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Stockton Meat Plant - Case Closure Page 4 March, 1996 Site Assessment Re�ort,,�1991-92} rIn March, 1991, ERM-West conducted a site assessment to identify if hydrocarbons from the former underground tanks on the Safeway site had ' migrated off site The work and findings were reported in a Site Assessment Report, dated January, 1992 The conclusions, figures, tables, and MW-5 and MW-6 construction logs are presented in Attachment E ' The ERM-West work documented diesel concentrations in soils and ground water off-site, south of the former underground tank site Soil and ground ' water samples were taken using HydroPunch sampling techniques Hydrocarbons in soils, as in previous investigations, were detected in deeper samples (approximately 25 feet below ground in the sandy soils underlying the silty clay upper strata) Ground water from HydroPunch samples were reported with petroleum hydrocarbons ranging from trace to 160 mg/l concentrations Duringthis site assessment, three monitoring wells MW-1 -2 and -3 were g destroyed and abandoned because of declining ground water levels and the ' assumption that the wells were installed upgradient of the area of concern However, to expand the groundwater monitoring, two additional monitoring wells were installed, MW-5 and MW-6 MW-5 was positioned Just south and east of the underground tanks MW-6 was constructed within Navy Dr and on the southern edge of the street MW-6 required special permitting, as well as exact placement, because of utilities (sewer, gas, and electric) within this area of the street Ground Water Monitoring 1992-95 After the site assessment work was completed in 1992, Safeway continued monitoring ground water quality and flow direction for the next three years From 1992 to 1995, eight sampling events were completed and documented in ground water monitoring reports submitted to San Joaquin County PHS The ' last sampling report, dated June 15, 1995, is included in Attachment F Table 1 summarizes the results of the groundwater sampling events Total ' petroleum hydrocarbons as diesel has been reported in every sampling event The concentrations are at trace levels, ranging from 150 ppb to 1,200 ppb In three sampling events, BTEX was requested for analysis No BTEX was ' reported in these samples In the March, 1995, analysis for polynuclear aromatics hydrocarbons (PNAs) was requested for the purposes of evaluating the ground water for a potential risk assessment Only three compounds were detected in MW-6 at trace concentrations (phenanthrene - 0 95 ug/l, anthracene - 7 7 ug/1, and pyrene - 0 038 ug/1) No PNAs were reported in MW-4 or MW-5 Because MW-6 was installed near the two main sewer pipes