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October 14 , 1987 <br /> MARLEY COOLING TOWER COMPANY <br /> STOCKTON, CALIFORNIA <br /> GROUNDWATER ASSESSMENT PROGRAM <br /> PHASE IV WORKPLAN <br /> Chromium has been detected at a concentration of 0.07 mg/1 in <br /> California Water Service Well 20-01. Additional subsurface investigations <br /> should be conducted to determine the extent of groundwater containing <br /> chromium in the downgradient off-site area. These additional investigations <br /> are necessary to plan remediation efforts and to assess future potential <br /> impacts on California Water Service'Well 20-01. <br /> Subsurface investigation should begin by determining the zones in <br /> the aquifer that are contributing groundwater containing chromium to <br /> Well 20-01. This may be accomplished by constructing a nest of monitor <br /> wells adjacent to California Water Service Well 20-01. It is anticipated <br /> that the completion intervals of these nested monitor wells will be <br /> 120 feet to 180 feet below Lind surface (bis) , 180 feet to 220 feet bls, <br /> 220 feet to 260 feet bls, and 260 feet to 300 feet his. Wells will he <br /> constructed, sampled and analyzed in sequence until the deepest well <br /> contains no chromium. Other special methods of well construction and <br /> sampling will be considered as an alternative to construction of a nest <br /> of wells for determining the zone of contribution. Once the zone that <br /> is contributing chromium to California Water Service Well 20-01 has been <br /> determined through laboratory analysis of water samples collected from <br /> the nested wells or alternative special wells, additional monitor wells <br /> completed in the zone identified will be constructed. These wells will <br /> serve to determine the extent of water containing chromium between <br /> California Water Service Well 20-01 and the existing monitor wells, and <br /> determine whether there has been any migration of chromium beyond Well 20-01. <br /> The approximate locations for these recommended wells are shown on the <br /> attached figure. The actual locations will depend on finding suitable <br /> locations accessible to the drill rig in the rights-of-way of the County <br /> streets. <br /> 11654. 100 1 <br />