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' Response to Comments on final Phase III Technical Memorandum • <br /> ' PG&E Stockton Former Manufactured Gas Plant Site <br /> May 4, 1995 <br /> Page 2 <br /> ' Responses to RWQCB's April 6, 1995 letter: <br /> ' 1. Section 2.4.1, Nearby Site Investigations <br /> PG&E is in the process of obtaining and evaluating additional data from the nearby City <br /> of Stockton Fire Department site and the former Morton Paint Company site. The <br /> ' evaluation of this information will be used during planning of the Phase IV groundwater <br /> investigation and will be included in the Phase IV work plan. <br /> 1 <br /> 2. Section 3.2.1, Drilling and Well Installation <br /> ' Revised geologic cross-sections will be presented in the Phase IV Technical <br /> Memorandum subsequent to further drilling on and offsite and will include additional <br /> ' information obtained during the Phase III and Phase IV fieldwork. <br /> 3. Section 3.2.3, Groundwater Elevation Measurements <br /> During PG&E's telephone conversation with DTSC on April 24, 1995 and at the February <br /> ' 28, 1995 meeting, it was agreed that PG&E would collect monthly groundwater level <br /> measurements for six months and then evaluate the groundwater gradient direction in all <br /> three zones. At that point, PG&E would evaluate the water levels and the quarterly <br /> analytical data with respect to conducting an additional groundwater investigation to <br /> determine the extent of constituents in groundwater (Phase IV). <br /> ' Section 4.4.1 of the RI and Risk Assessment Report <br /> The source of the regional groundwater gradient is sited on Page 2-6, section 2.1.3.3 of <br /> the RI and Risk Assessment Report, August, 1993. The regional horizontal gradient to the <br /> ' northeast was based on the Lines of Equal Elevation of Water in Wells Map (San Joaquin <br /> Flood Control District, 1991). The monthly groundwater level measurement rounds will <br /> be evaluated to determine if well MW-16 is upgradient or cross-gradient. <br /> ' 4. Section 3.2.4, Aquifer Test Design <br /> The Phase III Technical Memorandum mentions on Page 15 and Page C-1 that well MW- <br /> 19 in Zone B was selected as the pumping well based on modeling. The modeling <br /> ' indicated that pumping from both Zones A and B would be more effective at capturing <br /> Zone A groundwater in the central portion of the site than pumping from a Zone A well. <br /> ' Well MW-19 was installed for the pumping test as discussed on Pages 16 and 17. The <br /> Feasibility Study for groundwater will evaluate whether or not pump-and-treat is a viable <br /> alternative. <br /> 1 <br />