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Working to Restore Nature June 1993 Semiannual Groundwater Sampling & Analysis August 13, 1993 ' Quik Stop Market No 120, Stockton, California M120 93 Groundwater Sampling ' In a letter to Mr Jack Griffith of Quik Stop Markets, Inc (Quik Stop) from the San Joaquin County Public Health Services (SJCPHS) dated April 15, 1993 it was stated that regional ' groundwater recharge (presumably due to heavy winter rains) was resulting in rising groundwater levels Due to concerns of the SJCPHS that some residual petroleum hydrocarbon compounds from previous releases may remain in the soil beneath this site, tQuik Stop was requested to sample at a time of the year when the water table would be at its highest In an effort to comply with this request an additional sampling was conducted in May 1993 as well as the scheduled June 1993 sampling Groundwater samples were collected from the three monitoring wells on-site in accordance with RESNA's groundwater sampling protocol (Appendix B) Groundwater purged from the wells and equipment decontamination water was placed in a licensed, trailer-mounted container and disposed of at Gibson Environmental, a licensed recycling facility The volume of groundwater removed from each well is noted on the well purge data sheets and groundwater sampling logs included in Appendix C Laboratory Analyses The groundwater samples were transported to Sequoia Analytical, a state-certified laboratory Samples collected on May 3, 1993 were transported to the Sequoia Analytical laboratory located in Redwood City, California and samples collected on June 18, 1993 were transported to the Sequoia Analytical laboratory located in Sacramento, California Samples were analyzed for the presence of TPHG following modified Environmental Protection Agency (EPA) Method 5030/8015, BTEX following EPA Method 5030/8020 or 602 and TPHD following modified EPA Method 3510/8015 The laboratory analytical report and ichain-of-custody record are attached in Appendix D Summary of Results A summary of the analytical results from current and past well samplings is presented Table 1 Plates 2 and 3 show the groundwater elevation contours for May and June 1993 based on the water level data in Table 1 Between December 1992 and May 1993 groundwater elevations rose an average of 4 81 feet and between May 1993 and June 1993 a further average rise of 0 55 feet was observed This represents an average semiannual groundwater rise of 5 36 feet The apparent groundwater flow direction for May and June 1993 was to the southeast at a gradient of approximately 0 002 As shown in Table 1, TPHD, TPHG and BTEX has not been detected in groundwater samples collected from this site for over two years The next semiannual groundwater sampling and analysis is scheduled for December 1993 2 1