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1-11is w()rk was performed by WESTON and presented in it E•eport enlltled "Addendun) to Problem Assessment Report" date.." August ]9. 1991. The downgradient monitoring well, A9W-4, as sliown on figure 1, is located approximately 65 feet northwest of well MW-1. Soil samples were taken at locations SB-1 and S13-3 northwest of the former tank location at 30 and 10 feet from MW-1, respectively (soil sample SB-2 was not analyzed). The soil samples were collected on July 2, 1991 and MW-4 was sampled on July 10 and again on July 16, 1991. Groundwater analytical results from 'NIW-4 for July 10 showed no detectable BTEX or TPH-G. A confirmation sample,collected front this well six days later also showcd no detectable BTEX or TPH-G. The soil rZmple from SB-1 sheaved no detectable BTEX or TPH-G, while SB-3 showed no benzene, ethylbenzene or xylene aitd 0.03 ,parts per million (ppm) of toluene. Upon review of the above analytical results, the San Joaquin County Environmental Health Division (EHD), in conjunction with the California Regional Water Quality Control Board (RWQCB), ruled that six days between collection of the initial groundwater sample and the confirmation groundwater sample was inadequate. Consequently, in a letter to Souza Realty dated September 17, 1991, the EHD requested that Souza perform the following: I. Collect an additional groundwater sample from MW-4, analyze for BTEX, TPH-G and total lead. 2. '\1easure groundwater elevations in all four monitoring wells onsite and determine the site groundwater gradient and magnitude. 3. Provide additional explanation for the presence of 0.03 ppm of toluene in boring SB-3. This report addresses this additional request for information. 2.0 PROJECT SUMMARY In order to comply with the EHD letter of September 17, 1991, WESTON collected an additional groundwater sample from MW-4,measured the water levels in all four monitoring wells, calculated gradient and developed additional discussion of the toluene in soil issue. All field work was conducted under the direction of a registered California geologist and a report detailing the methodologies used is presented in Appendix A. 2.1 Groundwater Sampling The additional groundwater sample from MW-4 was collected on September 27, 1991. The sample was submitted for analysis of BTEX and TPH-G to the WESTON Analytics Stockton Iaboratory which is certified by the State of California for the requirtA analyses. A trip blank was collected, transported and analyzed as a Quality Assurance measure. An additional groundwater sample was collected on October 22, 1991 which was submitted to the WESTON laboratory for analysis of total lead.