SDMS Doc ID 2030051

2030051

UNITED STATES ENVIRONMENTAL PROTECTION AGENCYREGION IX

75 Hawthorne Street (WST-7)San Francisco, CA 94105

January 28,2000

Republic Disposal Urban Maintenance Processing Company, Inc.Alan Gaddy, Vice President770 E. Sahara Ave.Las Vegas, NV 89104

Clark County Comprehensive PlanningJohn Schlegel, Director500 S. Grand Central ParkwayLas Vegas, NV 89155-1741

Re: Landfill Assessment Work PlanSunrise Mountain LandfillFindings of Violation and Order for ComplianceDocket No. RCRA 7003-09-99-0005

Dear Alan and John:

Pursuant to Section VI. Work To Be Performed (B. 1) of the above-referencedAdministrative Order ("AO"), Respondents are required within 30 days to submit a LandfillAssessment Work Plan ("Work Plan"). In response to this requirement and within the requireddeadline we received your submittal on June 7,1999. On August 2, 1999, we provided you withdetailed comments and on November 2,1999, we received your final response to our comments.On December 1,1999, we provided partial approval of the Work Plan.

Pursuant to Section VHI. Approvals/Disapprovals after review of any deliverable, plan,report, or other item which is required to be submitted for review and approval pursuant to thisOrder, EPA may: (a) approve the submission; (b) approve the submission with modifications;(c) disapprove the submission and direct Respondents to re-submit the document afterincorporating EPA's comments; or (d) disapprove the submission.

EPA has reviewed the remaining portions of the Landfill Assessment Work Plansubmission and hereby grants final approval subject to EPA modifications (detailed in Enclosure1) to the Sections described below. Respondents shall incorporate EPA modifications toapproved Sections of the Work Plan and accordingly modify corresponding SAP elements.Within seven days of receipt of this letter Respondents shall proceed to take actions required inthese approved Sections of the Work Plan.

APPROVED WITH EPA MODIFICATIONSWith this letter, the following Sections are approved with EPA modifications as detailed inEnclosure 1:

Specific Work Plan Tasks§3.4 - including matrix§3.4.3.3, §3.4.3.5 - §3.4.3.8 Evaluation of Existing Final Cover§3.4.3.5 Waste Sampling and Characterization§3.4.4.5 - §3.4.4.7 Assessment of Landfill Gas Levels and Constituents§3.4.5, §3.4.5.4 - §3.4.5.9, §3.4.8 Geologic and Hydrogeologic Assessment

Drawing 2, 3,4 ModificationsAppendix B, Respondents shall incorporate EPA modifications to approved Sections of the WorkPlan and accordingly modify corresponding SAP elements.Appendix C

If you have any questions, do not hesitate to call Susanna Trujillo at (415) 744-2099.Technical questions can be directed to Steve Wall at (415) 744-2123 and legal questions can bedirected to Allyn Stem at (415) 744-1372.

Sincerely,

Heidi Hall, ChiefSolid Waste ProgramWaste Management Division

Enclosure

cc: Dave Emme, NDEPMike Moran, BLM

Enclosure 1EPA Requirements; Approvals By Section, Approvals With Modifications By Section

KEY TO COMMENTS:

Regular text is text as stated in Republic's August 1999 Work Plan submittalRegular text with strikeouts is Republic's proposed deletions to the August 1999 Work

Plan submittalRed text is Republic's November 1 proposed changesBlue text with strikeouts is EPA deletions to Republic's November 1 proposed changesBlue text is EPA Requirements; Approval, Approval with Modifications

GENERAL

EPA has reviewed the remaining portions of the Landfill Assessment Work Plan submission andhereby grants final approval subject to EPA modifications. Respondents shall incorporate EPAmodifications to approved Sections of the Work Plan and accordingly modify correspondingSAP elements.

Drawings:

Drawings 2, 3, and 4, Top Deck and Sidewalls:The area shown as "Top Deck Area" on drawings 2, 3, and 4 is not to scale. EPA hasspecified certain assessment activities be performed on the Top Deck Area and sidewalkof the Top Deck Area. Therefore, it is important that the Top Deck Area be accuratelydepicted and correspond to grid system shown on drawings.

Modify Drawings 2, 3, and 4 so to show Top Deck Area in scale and corresponding togrid system. Also, show the extent of the Top Deck sidewalk on Drawings 2, 3, and 4.

Drawings 2, 3, and 4, Lagoon/Pit Locations:Modify Drawings 2, 3, and 4 to show the location and approximate size of the fourLagoon areas as specified in Work Plan Section 3.4.3.4.2 and as approved and modifiedbelow.

Drawing 4:Modify Drawing 4 to show shallow boring locations, test pit locations, and samplinglocations as specified in Work Plan Section 3.4.3.3 and as approved and modified below.

Hydrogeologic Boring Locations Map/Drawing:Provide a 1" = 500' scale drawing of hydro geologic boring locations as specified in WorkPlan Section 3.4.5.4 and as approved and modified below.

APPENDIX C - Detailed Schedule of WorkModify Schedule of Work according to date of this approval letter.

SECTION BY SECTION APPROVAL OR APPROVAL WITH MODIFICATIONS BYSECTION

Approvals and modifications are inserted into the text of the December 22,1999 Work Plan asshown in following pages and provided in electronic version. USEPA requirements, approvals,and modifications are shown in blue.

34, LG-184, LG-223, and LG-224 ranged from 3,404 to 13,444 mg/L (TDS) in 1985 (Emcon,1986). One sample from well B at the Site contained 3,684 mg/L TDS.

Limited analyses for organic compounds have been obtained. Wells LG223 and LG224,about 2 miles south of the Site were sampled on September 18 and 22,1998, by ConverseConsultants West. One sample was obtained from a water tank used to store water from awell operated by Nevada Ready Mix. The well is located about 2 miles west of the Site. NoVolatile Organic Compounds (VOCs) were reported in any of the samples. The samplingprotocols used are described in previous reports.

CH2M Hill reports that a sample was collected from an existing spring along the SunriseMountain Fault. No VOCs were detected in the sample. Previous reports describe how thesample was obtained. This sample was obtained to test the idea that leachate from the Sitecould migrate along the fault and emerge at springs.

A leachate sample was collected from the Site on September 22,1998, during or after amajor storm event. This sample consisted of surface water that had come in contact withwaste and drained back into the erosion channel. No VOCs were detected in this sample.Previous reports describe sampling protocol used. Because of the lack of circumstancesconducive to VOC loss, no conclusions can be drawn about the results of VOC sampling.

3.4 D SPECIFIC WORK PLAN TASKS (APPROVED AS NOTED, 12/02/99)

The work performed under Task Items a through h, described in subsection 3.4.1 through3.4.8 below, will be used to produce a Landfill Assessment Report. Information generated bythese eight Tasks will be the basis for assessing what impact the Site may be having on thegroundwater and surface water, and for developing a Corrective Measures Plan.

The Work proposed in Task Items a through h, will be completed using various establishedscientific and field proven methods as specified in the Sampling and Analysis Plan (seeAppendix B). The Landfill Assessment Work Plan describes the data objectives for eachrespective Task; decision trees as to how and when each method will be used to obtain theobjectives; data collection frequency and general locations; and the use of the data andassessment methods for each Task. The Sampling and Analysis Plan describes eachmethod in detail that is proposed in the Landfill Assessment Work Plan.

The general approach to the Landfill Assessment Work Plan is to provide a systematicmethodology to assess the impacts to public health and the environment. The first step inthe proposed process is designed to characterize, identify, and analyze all areas where therecould be waste materials. Therefore, the proposed work includes a comprehensive historicaldata review; review of aerial photos and topographical maps; establishing a field grid systemfor survey and location control during the Work; comprehensive site reconnaissance;geologic mapping; and the performance of geophysical surveys with verification methodssuch as exploratory borings, confirmation borings, and test pitftrenches to provide calibrationand confirmation of geophysical surveys. These methods will be used to assess the SunriseMountain Landfill (720-acre parcel), the Eastern Perimeter Area, the Northeast Canyon, andthe Western Bum Pit Area as specified in the Landfill Assessment Work Plan. Data collectedduring these efforts will be used to assess the location and amount of waste in each area.

(The following paragraph is approved subject to USEPA modifications)1/28/2000

Republic DUMPCo proposes to remove all of the waste in the Western Bum Pit Area. Thefirst step will be to characterize the waste to develop a plan for disposal. During

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characterization and subsequent removal of waste landfill gas will be monitored andassessed.

Republic DUMPCo proposes to remove all of the waste in the Western Bum Pit Area.Thoreforo after the first stop has been completed, the Western Burn Pit Area will booxcavatod, characterized for disposal, and the materials will bo romovod and properlydisposed. During tho removal of tho Wostorn Burn Pit Aroa, landfill gas will bo assessed andtho waste will bo sampled and characterized. This is proposed to effectively eliminate allimpacts to public health and tho environment from this area.

There is minimal data available on the waste in the Northeast Canyon Area. As discussedabove in the first step processes, the Landfill Assessment Work Plan provides data collectionmethods that will enable characterization and identification of the Northeast Canyon Area.There are many critical path overlaps between the RCRA Administrative Order and theAdministrative Order under the Clean Water Act. If the data from either Administrative Orderreveals that waste needs to be removed from any area, Republic DUMPCo will remove it.During any removal of waste from the Northeast Canyon Area, landfill gas will be assessedand the waste will be sampled and characterized. If it is determined that waste can remain insome areas of the Northeast Canyon Area, the further methods as discussed below can beused to obtain data to demonstrate that public health and the environment can be protected.

Further methods are proposed to assess the Sunrise Mountain Landfill (720-acre parcel) andthe Eastern Perimeter Area. These methods include surface emission monitoring; shallowborings to assess existing final cover, landfill gas, and obtain waste samples; sampling andanalysis of waste and final cover soils; installation of gas sampling probes; and methanemonitoring in structures. These methods establish a comprehensive system for collection ofdata to assess the existing final cover, slope stability, and assess the applicability of analternative final cover system. It is the intent of Republic DUMPCo to prepare an equivalencydemonstration for an alternative final cover system that is protective of the public health andthe environment. This equivalency demonstration will include design, construction andmonitoring of on-site lysimeter facilities to provide field verification of proposed alternativecover system.

(The following paragraphs are approved subject to USEPA modifications)1/28/2000

There is conflicting data regarding the hydrogoological and geological conditions under thoSite, and It has been identified as a major data gap in tho Landfill Assessment Work Plan. Inordorto develop the Work Plan, certain assumptions havo boon made. Ono assumption isthat tho upper most aquifer is bounded by tho Muddy Crook Formation; and that the MuddyCrook Formation is the regional aquitard at tho Sito. Further, the Muddy Crook Formation,and tho upper most aquifer, pinch out somowhorc under tho Site. Republic DUMPCo isproposing to move forward with this assumption until facts roveal otherwise. RepublicDUMPCo is committed to comploting a comprehensive Landfill Assessment Report, but doesnot want to create or cause any unintended impacts to human health or tho onvironmont bytrying to obtain data without understanding the current conditions (e.g., blindly drilling througha perched zone or aquitard). Therefore, tho initial stops proposed arc fundamental andrudimentary data gathering stops necessary before a thorough characterization of tho Sitocan be complotod. These stops consist of performing the first stops as discussed above forall areas; performing exploratory borings to locate and assess tho oxtont of possible perchedor saturated zones; complete groundwator sampling wells in perched zones and thosaturated zono above tho Muddy Greek Formation; obtain verification data on lithology abovetho Muddy Crook Formation; perform initial sampling of groundwator and perched zonoo toaooosG water quality; and perform aquifer testing of tho saturated zono above tho Muddy

Crook Formation. This data will bo used to assess possible groundwator or perched zonoimpacts, assess tho validity of tho Work Plan assumptions, and to assess further data needsto develop a comprehensive groundwator monitoring program.

The hydrogeological and geological conditions under the Site have been identified as a majordata gap. In particular, conclusive data are lacking concerning the location of the uppermostaquifer. Therefore, an investigation to determine the three-dimensional extent and nature ofthe regional aquifer and associated perched zones will be conducted prior to defining thepoint of compliance and designing monitoring strategies. The assumption that the uppermostaquifer is bounded by the Muddy Creek Formation and that it is the regional aquifer at theSite will not be used as a basis for determining the depth of the exploratory boreholes. Theinvestigation will consist of locating and assessing the vertical and lateral extent of allpotential perched and saturated zones by the drilling of exploratory boreholes, obtainingverification of lithology by continuously coring; assessing of water quality by completion ofgroundwater monitoring wells in perched and saturated zones; and obtaining aquiferproperties by performing aquifer tests.

The Landfill Assessment Work Plan provides methods to identify areas of concern for landfillgas, landfill gas characterization, and landfill gas chemical composition. This data will beused for landfill gas emission modeling and projections. Republic DUMPCo intends todevelop and submit a landfill gas control and management plan for USEPA approval.

To assist the reviewer in understanding the Landfill Assessment Work Plan, a matrix isprovided below identifying proposed methods, areas for use of the proposed methods, anddata objectives for assessment. The results of these efforts will be presented in a LandfillAssessment Report.

3.4.1 D Task Item a - Identify The Location and Acreage of Disturbance or WasteDisposal (USEPA APPROVED 12/02/99)

The primary technical objective of this task is to identify and then to confirm the presence andlimits of waste in the Sunrise Mountain Landfill (720-acre parcel), the Northeast Canyon, theEastern Perimeter Area, and the Western Burn Pit Area. This objective will be met byperforming the following seven subtasks:

1. Search and Review Existing Information2. Comparison of Aerial Photographs and Topographic Mapping3. Establish Field Grid System for Survey Control4. Detailed Site Reconnaissance5. Perform Geophysical Survey6. Perform Field Work for Quality Assurance on Geophysical Survey7. Compile and Assess Data

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LANDFILL ASSESSMENT WORK PLANSUNRISE MOUNTAIN LANDFILL

MethodHistorical Data ReviewAerial Photos and Topo Maps

Surface Emission Monitoring

Reid Grid System (GPS)

Site Reconnaissance

Geologic Mapping

Geophysical Survey (CSAMT)

(Maximum Depth 650 meters)

Exploratory Boreholes

Well Completion and GroundwaterSampling

Aquifer Testing

Geophysical Survey (IP)(Maximum Depth 60 meters)

Confirmation Borings

AreaAll Areas

All Areas

All Areas

All Areas

All Areas

All Areas

All Areas

Loaocd Aroa

All Areas

Wootorn Burn Pito

All Areas

Wcotom Burn Pito

Northeast CanyonEastern Perimeter AreaPossibly used in WesternBum Pits

Eastern Perimeter AreaNortheast Canyon

ObjectiveHistorical identification of site featuresEstablish understanding of known waste volume, type and limitsProvide information on the location of possible waste disposal unitsProvide information on surface geologic conditions, features, and outcrop patterns

Obtain surface emissions dataRecord and identify ventingLocate and record cracks or vents in coverObtain Health and Safety informationEvaluate cover abnormalities and suitability

Survey controlEstablish field location markersUsed as ground reference points during field activitiesAssist GPS

Reid identification of site featuresWill be conducted concurrently with surface emission monitoring

Establish basis for geologic and hydrogeologic characterizationLocate bedrock and alluvial unit contacts and determine strike and dip of unitsLocate faults and determine strike and dip of fault planes

Assist in determining vertical limits of wasteObtain data on subsurface fault orientations and geologic units such as depth to bedrockand lateral continuity of geologic unitsObtain data on hydrogeologic characteristics such as depth to groundwaterConfirm data obtained from literature research and reviewCorrelate geologic units and hydrogeologic conditions between exploratory boringsIdentify possible leachate and landfill gas migration pathwaysAssist in developing comprehensive groundwater monitoring program

Confirm CSAMT dataGeologic characterization and determination of depth to perched and regional groundwaterzones

Information obtained will be used to assist in developing appropriate groundwater monitoringprogram

Used in conjunction with geologic map to produce subsurface hydrogeologic cross sectionsIdentify possible leachate and landfill gas migration pathwaysObtain groundwater samples

Assess groundwater qualityAssess possible groundwater impacts

Geologic and hydrogeologic characterizationAssess hydraulic properties that control groundwater flow

Confirm history and literature dataLocate depth and lateral extent of refuse (Northeast Canyon and Eastern Perimeter area)Locate and assist in confirming geological features (Northeast Canyon and EasternPerimeter Area)

Establish confidence level of IP/Resistivity dataConfirm waste depth limits

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LANDFILL ASSESSMENT WORK PLANSUNRISE MOUNTAIN LANDFILL

MethodGeophysical Survey (EM)(Maximum Depth 10 meters)

Test Pits & Trenches

Shallow Borings

Final Cover Soil Samples

Waste Sampling

Gas Sampling Probes

Methane Monitoring in Structures

Relocation & Removal

AreaLeased AreaWestern Bum Pits

Leased Area

Northeast Canyon

Leased AreaEastern Perimeter AreaNortheast Canyon

Leased AreaEastern Perimeter Area

Leased AreaEastern Perimeter AreaNortheast Canyon

Western Bum Pits andNortheast Canyon Lagoons

Leased AreaEastern Perimeter Area

All Areas

Northoaot CanyonWootom Burn Pito

NOTD — Shallow Borings moana not currently approved

ObjectiveLocate waste and define waste boundariesConfirm that areas not thought to contain waste, do not contain waste.Provide map of all waste unitsLocate possible other wastes in Western Burn Pita

Establish confidence level of EM dataConfirm waste limit boundariesLandfill gas assessmentCover material thickness evaluationWaste observationsWill be completed during waste relocation efforts, as required to characterize remainingwaste

Evaluate existing final cover for thickness and soil propertiesWaste characterizationLandfill gas characterizationDetermine if landfill gas probes are needed in Northeast Canyon, animal, construction demoarea, or septic disposal area.Determine what and where problems exist with coverProvide information needed to understand what fixes or work needs to be done on coverObtain information for erosion and modeling equations (RCRA & CWA)Cover material suitability

Field analysis (visual observation and logging)Laboratory analysisChemical compositionErosion, slope stability and cover characteristicsProvide information to run RUSLE, WEPP, and Un-Sat-H models

Waste characterizationWaste identification and confirmationVisual inspections and documentation for confirmationLaboratory analytical resultsNortheast Canyon during relocation effortsWestern Burn Pits, characterization samples for disposal

Landfill gas characterizationLandfill gas chemical compositionAssist in developing landfill gas control and recovery systemData for landfill gas emission modeling and projections

Assess landfill gas migration

Remove waste from study areasDiopooG of waote properlyMitigate otormwalor impacto

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3.4.3.3 D FIELD ASSESSMENT OF EXISTING FINAL COVER SOILS (USEPA APPROVEDAS MODIFIED 1/28/2000)

The existing final cover soils will be assessed by using the test pit/trenching and shallowboring methods as discussed in the SAP, Sections 1.5 and 1.6.2. The test pits will beexcavated prior to drilling the shallow borings. Fourteen test pits will be completed at thelocations shown on Drawing 4. In addition, a shallow boring will be performed once per every200-foot field survey grid in the Sunrise Mountain Landfill (720-acre parcel) and once every100-foot field survey grid in the Eastern Perimeter Area in the identified areas of wastedisposal. The shallow boring locations are illustrated on Drawing 4.

The test pit method will be used for quality control purposes. The pits will provide data on theinterface between the cover and the waste on a larger scale than the shallow borings arecapable of providing. Specifically, observations will be made of the variation in depth to thecover/waste interface, the degree of trash embedded in the cover material, the constructionpractices used to place the cover, and the identification of any oversized material (i.e., largestones). The locations of the test pits will be distributed such that four pits will be excavatedon the upper deck, four on the sidewalls of the upper deck, four on the lower southern flatsarea, and two in the eastern perimeter area. Two of the locations on the top deck willcoincide with areas where cracking has been observed in the cover, as defined by the BLM'sGIS coordinate data.

The shallow boring method will use a Geoprobe sampling device will bo usod to obtain a coresample from the surface to the interface with waste materials, approximately 6 inches into thewaste. The sampling device will be lined with a clear plastic tube to collect the sample. Thetube will be removed from the sampling device, the ends capped, and the plastic tube will belabeled with survey grid coordinates. The plastic tubes will be stored and archived for latercomparison to laboratory results. The depth of soil cover will be measured from the length ofsoil in the tube. Additionally, the shallow boring will be measured with a tape to ascertain thecover soil thickness. Visual observation of the depth of soil, percent recovery of the core,type of soil, color variation, moisture content, and type of waste material encountered will berecorded on the field log. If the percent recovery is poor, a second sample will be obtained.

At ten percent of the shallow boring locations, additional soil samples will be taken with a splitspoon or equivalent sampling device for geotechnical testing as described in the SAP,Section 1.6.2.4.

On the Top Deck and Western Side of Lower Southern Flats area, where a "prescriptivecover" was reportedly used, the top 6 inches will be compared visually with the remainingsample. It has been reported that the impermeable barrier layer used (18 inches of 10"5 soil)is visually different than the erosion layer (top 6 inches). This will be verified in these twoareas. Areas deficient in erosion layer material (less than 6 inches) will be estimated andrecorded in the field log. The top 6 inches of each sample will be separated and all tho 6-inchsamples from within tho areas defined on Drawing 2 will bo composited into a. 5 gallon plasticcontainer. This soil saved in a plastic bag. Portions of these samples from similar areas (theupper deck, the upper deck slopes, the lower southern flats, and the eastern perimeter area)will be composited and analyzed for particle size distribution. The individual sample bags willbe marked with appropriate location and sample identifiers and saved. The top 6-inch samplewill be representative of the 'Vegetative or erosion layer" of the final cover system. Thesesamples will be run for particle size distribution, first on the as-is composited sample. Thenthe sample will be remixed, acid treated, and rerun for particle size distribution to obtain dataon the effect of calcium carbonate and gypsum. The "vegetative or erosion layer" sample

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bags will be saved for further analysis, if required, to evaluate the soil for its intended use inthe final cover system. This data will be used to model tho final cover soils for erosionpotential as described below. The remaining depth of sample (6 inches to bottom of finalcover) will be used to obtain geotechnical information as follows:

1. Soil classification. One sample will be collected for laboratory testing from fef eachshallow boring location where additional soil samples are specified, as shown in drawingno. 4. The laboratory testing will consist of the following methods: classification of soils forengineering purposes (ASTM D2487), particle size distributions (ASTM D 422-63), andAtterberg Limits (ASTM D4318). An acid treatment of the soils as described above will beevaluated on 10 percent of these samples).

2. Compaction Testing; Standard Proctors One sample will be collected for laboratorytesting from 50 percent of the sample locations specified for Ifem-particle size distributionanalysis, as shown in drawing no. 4. The laboratory testing will consist of the followingmethod: Standard/modified Proctor (ASTM D698/ D1557).

3. Hydraulic Properties Testing. In-situ Pormoabilitios (Sholby tube collection); One samplewill be collected for laboratory testing from 50 percent of the sample locations specified forthe {few-compaction tests, as shown in drawing no. 4. The laboratory testing will consistof the following methods: specific gravity (ASTM D854), minimum/maximum density(ASTM D4253), saturated hydraulic conductivity (granular/porous materials) (ASTMD2434/D5084), soil moisture retention curves (Klute, 1986).

4. Strength Testing. One sample will be collected for laboratory testing from 50% of thesample locations specified for the compaction tests, as shown in drawing no. 4. Thelaboratory testing will consist of the following method: consolidated -undrained triaxialcompression (ASTM D5084).

>For quality assurance on tho in-situ permeability hydraulic properties testing, sand cono testswill bo performed to measure in-situ compaction at 25 percent of tho locations whore a Sholbytube is collected. Tho sample representing this location will be rocompactod in tho laboratoryto the density obtained in the field and a permeability analysis will bo performed on therocompactod soil sample. This will provide data to assess tho reliability of tho in situpermeabilities. Methods for running each of the above specified geotechnical tosts arespocifiod in the SAP.

Waste samples will also be obtained from the shallow borings as specified below. Some ofthe shallow borings will have a landfill gas sampling probe installed as described in subtask3.4.4.5. Information collected during performance of the shallow boring will be logged suchas cover thickness, visual observation of cover thickness and waste, sampling performed,survey coordinates, landfill gas monitoring data, etc.

3.4.3.4 D WASTE SAMPLING AND CHARACTERIZATION(USEPA APPROVED 1/28/2000)

Waste sampling and characterization work will consist of the following work:

3.4.3.4.1 D Waste Sampling of the Sunrise Mountain Landfill (720-acre parcel) and theEastern Perimeter Area(USEPA APPROVED 1/28/2000)

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Waste samples will be collected with the Geoprobe equipment as described in the SAP,Section 1.6.2.3. After the interface between the final cover soils and waste has been foundusing the Geoprobe method (the shallow boring should be about 6 inches into the waste), asplit spoon sampler equipped with brass sleeves will be driven into the waste mass. Thebrass sleeve will be removed from the split spoon sampler, capped, sealed, labeled, andplaced in a cooler as specified in the SAP. The waste samples collected will be characterizedby analyzing the samples for all the parameters in the SAP, Section 2.0 (all the TCLPconstituents).

The waste samples will be collected at the same locations that are designated to have alandfill gas sampling probe installed as illustrated on Drawing 4 (see subtask 3.4.4.5). Anadditional two shallow borings within each area specified below will be taken as illustrated onDrawing 4 solely for the purpose of obtaining a waste sample (no landfill gas probe installed).Therefore, there will be a total of seven waste samples collected from the following areas:

• A group of seven in the Eastern Perimeter Area• A group of seven in the eastern side of the Lower Southern Flats Area• A group of seven in the western side of the Lower Southern Flats Area• A group of seven in the Top Deck Area• A group of seven in the side-slope are of the Top Deck

These areas are shown on Drawings 2 and 4.

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3.4.3.4.2 Waste Sampling of the Western Burn Pit Lagoon Areas(USEPA APPROVED AS MODIFIED 1/28/2000)

Four lagoons which BLM identified in their CCJM Reconnaissance Investigation Reportof March 18,1998 will be preliminarily characterized to determine the vertical extent ofcontamination. Lagoons were found to contain concentrations of Volatile OrganicCompounds (VOC's). Tthe "Black Lagoons" contained black asphaltic-like material.The two "Black Lagoons" are located adjacent to the Northwest lease boundary, in thearea referred to as the 'Western Burn Pit Area". The other two lagoons are located inthe Northeast canyon area, 1) the NE Canyon Lagoon, 22770 N, 16660 E on sitecoordinate system, 2) the NE Trespass Sand and Gravel Lagoon, 18377 N, 14858 E onthe site coordinate system.

Within each lagoon, two boreholes will be drilled and continuously sampled through thealluvial sediment down to the Tertiary contact. The core from each 2-foot split spoonsampling interval will be logged by the supervising geologist and screened on-site forVOC contamination. The results of the VOC field screening will be recorded in a logbook along with a description of the sediment lithologies, thicknesses, percentage ofrecovered core, and any observed staining.

A sample will be selected from each 2-foot split spoon sampling interval for laboratorytesting. All samples will be selected from the finer-grained sediment intervals, and ifapplicable, from intervals where VOCs have been detected and/or staining is present.All selected samples will be laboratory tested for the following analytical parameters:

a. Target Analyte List for metals, EPA method 6010.b. Target Compound List for volatile organic compounds, EPA method 8260, and

semivolatile organic compounds using EPA method 8270;c. Cyanide using EPA method 901OA;d. Herbicides using EPA method 8150; ande. Pesticides and PCBs using EPA method 8081.

Tho first item complotod in waste sSampling of the Western Burn Pits is collection ofcomposite samples of wasto contained in tho Burn Pits using tho method described intho SAP, Section 1.6.2.3. Tho brass slcovo, specified sampling container, roprosontingtho samplo from tho Bum Pit will bo capped, scaled, labeled, and placed in a coolor asspecified in the SAP will bo performed during tho removal of materials and impactedsoils from tho Western Bum Pit Aroa. As tho materials and impacted soils arcoxcavatod from tho area, it will bo placed on plastic shooting in 100-yard stockpiles.Each stockpile will bo sampled.

Tho wasto 100-yard stockpile samples collected will bo characterized by analyzing thosamples for all tho TCLP characteristics and for total petroleum hydrocarbons by USEPAmethod 8015 (modified). This will be done to assess tho presence of hazardousconstituents properly characterize tho waste for disposal. This Tho data collected fromtho stockpile samples will bo used to determine the analytical parameters used fortesting of samples obtained from additional shallow borings obtained in tho WesternBum Pit Aroa to assess wasto presence outside the visible limits tho final cleanverification samples. Six clean verification samples will be obtained and analyzed for thoidentified analytical parameters. Two from the bottom of the excavation, and one from

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tho center of each of tho four walls of tho excavation. During tho excavation process,the excavation area will bo monitored for hydrogen sulfido gas, as well as landfill gasmethane.

3.4.3.4.3 D Waste Sampling and Characterization Northeast Canyon(USEPA APPROVED 1/28/2000)

As discussed in Section 3.4.1.5.2 of the Work Plan, the IP method will be utilized toconfirm and identify the location and volume of waste in the Northeast Canyon, andCSAMT will be used to further confirm and identify deep geologic features. Only afterthese tasks are completed, and the data evaluated, can final location and amount ofwaste in the area be determined. Borings from the Eastern Perimeter Area will beutilized for IP QA/QC confirmation in the Northeast canyon.

Waste sampling techniques and procedures depends on whether the waste will berelocated of not. The decision to relocate waste depends upon a number of factors.The intent is to remove all waste in Instant Study Areas (ISA) by relocation; waste inareas designed for stormwater control features will also need to be relocated; and it mayprove beneficial to consolidate and relocate areas containing small amounts of waste.Therefore, until all this information is obtained, the specifics can not yet be determined.

Once the above data is obtained, a waste relocation and assessment plan will besubmitted to USEPA for approval. The general elements of the Plan are as follows:

1. Provide proposed relocation area and cover material specifications.2. Provide proposed relocation procedures, sampling, and characterization ofwaste.3. Provide proposed specifications and details for all waste which will not be

relocated.

3.4.3.5 D ASSESSMENT OF SLOPE STABILITY (USEPA APPROVED 1/28/2000)

The slope stability of the existing final cover will be evaluated using the infinite slopemethod. This technique assumes a critical planar surface through the cover. Thetechnique is generally regarded as a conservative approach, since most slope failuresurfaces are not planar, but instead are semi-circular and three-dimensional. The valueof the two most critical soil parameters used in the analysis, shear strength and unitweight, will be based on laboratory tests on samples collected in subtask 3.4.3.3.

3.4.3.6 D ASSESSMENT OF EROSION POTENTIAL (USEPA APPROVED 1/28/2000)II.

The average annual soil loss on the cover (due to surface run-off) will be determined.One method of analysis will be the Universal Soil Loss Equation, which is a Soil

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Conservation Service method. This method is specified for use in the USEPA, SolidWaste Disposal Facility Criteria: Technical Manual. The soil parameter values used inthe equation will be based on actual laboratory test results on samples collected insubtask 3.4.3.3.

Additionally, the impact to the cover caused by sheet and rill erosion during individuallarge storm events will be evaluated using the 'Water Erosion Prediction Project (WEPP)model. The soil parameter values used in the model will be based on actual laboratorytest results on samples collected in subtask 3.4.3.3.

The models referenced above will be used to assess the existing landfill cover with nosurface water controls and then the recent added surface water controls will be modeledto assess adequacy.

3.4.3.7 D ASSESSMENT OF EXISTING FINAL COVER SUITABILITY (USEPAAPPROVED 1/28/2000)

The amount of precipitation that passes through the existing final cover soils will bedetermined by computer modeling using data obtained from the field investigation workand laboratory analysis. The computer model that will be used is the UNSAT-H model.This model uses a finite difference technique to solve unsaturated flow equations anddetermine an annual flow rate through the bottom of the cover. The modeling results willbe used to determine the adequacy of the existing cover in terms of minimizing leachategeneration. Cover thickness data and results of laboratory data collected in subtask3.4.3.3 will be used as input data in the model.

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as the base map for the Drawing. The Drawing completed during this subtask will also becompared to Drawings completed in subtasks 3.4.1.7,3.4.2.4, and 3.4.3.7 to collectivelyevaluate all the data presented.

3.4.4.3 D Conduct Methane Monitoring in Structures (USEPA APPROVED 12/02/99)

Two structures have been identified for in-structure methane monitoring. One is on the landfill(the Clark County Air Monitoring Station) and one is just off-site (the Doppler Tower). Themonitoring method for monitoring the structures is specified in the SAP, Section 4.4.Compliance or non-compliance with USEPA's 1.25- percent methane standard will beascertained. Permission to access these structures for monitoring will be obtained prior tomonitoring.

3.4.4.4 D Gas Monitoring for Field Work Performed in Work Task Items a, c, and e(USEPA APPROVED 12/02/99)

Gas monitoring for methane and hydrogen sulfide concentrations will be performed during theperformance of intrusive field work as specified in Work Task Items a, c, and e. The methodsused are presented in the SAP, Section 4.5. Field measured, concentrations nearing 5-percent for methane and approaching 15-ppm for hydrogen sulfide will require actions asspecified in the HASP (see Appendix D).

The test pit/trenches as specified in subtask 3.4.1.6.1, the confirmation borings as specified insubtask 3.4.1.6.2, and the shallow borings as specified in subtask 3.4.3.3 will be monitoredfor methane and hydrogen sulfide concentrations using methods described in the SAP,Section 4.5.3. Measurement of methane and hydrogen sulfide concentrations will beobtained. The monitoring data from each test pit/trench, confirmation boring or shallow boringwill be recorded on the respective field log. The data will be evaluated as part of subtask3.4.4.7.

The hydrogeological borings and wells in subtask 3.4.5.5 will be monitored as described inthe SAP, Section 4.5.1. The hydrological borings and wells are located near propertyboundaries. Therefore, compliance or non-compliance with USEPA's 5-percent methanestandard will be ascertained. The routine monitoring procedures as described in the SAP,Section 4.5.1 will be used until a 5-percent reading is approached. At this point, the work willbe stopped momentarily to allow the procedures in the SAP, Section 4.5.2 to be implemented.The methods in the SAP, Section 4.5.2 will allow an actual gas sample from the hydrologicalboring or well to be completed in the field. Measurement of methane and hydrogen sulfideconcentrations will be obtained. The monitoring data from each hydrogeologic boring or wellwill be recorded on the respective boring log. The data will be evaluated as part of subtask3.4.4.7.

3.4.4.5 D Landfill Gas Characterization (USEPA APPROVED 1/28/2000)

The purpose of this subtask is to characterize the landfill gas. This characterization willconsist of obtaining landfill gas samples from landfill gas sampling probes installed inaccordance with methods described in the SAP, Section 4.6.1. The landfill gas probes

will be installed concurrently with the work being performed for the shallow borings withsubtask 3.4.3.3.

Landfill gas sampling probes will be located as illustrated on Drawing 4. The probes will beinstalled in groups of five spaced within an area as follows:

A group of five in the Eastern Perimeter AreaA group of five in the eastern side of the Lower Southern Flats AreaA group of five in the western side of the Lower Southern Flats AreaA group of five in the Top Deck AreaA group of five in the side-slope area of the Top Deck

These areas are shown on Drawings 2 and 4. These areas were chosen based on reportsthat the areas were used to dispose of municipal solid waste and should produce the mostrepresentative landfill gas characterization. It is reported that the Eastern Perimeter Area andthe eastern side of the Lower Southern Flats did not have waste placed after early 1991. It isreported that the western side of the Lower Southern Flats and the Top Deck Area receivedwaste post 1991, but did not receive waste after October 8,1993.

Additional areas may be added for installation of the landfill gas sampling probes. Gasmonitoring results performed under subtask 3.4.4.4 of the shallow borings will be used as thedecision criteria for adding additional areas. If more than 25-percent of the shallow borings inan area exceed the 1.25-percent level, a group of five landfill gas probes will be installed inthat area. The other areas (shown on Drawing 2) that would be considered are as follows:

Construction Debris AreaSeptic Lagoon AreaWestern Bum PitsDead Animal AreaAsbestos Area

Gas samples will be collected using the procedures in the SAP, Section 4.6.1.

3.4.4.6 D Prepare Landfill Gas Generation Projections (USEPA APPROVED 1/28/2000)

The USEPA Landfill Air Emissions Estimation Model will be employed, using dry sitemodeling coefficients prescribed in USEPA's "Compilation of Air Pollutant Emission Factors"(AP-42), to project current and future quantities of landfill gas from the waste within theboundary identified in subtask 3.4.1.7. The overall boundary area will be divided into sub-areas based on waste characteristics identified in subtask 3.4.2.4, to evaluate the individualcontribution each makes to total landfill gas generation. The intent of this subtask is toquantify total landfill gas generation at the Sunrise Mountain Landfill (720-acre parcel), theEastern Perimeter Area,, the Northeast Canyon Area, and the Western Bum Pit Area and toassess the relative importance of various areas to total landfill gas generation.

3.4.4.7 D Compile and Assess Date(USEPA APPROVED 1/28/2000)

Information obtained through performance of subtasks 3.4.4.1 through 3.4.4.5 will beevaluated to assess landfill gas levels and constituents such as hydrogen sulfide and Non-Methane Organic Compounds (NMOCs) in the Sunrise Mountain Landfill (720-acre parcel),the Eastern Perimeter Area, the Northeast Canyon Area, and the Western Bum Pit Area.Data on landfill gas monitoring during the relocation of waste in the Northeast Canyon willalso be included. The Drawing produced in subtask 3.4.4.2 and the data collected in

subtasks 3.4.4.3 through 3.4.4.6 will be compiled and presented in the Landfill AssessmentReport.

Also the potential for off-site migration will be assessed through consideration of the limits ofthe refuse footprint with respect to property boundaries; refuse depths; site topography; fieldboring activities; the body of data collected under all landfill gas assessment work; sitehydrogeology; proximity of off-site structures; and land uses surrounding the landfill. All of theabove factors will be considered in developing a recommendation on the number, depth andspacing of subsurface monitoring probes. This evaluation will be presented in the LandfillAssessment Report.

SAP, Section 4.6 - PROCEDURES FOR SUBSURFACE METHANE MONITORING(USEPA APPROVED 1/28/2000)

3.4.5 D Work Task Item e - Assessment of Impacts to Groundwater. and Run-off Impacts toGroundwater and Surface Water and Work Task Item h - Thorough Characterization of theHvdrogeological Setting (APPROVED AS NOTED. 1/28/2000)

It is not possible to assess impacts to groundwater, or run-off impacts to groundwater, without firstcharacterizing the geological and hydrogeological setting of the Site. This has been identified as amajor data gap. The geologic setting, hydrogeologic setting, groundwater occurrence and quality, andpossible impacts to groundwater and surface water are all interconnected. Therefore, "e" and "h" havebeen combined into one section in the Work Plan. However, though the Landfill Assessment WorkPlan combines "e" and "h" into one section, the Landfill Assessment Report will address each itemseparately.

To complete Work Task Items e and h, educated assumptions have been made regarding the geologicconditions that may be encountered during this assessment. The landfill is known to be on the side ofFrenchman Mountain with the Las Vegas Wash downhill to the southwest. Portions of the landfill thatlie within the canyon are underlain by pre-Tertiary bedrock at shallow depths. Other portions of thelandfill southwest of the canyon may be underlain by hundreds of feet of alluvial deposits andsedimentary bedrock that includes the Tertiary Muddy Creek Formation as it pinches out somewhereunder the Site. The effect of bedrock and alluvial sediments on groundwater occurrence and flow, aswell as leachate and/or landfill gas migration beneath the landfill is unknown. The subsurfacepercolation of leachate or migration of landfill gas could take a number of paths. Percolation ofleachate from the landfill could encounter low-permeability bedrock and flow toward the Las VegasWash or encounter fractured/faulted bedrock and migrate vertically to the uppermost aquifer within thebedrock, whoro it would contact the Muddy Creek Formation. Flows may also percolate downwardthrough the surficial alluvial fan alluvial materials to create perched zones caused by hardpans, or otherlow permeability layers, above the Muddy Creek Formation.

Subsurface percolation could also find pathways through fractures or faults. There is currently nodirect information on the depth or occurrence of groundwater beneath the landfill. The fundamentalassumption used to develop the geologic and hydrogeologic characterization programs in the WorkPlan is that the regional groundwater flow direction beneath the Site is to the southwest, downhilltoward the Las Vegas Wash.

(The following paragraph is approved subject to USEPA modifications^728/2000

The seven proposed exploratory wells arc? designed to characterize the geologic and hydrogeologicconditions from the ground surface to the pro Tertiary bedrock or the Tertiary Muddy CrockFormation. Moro than one well may be completed in tho proposed areas depending upon thohydrogoologic conditions encountered. If a perched zono is encountered in the alluvial deposits, thoboring will bo stopped to prevent creating a pathway to deeper saturated zones. Borings completed tobedrock will bo usod to confirm the possible bodrock migration pathway hypothesis. Because thelandfill is over simple alluvial material, drive sampling and geophysical logging of boroholos isproposed only to confirm lithologic changes. Continuous coring has not boon proposed during this firststop, rudimentary data collection effort.

The ten proposed exploratory wells are designed to characterize the geologic and hydrogeologicconditions from the ground surface to within the confining unit defining the lower boundary of theuppermost aquifer. In accordance with 40 CFR 258.51, the investigation will include a "thoroughcharacterization of the saturated and unsaturated geologic units and fill materials overlying theuppermost aquifer, materials comprising the uppermost aquifer, and materials comprising the qonfiningunit defining the lower boundary of the uppermost aquifer, including thicknesses, stratigraphy,lithology, hydraulic conductivities, porosities, and effective porosities.

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More than one well will be installed in each of the proposed locations to avoid cross contaminationbetween perched zones and the uppermost aquifer. The exact number of wells per location will dependupon the hydrogeologic conditions encountered. Each time a perched zone of sufficient water yield (2to 3 gallons per hour) is encountered in the alluvial deposits, the boring will be stopped to preventcreating a pathway to deeper saturated zones, and then completed as a well. A new boring will then bedrilled, cased, and grouted to the base of the first encountered zone and subsequently drilled throughthe casing until the next deeper perched zone or bedrock contact is encountered. All borings will bestopped and completed as wells at the bedrock contact to test the possible bedrock migration pathwayhypothesis. Then, unless the bedrock contact is confirmed to be the uppermost aquifer, an additionalboring will be advanced to within the confining unit below the uppermost aquifer and completed as awell.

A conservative drilling and sampling method will be utilized during the initial characterization effortsbecause there is concern that drilling through the perched zones could cross contaminate the uppermostaquifer. The continuous coring method has been selected because it provides the best control andaccuracy in terms of depth determination and lithologic conditions. It will be used in the ten initialborings, and thereafter, until a detailed understanding of the site conditions has been objectivelydetermined. All drill core will be labeled, boxed, and stored for future reference.

A deep geophysical survey (CSAMT) is proposed as an additional characterization procedure. Thedata objectives of the deep geophysical survey are to: 1) identify the depth of perched and regionalgroundwater; 2) identify the depth and contact relationships of the pre-Tertiary bedrock, the TertiaryMuddy Creek Formation, the Quaternary alluvial deposits, and the landfill waste material; and 3)identify and locate faults that cut the different geologic units and assess which units are disrupted oroffset by the faults. This will enable Republic DUMPCo to determine if other subsurface leachatepaths exist. The deep geophysical survey method (CSAMT) can also detect any perched leachatewithin the survey area. Itshould-bejioted_fliatthe Muddy Creek Formation is considered bedrock for

program.

(The following paragraphs are deleted) USEPA modifications 1/28/2000

If a porched/saturatod zone is encountered in one of the proposed drilling areas prior to cncountoringpro Tertiary bodrock or the Tertiary Muddy Crook Formation, tho drill rig will be moved laterallyapproximately 100 foot away from tho landfill to advance a boring without creating a conduit throughthe perched zone aquitard. Republic DUMPCo has already obtained an access agreement with BLMfor the areas that may be needed for borings, but will allow BLM the chance to evaluate tho situationprior to additional borings.

The above methods and decision trees oro discussed at length in this Work Plan and SAP in order toaddress an identified data gap. These methods, tools, and procedures are proposed as the first stopfundemantal and rudimentary data gather effort to assess tho geologic and hydrogoologic conditionsunder and around tho Sito culminating in development of a groundwater monitoring program that isprotective of tho environment. Without having tho information from this initial assessment, creating aneffective groundwater monitoring program can not be successfully completed. Upon completion of theTasks in this Work Plan, it may bo determined that continuous coring of identified geologic features isnecessary to confirm and further characterize the geologic and hydrogeologic conditions. However,until this initial fundamental and rudimentary assessment of the Sito conditions has been completed,further investigative work above and beyond this proposed initial program can not bo identified.

3.4.5.1 General Overview and Objectives (APPROVED AS NOTED, 12/02/99)

The tasks described in this section will be implemented to obtain geologic, hydrogeologic, and water-quality information necessary to assess impacts to groundwater and the run-off impacts to groundwater

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and surface water at the Sunrise Mountain Landfill (720-acre parcel), the Eastern Perimeter Area, theWestern Burn Pit Area, and the Northeast Canyon. The physical conditions in which groundwaterimpacts may have occurred, that is, the geologic and the hydrogeologic conditions, must becharacterized and evaluated as part of the impact assessment. These geologic and hydrogeologicconditions control the distribution and movement of groundwater, and therefore, control the ultimateextent of the impact. The groundwater's chemical composition must also be characterized to determinewhether impacts have occurred, and if so, the nature of those impacts.

To obtain the geologic, hydrogeologic, and water-quality information objectives stated above, thefollowing tasks will be performed:

1. the site's geology will be mapped2. deep geophysical surveys will be conducted3. exploratory borings will be drilled and geophysically logged4. monitoring wells will be installed5. groundwater samples will be collected and analyzed6. aquifer hydraulic parameters will be measured

Engineering geologic mapping of the site will be conducted to document the geologic conditionsexposed at the surface. These conditions include such things as the distribution and characteristics ofsoil and bedrock materials, and the location, orientation, and the physical condition of faults andfractures. The information obtained from geologic mapping will form the basis for the hydrogeologicmodel and provide "ground truth" for surface geophysical surveys and interpolation of geologic andhydrogeologic conditions between boreholes.

Deep geophysical resistivity surveys will be conducted to evaluate, characterize and confirmsubsurface geologic and hydrogeologic conditions. The data objectives of the deep geophysical surveyare to:

1. Identify the depth of perched and regional groundwater;2. Identify the depth and location of hardpans;3. Identify the depth and location of perched leachate;4. Assess the depth and contact relationships of the pre-Tertiary bedrock (which is exposed along

Frenchman Mountain), the Tertiary Muddy Creek Formation (whichis exposed along the southeast mouth of the canyon), the Quaternary alluvial deposits (whichare exposed below the canyon), and the landfill waste material;

5. Identify and locate faults that cut the different geologic units and assess which units aredisrupted or offset by the faults.

6. Identify pools, or subsurface areas that contain leachate.

The geophysical survey, in parallel with the surface geologic mapping and drilling, should provide thebasis to construct a three-dimensional model of the physical conditions that affect and controlgroundwater flow.

Although there are numerous methods for measuring resistivity, the large depth of investigationrequired for the Site eliminates most near-field, galvanic methods. In these near-field methods, depthof investigation is determined by dipole size and dipole separation. Expanding dipole size andseparation includes a larger volume of earth in the measuring process, reducing significantly theresolution of the measurement. These methods, such as dipole-dipole, pole-dipole, and SchlumbergerVES, will not provide the resolution necessary for characterizing faults or fracture zones at largedepths.

Controlled source audio-frequency magnetotellurics (CSAMT) is a far-field method that shouldprovide the necessary resolution at large depths. Depth of investigation is determined by groundresistivity and the transmitted frequency, not by dipole sizes and separations. Lateral resolution isdetermined by dipole size, thus a CSAMT survey can be converted quickly from low resolution,reconnaissance mode to a high resolution, detailed survey by simply changing receiver dipole size.Depth of investigation is not influenced by this change.

A significant logistical advantage of CSAMT is the fact that with proper survey planning, thetransmitter dipole and equipment remains fixed throughout the survey, which increases data acquisitionspeed significantly. Other resistivity methods, such as VES or transient EM soundings, requireconstant repositioning of the source dipole or source loop, significantly increasing field time. As aresult of these and other advantages, CSAMT has become one of the most commonly used tools by themining and geothermal industries in areas where high resolution data are required at large depths.

(The following paragraphs are approved subject to USEPA modifications)1/28/2000

Seven Ten exploratory borehole locations will be drilled and sampled by the continuous coring methodair rotary methods and logged with borehole geophysical tools to obtain subsurface geologic andhydrogeologic data including stratigraphy and lithology of the vadose zone, the water-bearing zone(s),and aquitard(s), and depth and thickness of perched zones. The drilling and logging methods have beenselected to minimize impacts to the groundwater quality and maximize data acquisition until furtherdata is obtained. Specifically, the continuous coring method air rotary methods will be used because itthey maximizes the potential for identifying and stopping on a perched zone without penetrating theunderlying aquitard, and therefore, not creating a pathway for downward migration of contaminants.The physical information collected from the exploratory borings will provide "ground truth" forcorrelating borehole geophysical logging and deep geophysical resistivity survey results with sedimentand bedrock lithology and stratigraphy. The information obtained from drilling, sampling, andborehole geophysical logging will be incorporated into the 3-dimensional model to enhance and refinethe geologic and hydrogeologic characterization of the site.

Groundwater monitoring wells will be installed so that perched zones and the uppermost or regionalaquifer can be further characterized, identified, and understood. These wells will also allowgroundwater samples to be collected to characterize groundwater quality and determine whetherimpacts have occurred. They will also allow groundwater potentiometric elevations to be measured toconfirm the surface and borehole geophysical results and determine water-table gradients and flowdirections. Additionally, the wells will allow direct aquifer access so that aquifer hydraulic propertiescan be measured and groundwater flow velocities can be calculated.

Details of the scope of the field program are laid out in the following sections, and specific methodspecifications and requirements are in the SAP (see Appendix B). Procedures and specific informationregarding equipment and materials are also presented in Appendix B.

3.4.5.2 Engineering Geologic Map (USEPA APPROVED 12/02/99)

The following two subsections discuss the surficial geologic mapping program. Procedural details arepresented in the SAP in Appendix B. Mapping procedures include an office phase, followed by fieldgeologic reconnaissance, and detailed engineering geologic mapping. During the office phase,available literature and aerial photographs of the area will be obtained so that regional geologicconditions can be assessed and the location of contacts, faults, and photolineaments can be identified

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and placed on a base map for field confirmation. Geologic reconnaissance will be conducted to (1)determine if unusual geologic conditions are exposed, (2) delineate mappable geologic units, and (3)make correlations with information obtained from aerial photograph and literature review. Detailedgeologic mapping will be conducted to (1) collect and compile geologic unit descriptions, (2) measurefault, fracture, and bedding strike and dip orientations, (3) map geologic contacts, and (4) locate andrecord structure discontinuity and physical descriptive data at bedrock outcrops and on alluvialsurfaces. The geologic mapping, in combination with the surficial geophysical surveying, will providethe basis for the hydrogeologic characterization. Information obtained during the drilling phase willthen be added to enhance the characterization.

Based on our preliminary review of available data, at least one fault (the Frenchman Mountain Fault) isevident at the site. The nature and location of the fault(s) can affect the site groundwater conditionsand thus, the design of a groundwater monitoring program. Better definition of the location and natureof this and possible other faults is essential in designing an effective groundwater monitoring program.Because faults may act as significant barriers to groundwater flow, with groundwater elevationdifferences of more than several hundred feet across faults, or act as conduits for groundwater flow,locating and understanding the physical condition of the Frenchman Mountain and other faults will be afocus point of the mapping.

3.4.5.2.1 Prefield Services (USEPA APPROVED 12/02/99)

The following research activities will be performed before field mapping begins. This information willbe obtained so that existing information can be reviewed and the mapping can be conducted in thecontext of the regional geologic conditions. Specific areas will be identified to provide the bestopportunity to collect quality geologic information during the field mapping program.

1. Conduct a literature search and review of available geophysical and hydrogeologic literature andmaps pertinent to the site and pertinent to local or regional hydrogeology;

2. Conduct a literature search and review of available geologic literature and maps pertinent to the siteand pertinent to local or regional faulting;

3. Contact local, state, and federal agencies and obtain available water quality and water elevationdata and maps pertinent to the local or regional setting, and obtain information on water, oil andgas, or other wells within 6 miles of the site (including the "Diaz" well which may be located in theFrenchman Mountain fault zone);

4. Review available aerial photographs to identify map lineaments and geologic contacts; and5. Review historical water quality reports, tabulate water quality results, and chart or graph data.

3.4.5.2.2 Site Engineering Geologic Mapping (USEPA APPROVED 12/02/99)

Field services related to the geologic evaluation will consist of reconnaissance and detailed engineeringgeologic mapping of the landfill and surrounding terrain to:

1. Identify, define, and correlate onsite geologic units and faults with regional geologic units andfaults identified in the literature

2. Assess photolineaments previously identified on aerial photographs3. Define geologic, stratigraphic, and structural elements such as bedding, faults and fractures, which

may influence groundwater flow. Measure their strike and dip, and collect data on structuraldiscontinuities such as joint, fracture, shear orientation, spacing, length, openness, filling material,and gouge material.

4. Develop quality-control (ground truth) information for the surface geophysical surveying

The engineering geologic map will be prepared using tape and Brunton compass mapping techniques,as described in Compton's Manual of Field Geology (1962), on a topographic base map (1 inch equals

5

400 feet). The data compiled on the map will emphasize the physical characteristics that influence thehydrogeologic properties of the units exposed. Descriptions of the units will be based on outcrops andhand specimens using Compton's standard logging procedures. Fault and bedding orientation, andstructural discontinuity data (joint, fracture, and shear orientation, spacing, length, openness, fillingmaterials, gouge material, etc.) will be collected at bedrock out-crops and cut slopes. Structural datacollected during field mapping will be analyzed for trends or preferred orientations by stereonetanalysis.

3.4.5.3 Conduct Deep Geophysical Resistivity Survey (USEPA APPROVED 12/02/99)

In addition to confirming the landfill base grade elevations, as detailed in 3.4.1 and 3.4.1.5, deepgeophysical resistivity surveys will be used to evaluate the geological environment surrounding andunderneath the landfill area. In conjunction with surface geologic mapping, the survey will provideconfirmatory information on the location and nature of, lithologic contacts, faults, and fracture zones,as well as information on the occurrence and depth of water-bearing zones. The information obtainedfrom the geophysical survey will allow better interpolation of the geologic and hydrogeologicconditions between the exploratory boreholes.

A series of parallel lines of resistivity data, oriented approximately perpendicular to the FrenchmanMountain Fault, will be spaced approximately 2,500 feet apart The survey will cover the area fromapproximately two miles southeast of the landfill to approximately two miles northwest of the landfilland obtain data to a depth of several hundred meters. The geophysical survey crew will determinelocations and collect deep geophysical resistivity data at stations spaced at approximately 200-footintervals along these lines. A map showing the near-landfill line layout is attached. This data set willprovide information regarding the exact locations of faults, as well as their geophysical character(conductive or resistive, for example, possibly indicating water-bearing or impermeable conditions).Active flow paths should be evident as low resistivity features, and perched water may be evident aslow resistivity features.

3.4.5.4 Location of Exploratory Boreholes (USEPA APPROVED 1/28/2000)

Based on the geologic and hydrogeologic conditions described previously, seven exploratory boreholelocations have been selected to obtain data for the geologic and hydrogeologic characterization of thesite. Because the depth and direction of groundwater flow beneath the site has not yet beendetermined, the proposed locations have been selected based on the following two criteria. First, theinitial hydrogeologic assumption is that groundwater generally flows from areas of high ground surfaceelevation to areas of low surface elevation, that is, is- the water table generally produces exists as asubdued expression of the surface topography. Second, appropriate groundwater monitoring welllocations are should be along the downgradient edge of the waste management unit at the point ofcompliance. In the absence of defining site-specific information, groundwater flow beneath the canyonportion of the landfill is assumed to be down-canyon - to the south - becoming radial at the canyonmouth, with flow to the south and west. Using these two criteria, borehole No. 1 through No. 6 will belocated around the southern and southwestern perimeter at the landfill, and borehole No. 7 will belocated along the western (lowest) margin of the Western Burn Pit Area. Because the proposedborehole locations are based on fundamental hydrogeologic principles, some of their locations may notbe appropriate for the groundwater monitoring network. This will have to be evaluated after the sevenwells are installed. The proposed borehole locations are shown on the attached map.

Ten-inch diameter conductor casings have already been installed to a depth of 20 to 40 feet belowground surface for Exploratory boroholc/wells No. 1 through No. 6. The exploratory boreholes(described below) will be drilled approximately 15 to 20 feet from within these conductor casings. The

6

borehole/wells are located along the southern and western perimeter of the landfill at relatively evenspacing so that the breadth of existing hydrogeologic conditions are likely to be encountered during thissite hydrogeologic characterization. These locations are considered exploratory and additional wellsmay be added to the groundwater monitoring system following this initial characterization. It shouldbe noted that in tho geologic environment of the sito, sediments consist of hundreds of discrete debris-flow lobes of limited oxtont. Thoso lobos cut across one another, and extend out into braideddistributary networks.

Three additional well locations have been selected to obtain the preliminary information that is requiredto characterize the Frenchman Mountain Fault and correlate the hydrostratigraphic units beneath thesite. One well location will be within the area of the used sewage drying beds close to the FrenchmanMountain Fault. This well location will be used to obtain preliminary information regarding the faultgouge, its orientation and aspects at depth, and information on the facies of the Muddy CreekFormation. A second well location will be within the Northeast Canyon area to assess the depth togroundwater and nature of the bedrock, and also, to correlate the hydrostratigraphic units beneath thesite. The third well location will be within the vicinity of the previous landfill office complex tocharacterize the fault gouge, its orientation and aspect at depth, the occurrence of groundwater and thefacies relationship (e.g., pinchout) of the Tertiary bedrock along the margins of Frenchman Mountain.

After the groundwator flow direction in the regional aquifer has been determined as described bolow, alocation for monitoring A "background" monitoring location conditions for statistical evaluation ofwater-quality data in a detection monitoring program will be proposed after the groundwater flowdirection in the regional aquifer has been determined.

3.4.5.5 D Exploratory Drilling and Well Construction (USEPA APPROVED 1/28/2000)

The following subsections discuss the decision criteria for exploratory drilling, borehole geophysicallogging, proposed well design, well construction, and well development. Available data show that thelocal "regional aquifor" underlying tho site is bounded from bolow by the Muddy Creek Formation.Therefore, saturated alluvium directly overlying the Muddy Crook Formation will be considered theregional aquifer for this Work Plan. Perched aquifers may bo present at elevations above the regionalaquifer. A well will bo installed in tho saturated zono of perched aquifers unless the saturated thicknessis less than 2.5 feet because obtaining groundwater samples may not be feasible from a thinner zone.

Because boroholo geophysical logging requires the addition of water or drilling fluid to obtain gooddata using the intended suite of logging tools, and this water may affect the local groundwatorchemistry, separate borings will bo advanced insido tho existing 10 inch conductor casing for-monitoring woll construction in each area as specified in this Work Plan. Tho amount of potablo waterused to flood tho borehole for geophysical logging will be kept to a minimum, Tho volume usod ineach boring will bo monitored. A grab sample of this water will bo collected and analyzed for thoparameters listod for groundwatcr analysis in Section 3.4.5.5.5. The use of a separate boring forgroundwatcr well installation, and the uso of potable water (with the minimum amount of bentonitodrilling mud, if needed) is intended to minimize tho changes to the in situ groundwatcr chemicalcomposition.

If moro than ono exploratory boring is needed at a location for characterization purposes (sec bolow)and the second or third exploratory boring is located outside of tho leased area, tho Bureau of LandManagement will be allowed to evaluate tho situation.

3.4.5.5.1 Drilling Method (USEPA APPROVED 1/28/2000)

Boreholes will be air rotary drilled and continuously sampled/cored. The loggeding will beperformed by an experienced field geologist. The alluvial sediments will be logged using the

7

Unified Soil Classification System (USCS) visual-manual field method as described in ASTMD-2488-84, with bedrock logged appropriately. Logged features of the bedrock core will AHGrab samples of logged cuttings and all drive samples will bo rotalnod. Bedrock features thatwill bo logged include, but are not limited to, percent recovery, rock quality description (ROD),fracture frequency and orientation, rock strength, rock type, mineralogy, alteration, degree ofweathering and cementation, and hardness bedding features, and moisture content-:—tointervals whoro whole rock samples aro collected, fracture spacing and thickness will also borocordod. Munsell colors will be recorded and used to aid in identifying changes in geologicmaterials/conditions. Particular attention will be directed to observing shallow cementedzones, moisture conditions, color (indicating oxidized or reduced conditions), and plasticity toassist in identifying water-bearing zones. In addition, all samples will be screened on-site forVOC contamination. The results of the VOC field screening will be recorded in the geologist'slog book. All samples will be labeled, boxed, and stored for future reference.

Before the drill rig and drill stem is- are transported to the sSite, the rig, stem, drive casing, bit, andother equipment to be used downhole will be steam cleaned. Tho drill rig and ancillary equipment willbo cloanod in the same manner after installation of each additional boring. In addition, the drill rig andancillary equipment will be steam cleaned at the Site before beginning each exploratory boring.

A nominal 4-inch diameter pilot boring will be drilled at each of the seven ten locations to obtainsamples and facilitate geophysical logging. Borings 1 through 6 (see attached map) will be drilledwithin the existing 10-inch conductor casing; borings 7 through 10 have approximately 15 to 20 footsouth of the existing 10 inch conductor casing; boring 7 has no existing conductor casing. Tho narrowdiamotor of the pilot boring is moro stable than a largo diameter boring and will allow for borcholoadvancement using only air to quickly lift drill cuttings to the ground surface resulting in greateraccuracy in geologic logging. Additionally, the small diameter pilot holo can bo easily sampledthrough tho drill bit. These small diamoter drilling advantages minimize the potential for drillingthrough an aquitard and thereby roducingc the chances for opening pathways for downwardcontaminant transport. A small-diameter temporary conductor casing will be installed in the near-surface material to stabilize the upper portion of the pilot borehole. The decision criteria for boreholeadvancement are described below. After boreholes have reached their desired depth, they will begeophysically logged. The logging will be conducted within a 2-inch temporary casing to prevent lossor damage to the logging equipment in the event borehole stability problems occur. Followinggeophysical logging, the drill rig will ream a the 4 inch pilot boreholes will be groutod to tho groundsurface, the drill rig will move approximately 15 to 20 feet, and ream drill a nominal 10-inch diameterboring inside tho existing surface 10 inch conductor casing.

Boreholes will be advanced 40 feet bolow first encountered regional groundwator or until tho MuddyCrock Formation is encountered to bedrock (anticipated to be between 20 and 200 feet below groundsurface; this will with the depth to be approximated more closely by the deep CSAMT geophysicalsurvey before drilling commences and confirmed by drilling). A monitoring well will be completed atthe bedrock contact If crystalline pro Tertiary bedrock is encountered above the water table, thoboroholo will bo advanced 5 foot into tho bedrock, for confirmation. If water is not prosont in thoexposed portion of tho bedrock aftor a 24 hour period, a woll with 10 feet of screen (5 feet above thebedrock-alluvium contact and 5 feet below the contact) will be constructed to provide access forseasonal groundwator conditions If significant water is not encountered at this depth after a 24-hourperiod, a new boring will then be drilled, cased, and grouted to 5 feet below the bedrock contact andsubsequently drilled through the casing until the uppermost aquifer is encountered.

If a perched water zone or saturated zone is encountered above the regional uppermost aquifer (theuppermost aquifor is wator established above the Muddy Creek Formation), the borehole will beadvanced to the base of a the perched/saturatod zone aquifer (caliche layer or clay layer) and left opentemporarily (approximately 7 days or less) so water levels and saturated thickness can be measured.

8

This borehole will be used as a monitoring well or as a geophysical characterization boroholc. If thoborehole is flooded and usod for geophysical logging, a second borehole will be advanced to tho samedepth next to tho exploratory boroholo, and a monitoring woll will be installed if the perched/saturatedzone in greater than 2.5 feet thick. Drilling a second borehole to install a well will be done to minimizethe effect of tho water introduced for geophysical logging on tho aquifer water chemistry. The criticaltime factor in this process is tho geophysical logging of exploratory boreholes. It is important to haveas many exploratory wells stabilized and ready for geophysical logging as possible to minimize thomobilization timo required for tho geophysical logging team. A monitoring well will be installed if theperched zone yields approximately 2 to 3 gallons per hour.

The aquitard below Pperched zones will not be penetrated to prevent the possibility of crosscontamination from the perched to the next lower aquifer. After a perched aquifer has been identified,'Fthe drill rig will move approximately 100 feet down gradient and a second pilot boring will be drilled.If no perched zone is encountered, the second borehole will be advanced to regional groundwator thebase of the uppermost aquifer and the geophysical logging and drilling procedures described above willbe followed. If a perched zone is again encountered (at the same or at a different depth), the boreholewill be left open temporarily (approximately 7 days or less) so water levels and saturated thickness canbe measured. The drill rig will move approximately 100 feet farther downgradient and a third pilotboring will be drilled to either a perched zone (drilling will stop) or regional groundwatcr the base ofthe uppermost aquifer. This process will not be repeated a fourth time. However, if the perched zoneis encountered in all three borings, the third boring will be cased to the base of the perched zone toprevent cross contamination and then drilled to the base of the uppermost aquifer so that a well will becompleted within the perched aquifer and the uppermost aquifer at each location.

When water is encountered, approximately 5 foet of drive samples will be collected to assist incharacterizing tho stratigraphy and density of the sediments, obtain samples for visual grain sizeevaluation, and provide relatively intact lithologic samples for correlation with surface and boroholcgeophysical data. If a caliche layor or 1 foot of clay that is not part of tho Muddy Creek Formation isencountered during the drivo sampling, no additional samples will bo collected. The sedimentary layorresponsible for the pcrchod condition will likely be oncountorod. If tho borehole has boon advanced 35foot below first encountered groundwator and the Muddy Crock Formation has not boon encountered,tho noxt 5 feet (35 to 40 foet below water) will be sampled with a drive sampler. Tho borehole will beroamod to base of the samplingcd interval and drilling will stop. If tho Muddy Crook Formation isoncountorod within the first 35 foot of a saturated zone, a drivo sample will be collected forconfirmation. Tho boroholc will bo roamed to base approximately 10 foot past the top of tho samplingMuddy Crook Formation so that geophysical tools can cross the lithologic contact, and drilling willstop. In addition to tho geologic data obtained from the drive samples, tho samples will provide qualitycontrol and geophysical signature calibration for boroholo geophysical logging (soo bolow).

Tho following In the alluvial sediment, the method of drive sampling will be used. A 24-inch split-spoon sampler (3 inch OD, 2.5-inch ID) will be driven with a downhole 140-lb. wire-line hammerahead of the bit. The split-spoon sampler will fit down the center of the air-rotary drill bit on a wire-line assembly. The sampler will be lined with four 6-inch brass liners. Sand or rock catchers will beused to minimize sample loss from the sampler during retrieval. The driller will attempt to drive theentire 24 inches of the sampler. If rocks are present, or the formation is too cemented to drive thesampler, refusal will be noted. The drilling will proceed to the depth reached by the sampler, thesampler will be retrieved by wire-line, and the process will be repeated. If poor sample recoveryconditions persist due to the formation being too cemented, the sampling approach will be modified tosuit the new conditions, such as switching to a conventional coring approach (i.e., use of a split corebarrel equipped with a conventional coring shoe.) Soil coro sample depth and percent recovery will beindicated on tho drilling log and tho All samples will be labeled, boxed, and stored in saved in bags-

cardboard drilling core boxes for future reference.

9

After the 4-inch borehole has been drilled, the borehole will bo filled with fluid to facilitate downholegeophysical logging it will be geophysically logged to supplement the lithologic and hydrogeologicdata collected during drilling, identify potential saturated zones that may not have been identifiedduring drilling, and allow adjustments in the final design of the wells. If more than one pilot boring isdrilled in an area to characterize the lateral extent of a perched zone, the initial borehole will begeophysically logged. The managing geologist will determines- whether conditions are significantlydifferent (e.g., shallower or deeper perched zone, change in lithology, etc.) in one or both of theadjacent borings to warrant their geophysical logging. If tho Muddy Creek Formation bedrock isencountered in the second or third pilot boring, that boring will be geophysically logged. If a boroholodoos not hold fluid, dry holo geophysical tools will bo used. The purpose of geophysical logging is tosupplement tho lithologic and hydrogcologic data collected during drilling, identify potential saturatedzones that may not havo boon identified during drilling, and to allow adjustments in the final design ofthe wolls.

Tho suite of geophysical logs that will bo run for oach fluid filled 4 inch borehole may will includesingle point resistivity, 16 inch and 64 inch normal resistivity, spontaneous potential (SP), calipor,natural gamma ray, and, combinable magnetic resonance (CMR), epithermal neutron tool (ENT), sonic,compensated density, or temperature. If the borcholo doos not hold fluid, the suite of geophysical toolsthat will be run may include an array induction tool [ATT], natural gamma, spectral gamma, andcalipor., CMR, or ENT. Detailed descriptions of the geophysical logging tools aro presented in tho

SAP in Appendix B The Borehole geophysical tools will be run to determine basic physicalcharacteristics of the alluvium and bedrock such as degree of moisture, water content and its relativesalinity, porosity, degree of carbonate cementation, clay content, lithology, bedding thickness, and thediameter of the borehole annulus. Only methods that can be run in a dry borehole will be used such asthe array induction tool [AIT], natural gamma, neutron, and caliper tools. Natural gamma logs willprovide a record of the rate of emission of gamma rays by different rock layers. Higher gamma rayemissions are generally associated with clay layers. Caliper logs will provide a record of the boreholediameter. Soft or fractured layers typically erode faster during drilling and therefore result in a larger,irregular borehole diameter than indurated, cemented, or unfractured sedimentary layers or bedrock.The array induction tool is a focusod oloctrical induction probo that can bo usod in dry holo conditions.It provides will provide a record of conductivity/resistivity contrasts at multiple depths of investigationinto the side wall This tool can provide to quantitatively estimates-ef- the true bulk formationresistivity that reflects bedding, fluid volume, and fluid conductivity of the wall rock, and can bo usodto distinguish botwoen saturation and drilling fluid invasion. The final decision for selection ofgeophysical logging tools will be made by the managing geologist after reviewing lithologic samplelogs and discussing downhole conditions with the driller. Detailed descriptions of the geophysicallogging tools are presented in the SAP hi Appendix B.

Resistivity logs provide a record of the resistance to tho flow of alternating oloctric current offered bytho rock layers and thoir contained fluids and tho fluid in the borehole. Clay layers normally have lowresistivity because of thoir largo porosity, and the water that thoy contain tends to bo relatively highlymineralized. In contrast, sand layers saturated with fresh water tend to have high resistivity. Sandlayers containing salty wator, on tho other hand, tend to havo low resistivity.

SP logs provide a record of tho differences in voltagos of an electrode at tho surface and an electrode intho borehole. Variations in voltage occur as a result of electrochemical effects. High potentialsgenerally indicate impermeable bods such as clay, shalo, and bedrock. Low potentials generallyindicate sand, porous limostono, or other permeable layers.

Temperature logs provide a record of tho borehole fluid temperature. Changes in temperature typicallycorrespond to zonos of saturation where groundwatcr is entering the borehole and affecting thoboroholo fluid tomporaturo.

10

If the borehole doos not hold water long enough to complete the suite of logs, dry hole tools will boused. If a tool is tried in the first borehole logged and doos not produce tho desired data objective, itsuso may bo oliminatod from subsequent boroholos. This decision will bo mado by tho managinggeologist after discussions with tho geophysical logging company.

3.4.5.5.2 Well Design and Construction Methodology (USEPA APPROVED 1/28/2000)

Tho proposed woll design includes At each of the ten drilling locations, a 4-inch diameter monitoringwell that will be completed to the base of the uppermost aquifer. In addition, 4-inch diametermonitoring wells will be completed to the base of perched water zones with yields of approximately 2to 3 gallons per hour or greater. Six of the wells will be installed in the existing 10-inch diameterconductor casing and the rest in new 10-inch diameter borings. 40 foot into the regional aquifer (or totho top of the Muddy Crock Formation, including a short sump into tho Muddy Crook Formation) or totho base of tho perched aquifer. Six of tho wolls will be installed in the existing 10 inch diamotorconductor casings; a that aro 15 to 20 feot from tho proposed initial pilot borohole at oach location. Anow 10 inch diameter boring will bo drilled at the seventh location. The pilot boring will not bo ovor-roamod for woll installation because the addition of largo quantities of water to flood tho boreholo forgeophysical logging may affoct groundwator quality. The possible exception to this situation is if themanaging geologist determines that different conditions oxist in tho pilot borings drilled in ono area(sco discussion in previous section). The pilot borings will be backfilled with bontonito grout mixod tomanufacturer's specifications unless wells will be installed. The 4-inch well will be used to measureaquifer hydraulic properties, obtain groundwater samples, and evaluate the presence of dense non-aqueous phase liquids (DNAPLs). The following decision criteria have been established fordetermining well design. The decision criteria are also detailed in the SAP in Appendix B.

If the regional uppermost or perched aquifer has a saturated thickness of 20 feet or less (perchedaquifer must bo greater than 2.5 foot), the 4-inch well will be used to monitor for both light nonaqueousphase liquids (LNAPLs) by setting the top of the screens- 5 feet above the water table, and densenonaqueous phase liquids (DNAPLs) by setting the base of the screens- across the base of the waterbearing zone. The maximum screen length will not exceed 25 feet.

If the regional uppermost or perched aquifer has a saturated thickness greater than 20 feet, a 4-inch welland a 2-inch diamotor well will be installed in the borehole. Both the 4-inch and 2-inch wells' screenlength will be no greater than 20 feet (length criteria described below). The 2-inch well will monitorthe upper portion of the regional or perched aquifer with the screens extending 5 feet above the watertable to monitor for LNAPLs er and landfill gas. The 2-inch well will be constructed with the base ofits screens separated from the top of the 4-inch well's screens by a minimum of 10 feet so that verticalhydraulic gradient data can be collected. The 2-inch and 4-inch wells will be constructed so that theirsaturated screen length is approximately the same.

The design also calls for installation of one 1-inch diameter sounding tube along the outside of the 4-inch diameter casing. The sounding tubes will allow more accurate collection of water-levels-measurements during pumping ef- tests in the 4-inch well than collection of measurements from withinthe 4-inch well. 33MS- The sounding tube increases the options for use of the well, including conductingsingle-well aquifer tests. The 1-inch sounding tube will be screened across the same interval as the 4-inch well.

Following reaming of the borehole to a diameter of 10 inches, tho drilling of the 10 inch borehole, wellcasing and annular fill installation will proceed as follows. Drilling mud, if noodcd to stabilize thoborehole, will bo thinned with potable water by slowly circulating water through the drill stem with thebottom of tho drill stem located at the bottom of the borehole. Centralizers will be placed on the topand bottom of the 4-inch diameter well screens. The 1-inch sounding tube will be attached to the 4-

11

inch casing with Teflon tape. If the 4-inch well is the only well to be installed in the boring,centralizers wett will be placed at 75-foot intervals up the remainder of the casing. If a multiple casingcompletion is to be installed, no additional centralizers will be used because they will interfere with theplacement of the additional casing.

Annular fill materials (sand pack, bentonite pellets, and bentonite grout) will be delivered to the desireddepth through a tremie pipe that's bottom is not that has been lowered to no more than 15 feet abovethe base of the well bore or previously installed annular fill. It may be necessary to use potable wateror water bailed from the casing to wash the annular fill materials down the tremie pipe to their desireddepth. The sand pack will be installed to 2 feet above the top of the 4-inch well screen, using a tromiopipe. The casing will be bailed to tighten the sand pack. The bailed water will be contained for reuse(see below). Additional sand will be added if necessary to bring the sand to the desired height.

If a 2-inch well is to be installed, bentonite pellets will be installed (using a tremie pipe) to a height 10feet above the 4-inch well screens (8 feet above the sand). One foot of sand will be placed on thebentonite pellets and the 2-inch casing will be installed. The sand pack for the 2-inch well will beinstalled to 2 feet above the top of the screens. The casing will be bailed (water saved) and the sandlevel will be adjusted as necessary. An additional three feet of finer-grained sand will be installed as atransition seal above the highest screened interval (2-inch well in multiple casing completion, or 4-inchwell in single casing completion). Bentonite pellets will be installed to a height of 5 feet above thetransition sand pack and hydrated with water removed from the casing during "sand-pack" bailing. Asannual seal consisting of a bentonite grout product (Volclay or equivalent) will be installed above thepellets to the ground surface.

Wells sheH will have a 4' x 41 x 3" concrete pad, locking security cover and lock. Four traffic posts(one removable) will be placed to protect each well. The locations and elevations of the wells will besurveyed by a licensed surveyor, and shown on a scaled plot plan.

Installing the screen above and below the saturated zone(s) may allow migration of landfill gas, ifpresent, up the casing to vent to atmosphere. The introduction of oxygen from the atmosphere to azone that might normally have low concentrations of oxygen can also change groundwater chemistry inthe vicinity of the well, particularly metals concentrations that are sensitive to redox conditions.Therefore, well heads will be monitored for LFG components and oxygen prior to any samplecollection.

3.4.5.5.3 Well Construction Materials (USEPA APPROVED 1/28/2000)Each well will consist of one, 4-inch diameter, flush-threaded, Schedule 80 PVC casing with 0.020-inch slotted well screen and end cap at its base. Stainless steel centralizers will be used to center thewell screen in the borehole.

Each well will also consist of one, 1-inch diameter, flush-threaded, Schedule 40 PVC sounding tubewith 0.020-inch slotted well screen and end cap at its base.

If the saturated interval is greater than 20 feet, a 2-inch well casing will be installed to monitor theupper portion of the saturated interval. The casing will be flush-threaded, Schedule 40 PVC with0.020-inch slotted well screen and end cap at its base.

Cuttings will be stockpiled and sampled for proper disposal.

3.4.5.5.4 Well Development (USEPA APPROVED 1/28/2000)

Wells will be developed after construction by a combination or sequence of bailing, swabbing, andpumping. Development will be at the direction of the geologist, and it will continue until the water is

12

substantially silt-free and field parameters (pH, EC, and temperature) stabilize within 10 percent of theprevious reading, or until the geologist directs development to stop. Development water will becollected and held in appropriate containers such as drums or tanks. The water will be profiled anddisposed of based on analytical results from the groundwater samples collected during the fieldactivities. Wells will be allowed to rest a minimum of 24 hours after development before groundwatersampling begins to allow the groundwater level in the casing to stabilize.

3.4.5.5.5 Groundwater Sampling (USEPA APPROVED 1/28/2000)

Groundwater sampling procedures described below are based on the following documents.

1. Procedures Manual for Groundwater Monitoring at Solid Waste Disposal Facilities,USEPA/530/SW-611, August 1972

2. RCRA Groundwater Monitoring Technical Enforcement Guidance Document, USEPA Office ofWaste Programs Enforcement. September 1986

3. Test Methods for Evaluating Solid Waste: Physical/Chemical Methods, USEPA SW-846,November 1986, third edition, with current revisions

A detailed description of the groundwater sampling procedures and analytical methods is presented inthe SAP in Appendix B. This information is summarized below.

3.4.5.5.5.1 Presample Purging (USEPA APPROVED 1/28/2000)

Before groundwater samples are collected for laboratory analysis, the groundwater wells will be purgedso that samples which are representative of the aquifer can be collected. The volume to be purgeddepends on whether the well recovers quickly or slowly. Each well will be purged until fieldparameters (pH, EC, and temperature) stabilize within 10 percent of the previous reading, up to a totalof 4 casing volumes. If four casing volumes have been purged and the values have not stabilizedwithin 10 percent, samples will be collected. One well volume is calculated as the area of the casingtimes the length of the standing water column. When parameters stabilize within 10 percent of theprevious reading, purging may stop. Tho purgo rate is not critical as long as aeration and cavitation donot occur. However, Care will be taken to limit the aeration or cavitation of the recharged water. Also,purge rates will be kept low to minimize turbidity (< 10 NTU). If the well dries before parametersstabilize, the well will be considered adequately purged because recharge will be groundwater from thewater-bearing zone, not the well bore.

3.4.5.5.5.2 Sample Collection (USEPA APPROVED 1/28/2000)

Groundwater samples collected for laboratory analysis will be collected using either a bailer, or abladder pump. Bailers are to be disposable, and will not be reused between wells. If bailers are used,one field rinseate sample (consisting of deionized water poured into a clean sample bailer) will becollected during each daily sampling event and analyzed for VOCs. If bladder pumps are used, onepump blank will be collected during each daily sampling event and analyzed for VOCs. To collect apump blank, laboratory-certified organic-free water or deionized water will be placed in a clean 5-gallon container and pumped through the bladder pump. After approximately 3 gallons have beenpumped, a pump effluent sample (pump blank) will be collected for VOC analysis in standard VOAbottles using the same procedures used for the groundwater sampling as specified in the SAP. Sampleswill be collected in the following order: VOCs, metals, cations and anions, general minerals. Allbottles for VOC analysis will be filled with zero headspace. Samples will be collected in laboratory-prepared, pre-cleaned and certified bottles, that containing- appropriate preservatives for the type ofanalysis to be performed, following the procedures in USEPA SW-846. The list of parameters, bottlerequirements, and sample preservatives are discussed in the following sections and in the SAP.

13

3.4.5.5.5.3 Groundwater Analysis (USEPA APPROVED 1/28/2000)

Groundwater samples will be analyzed by the USEPA approved laboratory as- specified bolow in theSAP. The laboratory is certified for such analyses by the State of Nevada^ for tho USEPA Appendix Ilist consistent with the USEPA requirements. Analyses include VOCs by Method 8260 B, majoranions and cations (Ca, Mg, Na, K, HCO3, CO3, SO4, NO3, Cl), aad-Subtitle D Appendix I metals (As,Sb, Ba, Be, Cd, Cr, Co, Cu, Pb, Hg, Ni, Se, Ag, Th, V, Zn), TOC, and TDS, COD, NO2, ammonia, andsulfide (See following table). NEL (the soloctod laboratory) The laboratory will provide theappropriate containers with preservatives.

During this initial water quality characterization, individual metals will be analyzed for the total-phaseconcentration rather than a specific oxidation phase concentration that are affected by strong Eh and pHconditions (e.g., total chromium rather than hexavalent chromium). In addition to pH measurements,groundwater samples will be tested for binary phase parameter pairs (i.e., sulfate/sulfide andnitrate/nitrite) to evaluate redox conditions. Results from the initial water quality characterization willbe used to develop an appropriate groundwater monitoring program.

3.4.5.5.5.4 Sample Containers, Parameters, and Holding Times (USEPA APPROVED1/28/2000)

The table below summarizes parameters, containers, methods, suggested USEPA analytical methods,reporting units, containers, preservatives, and holding times. Parameters for which no method isspecified in tho following tablo, will bo analyzed in accordanco with the appropriate method Theserequirements are specified in the latest edition of "Standard Methods for the Examination of Water andWastewater", or "Test Methods for Evaluating Solid Waste: Physical/Chemical Methods", USEPASW-846, November 1986, third edition, with current revisions.

Parameter

Groundwater Depth

Temperature

Specific Conductance

PH

Turbidity

Total Dissolved Solids

Chemical. OxygenDemand

Total Organic Carbon

Chloride

Carbonate

Bicarbonate

Nitrate plus Nitrite asNitrogen

Nitrite as Nitrogen

SuggestedMethod

field

field

field

field

field

2540C

5520D

5310C

300.0

2320B

2320B

300.0

300.0

Units

0.01 feet

°F.

(imhos/cm

pH units

NTU

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

Container

Field

Field

Field

Field

Field

1 L Plastic

1 L Plastic

1L Plastic

1 L Plastic

1 L Plastic

1 L Plastic

100 mLPlastic

1 L Plastic

Preservative

Na

Na

Na

Na

Na

None

H2SO4 to pH <2

H2SO4 to pH <2

None

None

None

H2SO4 to pH <2

None

HoldingTime

na

na

na

na

na

7 days

28 days

28 days

28 days

14 days

14 days

28 days

48 hours

14

Parameter

Ammonia

Sulfate

Sulfide

Calcium

Magnesium

Potassium

Sodium

Iron

Total Metals: Sb, Ba,Be, Cd, Cr, Co, Cu,Ni, Ag, Th, V, Zn

Total Metals: As by7060, Pb by 7420,Hg by 7470, Seby7740

VOCs (Subtitle DAppendix I)

SuggestedMethod

4500

300.0

4500SD

6010

6010

6010

6010

6010

6010

7000 series

8260B

Units

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

Hg/L

Container

1 L Plastic

1L Plastic

1 L Plastic

1 L Plastic

1 L Plastic

1 L Plastic

1 L Plastic

1 L Plastic

1 L Plastic

1 L Plastic

3-40 mL glassvials

Preservative

H2SO4topH<2

None

ZnAC + NaOHto pH>9

HNO3 to pH <2

HNO3topH<2

HNO3topH<2

HNO3topH<2

HNO3 to pH <2

HNO3 to pH <2

HNO3 to pH <2

HC1 to pH <2

HoldingTime

28 days

28 days

7 days

6 months

6 months

6 months

6 months

6 months

6 months

28 days

14 days

3.4.5.6 Aquifer Testing (USEPA APPROVED 1/28/2000)

Groundwater pumping tests will be performed to characterize aquifer hydraulic properties so thatgroundwater flow velocities can be calculated and the rate of contaminant movement can be estimated.Slug tests will be performed on all 4-inch diameter wells to obtain "order-of-magnitude" hydraulicconductivity values. This information will be used to assist in selecting two wells for pumping tests.

The criteria for selecting the two wells for pumping tests is as follows. The wells- screened in theregional uppermost aquifer will be used if possible. If no regional aquifer wells arc present, porchod-zono wolls will be ranked in ordor of saturated thickness and tho wolls with more than 4 foot saturatedzones will be considered. Wells with less than 4 foot of water may not bo suitable for pumping becausethere may bo insufficient water to produce drawdown and cool the pumps. After this levol of wellsection has boon made, tho well with the highest hydraulic conductivity (determined by the slug test)will be tested. The other well will be the well in the uppermost aquifer with a hydraulic conductivityclosest to the geometric mean of the hydraulic conductivities determined by the slug tests. These twowells should provide aquifer properties at the upper end of the range and at the average range forconditions beneath the Site. The geometric mean, rather than the arithmetic mean will be used becauseit does a better job dealing with order-of-magnitude differences in numerical values.

Because of the poor recovery at the one available well on-site, it is expected that a style of single-wellgroundwater pumping test suited to low-permeability aquifers will be required. The type of test chosenwill depend on the production rate of the well. Wells that can produce more than 3/4 gpm for 24 hoursare suitable for testing using a constant-discharge test. Wells that bail dry and are slow to recover maybe suitable for testing using a constant-drawdown test. In a constant-drawdown test, the water level inthe well is kept constant, and the volume removed is recorded with time. Constant-drawdown tests are

15

suitable for use in wells with poor recovery to a certain point, and can give results that are superior toslug tests depending on aquifer permeability. The wells have been designed with an external soundingtube specifically so that either single-well method can be used. The anticipated length of the aquiferpumping test will be 6 hours, with the recovery measured for 2 hours or until 95 percent recovery hasbeen completed.

Before pumping tests begin, however, slug tests will be performed to obtain the general range ofhydraulic parameters and conditions and determine which wells should be used for pumping tests.Rising and falling head slug tests will be conducted in all 4-inch wells. These tests will look forgeneral aquifer conditions (boundaries, leakage, recharge, confined, unconfined), and will allowcalculation of transitivity and hydraulic conductivity. Transducers and data loggers will be used tomeasure water levels. Because of limitations on pumping rates caused by tho size of tho well, andbocauso the aquifer is probably unconfinod, tho aquifer tost radius- of influence will probably be lossthan approximately 200 foot. Aquifer testing procedures are presented in the SAP in Appendix B.

3.4.5.7 Decontamination Procedures (USEPA APPROVED 1/28/2000)

Before the drill rig and drill stem is transported to the Site, the rig, stem, drive casing, bit, and otherequipment to be used downhole will be steam-cleaned. The drill rig and ancillary equipment will becleaned in tho samo manner by steam-cleaning before beginning each exploratory boring and aftercompleting each well.

Well development equipment will be decontaminated before use at each sampling location. Thisequipment includes swabs, bailers, and development pumps, if used. The following decontaminationprocedure will be used:

1. Wash with potable water and a brush;2. Wash with Alconox, or similar lab-grade detergent;3. Rinse with potable water. Air dry; OR4. Steam clean

Groundwater sampling equipment (e.g., bailers and sampling pumps) will be decontaminated by thesame general procedure with the addition of a final rinse of de-ionized or distilled water as listedbelow.

1. Wash with potable water and a brush;2. Wash with Alconox, or similar lab-grade detergent using a brush;3. Rinse with potable water;4. Rinse with de-ionized/distilled water;5. Air dry; OR6. Steam clean.

To decontaminate a sampling pump and discharge pipe, the pump and hose will be placed into a 55-gallon drum containing the Alconox solution. The pump will then be cycled on and run for at least 5minutes to recalculate recirculate the wash water. The pump and hose will then be removed slowly afew feet at a time so that the liquid fains- drains back into the drum. The pump and hose will then beplaced into a drum of potable water and similarly run for at least 5 minutes to recycle the rinse water.A final rinse with deionized or distilled water will be completed in a third drum. Care will be taken notto allow the pump or tubing to touch the ground once it has been decontaminated.

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3.4.5.8 Investigation-Derived Waste Management (USEPA APPROVED 1/28/2000)

Four types of waste materials will be generated during these field programs; they include drill cuttings,decontamination water, purge or development water, and miscellaneous equipment.

Soil cuttings will be placed on Visqueen or into 20-cubic-yard roll-off bins. If the analytical results ofgroundwater sampling indicate the presence of contaminants, then the soil cuttings will be evaluated tocharacterize the waste for disposal. If groundwater sample analytical results do not indicate thepresence of contamination, the soil cuttings will be considered non-hazardous and will be disposed ofat the APEX Landfill.

Decontamination water, well development water, and purge water generated during field activities willbe collected and held. The decontamination water and miscellaneous equipment will be profiled anddisposed of based on analytical results from the groundwater samples collected during the fieldactivities.

3.4.5.9 D Date Evaluation and Report Preparation (USEPA APPROVED 1/28/2000)

The data generated during the surface and subsurface exploration will be compiled andevaluated. Findings and conclusions will be presented in the Landfill Assessment Report.

The report will include:

• A discussion of the regional geologic and hydrogeologic conditions;• A regional geologic map depicting regional faulting and geologic units;• A discussion of the site geologic and hydrogeologic conditions, including a

description of the surface geophysical survey findings and the subsurface materialand water-bearing characteristics of the zones penetrated by the explorationborings. This section will include a narrative and graphical conceptualization of thehydrogeologic model;

• A groundwater contour map of the landfill area, showing groundwater elevations andflow directions for the water-bearing zone penetrated by the monitoring wells. Anappendix to this section will include the as-built drawings, boring logs, geophysicalsurvey data, and field notes taken by the geophysicist(s), geologist(s), and driller(s);

• Geologic and hydrogeologic cross-sections through the landfill area based on boringlogs, borehole geophysical logs, and surface geophysical surveys;

• Findings regarding water quality, and evidence of impacts (or lack of impacts) fromthe landfill; and

• Recommendations for the future environmental groundwater monitoring networkthat will provide groundwater samples representative of the aquifer(s) and complywith RCRA groundwater requirements. The recommendations will include the areato be monitored, depths and locations of additional monitoring points, andmonitoring parameters.

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