soil-gas surveys for detection and delineation of groundwater contamination

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D Ishu (Editor), Zntroductzon to Mzcroscale High-Perfor- mance Llqurd Chromatography, VCH, New York, 1988 T Takeuchl and D Ishn, J Chromatogr ,213 (1981) 25 F J Yang,, J Chromatogr ,236 (1982) 265 J C Gluckman, A Hlrose, V L McGuffin and M Novot- ny, Chromatographza, 17 (1983) 303 M Novotny, M Alasandro and M Komshl, Anal Chem , 55 (1983) 2375 T Tsuda and M Novotny, Anal Chem ,50 (1978) 271 Y Hlrata, M Novotny, T Tsuda and D Ishn,Anal Chem , 51(1979) 1807 Y Hlrata and M Novotny, J Chromatogr , 186 (1979) 521 T Tsuda, I Tanakahnd G Nakagawa, J Chromatogr , 239 (1982) 507 J H Knox and M T Gilbert, J Chromatogr , 186 (1979) 405 G Gmochon, Anal Chem ,53 (1981) 1318 J W Jorgenson and E J Guthne, J Chromatogr , 255 (1983) 335 D Ishu and T Takeuchl, J Chromatogr Sa , 18 (1980) 462 T Tsuda and G Nakagawa, J Chromatogr ,268 (1983) 369 E J Guthne, J W Jorgenson and P R Dluzneslu, J Chro- matogr Scz ,22 (1984) 171 L A Knecht, E J Guthne and J W Jorgenson, Anal Chem ,56 (1984) 479 S Folestad, B Josefsson and M Larsson, J Chromatogr , 391(1987) 347 T Takeuchl, Y Watanabe and D Ishn, J High Resolut Chromatogr Chromatogr Commun ,4 (1981) 300 Y Hnata and K Jmno, J High Resolut Chromatogr Chro- matogr Commun , 6 (1983) 196

26 H McNalr and J Bowermaster, J High Resolut Chroma- togr Chromatogr Commun , 10 (1987) 27

27 T Takeuchl, Y Jm and D Ishn, J Chromatogr ,321(1985) 159

28 D Ishn, K Watanabe, H Asa, Y Hashlmoto and T Take- uchl, J Chromatogr ,332 (1985) 3

29 T Takeuchl and D Ishu, J Chromatogr ,288 (1984) 451 30 U A Th Brmkman and F A Mans, LC GC Mag , 5

(1987) 476 31 D Ishn and T Takeuchl, Trends Anal Chem , 8 (1) (1989)

25 32 F J Yang, J High Resolut Chromatogr Chromatogr Com-

mun ,3 (1980) 589 33 F J Yang, J High Resolut Chromatogr Chromatogr Com-

mun ,4 (1981) 83 34 M Verzele and C Dewaele, J Chromatogr ,395 (1987) 85 35 T Takeuchl and E S Yeung, J Chromatogr , 389 (1987) 3 36 T Takeuchl and D Ishn, Chromatographra, 25 (1988) 697 37 D Ishu and T Takeuchl, J Chromatogr Scz ,27 (1989) 71 38 T Takeuchl, M Asa, H Haraguchl and D I&u, J Chro-

matogr ,499 (1990) 549 39 T V Raghone, N Saghano, Jr , Th R Floyd and R A

Hartwick, LC GC Mag ,4 (1986) 328

Dr D Ishu 1s at the Department of Applied Chemistry, School of Engmeenng, Nagoya Unwerslty, Chlkusa-ku, Nagoya 464, Japan Dr T Takeuchl 1s at the Research Center for Resource and Ener- gy Conservation, Nagoya Unwerslty, Chlkusa-ku, Nagoya 464, Japan

Soil-gas surveys for detection and delineation of groundwater contamination

H. 6. Ketfoot Las Vegas, NV, U.S.A.

Sampling and analysis of subsurface pore gases is a technique that is finding increased application in preliminary evaluution of the extent and magnitude of subsu#ace contamination by volatile organic compounds. Relationships between pore-gas and subsu$ace contaminant concentrations can be affected by contaminant transport or transformation and caution must be used in interpretation of results.

Introduction Contammatron of groundwater due to leaky fuel

storage tanks and past waste disposal practices has become a major envuonmental concern and has driven the development of analytical technology m

two areas: detection of threats to groundwater quahty, such as underground fuel tank or landfill leakage, and characterrzation of the area1 extent and magmtude of existing contammation to effectively assess risks and design remedial actions Because of the rel- atively slow movements of liquids relative to gases and the high costs of installation of groundwater momtormg wells, much recent work m the development of leak-detection and site-characterization monitoring technologies has focused on techniques that sample and analyze mterstrtral subsurface pore gases for mdrcation of underlying or nearby contamr- nation by volattle organic compounds (VOCS)‘-~ This article describes the use of sampling and analyz- mg sol1 gases* for the raprd prehmmary evaluation of

* The term ‘soil gases’ is used for these pore gases, m concur- rence with common usage m the U S A , although the term ‘ground au-’ has been used m Europe smce 1877

0165-9936/90/$03 00 0 Elsevler Science Pubhshers B V

158 trends m analyttcal chemistry, vol 9, no 5,199O

the presence and area1 extent of subsurface contamination by VOCs, m order to more effectively plan costly soil and/or groundwater sampling and analysis efforts

Through the use of such rapid cost-effective techniques, significant cost-savings can be realized It should be emphasized, however, that such techniques are intended to be used m conlunction with traditional sampling and analyses and not as a re- placement for them the technique does not determme the parameter of interest (soil or groundwater contammation) but one that is related to it. This article will describe some of the factors that can mflu- ence the smtabihty of using soil-gas concentrations to indicate subsurface VOC contamination, it does not consider the vartous sensor-system designs that have been developed m response to the need for fuel-storage tank leak detection

In general, a soil-gas survey mvolves sampling and analyzing soil gases to obtain an mdication of contammation from VOCs some distance away m the subsurface This approach assumes transport of the VOCs from the contammation to the sampling location and conservative (non-degraded) behavior of the VOCs The transport of VOCs and their fate can depend on both compound-specific and site-specific factors

Subsurface transport processes The transport of VOCs from contammated ground-

water m the subsurface can be envisioned as a three- step process (Transport from contaminated soil is analogous or simpler ) The first step is the phase transfer of the VOC from the liquid (aqueous or neat hqmd contaminant) phase to the gas phase m contact with it Once m the gas phase, the contammant can move through the unsaturated zone between the water table and the land surface mto the atmosphere Upon reaching the atmosphere, the VOC is carried away by atmospheric processes. Because of the rela- tively rapid transport of gases m the atmosphere, it can be thought of as a smk for the groundwater source of contammant vapors Mathematical models for this process have been formulated8-‘6 Recent work has postulated effects of gas density on soil-gas transport of volatile orgamc contammants’1~15, but no field experimental data has been presented yet to support that hypothesis

In order to partition appreciably from groundwater mto the gas phase, contammants must have a suf- ficiently high volatility and low water-solubihty The eqmhbrmm ratio of gas-phase concentration to aqueous concentration is given by the Henry’s law constant Extensive tabulations of values for this constant are available17, usually for pure water at

298 K Caution should be exercised in application of these values to groundwater because of the ionic strength, temperature, and solute differences that can exist in the subsurface, as well as the potential for non-equihbrmm behavior However, they can be useful for evaluating the volatility of dissolved organic compounds Table I lists the 25 most frequently identified compounds at Superfund hazardous waste sites m the U S A. and their frequency of detection m groundwater at those sites. Of these contaminants, 17 have properties that make them amena- ble to the application of this technology for dehnea- tion of groundwater contamination plumes In addition, the major components of gasoline and Jet fuel also have physical properties that ensure sufficient partitionmg from solution mto the gas phase for the potential application of soil-gas surveymg to dehnea- tion of contamination

Once the VOCs are present m the gas phase at the water-gas interface or the capillary fringe, they must be transported vertically to the sampling location for the technology to work. Transport of the VOCs through the vadose or unsaturated zone is predommantly by diffusion through interconnected gas-filled pores m the soil and unsaturated materials,

TABLE I Most frequently reported groundwater contaminants at 546 superfund sites’

Rank Compound Percent

1 Trlchloroethene (TCE)* 33 2 Lead 30 3 Toluene* 28 4 Benzene* 26 5 Polychlormated blphenyls (PCBs) 22 6 Chloroform* 20 7 Tetrachloroethene (PCE)* 16 8 Phenol 15 9 Arsenic 15

10 Cadmmm 15 11 Chromium 15 12 1 ,l,l-Tnchloroethane* 14 13 Zinc 14 14 Ethylbenzene* 13 15 Xylene 13 16 Methylene chloride 12 17 trarzs-1,2-Dlchloroethene* 11 18 Mercury 10 19 Copper 9 20 Soluble cyanide salts 8 21 Vinyl chloride* 8 22 1,2-Dlchloroethane* 8 23 Chlorobenzene* 8 24 l,l-Dlchloroethane* 8 25 Carbon tetrachlorlde* 7

a Source ref 1 * Compounds amendable to detection by sod-gas analysis

trenak m analytzcal chemrstry, vol 9, no $1990 159

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due to the absence of bulk gas movement m that zone. According to Fick’s law: the rate of VOC mass &transport through a unit area of soil is proportional to the soil-gas diffusion coefficient and the change in the concentration along the direction of diffusion. The soil-gas diffusion coefficient is equal to that of the VOC m air multiplied by a tortuosity factor, which includes the gas-filled porosity raised to the second or higher power (The gas-filled porosity of unsaturated materials such as soil is typically up to 40% .) Therefore, transport of VOCs to the sampling point from the contaminated groundwater will be very strongly influenced by the subsurface gas-filled porosity between the contammation and the sampling location In fact, at gas-filled porosities below 5 to lo%, soil-gas diffusion of non-sorbed gases such as nitrogen drops off to negligible levels”. Any subsurface layers with gas-filled porosity below lo%, such as clay layers or perched water, will thus act as effective barriers to soil-gas transport of VOCs In addition, mteractions of VOCs with components of soil, such as organic matter or organic carbon, can add si sion8p14

mficantly to the resistance to soil-gas diffu-

For homogeneous and isotropic subsurface conditions, Fick’s law predicts a linear dependence of gas- phase concentration on depth under steady-state conditions Although isotropic homogeneous conditions are not at all common m the subsurface, such a situation has been observed in laboratory sim- ulations” and m field studieslT6 However, m other instances, such depth profiles have not been ob- servedlg These differences may be due to subsurface heterogeneity, non-steady-state conditions, degradation of the VOC, or other factors, but are mentioned here to demonstrate that such questions are quite site-specific and assumptions of steady-state conditions or other factors should be avoided. Depth profiles of gas-phase VOCs should not be compared to those of soil moisture m the subsurface, since soil moisture (water) can come from more than one source, including rainfall and mfiltration as well as evaporation from the water table

Heterogeneous subsurface conditions can drasti- cally affect the relationship between soil-gas VOC concentrations and underlymg contammation at a site. These influences can create situations where soil-gas concentrations provide either false positive or false negative mdications of underlying contamination Perched water or clay layers can impede soil- gas transport as mentioned above and can thus create elevated concentrations below them and very low concentrations above them. Similarly, paved surfaces can act as a cap, holdmg soil-gas VOC concentrations higher than they would be if the ground

surface were native soil and encouraging horizontal migration of gas-phase VOCs. Man-made conduits for gases, such as high gas-filled porosity gravel backfill around electrical lines or pipes, can create extremely confusing spatial patterns of soil-gas concentrations if their presence is not taken mto consid- eration

Other anthropogenic influences on subsurface conditions can also affect the utility of the technology At industrial locations, where surface spills or underground leaks may have taken place in the past, these potential shallow sources of VOCs m the soil gases can create such high concentrations that the much weaker signature of deeper groundwater contamination cannot be evaluated. However, the data in such instances can be very useful for planning remedial action m response to those situations, such as zn sztu stripping of the soi12’

Subsurface fate In addition to factors affecting the transport of

VOCs from the contammation to the sampling point, subsurface transformations of the contaminants can affect their concentrations in soil gases. Organic compounds in the subsurface can undergo either oxidation or reduction reactions, depending on the compound and the conditions at the site. The degradation process that is favored depends on the struc- ture of the contammant; for oxidized organic compounds, such as chlorinated solvents, reduction is the thermodynamically favored process, while reduced hydrocarbons, such as hydrocarbon fuels, are prone to oxidatron because of the potential larger energy yield Although subsurface microorgamsms can catalyze these processes, abiotic or chemical degradation can also occur. Because of the sigmfi- cant energy yield of the oxidation of hydrocarbons, that process can proceed at a rate sufficient to obht- erate soil-gas hydrocarbons above groundwater contaminated with fuel In fact, aerobic oxidation of cre- osote has been observed at a rate that was limited only by the rate at which oxygen could diffuse from the atmosphere to the subsurface for utilization De- termination of soil-gas carbon dioxide concentrations has been shown to produce results that correlate with underlying groundwater hydrocarbon con- tammation4 and has also been used to delineate carbon dioxide-rich groundwater The determination of soil-gas concentrations of degradation products of hydrocarbon contaminants has been proposed as a technique for detection of contaminants with msuffi- cient volatility for direct detection approaches4. However, the numerous factors that can affect subsurface degradation and transformation and the usual degree of knowledge of subsurface conditions

160 trends m analytical chemstry, vol 9, no 5,199O

at a site make these processes difficult to predict. It is most likely that high carbon dioxide concentrations m soil gases overlying contammation by reduced hydrocarbons will correlate with underlying contamination only m instances of low subsurface organic carbon content, so that the added organic carbon of the contammation increases the concentration of the rate-hmitmg factor m production of carbon dioxide In addition, there are numerous potential natural sources of elevated soil-gas carbon dioxide concentrations, such as lignite or peat layers

The above effects of transport and transformation factors on pore-gas concentrations will obviously re- quire a detailed understanding of the physical and biological properties of the subsurface, as well as the vertical and horizontal and the temporal variabihty of them Since it is impractical to perform such a detailed characterization of the subsurface at sites, interpretation of soil-gas data is the most challenging aspect of applying the technology Although quanti- tative determmations of contammation levels are not possible, experienced workers m the field can evaluate sources, age, and migration of contaminants from soil-gas data. However, as with all envi- ronmental momtormg data, a knowledge of the qual- ity of the data produced is required to meamngfully interpret soil-gas data Although much attention has been focused on samplmg and analytical hardware m recent work m the field, little attention has been focused on techniques for mterpretation of soil-gas survey data

Case study 1 A soil-gas survey was performed in a rural area

where groundwater contamination with 1 ,l ,l-tri- chloroethane had been detected at concentrations of up to 3000 ,~g/l m residential wells The depth to the aquifer was approximately 30 m, groundwater flow was to the south, and the unsaturated zone geology consisted of sand and gravelly sand with localized areas of perched water underlain by clay Because no mvestigation of the contammation had been performed, no momtormg wells had been installed and the oblectives of the soil-gas survey were to help site mvestigators determme the best locations for mon- itormg wells and to provide information to help identify the source(s) of the contammation

Soil gases were sampled from a depth of 1 5 m and were analyzed on site by gas chromatography Fig. 1 shows the results presented as isoconcentration contours of soil-gas concentrations on an order-of-magnitude basis Because soil-gas concentrations at the same site can vary by several orders of magmtude and since there are significant factors that can bias data m one direction or the other, order-of-magm-

tude mterpretation of data is a useful way to avoid effects of small errors m the data on its utility. From the figure, it can be seen that the soil-gas data show a narrow contaminant plume that follows a tortuous path generally to the south, m the direction of regional groundwater flow. Because of the rural nature of the site, the contours m Fig 1 were useful to indicate that a local landfill was the source of the contaminants The northeast displacement of the soil-gas contours from the landfill is due to subsurface geologic factors, which caused a significant horizontal flow of the contaminants in transit to the aquifer Subsurface geologic features are also re- sponsible for the narrow width of the plume, a geo- physical study of the site mdicated the presence of a buried erosional channel, and selective contaminant migration therem is the reason for the narrow plume indicated by the soil-gas data The cost of the sod-gas survey was approximately that of a single monitoring well and the data obtained resulted m the ehmma- non of several monitoring wells from the network that was subsequently Installed at the site.

Groundwater Flow

Fig 1 Concentratrons of I,l,l-tmhloroethane ln sod gases at a rural srte

trends m analyhcal chemrstry, vol 9, no 5,19!# 161

TCA CONCENTRATION IN GROUNDWATER tug/l)

Fig 2 Linear regresston plot of sod-gas concentrations as a func- tion of underlying concentrations of l,l,l-trrchloroethane (TCA) Hollow circles mdrcate location where drsconhnuousper- ched water bodies were known to exist

Sol1 gases had been sampled and analyzed adla- cent to eleven residential wells and the results were compared to data from analyses of groundwater from those wells Fig 2 shows a linear regression plot of those two data sets. If data from seven of those wells is considered, a correlation coefficient (r) of 0.88 results between the two data sets. Consrder- ing the depth to groundwater and the potential for subsurface heterogeneity effects on the soil-gas data, such a correlation represents a successful application of the technology The four wells that were not included m the above linear regression were located where well-drilling records showed that there were saturated layers, which can impede sod-gas transport and depress soil-gas concentratrons above them compared to subsurface condrtrons without those layers From Fig 2 it can be seen that the sorl- gas concentrations for those wells were lower in rela- tion to the underlying groundwater concentrations than the other data relative to the groundwater be- neath them These results indicate the potential for zones of low gas-filled porosity to hamper sod-gas transport and produce false negative or depressed soil-gas concentratrons and the need to consider the unsaturated-zone stratrgraphy when planning or m- terpretmg the results of a soil-gas survey

Case study 2 A soil-gas survey was conducted m the desert

Southwest U S A. m the vicmrty of a waste-fuel storage facrhty with four 7-m diameter in-ground con- crete tanks There had been leakage there m the past, but practrces had been changed to discontmue

use or limit fill levels of leaky tanks to prevent leakage. In order for the site operators to remove the tanks and abandon the site, a site-characterization was required. In that process a soil-gas survey was performed. Groundwater was at a depth of 25 m and flowed to the east-northeast Soil gases were sampled from a depth of 1.2 m and were analyzed on site for hydrocarbons

The site 1s shown m Fig. 3. The data were obtained

11 a

Fig 3 Sod-gas total hydrocarbon concentrations at a leaky fuel tank site Shaded area rndrcates total hydrocarbon concentration m sod gases above 100 mgl& Regional groundwater flow 1s to the northeast

162

using gas chromatogra hy, with flame-ionization detection and 100 mg/m P was the approximate detection limit The soil-gas data indicate that hydrocarbon fuel contammation has migrated in the east- northeast direction of groundwater flow Table II lists concentrations of aromatic hydrocarbons ob- tamed from analysis of groundwater samples from the wells that were installed at the site; when compared to the soil-gas hydrocarbon data, they can be seen to agree at those locations At the one well m Table II with significant hydrocarbon concentrations (well 12), a 2 5-m fuel layer was encountered float- mg on the water table when the well was mitially sampled, while none was detected m the others

Because it was anticipated that the contammation extended to a significant level past the lowest detect- able soil-gas total hydrocarbon concentration but subsurface degradation could be maskmg soil-gas m- dications of the contammation, a second soil-gas survey was performed to determme soil-gas carbon dioxide concentrations It can be seen m Fig 4 that a high soil-gas carbon dioxide concentration zone exists further along the direction of groundwater flow from the floating fuel layer Subsequent drilhng m that zone located a 1 5-m thick layer of floating fuel

The results of this case study should not be mter- preted as mformation to show what will happen m situations of groundwater contammation by fuels, but to indicate the potential for problems due to degradation of contammants m the subsurface and m- consistent behavior at different locations at the same site Such experiences are not uncommon m the field and are mdicative of the need for site-specific consid- eration of factors that can affect soil-gas data and demonstrate the need to confirm soil-gas mdications of contammation of cleanhness through direct samplmg and analysis.

Conclusions Sampling and analysis of soil gases is an emerging

technology that can be an effective tool m prehmi-

TABLE II Groundwater data from momtormg wells (mg/l)

Well number Benzene Toluene Ethyl- Total benzene xy-

lenes

11 03 NDb NDb NDb 12 520 4000 820 920 13 NDb NDb NDb NDb NAPL” (Well 12) 6000 9200 440 1510

’ NAPL = Non-aqueous petroleum hqmd b Not detected, detection hmlt = 50,&l

trends m analytlcalchemrstry, vol 9, no 5,199O

cesrlble Area

/ N

‘100 feet.

Fig 4 Sod-gas carbon dloxrde concentrattons (70) at a leaky fuel tank site Regronal groundwater flow IS to the northeast Shaded area 1s the same as tn Fig 3

nary site-characterization efforts to assist m planning cost-effective monitoring-well or soil-sampling efforts for delmeation of the magnitude, nature, and area1 extent of subsurface contammation Although the technology is limited m apphcabihty to only the most volatile contaminants, those compounds repre- sent a large fraction of groundwater contammation problems The apphcabihty of soil-gas surveys to specific situations is determined both by site-specific factors and compound-specific properties of the contaminant Both subsurface transport of the contaminant from the contammation to the samplmg location and non-degradation of the contaminant must occur for the technology to be successful Saturated subsurface layers and biodegradation can result m false negative results, where soil gases are clean above contammation, while pavement, surface spills, sewer lines or other cultural factors can result m false positive results, where soil-gas data indicates contammation although there is none m the underlymg groundwater Because of the site- and compound-specific nature of the factors that can mflu- ence the validity of soil-gas data for delineation of groundwater contammation, this tool enhances the effectiveness of traditional direct samplmg and analysis rather than replaces them The direct sampling and analysis can be used to validate the mdications of

trends tn analyttcal chemtstry, vol 9, no 5,1990 1 63

the soil-gas data or to identify problems with the data. In addition, soil-gas data (as any other analytical data) must be complemented by a good understanding of the hydrology at any site in order to be effectively used in planning groundwater remedia- tion or protection measures.

Fief@fences 1 D L. Marnn and H B Kerfoot, Envtron. Sct Technol, Au-

gust (1988) 740-745 2 M Albertsen and G Matthes, m Proceedings of Interna-

ttonal Sympostum on Ground Water Pollutton by Od Hydro- carbons, Int Assoc of Hydrol, Prague, 1978

3 H B Kerfoot and C L Mayer, Ground Water Momtormg Rewew, National Water Well Assoclatmn, Dublin, OH, Fall, 1986, pp 74-78

4 H B Kerfoot, C L Mayer, P B DurgmandJ J D'Lu- gosz, Ground Water Momtormg Revww, NaUonal Water Well Assoclatmn, Dubhn, OH, Fall, 1988, pp 67-71

5 E G Lappala and G M Thompson, m Proceedings of the Annual Sympostum on Charactertzatton of the Vadose Zone, NaUonal Water Well Assocmtlon, Dublin, OH, 1983, pp 295-3O5

6 D L Martin and G M Thompson, Ground Water, 25 (1) (1987) 21-27

7 R J Nadean, T S Stone and G S Khnger, m Proceedings of the NWWA Conference on Charactertzaaon and Momtor- mg of the Vadose Zone, NaUonal Water Well Assocaatmn, Dubhn, OH, 1985, pp 215-226

8 A L Baehr, Water Resour. Res, 23 (10) 1926-1938 9 A L Baehr, and M Y Corapcmglu, Water Resour Res, 23

(1) (1987) 201-213 10 L R Sflka, Groundwater Momtormg Revtew, 8 (2) (1988)

115-123 11 B E Sleep and J F Sykes, Water Resour Res, 25 (1)

(1989) 81-92

12 L M Abnola and G F Pmder, Water Resour Res, 21 (1) (1985) 11-18.

13 L M Abnola and G F Pinder, Water Resour Res, 21 (1) (1985) 19-26

14 R J Mdlmgton, Sctence, 130 (1961) 100-102 15 R W Falta, I Javamdel, K Preuss and P A Wltherspoon,

WaterResour Res, 25 (10) (1989) 2159-2169 16 J A Swallow and P M Gschwend, m Proceedmgs ofthe3rd

Nattonal Symposmm on Aqutfer Restoratton and Groundwa- ter Momtormg, National Water Well Assocaatmn, Dublin, OH, 1983

17 D M Mackay and W Y Shlou, J Phys Chem Ref Data, 10 (4) (1978) 1175-1198

18 H B Kerfoot, Ground Water Momtonng Revtew, NaUonal Water Well Assoclataon, Dubhn, OH, Spring (1988) 54-57

19 O D Evans and G M Thompson, m Proceedings of Petro- leum Hydrocarbons and Orgamc Chemwals tn Ground Wa- ter Preventton, Detection, and Restoraaon, Natmnal Water Well Assoeaauon, Dubhn, OH, 1986

20 H B Kerfoot, m Proceedmgs of the US EPA Workshop on Sod Vapor Extracuon, June 25-27, 1989, US Envtronmental Protection Agency, Edison, NJ

Henry B Kerfoot spectahzes m the momtormg and evaluauon of the subsurface fate and transport of volatde orgamc contamt- nants He has developed and evaluated several sod-gas survey and field analysts techmques and provtdes expert overstght tn de- szgn, quahty assurance, and data mterpretatton m sod-gas surveys and field analyses He also provtdes real-time momtonng, system destgn, and data evaluatton servtces for m sztu sod stripping (vapor extractton) cleanups and btocleanups of subsurface contamt- natwn and landfill gas mtgraaon momtormg He ts a prmctpal wtth Kerfoot and Assoaates, Las Vegas, NV, U S A , Tel (702) 361-1980 and has degrees m chemistry from Florida State Unwer- s,ty (M S ) and The Johns Hopkins Umversay (B S )

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soil-gas surveys for detection and delineation of groundwater contamination

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