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August 5, 1997 38737 001 Harding Lawson Associates Ms Mary Meays ' San Joaquin County Public Health Services Page 6 ' HLA recommends additional work necessary to provide the data required to demonstrate compliance with the above criteria and pursue classification of the Site with a "low risk'groundwater designation (RWQCB, 1996) The additional work also address issues raised by PHS/EHD during a September 5, 1995 meeting with TVG(see discussion above) The following additional data are required • The groundwater data collected by SECOR do not provide the information necessary to delineate the vertical extent of impacted groundwater and therefore allow estimates of the hydrocarbon mass in the groundwater • Additional soil data in the area between boring SB-1 and SB-7 and beneath the forklift building near boring HAl are needed to define the lateral and vertical extent of impacted soil 1 . Intraplume groundwater monitoring well data from near the impacted soils are necessary to demonstrate that free product is not present, and also for compliance monitoring of whatever remedial measure is chosen Site-specific physical and chemical subsurface data to assess the efficacy remedial measures HLA proposes to perform the following scope of work at the Site in accordance with the existing TVG workplan approved by PHS/EHD and as modified below ♦ Advance two soil borings in the approximate locations of SECOR boring SB-9, and SB-10 ♦ Install an intraplume monitoring well in the boring located near SB-10 ' ♦ Advance one boring in the area HA1 to assess the vertical distribution of impacted soil in this area • All borings will be continuously logged • Collect soil samples at 5-foot minimum intervals in each boring 1 • Collect Hydropunch groundwater samples at three depths in each boring e Submit selected soils samples for analyses for TPHg (EPA Method 8015M) and BTEX (EPA Method 8020) ♦ Test selected samples for physical, chemical, and biological indicator parameters for bioremedial effectiveness The existing monitoring wells have not been sampled recently and are proposed to be sampled within the third quarter of 1997 The sampling will include the measurements of depth to groundwater and determination of the groundwater gradient and flow direction Prior to sampling, wells will be purged of at least three well casing volumes and monitored during the purging process for temperature, conductivity, and pH Purge water will be containerized in DOT-approved 55-gallon drums which will be labeled with the well number and accumulation date and retained on Site pending receipt of the analytical data Purging will be considered complete when the minimum volume has been purged and when the indicator parameters have stabilized to within 10 percent on successive readings The samples will be transported in accordance with chain-of-custody protocol to a state certified analytical laboratory Samples will be analyzed for TPHg with EPA Method 8015M and BTEX with EPA Method 8020 The resulting monitoring data when completed will be forwarded along with analytical data in the form of a brief letter report that will be submitted to the PHS/EHD and the RWQCB REMEDIAL APPROACH After the collection of data outlined above alternatives to achieve site closure will be considered and a Remedial Action Plan(RAP) will be developed Three remedial alternatives will be proposed and evaluated based on technical applicability and on cost efficiency With the proposed intraplume well, the existing monitoring network appears adequate in number and position to perform compliance monitoring ti