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MEMORANDUM CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION 3443 Routier Road, Suite A Phone: (916) 361-5600 Sacramento, CA 95827-3098 ATSS Phone: 8495-5600 TO: Antonia Vorster FROM: Cori Condon Senior Eng. WRC Assoc. Eng. Geologist DATE: 26 June 1992 SIGNATURE: SUBJECT: CALIFORNIA FUELS, 838 NOKELUNNE STREET, NOODBRIDGE, SAN JOAQUIN CO. Aegis Environmental has proposed five soil borings within the boundary of the former excavation at Ca Fuels in response to Wendy Cohen's 21 February 1992 letter. This work is necessary to determine concentrations of petroleum hydrocarbons remaining in the native soils underlying the former excavation at this site. Soils taken from the excavated area were previously bioremediated to below detection limits ( i .e. less than 1ppm total petroleum hydrocarbons as gasoline and diesel and 0.005ppm benzene, toluene, xylene, and ethyl benzene) and placed back into the excavated area. Additional soil samples need to be taken at 5 foot intervals from below the excavated soils area, to the water table to investigate the vertical extent of fugitive fuels. Soil samples should be collected beneath areas previously documented to contain relatively high concentrations of diesel contamination in order to verify the vertical extent of the fuel products. Specifically, sample analysis should describe fuel constituents below the ramp area where 11,000 ppm and 4,100 ppm diesel were documented to be remaining in soils at ten feet below the ground surface (bgs). Continued sampling is necessary to confirm the vertical extent of 2,700 ppm diesel found at a depth of 32 feet bgs in the central/south eastern portion of the excavated area and soils in the north eastern area of the former excavation showed 2,600ppm diesel at 25 feet bgs. Borings should be located through these points to confirm the vertical extent. Information on the vertical and horizontal extent of pollutants in the south eastern portion of the former excavation where two previous samples showed 7,600ppm and 5,900ppm diesel need to be investigated. I recommend that a monitoring well be placed in this area to satisfy both the repeated requests by us for a monitoring well in this area and to facilitate the collection of soil samples to determine concentrations of fuels in the soils over depth. All soil borings must be backfilled with grout per San Joaquin County ordinances. An inspector from the County should be on-site to observe sample collection and backfilling processes. A time schedule for completion of this work and submittal of analytical results should be sent to us in the next two weeks.