/L can be assumed. This allows theapplication of computer simulation results to the initialconcentration of any chemical. For example, if the modelresults indicate a standardi zed concentration at a giventime and a given distance equal to 0.3, then the actualpredicted concentration would be 0.3 times the initialconcentration for the chemical of interest. _JThis approachreduces the time required for modeling by eliminating theneed for individual predictions for each chemical observed.

In ordar to calculate a mass loading or flux for the land-fill, an estimate of recharge is needed. The valueestimated is 4000 gpd for the entire landfill area, and isbased on the HELP model study (see Appendix P). Using thefollowing relationship, a mass flux for the landfill can becalculated for the standardized concentration of 1 mg/L.

where: * " . J » fluxQ « recharge volumeC • concentrationU s unit conversion term

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The last parameter which must be addressed with respect tomass transport is the adsorption coefficient. As flowtoward Artesian's wellfield is established after therecovery wells are shut off, contaminants would begin tomigrate along the flow path because of advective anddispersive mechanisms. In addition, the progress of some oftha contaminants will be impeded as a result of various

_ reactions with the medium. This may be a result of severalspecific processes which are difficult to distinguish andare observed as a single phenomenon called adsorption.Progress of a solute or contaminant that adsorbs to themedium is retarded with respect to a solute that is not

: adsorbed. This effect can be represented by a retardationfactor which is specific to a certain solute and a certainmedium.

There are methods which can be used to estimate theretardation factor. They require input of parameters whichhave not been measured for the particular combination ofmedia and chemicals present at this site. A calculation of

it! the retardation factor for this modeling effort would,0' therefore, be an estimate based on uncertain data. A more

appropriate approach is to assume no adsorption is takingplace between the chemicals and the media. Since there are

, I expected to be some reactions taking place, this is aconservative assumption. A transport prediction based on no

I' retardation will result in higher concentrations at a givenplace and time than a prediction made consideringretardation. The estimates of concentrations provided will,therefore, be greater than those actually observed assumingall other model parameters have been correctly represented.

Once all of the necessary data and parameters are developed,the next step is to select a mass transport model that ismost appropriate for the accuracy of the data and for the

"!'';' intent of the investigation. Most of the aquifer parametersavailable are estimates in this case, and the intent of theprediction exercise is very general. It would be

— inappropriate, therefore, to use a complex, sophisticatedmodel >hich is designed to provide a higher level ofaccuracy. A more practical and fitting approach is to use amethod which will provide a prediction of mass transportfrom the Army Creek Landfill and which is as accurate as thepreceding assumptions. Based on this framework, ananalytical solution model was chosen rather than a numericalsimulation of the plume.

4-8

An analytical solution to the mass transport equationrequires that certain assumptions be made about the physicalreality of the hydrologic system involved. Thoseassumptions will affect the form of the solution and varyfrom one solution to the next. In this case, a solutionprovided by Hunt (1978) is used. It is a solution thatconsiders transport in three dimensions. As with allanalytical approaches to solute transport, the most import-ant assumption has to do with isotropy and homogeneity.Application of this solution requires that either the mediumis fairly homogeneous or that averaging assumptions can bemade, such that the system can be represented as homogenous.While this is not a precise representation of. the ground-water flow system, this assumption is completely appropriatein many situations where very little is known about theexpected inhomogeneity of a system. It is a moreacceptable representation of a system to use an averagevalue for some aquifer parameter than to estimate spatiallydiscrete values from too little data. The assumptioninvolving isotropy will vary from one solution to the nextdepending on the complexity of the solution. Aone-dimensional solution does not allow description ofparameters in other directions. A three-dimensionalsolution does, however, allow anisotropy to be described forsome of the parameters. For example, a one-dimensionalsolution requires that the solute be evenly distributed inthe other two dimensions. The three dimensional solutionapplied to this problem, however, only requires that theaquifer be infinite in all directions. In practice, thisrequirement means that the plume cannot reach the bottom ofthe aquifer prior to reaching the horizontal distance ofinterest. Once the plume reaches the bottom of the aquifer,the solution acquires additional error.

In order to apply the analytical solution to a landfillsite, a computer algorithm is needed. Otherwise, solvingthe equation for a three-dimensional network of hundreds ofnodes would be a formidable task. An algorithm using theHunt .(19784- equation has been prepared fay Milovan S. Beljinat the International Ground Water Modeling Center (IGWMC),Using the BLUME3D program of IGWMC, several predictions weremade for the Army Creek Landfill. The grid used for thepredictions is shown in Figure 4-1, and the parameters usedare summarized in Table 4-3. A sample of the data outputfrom the program is shown in Table 4-4. The complete dataoutput is contained in Appendix R. It is important to note

;R300628

4-9

R300629

4-10

TABLE 4-3

ESTIMATED AQUIFER PARAMETERS

Hydraulic Conductivity 100. ft/day

Hydraulic Gradient 0.011

Thickness 70. ft

Specific Discharge 1 ft/day

Effective Porosity .... ..__ 0.20

Longitudinal Dispersivity 30 ft.

Horizontal Dispersivity 10 ft.

Vertical Dispersivity 3 ft.

Source Strength , 0.007 Ib/day

Distance Increment X-Direction 500 ft.

Distance Increment Y-Direction 500 ft.

Distance Increment Z-Direction 10 ft.

H3006:

4-11

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LOCATIONi N.C. COUNTY

DATEI 1O JULY 86

INPUT DATA*

DARCY VELOCITY. .......................EFFECTIVE POROSITY. ...................LONGITUDINAL DISPERSIVITY. ............LATERAL DISPERSIVITY. .................VERTICAL DISPERSIVITY.................DECAY CONSTANT (lambda) ...............NUMBER OF POINT SOURCES. ..............

1*00 ft/d.2

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4-12

that PT.,UME3D does not include a provision for retardation ofa non-conservative contaminant. The concentrationpredictions made by this program are, as discussed above,higher than concentrations that would be predicted for anadsorbing pollutant.

The results of the computer predictions provide the basisfor two important conclusions. First, the contaminant plumewill reach a stable configuration within the area ofinterest within five years from the time that the new flowsystem stabilizes. If the recovery pumps were stopped,groundwater flow patterns would gradually be reestablishedor stabilized in the direction of the Llangollen Wellfield.Following stabilization of the flow system, the contaminantplume will stop changing perceivably in less than fiveyears.

The second conclusion is the concentrations at theLlangollen Wellfield are conservatively predicted to bereduced by up to 3 orders of magnitude from those observedat the Army Creek Landfill. The estimated parameters usedas input to the predictive equation preclude a more precisedetermination of concentrations. This conclusion indicatesthat concentrations will likely approach the appropriatecriteria ,r but the predictions are not accurate enough to useas definite indication of final concentrations.

These conclusions are necessarily framed fay the underlyingassumptions discussed above. The most important of thoseassumptions are those regarding contaminant input, thedispersive nature of the aquifer, and the validity ofrepresenting the flow system parameters with average values.The pollutant flux into the system is based on a normalizedconcentration and an average infiltration rate through thelandfill. A macroscale dispersion characterization of theaquifer involved is based on values reported in theliterature, and is intended to be a conservative estimate,(Freeze, et al, 1979; Mackay, et al, 1985). The remainingaquifer parameters are estimated average values based onavailable regional data. These predictions are, therefore,estimates themselves and should not be interpreted as beingany more accurate than an order of magnitude estimate.

Despite the assumptions mentioned above, it is still usefulto evaluate the concentration that would result from a threeorder of magnitude decrease at the Artesian wellfield.Table 4-5 shows concentrations of chemicals identified at

300632

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4_u AR300633

various wells in the Army Creek Landfill and the resultantpredicted concentration at Artesian's wellfield. Theinorganic: compounds shown in Table 4-4 were selected topresent the current strength of common conservativeindicator parameters which are known to occur in thelandfill« The organic parameters presented in Table 4-4represent the only data available which are consideredreliable,, The values have been rounded to indicate thedegree of: accuracy of the predictions and should not beinterpreted as absolute values.

In addition, the lack of recent data on organic chemicalcomponents in the landfill itself limits the evaluationsthat can be made. A few base/neutral extractable compoundshave been observed in recovery wells, but no data exists forwells in the landfill. It is not possible, therefpre, topredict an estimated concentration range at the >rtesianwellfield for these chemicals.

Also, dilution of chemical concentrations in the well as aresult of clean water contributions from other directionshas not been addressed by this model, the predictions madeare of concentrations at the well field and not of expectedconcentrations in the well water. Additional dilution willoccur as a result of mixing the water from other areas inthe aquifer. This dilution will likely represent areduction factor of 3_. 5 as a maximum. With respect to theuncertainties involved in these predictions an additionalreduction of 3.5 is not considered significant.

It should be noted that the EPA has recently implemented asimilar approach to predicting solute transport forestablishing screening criteria for individual constituentsin hazardous wastes CFR* 19086). The EPA has chosen a threedimensional steady state advective dispersion analyticalmodel. This is the same type model applied in thisanalysis.

Finally, a more sophisticated numerical modeling effect isunderway as part of a Remedial Investigation/FeasibilityStudy at the Delaware Sand and Gravel Landfill. This modelwill -serve~to check the predictions made by PLUME3D.

flR3QQ63i*4-15

Another environmental impact involves the wetlands and ArmyPond. Under the No Action Alternative, no groundwater wouldbe discharged to Army Pond. This action would affect thewetlands, because the discharges maintain the current si zeof the pond. With no discharge, the wetlands would bemaintained by an intermittent stream with upstream flow ofless than 1 cubic foot per second, and during dry weatherconditions the pond size would decrease.

The wetlands areas maintained by the intermittent stream, inthe pond area and downstream would be reduced in size incomparison to the current wetlands. In addition, turnoverwithin the system would be reduced and the water fromupstream would not be diluted by the discharges. Since theupstream water has been termed "toxic" (EPA 1986), thewetlands would be effected by the full impact of thedegraded water from upstream. The wetlands boundaries wouldshift and _species composition would likely change. Thegreatest change would occur in the area downstream of ArmyPond.

4.2.2 ALTERNATIVE 2 - Downgradient Pumping

Alternative 2 reduces the public health risk by containingthe contaminant plume through the establishment ofhydrologic divide created by the downgradient pumpingnetwork located between the landfills and the Artesian WaterCompany wellfield. The quantity of leachate generated fromprecipitation and ground water infiltration through thelandfill will not be reduced uncler this alternative. Theresult will be the continued addition of contaminants to theupper Potomac aquifer, however, the contaminant plume isbeing effectively controlled near the landfill. This limitsth© extent of the environmental impact to the ground waterand reduces the public health risk.

4.2.3 ALTERNATIVE 3 - Downgradient Pumping and LandfillCapping

In addition to reducing the public health threat through thedowngradient pumping network, Alternative 3 includesmeasures to reduce the environmental impacts at the ArmyCreek Landfill site. Surface capping of the landfill with alow permeability soil cap will significantly reduce theinfiltration of precipitation into the landfill. The resultwill be a reduction in leachate generation. Theinfiltration of. ground water along the northwestern side ofthe landfill will, however, continue, and leachate maycontinue to be generated in the western section of thelandfill.

AR300635

4.2.4 ALTERNATIVE 4 - Downgradient Pumping, Landfill Cap-ping and Upgradient Controls

Alternative 4 provides the same reduction of the publichealth risk as Alternative 2 and 3 by containing thecontaminant plume through downgradient pumping. Alternative4 further .reduces environmental impacts at the site bycontrolling the ground water inflow along the north-western .side of the landfill utilizing upgradient controls(pumping or interception trench). This results in a reduc-tion of the amount of leachate generated in the north-western section. These actions will hasten ground watercleansing. Depending on the pumping configuration of thedowngradient and upgradient wells (if implemented), Alterna-tive 4 initially removes less than ten percent more waterfrom the local ground water . resources than is now beingremoved.

4.2.5 ALTERNATIVE 5 - Removal of Western SectionDisposal on Eastern Section, Landfill Capping, andDowngradient Pumping

Alternative 5 provides basically the same public health andenvironmental benefits as Alternative 4 but addresses thelateral ground water infiltration problem by eliminatingthe source of leachate generation through total removal ofthe refuse in the western section. This approach foraddressing the ground water infiltration has the benefit ofnot removing additional water from the local ground waterresource. This should hasten ground water cleansing afterthe disposed refuse on the eastern section is capped.During csxcavation, dust and odor problems s will occur inaddition to the draining of water from saturated refuse.The drainage and dust can be controlled using standardconstruction techniques; however, odor will present greaterchallenges for control.

Construction activities during excavation could affectwetlands habitats through noise, surface water diversionand dusto Drainage could also have an effect, if notcontrolled^,

4.2.6 ALTERNATIVE 6 - On-Site Incineration and Down-^gradient Pumping

Alternative 6 provides basically the same public health andenvironmental benefits as Alternatives 4 and 5 throughdowngradient pumping and removal of the source by excavationand incineration. Dry refuse must be transported to the

AR3008354-17

site and mixed with the saturated waste to make it burnable.Air pollution control devices required under RCRA wouldreduce the release of contaminants into the air.Incinerator ash and residue would be backfilled on-site onlyin areas above the ground water table and eventually capped.Dust, odor and drainage of liquids from the saturated wasteare problems associated with the excavation of landfillrefuse. Other environmental and health concerns will beassociated with the transport of dry refuse to the ArmyCreek Landfill site. These concerns include noise and dustfrom transportation and vector problems. Measures, such asvector control and site access routing, would be initiatedto mitigate these problems.

Construction activities during excavation could affectwetlands habitats through noise, surface water diversionpractices and dust. Drainage could also have an effect, ifnot controlled.

4.2.7 ALTERNATIVE 7 - Off-Site Disposal by Landfilling inan Approved Site and Downgradient Pumping

Alternative 7 provides basically the same public health andenvironmental benefits as Alternatives 4, 5, and 6 throughdowngradient pumping and the complete removal of the sourceof contamination by excavation and disposal in an approvedoff-site landfill facility. These actions will preventdirect human exposure and accelerate ground water cleansingas do Alternatives 4f 5, and 6. Dust, odor, and noiseproblems will arise from the excavation and hauling actionscontained in this alternative. The off-site facility mustbe a RCRA permitted landfill to assure that potentialenvironmental impacts at the new site are minimized.

Construction activities during excavation could affectwetlands habitats through noise, surface water diversionand dust. Drainage could also have an effect, if notcontrolled.

4.3 -CONCLUSIONS

4.3.1 JPublic Health S Environmental issues

A summary of the public health and environmental concernsdiscussed in this section are provided in Table 4-1.

AR300637

4-18

The No Action Alternative included in the alternative listto assess the effect of not performing additional remedialactions is an unacceptable alternative. The No ActionAlternative could result in possible exposure throughingestion of contaminants reaching community wells. Theground water monitoring provision would provide a possible"early warning" so that contingency plans could beimplemented if the potable water quality is threatened. Allother alternatives reduce the public health risk bycontaining the contaminant plume.

Alternatives 2 and 3 provide the same public health benefitsby containing the contaminant plume and maintaining the hy-drologic divide between the landfill and Artesian'sLlangollen Wellfield. Alternative 3 includes measures toreduce the precipitation infiltration into the landfill,subsequently reducing the amount of leachate generated.This alternative reduces the environmental impacts.

Alternatives 4, 5, 6, and 7 provide basically ' the samepublic health and environmental benefits although thetechnologies used are quite different. These benefitsinclude the reduction in the public health risk due toexposure and the hastening of ground water cleansing byreducing or eliminating the amount of leachate generated.Alternatives 5, 6, and 7 involve partial or total removal ofwastes in the landfill which offers an ultimate long-termsolution but may result in short-term environmental impactsduring excavation. Cost analysis is needed to better assessthese alternatives.

4.3.2 Cost Screening Factors

The object of the cost screening is to eliminatealternatives that have costs an order of magnitude greaterthan those of other alternatives but do not providesignificantly greater environmental or public healthbenefits or greater reliability.

Since the analysis of treatment options for recovered groundwater will be handled in a separate section, treatment costs-will" not ~ be included in the initial cost screening.Discharge =tp Army Creek will be assumed to require only aNPDES discharge permit. Cost would be incurred for samplingand analysis for the NPDES permit.

AR3006384-19 • ; ' , • ' • • .-

Alternative 1 - No Action - Monitoring Only

Estimated Capital Costs

• Fencing & monitor well installation $ 220,000

Estimated Post Closure Costs

• Monitoring & Maintenance $ 30,000/yr(10 monitoring wells)

Present Worth *

• Capital $ 220,000• Post Closure $ 280,000

TOTAL $ 500,000

* A 10 percent discount rate and an operationtime of 30 years is assumed.

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Alternative 2 - Downgradient Pumping


• Well relocations , $ 50,000/yr• Maintenance 50,000• Monitoring 25,000• Pumping 250,000

TOTAL $ 375,000/yr

Present Worth *

• Post Closure $3,500,000


Note: Treatment costs not included

4-21

Alternative 3 - Downgradient Pumping andLandfill Capping

Estimated Capital Costs _'

* Site Grading & Backfill $ 900,000• Multilayer Cap System 8,800,000• Drainage, fencing &

environmental controls 400,000

TOTAL $10,100,000


• Well relocations $ 50, 000/yr• Maintenance 75 , 000o Monitoring 25,000o Pumping 250,000

"* ~ $ 400, 000/yr

Present Worth *

* Capital $10 , 100 , 000• Post closure 3,800,000

TOTAL $13,900,000

* A 10 percent discount rate and an opera.ti.ontime of 30 years is assumed.

Notes Treatment costs not included

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Alternative 4 - Downqradient Pumping, Cappingand Upgradient Controls—(non phased approach)


• Install 5 upgradient wellswith discharge lines $ 200,000

• Site Grading & Backfill 900,000• Multi-layer cap system 8,800,000• Drainage, fencing &

environmental controls 400,000

TOTAL $10,300,000


• Well relocations $ 50,000/yr• Maintenance 100,000• Monitoring 25,000• Pumping 350,000

TOTAL $ 525,000/yr

Present Worth **

• Capital $10,300,000• Post Closure 5,000,000

TOTAL $15,000,000

* Upgradient pumping used for evaluation purposes

** A 10 percent discount rate and an operationtime of 30 years is assumed.

Note: Treatment costs not included, present worth costs will beless for phased approach than for non-phased approach.

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Alternative 5 - Partial Removal & On-Site Disposal,Capping, and Downgradient Pumping


• Site Preparation, Drainage &Environmental Controls 1,600,000

• Dewatering Wells & Pumping 450,000• Excavation & Redisposal 21,300,000

- • Backfill Excavation 3,500,000• Multi-layer cap system .._._. 5,800,000

TOTAL __. $32,650,000


• Well relocations (15 yr) $ 25,000/yr• Maintenance 75,000

-. « Monitoring ___ . 25,000« Pumping (15 yr) 250,000

TOTAL $ 375,000/yr

Present Worth *

fe | * Capital $32,650,000" • Post Closure (monitoring &

maintenance) - 30 yrs 950,000• Post Closure (pumping &

well relocation) - 15 yrs 2,100,000

TOTAL $35,700,000


Notes Treatment costs not included

4-24

Alternative 6 - On-Site Incineration and Downgradient Pumping



• Dewatering Wells & Pumping 500,000• Construct Incinerator Unit (1000 T/DA) 97,000,000• Power Generator 12,000,000• Cover & Site Closure (in 10 yrs.) 1,700,000

TOTAL $113,500,000


Well relocations (15 yr) _ _ $ 25,000/yrMaintenance 75,000Monitoring 25,000Pumping (15 yr) 250,000Excavation & Incineration (10 yr) 5,000,000Backfill Excavation & ResidueDisposal (10 yr) 2,500,000

Recovered Revenue

• Equipment Salvage (in 10 yrs.) $ 7,500,000• Annual Tipping Fees (500 T/DA x

$15/T) for 10 yrs. 2,200,000/yr• Annual Power Sales for 10 yrs. 6,000,000/yr

PRESENT WORTH

Expenses

• Capital $111,800,000• Site Closure in 10 yrs. 700,000• Post Closure (monitoring &


well relocation) - 15 yrs 2,100,000• Excavation, Incineration &

Backfill - 10 yrs. 46,000,000

_ J ETTOTAL - PRESENT WORTH $161,550,000

Revenues;

* Salvage - in 10 yr 2,900,000• Tipping fees - 10 yr 13,500,000• Power Sales - 10 yr 36,900,000

SUBTOTAL - PRESENT WORTH $ 53,300,000

NET PRESENT WORTH COST $ 108,25QfQOO

Note: Treatment costs not included;i+* fc- oft £*/>s

- - - 4-25>^, AR30Q6W

Alternative 7 - Off-Site Disposal by Approved Landfilland Downgradient pumping

Estimated Capital Costs.


* Dewatering Wells & Pumping 450,000• Excavation & Off-Site Transport 31,500,000• Off-Site Disposal (tipping fees) 182,000,000• Backfill Excavation, Grading, Seeding 24,250,000

TOTAL $239,900,000


* Well relocations (15 yr) $ 25,000/yr• Maintenance 75,000• Monitoring 25,000• Pumping (15 yr) 250,000

Present Worth *

* Capital $239,900,000• Post Closure (monitoring &


well relocation) - 15 yrs 2,100,000

TOTAL " $242,950,000

* A 10 percent discount rate and operation timeas noted.

Note: Treatment costs not included

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4.3.3 Summary

Table 4-5 provides a summary of the present worth costestimates for each alternative along with a summary of themajor public health and environmental issues.

In comparing costs with benefits, Alternatives 2, 3, 4, 5,6, and 7 all reduce the public health risk by containing thecontaminant plume through downgradient pumping.Alternatives 3 through 7 also address the pathways ofcontamination by .combinations of surface capping and groundwater controls and/or partial removal of the refuse, orcomplete removal of the refuse. All five alternatives (3,4, 5, tir and 7) will hasten the cleansing of the Columbiaand upper Potomac aquifers, Alternatives that involvepartial or complete removal, would be expected to result ina small Increase in the rate of ground water cleansing ascompared to Alternative 4 involving upgradient controls andsurface capping. Alternatives 6 and 7 which involveoff-site disposal and incineration are approximately five(5) to ten (10) times as costly as Alternatives 4 and 5which offer similar environmental and public health benefitsas well as overall reliability. Alternatives 6 and 7 willtherefore not be retained for further analysis.

Treatment of ground water at or near the source will beevaluated. Treatment at or near the source would involve.smaller volumes of water and may allow for reinjection ofthe treated water into the aquifer. A more detailedevaluation of the treatment scheme is found in Section 5.7.

4-27

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SECTION 5\ »,

ANALYSIS OF REMEDIAL ACTION ALTERNATIVES

5.1

Six remedial action alternatives remain after the initialscreening. Among them is the No Action Alternative retainedfor use as a basis for analysis of the potential environ-mental impacts posed by the Army Creek Landfill. Thissection is the second phase in the process of selecting theremedial action alternative that best satisfies the siteobjectives and involves a detailed analysis of screeneddeveloped alternatives.

This subsection presents a discussion of the criteria forfurther screening and evaluating the remedial actionalternatives that have been developed from the screenedtechnologies. The criteria will be used to conduct adetailed analysis of the six remaining alternatives whichhave passed the initial environmental, public health andcost screening.

The criteria described herein are consistent with theRemedial Action Phase VI (Section 300.68) of the NationalOil and Hazardous Substances Contingency Plan (NCP) asamended on November 20, 1985. The procedures in the NCPare specific for hazardous substance response and areconsistent with the requirements of the NationalEnvironmental Policy Act (NEPA).

The alternative evaluation criteria include the following:

Non-cost Analysis

o Technical Evaluationo Institutional Requirementso Public Health Issuesor Environmental Issues

Cost Analyses

These criteria are discussed in the subsections that follow.

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5-1

5.1.1 Technical Evaluation

The technical feasibility criteria address criticalobjectives in the technical evaluation of potential remedialaction alternatives. These objectives include performance,reliability, implementability and safety. Each remedialaction alternative is evaluated on the basis of its abilityto achieve these technical goals.

* Performance - Two aspects of remedial actionsdetermine their desirability on the basis ofperformance: effectiveness and useful life.Effectiveness refers to the degree to which anaction will prevent or minimize substantial dangerto public health, welfare, or the environment.The useful life is the length of time this levelof effectiveness can be maintained.

• Reliability - To be reliable, a potentialremedial action alternative should incorporateproven technologies that have a demonstrated anddependable record of use, and should be capable ofaccomplishing the desired corrective results overthe planned life of the remedial action. Also,the frequency and complexity of necessaryoperation and maintenance should be considered inevaluating the reliability of alternatives.

* Implementability - Another important aspect ofremedial alternatives is their implementability -the relative ease of installation and the timerequired to achieve a given level of response.The time requirements can be generally classifiedas the time required to implement a technology andthe time required before results are actuallyrealized.

• Safety - Each remedial alternative can beevaluated with regard to safety. This evaluation^-can include short-term threats to the safety of^"nearby communities, environment, as well as toworkers during implementation.

The Army Creek Landfill site study has considered a varietyof options, including those technologies outlined in theNational Contingency Plan that have proven track records andthat have allowed these technical objectives to be metelsewhere. All potential remedial action technologiesidentified for application at the Army Creek Landfill siteare technically implementable, although the effectiveness of

5-2

each can vary with the individual techniques employed andthe site-specific character isjtics encountered duringimplementation of remedial" actions .

5.1.2 Institutional Requirements

Institutional factors can be critical to the overallimplementability and selection of an effective remedialaction program. This evaluation criterion includes thefollowing factors:

• Short-term impacts during construction, includingodors, truck traffic and noise,

• Federal, state, and local government acceptance,

• Local resident perceptions,

• Regulatory permits,

• Local zoning or other land-use ordinances,

• 3Property easements and similar agreements, and

• Long-term management and operational requirements.

As an example, on-site actions generally requiresedimentation and erosion control plans, at a minimum. If amunicipal water supply distribution line were constructed,the necessary permits or easements need to be identified andevaluated. The removal of waste material from the siterequires identification of an approved disposal site.

A management arrangement should be identified to cover thelong-term operation, maintenance, and monitoring require-ments for each alternative.

5.1.3 Public Health Issues

The rem_edial^action selected must adequately protect publichealth, ..welafe re, and the environment. Documentation thatthe action adequately controls the long-term effects of anyresidual contamination, and protects the public both duringand after the action is required. Applicable health andenvironmental health standards are used to evaluate eachalternative.

.8300652

5-3

5.1.4 Environmental Issues

The overall goal of the selected remedial action program isto mitigate the existing environmental threats withoutcreating additional adverse effects. The environmentaleffectiveness evaluation criterion focuses on the keyenvironmental contaminants. The environmental effectivenessof each potential remedial action alternative is evaluatedaccording to the requirements outlined in the NationalContingency Plan. The factors to be incorporated into theenvironmental effectiveness evaluations include thefollowing:

* The likelihood of on-site source control or of f-site remedial actions being effective to mitigateand/or minimize the threat to public health andwelfare.

* The prevention of additional environmental (soil,surface water, and ground water) contamination.

• The potential for adverse environmental effects re-sulting from the alternative or its implementa-tion.

In considering the environmental effectiveness of remedialalternatives for the Army Creek Landfill site, the followingmore specific goals have been identified:

• Protect local residents from ingestingcontaminated water.

* Protect the residents from contacting wastematerial or contaminated water.

• Control the long-term leaching of identifiedsubstances.

» _ Minimize or prevent continued ground water^ contamination*jr -

* Control run-off or surface-water impacts fromon-site remedial actions.

* Properly dispose of any contaminatedmaterials that must be excavated and/orremoved from the site.

During the evaluation of on-site source control remedialactions, worker health and safety must be considered. Anymeasures that have the potential for worker contact or

5-4

release of hazardous substances must conform to OccupationalSafety and Health Act (OSHA) requirements.

5.1.5 Cost Analysis

A remedial cleanup program must be implemented and operatedin a cost-effective manner in addition to successfullyaddressing the environmental concerns at the Army CreekLandfill site. In considering the cost effectiveness of thevarious technologies, the following costs will beconsidered:

• Capital costs.• Maintenance costs.• Monitoring costs.

The present worth value method (1985 dollars basis) will beutilized to evaluate the total cost of a Remedial Actionstrategy including the post-closure period. The costeffectiveness of the various technologies will be comparedbased on total present worth.

Monitoring and maintenance operations can represent asubstantial portion of a Remedial Action strategy. Theadded costs for these operations should be minimized. Inthis study, strategies requiring intensive monitoring andmaintenance will be avoided.

5.1.6 Analysis of Treatment Options

As discussed in Subsection 2.6.1, the evaluation oftreatment options for recovered ground water will beevaluated on a stand alone basis within the overallalternatives analysis. Objectives and criteria used for theevaluation of the alternatives will also be used in theanalysis of the treatment options appropriate to the subjectsite.

5.2 ALTERNATIVE 1: NO ACTION-MONITORING ONLY

= The No - Action Alternative is presented as a basis foranalysis ofl^-the potential environmental and public healthimpacts posetf by the Army Creek Landfill with no remedialcontrols except monitoring and for comparison with the otherremedial action alternatives. Under the No ActionAlternative, no additional remedial activities will be takenand all current activities will be terminated at the Army

R30065U

5-5

Creek Landfill site. This would mean that the presenthydrologic divide between the landfill and the ArtesianWater Company wells, maintained by the recovery well system,would be eliminated.

This alternative includes a long-term monitoring program toprovide information concerning the contaminated ground waterplume location and concentrations. Regular long-termmonitoring would be required under this alternative due tothe unknowns involving attenuation and migration of theleachate plume. This alternative does not offer anycontingencies should the concentration of substances andcompounds associated with the contaminated ground waterplume reach levels above the drinking standards in the waterproduction wells.

5.2.1 Non-Cost Analysis

5.2.1.1 Technical Evaluation

Since no remedial actions are taken under this alternative,a technical evaluation is not applicable under thisalternative. Existing and new monitoring wells will be usedfor the long-term ground water monitoring program.

5.2.1.2 Institutional Requirements

This alternative is considered not acceptable to the publicdue to the potential of contamination of the downgradientproduction wells. This alternative does not follow theproposed guidelines of the EPA Ground water ProtectionStrategy for a Class 1 ground water source (GuidanceDocument CERCLA, 1985). The No-Action alternative thereforedoes not meet the institutional criterion.

Other institutional requirements included in thisalternative would be a provision for long-term, regularlyscheduled site inspections to check on security structuresand monitoring of the contaminated ground waterconcentrations and water table levels. The monitoring wouldcontinue to employ the existing monitoring wells and includea series of new wells.

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5.2.1.3 Public Health Issues

The primary public health concern of the No ActionAlternative is the possible health risk resulting from thepotential contamination of the downgradient production wellsof the Artesian Water Co. wellfield. Current productionfrom these wells is approximately 2 million gallons a day(MGD) , supplying the equivalent of 5,000 residences(approximately 400 gpd per residence) with drinking water.The effected population could increase should the ArtesianLjLangollen Wellfield be shut down and the contaminants bedrawn towards othe"r~ wellf ields in the area , includingArtisan's Village, and Fairwinds wellf ields.

Under the No Action Alternative, the downgradient recoverysystem that is maintaining a hydrologic divide between thelandfill and the water production wells would be terminated.It is expected that the hydrologic conditions existingprior to the installation of the recovery well would return .At that time, (1973), ground water flowed from the north-west to the southeast under a natural hydraulic gradient andin response to pumping of Artesian Water Company's wells.Some attenuation of both inorganics and organics by thesandy soils of the upper Potomac aquifer, as well as somedilution by the ground water flow is expected. It is notknown, however, to what levels all the concentrations willbe reduced or the time it will take to reduce concentrationsto acceptable standards .

Of main concern is the attenuation of organic compoundsfound at concentrations exceeding drinking water criteria innine of the twelve recovery wells. Table 5-1 lists theorganic compounds found in the recovery wells , the maximumconcentrations encountered, and the drinking water criteria.It is not known at what concentration these organics willpersist in the ground water. Therefore, a potential forhuman exposure by ingestion of organic compounds inconcentrations above the drinking water criteria isassociated with this alternative. This alternative does notmeet the remedial action objective of maintaining publichealth' and

Under No Action, the contaminants would most likely beattenuated by dilution, dispersion and adsorption prior toreaching a drinking water source. This conclusion issupported by the analytical model presented in Subsection4.2.1.

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TABLE 5-1

ORGANIC COMPOUNDS IN .RECOVERY WELLSEXCEEDING DRINKING WATER CRITERIA*

Max. Cone., CriteriaWell______Parameter _____________________(mg/L-) j*< <.. (mg/L)

Hfl-1 Benzene 12.0 .01,2-dichloropropane 40.6 6.0Methylene Chloride 32.0 0.19C

OT-10 2,4-dinitrotoluene 44.0 0.11 (N-nitrosodimethylamine <10.0 0.00141,2-dichloroethane 51.0 5.0

Bff-11 Benzene <10.0 5.Oa

5W-12 Benzene 10.3 5.01,2-dichloropropane 25.1 6.0Methylene Chloride 21.2 0-i|2,4,6-trichlorophenol 3.0 1.8 ,Bis(2-chloroethyl)ether <10.0 0.03

OT-13 1,2-dichloropropane 26.8 6.0Methylene Chloride 21.3 °-19dSix(2-chloroethyl)ether 46.0 0.QJBenzene 37.0 5.0

RW-14 Bls (2-chioroethyl)ether " <10.0 °*03d2,4-dinitrotoluene 38.0 0.11

28 Benzene 40.0 5.0a

29 Benzene 45.0 5.0a

31 - Benzene 150.0 5.OaMethylene Chloride 16.3 °-19cChlorodibromomethane 19.2 0.19.

- 2,4-dinitrotoluene 116.0 0.11^^r *jr -

* - All laboratories (1983-1985)

a 3 Proposed Primary MCL (EPA, 13 November 1985)

b = Proposed RMCL (EPA, 13 November 1985)

c « Water Quality Criteria for Human Health (Fish and DrinkingWater)? concentration of total halomethanes (CWA)

d » Water Quality Criteria for Human Health - Fish and DrinkingWater (CWA)

e Water Quality Criteria for Human Health - Adjusted forDrinkina Water (CWA)

.. .-... AH300657

5.2.1.4 Environmental Issues

At present conditions, the major environmental impact of theArmy Creek Landfill is the local contamination of groundwater. The ground water impacts are on the Columbia andupper Potomac aquifers; the Potomac being the major sourceof water supply. The No Action Alternative does not providefor effective environmental management nor control of thecontaminated ground water. Environmental management wouldinclude management of the pathways in which water enters thelandfill resulting in leachate generation.

These pathways include precipitation infiltration throughthe existing granular soil cover and ground waterinfiltration along the northwestern border from the Columbiaaquifer. Approximately 30,000 gallons of water enter thelandfill on a daily basis passing through the refuse andpotentially producing an equal volume of leachate. Theleachate then percolates through windows in the Potomac clayeventually reaching the upper Potomac aquifer. The upperPotomac aquifer is tapped further downgradient for drinkingwater for the local community. The No Action Alternativedoes not meet the remedial action objective of protectingand restoring the quality of New Castle County's waterresources*

5.2.2 Cost Analysis

The capital costs associated with this alternative includeinstallation of a security fence, construction of newmonitoring wells and removal of the existing recovery wells.Long-term monitoring is included in this alternative?existing and new monitor wells will be used. Tables 5-2(A),5-2(B), and 5-2(C) provide capital cost estimates, postclosure well monitoring analysis and sampling, and estimatedpost closure and operating costs, respectively. Presentworth analysis and total cost estimates for Alternative 1 aswell as the other alternatives are provided in Table 6-1.

5.3 ALTERNATIVE 2; DOWNGRADIENT PUMPING

5.3.1 Background

Background of the development of the present downgradientrecovery well system will be discussed in this subsection.The technical evaluation will begin with the discussion ofthe existing modified recovery well system.

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In 1972f when it was discovered that leachate had enteredthe underlying confined aquifer in the Potomac Formation andhad contaminated a nearby domestic well, WESTON was retainedby New Castle County to investigate the extent of theproblem and propose potential solutions. Preliminaryhydrogeologic investigations conducted by WESTON indicatedthat .the leachate had contaminated a substantial volume ofthe upper Potomac aquifer and contaminated ground water wasmoving in the direction of the Artesian Water Company1sLlangollen Wellfield in response to natural ground watergradient and to pumping effects of the Artesian wellfield.The nearest Artesian Water Company well was located about1,600 feet from the edge of the plume of contaminants.

Based on preliminary hydrogeologic investigations, acontaminant recovery and monitoring program was designed andimplemented in 1973 as an initial step towards eventualsolution of the problem. The recovery program was designedto achieve the following objectives:

• To control the migration of contaminants towardsArtesian Water Company's wells and to contain themin an area closer to the landfill.

• To create a ground water divide between theArtesian wellfield and the contaminated zone suchthat the ground water flow in the contaminatedzone could be reversed and the contaminated groundwater moved toward the Army Creek Landfill.

• To recover contaminated water and restore theaquifer water quality.

• To monitor the water quality and water levels inthe area and evaluate the effectiveness of therecovery program.

• To develop feasible leachate treatment and dis-posal methods until some type of permanent solu-tion to the problem was determined.

As a result --a large number of observation and recoverywells were constructed. While the observation wells wereconstructed in both the shallow Columbia sediments and theunderlying Potomac aquifer, the recovery wells wereconstructed only in the contaminated zone of the upperPotomac aquifer, which is the main source of water supply.

5-13

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Pumping tests were conducted on the recovery wells. Datawas analyzed to determine the hydrolpgic properties of theaquifer, interference between the wells, production rates ofthe recovery wells, and the quality of the ground water inthe area.

The basic concept in selecting locations of the recoverywells was to locate them such that the contaminant plumewould shrink north toward the landfill; then utilize onlythose recovery wells located closer to the landfill, whenthe ground water quality had improved at locations distantfron the landfill. It was recognized at the outset that:

• The volume of leachate would be minimized if itcould be intercepted immediately beneath or•adjacent to the landfill;

* The area covered by the landfill is_ small compared_."_fcQ the area! extent of the cone of depression-formed in response to Artesian wells pumping;

* The volume of water (precipitation fallingdirectly on the landfill and laterally enteringthe landfill) that will potentially becomeleachate, would also be small compared to thetotal volume of water that is available in theaquifer in this drainage basin and, which is usedby Artesian Water Company;

• Leachate would be highly concentrated within andbeneath the landfill and, therefore, its treatmentaild disposal could potentially pose problems ifintercepted within the landfill;

• The distant production wells would continue topull the contaminants from the landfill to theirpresent location or beyond, as long as they are inoperation;

It would be necessary to locate recovery wells asclose to the landfill as possible, to control andlocalize the migration of contaminants away fromthe landfill;

The recovery wells would experience periodicproblems due to incrustation and mechanicalbreakdowns and would require proper maintenance.

5-14

Prior to the installation of the recovery wells, groundwater in the upper = Potomac aquifer was flowing in anorthwest-southeast direction under a natural hydraulicgradient and in response to pumping of Artesian WaterCompany's wells. Figure 5-1 is a map showing theconfiguration of the piezometric surface in May, 1973 priorto recovery well pumping.

Figure 5-2 is a map showing the configuration of thepiezometric surface on March, 1976. In comparing Figures5-1 and 5-2, it is evident that the configuration of thepiezometric surface had changed significantly between 1973and 1976. When all the recovery wells were in operation, alarge cone of depression was formed in the vicinity of wellsRW-1, RW-3, and RW-5 and small cones were developed aroundthe other recovery wells. The ground water flows towardthese cones of depression is shown fay arrows in Figure 5-2.

Figure 5-3 is a map showing a net decline in piezometrichead that occurred between 1973 and 1977. A large troughdeveloped in the area south of the landfill. The totalpiezometric head decline was less than 5 feet to more than15 feet as shown on the figure.

Evaluation of chloride and TDS concentrations obtainedduring the periods of 1973 through 1977 (Appendix O)indicates that:

• The concentrations of chloride and TDS in thewells 27, 28, 29, 31 and RW-6 were higher than"those in the wells 44, 51, IB, RW-4 and in otherrecovery and observation wells west of 28;

• The concentrations of chloride and TDS decreasedover the period since leachate recovery started;this decrease is also evident in the wells locatedwithin the landfill;

• Generally, the chloride and TDS concentrationsdecreased away from the landfill;

concentrations of chloride and TDS in well 42increased and the quality of water continuouslydeteriorated;

Although the chloride and TDS concentrations inwells 27, 28, 29, 31 and RW-6 decreased over theperiod between 1973 and thrbugh 1977 they werestill relatively high;

R3G066U

5-15

• Leachate appeared to enter the aquifer beneath thelandfill in an area north of the wells 27, 28, 29and 31 and in the southwest corner of thelandfill;

• Leachate entering the aquifer in the southwestcorner of the landfill by-passed the cone ofinfluence imposed by the recovery wells and movedunder a natural hydraulic gradient and in responseto pumping of Artesian Water Companyfs wells 2, 6and 7;

• The slow but steady deterioration of water qualityin Well 42 perhaps reflected low permeability ofthe subsurface material in that direction; most ofthe area surrounding Well 42 is underlain by clayand silty material which retards the movement ofground water;

• The attenuation of contaminants and improvement ofwater quality in an area south of the wells 27,28, 29 and 31 was largely due to dilution inresponse to recovery efforts.

• The recovery wells not only removed thecontaminants present in their vicinity but theywere also effective in pulling additionalcontaminants to their present locations.

Based on the data collected from 1973 to 1977, an analysisof the recovery well system was performed. The followingconclusions were made from this analysis:

• The recovery wells have been successful incontainment of the contaminated ground water plumewithin the ground water flow south of the ArmyCreek Landfill.

• A ground water divide has been developed betweenthe Artesian Water Company's wellfield and the^contaminated zone of ground water. The groundw*ter flow in the contaminated zone between thelandfill and the Artesian wellfields has beenreversed towards the recovery wells and the ArmyCreek Landfill.

• Army Creek Landf ill wil1 co nt i nue to produceleachate until the refuse becomes inert or someother solution of the problem is determined.

R300668

5-19

4f|fp'1

* The recovery wells RW-1, RW-3, RW-4, and RW-5continued to pull the contaminants to as far astheir present locations; these recovery wellscould be phased out of the system in stages byreducing their pumping rates.

* It would be necessary to monitor the water qualityin the vicinity of the recovery wells RW-lf RW-3,RW-4 and RW-5 more frequently than usual whentheir pumping rates have been reduced. This wouldassure early detection of any deterioration causedby reduced pumping rates.

• It appears that most of the inorganic contaminantsare discharged into the upper Potomac aquifer inan area of the landfill north of the recoverywells 27, 28 and 29 and in the southwest corner ofthe landfill.

• The "total pumping rate of the recovery wells wasapproximately 1.5 million gallons per day, whichis about 7.5 times more than the average dailyrate of potential leachate production, Leachatewould be recovered more efficiently if the wellswere located within and closer to the landfill.

• Incrustation has caused a significant problemrequiring frequent rehabilitation of the recoveryw<§lls. To control the incrustation problem, thepumping rates of the existing recovery wellsshould be further reduced by about 50 percent.

• When RW-lr RW-2, RW-3, RW-4 and RW-5 have beenphased out of the recovery program, more rechargewill be available for Artesian Water Company'swells.

It was therefore recommended that new wells be installedcloser "to the landfill such that leachate and contaminatedground ter could be recovered more efficiently. This wasalso recommended by the Round Table Conference as discussedin Section 3.3. Phase I of the Round Table recommendationsincluded installation of recovery wells RW-10, RW-11, RW-12,RW-13 and RW-14 which are located closer to the landfill andthe phasing out of recovery wells RW-2, RW-3, RW-5 and RW-6.The evaluation of the downgradient pumping system as analternative will be based on data collected for the modifiedrecovery well system in place since May 1982.

ftR300669

5-20



Performance - The effectiveness of the modified down-gradient pumping system was evaluated in May 1982 through aseries of pump tests performed on the new recovery wells,RW-10, RW-11, RW-12, RW-13 and RW-14. Computed drawdowncurves, for each pumping well and selected observationwells, are found in Appendix M. Table 5-3 provides a datasummary for the new recovery wells during the pumping tests.

The time-drawdown curves, for the new recovery wells,indicate that there was little variation in the individualrates of drawdown. This would suggest that the wells areefficient and that well losses are small. The majority ofthe drawdown results from formation losses which arefunctions of the aquifer characteristics. Variations indrawdown were caused by variations in pumping rates and/ormutual well interference. The degree of interference amongthe new recovery wells is given in Table 5-3.

The primary aquifer characteristics that affect the groundwater movement are Transmissivity, Storativity and hydraulicconductivity of the aquifer matrix. Drawdown, time, andpumping rate data wer;e used in the calculation of theaquifer characteristics. Since the new recovery wells arecloser to the landfill than the original recovery system andgiven the fact that the outcrop or recharge area for theupper Potomac aquifer is located north of the landfill,several methods for calculating the aquifer characteristicswere initially tried in order to determine if water tableconditions, leaky artesian, or artesian conditions exist inthe vicinity of the new recovery wells.

Transmissivity for a selected observation well was cal-culated using the modified straight line method, developedby Jacob, the Theis standard type curve, leaky artesian typecurve, and water table type curve. There was good agreementamong.the methods used, and the standard type curve, de-veloped by*.Theis, was selected for the Transmissivity andStorativity*'calculations.

Transmissivity and Storativity were calculated for observa-tion wells where sufficient drawdown data curves existed.Table 5-4 lists the Transmissivity and Storativity valuesfor the selected observation wells. There is some variationamong the Transmissivity values which is due to the natureof the aquifer. The upper Potomac aquifer exhibits

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'AR30067

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TABLE 5-4

TRANSMISSIVITY AND STORATIVITY

NEW RECOVERY WELLS PUMPING TEST

RW-12 pumping 200 pgm

Well T_ (gpd/ft)

29 76,400 0.00531 40,930 0.00565 69,450 0.03

RW-10 pumping 200 gpm, RW-11 pumping 200 gpm

Well T S(gpd/ft)

RW-4 72,330 0.006.», 66 44,940 0.01Iji 67 38,200 0.02

ii!f.

RW-13 pumping 200 gpm

Well T S(gpd/ft)

RW-6 71,350 0.0139 52,800 0.01

RW-14 pumping 100 gpm

Well T S(gpd/ft)

71 36,970 0.003

R300672

5-23

considerable lateral changes in composition. This is due tothe fact that the sediments were laid down in streamchannels along flood plains and shallow embayments, ratherthan in homogeneous layers, so Transmissivity will varydirectionally depending on location. This directionaltranmissivity effect is illustrated on Figures 5-4 through5-7 which show the distance drawdown effects between the newrecovery wells and selected observation wells on 19 May19 8 2. In actuali ty, the di sta nee- drawdowns shown onFigures 5-4 through 5-7 will not be strictly linear due torecharge effects and the effects of pumping of the ArtesianWater Co. wells.

The distance-drawdown graphs indicate that, with acombination of pumping the new recovery system and theoriginal recovery system, mutual well interference willcreate a trough-like depression in the piezometric surfacein the upper Potomac aquifer. This depression, extendingnortheast to southwest from well RW-13 through well 31,RW-12, 297 28, 27, RW-1, RW-3, RW-5, RW-11, RW-10, RW-4, andRW-9 will effectively prevent leachate from migrating southof the landfill and will recover contaminated ground waterto the south of the recovery system.

The reason the new recovery system was located closer to thelandfill was so that more concentrated leachate could berecovered while pumping volumes of ground water for shorterperiods of time. It was intended that as water qualityanalysis indicated a decrease in leachate content in theobservation wells south of the landfill, selected recoverywells of the original recovery system would be phased out.In this way, rather than pumping large volumes of diluteleachate from the edges of the leachate plume for longperiods of time, the new recovery system will effectivelyrecover a higher proportion of leachate, faster and at lowerpumping rates, while at the same time preventing migrationof leachate to the south.

In order to determine the extent of the pumping effects ofthe ndfc- recovery system using the aquifer characteristicsdeterminVd during the pumping test, distance drawdownrelationships were calculated. It was assumed that theoriginal recovery system was shut off.

It was also assumed that pumping level equilibrium wasreached after 5 days of pumping which is suggested by theresults of the pumping test. Using Theis1 formula, the

5-24

distance was calculated ft which"point s is less than 0.5feet. This formula can be described as:

s « 114.6 Q W(u)T

where:

s =» drawdown in ft. at any point in the vicinity of awell pumping at a constant rate.

Q - pumping rate in gpm.

W(u) « well function of u.

where u is defined by the expression:

u = 1.87 r2 S/Tt

where:

r = distance in ft., from center of pumped well topoint where drawdown is measured.

S = Storativity, dimensionless.

T = Transmissivity, gpd/ft

t = time since pumping started, in days.

The drawdown value of 0.5 feet was chosen to represent theground water divide in the piezometric surface caused by thepumping wells. It is recognized that fluctuations willoccur in the piezometric surface, due to recharge and thepumping affects of other well systems, which will cause theground water divide to shift. So a distance drawdown of 0.5feet or less would effectively represent the edge of thecone of depression caused by the pumping well.

Table-5-5 lists the predicted distance from each of the newrecovery <fe»lls to the edges of their respective cones ofdepression.* " It should be understood that Table 5-5represents ideal conditions, that is an initially horizontalpiezometric surface, and no outside influence, eitherrecharge or additional discharge, on the aquifer system. Inreality the radii of influence are much smaller, as

AR30067U5-25

TABLE 5-5

DIRECTIONAL RADII OF INFLUENCE*

NEW RECOVERY WELLS AFTER 5 DAYS

RW-12 Q - 200 gpm

Direction Distance(ft> nrawdown(ft)

Northeast-Southwest 2,800 0.46

Northwest-Southeast 1,000 0.46

RW-10 and RW-11 combined Q = 400 gpm


Northwest-South-Southeast 1,850 0.48

RW-13 Q = 200 gpm


East-West 2,000 0.41

RW-14 Q = 100 gpm

Northwest-Southeast 2,200 0.45

*Note: Theoretical - under ideal.conditions withno outside interferences.

R300675

5-26

indicated by Figures 5-4 through 5-7. Figure 5-8 representsthe southern boundary of the combined cones of depression ofthe new recovery wells as indicated by Figures 5-4 through5-7, and Table 5-5. With the additional drawdown caused bythe pumping of the original recovery system, the radii ofinfluence would actually extend farther to the south. Evenwithout the original recovery system, the new recoverysystem would effectively intercept the landfill plume.

Utilizing this pump test data, historical ground waterelevation and flow data, and historical water quality data

—— — -—- ~ available for the Army Creek Landfill, an evaluation of thefeasibility of phasing out some of the recovery wells wasmade. The following provides a background of the wellrecovery program and factors used in determining potentialrecovery wells to be phased out.

': Performance Optimization - Following the combined pumpingtest of the new recovery wells (RW-10 through 14) from 10 to15 May 1982, these new wells were incorporated into theground water recovery program for the Army Creek Landfill.

' In June 1983, when all the operational recovery wells wereHI on line, a total of 15 wells were recovering ground water|j < and creating a trough-like depression south of the landfill.

Between June 1982 and April 1983 these recovery wellsdischarged between 1.37 mgd and 2.14 mgd, averaging 1.667mgd. During the same period, the Artesian Water Companypumped between 1.57 mgd and 1.97 mgd, averaging 1.895 mgd.Fluctuations in pumping rates of the recovery wells were dueto various wells being off line at times for repairs and thegradual loss of well efficiency due to well screen anddischarge pipe clogging by the iron bacteria, Clonothrixand Gallionella.

Table 5-6 tabulates the average daily pumping rate, in gpm,of the recovery wells and the Artesian Water Companywellfield from June 1982 to April 1983. It can be seen thatmany of the wells show decreasing pumping rates due to lossof efficiency through time. The effects of rehabilitationcan also be seen in the increase in the average dailypumping rafee of RW-1 from 83 gpm to 263 gpm.

It was concluded that the recovery program could be mademore cost effective by eliminating some of the lessproductive wells and maximizing the pumping rates andefficiencies of recovery wells closer to the landfill.Listed below are the average pumping rates for the recovery

flR300676

5-27

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FIGURE 5-4 DISTANCE VS. DRAWDOWNRW12 Q = 200gpm(5/15/82)

5-28

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FIGURE 5-5 DISTANCE VS. DRAWDOWNRW10 Q = 200 gpmRW11 Q = 200gpm « DOftn^r TO(5/15/82) ft H 30067 8

5-29

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u.| 15O"p

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tRW13 Well 39

tRW14tRW6

10 Distance (Ft) 10° 10°°

FIGURE 5-6 DISTANCE VS. DRAWDOWNRW13 Q = 200 gpm(s/15/82) AR300679

5-30

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5-31

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5-33

wells for May 1983 and for comparison the initialrates, after well construction, when the wells were mostefficient:

Current Most EfficientPumping Rate Pumping Rate

Wells (gpm)____ ___(gpm)____

RW-1 200 200RW-3 34 200RW-4 103 200RW-6 12 150RW-9 50 80RW-10 220 250RW-11 118 200RW-12 45 200RW-13 69 200RW-14 19 " " 10027 33 15028 127 16029 137 15031 67 165

From the listing above it can be seen that most ofrecovery wells were operating well below 50efficiency. It was suggested that, the cost-effectivenessof the recovery program could be improved by eliminating themarginally productive wells that are some distance from thelandfill while maximizing the use of the recovery wellscloser to the landfill. This would also increase thequantity of leachate recovered since the recovery wellscloser to_ the landfill pump a higher proportion ofcontaminated ground water versus clean ground water asopposed to the recovery wells located farther downgradient,which pump a smaller proportion of contaminated groundwater.

In order to determine which wells could be taken off-linethe pumping records (Table 5-6), general performance, andwater quality data for the recovery wells were examined.Table f^7 lists the average total dissolved concentrationsfor the recovery wells from June 1982 to April 1983. Totaldissolved solids was chosen for analysis since this

SR3006S3

5-34

TABLE 5-7

AVERAGE TDS CONCENTRATIONS

JUNE 1982 - APRIL 1983

Average TDS TDS RangeWells (mg/L) (mg/L)

SJ'i 243 137 - 300RW-3 94 63 _ 136RW-4 133 83 _ 195™~l 152 37 - 185RW-6 115 90 _ 160RW-9 219 74 - 273RW-IO in 81 _RW-11 164 110 _RW-12 193 96 _RW-13 TOO 70-124RW-14 191 166 _ 225II 203 131 - 285%l 431 416 - 45629 380 324 - 42831 133 65 - 220

5-35

parameter is conservative in that, once in the ground waterflow system, it is attenuated principally by physical meanssuch as dilution and dispersion. Table 5-7 indicates thatmost of the wells have a dissolved solids content below thelevel of 250 mg/L set for EPA interim drinking waterstandards, although the wells directly downgradient of thelandfill generally show higher dissolved solids than wellsfarther removed.

A review of the data lead to the suggestion that recoverywells RW-3, RW-4, RW-5 and RW-6 could be taken off-linewithout deterioration of the overall recovery program. Thepumping records and water quality data indicated that if theremaining recovery wells, RW-1, RW-9, RW-10, RW-11, RW-12,RW-13, RW-14, 27, 28, 29 and 31 are maintained at even 70percent of full efficiency, the recovery program would bepumping 1.87 mgd which is higher than the average pumpingrate for the full system from June 1982 through April 1983.The four wells (RW-3, RW-4, RW-5, and RW-6) suggested forremoval from the system have had generally poor performancerecords, are in the radii of influence of more productivewells, are farther from the landfill, or whose TDS valuesindicate a low leachate to ground water ratio.

The conclusions and recommendations from the pump testsresulted in the phasing out of reco"very wells RW-3, RW-4,HW-5 and RW-6. The current downgradient pumping systemsincludes RW-14, RW-13, RW-12, 31, 29, 28, 27, RW-1, RW-11,RW-10, and RW-9. The current system has maintained theground water divide necessary to intercept contaminatedground water as depicted in the piezometric surface map(Figure 5-9) based on current well data and summarized inSections 1.2.1.2 and 1.2.3.1 on ground water quality.

Reliability - The clogging of well screens and dischargeline by iron precipitate is a continuous problem that isaddressed through a regular program of well rehabilitationand pump repair. During the period June 1982 through April19"83 at "least one well was off-line during any given month,with 1?§e_ exception of June 1982, for maintenance, repair orrehabilitation. Since the phasing out of the four poorperformance wells, a biannual maintenance program has beenestablished to treat and rehabilitate the twelve operatingwells. Maintenance and replacement of parts have beenperformed as part of the maintenance program.

AR300685

5-36

WESTON developed a program for the rehabilitation of thedowngradient recovery wells to increase system reliability.The treatment and rehabilitation of wells affected byincrustation may be approached in two ways, (1) Pulling thepump and (2) Treatment of the screen and pump in place.For wells located in unconsolidated formations like those inthe Army Creek area, three methods of treatment aresuggested:

1) Treatment with polyphosphate salts and chlorine.2) Treatment with muriatic acid.3) A combination of the above.

A combination of mechanical surging and backwashing toprovide necessary agitation, along with the application ofchemicals is used to rehabilitate a well. The chemicalcomposition of the encrusting material determines thechemicals that should be used for well treatment. Althoughthe exact chemical composition of the encrusted material isnot known, the Army Creek Landfill wells are expected to beaffected by iron deposits due to its high concentration innatural ground water and in leachate from the landfill.Moreover, at such high concentrations the iron, probably ina ferrous state, exists in colloidal form and metal organiccomplexes. In such cases, treatment by use of polyphosphatesalts and muriatic acid is advised. Polyphosphate salts,such as Calgon, are deflocculants and emulsifying agentsthat act as detergents when surged in the well. They serveto break up and disperse soft iron deposits such as ironcomplexes. Muriatic acid will dissolve iron and manganeseoxides, hydroxides and carbonates. Appendix M provides anexplanation of the rehabilitation program currently in useat the Army Creek Landfill.

Implementability - Since the recovery well system isalready in place and operative, there is no implementationtime necessary for this alternative.

A ,definitive time period for phasing out the recovery wellsystemgfccannot be made at this time for the followingreasons*-*-

• Adequate water quality data for organics doesnot exist.

• The total impact of Delaware Sand and GravelLandfills is not known.

&R3G0687

5-38

• The remedial actions to be taken at Delaware Sandand Gravel Landfills is not known.

The following methodology will be considered for phasing outthe recovery well system:

The recovery well system will be evaluated in terms of boththe flow system and water quality for a period of five yearsafter the cap is installed or after the waste is excavated.If_ primary drinking water criteria levels are not metwithin this evaluation period, alternate concentrationlevels (ACL) will be considered. These ACLs will be basedon an evaluation to define if sufficient attenuation will beachieved downgradient of the Army Creek Landfill, so thatdrinking water criteria levels will be met at any potentialreceptors. These ACLs could be applied at the recoverywells or the property boundary. When the ACLs are met, therecovery well system could be phased out.

Safety - Safety precautions are required under thisalternative during pump rehabilitation. Procedures havebeen developed for the treatment and rehabilitation of therecovery wells that include safety measures. These includeproper handling .of treatment chemicals and shutting off thepower to the pumps prior to treatment and rehabilitation.


The following factors would have to be considered regardingthe implementation of downgradient controls:

• Long-term monitoring, operation, and maintenancecosts are involved in operation of the down-gradient pumping system. Long-term funding mustbe in place for these costs.

• Depending on the treatment option selected, aNPDES permit would be required for discharge oftreated water to Army Creek. A preliminary draft

- - - - - -— NPDES permit was issued in November, 1985.


Sampling and testing performed at the Artesian Water Com-pany's wellfield and concentration gradient maps of the area

Bo n n co Qu UUuu o

5-39

(Subsection 1.2.1.2) have indicated that the downgradientpumping system has been effective in containing the contamin-ated ground water plume through the creation of a hydrologicdivide between the landfill and the Artesian Water Company's

wellfield. Alternative 2 has therefore proven to have re-duced the public health risk that could result if the con-taminated ground water plume was not controlled.


The recovery pumping program in place at the Army CreekLandfill has proven to have contained contaminated groundwater. By controlling the contaminated ground water thepumping system has prevented the possible abandonment of theupper Potcmac aquifer as a source of water supply in theproduction wellfields near the landfill.

Alternative 2 does not, however, address * the source ofleachate entering the Potomac aquifer or the pathways inwhich water enters the landfill resulting in leachateproduction. Precipitation infiltration through the landfillsurface and ground water infiltration through theside of the landfill from the Columbia aquifer willunder this alternative. Therefore, leachate migrationthe Columbia and upper Potomac aquifer will continue forAlternative 2.

The environmental impacts from the discharge of thedowngradient pumping operation will depend on the treatmentoption choosen for the Army Creek Landfill site. This willbe discussed in Section 5.7.

5.3.3 Cost Analysis

Since the downgradient pumping system is in-place, the onlyfuture capital cost associated with this alternative is theinstallation of a security fence. Capital costs arepresented in Table 5-8(A). Operation and maintenance costsincluo *. well rehabilitation, well monitoring, pump andequipment maintenance and the electricity required to runthe pumps. Table 5-8(B) provides a summary of the estimatedpost closure and operating costs for Alternative 2. Presentworth analysis and total cost estimates for each alternativeis presented in Table 6-1.

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5-40

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AR30069

5-42

5.4 ALTERNATIVE 3 - DOWNGRADIENT PUMPING AND LANDFILLCAPPING

Alternative 3 consists of the downgradient pumping programevaluated under Alternative 2, and includes capping thelandfill. The capping techniques retained after thetechnology screening will be further evaluated under thetechnical evaluation criteria of this alternative and themost technically effective cap system for the Army CreekLandfill site will be discussed.

The surface cap, whether a single or multilayered system,will consist of a low permeability natural soil or soiladmixture layer. Capping of the landfill therefore offersgreater environmental effectiveness than Alternative 2 byreducing the precipitation infiltration through thelandfill, thus reducing leachate production. Capping of thelandfill includes site clearing, regrading of the existingcover surface, adding soil- backfill to achieve grades,installing the cap with gas vents, and construction ofdrainage ditches to direct run-off away from the landfill.



The technical evaluation of the downgradient pumping programhas been performed under Alternative 2 in Subsection-5.3.1.1. The non-cost analysis for this alternative willtherefore concentrate on evaluating the surface capping ofthe landfill which includes surface management and gasventing. It is anticipated that less pumping both inquantity and duration -by the downgradient recovery wellsystem will be required as a result of capping the landfill.Significant reduction in precipitation infiltrationshould hasten ground water cleansing.

Performance - The use of a cap system is a proventechnology for reducing percolation into containment areasand for controlling erosion. The technical feasibility of acap - system for control of infiltration is primarilydependent^* upon identifying the most suitable cappingtechnique.*" Cap materials which have a history of successfuluse include:

• Synthetic membranes• Low permeability soils• Soil admixtures• Asphalt or concrete

ftR300692

5-43

These capping techniques were described in Subsectio2.2.3.1 under the screening of remedial action technologies?The conclusions drawn from this screening were as follows:

• Synthetic Membranes; These materials can providea relatively low-cost cap which can be highly effi-cient when properly installed. Membrane installa-tion typically includes the following sequence ofactivities: sub-base grading and preparation, place-ment of a sand/cushion layer, membrane installa-tion, clean soil or sand placement, top soil place-ment and vegetation of top soil. Potential draw-backs of membranes include: possible damage duringinstallation, uncertain integrity of seaming,damage due to root penetration, and the potentialof failure due to differential settlement which isan on-going problem at the Army Creek Landfill-'site. These possible drawbacks could limit mem-brane use in this application, particularly with re-spect to assuring long-term integrity. The poten-tial installation problems can be resolved by meansof a thorough field QC program, however, the damagedue to differential settlement can not be adequate-ly resolved and must include long-term periodic in-spection. This technique was therefore not retained during preliminary screening.

* Low Permeability Soils; A low permeability soilcover as a cap is generally a slightly-higher costalternative than the synthetic membrane. It isalso highly efficient when properly placed and pro-tected. After grading, the compacted low permeabil-ity soil cover could be placed directly over thesurface soils and backfill material. The cap isgenerally covered with a protective cover of cleansoil followed by a vegetated top soil layer. Sincelow permeability soils are natural material, a longlifetime can be expected. In the event that signif-icant differential settling occurs, a low permea-

- bility soil cap could be repaired in the affected•to, areas using standard construction techniques.JT -

Typical design practices set the thickness of thecompacted low permeability soil layer generally at18 inches to two feet so that the desired degree ofimpermeability and reliability is attained. Thefeasibility of low permeability soil as a capmaterial is based on the availability of a suffi-cient supply locally.

AR300S935-44

A potentially feasibly. fc alternative to naturallyoccurring low permeability soils is dredge spoil,which is available locally in large quantities andat low cost. Potential borrow sources for thesematerials include a dredge spoil site at the Texaco(formerly Getty) refinery which is located a shortdistance from the site. These materials arepresently stored at man-made disposal sites ofapproximately 200-300 acres each, wherein materialsare deposited hydraulically from annual dredgingoperations. Generally, these materials range froma sandy silt to an organic silt of high plasticity.

In connection with conceptual design work recentlyundertaken for the use of these materials as a sur-face cap for the Tybouts Corner Landfill, alsolocated in New Castle County, a limited samplingand testing program of these materials was per-formed. Hydraulic conductivity testing of repre-sentative samples of available material- indicatedthat a design permeability of 1 x 10" on/sec orlower can be achieved with soil compaction in therange of approximately 90 percent of its maximumdry density as determined by the Standard ProctorTest (Duffield, 1985).

The samples tested were classified as high plastic-ity silt (MH) and organic silt (OH) according tothe Unified Soil Classification System. Naturalmoisture content for the MIT samples ranged from 29to 68 percent. The optimum moisture content forthis soil was determined to be 34 percent (ASTM-698). Natural moisture content for the OH samplewas 134 percent indicating a high organic content.The optimum moisture content for an OH soil is 47percent (ASTM-698). These results indicate thatsome aeration of these materials will be requiredbefore placement and compaction. Maximum dry den-sities (ASTM-698) of 68 and 70 pounds per cubicfoot (PCF) were recorded for the OH and MH soil•e pectiveiy. These -values are considered low(Values of 100 PCF are normal for these types ofmethods) and suggest that additional physicaltesting is required as part of the design phase(Duffield, 1985).

in addition to limited physical property testing,representative samples were submitted for completepriority pollutant analysis. Results indicated

.R30063U

5-45

that no PCBs were detected and that none of thetested volatile organics, acid extractable organicsor base/neutral extractable organics were presentin concentrations equaling or exceeding minimumdetection levels. Cyanides, phenolics and certainpesticides were detected at trace levels andcertain metals were detected in variousconcentrations. However, using E.P. Toxicity (EPA,1980) extraction testing, for the 13 prioritypollutant metals showed that none of thesematerials were detected at concentrations aboveapplicable maximum contaminant levels (Duffield,1985).

The use of dredge spoil as a cover material appearsas a feasible alternative to natural low permeabil-ity soil which are not readily available locally inlarge quantities. Additional sampling and physicaland chemical testing is needed as part of the de-sign phase. This sampling and testing shouldinclude:

• Physical testing to determine strength prop-erties and characteristics of dredge spoilmaterial.

• Further grain size analysis (hydrometer) todetermine clay content of dredge spoil.

• Additional sampling and classification ofmaterial 'at primary source location to determinevariability of material (variability of materialwill result in QC problems during installation).

• Slope stability analysis for slopes along the-gouth-southwest sides of the landfill.

• Analysis of the use of a drain layer and geotex-tile reinforcement in a dredge spoil cap system.•* -

• Additional chemical testing on organic contentand presence of petroleum hydrocarbons.

This cap technique was retained in the technologyscreening process.

Afl300695

5-46

Soil Admixtures; A .. low permeability soil/bentonite or other low permeability soil admixturecan be placed as the cap layer in the multilayercap system, or as a single layer cap system ifnatural low permeability soils are not locallyavailable or can not be used in a cost-effectivemanner.

Soil/bentonite admixtures are a proven capping (andlining) technique in waste management that is gain-ing acceptance in field construction applications.Soil/bentonite admixtures incorporate a combinationof natural and processed bentonite for use in capsystem applications. When mixed in the proper pro-portions with a native soil, permeabilities of10" cm/s and less can be achieved. Tables5-9(A) and 5-9(B) present the approximate bentoniteaddition rate suggested to yield a permeability of7 x 10 cm/s with each soil type listed. Be-cause of bentonite's unique molecular structurethat results in swelling up to 15 times theiroriginal dry bulk at full saturation, bentonite canprovide an excellent "self healing" mechanism in acap system. Composed of natural materials, a soil/bentonite layer would be expected to have a longdesign life.

Other low permeability soil admixtures that shouldbe considered during design optimization are flyash/fine grained soils/lime stabilization and flyash/lime stabilization/kiln dust. Detailed designevaluation and costing is needed before theseadmixtures can be considered for site application.

The soil admixture techniques were retained underthe initial screening of the remedial actiontechnologies.

Multilayer; With the exception of asphalt or con-crete, the multilayered cover system is generally

most expensive of the infiltration controlsIng considered. However, with proper placement,

it can also be the most efficient and long lasting.The grading, vegetation, cover soils, drain andcap layers all combine to reduce infiltration to aminimum, and since all construction materials arenatural, a long life can be expected. Differentialsettlement could reduce its effectiveness andrepairs would be more complex than for a basic lowpermeability soil cap, since it would be necessary

ftR3006

5-47

TABLE 5-9(AjSUGGESTED BENTONITE ADDITION

FOR SOIL ADMIXTURE CAP SYSTEMS

cw

OP

CM '

GC

SW

SP

SM

SC

ML

CL

OL' ^jr

MH

CH

OH

PT

K > 10'2

K > 10"2

K = 10"3-10"6

K = 10"6-10*8

K > 10"3

K > 10"3

K = 10~3-10~6

K = 10'6-10'8

K = 10'3-10-6

K = ny6-io~8

K = 10~d-1CT6

K = 10"4-10"fi

K = 10*6-10"S

K = 10"6-10'5

Variacse

Possibly not sealable without use ofborrowed materialPossibly not scalable without use ofborrowed material

2% - 8% by weight of soil

None

> 8% by weight of soil

> 8% by weight of soil

2% - 8% by weight of soil P

None

2% • 8% by weight of soil

None

2% - 6% by weight of soli

2%. 6% by weight of soil

None

AR3QOb^/ ANone P

Unsuitable soil for sealing'—SOURCE:Wyo~Ben,Inc.,Billings,MT

5-48

TABLE 5-9(_B)SOIL CHARACTERISTICS

COARSEGRAINEDSOILS

. .

>

FINEGRAINEDSOILS

>

•

GRAVELAND

GRAVELLYSOILS

SANDANDSANDYSOILS

SILTSANDCLAYS11<5C

^^r *jr -

C!L^CAVr*.r-v! *. -CLAYSLL > 50

cw

CP

CM

cc

sw

SP

SM

sc

ML

CL

OL

MH

CH

OH

Well-graded gravels or gravel-sandmixtures, little or no fines

Poorly-graded gravels or gravel-sandmixtures, little or no fines

Silty gravels, gravel-sand-silt mix-tures

Clayey gravels, gravel-sand-daymixtures

Well-graded sands or gravelly sands,little or no fines

Poorly-graded sands or gravellysands, little or no fines

Silty sands, sand-silt mixtures

Clayey sand, sand-silt mixtures

inorganic silts and very fine sandsrock flour, silty or clayey finesands or clayey silts with slight plasticity.inorganic days of low to mediumplasticity, gravelly clays, sandyclays, silty clays, lean clays

Organic silts and organic silt-ciaysof low plasticity

Inorganic silts, micaceous ordiatomaceous fine sandy or siltysoils, elastic silts

inorganic clays of high plasticity,fat clays ;

Organic clays of medium to highplasticity, organic silts !i

5-49

to "key-in" repairs on a layer by layer basis. Thmultilayer cover was also retained during thinitial screening process.

» Asphalt or Concrete: The cost of a constructedcap of asphalt or concrete would be greater thanthat of the synthetic membrane. Long-term effectsof differential settlement, sun aging, creep andsubgrade movement, and possible freeze/thaw damagecould combine to reduce the effectiveness of thecap and damage the integrity _ of the asphalt.Differential settling problems at the site repre-sent the major potential damage to a constructedcap, reducing the effectiveness of the cap system.These techniques were not retained under theinitial screening process presented in subsection2.2.3.1 due to high cost and uncertainties of long-term integrity due to settlement.

For the retained capping techniques a performance assessmentwas conducted using performance criteria. This assessmentis shown on Table 5-10. The 3 capping techniques areassessed on a relative basis with each other. If a covermaterial was given a positive relative performance rating aplus sign appears in that criteria column. If arelative performance rating was given, a minus sign

f in the criteria column.

It can be seen that in a relative sense the multilayeredcover system shows the overall best performance. The singlelayer low permeability soil (native soil or soil, dredgespoil admixture) cover is slightly less effective in imped-,ing infiltration in the long-term due to weathering damage(i.e., cracking, freeze/thaw, desiccation, etc.). Some ofthese potential long-term uncertainties may be minimized byplacing a cover soil layer (which includes a topsoil,vegetated layer) and proper design of the cover grades andslopes or use of geotextile reinforcement. The single layerlow permeability cover would be easier to repair as comparedto the, multilayer cover system. The multilayer cover ismore qg tly to construct and repair/maintain if needed. Alow .permeability soil cap system may be the most cost-effective cap system. The final cap system will be deter-mined as part of the design phase. An evaluation ofpotential cap systems will be discussed in this section.

A low permeability soil cover system includes the use of aclean soil and top soil cover layer placed over the lowpermeability soil cap. The upper soil layers are placed .to

SH3006995-50

TABLE 5-10

CAPPING TECHNIQUE ASSESSMENT

COVER MATERIALLow

Performance Permeability Soil Multilayered____Criteria__________Native Soil Admixtures____System____

Historical applicationsas a cover material + -

Trafficability - _ - +

Impede waterpercolation + + +

Erosion control - +

Aid surface run-off + + +

Desiccation - - +

Freeze/thaw stability - - +

Ease of Repair + +

Crack resistance , - +

Side-slope stability -

Potential for Side Slope + + +Seepage

Resistance to rodentburrowing - - +

Supports vegetation + + +(assumes *6-inch topsoillayer on each^EOver(material) **"

Ease of construction +

Cost of placement + +

.Resistance to Biologicaldeterioration + + +

Resistance toRoot penetration - +

+ Positive relative performance rating (.. , ,- Negative relative performance rating '.' i - - - ' 1

5-51

promote surface water run-off, control erosion, providegrowth for cover vegetation, and protect the low permeabiity soil cap against freeze/thaw effects and damage frominspection and maintenance operations. The thickness of theclean soil cover layers depend on the following factors:

a) Availability of suitable material.b) Thickness of top soil layer.c) Possible root penetration depth.d) Frost depth.e) Climatic conditions and extremes in precipitation.f) Possible long-term soil losses.

The effectiveness of a capping system composed of an upperclean soil and top soil layer overlying a low permeabilitysoil cap layer was evaluated using the Hydrologic Evaluationof Landfill Performance (HELP) model program developed byP.R. Schroeder, et. al. (1983). The program models theeffects of hydrologic processes including precipitation, sur-face storage, run-off, infiltration, percolation, evapotrans-piration, soil moisture storage, and lateral drainage usinga quasi-two-dimensional approach. Climatologic data fromPhiladelphia, Pennsylvania from 1974 to 1978 was used tobest represent site conditions from available data. A poten-tial two layer cap system with the following characteristic^was developed and read into the program.

GOOD GRASS VEGETATED COVER

Layer 1 - Soil Cover

Vertical Percolation Layer- ,Thickness » 24 inches

Evaporation Coefficient = ,4.5 mm/day**0.5Porosity * 0.458 vol/volField Capacity = 0.223 vol/volWilting Point = 0.092 vol/volEffective Hydraulic Conductivity = 2.31 inches/hr

1 - *Td|T cover layer to consist of 6 inches oftop soil and 18 inches of clean soil cover.

5-52

Layer 2 - Soil Cap

Soil Cap Layer Thickness = 24 inchesEvaporation Coefficient = 3.1 mm/day**0.5Porosity = 0.52 vol/volField Capacity = 0.45 vol/volWilting Point = 0.36 vol/volEffective Hydraulic Conductivity = 0.000142 inches/hr

Layer 3 - Waste Material2Waste Layer Thickness = 300 inches

Evaporation Coefficient = 3.3 mm/day**0.5Porosity = 0.52 vol/volField Capacity = 0.32 vol/volWilting Point = 0.96 vol/volEffective Hydraulic Conductivity = 0.283 inches/hr

o A 25 foot landfill thickness was assumed.

The complete output of the program is provided in Appen-dix P.

The average annual totals (using 1974 through 1978 weatherdata) are presented below.

Two Layer Cap System Performance Summary

Inches

PrecipitationRun- offEvapotranspirationPercolationPercolation

fromdfcrom

basebase

Drainage fro* -base of

ofof

coverlandfill

cover

43.8.31.1.1.0.

67958871585800

cu. ft. Percent

7,679,1,575,5,604,

279,277,

0000000000000000

1002073330

.63

.61

.00

R300702

5-53

The results of the simulation indicate that the low perme-ability soil layer is very effective in reducing the infil-tration of precipitation into the landfill. A reduction ofover 96 percent was achieved for this potential cap system.The output from this simulation also shows that only 20percent of the incident precipitation is carried off thelandfill as run-off and almost 73 percent is retained in thecap system that is eventually lost to evapotranspiration.This indicates that the precipitation is being trapped inthe upper soil layer. The moisture content of the upperlayer was shown in the simulation output to be very high,especially at the upper layer/low permeability soil layerinterface. These conditions could effect the long-term per-formance of the cap system as the low permeability soillayer becomes saturated. Softening of the low permeabilitylayer and loss of stability of the entire cap system (i.e.,slumping) could result from these conditions particularly onslopes. Final engineering design techniques could be usedto reduce long-term stability concerns.

The^addition of horizontal drain layer to the two layer capsystem can address these long-term performance concerns.The horizontal drain layer is "sandwiched" between the uppesoil layer on top and the low permeability soil cap underneath. The horizontal drain layer consists of a relativelyhigh permeability material (10~ cm/s or greater) toprovide a lateral drainage path for water that percolatesthrough the upper soil layer.

The effectiveness of a horizontal drain layer was evaluatedusing the HELP model program with the same climatologicconditions as in the two layer cap system simulation. Thefollowing potential multilayer cap system was developed andused for model simulation.

Layer 1 - Vegetated soil cover layer composed of 6inches of top soil and 18 inches of a local silty

. - sand.^^« _ _ _* " Layer 2 - Lateral drainage layer composed of a 12

inch layer of sandy gravel.

Layer 3 - Low permeability soil cap layer composedof a 24 inch layer of well compacted clay.

R300703

5-54

The parameters used for each of the layers comprising themultilayered cap system are as follows:


Vertical Percolation LayerThickness = 2 4 inches

Evaporation, Coefficient --* 4.5 mm/day**0.5Porosity = 0.458 vol/volField Capacity « 0.223 vol/volWilting Point = 0.092 vol/volEffective Hydraulic Conductivity = 2.31 inches/hr

Layer 2 - Drain Layer

Lateral Drainage Layer Soil = 5 percentDrainage Length = 100 feetThickness = 12 inchesEvaporation Coefficient = 3.3 mm/day**0.5Porosity = 0.351 vol/volField Capacity = 0.174 vol/volWilting Point = 0.107 vol/volEffective Hydraulic Conductivity = 11.95 inches/hr

Layer 3 - Soil Cap

Soil Cap Layer Thickness = 24 inchesEvaporation Coefficient = 3.1 mm/day**0.5Porosity = 0.52 vol/volField Capacity = 0.45 vol/volWilting Point « 0.36 vol/volEffective Hydraulic Conductivity _* 0.000142 inches/hr

Layer 4 - Waste Material

Waste Layer Thickness (25 feet) = 300 inchesEvaporation Coefficient = 3.3 mm/day**0.5Porosity ' " ~ ~= 0.52 vol/volField Capac y. . = 0.32 vol/volWilting Point s 0.96 vol/volEffective Hydraulic Conductivity =« 0.283 inches/hr

The complete output of the simulation is provided inAppendix P.

5-55

The average annual totals (using 1974 through 1978 weatherdata) are presented below. A 48.5 acre permeable surfacearea for the landfill cover was assumed for modelling pur-poses .

Multilayer Cap System Performance Summary

Inches

PrecipitationRun-offEvapotranspirationPercolationPercolation

fromfrom

basebase

Drainage from base of

ofof

coverlandfill

cover*

431221118

.67

.03

.59

.479

.471

.22

cu. ft

7,679,181,

3,972,260,259,

3,205,

.

000384000000000000

Percent

1002523342

.4

.39

.37

* Drainage through the horizontal drain layer.

The results_qf the HELP model program clearly show theeffectiveness of the horizontal drainage layer in removingthe water that has percolated down from the cover soillayer. In comparing the results of the two simulations,drainage from the base of the upper soil cover increasedfrom 0 percent for the 2 layer system to 42 percent of totalprecipitation for a 3 layer system including a horizontaldrainage layer. With the effective removal of water at thetop of the low permeability soil layer, the long-termstability and integrity of the cap system is better assured.Physical testing of the cap material along with slopestability analysis may, however, show that a drainage layeron most of the cover area (where the final grade will be 5percent or less) is not cost-effective.

Based on this preliminary analysis, a multi-layered capsystem consisting of a vegetated top soil, clean soil cover,a horizontal drainage layer (may be limited to steepslopes},, and a low permeability soil cap layer would be atechnic^ly effective cap system at the Army Creek Landfillsite. further detailed analysis and design optimization isneeded to determine the layer thickness and the most costeffective layer materials.

Tha following considerations for each component layer shouldbe made when designing the multilayered cap system. Theseconsiderations will also effect the final cost analysis ofthis alternative.

AR3007Q5

5-56

Soil Cover Layer - The upper soil cover layer typicallyincorporates clean fill soils, topsoil, and a vegetativecover. Clean fill may be utilized as a general grade-and-fill material to form the basis of the soil cover layer.Top soil, which is usually placed above clean fill, istypically a loose, uncompacted^ surface layer of loams forvegetative support. Vegetation serves to reduce thepotential for wind and water erosion, enhances evapotrans-piration, and helps to establish a naturally fertile andstable soil base. The key to the effectiveness of the uppersoil layer is the success in establishing and promoting aneffective vegetative cover.

The layer of clean fill soils may range in thickness from aminimum of 12 inches to 3 feet or more. This soil layermust be free of large rocks or stones; roots, branches, orwood; cind rubble, debris, or other waste material. Theselection of the thickness of this soil fill layer shouldconsider factors such as the following:

a) Availability of suitable material.b) Thickness of top soil layer.c) Possible root penetration depth.d) Frost depth.e) Climatic conditions and extremes in precipitation.f) Possible long-term soil losses.

Top soil thickness is usually limited to about 6-12 inchesbecause of its relatively high cost. If adequate qualitytop soil is not available, it may be necessary to supplementexisting soils with fertilizers and conditioners. Thissupplemental enrichment will provide the general soilcomposition and macronutrients needed to adequately supportvegetation.

Several vegetation characteristics are important to the es-tablishment of a successful vegetation cover over the multi-layer cap system. These include (JRB Associates, 1982) thefollowing:

~~ a) tow-growing vegetation.b) limited soil penetration of plant roots.c) Rapid germination and development.d) Long-term durability (resistance to fire, insects

and disease).e) Low maintenance requirements.

.R30Q706

5-57

Slope stability represents an important aspect of the uppersoil layer. Side slopes should be limited to a maximumratio of 3 horizontal to 1 vertical (3:1) to ensure slopestability. This represents the maximum slope on whichvegetation can be established and maintained, assuming soilswith low erosion potential and adequate moisture-holdingcapacity. Top surfaces should utilize a slope ofapproximately 3-5 percent to promote drainage and encouragerun-off.

Another concern that could effect the useful life of themultilayared cap is protection of the side slope along thesouthern side of the landfill that lies in the floodplain.The Federal Emergency Management Authority has identifiedthe boundary of the floodplain as extending to the 10 footcontour line. The extent of the floodplain is shown inFigure 5-10. In those areas where the slope of the cappedlandfill extends in the flood plain, a rip-rap protectivecover layer and/or other protective measures should beinstalled as part of the cap construction.

|| Drainage Layer - The drain layer (horizontal drain layer)i'i is "sandwiched" between the soil cover layer on top and the

low permeability cap layer underneath. The drain layer isseparated from the underlying cap material and overlaying

• j soil .using geotextile fabric placed above and below. Thiswould reduce the potential for drain layer clogging byrestricting the possible movement of fine particles into theporous soil voids.

The drain layer consists of a relatively high permeabilitymaterial (1Q~ cm/s or greater) to provide a lateral drain-age path for water that percolates through the soil coverlayar. The drain layer must provide rapid transmission ofthe water that will tend to collect (perch) on the caplayer. Drain layer performance can be modeled using theHydrological Simulation for Solid Waste Disposal Sites(HSSWDS) computer simulation model developed for the U.S.EPA, (Moor e, 1980). From the model, the required drain layer

—"• thicknesat, can be evaluated. The layer thickness requirementis a function of the following design considerations:

a) Annual infiltration rate.fa) Drain layer length.c) Permeability of drain layer material.d) Drain layer slope.

SB300707

5-58

'iIII

01cr

z_J

ao

H2_i

5-59

Physical testing of the low permeability soil layer alongwith slope stability analysis are also part of theevaluation of the horizontal drainage layer. Analysis mayshow that a horizontal drainage layer is not cost-effectiveon areas of the landfill where the slope is less than 5percent. Along the steep side slopes a geogrid couldprovide a cost-effective drain layer to provide greaterslope stability.

Low Permeability Soil Cap Layer - The cap layer can beconstructed using the cover materials discussed in thissubsection. The type of material and thickness that is themost cost affective for use in the cap layer is determinedas part of the design optimization process. Native clay,dredge spoils, soil/bentonite admixture and fly ash/soillime admixtures can all achieve permeabilities of 10"on/s or less when properly compacted. The availability ofthesa materials will determine their cost effectiveness.For cost analysis purposes under this alternative, the costof low permeability soils as quoted from a local supplierwill be used. One of1 the first steps in the performanceverification^ process is materials verification. If thematerials do not meet the desired specifications, acomponent in the in situ closure design may not achievetha desired performance. This type of materials test cangenerally be performed in a soils laboratory and maytypically include the parameters shown in Table 5-11.

Tha effectiveness of a multilayer cap system as outlinedabove was compared with the existing granular soil coverusing the HELP model program. The same climatological dataused in the simulation of a multilayer cap system was usedto simulate the present conditions. The existing cover wasdescribed as a. vegetated silty sand approximately 24 inchesin thickness. The material parameters used in the programare given below:

EXISTING SOIL COVER

».~~ FAIR GRASS VEGETATED COVERjr - : :: ."


Vertical Percolation LayerThickness « 24 inches

Evaporation Coefficient ^ 3.3 mm/day**0.5Porosity = 0.371 vol/volField Capacity = 0.172 vol/volWilting Point » 0.050 vol/volEffective Hydraulic Conductivity = 16.2 inches/hr

5-60

TABLE 5-11TYPICAL MATERIALS TESTING PARAMETERS

Component

Upper soil layer material

Topsoil 1.2.3.

Soil fill 1.

2.

3.

Drain layer material 1.

2.

3.

Cap layer (clayey soill 1.

2-

3.

^ 4.JT -

5.

Characteristics

Organic contentPHSuitability-clean

Low course fragments

Suitability-clean

Compactable

Soil type

Allow rapid watermovement.Suitability-clean

Workability

Soil type

Restrict water move-ment

Coap actable

Suitability-clean

1.2.3.

1.

2.

3.

1.

2.

3.

1.

2.

3.

4.

5.

Test protocol

Soil classification.Field testing procedure.Visual « free from for-eign matter and other.debris.Sieve analysis AASHTOT-27.

Visual -- free from rocks,stones* debris, wastematerial, roots, sticks.

Density at optimum mois-ture — AASHTO T-99.

Soil classification.Sieve analysis — per-meability.

Visual — free fromplants, roots P stones,debris.Liquid limit — AASHTOT-89. Plastic limit --AASHTO T-90.

Sieve analysis — AASHTOF-ll and AASHTO F-27.

Permeability.

Maximum density at opti-mum moisture -- AASHTOT-130.

Visual « free fromstones, roots, plants,debris.

AR3007IO

5-61

Layer 2 - Waste Material

Waste Layer Thickness (25 feet) = 300 inchesEvaporation Coefficient » 3.3 mm/day**0.5Porosity = 0.52 vol/volField Capacity = 0.32 vol/volWilting Point • 0.19 vol/volEffective Hydraulic Conductivity = 0.283 inches/hr

A complete copy of the output from this simulation isprovided in Appendix P.

Presented below are the average annual performance for theexisting cover. Weather data for this analysis is based onthe 1974 through 1978 Philadelphia Weather Bureau period.

Existing Soil Cover Performance Summary-

PrecipitationRun-offEvapotranspirationPercolation from base of landfill

inches

43.670.12

13.7629.69

cu. ft.

7,679,00020,0002,420,0005,221,000

Percent

1000.3

3268

Summarizing the output of the simulation for existingconditions and for a potential multilayer cap system, it hasbeen shown that a multilayered cap would significantlyreduce the amount of precipitation infiltrating into thelandfill refuse. The output from both simulations can besummarized as follows:

AVERAGE ANNUAL PERFORMANCE SUMMARY

Total precipitation 1,027,000 gal/yr

^-_ ^ = MultilayeredExisting Cover Cap

(gal/yr) (gal/yr)

Amount of precipitationinfiltrating to the refuse(potential leachate production) 698,000 34,600

Percent reduction inprecipitation infiltrationinto landfill 32% 96.5%

5"62 AR3007I

In comparing the effectiveness of the two simulations, themultilayered cap will reduce the current amount of precipita-tion infiltrating into the refuse and potentially generatingleachate by over 60 percent. That equals a potential reduc-tion in leachate production of 663,400 gallons/year ascalculated by the HELP Model simulation using a 48.5 acrepermeable surface area.

Surface Mcinagement and Gas Venting

Additional measures that will enhance the overall effective-ness of the multilayered cap system are surface managementtechniques and gas venting. Surface regrading and backfill-ing will be performed prior to the placement of the lowpermeability barrier layer to assure proper compaction andoverall integrity of the cap system. Surface regrading willeliminate the existing depressions in the landfill andestablish a site contour pattern that promotes run-off awayfrom the landfill. Additional surface management measureswill include the construction of a drainage ditch along thenorth side of the landfill to direct run-off away from thelandfill. The ditches will be equipped with sedimentationcontrols such as hay bales, fabric fences, stone fillerberms, etc. These sedimentation controls would serve on atemporary basis to remove any transported sediments untilthe final cover is revegetated and stabilized. Thesesurface management measures are presented in Figure 5-11.

Presently, off-site gas migration has not posed a problem atthe site. The existing soil cover allows methane gas to bereleased naturally through the top surface of the landfill.It can be anticipated, however, that increased gascollection of methane could occur under the low permeabilitysoil cap in the multilayer cap system. This could result inincreased pressures and potential for some lateral migrationof methane. This issue could be addressed by utilizing theexisting sandy cover, that will be regraded prior toplacement of the barrier layer, as a gas venting layer.Venting of the gas from the regraded sandy layer could thenbe performed with the installation of vents along theperime'ter of the landfill.^^«

jf - . . , _ : . - .

Reliability - Once the vegetation on the multilayered capsystem is established, it will require limited regularmaintenance. The entire vegetated area should be mowed once

ftR3007l25-63

or twice a year to minimize the potential for growth ofdeep-rooted vegetation. The surface cap should beperiodically inspected to assure continued integrity of thacapping system and repair of any erosion damage.


The following institutional requirements must be consideredunder this alternative:

• Long-term monitoring, operation, and maintenancecosts are involved in operation of the downgradientpumping system. Long-term funding must be in placefor these cost.

• The discharge of recovered/treated ground watermust be performed within the necessary permitting/-approval process. Surface discharge to Army Creekmust comply with NPDES requirements. A draftNPDES permit was issued by the State in November1985.

* There are C A design standards for surfacecapping. EPA' has documents identifying proceduresand materials that meet standards. The lowpermeability soil cap system discussed under thisalternative meets £c£A guidelines.

* All state erosion, sediment, and dust controlordinances would apply during construction anduntil a vegetated cover is established.

5.4.1.3 Public Health and Environmental Issues>.

Alternative 3 provides the same health benefits asAlternative 2 by containing the contaminant plume throughthe creation of a hydrologic divide between the landfill andtha" Ariasian Water Company's wellfield by downgradientpuirping. .-The recovery pumping program in place at the ArmyCreek Landfill has also proven to have containedcontaminated ground water close to the landfill. Bycontrolling the contaminant plume, the pumping system hasprevented the possible abandonment of the upper Potomac

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aquifer as a source of water supply in the productionwellfialds near the landfill.

Tha environmental impacts from the discharge of thedowngradient pumping operation will depend on the treatmentoption chosen for the Army Creek Landfill site. This willbe discussed in Section 5.7.

Additional measures that mitigate, the environmental impactsof the landfill are provided under Alternative 3.Alternative 3 includes the capping of the landfill, surfacemanagement measures, and gas venting. Simulation usingclimatological data similar to the site conditions show alow permeability soil cap system can reduce precipitationinfiltration by more than 96 percent. This could translateinto a potential reduction in leachate production equal toover 650,000 gallons per year. The reduction in leachateproduction will hasten the cleansing of the ground water andwill reduce the environmental impact of the landfill.

Alternative 3 does not, however, address the infiltration ofground watar from the Columbia Formation along the northwestside of tha landfill.

5.4.2 . Cost Analysis

Tha primary cost associated with Alternative 3 is thecapital cost of capping the landfill. The final cost of acap system depends on the layer thickness and the type oflayer material determined after final design optimizationand more importantly on material availability. Table5-12(A) presents the capital cost of a multilayer cap systemand provides an estimate for an alternate _cap design forcost sensitivity analysis. Table 5-12 (B) presents the postclosure and operating costs for Alternative 3. A summary ofthe total costs along with present worth analysis for eachalternative is presented in Section 6.

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5-68

5.5 ALTERNATIVE 4 - DOWNGRADIENT PUMPING, LANDFILLCAPPINGr AND UPGRADIENT CONTROLS

a) NON-PHASED APPROACH - The non-phased approach toAlternative4includes the continuation of the downgradientpumping program and simultaneous construction of the finalcap system and the upgradient controls. This approach toAlternative 4 provides additional immediate measures tofurther mitigate the environmental impacts of the landfillas compared to Alternative 3. The upgradient controls willsignificantly reduce the ground water entering the landfillalong the northwestern side, thus reducing the potentialvolume oi: leachate produced.. The flow of ground water intothe landfill along the northwestern side has been estimatedat 25,000 gpd as compared to 4,000 gpd of precipitationinfiltration.

k) PHASED APPROACH - The phased approach to Alternative4 involves two phases. Phase 1 includes the installation ofthe final cap system with the continuation of the down-gradient pumping system. The effect on the ground waterquality as a result of capping the landfill will then bemonitored and assessed prior to initiating upgradient con-trols. It is possible that although a significantly greatervolume of ground water passes through the site than doesprecipitation, the refuse that comes in contact with theground water has already been leached after almost seventeenyears in a saturated state. Monitoring has also shown thatthe ground water table elevations have dropped over the pasttwelve years due to the additional pumping, resulting in alesser quantity of refuse that is saturated. Precipitation,on the other hand, percolates through the entire refusestratum, allowing for more contact with a greater volume oflandfill material. Following an evaluation period of 5years after the cap is installed, the need for additionalmeasures to reduce leachate production will be determined.Phase 2 involves the installation of upgradient controls tointercept the ground water in the Columbia aquifer before itenters the landfill.

Both approaches include surface management measures and gasvlnting a»r,part of the construction of the cap system.Monitoring «fnd discharge to an appropriate treatment schemeis included with both the downgradient, pumping program, andupgradient controls. Figure 5-12 presents a possible

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cross-section of the landfill after both phases of Altern-ative 4 have been completed, using pumping wells as theupgradient controls.



The technical evaluation of the downgradient pumping programhas been performed under Alternative 2 in subsection5.2.1.1., and the evaluation of the multilayer cap systemunder Alternative 3 in subsection 5.3.1.1. Final designanalysis will be used to determine the material types andspecifications for the number of layers and thickness of thefinal cap system. The non-cost analysis for thisalternative will therefore concentrate on evaluating thaupgradient controls, which includes monitoring and dischargeto an appropriate treatment system. The upgradient pumpingnetwork is used for evaluation purposes only. the finalupgradient control (pumping or trench) will be determinedduring the design phase. It is anticipated that lesspumping, both in quantity and duration, by the downgradientrecovery well system will be required as a result of cappingthe landfill. Upgradient controls should further hastenground Wetter cleansing, further reducing the time thedowngradient system has to be operated.

Performance - The drawdown effectiveness of an upgradientpumping scheme would be comparable to the downgradientpumping system already in use. The following discussionaddresses the amount of lateral ground water inflow nowoccurring and provides a technical evaluation of theproposed system.

The arrangement and number of recovery wells necessary toprevent i-he lateral inflow of ground water into the ArmyCreek Landfill is contingent upon several of the followingfactors; the volume of inflowing water, the depth to which"the water tfjale must be lowered, and the ability of theColumbia aqiM'fer to transmit water.

The primary aquifer characteristics that affect ground watermovement are Transmissivity, Storativity and hydraulicconductivity. Results of aquifer tests performed on wellslocated approximately 4 miles north and wells located

ftB300720

5-71

approximately 15 miles west of the landfill indicate a widerange of permeabilities (120-2400 gpd/ft ) (Johnston,1973). Therefore, to further refine these values for use atthe landfill, estimations were made using geologic logs fromwells installed at the landfill. In applying this method, apermeability was assigned to each lithologic interval(Lohman, 1979) and averaged within the borehole (Johnston,1973). The permeabilities obtained from this procedureaveraged 200 gpd/ft . Storativity of the Columbia aquiferranges from 0.01 to 0.07 (Johnston, 1973).

An approximation of the amount of ground water flow acrosstha northwestern boundary of the landfill, in the Columbiaaquifar was calculated by applying Darcy's Law:

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K s^Hydraulic Conductivity, gpd/ftI » Hydraulic Gradient, ft/ftA » Cross-Sectional Area, ft

The saturated thickness along the northwestern boundary oftha landfill was estimated from well logs to be 18 feet.Using the method discussed above the permeability (hydraulicconductivity) was estimated to be 200 gpd/ft . Thehydraulic gradient, determined from the difference in waterlaval elevations between wells B-18 and B-2, is 23 ft/mile.Thus, the volume of inflow across the northwestern boundary(1600 ft) is approximately 25,100 gpd under non-pumpingconditions.>To intercept the inflowing ground water and lower the watertable within the landfill, WESTON estimates that fiverecovery wells, spaced at 320-foot intervals, will beneeded. The wells could be located directly south of therailroad tracks along the northwestern boundary of thelandfill. (Figure 5-13). To ensure maximum drainage fromtha Columbia aquifer, the depth of the wells should extendto the bjtse of the aquifar (25 to 30 feet).

Optimal pumping rates were analyzed using the Theis non-equilibrium well formula modified for water table conditions(Walton, 1970). An estimated average Transmissivity of 3600gpd/ft and a Storativity of 0.05 for the Columbia aquiferwas used in the calculations. It was necessary to ensurethat the drawdown at the pumping wells would not exceed 20to 25 feet, so that the depth to water in the wellsremained at acceptable levels for pumping. ftR300721

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Evaluation of various pumping rates estimated that adischarge rate of 20 gpm per well would provide maximumdrainage of the Columbia aquifar without exceeding thecritical well drawdown limits. The pumping rate of 20 gpmat each of the five wells would remove approximately 144,000gpd of ground water, creating a hydrologic drain for theground water enroute to the landfill. The drawdowninfluence from the pumping wells would lower the water tablewithin the refuse. Table 5-13 presents calculated totaldrawdowns in tha Columbia aquifer at each of the pumpingwells. Upgradient pumping would essentially dewater a majorportion of the refuse, leaving only a fraction of the totalwaste volume saturated near the base of the ColumbiaFormation.

The efficiency of the upgradient pumping well scheme islargely dependent on the amount of recharge through thelandfill and the water level elevations in Army Creek.Recharge values from precipitation on the landfill wereestimated at 3870 gpd, using the Hydrologic Evaluation ofLandfill Performance (HELP) model. Lowering of the watertable through upgradient pumping, to reduce the volume ofsaturated refuse, without limiting the infiltration ofprecipitation into the refuse, may not substantially reduceleachate production. In addition, precipitation rechargethrough the landfill could sustain a higher water table intha landfill than would be anticipated following reductionin tha upgradient ground water inflow.

The water lavel in Army Creek could potentially impact thedewatering influences of the upgradient wells. If thecumulative drawdowns from the five recovery wells lowers thewater table below the water level in Army Creek, thensurface water flow into the Columbia aquifer may be induced.This would eventually create a steady-state conditionbetween the water levels in the wells and the stage of thestream. At this time, the variation in the elevation of thesurface water in Army Creek is unknown, and the effect ofthe st am on the maximum water table drawdowns could not bedeterminiTd".

Reliability - The clogging of the well screens anddischarge line would be a problem, perhaps only initiallywhen tha water would be the most contaminated. As with thedowngradient system (5.3.2.1), well rehabilitation could beinstituted as necessary.

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Implamentability - The installation of recovery wells is aproven technology. Competent drilling contractors arereadily available who can implement this technology.Implementation time would be approximately six months fordrilling and well installation, pump installation,construction of discharge lines, and electrical power to thesystem.

Safety - Safety precautions required under thisalternative have been developed for the installation ofrecovery wells.


Tha following institutional requirements must be consideredunder this alternative:

• Long-term monitoring, operation and maintenancecosts are involved in operation of" the downgradientarlS upgradient pumping systems. Long-term fundingmust be in place for these costs.

• Depending on the treatment option selected, anNPDES permit would be required for discharge ofwater to Army Pond. The preliminary draft NPDESpermit was issued in November 1985.

• There are RCRA design standards for surface cappingand tha low permeability soil cap system discussedunder this alternative meets RCRA standards.

• All state erosion, sediment, and dust controlordinances would apply during construction anduntil a vegetated cover is established.

• Well installation permits for the new upgradient. wells will have to be obtained from the State of

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5.5.1.3 Public Health and Environmental Issues

Alternative 4 provides the same health benefits as Altern-atives 2 and 3 by containing the contaminant plume throughthe creation of a hydrologic divide between the landfill andthe Artesian Water Company's wellfield by downgradient pump-ing. Alternative 4 provides further measures to mitigate

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the environmental impacts in addition to downgradientpumping and landfill capping included in Alternative 3.Under the non-phased approach to Alternative 4, upgradientcontrols will be installed at the same time the landfill iscapped. Both pathways of infiltration into the landfillwill, therefore, immediately be addressed. Potentialleachate production could be reduced as a result of theseactions. It is therefore anticipated that ground watercleansing would be further hastened under Alternative 4.

The phased approach allows for a period of monitoring andassessment of the effectiveness of capping the landfill onground waiter quality. Following an evaluation period of 5years after the cap is installed, the need for additionalmeausres to reduce leachate producltion will be determined.

5.5.2 Cost Analysis

The capital cost estimate for Alternative 4 is presented inTable 5-14(A). Costs associated with each phase under thephased approach to Alternative 4 are outlined in Table5-14(A). The post closure and operating costs forAlternative 4 are provided in Table 5-14(B). Present worthanalysis and total cost estimates for both phased and nonphased approaches to Alternative 4 as well as for the otheralternatives are presented in Section 6.

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5.6 ALTERNATIVE 5 - DOWNGRADIENT PUMPING, PARTIAL REMOVALAMD LANDFILL CAPPING

Alternative 5 consists of the downgradient recovery wellsyst.em also included in Alternatives 3 and 4, the excavationof the landfill refuse in the western section, and thedisposing of the refuse on the eastern section. The easternsection will then be graded and capped with a multilayer capsystem, and the western section backfilled with clean fillmaterial, graded to drain surface run-off and vegetated.Erosion and run-off controls will be established in exca-vated and fill areas. The saturated refuse in the westernsection will require "dewatering" or draining as it is exca-vated and mixed with dryer refuse to be placed and compactedon tha eastern section of the landfill. A combination ofdraining/pumping of free liquids from the saturated refuseand upgradiant controls will be required for the dewateringprocess. Figure 5-14 provides a graphical presentation ofAlternative 5.

5.6.1 Non Cost Analysis

5.6.1.1 Technical Evaluation \

Performance - This alternative will remove one of thesources of contamination of the Columbia aquifer andsubsequently the upper Potomac aquifer by the excavation oftha western section of the landfill. Field informationsuggests that ground water is infiltrating the refuselaterally in this section of the landfill. This alternativealso addresses the precipitation infiltration through theremoval and redeposition of refuse to the eastern section oftha landfill which is then capped with a multilayer capsystem. The multilayered cap system was evaluated inSubsection 5.3.1.1. Alternative 5 will be effective inaddressing tha pathways of infiltration and reducing thepotential volume of leachata produced from an estimated129,000 gal/day (25,000 gal/day ground water infiltrationplus 4,000 gal/day of precipitation infiltration) to anestimated. 200 gal/day (precipitation infiltration throughmultilayaraol cap system). Source removal provides aneffective*-'- long-term solution to ground water contaminationat tha sita. Tha useful life of the multilayer cap systemdepends on the establishment of a maintenance program thatmaintains a proper vegetated cover and integrity of the cap.

5R300729

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Reliability - Once the vegetation on the multilayered capsystem is established it will require routine regularmaintenance. The entire vegetated area should be mowed onceor twica a year to minimize the potential for growth ofdeep-rooted vegetation. The surface cap on the easternsection should be periodically inspected to assure continuedintegrity of the capping system. Cracking, erosion damage,and differential settlement damage will require repairs.

Implementability - Two of the major concerns resultingfromtheexcavation of the western section of the existinglandfill include the following:

• Dewatering of the western section will be requiredbefore the saturated refuse is excavated from belowthe water table. Upgradient controls similar tothe system outlined under Alternative 4 can be usedto lower the water table below the refuse. Com-plete dewatering may include the construction ofdrains and sump controls, but it is anticipatedthat most of the free liquid will be removed by theupgradient controls. The discharge from the up-gradient controls may require treatment. Since theduration of punning (if used) will be short-term(time required to excavate the western section) themost cost effective treatment option may be dis-charge to the local water treatment facility(Wilmington Waste Water Treatment Plant). Flowrates determined under Alternative 4 can be usedfor cost analysis.

* A potential slope stability problem may resultalong the exposed cut section between the eastern

, section and the western section as excavation ofthe western section results in deep cuts intolandfill refuse. The excavation should proceed inan "area" type manner to minimize deep cuts andpossible stability problems. Final side slopes•*|ter backfilling in the eastern section should beirmited to a maximum ratio of 3 horizontal to 1vertical (3:1) to ensure slope stability.

Construction methods and conceptual procedures to minimizeenvironmental impacts as well as constructability concernsassociated with Alternative 5 are outlined in the following:

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Methods for Refuse Handling

The four types of refuse that will be encountered during theexcavation of the western section of the Army Creek Landfillare the following:

• Unsaturated refuse;

• Saturated refuse;

* Bulky items;

• Other wastes from industrial and commercialsources.

All of the buried material, with the exception of non-refusetype wastes, will be handled by conventional heavyconstruction equipment (e.g., front-end loaders, crawlertractors, tracked backhoes, clamshells, draglines, and dumptrucks). Much larger equipment such as reclaiming wheelsand electric shovels found at strip mining operations andself-propelled earth movers (23 cubic yard scrapers) andlarge dump trucks (50 cubic yards) found at highwayconstruction sites are also applicable for excavation of thewestern section. If readily available and if themobilization costs are low, this type of equipment wouldlower both the costs and time required for excavation.

Material excavation will be an estimated 2,000,000 cubicyards. The majority of the refuse is probably unsaturated.Excavation of this unsaturated refuse is an operationsimilar to excavating earthen materials. Crawler tractorsand front-end loaders will be used to excavate and load thedump trucks. As much of the water as possible will beremoved from the saturated refuse by the dewateringprocedures mentioned at the beginning of this subsection.

During refuse excavation, leachate present in the Army CreekLandfi-11 will be controlled by msans of the upgradient anddowngradienfl?- ground water pumping wells. During theexcavation * and redisposal operations, small volumes ofleachate may be generated as surface seeps. These seeps ofcontaminated run-off if they occur in the eastern sectionshould be intercepted, collected and treated.

Excavation of the saturated refuse will be accomplishedusing either backhoes or draglines working from the top ofthe working face. If a packet of non-refuse or industrial/

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potentially hazardous wastes has been identified, specialexcavation and handling procedures will be initiated.

All of the refuse, with the possible exception of wasterequiring special handling, will be loaded on to dumptrucks, These vehicles can then haul the refuse. on atemporary access road along the north side of the landfillrunning parallel to the existing railroad. Free liquid fromtha transportation of the refuse will therefore be containedwithin the existing landfill area. Extensive odor controlwill be necessary within and around the perimeter of theexcavation site, at the open excavation face, and at theloading site for the dump trucks. Methods, equipmentrequired, and equipment siting for odor control arediscussed under the Environmental Issues evaluation.

Site, Preparation - Site preparation will be accomplishedin such a Inanner (use of noise and dust abatement methods)so as to have as little effect as possible on the generalenvironment of the area surrounding the site. Access roadsand staging areas (if necessary) will be constructed alongwith site security measures.

Transportation - All excavated refuse, with the exceptionof wastes requiring special handling, will be transported tothe eastern section by dump trucks. Five (5) tons isconsidered the minimum effective size and approximately 20tons the maximum effective size for this operationconsidering tha mobility, short haul distance, and need tominimize congestion. Transportation will be via a temporaryaccess road that runs from the western to the easternsection probably along the northern border of the landfill.Tha road will have a heavy stone surface and be designed andconstructed to handle the necessary loads. Since saturatedrefuse, resulting in seepage from the trucks, will be hauledover this road, provisions for the collection of run-offwill be established to assure free liquid is not carriedoffrsite.-

Mixing of^Excavated Wastes - Approximately 30-40 percentof the refuse is saturated; in order to achieve bettercompaction and uniformity of the landfilled material thedrier refuse will be mixed with tha saturated wastes. Amixing ratio in the range of 2:1 to 1:1 dry refuse tosaturated refuse will be attained. This is possible since

Rf\ t"l £°\ ™"f '"V O300733

5-34

excavation of both materials could occur simultaneouslyafter an initial start-up period.

Placement and Compaction - Placement and compaction of therefuse would be by _ the area, method utilizing crawlertractors (or other suitable means of compaction; i.e.,sheepsfoot rollers, landfill compactors, etc.). The size ofthe area would not exceed what can be compacted and handledvia odor & vector control measures. Refuse would be spreadand compacted in thin layers not to exceed a depth of twofeet (compacted material).

Intermediate Cover - As an area is backfilled with refuseand attains specified rough grades, a 12 inch intermediatesoil cover will be placed over the refuse. This will serveas the base for the final cap system and a control for odorand vectors.

Landfill Capping - After the western section has beencompletely excavated and backfilled with a clean soil fill,the eastern section would be prepared for the final capping.The cap would be placed over the intermediate soil coverand utilize a multilayer design. The multilayer cap systemwill significantly reduce precipitation infiltration.Simulations show reductions of 96 percent in precipitationinfiltration can be achieved. Erosion and sedimentationcontrols will be initiated until a proper vegetated cover isestablished. Gas venting and surface management measureswill be installed during the construction of the cap system.


The following institutional requirements must be consideredunder this alternative:

• Long-term monitoring, operation, and maintenancecosts are involved in operation of the downgradientpumping system. Long-term funding must be in placefor these costs.

• Depending on the treatment option selected permit/approval compliance would be required for dischargeof the treated water.

• There are RCRA design guidelines for surfacecapping and the multilayered cap discussed underthis alternative meets RCRA standards.

5-C5

* All stata erosion, sediment, and dust controlordinances would apply during excavation, disposal,and cap construction operations until a vegetatedcover is established.

* Odor would be a significant concern to the localpublic. Increased noise is also a concern duringexcavation and disposal operations.

• A long-term monitoring and maintenance programwould have to be set up following closure.

Accident Prevention and Safety - An operation safetyprogramwouldbe established for the site. The safety planshould include ambient air monitoring, worker medicalmonitoring and training. All workers would be familiar withthis plan, and especially the emergency plan for responseaction. It is expected that excavation would be conductedusing Level D safety protocol. This is how the costestimate and technical scope has been based. If significantquantities of special/hazardous waste is encountered,upgrade to Level C or B may be necessary. This upgradewould greatly increase the cost and time needed to completethis work. Air monitoring should be used to gauge the needfor upgrading the safety protection.

A contingency plan and emergency response plan would berequired. An evacuation plan should also be on hand ifneeded.

While this alternative does represent a potential safetyrisk to tha construction worker, proper safety protocolshould reduce the risk. However, the type and condition ofburied waste at this site has not been thoroughlycharacterized.

5.6.1.3 ^public Health and Environmental Issuesj r - - . _ . - , .

Alternative 5 provides the same health benefits asAlternatives 2f 3, and 4 by containing the contaminant plumethrough the creation of a hydrologic divide between thelandfill and the Artesian Water Company's wellfield by thaaxisting downgradiant pumping program.

Alternative 5 provides basically the same environmentalbenefits as Alternative 4 but addresses the ground water in-

AR300735

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filtration condition in the western portion of the landfillby eliminating the source of -leachate generation throughtotal removal of the refuse in the western section.

Ground water cleansing will be hastened by the eliminationof the source of contamination. Capping the eastern sectionwith a multilayer cap will - significantly reduceprecipitation infiltration (estimated at 96 percent) whichwill further hasten ground water cleansing.

During excavation, odor and vector problems will likelyoccur in addition to the draining of water from saturatedrefuse. Leachate punped during dewatering operations beforethe saturated refuse is excavated must be collected andtreated,, The most cost effective treatment option may be todischarge to the Wilmington Waste Water Treatment Plantbecause of the short-term duration of the pumping operations(see subsection 5.7). .

Several environmental problems are envisioned duringlandfill construction- phases including: odor, leachateseepage, vectors, worker safety, etc. The , followingdiscussion will define such problems and recommend remediesfor their control.

The criteria for selecting various environmental controlswas based on: economics, effectiveness, practicality,acceptability to the public and environmental agencies, andflexibility of operations. However, it is important toemphasize that most of these controls will not eliminatethe problems, but will rather minimize their impact on theenvironment, local residents and construction personnel. Itis expected that, even with the controls, some adverseimpacts and inconveniences will result from the excavationof the western section and depositing it on the easternsection.

Odor and Nuisance Impacts and Control - An importantenvironmental consideration in the partial removal of theArmy Creek^Landfill is the control of malodor from partiallydecomposed refuse. A positive odor control program isnecessary.

Additional environmental nuisance problems must also beconsidered including fugitive dust, vector and wastehandling problems.

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Tha odor problems that will be experienced during thlandfill excavation are of such an extent that collectionand venting the odors to control devices are not feasible.The cost for destruction of the malodors by combustion oradsorption would be unreasonably high. Additionally, it isnot technically feasible to implement collection of themalodorous air volumes. Counteracting the malodors withchemicals or foam blanketing may be a technically andeconomically feasible odor control. Nearby residents shouldbe protected by:

1) Constructing a chemical screening system betweenthe landfill and nearby residences.

2) Spraying refuse with odor-modifying chemicals orcovering the exposed waste with a blanketing foam.

This typa of odor control program has been successfullycompleted at a Buffalo, New York landfill. At thislandfill, two million cubic yards of buried solid wasteswere dug up and transported six miles to another landfillsite.

The chemical screening system is implemented byodor-counteracting, aromatic chemicals through orificespipe which is laid around the landfill perimeter between theodorous sources and the residences. At tha Army creekLandfill, approximately 4,800 feet of pipe (stove pipe)would ba necessary to implement the chemical screeningbetween tha landfill and nearby residence at LlangollenEstates and Wilton and the commercial and businessestablishments along Routes 13 and 40. Twenty-four hour perday screening could be implemented.

In addition to the chemical screening system implemented atthe Buffalo landfill, these systems have been installed atsewage treatment plants, composting operations and cattlefeed lots—all malodorous operations.

In addition to the odor screening system, spraying therefusa^Vith odor-abating chemicals or blanketing foam wouldba used as an integral part of the positive odor controlprogram. The landfill operating face would be sprayed withtha water soluble odor abating chemical mixture or blanket-ing foam. Only on-site experience can dictate the frequencyof spraying the open face. However, this spraying would be

R300737

5-38

conducted as a minimum at the end of each working day. Theexcavated material would also be sprayed after the refusehas been loaded onto trucks or the trucks tightly covered.The roadway would also be periodically sprayed with thechemical solution. This will be necessary especially afterwet refuse has been transported. The new landfill workingarea would also need to be sprayed on a regular basis withfoam or odor .control chemicals. At the end of the workingday, all truck beds and operating equipment should besprayed with the odor-abating chemical solution.

A spray truck, 1,000-2,000 gallon capacity, containing theodor-abating chemical solution, would be available for useas needed. It is possible that all loads may not need to besprayed and that the roadways may need spraying onlyintermittently.

It does not seem feasible to totally eliminate all malodorsduring the landfill relocation. Thus, the followingmeasures should be considered:

1. The refuse in the new landfill must be completelycovered with intermediate soil cover or foam,regularly.

2. The landfill excavation and redisposal time shouldbe reduced as much as possible, by using moreequipment to double the amount of refuse removed.

3. A public relations effort should be conducted amongthe nearby residents to explain the short-terminconveniences (i.e., malodors,) as well as thelong-term environmental and public healthimprovements.

An adjunct environmental problem would be that of dustcontrol. Fugitive dust caused by truck traffic andlandftiling operations would be controlled. A spray truckwould be .provided—a separate truck from the odor controlspray truqfc—in order that the roads and open ground areasmay be sprayed. The main roadway between the western andeastern section would be watered at intervals to preventfugitive dust emissions.

The second spray truck would also be available as fire-fighting equipment to douse small fires or contain largerfires until fire-fighting equipment arrives at the landfill.

ftR3007385-£9

It is possible that fires could occur, due to ignition oftrapped methane gas from decomposition of garbage and/orchemical wastes that could have been disposed at thelandfill. Provisions for fire-fighting equipment canreadily be made with the spray trucks that will be at thelandfill for odor and dust control.

It is also recommended that all loading and haulingequipment hava air-conditioned cabs for the operators toalleviate odor problems.

It is expected that as the landfill is disturbed, rodents,and other vectors could be a problem. These vectors couldbe a problem for nearby residences and workers if no vectorcontrol program is implemented. Thus, it is necessary toconduct a vector control program.

5.6.2 Cost Analysis

The capital cost estimate for Alternative 5 is presented inTable 5-15(A). Costs and, time needed to completeAlternative 5 could greatly increase if significantquantities of special/hazardous waste is encountered. Postclosure and operating costs are provided in Table 5-15(BA summary of the total costs and present worth analysiseach alternative is presented in Section 6.

AR300739

5-90

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5-92

5.7 GROUND WATER TREATMENT ALTERNATIVES

With the exception of the No Action Alternative, all otherremedial alternatives involve a ground water recovery andtreatment component. In addition to the downgradientpumping technology, upgradient controls may also requiretreatment depending upon water quality. The ground watertreatment alternatives can be evaluated on a "stand alone"basis depending upon desired treatment levels. This willalso facilitate review of the ground water treatment issuesas they will be affected by the Delaware Sand and GravelRI/FS. The selected ground water treatment alternative canthen be combined with the selected source controlalternative as the complete remedial program.

In this section, the - four alternatives for ground watertreatment are evaluated. Certain assumptions were maderegarding the design flow and pollutant loading in order tocompare the effectiveness and cost of the alternatives.Although the final design basis will depend on additionalground water quality characteristics , laboratorytreatability work, final conceptual engineering design anddetailed design for control of contaminant migration, thissection will provide an adequate comparative evaluation forthe selection of a ground water treatment alternative.

5.7.1 Recovered Ground Water Characteristics

In order to perform an evaluation of alternative groundwater treatment processes, the expected ground waterchemical characteristics and flows must be established. Thecurrent analytical data base for combined ground water flowsis limited particularly for organics (2 sampling rounds).Using the available chemical data collected from theexisting recovery wells (Tables 1-13 through 1-18) andflows, the combined maximum flow characteristics have beenestimated and are presented in Table 5-16 . Total maximumflow for this evaluation is estimated to be 2.88 mgd. Thischemical and flow data would have to be confirmed tofinalize th^ treatment system conceptual engineering design.

.5.7.2 Alternative 1; Army Pond Treatment

Extracted ground water would continue to be discharged toArmy Pond for treatment prior to ultimate discharge to ArmyCreek. Army Pond acts as a passive treatment system where

ftR3QG7U2

5-93

TABLE 5-16

COMBINED MAXIMUM GROUND WATER CHARACTERISTICS

Parameter Maximum1

Flow 2,000 gpm (2.88 mgd)

pH 5.82

BOD 3.9 mg/L

NH3-N 8.8 mg/L

TSS 16.8 mg/L

TDS 255 mg/L

Fe 13.0 mg/L3

Pentachlorophenol 3.6 ug/L

Bis (2-ethyl hexyl) phthalate 22.9 ug/L

Diethyl phthalate 27.1 ug/L

1 Assumes all wells at full flow. Maximum result fromsampling data from 1983-4. Includes compounds expected t

•have concentrations above the surface water criteria.

2f Approximate composite minimum was flow weighted toproduce a composite maximum.

3 Omits a questionable data point for HW-4 taken 4/12/83.

SR3007H3

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iron in the ground water is oxidized to form ferrichydroxide which .precipitates and settles. In addition toiron removal, Army Pond provides retention time forsettlement of suspended solids in the ground water. Thewater from Army Pond discharges to Army Creek.


Army Pond has been used foreground water treatment at ArmyCreek Landfill for the past twelve years. Surface water^monitoring data have indicated that approximately 80% of theiron present in the combined recovered ground water isremoved in Army Pond. The iron concentration downstream ofthe Army Pond discharge has been measured at 2.2 mg/L.

Surface water discharges in the State _of Delaware areregulated by the Department of Natural Resources andEnvironmental Control (DNREC, 1983). Effluent standards arelisted for 16 parameters as maximum concentrations forwastewater discharges. In addition to the listed maximumconcentrations, average and maximum daily loadings wouldalso be established based on flows. A preliminary draftNPDES permit has been issued by DNREC and utilizes theseeffluent standards to set effluent limits along withbioassay requirements.

Based on the existing analytical data for the recovery welldischarges (Tables 1-13 through 1-16), the two parameterswhich could exceed the surface water discharge limits areiron (limit of 2 mg/L) and suspended solids (limit of 30mg/L). The iron constituent is strongly influenced by thenaturally-occurring iron concentration in the regionalground water which can range from 3 mg/L to 11 mg/L in thePotomac aquifer (Woodruff, 1970). The County has requestedthat the background (naturally-occurring) iron levels beconsidered by DNREC in setting final NPDES limits.

Existing analytical data for the Army Pond dischargeindicatess an iron concentration of 2.2 mg/L. Depending uponthe final NPDES permit limitations which are set and someadditional!*?.discharge characterization, it is possible thatArmy Pond cVuld_ provide adequate treatment to meet NPDESlimits i:or the combined flows from all wells.

An alternative to using Army Pond for treatment of all flowsis to split flows. The combined flow of wells 27, RW-10,and RW-13 contain less than 1.4 mg/L of iron and could bedirectly discharged to Army Pond. Wells 28 and 29, with

5-95

relatively higher iron concentrations, could be selectivelydischarged to a POTW as described in Treatment Alternative4.

Although some modification of present operation may berequired based on institutional factors, this alternativeremains a feasible alternative for ground water treatment.It is both reliable and readily implementable and presentsno worker safety hazards during implementation.


Institutional factors for this alternative include the NPDESpermit renewal conditions, and remedial actions taken at theadjacent Delaware Sand and Gravel Landfill.

5.7,2.3 Public Health Issues

Army Pond discharges to Army Creek and then to the DelawareRiver. Although some of the compounds found in the groundwater exceed the drinking water criteria, no harmful publichealth affects are anticipated, since the receiving bodiesara not used as drinking water sources. Surface watersampling in Army Creek/Pond in 1983 indicated no volatile orextractable organic compounds and 1985 sampling detected nc(organic compounds of concern. Surface water sampling inArmy Craak and Pond have indicated only a few constituentswhich have exceeded surface water criteria. The analyticaldata indicate that the criteria are exceeded for bothupstream and downstream sampling locations. In fact, the1983 data (Table 1-27) indicate higher concentrationsupstream than downstream.


The affects of the recovered ground water on the ecosystemsof Army Creek and Army Pond have been investigated inseveral surface water, sediment, and biotic surveysconduced since 1973. Details of these surveys areprasanlied in Subsection 1.2.2.2 and Appendix L. Overall,the water quality has remained fairly stable with nodramatic increases or decreases in constituentconcentrations.

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The most recent (April 1985) water quality analyses (Table1-28) indicate total iron concentrations, within the pondand at the pond outlet, ranged from 1.8 mg/L to 4.6 mg/L.However, fish and benthic surveys concluded that therecovered water was not toxic (as presented in Subsection1.2.2.2). Precipitation of the iron as ferric hydroxide,which has settled in pond sediments has also been noted, andcould potentially affect the benthic environments and fish.Effects of the precipitate observed in the biologicalsurveys appeared to be minimal or not discernible. In"addition, erosion from unstabilized banks along the pond andcreek cause more siltation and sedimentation on the pondthan iron precipitate

5.7.2.5 Cost Analysis

This alternative would be implemented without significantcapital expenditures. Operating and monitoring costs wouldinclude sampling and analysis according to the NPDES permitrequirements, and eventual decommissioning of the pumpingwells arid pond (see Tables 5-17 (A) and 5-17 (B).

5.7.3 Alternative 2: Iron and Solids Removal

The objective of this alternative is to treat ground waterfrom any existing or future recovery wells to meet or exceedexpected NPDES requirements for surface discharge withoutthe us<» of Army Pond for treatment. The objective of thetreatment process is to remove iron and suspended solids.Aeration and clarification would be utilized to remove ironto levels acceptable for discharge. The design basis forthis proposed process would have to be confirmed based onadditional flow and chemical characterization of therecovered ground water and treatability studies.


Aeration would provide., oxygen to oxidize ferrous iron(Fe ) to ferric (Fe ) iron which has low solubility injwater at neutral pH. The precipitate can be removed byfiltration?-_at lower solids loading and by coagulation andclarification at higher solids loading. The solids would befurther dewatered by filtration before disposal. A typicalblock flow diagram for the process is shown in Figure 5-15.

5-97

TABLE 5-17A

TREATMENT ALTERNATIVE NO. 1ARMY POND TREATMENT

CAPITAL AND PRESENT WORTH COSTS

PHASE OUT OF PUMPING WELLS AND ARMY POND

Description Total Cost($)

1) Shutting down and securing of $ 75,000wells and accessories, limitedsampling and analysis, noconstruction or removal ofsediments from Army Pond ^____

TOTAL COST FOR PHASE OUT $ 75,000

PRESENT WORTH ANALYSIS(1)

Option A Option B

o Effluent Monitoring $680,000(2) $250,000(2)

o Phase Out of Pumping Wells ,-, r?.and Army Pond • 4,300IJ; 4,3QQIJJ

TOTAL PRESENT WORTH COST , $684,000 $254,000

1 Costs presented to two (2) significant figures with round off

2 Based on 30 yrs. operation and 10% discount rate.

3 Basad on phase out at end of 30 yrs. and 10% discount rate.

AR3QQ7U

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TABLE 5-17B

TREATMENT ALTERNATIVE NO. 1

ARMY POND TREATMENTOPERATING COST ESTIMATE

Effluent Monitoring

- Option A Option B

• Daily grab sample for pH • Weekly grab sample forpH

• Weekly, 24 hour composite, • Week, 24 hour compositefor TSS and Fe for TSS and Fe

• Monthly, 24 hour composite • Monthly, 24 hours compositfor inorganics for inorganics

Description Total Cost ($)

Option A

1) Sampling the effluent*1' 67,000

2) Analytical 5,000

TOTAL ANNUAL COST-OPTION A $72,000

(1) Costs have been estimated based on a contractor performingthis task. Cost estimate includes labor and expense forsampling, delivery of samples and report preparation.

Option B

1) Sampling the effluent* ' 22,000

2) Analylical 4,000. . a r - - . - . . . _ _ . .

TOTAL ANNUAL COST-OPTION B $26,000

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5-99

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Implementation of this alternative would requiretreatability studies to: identify any treatmentinterferences; determine optimum pH for oxidation andprecipitation (and any associated lime addition rates);determine optimum dosage of polymer for coagulation; anddetermine design oxidation, settling or filtration andsludge filtration rates.

Aeration and solids separation has an established operatinghistory for the removal of iron and manganese from municipalwater supplies. In the absence of treatafaility results itis assumed that reactor-clarifier will be used for solidsseparation due to the presence of other suspended solids inthe ground water and tha possible addition of lime for pHadjustment.

This alternative can reliably achieve the anticipatedtreatment requirements before discharge to Army Pond or ArmyCreek. Organic compound levels can be expected to declineas a result of aeration but some may remain above surfacewater criteria.


This alternative should achieve the anticipated NPDES permitrequirements for surface discharge. Like Treatment Altern-ative 1, however, treatment is not designed to achievemaximum organics removal.

5.7.3.3 Public Health-Issues

No significant adverse public health impacts are anticipatedas a result of ground water treatment. Water quality in^Army Pond and Army Creek is expected to improve as a resultof lower iron and suspended solid.levels. The accumulationof~ferric hydroxide and solids due to settling in Army Pondwill be greatly reduced. The system will also provide some_r_emo-val of- volatile organics during the aeration step.

* ~5.7.3.4 Environmental Issues

Inplementation of this alternative would have a positiveimpact on the water quality and sediments of Army Pond andArmy Creek due to reduced iron loading. This improvementmay not be apparent from a biological/chemical standpointsince there is currently no measureable impact. Thetreatment process will result, however, in the generation of

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a ferric hydroxide sludge which will require disposal atappropriate landfill. Also a small release of volatil^organics to the ambient air will occur. This is expected tobe essentially negligible due to the low or trace levelsobserved in the recovered ground water.


Engineering expenses would include additional ground waterchemical characterization, treatability studies and detaileddesign. Capital equipment would include an aeration basin,reactor-clarifier, and sludge filter. Operating costsinclude operation and maintenance, labor, power, chemicalsand sludge disposal.

1 The estimated capital, operating and maintenance costs aresummarized on Tables 5-18A through 5-18C.

; 5.7.4 Alternative 3; Iron Removal and Activated'i Carbon Treatment

The objective of this alternative is to treat ground waterf||| for iron and organics removal. Depending on the degree ofill organics removal which can be achieved, the treated

water may be considered for ground water recharge byof rainjection. A preliminary analysis indicated

j treating the recovered ground water for reinjection wouldbe prohibitively expensive (on the order of several millionto several billion dollars) due to the presence of poorlyadsorbed solutes. Therefore, in response to EPA commentsregarding this alternative, this evaluation will utilizesurface water criteria for the discharge limitations insteadof drinking water criteria.

Potential conceptual designs could utilize aeration additionof chemical precipitants, and solids removal to pretreat for

: iron, followed by either granular activated carbon (GAG) or'! powdered activated carbon (PAC). While PAC could be applied

using aeration and settling equipment, the carbon is nottypically regenerated. In systems with high carbon utiliza-

—- tion a*tesf regeneration is necessary to reduce operatingcosts.* " For ' the purpose of this evaluation, the system willutilize an aeration basin, clarification, multimedia filter,filter press for solids dewatering and a GAC system withoff-site commercial regeneration of the spent carbon forremoval of organic compounds.

AR300755-102

TABLE 5-18A

TREATMENT ALTERNATIVE NO. 2IRON AND SOLIDS REMOVAL

CAPITAL AND CONSTRUCTION COST ESTIMATE

I. Installed Equipment and Technical Costs

Description Estimated Cost

1) Aeration Unit $ 130,000(1)

2) Lime Addition Unit 56,000(1)

3) Reactor Clarifier/ .Flocculator Unit 739,0001<U

4) Polyelectrolyte . .Addition Unit 72,OOO11'

5) Sludge PressureFiltration Unit 192,000

6) Sludge Holding Tank - 85,000(1)

7) Miscellaneous Structures(yard piping, buildings,sanitary pump station,electrical support, yardlighting, etc.) _

SUBTOTAL $1,644,000

8) Design, Construction Management,and Site Services (15%) 247,000

SUBTOTAL $1,891,000

9) Confjl-ngency (15%) 284,000

TOTAL $2,175,000

ftR300752

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TABLE 5-18A(continued)

II» Phase Out of Recovery Wells and Treatment Plant


1) Phase out of Recovery Wells $ 30,000

2) Phase out of Treatment Plantincluding removal of processbuilding, piping, pumps, tanks,equipment and accessories, ,,.decontamination and restoration 150,000

SUBTOTAL $ 180,000


SUBTOTAL $ 207,000

4) Contingency (15%) 31,000

TOTAL $ 238,000

1 Cost estimated from EPA Publication 430/9-78-009 withENR adjustment to 4,200.

2 Cost estimated from EPA-600/2-82-001d with ChemicalEngineering Plant Cost Index adjusted to 325.

3 Assumed that equipment and buildings have no salvage orresale value.

HR30Q753

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TABLE 5-18B

TREATMENT ALTERNATIVE 2IRON AND SOLIDS REMOVAL

OPERATION AND MAINTENANCE COST ESTIMATE

ANNUAL OPERATION AND MAINTENANCE COST

-Description Estimated Cost

1) Power requirement (aeration, limeaddition, polymer addition, reactorclarifier/flocculator filtrationunit) 8 $0.08/KwH $ 53,000

2) Materials (lime, polyelectrolyte) 87,000

3) Maintenance, insurance, services(6% of capital) 99,000

4) Disposal of filter cake (sludge)8 $150/ton 165,000

5) Operations (labor, supervision andoverhead) - - - - - - 283,000

6) Permit related monitoring 23,000<1)

SUBTOTAL $ 710,000

CONTINGENCY (15%) 106,000

ADMINISTRATIVE (15%) _ 106,000

TOTAL $ 922,000

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TABLE 5-18C

TREATMENT ALTERNATIVE 2IRON AND SOLIDS REMOVAL

PRESENT WORTH COST ESTIMATE

PRESENT WORTH ANALYSIS*!)

1) Installed Equipment andTechnical Cost $ 2,175,000

2) Phase out of Recovery Wellsand Treatment Plant 14,000*2)

3) Operation and Maintenance Costs 8,692,000^3)

TOTAL PRESENT WORTH COST $10,881,000

(1) All o sts presented to two (2) significant figures withround off.

(2) Phase out at and of 30 yr. period and 10% discount rate.

(3) Operating period of 30 yrs. and 10% discount rate.

SR30Q755

5-106


Aeration and clarification can be effective for removal ofiron as described in Section 5.7.2. Activated carbonpolishing has been successfully used for removal of organicsin wastewater to achieve high "purity" effluent. Figure5-16 depicts this alternative.

Evaluating the feasibility of treatment of a complex,variable mixture of contaminants in ground water to possiblyachieve drinking water quality is a complex task. Theavailable data indicate that there are a large number oforganic contaminants at concentrations which vary betweenwells and over time. Recognizing that additional sourcedata (particularly for organics) and treatability studieswould be necessary to properly determine the feasibility andcost, this analysis is conducted based on a conservativeinterpretation of available data and literature treatabilitydata.

Table !>-19 presents the data utilized to estimate theperformance of GAC for organic compound removal. Themaximum concentration found for each well was utilized todevelop a flow weighted maximum composite concentration forthe inifluent to the GAC system. The estimated carboncapacity based on single solute solutions indicates that,based on the compounds which have exceeded surfaced watercriteria!, diethyl phthalate is the limiting factor in theperformance of carbon adsorption in this application. Theadsorption isotherm data available in the mg/L concentrationrange (Ref. EPA-600/ 8-80-23) indicates that 0.00065 gramsof carbon would be required per liter of solution at theestimated maximum influent concentration. Conditions foradsorption are generally favorable for the compounds,identified for removal.

Before the-conceptual engineering design for this altern-ative era*- be finalized, study is necessary in order torefine thSs'e performance estimates. This analysis issensitive to the accuracy of the identification and quantifi-cation of organic constituents in the available data baseand removal kinetics at the low target effluent concentra-tions. Treatability studies and design would be necessarydue to the large sensitivity of cost and design to theaccuracy of existing data.

5-107

ftR300757

TABLE 5-19

GAC ADSORPTION CAPACITIES FOR SINGLE SOLUTE SOLUTIONS

Maximum Estimated Estimated CarbonInfluent ^ Treatment- Carbon « Consunption per

Concentration Objective Capacity Unit of Groundwaterompound___________(uq/L)______(ug/L)_______(mg/g).________(g/L)________

entachlorophenol " ~3~T 3."2"* 14. 0.00026is (2-athyl hexyl) 22.9 3.Q* 39. 0.00059phthalate ,*

,'iethyl phthalate 27.1 3.0* 41.5 0.00065

Based on the flow weighted average from all wells of the maximumconcentration obtained during sampling conducted between 1983 and1985.

Capacities based on isotherms from EPA-600/8-80-023, CarbonAdsorption Isotherms for Toxic Organics. Values are based on maximumexpected concentrations assuming the single solute isotherm applies.Actual removals may be more or less due to preferential removalswithin a multi-specie solution. Units given in mg, of soluteadsorbed per gram of carbon.

Criteria for freshwater aquatic life (CWA)

Criteria for freshwater aquatic life; total of all phthalate esters,(CWA)

Apparent Threshold Limit Values

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5-109


This alternative will achieve the anticipated NPDES permitrequirements for surface discharge. In addition, organiccontaminants will be removed from the discharge.


No significant adverse health impacts are anticipated as aresult of ground water treatment. Water quality in ArmyPond and Creek is expected to improve as a result of loweriron, suspended solids and organic compounds concentrations.

5.7,4.4 Environmental Issues

Surface discharge of this effluent stream would havepositive impacts on the surface water quality, as describedin Treatment Alternative 2.


Engineering expense would include additional ground wate;chemical characterization, treatability studies, anadetailed design. The cost for the characterization andtreatability studies have not been included in thisanalysis. Capital costs include all equipment specified forTreatment Alternative 2, as well as multimedia filtrationand carbon adsorption equipment. Operating cost estimatesinclude operation and maintenance, labor, power, chemicals,sludge disposal and carbon replacement. Capital andconstruction costs are presented in Table 20(A).

Operating cost estimates are based on commercial off-siteregeneration of spent carbon. Operation and maintenancecosts are presented in Table 20(B). Present worth estimatesare presented in Table 20(C).

^v *

5.7.5 Alternative 4; Off-Site Treatment of GroundWafMr-Discharge To Wilmington WWTP

The objective of this alternative is to provide treatment,assuming Alternative 1 will not meet NPDES permit limits,without shutting down wells with high contaminant concentra-tions and without constructing new treatment facilitiesoft-site. Ground water from either all or selected recoverywells would be directed to the Wilmington &t t«urcTreat

5-110'

ttr

TABLE 5-20 (A)

TREATMENT ALTERNATIVE NO. 3IRON REMOVAL AND ACTIVATED CARBON TREATMENT

CAPITAL AND CONSTRUCTION COST ESTIMATE

I. Installed Equipment and Capital Costs


1) Aeration Unit $ 130,000(1>

2) Lime Addition Unit 56,000(1)

3) Reactor Clarifier/Flocculator Unit 739,000C1}

4) Polyelectrolyte • ,-.Addition Unit 72,000CXJ

(1)5) Sludge PressureFiltration Unit 192,000

6) Sludge Holding Tank 85,000(1)

7) Multi-media Filtrationsystem (includes filtrationunits, backwash holding,associated pumps, compressors,piping, insulation pond instru- ...mentation) 1,65 2,000 *

8) Activated Carbon System 1,350,000(3)

9) Miscellaneous Structures(yard piping, buildings,

"satitijbary pump station,electrical support, yard f-.lighting, etc.) 725,000*^*

SUBTOTAL $5,001,000

10) Design, Construction Manage-ment and Site Services (15%) 750,000

SUBTOTAL $5,751,000ftR300760

11) Contingency (15%) 863/000

TOTAL $.6,6.14,000.-

5-111

TABLE 5-20 (A)(continued)

Phase Out of Recovery Wells and Treatment Plant


1) Phase out of Recovery Wells $ 30,000

2) Phase out of Treatment Plant(including demolition, removaland restoration) 350,000

SUBTOTAL $ 380,000


SUBTOTAL $ 437,000

4) Contingency (15%) 66,000

TOTAL $ 503,000

1 Based on EPA Publication 430/9-78-009 with ENRadjustment to 4,200.

2 * Base£> on EPA-600/2-82-001d, Treatability Manual, withChemical Engineering Plant Cost Index adjusted to $325.

3 Design and capital cost is based on carbon capacity for2,6-Dinitrotoluene. Conventional plant design and costestimating are not applicable for the high carbon utiliza-tion rates necessary for benzene or Bis (2-choroethyl)ether removal. Design and cost estimation would requiretreatability studies and possibly process development.

4 Assumed that equipment and buildings have no salvage orresale value.

S-112 AR30076I

TABLE 5-20 (B)

TREATMENT ALTERNATIVE 3IRON REMOVAL AND ACTIVATED CARBON TREATMENT

ANNUAL OPERATION AND MAINTENANCE COST ESTIMATE


1) Power (8 $0.08/KwH) $ 73,000

2) Chemicals (lime, polyelectrolyte) 87,000

3) Operations (labor, supervisionand overhead) 530,000

4) Maintenance, insurance and services(6% of capital equipment) 300,000

5) Sludge Disposal (8 $150/ton) 165,000

6) Regenerated Carbon 2,600(Supply and servicing @ $0.50/lb)

7) Permit Monitoring Analytical Services 137,800

SUBTOTAL ""__."_ - ... . _"", __ _ '_ $1,295,000

CONTINGENCY (15%) 194,000

ADMINISTRATIVE (15%) 194,000

TOTAL ". $1,683,000

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TABLE 5-20 (C)

TREATMENT ALTERNATIVE 3IRON REMOVAL AND ACTIVATED CARBON TREATMENT

PRESENT WORTH COST ESTIMATE


1) Capital Cost1 $ 6,614,000

2) Phase out of Recovery Wellsand Treatment Plant 29,000

3) Present Worth of Operation andMaintenance(30 yr. operation; 10% discount rate) 15,866,000

TOTAL PRESENT WORTH T 22,509,000

1 Detailed design and cost estimation would requiretreatability studies not reflected in these costs

2 Phase out occurs at year 30, 10% discount rate.

3R3007S3

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ment Plant. (WWTP). The remaining ground water flow whichwould likely meet the NPDES permit limits would be dis-charged to Army Pond as described in Alternative 1.

This alternative will require construction of piping systemsand possibly a pumping station (depending on the hydraulicload at the State Road Pump Station). Pretreatment of theground wa.ter prior to discharge into the Wilmington WWTP isnot anticipated at this time. However, a further evaluationof the pretreatment requirements should be made to finalizethe conceptual engineering design if this alternative ischosen as the remedial action for the Army Creek Landfill.


A feasibility study for the discharge of contaminated groundwater from Army Creek Landfill recovery wells to WilmingtonWWTP was completed by WESTON in 1980 (Appendix J). Based onthe data presented in that report and recent preliminarydiscussions with sanitary engineers at_the Wilmington WWTP,discharge and treatment off-site appears to be a technicallyfeasible option.

The levels of organics and inorganics monitored in therecovered ground water are at sufficiently low levels thatthey should not interfere with the operations of thetreatment plant. The 1980 feasibility study estimated thatintroducing the recovery well discharges to the WilmingtonWWTP system would not impact the effluent quality, unitoperations or sludge disposal. Since the key contaminantparameters in the ground water have, in general, decreasedor remained constant since the 1980 study, the conclusionsof that study with respect to treatability should stillhold. If this option is selected, however, additional studymay be rec[uired before implementation.

Another primary consideration in determining the feasibilityof this option is the hydraulic capacity of pumping stationsin the area -as well as the capacity of the treatment plantitself. Ifca plant is currently operating at 75 mgd with apeak capcicfty of 90 mgd; hence, hydraulic capacitylimitations at the WWTP should not preclude implementationof this option. Furthermore, the State Road Pump Stationand State Road Interceptor should be able to accommodate theEntire hydraulic load (up to 2.0 mgd) from the Army CreekLandfill recovery wells (Appendix J).

5-115

Implementation of this option would involve construction ofthe piping system to convey the well flows to tha selectedpump station. As indicated earlier, this alternative may beused in conjunction with treatment Alternative 1 (Army Pond)to formulate a system that allows for discharge to both ArmyCreak/Pond and the WWTP. In this case, those wells with thehighest loadings ' of iron and other parameters could bedischarged to the WWTP, while those that meet NPDESrequirements could be directly discharged to Army Creek.


Implementation of this option would require acceptance ofthe wastewater stream, and compliance with applicablecriteria.*


Iron and other metals in the ground water would beeffectively removed at the Wilmington WWTP. In additionorganic contaminants would be effectively removedbiological degradation and aeration in the WWTPsludge process.

Further, the 1980 study estimated, based on discussions withD BC, that the water quality in Delaware iver would beminimally affected by discharge of recovery well flows toeither the Wilmington WWTP or Army Pond.

Depending on the final NPDES permit conditions, certainwells may be considered for discharge to the WilmingtonWWTP. Currently, the combined discharge from recovery wells27, W-10, and W-13 meets the expected NPDES requirementsand wduld most likely not be directed to the WWTP.

^ ^ *If none of the recovery wells were discharged to Army Pondunder this Alternative, the existing pond would be reducedin siza and may disappear altogether. The wetlands could besustained by an intermittent stream fed by less than onecubic foot per second upstream; however, during periods ofdrought the stream would probably not exist.

AR300765

5-116


Currently, the City of Wilmington is reviewing thesuitability of discharge of recovered ground water to theWWTP. The discharge of ground water pumped from therecovery wells into the WWTP will not present a threat topublic health. The concentration of volatile organiccontaminants in the ground water pumped from recovery wellsare low .and further reduction in concentration can beexpected due to mixing with other influents in the WWTPsewer system. Therefore, significant devolatization oforganics into the head space of the sewer system and otherunits from the WWTP is not expected.

In addition, organic contaminants in ground water pumpedfrom the recovery wells into the WWTP are not expected toadversely impact the composition of the sludge and effluentfrom the WWTP (Appendix J).


The capital costs incurred in this option include design andconstruction of a recovery well discharge conveyance system.perating costs include electricity for pumping, labor,maintenance and charges levied by the Wilmington WWTP. TheWWTP charges are based on hydraulic load, suspended solids,and B D content of the flow. Assuming that wells 27, W-10,and W=13 are discharged to Army Pond/Creek and that theremaining wells are pumped at full capacity to WWTP,discharge loadings to WWTP were calculated using peak loadsfrom recent data (see Table 5-21). The annual operatingcosts amounted to approximately $1.0 million with about 98%of the cost contributed by the hydraulic load as shown inTables 3-22(A) through 5-22(C). An application processingfee, in addition to the costs shown in Tables 5-22(A)through 5-22(C), may also be levied.

Capital and operating costs for the pumping system itselfwere bcissd on an initial conceptual design prepared as partof the 19y). study. This design was based on pumping fromthe wellfield to the State oad Punp Station. Although thewellfield at that time consisted of different wells, thecumulative flow of the new wellfield is approximately thesame as the old wellfield. Incorporating the ability toconvey any of the wells into the transportation system wouldallow for flexibility should the parameter loadings inindividual well flows, which are now acceptable fordischarge, later exceed NPDES limits. Under such a systemthe capital costs would be comparable. sn^^rt*?^^fin300766

5-117

TABLE 5-21

LOADINGS OF WELLS SELECTED FOR POSSIBLE DISCHARGE TO WWTP

Well Peak flow TSS3 BOD3 4(gpm) (mgd) Ib/day Ib/day

28 150 0.22 60.56 8.65

29 200 0.29 129.8 38.93

31 200 0.29 46.14 21.34

RW-1 270 0.39 38.93 7.79

RW-4 200 0.041 5.77 .82

RW-9 80 0.062 17.3 1.155

RW-11 160 0.23 23.07 4.61

RW-12 150 0.22 30.28 4.33

RW-14 100 0,14 23 .07 2.88

TOTAL 2,510 1.87 375.0 90.5

1 Pumps 24 hrs/wk only2 Pumps 12 hrs/day only3 - Peak value from 1984 data used, except for RW-4. For RW-4

1981*1983 data was used. 4/12/83 data appeared inconsistentand therefore was not used.

4 1985 sampling data used5 Where BOD was less than 2.4 mg/L, value of 2.0 mg/L was

assumed6 BOD data not available. Value of 2.0 mg/L assumed.

AR300767

5-11C

TABLE 5-22 (A)

TREATMENT ALTERNATIVE NO. 4DISCHARGE TO WILMINGTON WWTP

CAPITAL/CONSTRUCTION COST ESTIMATE

I. Construction of Connecting Sewers fromRecovery Wells to State Road Pump Station


1. Total,Construction and EngineeringCosts

CONTINGENCY (15%)

TOTAL $ 178,000

II. Phase Out of Pumping Wells, Army Pondand Connecting Sewer System

1. Phase out of pumping wells andArmy Pond $ 75,000

2. Phase out of connecting sewer system $ 110,000

TOTAL $ 185,000

1 Based on preliminary design and cost estimate includedin report entitled "Feasibility Study For The Discharge OfContaminated Ground Water From Army Creek Landfill RecoveryWells, New Castle County, Delaware" prepared by WESTON in19980. See Appendix J - Cost Estimate UpdatedDollars.

5-119

TABLE 5-22 (B)

TREATMENT ALTERNATIVE NO. 4DISCHARGE TO WILMINGTON WWTP

OPERATION AND MAINTENANCE COST ESTIMATE

Description Quantity Unit Cost Estimate Cost

1) Total flow charges 1.87 mgd $1.44/1000 gal $ 983,000

2) Total suspendedsolids charges 375 Ib/day $0.16/lb 21,900

3) BOD charges 90.5 Ib/day $0.11/lb 3,600

4) Sampling on a 1 sample/monthly basis month $200/sample 2,400

5) OS M,of GravitySewer line 5,670 ft. $0.20/ft 1,200

6) Monitoring Effluent (See Option B ofat Army Pond Alternative No. 1) 26,000

SUBTOTAL $1, 037,000

CONTINGENCY (.15%) 156,000

ADMINISTRATIVE (15%) 156,000

TOTAL $1,349,000

&R3007691 Source: EPA-430/9-78-009, February 1980

ENR m 4200

5-12C

TABLE 5-22 (C)

TREATMENT ALTERNATIVE NO. 4DISCHARGE TO WILMINGTON WWTPPRESENT WORTH COST ESTIMATE

PRESENT WORTH ANALYSIS(1)

Description Estimate Cost

(2 )1) Operation and maintenance 12,717,000

2) Construction of connectingsewer system __.... .__._ 178,000

3) Phase-out of pumping wells,Army Pond and sewer system _ _ 10,000

TOTAL PRESENT WORTH COST $12,905,000

(1) All costs presented to two (2) significant figures withround off.

(2) Based on 30 yr. operation period and 10% discount rate.(3) Based on phase out at end of 30 yrs. and 10% discount rate.

5-121 .' 3R30Q77Q

The recommended alternative is Alternative 4a, the phasedapproach. This alternative includes downgradient pumping,landfill capping, and upgradient controls. Following anevaluation period of five years after the cap is installed,a decision would be made concerning the necessity ofupgradient controls (pumping or an interception trench).This decision would be based on an evaluation of waterlevels and water quality at tha Army Creek Landfill. Anadditional component of this alternative is a wellmonitoring program.

At this point, no selection of a treatment alternative hasbeen made. This is because the final NPDES permit has notbeen issued and the conclusions of the Delaware Sand andGravel RI/FS have not been made. It is EPA's intention tocombine the remedial actions of both sites where everpossible.

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Minutes

New Castle County

10 July 1975Roy F. Weston Conference Room

Attendees

-.._ . _ _ Steve Kowalchuk, NCC Amir A. Metry, RFWDave Clark, NCC Walt Leis, RFW

This technical meeting was called to evaluate the technical feasibilityof developing a rehabilitation plan for the Llangollen landfill. This

plan is defined as follows:

• A hydrogeologic program for site dewatering, groundwater protection,pollutants containment and recovery and aquifer rehabilitation,

• Refuse excavation, handling, storage and transport to reconstructedareas or to off-site disposal area.

• Site rehabilitation, including site preparation and installation .r—; of liner, leachate collection system and groundwater control systems

• Refuse f i I I ing in reconstructed areas in Llangollen landfi11.

• Landfill finishing, including covering, grading and vegetation.

• Leachate collection, treatment and/or disposal during and aftercompletion of the rehabilitation program.

Weston's project team* identified potential problem areas and presentedpossible options for their control. Some of these areas are:

• Dewatering of leachate and groundwater during the program.

» Containment of .contaminants during and after the program.

• Refuse excavation, handling and transport.

• Selection and design of landfill liner and leachate collectionsystem.

• Control of nuisances (odors, vectors, fires, etc.) during theprogram.

Lr.r(jjjl APPENDIX A through APPENDIX H.

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APPENDIX A

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EVALUATION OF GROUND WATER AVAILABILITY AND PUMPING CAPACITY

_________________LLANGOLLEN AREA____________________

Problem

Leachate from the old Llangollen Landfill has entered the underlyingPotomac aquifer and is moving in the direction of high volume wellsapproximately 3,000 feet southeast of the landfill. The leachatecontains high concentrations of dissolved metals, salts and organiccompounds. The taste and odor as.well as the objectionally highconcentrations of certain of the chemical species renders theleachate totally unapceptable for potable or most other water uses.

Geologic Setting

The geology of the Llangollen area as it affects the leachateproblem has been described in an earlier project report. Briefly,the area is blanketed by approximately 30 - 60 feet of generallycoarse sandy sediments of Pleistocene Age. This veneer has beenextensively quarried in the Llangollen area. The LlangollenLandfill itself is constructed in such an old gravel pit.

The Pleistocene-sands directly overlie the Lower Cretaceous Age_Potomac Fprmatjqn. The Potomac was deposited by sluggish streamsand consists of an interbedded sequence of clay, s i l t and fine tomedium sand with smaller amounts of coarse sand and fine gravel.Some parts of the formation are predominantly sandy and have beendeveloped for water supplies, while others are predominantly clayeyor silty and retard the movement of water. In the Llangollen areathe upper part of the Potomac Formation is an aquitard which separatesthe Pleistocene sands from the deeper Potomac sands. The aquitardconfines water in the Potomac sands under artesian pressure so thatwater in a wel'i screened in the Potomac sand rises above the levelof top of the sand.^^ i* ~ -Large scale withdrawals from wells in the Potomac aquifer havelowered water pressure through the formation. The result has beento create a water pressure gradient from the Pleistocene sands tothe Potomac sands and — once in the Potomac aquifer — towardsthe pumping wells. This situation has caused the migration ofleachate from the landfill into the Potomac aquifer where theaquitard is afa.sent and the front of leachate contaminated wateris moving toward the existing major wells in the aquifer.

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Aquifer Evaluation "

An extensive test d r i l l i n g program in the Potomac aquifer hasdefined the approximate extent of leachate contamination In theaquifer. This pattern of contamination is shown in Figure 1.

In order that the contaminants be prevented from spreading furtherthrough the aquifer and eventually reaching the existing wellsa contaminant recovery program has been initiated. The programIs intended to Intercept and recover contaminants through properlylocated wel Is.

The recovery wells are being drilled in the part of the aquiferwhich has already been contaminated to minimize the amount of goodwater which Is removed. The recovery wells must locally reversethe present water pressure gradient towards the existing wellsso that all contaminants move to the recovery wells. In orderthat this be accompHshed it was necessary to evaluate the aquiferparameters governing water movement so that a quantitative groundwater management program could be established.

Because little quantitative information on aquifer transmtssivlty,storage and boundary conditions existed prior to the need to designthe recovery system, Roy F. Weston undertook an aquifer evaluationprogram. This program consisted of pumping and recovery tests ofwells drilled for New Castle County during the contaminantinvestigation and the existing wells belonging to the ArtesianWater Company,

The aquifer transmlsslvlties calculated from these tests rangedfrom 40,000 gpd/ft. to 150,000 gpd.ft. Storage coefficients rangedfrom 5.7 x 10~5 to 5-6 x 10" , The transmissivlties are greateralong the axis of the old sand fi l l e d channels and across channels.Average aquifer parameters used In the ground water managementcalculations were as follows:

1. along aquifer strike (NW - SE direction)transmisslvity = 74,000 gpd/ft., storage coefficient « 2.87 x 10

2. aloniptea.quifer dip (SW - HE direction) .*~ trans«rlsslvity - 40,000 gpd/ft., storage coefficient » 5-7 x 10

Ground Water Management Plan for Contaminant Recovery

Any Increase In withdrawal of ground water from the aquifer down-! gradient from the Llangollen Landfill would accelerate the rate of

movement of the front. For example, if the wells In the nearby* well fields are pumped at 3,000 gpm, the front could travel 100 feet

In only 75 days. On the other hand, the front could take 226 days tto travel 100 feet if the wells are pumping at 1,000 gpm. In any <&fefej

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the velocity of contaminant movement will increase as the" frontapproaches the pumping centers. Although it does not appear thatthe front is moving at an alarming rate now, it would be a matterof time before most of the wells in the aquifer start pumpingcontaminated water If present conditions were to persist. Ifpermeability of the aquifer material in a zone between the Llangollen'landfill and the nearby well fields is as high as 6,000 gpd persquare foot, which appears to be the upper limit of the permeabilityof the aquifer material In this area, the front could travel 100feet in 18 to 20 days.

" The most desirable solution would be to curtail the large wellfields, presently pumping several mi l l i o n gallons of water from

j' the aquifer. If these wells were to stop pumping as soon as possible*'- -and not restart until most of the contaminated water has been removed,

the recovery operation could be accomplished with minimum withdrawaland a shorter time span with the absence of competing wells.

In view of the increasing demand of ground water during the incomingsummer, it may not be practical to shut down all existing wellfields. A reduction in the present pumping rates w i l l be necessaryto slow down the contaminant movement so that the retrieval wellswould be more effective in creating the desired ground water divide.

It appears that If the existing well fields continue to pump atthe present rates and the retrieval wells have started pumping,a ground water divide would exist at about 500 feet from well 23along a line between wells 30 and J-l (figure 1,2). Under theseconditions, the gradients to northwest (toward landfill) and tosoutheast (toward well field) of the ground water divide would beapproximately 7-38 x I0~3 ft./ft. and 4.94 x 10"' ft./ft. , respectively.Although the retrieval wells would create local cones of depressionand gradients thereby causing the contaminant front to move ultimatelytowards the landfill, there w i l l be an overall gradient towardssoutheast. ___

Conclusions

The main Influence- of the retrieval wells is limited to a radiusof approximately 250 feet downdip in the aquifer if the existingwell fields continue to pump at the present rates. , Movement ofcontaminants downdip past this radius would probably not be reversedto the recovery wells. Thus, the recovery wells would have a-greater chance of success in recovering all contaminants If thepumping rates of the existing wells are reduced.

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Another Important factor to be considered is the capacity of theaquifer which may not be able to sustain 3,000 gpm of the retrievalwells in addition to the pumping rates of the existing well fields.Although necessary and sufficient data are not available a roughestimate Indicates that approximately 6.83 x 10"3 gpd/sq. ft. maybe available for recharge from the annual precipitation. Overpumpingthe aquifer Is not a sound practice and it seems necessary thatIn order to recover the contaminated water from the aquifer, thepumping rates of the wells in the existing well fields should bereduced as soon as possible. In any case, no additional wellsshould be allowed to start pumping In the nearby well fields.

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R300789

2.6 results of technologies screening and … · ards but will reduce the likelihood of present or...

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