SITE INFORMATION AND CORRESPONDENCE

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GEOMATRIX Mr. Robert Mihalovich Chevron Environmental Management Company July 12, 2001 Page 6 • Groundwater samples from these four wells would be sampled once per quarter for analyses of BTEX and TPHg. No other groundwater monitoring would be conducted during the pilot study; specifically, semi-annual monitoring and sampling would be suspended for this time period. • ORC would be replaced an additional three times (or as necessary based on observa- tions of exhaustion of the ORC "socks") in the four wells for the remainder of the study. • A report summarizing and evaluating the data would be prepared for submittal to the RWQCB at the end of the pilot study. It should be noted that the information obtained from the pilot study would be limited to the frequency of ORC replacement at the site for the first year, and would not provide additional information regarding the time of remediation. As describe previously, the degradation of dissolved petroleum via ORC is limited by the transport of dissolved-phase petroleum hydro- carbons from the fine-grained soil beneath Grant Line Road to the four wells that would con- tain the ORC. It should be noted that a 1-year ORC pilot study to better estimate the actual amount ORC needed at the site is estimated to cost approximately$30,000 (Table 3). Based on these reasons, it is unlikely that an ORC pilot study at the site will provide sufficient information to significantly modify the conceptual design for Alternative 3 for cost compari- son with monitored NA. As such, Geomatrix does not recommend that an ORC pilot study be conducted at the site. In summary, historical site data indicate that NA is occurring, and will continue to occur, at the site and will remediate the site within a reasonable timeframe (less than 20 years). Over 10 years of actual site data was used to provide reasonable rates of degradation of petroleum hydrocarbons (i.e., benzene), along with estimates of the frequency of ORC replacement. The effectiveness of ORC at the site is limited by site constraints that result in the ORC being place outside the source area, thus the estimated remediation duration using ORC is qualitatively estimated to be slightly less than that of NA. These site constraints also limit the amount of information that would be gained from a pilot study. Information gained would be primarily limited to the frequency of ORC change out at the site, a parameter that would not change the relative cost of using ORC verses monitored NA. POTENTIAL DEVELOPMENT ACTIVITIES The property owner has indicated plans to sell and develop the subject property in the near future. Wells MW-10 and WM-14 are located within the property boundaries (Figure 3). Significant detections of petroleum hydrocarbons have not been reported for the groundwater samples collected from MW-10 and MW-14 for the past 9 and 12 consecutive sampling events, respectively. Continued monitoring of these two wells will not provide additional information for understanding and evaluating site conditions. As such, it is requested that the