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L V V4kTC A S S O C I A T E S I N C . G sample collection, each sampled well was purged of a minimum of three well casing volumes of water. Purged water was contained in labeled 55-gallon drums (DOT H), and stored on site. Groundwater samples were collected after physical parameters (pH, temperature, and conductivity) were monitored and had stabilized. Dedicated disposable bailers with bottom- emptying devices were used to collect samples from the wells. All field activities were performed in accordance with the Field Methods included in Attachment 1. Field purge logs are presented in Attachment 2. LABORATORY ANALYSES Collected groundwater samples were analyzed for total petroleum hydrocarbons as diesel (TPHd) by Sequoia Analytical, a State-certified laboratory, utilizing EPA method 8015. The analysis of groundwater samples for benzene, toluene, ethylbenzene, and xylenes has been discontinued in accordance with verbal approval by San Joaquin County Public Health Services/Environmental Health Division on March 26, 1997. Analytical results are summarized in Table 3. Laboratory data sheets and chain-of-custody documentation are included in Attachment 3. Laboratory results indicate that TPHd was detected in groundwater samples collected from wells MM3 and MW6 at concentrations of 520 parts per billion (ppb) and 88 ppb, respectively, but was reported by the laboratory as an unidentified hydrocarbon, ADDITIONAL FIELD ACTIVITIES On May 8, 1998, ATC personnel installed a free product skimmer in well MW4. Because the top two feet of PVC pipe in well MW4 was bent, the skimmer would not fit into the well. The top two feet of the well casing was excavated and the bent PVC pipe was removed. The bent PVC was replaced and re-concreted into place. The well was also resurveyed. After the concrete had been allowed to set, the skimmer was installed. The skimmer was suspended in the well using a Teflon coated steel cable which is tied down just outside the well box. The skimmer will separate floating free product from the groundwater and store the free product until the skimmer can be emptied by ATC personnel. The skimmer has a maximum capacity of almost one-half gallon. All work was completed in accordance with ATC's Workplan for Skimmer Installation, dated April 14, 1998. On May 27, 1998 ATC personnel checked the skimmer installed in well MW4 on May 8, 1998. Only a slight sheen was visible and no free product had been collected into the skimmer. As groundwater elevations decrease during the summer, the skimmer will collect more free product. w:1943691quaft1yl2gmr1996.doc 2