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As shown in the table, only a low concentration of total extractable petroleum hydrocarbons 1 I (TPH-D) was found in the soil sample taken at 27 feet below grade in the northwest corner of the excavation area. No volatile petroleum hydrocarbon components were found in any soil ' samples and all analytical parameters were nondetectable inIthe well water sample. 3 , x Additionally, a 6,000 gallon gasoline tank (Tank 3) was removed from along the north wall of the shop building and a 12,000 gallon aviation fuel tank (Tank 4) was removed from the northwest corner of the shop building. Soil sampling from beneath each tank indicated that while no volatile hydrocarbons were found in the soil, extractable hydrocarbons were inexplicably found. A sample from the west end of Tank 3 contained 50 mg/Kg while a sample from the south end of Tank 4 contained 70 mg/Kg. A review of available records does not indicate why extractable hydrocarbons were found at these locations nor if there was a possibility of sample mismanagement or analytical error. r L 1.2 Hydrology F t - The site is located in the south central portion of the San Jaquin'County Groundwater Basin. At the time of the remedial excavation project in April 1987,11the water table was approximately 28 feet below grade as observed during the well sampling'I However, according to the San Joaquin County Flood Control District (SJCFCD), "Lines of Equal Depth to Water in Wells, Spring 1993," groundwater is currently expected at a depth of 45 to 50 feet below ground 'f surface (bgs). Based on the SJCFCD, "Lines of Equal Elevation of Water in Wells, Spring 1993, groundwater flows to the northeast in the vicinity of the site. 11 1 2.0 PROPOSED SITE INVESTIGATIONS ACTIVITIES The available site investigation data suggests that there may be lingering environmental concerns with the remediated area at the former locations of Tank 1 'and 2 due to the low concentration of extractable hydrocarbons present at 27 feet below grade. Furthermore, the apparent presence of extractable hydrocarbons at the former locations of Tank 3 and Tank 4 presents an additional uncertainty. I; I The proposed field investigation activities will consist of installing and sampling two soil borings i at the location of former Tanks 1 and 2, installation of three monitor wells and groundwater sampling to evaluate groundwater quality around Tanks 1 and 2 and the placement of one soil boring for the collection of soil samples and Hydropunch groundwater sampling at Tank 3 and Tank 4. The monitor well installation is focused on the Tank 1 and 2 area which has shown extractable hydrocarbons near the water table. At the Tank 3 and Tank 4 areas, only Hydropunch sampling is proposed as there is currently no reason to expect groundwater impacts at these locations. 2.1 General Requirements i This work plan has been developed to conform to the Tri-Regional Recommendations and is structured to address the concerns of the San Joaquin County EHD. All work described below ' will be completed under the direction of a California Registered 'Geologist and all analytical nX%APPSWCMVCD.WM 4 04108M