SITE INFORMATION AND CORRESPONDENCE

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Mr. Terry Lau Page 2 July 24, 1995 Response: Because the sample matrix interfered with the analyte quantitation process when the sample was analyzed undiluted, dilution of the samples was necessary. This dilution increased detection limit for BTEX compounds. 3. Page 4-2 of the work plan states that the Phase I field work will consist of soil and ground sampling and installation of temporary piezometers using the Geoprobe system to define the extent of contamination; Phase II will consist of monitoring well (MW) installation, development, and sampling, and sump sites will not be assessed beyond the Phase I level. If the Phase Iinvestigation for the sump sites shows ground water contamination, then a Phase II investigation also must be conducted at these sites. Response: The installation of groundwater monitoring wells for the sump sites is not included with this investigation. However, if evidence indicates that groundwater has been impacted at either or both of the sump sites, ERM will recommend to the Navy that a "Phase II" investigation may be required. 4. Page 4-7 describes MW development by bailing only. Well development is usually accomplished by surging the well with a surge block, or by pumping , jetting, etc. Bailing does not provide the surging _ action that is needed to remove fines in the filter pack or screen. Therefore surging or pumping should be used to develop the MWs. Response: A low-volume, submersible pump will be used to develop the monitoring wells at NCS Stockton. In the event that recharge in the wells is inadequate for the submersible pump, the wells will be developed through bailing. 5. Page 4-9 of the work plan psroposes to analyze soil samples for total lead using USEPA Method 7420 and compare the results with published data for naturally-occurring lead in California soils. Comparison of sample results with published data is unacceptable. Instead, the remedial investigation (RI) must include a water quality assessment to evaluate impacts and potential impacts of soil contaminants on ground water. A demonstation must be made to the satisfaction of the Board that any potential leaching from contaminants remaining in soil does not pose a threat to ground water quality. Contaminant concentrations found above background levels in soil could pose a threat to water quality. Potentially-contaminated site soils must be compared to background soil to evaluate if a potential threat to-,water quality exists. Data obtained from performing the Waste Extraction Test (WET) using de-ionized water can be used to evaluate