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EVALUATION OF FATE AND TRANSPORT Or HYDROCARBONS <br /> . Western- Lift <br /> 3=130 South EI Dorado Street <br /> Stockton, California <br /> May 1995 <br /> 1.0. IN'rRODUCTION AND SCOPE OF WORK <br /> Low concentrations of petroleum hydrocarbons continue to be detected ill ground water <br /> Inonitoring wells at the referenced site. A fate, and transport modeling program was used <br /> to.determil]e the effects of hydrocarbon-impacted ground water orr a down gradient water <br /> stlpply source. A description of the I]]odeling program, ]methods used for analysis and results <br /> are included in the following sections. <br /> 2.0. BACKGROUND <br /> The facility consists of a large warehouse, an acljoining office and a fenced park ingldelivery <br /> area (Figure 1 - Site Plan). The [)I,operty to tale 1101-til I'S cllrrel]tly occupied by Cutter <br /> Lumber, Who n]annfactllres W00den pallets. <br /> • The follolvina ]nformatio]] l�raS,5lt11]I]lilrtZeCl fl-0111 1'epo]'lS l)repaled by [ieO1Q6lCal Audit <br /> Services, hic, (GeoAuclit) between 1992 and 1994: <br /> Evidence of a hydrocarbon release was encountered following the removal of three <br /> underground tanks in JuIle of 1991. 111 coinpliance with requirenleIlts frons the San Joaquin <br /> County Public Health'Services - Envii-onmental Health Division (PHS/EHD), the removal <br /> of impacted soils was performed. The impacted Soils were overexcavated followed by the <br /> collection and analyses of soil samples froim the walls and floor of the eNcavation. ; <br /> On 1 .lune 1992, a groundwater morlitorillg well (ivff-1) was installed immediately north " <br /> of the former tank excavation. The results of soil samples during drilling of MNV-1 indicated <br /> that very low residual levels of tolliene.11)d xylelle. remained in the soil between 35 and 45 <br /> feet. Based on detectable' hydrocarbons• ill the the water sample frolll tills well, the <br /> PHS/EHD required further groundwater assessment. <br /> Two additional monitoring wells, MW-2 and MW-31, \mere installed by GeoAuclit ill <br /> November 1992, followed by N W-a- and 1\IW-5 in June 1993. Petroleum- hydrocarbons were <br /> not detected in soil sail]ples collected during drilling of pilot borings of these wells. <br /> Hyd -ocai-boii coml)ol€nds were consistelltly detected in salllples frons NIW-1 throughout eight <br /> ImoIlitoring periods since 1.992..Concentratior]s of total petroleum] hydrocarbons as gasoline <br /> (TPH-g) ranged between 99 and 260 parts per Hhon (ppb). Benzene, was detected at <br /> colicentrations- L11) to 15 ppb during the '-same period in this well. Sa]nples from the <br />