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PES Environmental, Inc. <br /> Eleanor Ratliff <br /> September 9, 1991 <br /> Page 2 <br /> • Because water-level elevations collected during routine monitoring will be used to <br /> define the capture zone of the proposed extraction system and also to define the <br /> magnitude and direction of the hydraulic gradient, there is no value in further defining <br /> aquifer properties for the purpose of designing an extraction and treatment system; <br /> and <br /> • If reinjection of treated groundwater is selected as the disposal method, then <br /> additional testing of aquifer materials will be necessary. <br /> (3) The following equation was used to estimate the downgradient capture radius or <br /> stagnation point ('Todd, 1980): <br /> x = Q/(2wKbi) where <br /> x: stagnation point <br /> Q: extraction rate <br /> K: hydraulic conductivity <br /> b: saturated thickness <br /> is hydraulic gradient. <br /> (4) Remediation of fuel hydrocarbons in soil as deep as 50 feet below ground surface will <br /> be considered after the effectiveness of the groundwater remediation system is <br /> evaluated. Because groundwater levels are depressed due to the fifth year of drought <br /> conditions, any soil vapor extraction system designed under these conditions will <br /> require major revisions as rainfall and groundwater levels return to average <br /> conditions. <br /> In your August 19, 1991 letter to Jeff Werner regarding groundwater monitoring, you <br /> requested that wells MW-4 and MW-2 or MW-7 be monitored on a quarterly basis. PES <br /> originally proposed to monitor these wells on an annual basis. Given the location of these <br /> wells with respect to the groundwater plume and the historical concentrations observed in <br /> these wells, PES recommends that these wells be sampled at a frequency no greater than <br /> twice each year. <br /> We trust that the issues raised in your August 28, 1991 letter have been adequately addressed <br /> in this letter. Please provide written correspondence regarding your position on the issues <br /> discussed in this letter at your earliest convenience. In addition, we are awaiting your <br /> response to our August 14, 1991 letter regarding the proposed soil and groundwater disposal <br /> plan. <br /> kobvu\ntMn.wp5 <br />