Environ Monit Assess (2007) 124:331–341DOI 10.1007/s10661-006-9230-9

O R I G I N A L A R T I C L E

Petroleum contaminated soil in Oman: Evaluationof bioremediation treatment and potential for reuse in hotasphalt mix concrete

Ahmad Jamrah · Ahmed Al-Futaisi ·Hossam Hassan · Salem Al-Oraimi

Received: 18 October 2005 / Accepted: 28 February 2006 / Published online: 7 September 2006C© Springer Science + Business Media B.V. 2007

Abstract This paper presents a study that aims atevaluating the leaching characteristics of petroleumcontaminated soils as well as their application in hotmix asphalt concrete. Soil samples are environmen-tally characterized in terms of their total heavy metalsand hydrocarbon compounds and leachability. The to-tal petroleum hydrocarbon (TPH) present in the PCSbefore and after treatment was determined to be 6.8%and 5.3% by dry weight, indicating a reduction of 1% inthe TPH of PCS due to the current treatment employed.Results of the total heavy metal analysis on soils indi-cate that the concentrations of heavy metals are lowerwhen extraction of the soil samples is carried out usinghexane in comparison to TCE. The results show thatthe clean soils present in the vicinity of contaminatedsites contain heavy metals in the following decreasingorder: nickel (Ni), followed by chromium (Cr), zinc(Zn), copper (Cu), lead (Pb), and vanadium (V). Thecurrent treatment practice employed for remediationof the contaminated soil reduces the concentrations ofnickel and chromium, but increases the concentrationsof all remaining heavy metals.

Keywords Petroleum contaminated soil . Toxicitycharacteristic leaching procedure . Heavy metals .Hydrocarbons . Hot asphalt mix

A. Jamrah · A. Al-Futaisi · H. Hassan · S. Al-OraimiDepartment of Civil and Architectural Engineering, SultanQaboos University, P.O. Box 33, Al-Khod, Muscat 123,Oman

1 Introduction

Oil pipeline leakage and accidental oil spills are com-mon problems in petroleum industry resulting into con-tamination of soils. Toxic heavy metals and petroleumhydrocarbons present in such contaminated soils canleach into the surrounding subsurface and groundwa-ter, posing a threat to the environment and to hu-man health. Petroleum-contaminated soil (PCS) is amixture of sand, silt, clay and petroleum products(Meegoda and Muller, 1993). In Oman, PetroleumDevelopment Oman (PDO) generates approximately53,000 tons/year of PCS which raises a real disposalproblem. Disposal of PCS in waste dumping sites is notconsidered an option because of the lack of proper de-sign and control of dumping sites in Oman which posesa continuous threat of further contamination to the soil.Thermal treatment of PCS is considered expensive pro-cess and is suspected to cause air pollution. PDO hasattempted treating the PCS using biodegradation pro-cesses, namely land farming. This treatment methodhas been employed by many researchers (Trindadeet al., 2005; McCarthy et al., 2004; Gogoi et al., 2003;Nocentini et al., 2000). The treatment utilizes aerobicbacteria at a treatment area of approximately 85 by8 meters. The contaminated soil is mixed with cleandesert sand to reduce the hydrocarbon concentrationto less than 5% by weight. The depth of contaminatedsoil is typically limited to 20 cm. Water is added dailyto keep the water content within 30–60% of the soilholding capacity. Nitrogen and phosphorus are added

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with 2 and 0.4 parts to 100 part contaminated soil, re-spectively, as nutrients for bacteria. This process is con-tinued for 3–4 months. After that, the soil is dumpedwithin the premises of the treatment plant. PDO is real-izing that their land farming practice is not an effectivetreatment and the level of reduction in the concentra-tion of petroleum contaminants in the soils is minimalas will be clearly indicated in this paper.

Recently, PDO has indicated an interest in evaluat-ing the potential use of its petroleum contaminated soilin engineering construction applications such as roadsand buildings as a beneficial and economical approach.The use of material into construction applications ap-pears to be an appealing approach (Hassan et al., 2005;Taha et al., 2004). However engineering and environ-mental aspects need to be addressed. In other words,the effect on engineering properties and leaching char-acteristics of contaminants such as heavy metals andpetroleum hydrocarbons from such applications needsto be thoroughly investigated.

Several studies have attempted to use PCS in hotmix asphalt concrete (HMA). In Massachusetts, ne-gotiations with the Massachusetts Department of Envi-ronmental Quality and Engineering (DEQE) resulted inallowing the use of contaminated soils containing 3% ofoil, gasoline or kerosene and allowing up to 5% contam-inated soil replacement for aggregate to produce a goodquality HMA (Czarnecki, 1988). Meegoda and Muller(1993) investigated the incorporation of PCS into HMAin New Jersey and found that it was possible to includeup to 35% PCS in the mix. The mixes were evaluated forstability using the Marshall method and durability us-ing the tensile strength ratio for conditioned and uncon-ditioned specimens (AASHTO, 1997). Meegoda et al.(1994) showed that the tensile strength ratio (TSR) forHMA mixes prepared using PCS were not significantlydifferent from the control mix. In Massachusetts, this isdone by limiting the hot mix in the plants to an admix-ture of 5–10% of contaminated soil in their aggregate(Eklund, 1988).

This paper addresses the leachability characteristicsof PDO-contaminated soils and their possible applica-tion in hot mix asphalt. First, experimental proceduresare presented and discussed. Second, the collected PCSsamples are environmentally characterized in terms oftheir content of total heavy metals and toxic petroleumhydrocarbons. In the same section, we also discuss theefficiency of the treatment procedure (land farming)that PDO currently implements. Third, the leachabil-

ity characteristics of some selected heavy metals fromthe PCS are investigated using the leaching test TCLP.Finally, with the same leaching test, the leachability ofthe heavy metals from the PCS asphalt mix applicationis studied.

2 Experimental procedure

2.1 Samples collection and preparation

Three different soils were used in this study: clean(uncontaminated desert soil), contaminated soil, andtreated soil. All three soils were obtained from thepetroleum asset area in Fahud (northern Oman). Thetreated soil is actually the contaminated soil after sub-jecting it to bioremediation. An actual hot mix used ona construction project in Oman was used as a controlin the experiments of asphalt applications of the PCS.The mix was composed of 20 mm and 10 mm coarseaggregate sizes. The sand sizes varied between 3–5 mmand 0–3 mm. In addition, mineral filler, which is a pow-der produced from the drying and heating of the sameaggregates in the mixing plant, was used. Asphalt ce-ment was a penetration grade 60–70. The Marshall Mixdesign method using 75 blows per face was used in allmixes. The 0–3 mm fine aggregate size was replaced byPCS with different percentages, namely; 5, 10, 15, 20,30, and 40%, by total aggregate weight. The trial rangeof asphalt content was 3.5 to 5.5%, of total weight of themix, in 0.5% increments. Three samples were preparedfor each asphalt content.

2.2 Separation of phases

The gravimetric method EPA 9071B was used in thisstudy for separating water, oil and solids in PCS sam-ples and hence estimating the moisture, hydrocarbonsand total heavy metals in each sample. It should benoted that the gravimetric method EPA 9071B is themethod recommended for quantifying the concentra-tions of oil and grease in soil, sediments, oily sludge,and other solid materials amenable to chemical dryingand solvent extraction. The method is specifically suit-able for extracting relatively non-volatile hydrocar-bons. The solvents used in the extraction processeswere n-hexane and trichloroethylene (TCE). The mois-ture content of the PCS was determined based on thegravimetric method using a 5 gram sample.

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The petroleum hydrocarbon analysis was carried us-ing 10 grams of PCS sample blended with 10 grams ofanhydrous sodium sulfate and extracted with 90 ml ofsolvent (hexane or TCE). Extraction of petroleum hy-drocarbons from a PCS sample lasted for a period of4 hrs. Then, a rotary evaporator was used to remove thesolvent from the extract. Finally, the total petroleumhydrocarbon (TPH) is gravimetrically determined inmg/kg. A third portion of the same PCS sample wasextracted with the same procedure but without addingthe anhydrous sodium sulfate. In this case, the remain-ing solid phase in the extraction thimble is used for thecalculation of total heavy metals in the PCS.

2.3 Total heavy metals

A mass of 0.25 g from the separated solids of the PCSsample was weighed into a microwave digestion bomb(Milestone Microwave Lab System) to which 5.0 mlof concentrated nitric acid was added, and the samplewas digested in a microwave oven for 40 minutes. Af-ter the sample was cooled to room temperature, 5 ml of30% hydrogen peroxide was added and the sealed mi-crowave bomb was reheated in the microwave oven foranother 40 minutes to speed and complete the digestion.Samples were then filtered through prerinsed Whatman45 filter paper and diluted to 50 ml. The metals Cd, Ni,Pb, Cr, Cu, V and Zn were then measured using Induc-tively Coupled Plasma Optical Emission Spectrometry(Perkin-Elmer Model 3300 DV ICP-OES), with a meanerror of analysis of less 2%.

2.4 Hydrocarbon analysis

The oil extract obtained from the separation of phasesis first used to gravimetrically determine the totalpetroleum hydrocarbon (TPH in mg/kg) by dividingthe calculated weight of the remaining oil, after evap-orating the solvent, by the weight of the wet sample.Then, using Gas Chromatography with mass spectrom-eters (GS/MS Varian Model), chromatogram plots ofthe various hydrocarbons in the PCS sample were pro-duced and compared. As will be shown in Table 3,concentrations of selected volatile organic compounds(VOC), non-halogenated VOC, and semi-volatile or-ganic compounds (SVOC) listed by EPA were mea-sured using same GC/MS.

2.5 Leaching experiments

The Toxicity Characteristic Leaching Procedure(TCLP) as developed by the U.S. EPA was designed tosimulate the leaching of metals and organic compoundsfrom the untreated PCS, treated PCS, and their asphaltapplications considered in this study. An appropriateextraction fluid for each application mixture wasdetermined based on the pH of sample as described inTCLP. Control of pH was carried out during the tests.Dry sample of (10 g) and the appropriate extractionfluid were put with a 20:1 ratio of liquid to dry sampleinto polypropylene extraction bottles for metals andborosilicate glass bottles with Teflon-lined caps forhydrocarbons. The extraction bottles were sealed andthen rotated on a specially designed rotator for 18 hrs.All samples in this study were ground to <0.85 mm.At the end of 18 hrs extraction period, the phases wereseparated. Metal concentrations in the extract wereanalyzed using Inductively Coupled Plasma OpticalEmission Spectrometry (Perkin-Elmer Model 3300DV ICP-OES). Concentrations of Cd, Ni, Pb, Cr, Cu,V and Zn were measured by ICP using the methoddescribed in Standard Methods (Greenberg et al.,1992). The level of concentration are compared withthe TCLP limits (EPA, 1998).

3 Results and discussion

3.1 General characteristics

The geotechnical properties of the raw soils are pre-sented in Fig. 1 and Table 1. The grain size distributionof the soil particles is shown in Fig. 1 and indicatesthat 95% of the gradation of all the three soil samplesfall in the range between 4.75 and 0.075 mm, which ismainly the range for sands as classified by Unified SoilClassification System (USCS).

The results presented in Table 1 indicate that the un-treated soil had the lowest bulk specific gravity of 1.96due to its high oil content in comparison to the treatedand natural soils which had values of 2.23 and 2.59,respectively. The three soils were classified as poorlygraded sand according to the Unified Soil ClassificationSystem.

The uniformity coefficient (Cu) and coefficientof curvature (Cc) were calculated from the grain

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Table 1 Geotechnicalproperties of the three soilsused in this study

Properties Untreated soil Treated soil Clean soil

Moisture content (%) 6.15 1.51 2.93Maximum dry density (kg/m3) 2002 2080 1838Optimum moisture content (%) 8.2 10.02 17.10Bulk specific gravity 1.96 2.23 2.59Bulk specific gravity (SSD) 2.05 2.58 2.67Apparent specific gravity 2.13 2.58 2.67Absorption (%) 4.1 6.1 1.2Uniformity coefficient, Cu

a 1.85 6.11 9.44Coefficient of curvature, Cc

b 0.82 0.40 0.33Liquid limit, % 20 21 –d

Plastic limit, % NP NP –d

Sand equivalent, % 82 84.2 –d

USCSc SP SP SP

SSD = saturated surface drycondition, NP =non-plastic, SP = poorlygraded sandaCoefficient of uniformitybCoefficient of curvaturecUnified soil classificationsystemdNot available

Fig. 1 Grain size distribution curves of Clean desert, Untreatedand Treated soils used in this study

size distribution curves as Cu = D60/D10 and Cc =D2

30/D60.D10, respectively.

3.2 Heavy metals

Results of the total heavy metal analysis on soils areshown in Figs. 2 and 3 for the Clean desert, Untreatedand Treated soils used in this study. The figures showthe results of total heavy metal analysis for the soils af-ter the separation of oil for the metals which are of mostimportance with regard to PCS (Hong et al., 1995). Itshould be noted that most of these metals have cu-mulative effect, and are of particular hazard (Metcaland Eddyi 2003, Peavy et al., 1985). In general, heavymetals present in PCS can be concentrated in the foodchain, which eventually results in more risk to humans.

The results presented in Fig. 2 indicate lower heavymetal content in all of the soils when oil was extractedusing hexane than TCE. This observation can be ex-plained by the nature of the method used for separationof oil from soils. The gravimetric method EPA 9071B is

the method recommended by the EPA (USEPA, 1994)for quantifying the concentrations of oil and grease insoil, sediments, oily sludge, and other solid materialsamenable to chemical drying and solvent extraction.The method is specifically suitable for extracting rela-tively non-volatile hydrocarbons. Method 9071B em-ploys n-hexane as the extraction solvent with Soxhletextraction. In the original EPA procedure for such ex-periment, EPA 418.1, Freon-113 was used as a solvent.However, it has been reported that n-hexane was judgedto be the best alternative solvent for Freon-113 (EPA,1993).

Figure 3 shows that the clean soils present in thevicinity of contaminated sites contain relatively highconcentrations of nickel (Ni), followed by relativelylower concentrations of chromium (Cr), zink (Zn), cop-per (Cu), lead (Pb), and vanadium (V) in decreasingorder. The contamination of the soils by petroleum hy-drocarbons, represented here by Untreated, results inalmost doubling the concentrations keeping the sameorder observed in the clean soil. The high concentra-tions of nickel can be attributed to the compositionof natural soil, as some natural soils are known to berich of certain metals such as nickel (USDA, 2001).With regard to the treatment practice that PDO imple-ment for treating the contaminated soils, it is observedthat the practice indeed reduces the concentrationsof nickel and chromium. However, it unfortunatelyincreases the concentrations of all remaining heavymetals. These soils are the weathering products of theSemail Ophiolite rocks which are known to containhigh Ni and Cr. This could be the source for high Ni inthe samples.

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Fig. 2 Comparison of totalheavy metal content of theuntreated soil after oil wasseparated using Hexane andTCE

Fig. 3 Comparison of totalheavy metal contents of thethree soils used in the study

3.3 Hydrocarbons

The organic content of PCS is of great importancewhen treatment of PCS is being considered and eval-uated. Organics, similar to inorganics, can be of natu-ral or manufactured source. However, unlike inorganiccompounds, organics are usually less soluble in water(Sawyer et al., 2003). This indicates that organic com-pounds may persist in PCS unless they are destroyedduring treatment.

The total petroleum hydrocarbon (TPH) present inthe PCS before and after treatment was determinedgravimetrically using the soxhlet apparatus, and the re-sults are shown in Table 2. The table shows that theTPH of untreated and treated PCS soils is 6.8 and 5.3%by dry weight; respectively. This indicates a reduction

Table 2 Total petroleum hydrocarbon (TPH) content inthe extract of PCS before and after treatment in mg/kg

Extraction solvent Untreated sample Treated sample

Hexan 63,000 53,125TCE 68,000 58,000

of 1% in the TPH of PCS due to the current treat-ment employed. It should be noted that TPH levelsobtained in this study are substantially different fromthose reported by Itrube et al. (2005) for petroleum-contaminated soils in Mexico.

This finding was further substantiated through chro-matogram plots of the various hydrocarbons in the PCSsoils. Figure 4 presents chromatograms of hydrocar-bons present in the extracts of treated and untreatedPCS generated using gas chromatograph equipped withmass spectrophotometer (GC/MS). The figure showsthat the chromatogram of treated PCS soil is very sim-ilar to that of the untreated PCS, and that the concen-tration of hydrocarbons as measured by TPH is notexpected to be significantly different.

The concentrations of specific volatile organic com-pounds (VOC), non-halogenated VOC, and semi-volatile organic compounds (SVOC) listed by EPA andpresent in the extracts of treated and untreated PCS soilswere also measured using same GC/MS. The results ofthe analysis are shown in Table 3, and the reported con-centrations are in μg/L. The table shows that treatedand untreated soils have similar low undetectable lev-els of these hydrocarbons. Additionally, unlike the

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Fig. 4 Chromatograms of hydrocarbons present in the extracts of treated and untreated PCS generated using gas chromatographequipped with mass spectrophotometer (GC/MS)

untreated soil, the treated soil contains very low lev-els of dibutylphthalate and bis(2-ethylhexyl)phthalatewhich constitute no risk (EPA, 2000 and OSHA, 1996).The source of these hydrocarbons should be investi-gated, and may very well be due to the current treatmentmethod employed.

3.4 TCLP experiments

With the very low levels of toxic hydrocarbons detectedin the soils, only the leaching characteristics of heavymetals will be considered.

3.5 Raw soils

Results of the Toxicity Characteristic Leaching Proce-dure (TCLP) for the three soils used in this study are

shown in Table 4 and plotted in Fig. 5. It should benoted that the TCLP limit is not reported in the litera-ture for Ni, Cu, and Zn. The table indicates that TCLPconcentrations of these metals are well below the TCLPregulatory limit. This indicates that these soils wouldpose no immediate or long-term threat to the environ-ment.

Figure 5 shows that copper and zinc are the majormetals that can be found in the leachate of the threesoils. The presence of zinc is expected, and follows arelatively similar trend to that observed in Fig. 3 forthe total heavy metal content of the three soils. Thepresence of copper in the leachate can be explained bythe fact that free copper tends to be the predominantcopper-containing species when the pH is below 6.5(Snoeyink and Jenkins, 1980). It should be noted thatthe TCLP extraction fluids throughout this study hadpH values below 5.0.

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Table 3 Concentrations of specific volatile organic compounds (VOC), non-halogenated VOC, and semi-volatile organic com-pounds (SVOC) present in the extract of PCS before and after treatment in μg/L

Compounds Untreated PCS Treated PCS Compounds Untreated PCS Treated PCS

Bis (2-chloroethyl) ether 0.000 0.000 3-nitroaniline 0.000 0.0002-chlorophenol 0.000 0.000 Acenaphthene 0.000 0.0001,2-dichlorobenzene 0.000 0.000 Dibenzofuran 0.000 0.0001,3-dichlorobenzene 0.000 0.000 2,4 dinitrotoluene 0.000 0.0001,4-dichlorobenzene 0.000 0.000 Diethyl phthalate 0.000 0.0002-methylphenol 0.000 0.000 Fluorene 0.000 0.0004-methylphenol 0.000 0.000 4-chlorophenyl phenyl eth 0.000 0.000Hexachloroethane 0.000 0.000 4-nitroaniline 0.000 0.000Nitrobenzene 0.000 0.000 Azobenzene 0.000 0.000isophorone 0.000 0.000 4-bromophenyl phenyl ethe 0.000 0.0002-nitophenol 0.000 0.000 Hexachlorobenzene 0.000 0.0002,4-dimethylphenol 0.000 0.000 Phenanthrene 0.000 0.000Bis (2-chloroethomethane) 0.000 0.000 Anthracene 0.000 0.0002,4-dichlorophenol 0.000 0.000 Carbazole 0.000 0.0001,2,4-trichlorobenzene 0.000 0.000 Dibutyl phthalate 0.000 0.589Naphthalene 0.000 0.000 Fluoranthene 0.000 0.0004-chloroaniline 0.000 0.000 Pyrene 0.000 0.000Hexachlorobutadiene 0.000 0.000 Benzyl butyl phthalate 0.000 0.0004-chloro-3-methylphenol 0.000 0.000 Benz [a] anthracene 0.000 0.0002-methylnaphthalene 0.000 0.000 Chrysene 0.000 0.000Hexachlorocyclopentadiene 0.000 0.000 Bis (2-ethylhexyl) phthala 0.000 0.9232,4,6-trichlorophenol 0.000 0.000 Di-n-octyl phthalate 0.000 0.0002,4,5-trichlorophenol 0.000 0.000 Benzo [b] fluoranthene 0.000 0.0002-chloronaphthalene 0.000 0.000 Benzo [k] fluoranthene 0.000 0.0002-nitroaniline 0.000 0.000 Benzo [a] pyrene 0.000 0.000Dimethy phthalate 0.000 0.000 Indeno [1,2,3-cd] pyrene 0.000 0.0002,6 dinitrotolunene 0.000 0.000 Dibenz [a,h] anthracene 0.000 0.000Acenaphthylene 0.000 0.000 Benzo [ghi] perylene 0.000 0.000

Table 4 TCLP regulatorylimits and results of heavymetal concentrations inmg/L of the TCLP for thethree soils used in the study

Cd Ni Pb Cr Cu Zn

Clean <0.002 0.0085 0.007 <0.005 0.5185 0.243Treated <0.002 0.0095 0.009 <0.005 0.092 0.4195Untreated <0.002 0.023 0.016 <0.005 0.2235 0.3045TCLP limit 1.0 − 5.0 5.0 − −

3.6 Applications

The leaching test was performed on the upper andlower limits of PCS replacements together with threeasphalt contents: lower (3.5%), upper (5.5%), and mid-range (4.5%). The reported results are the average ofduplicate samples. Results of the Toxicity Character-istic Leaching Procedure (TCLP) for the three soilsreused in asphalt applications this study are shown in

Table 5 and plotted in Fig. 6. It should be noted thatthe leaching experiments were not carried out on themid-range asphalt content of the clean soil, and theupper-range asphalt content of the untreated soil. Thetable indicates that TCLP concentrations of these met-als measured for the three soils and their asphalt ap-plications are well below the TCLP regulatory limit.This indicates that these soils and their asphalt appli-cations would pose no immediate or long-term threat

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Table 5 TCLP regulatory limits and results of heavy metal concentrations in mg/L of the TCLP for the three soils andtheir asphalt applications used in the study

Soil Type % Soil % Asphalt Cd Ni Pb Cr V Cu Zn

Clean 5 3.5 <0.0005 0.014 0.0145 0.0055 < 0.001 < 0.001 0.024540 3.5 <0.0005 0.0055 0.0185 0.0065 < 0.001 < 0.001 0.00755 4.5 <0.0005 0.0035 0.0155 0.006 < 0.001 0.0015 0.025540 4.5 − − − − − − −5 5.5 <0.0005 0.004 0.0245 0.0115 <0.001 0.053 0.10640 5.5 <0.0005 0.005 0.0235 0.0085 <0.001 0.041 0.097

Treated 5 3.5 <0.0005 0.0085 0.14 0.0081 <0.001 0.3585 1.1840 3.5 <0.0005 0.0079 0.04 0.0085 <0.001 0.1535 0.14155 4.5 <0.0005 0.0074 0.186 0.008 <0.001 0.2835 0.554540 4.5 <0.0005 0.00875 0.0745 0.0077 <0.001 0.285 0.23755 5.5 <0.0005 0.002 0.031 0.005 <0.001 0.077 0.085540 5.5 <0.0005 0.00455 0.038 0.0056 <0.001 0.191 0.226

Untreated 5 3.5 <0.0005 − 0.0145 0.0054 <0.001 0.0415 0.036640 3.5 <0.002 0.0135 0.0175 <0.0005 0.214 0.4645 0.1795 4.5 <0.0005 <0.001 0.017 0.0057 <0.001 0.0135 0.026540 4.5 <0.0005 0.005 0.0155 0.0053 <0.001 0.0315 0.07555 5.5 <0.0005 0.00125 0.019 0.0054 <0.001 <0.001 0.023540 5.5 − − − − − − −

TCLP limit 1.0 − 5.0 5.0 − − −

Fig. 5 A plot of heavymetal concentrations inmg/L of the TCLP for thethree soils used in the study

to the environment. Moreover, very low concentrationsof other metals would be detected in the TCLP extractof these soil-asphalt applications.

The table clearly indicates that the TCLP extractsfrom asphalt applications with the three soils used inthis study would result in undetectable levels of cad-mium and vanadium. Moreover, very low concentra-tions of other metals would be detected in the TCLPextract of these soil-asphalt applications.

An understanding of the effect of the amount of soiland asphalt on the TCLP metal concentrations can bemade through Fig. 6. The figure contains a matrix of

10 plots representing the concentrations of the variousmetals and soil-asphalt mixtures shown in Table 5. Theplots in the left column of the matrix are for soil percentof 5, and the plots in the right column are for soil percentof 40. All applications were carried out for 3.5, 4.5, and5.5 percentages of asphalt.

A comparison of Figs. 5 and 6 indicates that the lev-els of zinc in the leachate are reduced when clean soilis mixed with asphalt, and a further reduction is ob-served for treated soil when the percent of soil used inthe mixture is increased from 5 to 40 at 3.5% and 4.5%asphalt contents. Chromium levels in the leachate are

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Fig. 6 Plots of metal concentrations in mg/L of the TCLP soil-asphalt applications

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indifferent to the percent of soil used in the mixture,however, a reduction in the level of chromium is ob-served for clean soil when the 4.5 percent of asphalt iscombined with a percent soil of 40. A comparison ofFigs. 5 and 6 indicates that the levels of copper in theleachate are reduced when soil is mixed with asphalt.TCLP extract from the treated soil contains less cop-per when a combination of 4.5 percent asphalt is usedwith 40 percent soil, while the TCLP extract from theuntreated soil contains less copper when 5.5 percentasphalt is used with 5 percent soil. Lower levels of leadare detected in the TCLP extract when 40 percent soilis used compared to 5 percent. Finally, when Figs. 5and 6 are compared, it can be seen that the levels ofnickel in the leachate are reduced when soil is mixedwith asphalt. TCLP extract from the clean soil containsless nickel when 40 percent soil is used for 3.5% and4.5% asphalt contents, while the TCLP extract from theuntreated soil contains less nickel when 5 percent soilis used.

4 Conclusions

Results of the total heavy metal analysis on soils indi-cate that the concentrations of heavy metals are lowerwhen extraction of the soil samples is carried out usinghexane in comparison to TCE. The results show thatthe clean soils present in the vicinity of contaminatedsites contain heavy metals in the following decreasingorder: nickel (Ni), followed by chromium (Cr), zinc(Zn), copper (Cu), lead (Pb), and vanadium (V). Thetreatment practice that PDO implements for treatingthe contaminated soils reduces the concentrations ofnickel and chromium, but increases the concentrationsof all remaining heavy metals.

The total petroleum hydrocarbon (TPH) present inthe PCS before and after treatment was determined tobe 6.8 and 5.3% by dry weight, indicating a reduction of1% in the TPH of PCS due to the current treatment em-ployed. The chromatogram of treated PCS soil is verysimilar to that of the untreated PCS. The treated and un-treated soils have similar low undetectable levels of thevolatile organic compounds (VOC), non-halogenatedVOC, and semi-volatile organic compounds (SVOC)listed by EPA.

Results of the Toxicity Characteristic Leaching Pro-cedure (TCLP) indicate that TCLP concentrations ofselected heavy metals are well below the TCLP regu-

latory limit. Results of these metals show that copperand zinc are the major metals that can be found in theleachate of the three soils used in the study. The leach-ing test performed on the upper and lower limits of PCSreplacements together with three asphalt contents indi-cates that TCLP concentrations of these metals mea-sured for the three soils and their asphalt applicationsare well below the TCLP regulatory limit.

The levels of zinc, copper and nickel in the leachateare reduced when clean soil is mixed with asphalt, whilechromium levels in the leachate are indifferent to thepercent of soil used in the mixture. Lower levels of leadare also detected in the TCLP extract when 40 percentsoil is used in the mix compared to 5 percent.

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