EVALUATION OF SOIL VAPOR EXTRACTIONFOR THE REMEDIATION OF

THE DELAWARE SAND AND GRAVELDRUM DISPOSAL AREA

Prepared for

Delaware Sand and GravelSteering Committee

Prepared by

ENVIRON CorporationArlington, Viiginia

April 30, 1992

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CONTENTS

Page

I. EXECUTIVE SUMMARY 1

n. INTRODUCTION . .... 2A. Purpose and Scope 2B. Site Description and History 2C. Organization of Report 3

IE. SOIL VAPOR EXTRACTION TECHNOLOGY 4A. Process Description 4B. System Components and Configurations 4C. Status of the Technology 6

IV. SUITABILITY OF SOIL VAPOR EXTRACTION 7A. Site Conditions 7

1. Soil Conductivity and Porosity 72. Soil Moisture Characteristics 73. Stratigraphy 84. Depth to Groundwater 8

B. Contaminant Characteristics 81. Volatility 92. Absorptive Properties 93. Distribution of VOCs 11

V. PREVIOUS APPLICATIONS OF SOIL VAPOR EXTRACTIONAND EXPECTED PERFORMANCE 12A. Case Studies 12

1. Groveland Wells Superfund Site 122. Midwest Industrial Facility 143. Hill Air Force Base 14

B. Potential SVE Perfonnanpe in Sandy Soils 14C. Performance Modeling 14

VI. REFERENCES 20

ATTACHMENT (SVE Case Studies) 22

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CONTENTS(continued)

TABLES

Table 1: Volatility of Contaminants of Concern 10Table 2: Comparison of Case Studies 13Table 3: Chemical-specific Parameters Assumed for 16

Modeling SVE PerformanceTable 4: Site-specific Parameters Assumed for _ 17

Modeling SVE Performance

FIGURE

Figure 1: Generic Soil Vapor Extraction System 5Figure 2: Modeled Decrease of VOCs in Soil Under the DS&G 18

Drum Disposal Area during Vapor Extraction in situFigure 3: Modeled Decrease of VOCs in Soil Outside the DS&G 19

Drum Disposal Area during Vapor Extraction in situ

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L EXECUTIVE SUMMARY

In October 1991, the Delaware Sand and Gravel Steering Committee presented to EPARegion IE a Remedial Action Evaluation'prepaiQd by McLaren/Hart providing a remedialaction plan for the Delaware Sand and Gravel (DS&G) Drum Disposal Area (DDA), locatedin New Castle, Etelaware. As part of die plan, a soil vapor extraction (SVE) andbioremediation system was proposed to remove contamination from the soils in, beneath, andsurrounding the DDA. ENVIRON was subsequently retained by the Steering Committee toprepare a technical paper evaluating the suitability of SVE as a treatment technology for thesesoils. This report provides a technical evaluation of the recommended use of SVE to theDDA on the basis of site conditions, soil properties, contaminant characteristics, and previousapplications at other sites. Potential SVE performance is also discussed.

In conjunction with other remedial measures in the proposed plan, SVE provides a cost-effective means of removing organic contamination in, below, and surrounding the DDA,thereby contributing to the remedial action objective of source control. It is extremely wellsuited to the characteristics of the DS&G site. The Columbia Aquifer, which contains thesoils being addressed by this treatment, contains very permeable sand and gravel. Thepermeable qualities of this soil will allow subsurface air flow and subsequent volatilizationand removal of contaminants. Moreover, geological surveys of the area reveal a horizontallylayered system, which is conducive to the desired horizontal air flow that can make SVEeffective through the entire sandy layer. The volatile organic compounds (VOCs), whichconstitute the vast majority of the contamination at the site, are extremely suitable forremoval by SVE. Certain semi-volatile compounds (SVOCs) are also expected to exhibitsignificant removal.

The proposed remedial action plan targets large volumes of soils up to 40 feet deep forSVE treatment; soils at these depths can be readily accessed for treatment by SVE.Dewatering of the sand layer, which is proposed in conjunction with SVE, will allow SVE totreat soils throughout this depth. The permeable qualities of the sandy zone also suggest thatthe aquifer can be effectively dewatered, minimizing pore blockage by residual soil moisture.

Case studies; reviewed by ENVIRON indicate that SVE has been effective on other siteswith similar soil properties, similar depths of contamination, and similar substances ofconcern. In cerfcrin cases, contaminated sands similar to those at the DS&G site have beenbrought to non-detectable levels of VOCs. Attainable levels of residual contamination willdepend on SVE design characteristics and length of treatment.

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H. INTRODUCTION

A. Purpose and ScopeIn October 1991, the Delaware Sand and Gravel Steering Committee presented to EPA

Region HI a Remedial Action Evaluation prepared by McLaren/Hart providing a remedialaction plan for the Delaware Sand and Gravel (DS&G) Drum Disposal Area (DDA), locatedin New Castle, Delaware. As part of the plan, a soil vapor extraction (SVE) andbioremediation system was proposed to remove contamination from the soils in, beneath, andsurrounding the DDA. ENVIRON was subsequently retained by the Steering Committee toprepare a technical paper evaluating the suitability of SVE as a treatment technology for thesesoils.

Final cleanup levels and residual contamination will depend on SVE designcharacteristics and length of treatment. The intent of this report is to evaluate the anticipatedeffectiveness of SVE on the basis of existing information concerning site conditions, soilproperties, and contaminant characteristics. In making this determination, previousapplications of SVE at other sites were also reviewed and evaluated. Based on this research,potential SVE performance is also described in this report.

B. Site Description and HistoryThe Delaware Sand and Gravel (DS&G) Site is approximately 27 acres, however the

area of concern for this report is the DDA. The DDA occupies three quarters of an acre andwas originally a 150- by 75- by 15-foot pit used to dispose an estimated 2,000 drums. SVEis proposed for approximately 50,000 cubic yards of contaminated soils below and outside theDDA. These soils are located in the Columbia Aquifer, a permeable layer of sands andgravel. The contamination is underlain by an impervious layer of clay at a depth ofapproximately 40 feet.

In 1984 EPA and the Delaware Department of Natural Resources and EnvironmentalControl (DNREQ implemented a removal action, removing 600 drums from the site aftercontamination was identified. EPA subsequently began Remedial Investigation andFeasibility Study (RI/FS) work, which was completed in 1988. A Record of Decision (ROD)was prepared by EPA Region HI identifying excavation and on-site incineration as itspreferred remedial solution for the DDA, based upon existing site characterization data in theFS (Dunn Geosciences 1988). Further site investigation by McLaren/Hart now suggests agreater aerial and vertical extent of contamination than was previously recognized. Afterpresentations to a Blue Ribbon Panel, the DS&G Steering Committee, McLaren/Hart, and the

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Panel concluded that the most protective and appropriate remedy for the DS&G site includedcontainment and extraction of groundwater, excavation and disposal of drums and surfacesoils, SVE and biological treatment of subsurface soils, and a surface cap,

C. Organization of ReportThis report includes a general description of SVE technology (Chapter HI), an

evaluation of the suitability of vapor extraction to this site (Chapter IV), and a summary ofprevious applications of SVE and modeled SVE performance (Chapter V). The evaluation ofthe suitability of SVE for the DS&G Site includes discussions of site conditions, soilproperties, and <x>ntaminant characteristics known to influence SVE effectiveness andimplementability.

This report: has been developed based on site information provided in the RemedialAction Evaluation by McLaren/Hart. ENVIRON did not collect any additional, independentsite data. Frequent reference is made to the Remedial Action Evaluation report.

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. SOIL VAPOR EXTRACTION TECHNOLOGY

A. Process DescriptionA soil vapor extraction (SVE) system consists of a network of perforated wells

extending through the unsaturated contaminated soil. These wells are packed with gravel andare sealed at the top to prevent short circuiting of airflow through the soil. The extractionwells are connected to the suction side of a vacuum extraction unit through a collectionmanifold. The vacuum induces a flow of air through the subsurface into the extraction wells.The vacuum not only draws vapors from the unsaturated zone, but also decreases the pressurein the soil voids, causing an additional release of volatile organic compounds (VOCs) andsemi-volatile organic compounds (SVOCs). The extracted gas flows through the manifoldand is either vented to the atmosphere or undergoes further treatment. Figure 1 shows thecomponents of a SVE system.

B. System Components and ConfigurationsThe major dements in a SVE system are wells, piping, blowers, and a vapor treatment

unit. Well construction is similar to that of monitoring wells, consisting of slottedpolyvinylchloride (PVC) piping, a gravel pack, and a seal of some type. The piping used toconnect the wells, the blower, and the vapor treatment unit may be made from PVC,polypropylene, high density polyethylene, or stainless steel and can be above or belowground. The blowers are the source of the applied vacuum and the subsequent air flow. Forthis purpose, a positive displacement blower or a centrifugal or a vacuum pump may be used;a decision, among these types is made on the basis of required vacuum and displacement. Thetreatment of vapors can include any or all of the following: removal of silt, condensation ofwater, and organics removal. Necessary air treatment equipment depends on waste streamcharacteristics, flows, and effluent and emissions standards.

Several configurations of this technology have been implemented to respond to a varietyof site conditions. The most commonly used among these is the installation of in situ verticalwells extending to the bottom of the contamination with well slots in the contaminated zone(EPA 1991). This is only feasible in cases where the contamination extends significantlybelow the land surface and the ground water table is not shallow (less than 12 feet).Trendies may be installed in cases where the zone of contamination and the ground watertable are close to the surface. A trench is excavated and a horizontal well is installed throughthe contaminated zone. Trenches minimize the upwelling of ground water and allow agreater area to be treated. It is also possible, in cases where contaminated soils are shallow

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and small in volume, to excavate the soil and install horizontal or vertical wells to the soilpile. In situ vertical wells are the most appropriate to the conditions found at the DS&G siteand further discussion will be limited to the application of this form of SVE.

C. Status of the TechnologyAlthough SVE is still considered to be an innovative technology, many full-scale

applications have akeady been installed and are currently operating or have already achievedperformance objectives. Thirty-one SVE projects have been undertaken at Superfund sites(Roy 1991). Of these, one is completed, five are currently operating, and twenty-five are indesign or pre-design stages. Information is available for previous applications and Chapter Vis dedicated to describing relevant case studies.

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IV, SUITABILITY OF SOIL VAPOR EXTRACTION

To assess the suitability of SVE to the DS&G site, this section reviews site conditions,including soil properties and contaminant characteristics, to determine their influence on theimplementability and effectiveness of SVE.

A. Site Conditions

1. Soli Conductivity and PorosityThe soil's air conductivity is the measure of the ability of the vapor to flow

through the porous media. It is analogous to water flow in the saturated zone. The airconductivity is perhaps the single most important parameter with respect to the successof SVE (EPA 1991). When site-specific air conductivity data are not available, theycan be predicted approximately from the water (hydraulic) conductivity.

The soils to be treated with SVE at the DS&G site are part of the ColumbiaAquifer. This aquifer consists of surficial sands and gravel and represents the regionalground water table in New Castle County. Published values of the hydraulicconductivities range from 15 to 150 feet/day (McLaren/Hart 1991). This can bedescribed as a very permeable soil. The ratio of the hydraulic conductivity to the airpermeability at 20°C is 10.8 (Krishhhnayya 1988). Expected air permeability valuesrange, therefore, from 1.4 to 14 feet/day.

Vapor flow in the subsurface occurs predominantly through air-filled voids in thesoil. If a soil has low porosity, vapor flow will be inhibited. Although no laboratorydata were readily available for this soil, coarse sands and fine gravel generally haveporosities in the range of 0.25 - 0.46 (EPA 1985), providing ample and continuousvoids for the vapor to travel.

The high permeability and existence of sufficient soil voids in the ColumbiaAquifer make this Site well suited for SVE.

2. Soil Moisture CharacteristicsWater content of the soil has two major effects on SVE. The primary effect is that

water existing in the voids of the soil matrix occupies volumes that subsequently cannotbe used in iiie transport of vapor. For this reason, a high water content diminishes theeffectiveness of an SVE operation. A secondary effect is the influence of water contenton the sorption properties. Organic contaminants are more strongly sorbed to soil

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particles in very dry soils. The optimal soil moisture is, therefore, one where soilmoisture is low enough to ensure adequate air permeability, yet wet enough to reduceelectrostatic sorption forces (EPA 1991).

Because of the highly permeable nature of these soils, it can be expected that theywill dewater quickly and although some residual soil moisture may remain, it should beremoved as water vapor early in the extraction process. The soil moisturecharacteristics of the site should be suitable to SVE treatment after dewatering hasoccurred.

3. StratigraphyAir movement in the subsurface is influenced by the stratigraphy of the site. The

proposed SVE system will have long vertical wells and, therefore, flow lines for thevapor should ideally be horizontal. Horizontal flow lines assure vapor movementthroughout the entire depth, of contaminated soils. Any vertically orientedheterogeneities will inhibit the flow of vapor. These heterogeneities may create stagnantzones, where no vapor flow occurs, and, therefore, treatment is not possible. As seenin the geological cross sections in the Remedial Action Evaluation (McLaren/Hart 1991,Appendix Al), the formations are generally horizontally stratified. The stratigraphy ofthis Site is generally conducive to horizontal subsurface airflow, which is ideal forvertical well SVE systems.

4. Depth to GroundwaterSVE only provides direct treatment to unsaturated soils, because in saturated soils

water fills the voids needed for vapor flow. The sandy layer (Columbia Aquifer) has aground water table just above the confining layer. This enables almost the entirecontaminated zone to be treated by SVE.

B. Contaminant CharacteristicsThe contaminant characteristics, in conjunction with the Site conditions and soil

properties, determine the feasibility of using a SVE treatment system. SVE is most effectivein removing VOCs, although some removal of SVOCs can also be expected. Organicanalytical results reveal that toluene, xyienes, methyiene chloride, ethylbenzene, 1,2-dichlorobenzene (1,2-DCA), benzene, chlorobenzene, and trichloroethene were the mostabundant VOCs in the soil beneath and surrounding the DDA. Bis (2-chlorethyl) ether and 4-chloro-3-methyl phenol aie the most abundant semi-volatile compounds in this area.According to McLaren/Hart calculations (McLaren/Hart 1991, Table 3-4), the total mass ofsemi-volatile components are only approximately 12% of the mass of the VOCs in theseareas. . ' - .

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1. VolatilityThe volatility of dissolved organic compounds (i.e. the tendency to be removed by

SVE) can tie indicated by the Henry's Law Constant and by the vapor pressure.Henry's Law constant quantifies the relative tendency of a contaminant to exist in vaporphase relative to a dissolved phase. The higher the Henry's Law Constant, the morevolatile. The vapor pressure quantifies the relative tendency of a contaminant to exist invapor phase relative to a pure organic phase. As with the Henry's Law coefficient, thehigher the vapor pressure the more volatile the compound.

As a guideline, a compound is an ideal candidate for successful removal by SVE ifit has both of these characteristics (EPA 1990b):

• Vapor pressure of 1.0 mm or more of mercury at 20°C.• Henry's Law Constant greater than 0.01 (dimensionless)

SVE is absolutely applicable if VOCs are the primary contaminants hi the soil, becausethey tend to meet the above criteria. Although the SVE process is not the most efficientway to remove SVOCs, any compound that meets the above criteria would be expectedto volatilize to a significant degree (EPA 1991).

Table 1 summarizes these properties for the most abundant contaminants identifiedat the DS&G site. All of the VOCs most commonly identified at the Site meet thepreviously mentioned criteria for SVE treatment and are ideal for SVE removal.Therefore, the VOCs that are present and that constitute the vast majority of thecontamination in the areas of concern are sufficiently volatile to make SVE an efficientand effective removal option for VOC contamination. Of the two SVOCs listed, bis(2-chloroethyl) ether appears to be potentially removed by SVE treatment, based upon itsvapor pressure, but 4-chloro-3-methylphenol does not. Therefore, some removal ofSVOCs by SVE is also expected.

2. Adsorptive PropertiesThe propensity of a compound to be adsorbed to the organic carbon in soil is

quantified by the soil-to-water partitioning coefficient (Kj). A high K -value indicatesstrong sorptive properties. K is the product of two other parameters f and K . The^ is the fraction of organic carbon and is a characteristic only of the soil. The K isthe organic; carbon-to-water partitioning coefficient. K -values for the contaminants ofconcern at this site range from 2.2 L/kg for acetone and 4-raethyl-2-pentanone to1,100 L/kg for ethylbenzene and styrene (EPA'1990, Appendix A). These are generallyconsidered to be low. By comparison, highly adsorbable compounds have K -values in

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TABLE 1Volatility of Contaminants of Concern

Compound

Toluene

Xylene, o-Xylene, m-Xylene, p-

Methylene chloride

Ethylbenzene

1,2 Dichloroethane

Benzene

Chlorobenzene

Trichloroethene

bis(2-chloroethyl) ether

4-chloro-3-methyl-phenol

Henry's Law Constant(dimensionless)

0.28

0.220.480.31

0.09

0.29

0.044

0.25

0.17

0.41

0.00058

0.0001

Vapor Pressure(mm Hg)

28.1

6.61010

362

7

64

95.2

11.7

58

0.7

0.05

Source: EPA (1990)

All listed values are at 20°C. These values generally agree withthose listed by other well-established references (e.g., Lyman et al(1990)).

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the range of 50,000 L/kg (Lyman et al 1990). The low adsorption expected from theseVOCs and certain SVOCs is further compounded by the fact that low levels of organiccarbon (i.e., low f can be expected in sands and gravel. Of all soil types, sands andgravels have the lowest adsorption properties (Brady 1990).

The adsorptive properties of the contaminants and soil at the DS&G site indicatethese VOC contaminants can be effectively removed by SVE.

3. Distribution of VOCsAs proposed in the Remedial Action Evaluation (McLaren/Hart 1991), the SVE

operation is to address 50,000 cubic yards of contaminated soil (15,600 cubic yards ofsoil beneath the DDA and 34,400 cubic yards of surrounding soils within the proposedslurry wall). The vertical extent of contamination has been established to include theentire depth of the Columbia Aquifer to the Upper Potomac Confining Layer whichoccurs at 25 to 40 feet below ground surface. The highest concentrations ofcontaminant are found generally at depths greater than 20 feet.

SVE with vertical wells allows the treatment of the most contaminated soils withoutdisturbing the less contaminated or uncontaminated soils. This can be accomplished byinstalling wells with perforation only in the contaminated zones. Installation of wells todepths of 40 feet is a standard construction practice. The large volumes of contaminatedsoils that occur at depths of up to 40 feet can be easily accessed by a SVE system oncethe soils are dewatered, as planned.

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V. PREVIOUS APPLICATIONS OF SOIL VAPOR EXTRACTIONAND EXPECTED PERFORMANCE

Final cleanup levels and residual contamination will depend on design characteristics andlength of SVE treatment. The intent of this report is to evaluate the anticipated effectivenessof SVE on the basis of existing information concerning site conditions, soil properties, andcontaminant characteristics. In making this determination, previous applications of SVE atother sites were also reviewed and evaluated. This section summarizes the relevant casestudies and presents the results of simulation modeling of potential SVE performance at theDS&G site.

A. Case StudiesSVE has been implemented at several Superfund sites with VOC contamination. With a

total of 31 projects (1 completed, 5 in progress and 25 in design stage), SVE has been citedmore often than any other innovative technology as a remedy at Superfund sites (Roy 1991).Three case studies of SVE treatment with site and contaminant characteristics similar to thoseat the DS&G site were identified and are summarized below. Their site characteristics arecompared in Table 2 to those found at DS&G.

1. Groveland Wells Superfund SheA demonstration of SVE was conducted under the Superfund Innovative

Technology Evaluation (SITE) Program at the Groveland Wells Superfund Site inGroveland, Massachusetts (EPA 1989c, Michaels 1989). The demonstration included aneight-week pilot test to remove VOCs from the underlying soils. The predominantcontaminant found at this site was trichloroethene (TCE), which has been identified atthe DS&G site and has similar volatility characteristics to other contaminants found atthe DS&G site (see Table 1). A vertical well extraction system was installed throughoutthe zone of contamination, which included a layer of unconsolidated glacier outwashsands and fill.

Initial TCE concentrations in the sands averaged 111 parts per million (ppm).After the eight-week test the average concentration in the sand layer was 12.3 ppm. Ofspecial interest to the DS&G site is the fact that, when analyzed by soil type, VOCs inall of the medium and medium-coarse sands, some of which contained gravel, werereduced to non-detectable levels. A total of 1,300 pounds of TCE was removed.

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TABLE 2Comparison of Case Studies

SiteCharacteristic

Soil Type

Depth ofContamination(feet)

Contaminant ofPrimaryConcern

Average SoilConcentration(mg/kgorppm)

Maximum SoilConcentration(mg/kgorppm)

Site with VOCs in Soil

DS&G

sands andgravel

40

VOCs

2902

6,410

Groveland1

sands andgravel

24

TCE

114

351

Midwest Ind.

fine to mediumsand

14

PCE

13

55

HillAFB

medium to finesand

50

Jet Fuel

no soilsampling data3

no soilsampling data3

FOOTNOTES:(1) Only data from medium-course sands were considered.(2) Calculated from average concentrations and volumes from Remedial Action

Evaluation, Table 3-4.(3) Only soil gas samples were taken and analyzed.

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2. Midwest Industrial FacilitySVE is part of a mandated soil clean up in an industrial facility in the midwest

(Ball and Wolf 1990). The soil is contaminated with tetrachloroethene (PCE), whichhas similar volatility characteristics to those found at the DS&G site. The soil in .thiscase is a fine to medium sand and 1,500 cubic yards were treated.

Initial concentrations of PCE averaged 13 ppm, with a maximum level of 55 ppmrecorded. Field data from extraction wells show that the PCE concentration in thevapors decreased more than 90% in five to six months, corresponding to an expected90% reduction in soil concentrations.

3. Hill Air Force BaseA fuel yard, where a 100,000-liter JP-4 jet fuel spill had occurred, was chosen to

test the applicability of SVE to heavier fuels (Downey and Elliot 1990). The spill hadcovered an area of approximately 120 by 120 feet and had penetrated to a depth ofapproximately 50 feet. No confirmatory soil testing was done at this site, however, soilgas readings dropped from 38,000 to 500 ppm within 10 months. Because of theheavier, non-volatile components of jet fuel, a total removal cannot be easily predicted.

What the success at the Hill Air Force Base does demonstrate is the logisticalfeasibility of applying this technology to larger and deeper zones of contamination, suchas those present at the DS&G site.

B. Potential SVE Performance hi Sandy SoilsBased on these case studies, from 90% to > 99% of the VOCs can be expected to be

removed in between 2-6 months from sandy soils, such as those found at the DS&G site. Noinformation is available for longer term projects.

These case studies establish the general treatability of VOCs in sandy soils, however, theactual achievable removal rates are dependent on the duration of operation and the SVEdesign characteristics, which must be established by appropriate field studies on the soil.

C. Performance ModelingThe performance of SVE at the DS&G site will depend upon the system design. With

the objective of estimating how quickly SVE can decontaminate dewatered soils within theproposed slurry wall system, a simple model of SVE was developed, programmed, andevaluated using parameters believed to be representative of the Site. The model is basedupon the work of Johnson et al (1990). It considers:

• simultaneous equilibrium of multiple VOCs in a three-phase (air, water, and soil)system;

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• the relationship between ambient pressure and gas density;

• VOC removal by vapor extraction, but not simultaneous biodegradation; and

• the effect of temperature on vapor flow.

It assumes that:

• the steady-state vapor air flow is uniform throughout the treatment zone, at a ratedetermined by the intrinsic permeability of the soil, the vacuum pressure in theextraction well, and the ambient pressure;

• the treated zone is dewatered to its residual moisture level before vapor extractioncommences; and

• VOCs are uniformly distributed throughout the treatment zone.

The resulting model was used to simulate the potential performance of SVE for removingVOCs from soils under and surrounding the DDA. The chemical-specific inputs for thesesimulations are listed in Table 3. The average VOC concentrations under and outside theDDA are as estimated by McLaren/Hart in the Remedial Action Evaluation (Table 3-4). Thesite- and system-specific inputs for these simulations are listed in Table 4. Figures 2 and 3present sample results for soils under and outside the DDA, respectively. The results indicatethat under conditions of ideal vapor flow SVE should be able to reduce averageconcentrations of most VOCs to below 1 mg/kg (ppm) levels within 1 year. Ethylbenzene(Figures 2 and 3) and acetone (Figure 3) are anticipated to be potential exceptions. Longertreatment durations may be required to attain less-than-1-ppm levels of these substances.Actual concentrations within the treated zone will differ from those predicted, dependingupon the initial levels at a particular location, its proximity to the extraction well, and theheterogeneity of the Site soils. The model results, however, support the conclusion that SVEcan rapidly remove VOCs from soils around and under the DDA at the DS&G site. Basedupon the modeling results for 4-chloro-3-methyl phenol1, however, SVOCs at the DS&G sitemay not be appreciably removed by SVE technology.

1 The .modeling results for 4-chloro-3-methyl phenol are not shown in Figures 2 or 3.

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Table 3Chemical-specific Parameters Assumed

for SVE Performance Modeling

Compound

Methylene chloride

Acetone

Chloroform

1,2-Dichloroethane

2-Butanone

1,1,1-Trichloro-e thane

Trichlorofluoro-methane (TCFM)

TrichloroetheneBenzene

Toluene

Chlorobcnzenc

EthylbenzeneStyreneXylcnes

4-Methyi-2-pentanone

4-Chloro*3-methyi phenol

VaporPressure(mmHg)

362

270

151

64

77.5

123

667

57.9

95.2

28.1

1L7

7.0

4

10

120

005

K_(mL/g)

8.8

2

47

14

4.5

152

159

126

83

300

330

1,100

uoo240

2

490

WaterSolubility(mg/L)

20,000

1,000,000

8,200

8420

268,500

1400

1,100

1,100

1,750

535

466

152

300

198

17tOOO

3 50

MolecularWeight(1/mol)

84.9

58.08

11938

98.96

72.12

133.4

137.4

131.4

78.11

92.13

112.6

106

104.14

106

100.2

14 6

BoilingPoiat(-K)

313

329.2

3343

365

35Z8

347

297

360

353

384

404.5

409

418.2

413

389

508

Initial SoUConcentration(mi/kg)

BelowDDA

483

0.0

0.0

106

0.0

1.97

L4

12.9

70

215

35

46.7

0.0

1803.94

22J5

OuUideDDA

2.6

6.11

0 4

0.6

0.67

0.0002

0.0

0.2

432

43.4

0.16

62

051

35.8

0.06

0.0

Sources: - -Vapor pressures, K s, and solubilities from EPA (1990, Appendix A)Molecular weights and boiling points from ITE (1986)Concentrations from the Remedial Action Evaluation (McLaren/Hart 1991, Table 3-4)

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TABLE 4Site-specific Parameters Assumed for

Modeling SVE Performance

Description

well spacing

average treatment volume per well

soil temperature

average air flow rate per well

moisture content of the soil afterdewatering

void volume ratio, or total porosity

bulk density of the soil matrix

organic carbon fraction in soilmatrix

vacuum pressure in the extractionwell

ParameterValue

75 feet

4,000 m3

289 °K

112.5 scfin

0.104

0.473

1.76 g/cc

0.2

0.95 atm

Basis for Parameter Value

assumed

calculated from a 75-ft well gridand 25-ft screened interval

represents 60.8 °F

typical extraction rate for sandysoils is 4.5 scfm/ft-screened

(EPA 1990b)

wilting coefficient torsandy/gravelly layer, previouslyassmrrd by McLaren/Hart in

HELP modeling

previously assumed byMcLaren/Hart in HELP

modeling

value assmnrd by McLaren/Hartin estimating VOC mass in the

DDA (Table 3-4 of theRemedial Action Evaluation)

previously assumed byMcLaren/Hart in HELP

modeling

typical vacuum pressure(EPA 1991)

rbk\dsg\sve3.rpt -17- ENVIRON

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VI. REFERENCES

Ball, R. and S. Wolf. 1990. Design Considerations for Soil Cleanup by Soil VaporExtraction. Environmental Progress. Vol.9, No.3, pp. 187-189

Brady, N. C., 1990. The Nature and Properties of Soils. Macmillan Press. New York, 94

Downey, D.C. and M.G. Elliot. 1990. Performance of Selected In Situ SoilDecontamination Technologies: An Air Force Perspective. Environmental Progress.Vol. 9, No. 3, pp. 169-173.

Dunn Geosciences Corp. 1988. Feasibility Study For the Delaware Sand and GravelLan&tt.

Environmental Protection Agency (EPA). 1991. Soil Vapor Extraction Technology -Reference Handbook. EPA/540/2-91/003. pp. 17-27. Office of Research andDevelopment, Cincinnati, Ohio.

Environmental Protection Agency (EPA). 1990. Basics of Pump and Treat GroundwaterRemediation Technology. EPA/600/8-90/003.

Environmental Protection Agency (EPA). 1989a. State of Technology Review - Soil VaporExtraction Systems. EPA/600/2-89/024. p. 2-7

Environmental Protection Agency (EPA). 1989b. Guidance for Conducting TreatabilityStudies under CERCLA. EPA/540/2-89/058, Office of Research and Development,Cincinnati, Ohio,

Environmental Protection Agency (EPA). 1989c. Terra Vac In Situ Vacuum ExtractionSystem. Application Analysis Report. EPA/540/A5-89/003. Office of Research andDevelopment, Cincinnati, Ohio.

Environmental Protection Agency (EPA). 1988. Record of Decision- Delaware Sand andGravel.

Environmental Protection Agency (EPA). 1985. Water Quality Assessment- A ScreeningProcedure for Toxic and Conventional Pollutants in Surface and Ground Water - PartH. EPA/600/6-85/002b. p. 318

International Technical Information Institute (rni). 1989. Toxic and Hazardous IndustrialGiemicals Safety Manual. Tokyo, Japan.

rbk\dsg\sve3.rpt -20- ENVIRON

AR30I8B2

Johnson, P.C., M.W. Kemblowski, and J.D. Colthart. 1990. Quantitative Analysis for theCleanup of Hydrocarbon-contaminated Soils by in situ Soil Venting. Ground Water _:413-429.

Krishnayya, A.V., M.S. O'Conner, J.G. Agar and R.D. King. 1988. Vapor ExtractionSystems Factors Effecting Their Design and Performance. Proceedings of PetroleumHydrocarbons and Organic Chemicals in Groundwater Prevention, Detection andRestoration, Nov. 9-11. as cited in EPA (1991, p. 27)

Lyman, W, Reehl, W. and Rosenblatt, D. 1990. Handbook of Chemical Property EstimationMethods. American Chemical Society.

Maiot, J.J., and Wood, P.R.. 1985. Low Cost, Site Specific, Total Approach toDecontamination. Conference on Environmental and Public Health Effects of SoilsContaminated with Petroleum Products University of Massachusetts, Amherst. October(as cited in EPA 1990b).

McLaren/Hart. 1991. Drum Disposal Area Remedial Action Evaluation, Delaware Sand andGravel

Michaels, Peter A. 1989. Site Demonstration of the Terra Vac In Situ Vacuum ExtractionTechnology.

Roy, K.. 1991. Vacuum Extraction Provides In Situ Clean-up of Organics-ContaminatedSoil. HazMat World. October, pp. 38-41.

Sellers, K., and C.-Y. Fan. 1991. Soil Vapor Extraction: Air Permeability Testing andEstimation Methods. In Remedial Action, Treatment, and Disposal of Hazardous Waste-Proceedings of the Seventeenth Annual RREL Hazardous Waste Research Symposium,EPA/600/9-91/002. April.

Wilson, D.J., R.D. Mutch, Jr. and A.N. Clark. 1989. Modeling of Soil Vapor Stripping.Presented of Workshop on Soil Vapor Extraction, R.S. Kerr Environmental ResearchLaboratory Ada, OK. as cited in EPA (1991, p. 58)

rbk\dsg\sve3.rpt . -21- , -ENVIRON

flR30!883

ATTACHMENT ASVE CASE STUDIES

QEMQNSTRATrQM QF THE TERRA VAC IN SITU VACUUM EXTRACTS TECHNOLOGY

by: Peter A. Michaels Mary K. StinsonFoster Wheeler Envlresponse, Inc. USEPA, RC8, RRELEdison, NJ 08837 Edison, NJ 08837

ABSTRACT

Term Vac Inc's vacuum extraction system was the subject of a SITEprogram demonstration test in Groveland, Massachusetts. The site chosen wascontaminated «1th volatile organic compounds, mainly trlchloroethylene, whichwere used as degreasing solvents in an operating machine shop on the site. *

The eight-week test run produced the following results:o extraction of 1,300 1b of VOCso a steady decline in the VOC recovery rate with timeo a marked reduction in soil VOC concentration in the test areao an Indication that the process can remove VOCs from clay strata

The system operation proved to be very reliable. Upon achievement of asteady operation, the only stoppages occurred in order to replace spentactivated carbon canisters with fresh canisters.

flR3.0!885

INTRODUCTION

This SITE program demonstration test was planned to determine theeffectiveness of Terra Vac Inc's vacuum extraction technology in theremoval of volatile organic compounds from the vadose zone. The locationof the test was on the property of an operating machine shop. The propertyis part of a Superfund site and is contaminated by degreasing solvents,mainly trkhloroethylene.

OBJECTIVES

The main objectives of this project were:o The quantification of the contaminants removed by the process.o The correlation of the recovery rate of contaminants with time.

o The prediction of operating time required before obtaining siteremediation.

o The effectiveness of the process in removing contamination fromdifferent soil strata.

APPROACH

The objectives of the project were achieved by following ademonstration test plan which included a sampling and analytical plan. Thesampling and analytical plan contained a quality assurance project plan.This QAPP assured that the data collected during the course of this projectwould be of adequate quality to support the objectives.

The sampling and analytical program for the test was split up into apretest period, which has been called a pretreatment period; an activeperiod; midtreatment; and a posttreatment period.

The pretreatment period sampling program consisted of:o soil boring samples taken with split spoonso soil boring samples taken with Shelby tubeso soil gas samples taken with punch bar probes

Soil borings taken by split spoon sampling were analyzed for volatileorganic compounds (VOCs) using headspace screening techniques, purge andtrap, GC/W procedures, and the EPA-TCLP procedure. Additional propertiesof the soil were determined by sampling using a Shelby tubt, which waspressed hydraulically into the soil by a drill rig to a total depth of 24feet* These Shelby tube samples were analyzed to determine physicalcharacteristics of the subsurface stratigraphy such as bulk density,particle density, porosity. pH. grain size, and moisture. These parameterswere used to define the basic soil characteristics.

AR3 6T8 8 6

Shallow soil gas concentrations were collected during pre-, mid-, andposttrentment activities* Four shallow vacuum monitoring wells and twelveshallow punch bar tubes were used at sample locations. The punch barsamplts wtrt collected from hollow stainless steel probes that had beendriven to a depth of 3 to 5 feet. Soil gas was drawn up the punch barprobes tilth * low-volume personal pump and tygon tubing. Gas-tight SO-mlsyringe*; were used to collect the sample out of the tygon tubing.

The active treatment period consisted of collecting samples of:o wellhead gaso separator outlet gaso primary carbon outlet gas

o secondary carbon outlet gaso separator drain water

All samples with the exception of the separator drain water wereanalyzed on site. On-site gas analysis consisted of gas chromatographywith a flame ionization detector (FIO) or an electron capture detector(ECO). The FID was used generally to quantify the trichloroethylene (TCE)and trans l,2-d1chloroethylene (DCE) values, while the ECO was used toquantify the 1,1,1-trichloroethane (TRI) and the tetrachloroethylene (PCE).values. The use of two detectors, FID and ECO, was necessitated by highconcentrations of TCE in the extracted well head gas. Owing to the highTCE concentrations, most of the samples injected on the ECO had to bediluted* Even with dilution factors of 333 to 1, the TCE concentration onthe ECO would exceed the linear range of the detector, thus necessitatingthe use of two detectors.

The separator drain water was analyzed for VOC content using SW8468010. [Moisture content of the separator inlet gas from the wells wasanalyzed using EPA Modified Method 4. This method is good for thetwo-phase flow regime that existed in the gas emanating from the wellhead.Table 1 lists analytical methods used for this project.

The posttrtatment sampling essentially consisted of repeatingpretreatment sampling procedures at locations as close as possible to thepretreatment sampling locations.

Thit activated carbon canisters were sampled, as close to the center ofthe canister as possible, and these samples were analyzed for VOC contentas a chtck on the material balance for the process. The method used wasP&CAM 127, which consisted of desorption of the carbon with CS2 andsubsequent gas chromttographic analysis.

PROCESS DESCRIPTION

Tho vacuum extraction access is a technique for the removal and

AR30I887

TABLE 1. ANALYTICAL METHODS

Parameter Analytical method Sample Source

Grain size ASTM 0422-63 Soil borings

pH SW846* 9040 Soil borings

Moisture (11Q°C) ASTM 02216*80 Soil borings

Particle density ASTM 0698-78 Soil borings011 and grease SW846* 9071 Soil borings

EPA-TCLP F.R. 11/7/86, Soil boringsVol. 51, No. 216,SU846* 6240

TOC SW846* 9060 Soil borings

Headspace VOC SW846* 3810 Soil boringsVOC GC/FID or ECD Soil gas

VOC GC/FIO or ECO Process gasVOC SW846* 8010 Separator liquid

VOC SW846* 8010 Groundwater

VOC Modified P&CAN 127 Activated carbon

VOC SU846* 8240 Soil borings

*Third Edition, November 1986.

AR3QI888

venting of volatile organic constituents (VOCs) from the vadose orunsaturated zone of soils. Once a contaminated area is completely defined,an extraction well or wells, depending upon the extent of contamination,will be Installed. A vacuum pump or blower induces air flow through thesoil, stripping and volatilizing the VOCs from the soil matrix into the airstream. Liquid water is generally extracted along with the contamination.The two-phase flow of contaminated air and water flows to a vapor liquidseparator where contaminated water is removed. The contaminated air streamthen flows through activated carbon canisters arranged in a parallel-seriesfashion. Primary or main adsorbing canisters are followed by a secondaryor backup adsorber in order to insure that no contamination reaches theatmosphere. Figure 1 illustrates the layout of wells and equipment.

EQUIPMENT LAYOUT AND SPECIFICATIONS

Specifications are given in Table 2 for the equipment used in theinitial phase of the demonstration. This equipment was later modified whenunforeseen circumstances required a shutdown of the system. Thevapor-liquid separator, activated carbon canisters, and vacuum pump skidwere inside the building, with the stack discharge outside the building.The equipment was in an area of the machine shop where used cutting oilsand metal shavings had been stored.

Four extraction wells (EW1-EW4) and four monitoring wells (MW1 - MW4)were drilled south of the shop. Each well was installed in two sections, •one section to just above the clay lens and one section to just below tht •clay lens. The extraction wells were screened above the clay and below theclay. As shown in Figure 2, the well section below the clay lens wasisolated from the section above by a bentonite Portland cement grout seal.Each section operated independently of the other. The wells were arrangedin a triangular configuration, with three wells on the base of the triangle(EM2, EH3, EH4) and one well at the apex (EW1). The three wells on thebase were called barrier wells. Their purpose was to interceptcontamination, from underneath the building and to tht side of thedemonstration area, before this contamination reached the main extractionwell (EN1). The area enclosed by the four extraction wells defined thearea to bo cleaned.INSTALLATION OF EQUIPMENT

Well drilling and equipment setup were begun on December 1, 1987. Amobile drill rig was brought in, equipped with hollow-stem augers, splitspoons, and Shelby tubes. The locations of the extraction wells andmonitoring wells had been staked out previously based on contaminantconcentration profiles from a previously conducted remedial investigationand from bar punch probe soil gas monitoring.

Each well drilled was sampled at 2-foot Intervals with a split spoonpounded into tht subsurface by the drill rig in advance of tht hollow stemauger. Tht hollow stem auger would then clear out tht soil down to thtdepth of tht split spoon, and the cycle would continue in that manner to adepth of 24 feet. Tht drilling tailings wtre shoveled into 55-galIon drums

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TABLE 2. EQUIPMENT LIST

Equipment Number required Description

Extraction wells 4 (2 sections each) 2" SCH 40 PVC 24* total depth

Monitoring wells 4 (2 sections each) 2" SCH 40 PVC 24* total depth

Vapor-liquid 1 1000-gal capacity, steelseparator

Activated carbon Primary: 2 units in Canisters with 1200 Ib of carboncanisters parallel in each canister - 304 SS

Secondary: 1 unit 4* inlet and outlet nozzles

Vacuum pump skid 1 25 HP motor * positive displace-ment lobt typt blower - 3250 rpm

Holding tiink 1 2000-gal capacity • steelPump 1 1 HP motor - centrifugal

for eventual disposal. After the holes were sampled, tht wells wtrtinstalled using 2-inch PVC pipes screened at various depths depending upontht characteristics of tht soil in tht particular holt. Tht deep well wasinstalled first, screened from the bottom to various depths. A layer ofsand followed by a layer of bentonite and finally a thick layer of groutwere required to seal off tht section below tht clay lens from the sectionabove tht clay Itns. Tht grout was allowtd to stt overnight before theshallow will pipe was installed at tht top of tht grout. A layer of sandbentonitt and grout finished tht installation.

VOC REMOVAL FROM THE VAOOSE ZONE

Tht piirmtablt vadost zont at tht Groveland sitt is divided into twolaytrs by a horizontal clay lens, which is relatively impermeable. Asexplained prtviously, each extraction wtll had a stparatt shallow and deepsection to enable VOCs to be extracted from that section of tht vadost zoneabove and btlow tht clay lens. The quantification of VOCs removed wasachieved by measuring

o cias volumttric flow rate by rotamtttr and wellhead gas VOCconcentration by gas chromatography

flR3QI89l

o tht amount of VOCs adsorbed by tht activated carbon canisters bydtsorptlon into CS2 followtd by gas chromatography.

VOC flow rates were measured and tabulated for each well section separ-ately* Tht rtsults of gas sampling by syringe and gas chromatographicanalysis Indicate a total of 1,297 Ib of VOCs were extracted over a 56-dayperiod, 95% of which was trichloroethylent. A very good check on thistotal was madt by tht activated carbon VOC analysis, tht rtsults of whichindicated a VOC recovery of 1353 Ib; virtually the samt result was obtainedby two very different methods.

One view of tht reduction in VOC concentrations in the vadose zone canbe seen fro* examining the three-dimensional shallow soil gas plots. Soilgas was collected during pretreatment, midtrtatmtnt, and posttreatment frompunch bar probes and shallow vacuum monitoring wells. Tht collectionpoints wtrt located on a coordinate system with extraction well 1 as theorigin (0,0). Each collection point has an x and y coordinate, and TCEconcentrations are plotted on a "Z" scale, which gives a three-dimensionalplot across tht grid. Values of "Z" bttween data points and around thegrid art gtntrated by the Kriging technique, which uses given data pointsand a regional variable theory to generate values betwttn and around samplelocations. Kriging 1s the name given to the least squares prediction ofspatial processes and is used in surface fitting, trend surface analysis,and contouring of sparse spatial data.

A total of twelve shallow punch bar tubes were utilized along with thtfour shallow vacuum monitoring wells. Tht punch bars wtrt driven to adepth of 3 to 5 feet, and as with tht vacuum wells, soil gas was drawn upthe punch bar probes with a low-volume personal pump and tygon tubing.50-*1 gas-tight syringes were used to collect the sample out of tht tygontubing. Tht gas samples were analyzed in tht field trailer using gaschroMtographs with flame ionization dtttctors and tltctron capturtdetectors.

The soil gas rtsults show a considerable reduction in concentrationover tht courst of tht 56-day demonstration period as can bt seen fromFigures 3 and 4. This is to bt expected since soil gas is tht vapor haloexisting around tht contamination and should bt relatively easy to removeby vacuum methods.

A more modest reduction can bt sttn in tht rtsults obtained for soilVOC concentrations by fiC/MS purgt-and-trap analytical techniques. Soilconcentrations include not only the vapor halo but also Interstitial liquidcontamination that is either dissolved in tht moisture in tht soil orexisting as * two-phase liquid with tht moisture.

Tablt 3 shows tht reduction of tht weighted avtragt TCE levels in thesoil during tht courst of the 56-day demonstration test. Tht weightedaverage TCE level was obtained by averaging soil concentrations obtainedevery two feet by split spoon sampling methods ovtr tht entire 24-footdepth of tht wtlls. The largest reduction in soil TCE concentrationoccurred 1n EM, which had t*e highest initial level of contamination.

flR3QI892

3. PrfCrt«i«tnt ;-tita» tail 911 canctfltrutM.

flR30!893

TAiLE 3. REDUCTION OF WEIGHTED AVERAGE TCE LEVELS IN SOIL(TCE Cone, in mg/kg)

Extraction Well

1234

Monitoring Well1234

Pretreatment

33.983.386.39

96.10

1.1014.75227.31

0.87

Posttreatment

29.312.366.304.19

0.348.9884.50l.OS

% Reduction

13.7430.138.5695.64

69.0939.1262.83

EU1, which was expected to achieve tht greatest concentration reduction,exhibited only a minor decrease over the course of tht test. Undoubtedlythis was because of the greater-than-expected level of contamination thatexisted in tht arta around MW3 that was drawn into tht soil around EW1.Tht decrease in the TCE level around HW3 tends to bear this out.

EFFECTIVENESS OF THE TECHNOLOGY IN VARIOUS SOIL TYPES

Tht soil strata at tht Grovtland site can bt characterized generally asconsisting of tht following typts In ordtr of increasing depth:

o medium to vtry fine silty sands

o stiff and wtt clays

Soil porosity, which is tht ptrcentagt of total soil volumt occupied byports, was relatively the same for both tht clays and tht sands.Typically, porosity ovtr the 24-foot dtpth of tht wells would rangt between40* and SO*. Permeabilities, or more accurately hydraulic conductivities,ranged froa 10"* on/sec for tht sands to io:8 cm/stc for tht clays,with corrtspondlng grain sizes equal to 10"1 m to 10° im.

Pretest soil boring analyses indicated In general that most of thtcontaalnation «as in tht strata abovt tht clay Itns with a considerablequantity ptrchcd on top of the clay lens. This was tht cast for EW4, which

showed an excellent reduction of TCE concentration in tht medium to fintsandy soils existing abovt tht clay layer, with no TCE dtttcted in the clayin either tht pretest or posttest borings (set Tablt 4). One of tht wellshowever, w«s an exception. This was NU3, which contained tht highestcontamination levels of any of tht wtlls, and was exceptional in that mostof tht contamination was in a wet clay stratum. Tht levels ofcontamination wtrt in tht 200-1600 ppm rangt btfort tht test.

After the test, analyses of tht soil boring adjacent to HW3 showedlevels in tht rangt of NO-60 ppm in tht samt clay stratum. Tht data, asshown in Tablt 5, suggtst that tht technology can dtsorb or otherwisemobilize VOCs out of ctrtain clays.

From tht rtsults of this demonstration It appears that tht permeabilityof a soil need not bt a consideration in applying tht vacuum extractiontechnology. This may bt explained by tht fact that tht porosities wereapproximately tht samt for all soil strata, so that tht total flow area forstripping air was tht same in all soil strata. It will take a long timefor a liquid contaminant to percolate through clay with its small port sizeand consequent low permeability. Howtvtr, tht much smaller air moleculeshave a lower resistance in passing through tht samt ports. This mayexplain why contamination was generally not present in tht clay strata, butwhen it was, it was not difficult to remove. Further testing should btdont in ordtr to confirm this finding.

CORRELATION OF DECLINING VOC RECOVERY RATES

Tht vacuum extraction of volatile organic constituents from tht soilmay bt viewed as an unsteady state process taking pi act in a nonhomogeneousenvironment acted upon by the combined convective forces of Inducedstripping air and by tht diffusion of volatllts from a dissolved or sorbedstatt. As such it Is a vtry complicated process, even though tht equipmentrequired to optratt tht proctss is vtry simple.

Unsteady statt diffusion proctssts in gtntral correlate well byplotting tht logarithm of tht ratt of diffusion vtrsus tint. Although therepresentation of tht vacuum extraction process presented htrt might btsomtwhat simplistic* tht correlation obtained by plotting tht logarithm oftht concentration of contaminant in tht wellhead gas vtrsus time andobtaining a least squarts btst fit lint was reasonably good. This typt ofplot, shewn in Figurt 5, represents tht data vtry well and 1s more validthan bothi a 1 Inter graph or ont plotting concentration vtrsus log timt, inwhich a test fit curvt would actually predict gas concentrations of zero or.less.

Looking at tht plots for EW1, shallow and dttp, equations art givtn fortht least squarts btst fit lint for tht data points. If tht vacuumextraction proctss Is run long enough so that tht detection limit for TCEon tht ECO, which 1s I ppbv, is reachtd, tht Itngth of timt rtqulrtd tortach that concentration would bt approximately 250 days on tht shallowwell and approximately 300 days on tht dttp well.

AR3GI895

TABLE 4. EXTRACTION WELL 4:TCE REDUCTION IN SOIL STRATA

Otpthft

0-22-44*66-88-10

10-1212-1414-1616-1818-2020-2222-24

Otscriptlon Permeability TCE Cone, ppmof strata on/ sec pre post

Htd. sand w/gravtlLt. brown fine sandMed. stiff It. brown fint sandSoft dk. brown fine sandHtd. stiff brown sandV. stiff It. brown mtd. sandV. stiff brown fint sand w/slltH. stiff grn-brn clay w/siltSoft wet claySoft wtt clayV. stiff bm mtd-coarst sandV. stiff brn mtd-coarse w/gravel

lo-J10 s10 S10-J10 *J10 110 «lO'JlO'JID-;10-*10*3

2.9429.90260.0303.0351.0195.0

3.14NONONONO6.71

NONO399

NONO2.3

NONONONONO

TABLE 5. MONITORING HELL 3:TCE REDUCTION IN SOIL STRATA

Dtpth Otscription Ptrmablllty TCE Cone, ppmft of strata cn/stc prt post

0-2 H. stiff brn. f1n« sand 10'f 10.30 NO2-4 M. stiff grty fint sand 10** 8.33 3004-6 Soft It. brn. f1n« sand 10'* 80.0 846-S Lt. brn. f1n« sand 10'* 160.0 NO8-10 Stiff V. f1n« bm. silty sand 10'* NO 6310-12 Sllty sand 10'* NR 2.:12-14 Soft brown silt 10'* 316.0 NO14-1S Wtt grwn-brown silty clay 10'f 195.0 . NO16-18 tfet grtm-brown silty clay 10'! 218.0 6218-20 Vfct grwn-brown silty clay 10*° 1570.0 2.20-22 Silt, grtvtl, and rock frag. 10'? 106.0 NO22-24 «. stiff H. brn. med. sand 10'* 64.1 NO

flR30!896

PREDICTION OF TIME REQUIRED FOR SITE REMEDIATION

Tht soil concentration that would bt calculated fro* tht wellhead gasconcentration using Henry's Law is included in tht last column of Table 6.Calculations for tht predicted soil concentrations wtrt made assuming abulk dtnslty of tht soil of 1761 kg/m*f a total porosity of 50%, and amoisture content of 20%. The calculated air filled porosity of the soil 1sapproximately 15%. Henry's constant was taktn to bt 0.492 KPa/nr-gmol at405F.

Given the nonhomogeneous nature of tht subsurfact contamination andinteractions of TCE with organic matter in tht soil, it was not possible toobtain a good correlation between VOC concentrations in wellhead gas andsoil In order to prtdict site remediation tints. Henry's Law constantswtrt ustd to calculate soil concentrations from wellhead gas concentrationsand the calculated values obtained, correcting for air filled porosity,were lowtr than actual soil concentrations by at least an order ofmagnitude (set Tablt 6).

COMPARISON OF WELLHEAD GAS VOCCONCENTRATION AND SOIL VOC CONCENTRATION

Predicted by-TCE concentration Henry's Law

Extraction Well ppmv in soil ppmw ppmw

IS 9.7 54.5 0.11ID 5.6 7.2 0.072S 16.4 NO 0.2020 14.4 20.4 0.173S 125.0 20.9 1.533D 58.7 18.Q 0.744S 1095.6 9.1 12.49

Before one can attempt to makt a rough estimation of tht remediationt1»t, a targtt value for tht particular contaminant in tht remediated soilmust bt calculated. This targtt concentration is calculated by.using twomathematical modtls, the.Vertical and Horizontal Spread Model I*' and thtOrganic Ltachatt Model**'. The mathematical modtls allow tht ust of aregulatory standard for drinking water in order to arrive at a target soilconcentration.

Tht VHS model Is expressed as tht following equation:Cy m C0 erf (Z/(2(a2Y)° 5)) erf (X/(atY)°-5)

flR30!897

where:

erfZYX

az

concentration of VOC at compliance point (mg/1)concentration of VOC in Itachate (mg/1)error function (dlmtnsionltss)penetration depth of leachate into the aquiferdistance from site to compliance point (m)length of site measured perpendicular to the direction ofground water flow (m)lateral transverse dispersivlty (m)vertical dispersivity (m)

A simplified version of the VHS model 1s most often used, which reducesthe above equation to:

Cy - C0Cf

where:Cf - erf (Z/(2(azY)°-5)) erf (X/(atY)°-5), which Is

reduced to a conversion factor corresponding to the amount ofcontaminated soil

The Organic Leachate Model (OLM) is written as:

C0 - 0.00211 CS°-678S°-373

where:CQ * concentration of VOC in leachate (mg/1)C" - conctntration of VOC in soil (mg/1)S - solubility of VOC in wattr (mg/1)Tht regulatory standard for TCE In drinking wattr Is 3.2 ppb. This

regulatory limit is used in tht VHS modtl as tht compliance pointconcentration in order to solvt for a value of tht leachate concentration.This value of leachate concentration Is then used in tht OLM modtl to solvefor tht targtt soil conctntration.

Onct tht targtt soil conctntration is determined, a rough estimation oftht remediation t1at can bt made by taking tht ratio of soil concentrationto wellhead gas conctntration and extrapolating in order to arrive at awellhead gas concentration at tht targtt soil conctntration. Thtcalculated targtt soil concentration for this site Is 500 ppbw. Thiscorresponds to an approximate wellhead gas conctntration of 89 ppb forEU1S. Tht aquation correlating wellhead gas conctntration with timt (setFigurt 5} 1s then solved to givt ISO days running timt.

Afttr 150 days tht vacuum extraction system can bt run intermittentlyto stt if significant increases in gas concentrations occur uponrestarting, afttr at Itast a two day stoppagt. If thtrt art no appreciableIncreases in gas conctntration, the soil has reached Its residual

AR30I898

equilibrium contaminant concentration and tht system nay bt stopped andsoil borings taktn and analyzed.(a) EPA Ihraft Guidelines for Petitioning Waste Generated by tht Petroleum

Refinery Industry, June 12, 1987.ACKNOWLEDGMENTS

Tht authors wish to thank Mr. Jamts S. Ciritllo, formerly of tht U.S.Environmental Protection Agency, Region I, Boston, Massachusetts at thetime of tht projtct, for his efforts during tht courst of this project. Aspecial note of gratitude is to bt givtn to Mr. Thomas Quinlan of thtValley Manufactured Products Company, Inc. for his special support andcooperation that helped make this project a successful one.

*c oo*o«Tn»rH» EXTRACTION WELL ftSHALLOW

1000

SQ.^ 100

O '

Oo0.1UJ

CJ

0.01

CUflVC

20 *0 60 80 100DAY OF ACTIVE TREATMENT

Figure 5. Vtllhtad TCE concentration vs. time.

Design Considerations forSoil Cleanup by

Soil Vapor Extraction

Raymond Ball and Steve WolfENSR Consulting and Engineering, 35 Nagog Park, Acton, MA 01720

The development and application of innovative technologies for soilremediation it rapidly evolving. Soil vapor extraction hat been identified atone of the most attractive technologies for remediating volatile organic

compound* in unsaturated zone (above the groundwater table) soil, becauseit is effective and economical. However, the design basis for applying thistechnology is not well documented. This paper presents a state-of-the-artapproach for design and implementation of a soU vapor extraction system

to remediate soil at a federal site in the Midwest contaminatedwith tetrachhroethylene.

INTRODUCTION excavated soil piles. When applied in «fu, very littleabove-ground space is required; hence, disruption to sur-

One of the most attractive technolofies for remediating fae activities is minimal. In certain situations, soil vaporsoils contaminated with volatile organic compounds extraction can be combined with biore-nediation to reme-tVOC) or light petroleum hydrocarbons, such as gasoline, diate unsaturated zone soils containing less volatile resid-is soil vapor extraction. Also known as soil venting or vac- ua] contaminants or it can be integrated with groundwateruum extraction, this method can usually be perfoimed treatment systems for complete remediation of the unsat-within a relatively short time and for minimal cost urated and saturated zones.Typical remediation co*ts for sod vapor extraction a* Soil vapor extraction is performed by applying a vac-

small sites with shallow sods in the unsmturated zone are uum to the soils to induce volatilization of soil contami-approximately S30 to $60 per cubic yard (0.8 cubic meter)/ nants. The extracted air is usually treated for VOC re-Typical remediation times are four to eight months. Ac- moval prior to discharge to ambient air. However,timl remediation costs and times will vary from site to site treatment requirements depend on the air discharge reg-und depend on many factors, such as contaminant type ulations of the state in which the project is located. Cur-and quantity, areal «tent and depth of soil contamina- rently available treatment technologies for the extractedtion, and soil stratigraphy [1 ]. air include activated carbon adsorption, incineration, and

biofiltration.APPLICATIONS Typical data requirements necessary for site characteri-

zation and soil vapor extraction system design are pre*Soil vapor extraction has proved to be effective for the sented in Table 1. The amount of data and analyses

removal of VOC and light petroleum hydrocarbons from needed for such characterization and design depends onsubsurface soils beneath underground storage tanks and the size and complexity of the site. For example, a smallpipelines as well as in surftcial spill areas. It can be ap- site with homogeneous and i so tropic soil and a singleplied either in situ to subsurface soils, or above ground to contaminant will require less data and analyses than aEnvironmental Progress (Vol. 9, No. 3) fi P '•j 0 I Q fl fl Augutt, 1990 187

TKBLE I EM DESIGN

Data Requirement Method of Data Collection

Areal and Vertical Extent Soil Borings, Soil Gas Surveyof Soil Contamination

Areal and Vertical Extent Groundwater Monitoring Wellsof GroundwaterContamination

Depth to Croundwater Groundwater Monitoring WellsPhysical Properties of Lab Analysis, Borehole Geophysicsthe Soil

Contaminant T> pe and Field and Lab AnalysesConcentration ' Gag >

Chemical Properties of Reference Materials. Lab Analysis _ .Contaminants - fiqun 2. Conceptual diagram of soil vapor ttrroction and tiwtmtnt

boil Cleanup Standards Regulatory Agency and/or equipnwntRisk Assessment

TABLE 2. DESIGN CONSIDERATIONSlarge complex site with heterogeneous and anisotropic ———-—-————————————————————————————soils containing multiple contaminants. Analytical tools Physical Site Constraints Above or Below Groundsuch as computer models can be used for evaluating pro- Partitioning of Contaminants in the Vadose Zone Soilsposed designs of the soil vapor extraction system. Potential for Volatilization of Contaminants from the Ground-

_, . i ^ - i i , -i i water and Subsequent Recontamination of Vadose Zone SodsThe data presented in Table 1 are required to evaluate Potential Integration of Soil Vapor Extraction System with En-

the feasibility ok applying soil vapor extraction at a speci- hanced Biodegradatipn and/or Groundwater Treatmentfie site. In general, the contaminants must have sufficient Optimization of Subsurface Airflow Pattern (Airflow Rate andvolatility, and the soil must have sufficient air permeabil- Extraction/Injection Well Layout)ity for soil vapor extraction to be feasible. Sometimes a Off-Gas Treatmentfraction ok" the site contaminants is sufficiently volatile to Management of the Soil Vapor Extraction Systembe removed by soil vapor extraction, and the remaining Remediation Time and Total Project Costsfraction is not. [f the nonvolatile fraction is biodegradableand the soil has sufficient air permeability, it may be pos- REPUDIATION CASI STUDYMble to perform m ?i£u bioremediation of the unsaturatedzone soil by inducing subsurface air flow as with soil One example of a soil remediation project by soil vaporvapor extraction and by adding nutrients. In certain situ- extraction is an ongoing (January, 1990) mandated reme-ations. buxlegradation occurs naturally without nutrient diation of soils contaminated with tetrachloroethyleneaddition. (PCE) at an industrial facility in the Midwest The soil

I An integrated systems approach must be taken to reme- contamination resulted from past industrial wastewaterdiate a Mte with contaminated soil and groundwater. As discharge to a network of leaching sumps. This practiceshown in the left hand side of Figure I. the groundwater was curtailed in the early 1980s when groundwater con-table is lowered during groundwater pumping and treat- tamination was discovered near the site. The PCE-con-ment. This effectively increases the depth of the unsatu- tain ing wastewater had leached from the sumps and infil-rated zone, and thus can improve volatilization and cap- trated the soils, eventually reaching the groundwatertare efficiency of VOCs by the soil vapor extraction table. From there, the groundwater transported the PCEsystem. As shown on the right hand side of Figure 1, the off-site, forming a large contamination plume. Under agroundwater treatment system will often be in operation consent decree, the EPA mandated that the potentiallyduring and after the unsaturated zone soil remediation is responsible party (PRP) remediate on-site contaminatedcomplete, and the soil vapor extraction system is re- soils as part of the remedial solution to reduce futuremoved. Note that bioremediation of soil or ground water is groundwater contamination.not depicted in this figure. ENSR investigated the extent of soil contaminationA conceptual diagram for a soil vapor extraction system wit*» soil borings and a soil gas survey. Table 3 presents

is shown in Figure 2 with activated carbon treatment of «te characteristics which were determined to assess thethe extracted 4iir prior to ambient discharge. Design con. feasibility of remediation by soil vapor extraction. TheseMderations tor a soil vapor extraction system are given in «*«j characteristics were used to develop a conceptualTable 2 model ok the subsurface contamination, which was

critical to design of the air extraction and injection well

TAILE 3. CASE STUDY-SITE CHARACTERISTICS

Size 40ft x 75ft(12m x 23m)Area 3000 square ft (280 square

meters)Soil Volume 1500 cubic yards (1200 cubic

meters)Unsaturated Zone Depth 14 ft (4.3 m)Contaminant: Tetrachloroethylene (PCE)Maximum Concentration 55 ppmAverage Concentration 13 ppm

Soil Type Fine to Medium SandHomogeneous and ho tropic

: Soil Moisture 8.5%Soil Porosity 0.35

1. Inttgrattd sysrwit approach to sit* ramtdiatioii. Air Permeability of Soil 6.0E-7 square cm

189 August, 1990 ADO n EpYJfyf I*11*0! Progr*** (Vol. 9, No. 3)

, C\SE STUDY—OPERATING CHARACTIRISTICS

Vacuum Source Single Vacuum SourceWell Vacuum 6 inch HjO (15 cm H2O)Air Flow Rate £60 cftn tT400 liten/min)Extraction Wells 6Injection Wells 11Impermeable Cap Pavement—HOPE LinerMonitoring PCE Concentrations:

Exhaust GAS. Soil Gas, Soil

Figure 4. COM study «t« pten.

ENSR constructors installed the soil vapor extractionsystem and is implementing the soil cleanup (Figure 4).During cleanup, the subsurface vacuum, the in-groundsoil PCE vapor concentrations, and the extracted air PCEconcentrations are being monitored. A comparison of theactual extracted air PCE concentrations with predictedconcentrations is presented in Figure 3. The field data inFigure 3 are the average PCE concentrations of the air ex-tracted from the six extraction wells. The decay in PCEconcentration in the extracted air from field operations

o 2000 4000 sooo 8000 10000 parallels that of the laboratory column test. Asexpected, itis somewhat lower because the soil used in the laboratory

*« V«kmw< *f Itatod Vopw column test was collected from the area of the site withthe highest PCE concentrations. The spike in the field

Fiqtw. 3. COM rtWy ttrracfclorocrhylm tmtuioit «t« from laboratory concentrations at 2500 pore volumes was due to a shiftcolumn itutfy «*4 fitW 4«t« from soil v**«r •xtrKriwi. from equai extraction rates at all six wells to extraction at

only the two wells with the highest residual concentra-tions.

system. In addition, state-of-the-art computer analyses ofthe subsurface airflow induced by the soil vapor extrac-tion process were performed to select optimal locations CONCLUSIONSfor the wells [2], Operating characteristics of the soilvapor extraction system are presented in Table 4. Soil vapor extraction has found wide application for siteTo estimate the remediation time required to achieve remediation of VOC-contaminated soils. However, the

the desired cleanup criteria of 1 ppm in the soil, a labora- subsurface airflow and contaminant transport processestory column study was performed [3]. A sample of soil are complex and not generally understood. Based on em-taken from an area of the site containing the maximum pineal analysis of the complex contaminant transport pro-amount of PCE was loaded into a laboratory soil column. cesses induced by the subsurface airflow using a labora-A siTul I .airflow representative of the airflow rate achieved tory soil column and subsurface airflow modeling, it isin a full scale soil vapor extraction system was passed possible to provide an estimate of soil remediation timethrough the laboratory soil column. The PCE emission and cost at contaminated sites. Additionally, the fe as i bit-rate- was determined by measuring the concentration of ity of different remedial options in which soil vapor ex-PC E in the exhaust air from the column as a function of traction might be used in conjunction with other technol*the pore volumes of air that had been eluted through the ogies is more readily assessed using the approachcolumn {Figure 3). An exponential decay equation was fit described in this paper. This approach is well suited toto the laboratory data. As the site was relatively small and small sites without excessive complexity due to heteroge-the on-Mte soils were homogeneous and isotropic, the neous and anisotropic soils or multiple contaminants.modeled PCE emission rate curve from the laboratory Where this is not the case, an in situ vacuum pump testcolumn study was scaled-up to predict the PCE emission may be more appropriate than a laboratory soil columnrate for the full scale soil vapor extraction system. test for determination of design data.Average PCE concentrations at the site were deter-

mined from borehole soil samples. Th« laboratory-deter- imtATUMCITtDmined emission rate was used to estimate the total soil re-mediation time (five to six months at the given extraction „ , « . , , - , , ,~~~.*rate) and the cost of remediation. ENSR also used this l- £PA Superfund Innovative Technology Evaluation (SITE)analysis to demonstrate to state regulators that the PCE J 0*"- P f0" Terr\V!± iSffSSSSnS&emission rate during the predicted remediation period ££' <*»***• M«s«hiuett» (May 1989) EPA*MO/5WK*would not exceed the state air quality standards. Require- 2. Personal Communication, Gabriel Sabadell. Department ofments for treatment of the extracted soil vapor were Civil Engineering, Colorado State University (June 1989).waived, reducing the cost of remediation for the PRP by 3. Report on Laboratory Column Study submitted under sub-approximately 15%., ___ _ contract to ENSR Corporation by VAPEX Inc. (May 1989).

ft R3QI 902EnvirofinMittal Pregms (Vol. 9, No. 3) W n A «*.

Performance of Selected In Situ SoilDecontamination Technologies:

An Air Force PerspectiveDouglas C. Downey and Michael G. EIHott

Air F:orce Engineering and Services Center, Tyndall AFB, FL 32403Every year, the U.S. Air Force stores and transfers three billion gallons ofJP-4 jet fuel. Unfortunately, not every gallon of fuel has been consumed inflight. Fuel spills account for nearly half of the chemically contaminated

sites on Air Force installations and that percentage is growing asunderground storage systems are more closely inspected. The Air ForceEngineering and Services Laboratory is responsible for developing and

testing new and more cost effective technologies capable of cleaning up fuelspills in a variety of soil and groundwater conditions. Special emphasis has

been placed on soil decontamination because our sampling data hasconfirmed that the majority of spilled fuel is adsorbed or occluded in the

soil above the water table.

INTRODUCTION _ accessible fuel residual. Fuels become trapped in soilmicro pores and form a thin film over the large surface

This paper summarizes the results of several field tests area of these fine-grained materials. Water attempting towhich have used a variety of in situ technologies to treat convey a chemical or biological treatment media to thesesoil contamination. Observations on the success and fuels is limited both by a low hydraulic permeability andshortfalls of in situ soils washing, enhanced biodegra- channeling through larger pore spaces. Even in larger-dation, soil venting and radio-frequency soil heating are grained sandy soils, fuel blobs can become trapped inpresented in an abbreviated format. These field tests have pore throats and in small pores, causing water to channelshown that in situ decontamination methods which use through only the large, unblocked pore spaces [4],water as a contact medium to remove hydrocarbons from The type of fuel also impacts accessibility for treat-the vadose zone have consistently fallen short of their menL The viscosity, solubility and bulk vapor pressurecleanup goals. Technologies which use vented air and axe important factors in predicting fuel residual accessi-thermally enhanced venting for contacting fuel residuals bility and response to water or air contact For example,in the soils have met with greater success. These results gasoline typically contains a greater fraction of water sol-indicate that the physical accessibility of fuel residuals to uble compounds and has a higher bulk vapor pressuretreatment media is critical to the success or failure of soil than jet fuels. As a result, gasoline is very accessible todecontamination technologies. water- and air-based treatment methods. Less viscous

diesel and hearing fuels are more likely to completely fillUMITID ACCISS available pore spaces and retard the advancement of

treatment media. Accessibility is also limited by theDuring the past two decades, researchers have primar- '°*er v»P°r Pressure md water «*»bilftr °f heavier

ily focused on discovering and optimizing chemical and IuelJ-biological reactions which will alter or degrade fuel hy- The location of the initial fuel release relative to thedrocarbons with little regard for the engineering of effec- water table and capillary fringe also effects the distribu-tive application systems. Using batch and column expert- tion of fuel residuals in soils. Laboratory experiments in-ments, laboratory success has been achieved in biological dicate that when hydrocarbons are released in water-degradation [i], surfactant soils washing [2], and chemical saturated or near-saturated conditions, they form largeoxidation [3]. However, field testing has shown that con- blobs which are trapped in larger pore spaces with littletact between injected or infiltrated treatment chemicals displacement of water from micropores. However, fuelsand hydrocarbon contaminants is very difficult to achieve. released in drier soils above the water table tended to mi-Soil structure, fuel composition, and the depth at which grate into micropores and form thin films over soil parti-the release of fuels occurred are just a few of the factors cles [5]. These residuals may have more limited contactaffecting accessibility that should be examined prior to with treatment fluids. Our field experiments have clearlyselecting any in situ technology. shown that fuel accessibility, and the factors which deter-Low permeability silts and clays slowly accept fuel hy- mine fuel location in the soil matrix, deserve far more at-

drocarbons into their available pore space. This can re- tention by both the scientific and engineering com-tard the advance of fuel spills, but it results in a highly in- muniry.

Environmental Progrou (Vol. 9, No. 3) 3 R T fl I Q fl 9 August, 1990 169

**•*""** u<uiuii uic~*e. .ti.wiuuic aciuuti. *_!jumvtuu:>. c.nnam.ea,in situ biodegraddtion is an attempt to create these favor-

In the early 1980s the EPA Hazardous Waste and Engi- able aerobic conditions in an environment of heteroge-neering Research Laboratory at Edison, New Jersey per- neous soils and delicate geochemical balances. Whileformed experiments using a variety of surfactant solutions several commercial firms have claimed successful site re-to remove crude oils and PCBs from contaminated soil mediations, published results often lack sufficient data tocolumns [6]. The results of these column tests showed determine the effectiveness of biodegradation in reduc-that after passing ten pore volumes of a 4 percent sur- ing fuel residuals in the soil. For this and other reasons,factant solution through the columns, 86 percent of the our laboratory decided to conduct independent field testscrude oil and 98 percent of the PCBs were washed from of this technology prior to recommending it for wide-the soils. With these promising results, the EPA and spread Air Force application.AFESC initiated a joint project to pilot test m sit u soils ln 1984, our laboratory initiated a pilot-scale test of en-woshmg at a contaminated Air Force site. hanced biodei?radation at a site on Kelly AFB, TX [10]. AsBecause soils washing is best suited for permeable this test progressed, problems with soil permeability

soils, a sandy site was desirable. An abandoned fire train- were encountered reducing the delivery of hydrogen per-tnK area at Volk Field Air National Guard Base (ANGB) in oxide and nutrients through injection wells. This reduc-Wisconsin was selected as a research site. Historical data tion in permeability was attributed to both natural silt and[T] indicated that the fire training area had been used clay soils and the precipitation of calcium phosphatessince 1955 and that as much as 200,000 liters of JP-4, which formed as injected phosphates reacted with cal-waste oils and solvents may have soaked into the soils. cium in the soil. Permeability problems reduced the de-A sieve analysis of the soil confirmed a uniform sand livery of oxygen and consequently little biodegradation

with less than 5 percent fines by weight. The soil was un- occurred. Based on these results a second site was se-consolidated to a depth of 3 to 5 meters where a highly lected at Eglin AFB, FL for additional testing under morecompacted sandstone was encountered. The vertical per- favorable hydraulic conditions.meability of the soil in the unsaturated zone was meas- In 1934 a fuel leak was discovered in a 15 cm (6 in.) un-ured in a laboratory permeameter at 4 x 10"1 to 5 x iO-" derground JP-4 fiiel supply line inside the base fuel stor-cm/sec. The hydraulic properties of this soil seemed ac- age compound on Eglin AFB. At the time of discovery, anceptable for a soils washing application. estimated 75,000 to 100,000 liters of fuel had contami-A series of m situ test beds, each containing 0.2 nV of un- nated Over 3000 m3 of soi| Uid shallow groundwater. A

disturbed soil was established in the fire training series of shallow, gravel filled trenches and skimmerarea and initial soil samples were taken to establish base- pumps were used to recover over 30,000 liters of fuel Inline contaminant levels. Soils were analyzed using two 1986T we initiated a field test of enhanced in situ biode-methods, an oil and grease extraction was used as a gen- gradation. The site is located in an area of unconsolidatederal indicator of hydrocarbon contamination, and a gas coastal sands that extend from the surface down to 12 me-chrpmatograph was used to analyze the volatile aromatic ters whcre a thick layer of clay is encountered. Ground-and aliphatic fractions of the fael. Initial oil and grease water is found only one mctcr low Surface and has avalues ranged from 1000 to 6000 mg/kg of soil. high hydraulic conductivity of 6 x H)'2 cm/sec. These fa-Three synthetic surfactant solutions mixed in clean vorable soil and hydraulic properties made it an excellent

water were used in this field test and circulated ground- site for testing enhanced biodegradation.water was used » a control. Wash solutions were applied Extensive soil and groundwater sampling preceded theAt J! 0 htCrS/!n/dv £Kftt C°S!eCUtWR daXLAn *«<• S*» *amP*« were **en from 4 to 6 in depth inter-unexpected decrease m percolation rate was observed m vab at 12 san£Ung locmtions TO** the site and analyzedS u*u T7u >> IJ0 voiumef,w«« P*?sed for total petroleum hydrocarbons using EPA Methodthrough die soil, the test beds were rued with ctan 418>lt Soil and g ter samples from four of lo_groundwater to remove excess surfactants. The test beds cafcion$ wftre ^ using a 0 3 and 43 teserto-were then resampled to determine contaminant removal tive p ^ were identified for special monitoring.5s;, , M j c_ _ j _*u /« m Sitecharacterizarionconfirmedthatover90percentofthe?iLs*mpietwere S?11*6*?1 ™" l JriS0111 J>t fuel remaining on the site was above the water table,and 30-35 cm below the surface* m each test bed.These 3 ^ and i ^ in mc soii matrix. Although the

samples were again analyzed for oil and grease. TJe re- lcak occurred at or $Ughdy Mow ^ water M risingsuits of die post-test analysis; showed that sur&cUnt solu- and M{n d J j d<5 ited hydrocarbonstions did not provide a statistically signiHcmnt decrefie in acfoss onc mctef file *°fuel and otl contamination at either depth. Despite there- *Vpeated success of engineered sur&ctanti to clean contain- J A nutrient and hydrogen peroxide delivery system wasinated soils in laboratory columns, the sandy soil at the designed to test the relative effectiveness of three dehv-Volk Field site was not cleaned in situ. Within statistical ery methods in stimulating biodegradation, in the vadoselimits, there was no sifni8c*nt difference in pre- and *on« ««£ in the groundwater. Two shallow injectionpost-wash contaminant tevels. wc"s* infiltration galleries and a spray imgation systemAlthough the laboratory columns were packed to simu- **« all installed for a side-byside companion. Four

late in situ soil density and permeability, the reduction in downgradient recovery wells wen installed and initiallypermeability and incomplete contact with fiiel residuals produced 150 to 190 liters/nun (40 to 50 gpm) for rear-encountered in the field test was not predicted in the lab- culation through the site. Due to the presence of 10 mg/1oratory. This underscores the importance of pilot testing <* ™* ™ *« shallow groundwater, an aeration basin andon contaminated sites before committing to tull-scale de- setdmg tank were added to precipitate and remove ironcontamination technologies. P"or f reinjection. Iron fouling is a common cause of re-

duced permeability and failure of remjection systems.Several important tests were completed in advance of

full-scale operation which began in June of 1987. Prior toIMHANCOfNSmiUOOfQIUOATION nutrient/peroxide additions, site hydrology was studied

under pumping and delivery conditions. The initial ca-Common soil microorganisms have the ability to de- pacity of the three delivery systems was measured to pro-

grade virtually ail of the hydrocarbons found in common vide a baseline for site permeability. A conservative chlo-fuels. Many scientists [8,9] have confirmed fuel biodegra- ride tracer was introduced into the infiltration gallery and

170 August, 1990 * environmental Prosrets (Vol. 9, Ho. 3)

its transport monitored across the well tietd to ensure hv- clearly a major design consideration cnac *houKl oe aeter-dnu&c connection across the Site. mined through a carefully monitored pilot test on eachFuel contaminated soil and groundwater were observed s»*e. If the potential oxygen concentration achieved with

in laboratory microcosm studies to determine the general hydrogen peroxide is not substantially greater than theactivity of existing fuel degrading microorganisms and 40 mg/1 available through pure oxygen aeration, then thetheir response to nutrient and oxygen additions. Simple use of hydrogen peroxide is not cost effective.bench-scale microcosm studies confirmed that under en-

! riched oxygen and nutrient conditions, existing soil bac- iuerr»i«rt« vru-riku- *teria could degrade soluble, aromatic hydrocarbons in IN SITU sow. vt HTINGless than two weeks. Unfortunately, success is not meas-ured in laboratory flasks butt in the field where these opti- In »«*« soil venting is a soil decontamination techniquemum conditions are much more difficult to achieve. which uses vacuum blowers to pull large volumes of air

. , .. , ., t. . . , . ., ,-.,1 *n through contaminated soil. The air flow sweeps out theOxygen supply and distribution * ^ **** soil gas. disrupting the equilibrium existing between the

field success. Although estimates vary, complete biodeg- contaminants on the soa and in the soil vapor. This causesradation of fuel compounds will require 2 to 3 grams of vo!atilization of the contaminant and subsequent removaloxygen per *ram of fuel degraded. An interesting discus- in the .^ stream /(| s(jil yen ^ re ortedl ^sion on the importance of the oxygen requirement is successfu, for removal of voiatile contarninants such asbund in a recent publication by Hmchee [II]. gasoline [IS] and trichloroethylene [16].Hydrogen peroxide is the most frequently used oxygen f d f h techno, on

source tor enhanced biodegradation. Peroxide is capable ^ contaminants* soils, the Air Force Engineeringof releasing enough oxygen to saturate injected ground- d Laboratory began a research project withwater to its oxygen solubility limit of approxima ely to fc d j uborato8 to conduct a £1, testo S r f*511 11"115 [ TJ) T , H^ ^ instil .soil venting rt a jet foelUP-4) spill site. In gen-02 solubility for standard aeration ot gr oundwater How- } | molecular weight hydrocarbonsever hydrogen peroxide is *»***« »» * and is less volatile thar/gasoline and other contaminantsuse depends upon a gradual breakdown ot peroxide ana , . , , • i i: - ^ _ t j c _ j- *•*i c „ j __ i; -»«c ;„;„*;«« _ ;„*.„ which have previously been investigated for remediationtime release of oxygen downgradient of injection points. fay {n u sojj venting.Shortly after initiating 500 ppm hydrogen peroxide ad- TU •* u r * * • ri _i «r-n»^n

ditions a. the Eglin site gas bubbles were noH«d coming . ™e,s C ?£& *St,£2 "ft ej Y"d !L?'" FB'up through the water in the shallow infiltration galleries UT «« lf»-°P° ! fr Jp .««»» had occurred in Janu-Gas sampling showed that this was virtually pure oxygen; *£ l 8LTh!JP JSZXFJff ""* OJmf T 'the product of rapid peroxide decomposition. Iron was d . s™& ** ,'h'n ""P* ?1 laye" °ftsl,lty, ay' ?"*first suspected as the catelyst of this rapid decomposition. KteS1? - S JS T" t "*Howeven laboratory tests showed that the rate of HzOj J"'/..!"1 'l""'! n **'" ""idecomposition in iron solutions was at least an order of COU"fter °" ?» °? *2 Sllty °lay "'J** ngl°magnilide slower than field decomposition rates. Subse- £"** °f H "4!M m " f * ™f* * T"8 U"lt 1quent laboratory experiments by Spain [12] found that "lf:'™J?e1Ph*i°! mete"' **?» elrtjn"ve. SO'Jperoxidase enzymes produced by indigenous bacteria ""J "" n,? ?« W ga urveys' " *" determ.nedwere the cause of uncontrolled H,O2 decomposition. As a S W c?n ? , 1" ?? * 7 "tfi "T Iresult of this oxygen off gassing, only an estimated 16 per- ™£™tO * depth °f »PPro«ma««ly »» «etw below landcent of the potential oxygen supply was actually de-livered to the contaminated soil and groundwater. Al- Information from the site characterization and the one-though there was a slight increase in dissolved oxygen vent pilot test [28] provided the basis for the design of alevels downgradient of injection points, there was no evi- full-scale in situ soil venting system for remediation ofdence of HaO2 transport. tnc JP"4 contaminated soil. The full-scale venting system

» G. i o " \L. r - j j ^ * jj- - _ design consisted of the three subsystems: 1) A vertical ventAfter 18 months of peroxide *nd nutnen. adAhon, , aro- »•„ rf m 2 , '

sampling of soils above and beneath the water table did ^ ^ jle of fr<jm thc;excavation of thc"fr'i ri .Sn1 re;novf ° t f !I ™« ' includ«» **«~ which P««tt evaluation ofals[/3].Thefailureofnutnentaiidhydrogenperoxidead- sevm{ factor| ajfe j contaminanr&ansport and sub-ditions to impact soil contamination was particularly evi- surface air flowdent in the unsaturated zone of the spray application area.Over 190 pore volumes ol treatment water passed through Tn* vertical vent subsystem consists of 15 vents placedthese sandy soils with no significant fuel removal meas- in th* contaminated area to depths of 15 meters. Theured. It appears that neither hydraulic washing nor biodeg- venting subsystem under the new concrete pad includesradation had an impact oil this tightly bound fuel residual. six lateral vents spaced 46 meters apart at a depth of ap-We have concluded that fuels trapped within the micro- proximately 6 meters below land surface. The subsystempores of the soil were largely inaccessible to the nutrients for the excavated soil pile consists of eight vents spaced 5.5and oxygen that were being provided. meters apart at a depth of 1.5 meters below the top of the

or gravel aquifers where the majority ot the contamina-lion is in the saturated zone. A similar test of this technol- Operation of the full-scale, in situ soil venting systemogy conducted by the EPA's H. S. Kerr Laboratory began in December 1988. As of October 1, 1989, approxi-showed some improvement in hydrogen peroxide stabil* mately 50,000 kilograms of JP-4 hydrocarbons have beenity, particularly when thc hydrogen peroxide was injected extracted in the vented soil gas. Decontamination of theinto the saturated zone [14]. In situ peroxide stability is site can be seen by comparison of soil gas concentrations

Environmental Progress (Vol. 9, No. 3) g p O n | Q n C Augiwt, 1990 171

in an ttre^ Ul . .._.„ . fc. «,hydrocarbon concentrations have dropped from 179 per- WI was selected AS a test site because of its uniform soilcent of the lower explosion limit (LEU m February 1989, and contaminant profile. Although a description of theto 88 percent LEL in April 1989, to 33 percent LEL in site is contained in the soils washing section, it is impor-June 1989, to 5 percent LEL in August 1989. Also, the tant to point out that a great deal of additional soilconcentration of hydrocarbons in extracted gas from the sampling was performed for this test to study the removalentire venting system has dropped from 38,000 ppm hex- of different compounds at different depths in the treat-ane equivalent in December 1988 to 500 ppm hexane ment volume. Over 84 different soil samples were ob-equivalent in October 1989. This is below the level re- tained from three depths within the 500 ft3 test volume.quired for mandatory site cleanup in some states (e.g., A trailer-mounted 40 kw RF generator was availableFlorida [8]). The state of Utah has not set standards for from past DOE research and was transported to the testcleanup levels of petroleum contaminated soils. site. The test volume measured 4 meters long, 2 metersAnother important mechanism of remediation from wide and 2 meters deep and was heated by 39 electrodes

in situ soil venting, besides volatilization and removal, is in 3 rows of 13 each. A vapor barrier was placed over thebiodearadation. The increased oxygen levels in the soil heated area to collect escaping soil gas and to transportgas due to infiltration of Atmospheric air may considerably the gas to a vapor condenser for separating liquid hydro-stimulate biological Activity. To evaluate this factor, car- carbons, and a carbon bed to treat remaining volatile or-bon dioxide and oxygen are being measured in the ex- ganics. A 560 liter/min (20 cfm) vacuum provided a slighttracted gas at the soil venting test. Initially, high COa negative pressure to ensure that all vapors were collected(11%) and low oxygen (1%) levels were measured in the and treated. The test volume and gas handling systemsoil gas. As venting continued, the COi levels decreased was heavily instrumented to provide soil temperatureand the oxygen levels increased. Carbon dioxide levels data and hydrocarbon concentration data in the escapinghave continued to be an order of magnitude higher than gas stream.atmospheric, which suggests biodegradation may play a RF energy was applied to the soil over a period of 12significant roll in the remediation of the site. days. After 8 days the 150*C target temperature wasThe results obtained to date from the JP-4 in situ soil achieved throughout the test volume and this tempera-

venting test have shown that this technique is very effec- ture was maintained for a period of 4 more days. Duringtive In removing large amounts of jet fuel from the soil in this heating period, careful records were kept on the re-a relatively short penod of time. Continued testing is lease of hydrocarbons and water vapor from the soil. Ataimed at determining the importance of various factors in one point an inert tracer was injected into the soil outsidehydrocarbon removal. We are continuing to sample the of the treatment area to confirm that migration was intoextracted gas to determine both the total hydrocarbon lev- the heated zone and to estimate soil gas velocity. Powerels and hydrocarbon distribution. The effects of moisture consumption was also monitored to determine the ope rat-on volatilization and bioactivity will be determined by ing cost of this process. After 12 days, power was turnedmonitoring soil moisture and extracted gas humidity. In off and the soil was allowed to cool prior to resampling.October 1989. the system was shut down for an extensive The efficiency of the RF decontamination process wassoil sampling to determine the extent of the JP-4 hydro- determined by Dev, et al. [19] through a careful compari-carbon removal. Based on the data from the extracted gas, son of pretest and posttest soil samples. Samples were an-we project that 70 to 80 percent of the 100,000*1 iter spill alyzed to determine changes in moisture, volatile aliphat-will have been removed by the time of the sampling. Final ics, volatile aromatics, and semi volatile aliphatics anddata from this site will provide a valuable tool for full-scale aromatics. The average removal rates from the heated vol-design of In littt venting systems for JP-4 and other fuel ume were impressive with 97 percent removal of semi vo-contaminated sites. latile hydrocarbons and 99 percent removal of volatile ar-

omatics and aliphatics. Closer examination of the samplesshowed that contaminant removal at the 6-foot depth, the

MWMUQUDCriW^LMLMBOHrMMUfMM ^ nof a state-of-the-art RF generator for frill-scale applica-

In 1985, the Air Force Engineering and Services Labo- tions could reduce the power input to less than 500 kw-hr/rat ory and the Environmental Protection Agency began a yd3.joint research project with the Illinois Institute of Tech-nology Research Institute (HTRI) to explore the use of ra-dio-frequency {RF) heating for in situ soil decontami-nation. Radio-frequency heating uses electromagnetic WITUtl UStAftCHenergy directed through electrodes in the soil to createmolecular vibration and rotation, which uniformly heats Future research conducted by the Air Force Engineer-the soil. Radio-frequency heating was first developed for ing and Services Laboratory will emphasize new applica-recovering oil from oil shale and tar sands in the 1970s. tions of the soil venting process to remove or destroy fuelField tests proved the feasibility of beating rock forma- residuals in the unsaturated zone. The demonstrated abil-tions from 200*C to 4QO*C. As the energy crisis calmed, ity of air to access soil-bound fuel residuals represents a[ITRI sought out alternative applications for in situ soil distinct advantage over water based treatment systems.heating. Because most Air Force contaminants, including Although the authors' conclusions are based primarily onJP-4 fuels, have boiling points less than 150*C, RF heat- personal field experiences, we have found no convincinging was seen as having great potential for soils decon- evidence in open literature to suggest that m situ waterlamination on Air Force installations. based treatment has consistently remediated fuel contam-Laboratory experiments, using soils contaminated with mated soils.

fuels and solvents, produced excellent results, with over Two enhancements to the soil venting process will be95 percent removal at temperatures of 100*C to 150*C. developed and tested during the next year. One enhance-Fo I low-on experiments in 5 foot soil columns proved the ment is the combination of soil venting and RF heating tofeasibility of uniformly removing volatilized hydrocar- more rapidly volatilize fuel residuals and to increase thebons over the depth profile. These promising results led to volatilization of compounds with higher boiling points.a decision to conduct a pilot test of this technology at a con- The uniform heating provided by radio-frequency energylaminated Air Force site. is also expected to improve soil porosity and improve re-1 72 August, 1 990 Environmental Progress (Vol. 9, No. 3)

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heiitinz/ventina system wij,i t>e conducted on an Air force — om-uni ic jokw ~, » .P°rt 60CVS2-83/129 { 1985).

e soil venting process willattest to optimize the biodegradation of fiaels thai : re- a ^^sufes when vented air provides oxygen to subsurface bac- carbons: An EnvironmenSpenpective," M*rofeioio«ica<tei*a. The goal of this research will be to determine the Reviews, Vol. 45, 180-199(1981).opt-mum range of soil moisture, nutrients, and venting 9. Lee. M. D., "Biorestoration of Aquifers Contaminated withrates to achieve in situ biodegradation while minimizing Organic Compounds." CHC Critical Reviews in Enciron-the emission of volatile 01 games to the atmosphere. A pi- 'mental Control. Vol. 18. 29-89 (1988).lot-scale test of this enhanced biodegradation method is 10- Wctzel, R. S,, "fn Situ Biological Treatment Test at Kellynow underway at a fuel contaminated site on Tyndall AFB. Vol. U Field Test Results and Cost Model," Air ForceAFB, FL and is producing encouraging results. JlM ffflS? Scrvices L»*>or*°n' Technical Report No.Research is continuing in the use of m situ and above- [ { Hi R '£ D ^ ^ VotM^ "The Role

ground biological physical and chemical treatment tech- of Hydrogcn peroxide Stability in Enhanced Biodegradationnologies to remediate contaminated groundwaters. Be- Effectiveness." Proc. of NWW A/API Conference on Petro-cause site remediation wi 11 generally require two or more |eum Hydrocarbons in Ground Water, 715-722. Houston, TXtechnologies, more emphasis will be given to systems in- (1988).tegration to impact both source and dispersed contami- 12, Spain, J. C., J. D. Milligan, D. C. Downey, and J. K. Slaugh-nants at minimum expense. ,„ ;«*•/<>«"«'' of Ground Water, Vol 27 No. 2, 163-167 (1989).

13. Hinchee, R. E., D. C. Downey, M. S. Westray. Slaughter. "En-hanced Biodegradation of jet Fuels — A Full-Scale Test at

LITIRATURI CrriD E«lin AFB, FL," Air Force Engineering and Services Labora-tory Technical Report No. 88-78 1 L989).

1. Downey. D. C., R. E. Hinchee. M.S. Westray, and J. K. 14. Ward, C. H., J. M. Armstrong, A Quantitative DeterminationSlaughter, "Combined Biological and Physical Treatment of of the Raymond Process for In Situ Biorestoration of Con-A Jet Fuel Contaminated Aquifer." Proceedings of NWW A/ taminater Aquifers, Proc. of NWWAMPI Conference on Pe-AP1 Conference on Petroleum Hydrocarbons in Ground rroleum Hydrocarbons in Ground Water, 723-743, Houston,Water. 627-643, Houston. TX ( 1988). TX ( 1988).

2. Nash. J., R. Traver, Arid D-C. Downey. "Surfactant- En- LS. Anastos, G. J.. P. J. Marks, M. H. Corbin. and M. F. Coia.hanced In Situ Soils Washing," AF Engineering and Sevices t n Situ Air Stripping of Soils Pilot Study, Final Report,Laboratory Technical Report No. S7- 18 ( 1987). AMXTH-TE-TR-85026 ( 1985).

3. Rauch. P. A. and R. J. Watts. "In Situ Treatment of Pentachlo- 16. Thorn ton, J. S., R. E. Montgomery, T. Voynick, and W. L.rophenol Contaminated Surface Soils Usinz Fenton Reagent." Wootan, "Removal of Gasoline Vapor from Aquifers byProceedings — 6lst Annual Conference of the Water Pollution Forced Venting." Hazardous Material Spills Conf. Proc.Control Federation. Dallas. TX < 1988). ( 1984).

4. Wilson, J. S., and S. H. Conrad. "Is Physical Displacement of 17. Etliott, M. G. and D. W. DePaoli. "In Situ Venting of JetResidual Hydrocarbons a Realistic Possibility in Aquifer Fuel-Contaminated Soil," 44th Purdue Industrial WasteRestoration," Proceedings of NWW A/API Conference on Pe- Conference { 1989).troleum Hydrocarbons in Ground Water, 274-297, Houston, 18. Florida Department of Environmental Regulation. "Guide-TX ( 1984). lines for Assessment and Remediation of Petroleum Contam-

5. Wilson. J. L.. S. H. Conrad, E. Hagan. W. R. Mason, and Pep- mated Soils" { 1989).tinski. "The Pore Level Spatial Distribution and Saturation 19. Dev, H., D. C. Downey, C. Stretsy. and]. E. Bridges, "Fieldof Organic Liquids in Porous Media," Proceedings of Test of the Radio Frequency Soil Decontamination Pro-NWWA/AP! Conference on Petroleum Hydrocarbons in cess," Proc. of Superfund 88 National Conf. and ExhibitionGround Water, 107- 133, Houston, TX ( 1988). ( 1988).

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