SITE INFORMATION AND CORRESPONDENCE

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Z June 2,2000 Harding Lawson Associates 50441 Margaret Lagorio, Supervising REHS San Joaquin County Public Health Services Environmental Health Division Page 2 HLA summarized the above information and specifically discussed HLA's proposed approach to remove the sand in the USTs prior to lifting the USTs out of the excavation. Mr. Wilson indicated that a pre-removal assessment would be required for PHS/EHD to view site conditions prior to removal of sand from the USTs and prior to the subsequent equipment mobilization for normal UST-removal sampling as directed by PHS/EHD. To assess potential petroleum hydrocarbon concentrations within the sand inside the USTs, a sample of sand from each of the two intact USTs was collected from just above the tank inverts where the highest concentrations were likely to occur. These samples were submitted for the following analyses: • Total petroleum hydrocarbons as gasoline(TPHg)with EPA Method 8260B, • Total petroleum hydrocarbons as diesel(TPHd)and Total petroleum hydrocarbons as motor oil(TPHmo) with EPA Method 8015M, • Benzene,toluene, ethylbenzene, and total xylenes(BTEX); and methyl tertiary butyl ether(MTBE),with EPA Method 8260B, The results indicated that BTEX and MTBE were not detected above normal reporting limits of 0.005 milligrams per kilogram(mg/kg). The maximum TPHg,TPHd, and TPHmo concentrations detected were 38 mg/kg, 23 mg/kg, and 16 mg/kg,respectively. Copies of the analytical reports and chain of custody forms will be included in the closure report. OVEREXCAVATION AND SAMPLING If the UST-removal samples contain detectable concentrations of petroleum hydrocarbons,HLA will analyze these samples for the soluble fraction of detected hydrocarbons. These data will be used to determine whether impacted soils must be excavated or may remain in-place. Typically the most cost-effective approach at mitigation of these impacts is over-excavation following UST removal and prior to backfill of the UST excavation. However,more recent regulatory approaches allow some impacted soils to remain in-place if they pose no threat to groundwater quality. This is typically assessed by using analytical data on the soluble fraction of the chemicals of concern(COC) in conjunction with Designated Level Methodology (DLM)(RWQCB, 1989). DLM utilizes the water quality goals for the COCs, site-specific data on depth to groundwater, and expected environmental attenuation factors to calculate a Soluble Designated Level(SDL) for each COC. The SDL is a site-specific level(concentration),below which impacted soil does not pose a threat to groundwater. Analytical data on the soluble fraction of COCs in the impacted soil are compared directly with the SDL. If the soluble concentration of a COC in impacted soil is less than the SDL, it poses no threat to groundwater quality and need not be excavated. Should over-excavation of impacted soils be required,following the approval of this work-plan,over- excavation of impacted soil will proceed and soils will be stockpiled on Visqueen onsite for subsequent profiling and disposal at Forward landfill in Stockton. A registered hauler identified in the application permit 00