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I :.P., is consistent with the gradient last quarter. A summary of groundwater monitoring data is ER, presented in Table 1. Groundwater elevations are referenced to feet above mean sea level. Groundwater samples were collected from monitoring wells MW-1, MW-2, and MW-3. Prior to collection of groundwater samples a minimum of three well casing volumes were purged. The depth-to-water, pH, electrical conductivity, and temperature were measured and allowed to stabilize before groundwater samples were collected. Additionally, Eh was measured in the groundwater purged from the wells. Samples were then collected from each well using disposable bailers. Purge water was contained in 55-gallon DOT approved drums. Purge water from monitoring well MW-1 from the previous sampling event did not contain detectable concentrations of petroleum hydrocarbons and was discharged to the ground surface. Groundwater well purge and sample logs are provided in Appendix A. The groundwater samples collected from each well were submitted with Chain of Custody Record to Sequoia Analytical Laboratories, Inc. in Redwood City, California, a State Certified laboratory. The samples were analyzed for TPHg and BTEX by EPA methods 801518020, respectively; MTBE by EPA method 8020; and dissolved oxygen, carbon dioxide, alkalinity, nitrate, sulfate, and ferrous iron. Groundwater analytical results are summarized in Table 2. The Chain of Custody Record, laboratory analytical reports, and chromatograms are included in Appendix B. RESULTS OF LABORATORY ANALYSES rr � Results of the laboratory analysis of groundwater samples from monitoring wells MW-1, MW-2 and MW-3 indicate the presence of petroleum hydrocarbons in groundwater in monitoring wells MW-2 and MW-3. TPHg and BTEX concentrations in well MW-2 increased approximately one order of magnitude since last quarter and appear to be influenced by fluctuating water levels. In MW-3, concentrations of TPHg, benzene, ethyl benzene and xylenes increased but were the same order of magnitude as previous quarters. MTBE was detected in wells MW-2 and MW-3 at concentrations well below the 3 5.0 ugll State Advisory Level (OEHHA) for MTBE. MTBE was not confirmed through analysis by EPA Method 8260 per recommendations by Ron Rowe of PHS/EHD (Rowe 1996). No petroleum hydrocarbons were detected in monitoring well MW-1. The analytical results of the analysis of groundwater samples for dissolved oxygen, carbon dioxide, alkalinity, nitrate, sulfate, and ferrous iron are summarized in Table 2. CONCLUSIONS Based on the results of this quarterly monitoring and sampling, Smith Technology recommends continued groundwater monitoring and sampling of wells MW-1, MW-2 and MW-3 in order to detect changes in groundwater quality beneath the site. With regard to the potential for bioremediation occurring at the site, Eh readings, nitrate, sulfate and total alkalinity levels do not indicate a clear pattern consistent with the distribution of petroleum hydrocarbons present in the wells. However, the data show that over time dissolved l w:1951221Reporlsl2QMR1997.doc 4 • SMTH