SITE INFORMATION AND CORRESPONDENCE_1985-1997

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Ed Koberstein page 2 With this in mind, PHS-EHD is concerned that by only addressing SVE testing in the shallow areas (maximum depth proposed is 35' bgs), you may not be addressing remedial efforts towards the area(s) that need it the most. Previously collected soil samples from soil boring B-11 indicated that the contamination increased in concentration from 40' bgs (TPH-G =36.4 mg/kg, and Benzene =0.2 mg/kg) to a maximum at 50' bgs (TPH-G = 2270 mg/kg, and Benzene = 6.57 mg/kg). With the highest level of contamination noted at the deepest level reached, PHS-EHD is concerned that a full assessment of this area has not been completed. PHS-EHD will require additional soil samples from this area (B-11) and at depths well into the saturated zone to verify the vertical limit of the contamination. In order to verify the vertical limit of the soil contamination in this area directly beneath the former UGTs, soil samples will need to be collected at 50', 55', 60', and 65' bgs and analyzed for all of the constituents known to be of concern on this site. Your vapor well proposed for this area (VEW-1 B), or another soil sampling technique, should be advanced to these depths. Once the soil samples have been collected, the vapor extraction well construction you have proposed may proceed. No mention was made of the existing two foot thick concrete slab still in place all around MW-1 and the soon to be, VEW-1 B. Have you taken into consideration the effect that this large mass may have on your area of vapor extraction influence? Please reference this anomaly in the revision or addendum. Additionally, the area between the two plumes that you have designated has not been investigated at the deeper levels. PHS-EHD recommends that one of the seven vapor probes be placed in this area and soil data be collected from sequential depths starting at 35' bgs and continuing to at least 65' bgs. My field notes indicate that odors were noted at the 65' bgs sample depth from MW-1 back in February, 1993. Current Underground Tank Regulations (California Code of Regulations, Title 23, Chapter 16, Article 11) stipulate that sites within groundwater basins designated as beneficial use aquifers are to evaluate at least two remedial alternatives for restoring or protecting the beneficial uses of the groundwater. You will be required to evaluate at least two remedial methods and submit the findings to PHS-EHD in a Feasibility Study. PHS-EHD will evaluate the two alternative methods for restoring the beneficial use of the groundwater and will approve the method that is the most feasible and cost effective. A Corrective Action Plan (remediation plan) that does not take into consideration all of the sites' contamination will not be approved by PHS-EHD.