Studies on soil contamination due to used motor oil and its remediation

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Studies on soil contamination due to used motoroil and its remediationS.K. Singh, R.K. Srivastava, and Siby JohnAbstract: An experimental program was undertaken to evaluate the changes in behaviour of soils due to interaction withused motor oil (U.M.O) followed by their remediation. Different types of soils classified as clay with low plasticity (CL),clay with high plasticity (CH), and poorly graded sand (SP) were used for the study. Laboratory studies were conductedon virgin (uncontaminated) soil samples and soil samples simulated to varying degrees of contamination (i.e., 3%, 6%,and 9% by dry weight of soil) to compare the geotechnical properties before and after contamination. The engineeringproperties altered due to contamination. Surfactant (sodium dodecyl sulphate (SDS)) enhanced washing was employed todecontaminate the soils. It was observed that the original geotechnical properties of soils could be almost restored (varia-tion ranging from 0 to 12%) upon decontamination with SDS at an optimum dosage.Key words: used motor oil, contamination, types of soils, decontamination, surfactant.Resume : Un programme experimental a ete entrepris pour evaluer les variations du comportement des sols soumis a` uneinteraction avec de lhuile a` moteur usee suivie par leur restauration. Des sols de type argile a` faible plasticite (CL), argilea` plasticite elevee (CH), et du sable uniforme (SP) ont ete utilises dans cette etude. Des etudes en laboratoire ont ete effec-tuees sur des echantillons de sol vierge (non contamine) et sur des echantillons simulant differents degres de contamination(i.e. 3%, 6% et 9% de la masse se`che du sol) afin de comparer les proprietes geotechniques avant et apre`s la contamina-tion. Les proprietes ont ete alterees par la contamination. Un lavage intensif avec un surfactant (dodecylsulfate de sodium(SDS)) a ete utilise pour decontaminer le sol. On a observe que les proprietes geotechniques originales des sols peuventetre restaurees a` divers degres (variation de 0 a` 12%) suite a` la decontamination a` un dosage optimal de SDS.Mots-cles : huile a` moteur usee, contamination, types de sols, decontamination, surfactant.[Traduit par la Redaction]IntroductionPetroleum and its refined products (gasoline, diesel, kero-sene, engine oil, jet fuel, etc.) are major resources used forenergy requirements in industrial and transportation sectorsthroughout the world. Motor oil is used for lubrication re-quirements of various kinds of automotive and other engines.During these types of uses, motor oil picks up a number ofadditional components from engine wear. These includeheavy metals, such as lead, chromium, cadmium, and othermaterials like naphthalene, chlorinated hydrocarbons, sul-phur. After the passage of time, oil changes become neces-sary due to a change in the viscosity of the oil. Any such oilthat becomes unsuitable after use due to contamination, mak-ing it unfit for its original purpose, is known as used motoroil (U.M.O) and is required to be suitably disposed of. Usedoils have the potential to be recycled and re-refined if safelyand properly collected, yet in many cases it is poured into anopen drain or thrown into the trash where it can contaminatethe subsurface soil and ground water. One litre of oil cancontaminate up to 1 million litres of water and can accumu-late in the subsoil system, posing a risk to the environment.A single automotive oil change is estimated to produce 45 L of used oil.The bulk of U.M.O generated in India (about 0.4 milliontons (1 ton = 0.907 t) annually) generally goes into undesir-able applications and only a very small amount (10 tons an-nually) is currently re-refined (IIP 1997). A large number ofroadside garages drain used oils from automobile enginesand there is no record of the next destination of such oils.Major oil-contaminated spots reported are Meethi River atKurla (Mumbai) and in the Mundka and Rohtak road areanear New Delhi (India) (IIP 1997). In the US, 11 milliontons of motor oil are sold annually, out of which 50% areconsumed (burned or leaked from engines). Out of the5 million tons of used oil generated, about 2 million tonsnever reach a recycling platform facility (TRB 1983; USEPA1988; Irwin et al. 1997). Likewise, about 0.1 million tons ofU.M.O is reported to be wasted annually in Australia (Kemp2004).The contaminants in the soil matrix are held either bychemical adsorption and (or) entrained within the pore spacesurrounding the soil grains. As the soil and used oil are rel-atively inert, they are held mostly in soil pores either bycapillary forces or as a small pool of liquid over clay andsilt lenses as residual nonaqueous phase liquids (NAPL)(Payatakes 1982). The properties, and hence behaviour, ofsubsurface soils get modified due to change in the character-istics of their pore fluid and its interaction with soil particle.Received 14 June 2007. Accepted 9 April 2009. Published onthe NRC Research Press Web site at on 31 August2009.S.K. Singh1 and S. John. Punjab Engineering College,Chandigarh 160012, India.R.K. Srivastava. Motilal Nehru National Institute OfTechnology (MNNIT), Allahabad 211004, India.1Corresponding author (e-mail: Geotech. J. 46: 10771083 (2009) doi:10.1139/T09-047 Published by NRC Research PressThe sensitivity of soil to the contaminants depends not onlyon the local environment, but is also influenced by the min-eral structure, particle size, bonding characteristics betweenparticles, ion exchange capacity, etc. The smaller the soilparticles, the greater the chances for a soil particle to inter-act with the contaminants. Based on the grain sizes of soil,Fang (1997) assigned a sensitivity index (ranging form 0 to1) to different types of soil. The sensitivities of sand andgravel (0.010.1) are much lower than clay particles (0.60.9).Contaminated land requires remediation with respect to ei-ther engineering or environmental considerations. A numberof techniques (i.e., excavation and disposal, washing, thermaltreatment, bioremediation, air sparging, electrokinetics andsolidification, etc.) are now available for the remediation ofcontaminated land (Ellis et al. 1984). However, the applic-ability and feasibility of the various options depend on thefield conditions. Pincus et al. (1995) conducted experimentson the decontamination of motor-oil-contaminated soil usingfour methods: thermal treatment (low and high), extractionmethod, and surfactant washing. An anionicnonionic surfac-tant without phosphorous was found to be the best surfactanttype to remove oils from different soils used in their study.The present paper first deals with an experimental evalua-tion of changes in the geotechnical properties of soil due tointeraction with U.M.O, followed by decontamination stud-ies with surfactant (sodium dedecyl sulphate (SDS)) washingtechnique.Materials and methodsThe three types of soils used in the present study wereclassified as low-plastic, high-plastic, and nonplastic soils.Used motor oil was the contaminant and SDS was used asthe surfactant for decontamination. The characterization ofthese materials and their basic properties are given in thefollowing sections.SoilsThree types of soils were selected: clay with low plasticity,clay with high plasticity, and sand, to cover the broad spec-trum of soils generally encountered. These soils were namedS-1, S-2, and S-3 as per the description given in Table 1.Soils S-1 and S-3 were natural soils collected locally fromopen pits. As the high-plasticity clay was not found in anearby region, it was decided to fabricate the soil by mixingcommercially available kaolinite (H4Al2Si2O4) with 15%bentonite (CaOAl2O35SiO22H2O) by weight. The plasticitycharacteristic of kaolinite soil was augmented with additionof bentonite powder. This fabricated soil with high plasticityis referred as S-2.Table 2 depicts composition based on grain-size analysis,Atterbergs limits (liquid, plastic, and shrinkage), and theclassification of the soils. The chemical characteristics ofthe soils are shown in Table 3.ContaminantUsed motor oil was chosen as the contaminant for thestudy. It was procured from a local automobile workshop.The grade of used oil was SAE 10W. Physical properties ofthe U.M.O are given in Table 4.Degree of contaminationIn this paper, degree of contamination is defined as thepercentage weight of contaminant (U.M.O) with respect todry weight of soil. The observed contamination level at thecontaminated sites provided a basis for contamination of thesoil in the laboratory at varying percentages (Singh 2005).Based on this consideration, the soil was contaminated at a3%, 6%, and 9% degree of contamination for further studies.The initial degree of contamination was fixed at 3% becausethe State of New Jersey classifies soils with an oil concen-tration above 3% as hazardous waste (Pincus et al. 1995).ContaminationThe calculated weight of U.M.O to achieve the desireddegree of contamination was sprayed on 5 kg of each typeof soil. The soilcontaminant mixture was pulverized man-ually and thoroughly mixed for 1 h in a covered tray. Themixture was placed in a covered container for 1 week sothat the U.M.O would come to equilibrium with the soils.During this period, the soils were mixed periodically. Drysoils required 24 to 48 h to come to equilibrium with water(USACE 1970; ASTM 1993).Evaluation of geotechnical propertiesThe index and engineering properties of the virgin soilswere determined as per relevant parts of SP36 (Bureau ofIndian Standards (BIS; former Indian Standards Institute)1987a). Similarly, geotechnical properties of the contami-nated samples were determined.Decontamination of soilThe optimum dosage of the SDS surfactant for decon-tamination was found by the trial and error method. The op-timum percentage of surfactant (SDS) was considered as theminimum dose that could restore the index properties of thecontaminated soil to those in the uncontaminated state. Theoptimum doses of SDS found from the trial tests were 1.5%,3.0%, 4.5%; 1.5%, 3.5%, 5%; and 1.0%, 2.0%, 3.0% forsoils S-1, S-2, and S-3 contaminated with 3.0%, 6.0%, and9.0% U.M.O, respectively. After determination of the opti-mum concentration of SDS, 5 kg of each of the contami-nated soils were batch-washed in a 30 L steel container.The required amounts of SDS were thoroughly mixed withthe soil in dry condition. Then, 12.5 L of water was addedto the SDS-mixed contaminated soil and vigorously stirredfor 0.5 h and was left to stand for 2 h. Subsequently, wateralong with the foam produced during mixing was decanted.The soil in the container was washed again with 12.5 L offresh tap water and decanted. During the process of decant-ation, care was taken that fines present in the soil would notdrain along with the liquid. The decanted solution was keptstanding in a separate container for 24 h. It was then filteredTable 1. Description of soil.Sample No. Classification of soil Name1 Clay-I (low plasticity) S-12 Clay-II (high plasticity) S-23 Sand S-31078 Can. Geotech. J. Vol. 46, 2009Published by NRC Research Pressto retain the soil fines that could have been discarded withthe decant. The filtered soil was remixed with washed soil.The washed soil was left to be air-dried for 67 days.Results and discussionTables 5 through 7 compare the engineering properties oforiginal, contaminated, and decontaminated soils. It can beobserved that the geotechnical properties change due to con-tamination with U.M.O.In general, maximum dry density deceases and uncon-fined compressive strength of the soil increases with degreeof contamination for the CL and CH clayey soil. Effectivecohesion increases and effective angle of internal frictiondecreases for the CL soil; whereas both shear parameters in-crease for the CH soil. However, effective angle of internalfriction for poorly graded sand decreases significantly uponcontamination, from 36.58 in the virgin state to 24.58 at 9%a contamination level, thereby reducing its bearing capacityin shear failure. Al-Sanad et al. (1995) and Shin et al.(2002) reported similar results.Hydraulic conductivity of both fine-grained soils classifiedas CL and CH increases with degree of contamination. In thecase of poorly graded sand (SP), hydraulic conductivity hasbeen found to decrease in comparison with its virgin state,the maximum value being at a 3% contamination level.These results are in agreement with the reported trends (Fer-nandez and Quigley 1991; Al-Tabba and Walsh 1994). Inpractice, clayey soils with low hydraulic conductivity(Table 5. Comparison of properties in original, contaminated, and decontaminated soil S-1.Contaminated soil:degree of contamination(% by weight)Decontaminated soil:optimum dose of SDS(% by weight)Engineering properties of soilStandard usedIS 2720Originalsoil S-1 3 6 9 1.5 3 4.5Variance for original soil S-1and decontaminated soilStandarddeviation, sVariation(%)Optimum moisture content (%) Part 7: 1980a 14.9 15.5 16.2 16.8 14.1 14.4 13.8 0.165 0.41 2.7Maximum dry density (kN/m3) Part 7: 1980a 18.15 17.85 17.26 16.77 18.05 17.85 17.56 0.203 0.45 2.48Unconfined compressive strength (kPa) Part 10: 1980b 96.1 137.3 167.7 144.2 93.2 96.1 84.4 9.20 3.03 3.15Effective cohesion (kPa) Part 12: 1981c 30.4 37.3 40.2 32.4 29.4 27.5 27.5 6.26 2.50 8.2Effective angle of internal friction (8) Part 12: 1981c 26.0 22.5 18.6 19.5 27.0 28.5 29.4 1.72 1.31 5.0Compression index Part 15: 1986d 0.17 0.23 0.24 0.27 0.16 0.16 0.13 2.5 104 0.01 5.9Coeff. of consolidation (m2/s 107) Part 15: 1986d 2.37 1.31 2.28 2.31 2.15 2.38 2.40 1.02 103 0.03 1.2Hydraulic conductivity (m/s 108) Part 17: 1986e 2.26 2.31 2.45 2.87 2.27 2.26 2.28 6.8 105 0.0082 0.4Differential free swell (%) Part 40: 1977 f 6.89 65.0 38.4 25.0 7.10 8.4 8.9 0.72 0.85 12.3% fines (passing 75 mm) Part 4: 1985g 90 88 86 85 89 88 86 9.25 3.04 3.37aBIS 1980a.bBIS 1980b.cBIS 1981.dBIS 1986b.eBIS 1986c.fBIS 1977.gBIS 1985.Table 6. Comparison of properties in original, contaminated and decontaminated soil S-2.Contaminated soil:degree of contamination(% by weight)Decontaminated soil:optimum dose of SDS(% by weight)Engineering properties of soilStandard usedIS 2720Originalsoil S-2 3 6 9 1.5 3.5 5Variance for original soil S-2and decontaminated soilStandarddeviation, sVariation(%)Optimum moisture content (%) Part 7: 1980a 19.5 21.6 21.7 23.3 19.1 18.5 17.6 0.51 0.71 3.6Maximum dry density (kN/m3) Part 7: 1980a 15.60 15.30 15.10 15.01 15.70 15.50 15.30 0.087 0.29 1.9Unconfined compressive strength (kPa) Part 10: 1980b 186.4 225.6 256.0 235.4 177.6 188.3 194.2 141.68 11.9 6.4Effecive cohesion (kPa) Part 12: 1981c 83.4 90.2 109.9 93.2 84.4 83.4 86.3 5.61 2.37 2.83Effective angle of internal friction (8) Part 12: 1981c 14.5 15.2 17.5 16.7 14.0 14.8 15.1 0.17 0.41 2.8Compression index Part 15: 1986d 0.50 0.56 0.62 0.54 0.46 0.51 0.48 3.7 104 0.02 4.0Coefficient of consolidation (m2/s 107) Part 15: 1986d 5.63 3.18 3.66 3.5 5.25 5.89 5.10 0.08 0.28 4.9Hydraulic conductivity (m/s 1010) Part 17: 1986e 2.86 3.82 4.25 4.46 2.97 3.10 3.17 0.05 0.22 7.7Differential free swell (%) Part 40: 1977f 84.2 95.0 115.0 155.8 85.0 87.5 87.5 2.18 1.47 1.74% fines (passing 75 mm) Part 4: 1985g 98 96 95 95 97 96 95 5.00 2.23 2.27aBIS 1980a.bBIS 1980b.cBIS 1981.dBIS 1986b.eBIS 1986c.fBIS 1977.gBIS 1985.1080Can.Geotech.J.Vol.46,2009PublishedbyNRCResearchPressphysical interaction are viscosity, density, and surface ten-sion of contaminating oils. Physical interaction is predomi-nant in the case of granular soils, whereas physico-chemicalinteraction may take place in fine-grained soils. For soilswith high plasticity, chemical interaction overrides the phys-ical interaction. For nonpolar organic contaminating fluid,the dielectric constant is the important parameter that bringschanges in the thickness of the diffuse double layer inclayey soils. A smaller value of the dielectric constant forpetroleum oils decreases the thickness of the diffuse layerand consequently, the structure of clays tends to be moreflocculated.For remediation studies, the optimum percentage weightsof the surfactant with respect to the weight of contaminatedsoils is one-half and one-third of the degree of contamina-tion in the CL soil and SP soil, respectively. The surfactant(SDS) washing is found to be effective in restoring the orig-inal soil properties with a variation ranging from 0 to 12%.The Fourier transform infrared (FTIR) spectra (Figs. 13)for the contaminated and decontaminated soil samples alsoconfirm the physical removal of U.M.O from the soil matrixas the peak corresponding to 2930 cm1 vanishes after wash-ing. In FTIR spectroscopy, transmission of infrared (in %)through soil samples as the ordinate is plotted against thewave number (in cm1) as the abscissa to identify the func-tional groups corresponding to different peaks, i.e., maxi-mum absorbance. The characteristic peak for the C-H bondoccurs at a wave frequency of 2930 cm1.Table7.Comparisonofpropertiesinoriginal,contaminatedanddecontaminatedsoilS-3.Contaminatedsoil:degreeofcontamination(%byweight)Decontaminatedsoil:optimumdoseofSDS(%byweight)EngineeringpropertiesofsoilStandardusedIS2720OriginalsoilS-3369123VariancefororiginalsoilS-3anddecontaminatedsoilStandarddeviation,sVariation(%)Max.voidratioPart14:1983a0.910.950.810.770.910.940.921.51040.011.1Min.voidratioPart14:1983a0.500.450.440.450.490.500.492.51050.0051.0Angleofinternalfriction(8)Part13:1986b36.529.526.724.536.034.534. )Part17:1986c3.151.861.671.353.102.892.950.010.103.1Californiabearingratio,unsoakedcondition(%)Part16:1987d15.122.516.83.518.615.813.92.981.7211.4CompressionindexPart15:1986e0. BIS1986a.cBIS1986c.d BIS1987b.eBIS1986b.f BIS1985.Fig. 1. FTIR spectra of soil S-1: (a) contaminated with 6% U.M.O;(b) decontaminated with optimum dose of SDS.Singh et al. 1081Published by NRC Research PressConclusionsThe performance of soil as a supporting medium or con-struction material is affected adversely by contaminationwith U.M.O due to changes in some of the soil properties.Volume-change characteristics, i.e., consolidation settlementand swelling characteristics, are augmented in the contami-nated state for clayey soils (CL and CH). The effective an-gle of internal friction of sandy soil (SP) decreases sharplyupon contamination with U.M.O. Soils contaminated withU.M.O are prone to undergo more settlement and suscepti-ble to large volume changes upon saturation. The shearstrength and allowable bearing pressure on granular soil de-creases significantly upon contamination with U.M.O,thereby restricting its use as a supporting medium. A struc-ture that is already constructed will experience distress, suchas cracks, upon subsequent contamination of the supportingsoil. Sand containing up to a 6% U.M.O content can be ad-vantageously used as a subgrade or subbase material underflexible pavement. In the design of of clay liner thickness,the hydraulic conductivity of clays to be used as liner mate-rial should be determined using the actual contaminatingfluid.Remediation of contaminated soils is a practical necessitywith respect to geotechnical and environmental considera-tions. Although laboratory results indicated the restorationof original geotechnical properties of the soil and physicalremoval of contaminants from the soil matrix with surfactant(SDS) washing, a mechanized system needs to be developedfor its practical application in the reclamation of contami-nated land.ReferencesAl-Sanad, H.A., Eid, W.K., and Ismael, N.F. 1995. Geotechnicalproperties of oil contaminated Kuwaiti sand. Journal of Geotech-nical Engineering, 121(5): 407412. doi:10.1061/(ASCE)0733-9410(1995)121:5(407).ASTM. 1993. Standard test method for liquid limit, plastic limitand plasticity index of soils. ASTM standard D4318-84. In An-nual Book of ASTM Standards. Vol. 04.08. American Societyfor Testing and Materials (ASTM), West Conshohocken, Pa.ASTM. 2006. Standard practice for classification of soils for engi-neering purposes (Unified Soil Classification System). ASTMstandard D2487. American Society for Testing and Materials(ASTM), West Conshohocken, Pa.Al-Tabba, A., and Walsh, S. 1994. Geotechnical properties of aclay contaminated with an organic chemical. In Proceedings ofthe 1st International Congress on Environmental Geotechnics,Edmonton, Alta., 1015 July 1994. Bitech Publishers, Rich-mond, B.C. pp. 599604.Fig. 2. FTIR spectra of soil S-2: (a) contaminated with 6% U.M.O;(b) decontaminated with optimum dose of SDS.Fig. 3. FTIR spectra of soil S-3: (a) contaminated with 6% U.M.O;(b) decontaminated with optimum dose of SDS.1082 Can. Geotech. J. Vol. 46, 2009Published by NRC Research PressBIS. 1972. Determination of shrinkage factors. IS 2720 Part 6. Bu-reau of Indian Standards, New Delhi, India.BIS. 1977. Determination of free swell index of soils. IS 2720Part 40. Bureau of Indian Standards, New Delhi, India.BIS. 1980a. Determination of water content dry density relationusing light compaction. IS 2720 Part 7. Bureau of Indian Stan-dards, New Delhi, India.BIS. 1980b. Determination of unconfined compressive strength.IS 2720 Part 10. Bureau of Indian Standards, New Delhi, India.BIS. 1981. Determination of shear strength parameters of soil fromconsolidated undrained tri-axial compression test with measure-ment of pore-water pressure. IS 2720 Part 12. Bureau of IndianStandards, New Delhi, India.BIS. 1983. Determination of density index (relative density) of co-hesionless soil. IS 2720 Part 14. Bureau of Indian Standards,New Delhi, India.BIS. 1985a. Grain size analysis. IS 2720 Part 4. Bureau of IndianStandards, New Delhi, India.BIS. 1985b. Determination of liquid and plastic limits. IS 2720Part 5. Bureau of Indian Standards, New Delhi, India.BIS. 1986a. Direct shear test. IS 2720 Part 13. Bureau of IndianStandards, New Delhi, India.BIS. 1986b. Determination of consolidation properties. IS 2720Part 15. Bureau of Indian Standards, New Delhi, India.BIS. 1986c. Laboratory determination of permeability. IS 2720Part 17. Bureau of Indian Standards, New Delhi, India.BIS. 1987a. Compendium of Indian standards on soil engineering,Part 1: Laboratory testing of soils for civil engineering purposes.Special Publication SP36. Bureau of Indian Standards, NewDelhi, India.BIS. 1987b. Laboratory determination of CBR. IS 2720 Part 16.Bureau of Indian Standards, New Delhi, India.Ellis, W.D., Payne, J.R., Tatuni, A.N., and Freestone, F.J. 1984.The development of chemical countermeasures for hazardouswaste contaminated soil. In Proceedings of the Hazardous mate-rials spills conference, Nashville, Tenn., 912 April 1984. Edi-ted by J. Ludwigson. Government Institutes Inc., Rockville, Md.pp. 116125.Fang, H.Y. 1997. Introduction to environmental geotechnology.CRC Press, Boca Raton, Fla.Fernandez, F., and Quigley, R.M. 1991. Controlling the destructiveeffects of clay organic liquid interaction by application of effec-tive stress. Canadian Geotechnical Journal, 28(3): 388398.doi:10.1139/t91-049.IIP. 1997. A report on lubricating oil. Indian Institute of Petroleum,Dehradun, India.Irwin, R.J., Van Mouwerik, M., Stevens, L., Seese, M.D., and Ba-shum, W. 1997. Environmental contaminants encyclopedia. Na-tional Park Service, Water Resources Divisions, Fort Collins,Colo.Kemp, D. 2004. Do the right thing: responsibly dispose of usedmotor oil. Available from [cited5 May 2007].Payatakes, A.C. 1982. Dynamics of oil ganglia during immiscibledisplacement in water wet porous media. Annual Review ofFluid Mechanics, 14(1): 365393. doi:10.1146/annurev.fl.14.010182.002053.Pincus, H.J., Meegoda, N.J., and Ratnaweera, P. 1995. Treatmentof oil contaminated soils for identification and classification.Geotechnical Testing Journal, 18(1): 4149. doi:10.1520/GTJ10120J.Shin, E.C., Omar, M.T., Tahmaz, A.A., Das, B.M., and Atalar,C. 2002. Shear strength and hydraulic conductivity of oil-contaminated sand. In Proceedings of Environmental Geotech-nics IV (ICEG), Rio de Janeiro, Brazil, 1115 August 2002.Edited by L.G. De Mello and M. Almeida. A.A. Balkema,Lisse, the Netherlands. pp. 913.Singh, S.K. 2005. Characterisation and evaluation of behaviour ofsoil contaminated with petroleum hydrocarbons. Ph.D. thesis,Department of Civil Engineering, Panjab University, Chandi-garh, India.Sridharan, A., and Rao, G.V. 1973. Mechanisms controlling vo-lume change of saturated clays and the role of effective stressconcept. Geotechnique, 23(3): 359365.TRB. 1983. Transportation of hazardous materials: Towards a na-tional strategy. Vol. 1. Transportation Research Board, Washing-ton, D.C.USACE. 1970. Laboratory soil testing. Engineering Manual 11102-1906 [updated through 20 August 1986]. US Army Corps ofEngineers, Washington, D.C.USEPA. 1988. Superfund exposure assessment manual. EPA/540/188/001. Office of Remedial Responses, U.S. EnvironmentalProtection Agency, Washington, D.C.Singh et al. 1083Published by NRC Research Press /ColorImageDict > /JPEG2000ColorACSImageDict > /JPEG2000ColorImageDict > /AntiAliasGrayImages false /CropGrayImages true /GrayImageMinResolution 150 /GrayImageMinResolutionPolicy /OK /DownsampleGrayImages true /GrayImageDownsampleType /Average /GrayImageResolution 225 /GrayImageDepth -1 /GrayImageMinDownsampleDepth 2 /GrayImageDownsampleThreshold 1.00000 /EncodeGrayImages true /GrayImageFilter /DCTEncode /AutoFilterGrayImages true /GrayImageAutoFilterStrategy /JPEG /GrayACSImageDict > /GrayImageDict > /JPEG2000GrayACSImageDict > /JPEG2000GrayImageDict > /AntiAliasMonoImages false /CropMonoImages true /MonoImageMinResolution 1200 /MonoImageMinResolutionPolicy /OK /DownsampleMonoImages true /MonoImageDownsampleType /Average /MonoImageResolution 600 /MonoImageDepth -1 /MonoImageDownsampleThreshold 1.00000 /EncodeMonoImages true /MonoImageFilter /CCITTFaxEncode /MonoImageDict > /AllowPSXObjects true /CheckCompliance [ /None ] /PDFX1aCheck false /PDFX3Check false /PDFXCompliantPDFOnly false /PDFXNoTrimBoxError true /PDFXTrimBoxToMediaBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXSetBleedBoxToMediaBox true /PDFXBleedBoxToTrimBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXOutputIntentProfile (None) /PDFXOutputConditionIdentifier () /PDFXOutputCondition () /PDFXRegistryName ( /PDFXTrapped /False /CreateJDFFile false /SyntheticBoldness 1.000000 /Description >>> setdistillerparams> setpagedevice


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