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Harding Lawson Associates April 5, 1994 276901 San Joaquin County Mr Harlin Knoll Page 3 HLAs proposed field investigation presented below is intended to be generally consistent with the requirements of the California Regional Water Quality Control Board (RWQCB) for investigation of USTs HLAs field program has been designed to allow coverage of a larger area to evaluate the distribution of potential groundwater contaminants while m unizang the number of permanent monitoring wells to be installed Prior to drilling HLA will obtain the appropriate perrmts from the SJCEHD This field investigation is broken clown into four tasks presented below Task 1 - Site A and B field investigation Task 2 - Oil Bunker Investigation Task 3 - Analytical Program Task 4 - Prepare report of findings and a closure plan A detailed description of each task is presented below Task 1 - Site A and Site B Investigation • Analytical testing of the groundwater sample from the Site A tank pit indicates the presence of an existing groundwater contamination problem At Site B, groundwater has not been tested but soil contamination is present HLAs approach is to evaluate the groundwater conditions an the vicinity of the Sites A and B excavation to assess the presence of groundwater contamination To accomplish this, HLA proposes to qualitatively assess groundwater contamination by conducting a survey using a soil gas rig followed by the installation of two wells The soil gas rig will collect groundwater samples by using a steel probe pushed into the soils below the water table A sample of the groundwater is collected and placed in a 40 milliliter VOA vial and an analysis of the headspace is conducted to screen for the presence of total petroleum hydrocarbons as gasoline (TPH-G), a benzene, toluene, ethylbenzene, and xylenes HLA wall use Tracer Research to conduct the work HLA proposes 1 day of soil gas work to evaluate both sites Based on discussions with Tracer regarding site conditions, it is estimated that 8 to 12 points can be sampled in one day (4 to 6 at each site) Based on the results of the survey, the two monitoring wells can be effectively located to confirm the results of the survey This method has several advantages including reducing the number of wells required for plume definition, and allow for quicker assessment of the plume If based on the soil gas survey, additional wells are required, HLA will provide HSC and the RWQCB with our recommendations After completion of the groundwater survey, HLA will drill two groundwater monitoring wells down gradient of the former UST locations Actual locations will be based on the groundwater survey results Groundwater flow direction is estimated to be to the north (San Joaquin County Flood Control and Water Conservation District, Fall 1989) The wells will be drilled to a depth of approximately 20 feet BGS using hollow stem auger drilling equipment The wells will be constructed of 2-inch diameter PVC casing with 10 feet of screen The annular space will be filled with clean water washed sand up to 2 feet above the top of the screen Two feet of bentonite pellets will be place above the screened interval Cernent/bentomte grout will be place in the remaining portion of the borehole At