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i <br /> Quarterly Ground-Water Monitoring March 8, 1989 <br /> Beacon Station No. 1-502, Lodi, California AGS 86091-6 <br /> mitigation of ground-water contamination is warranted at the <br /> site. Vapor-extraction wells are currently in place in the <br /> vicinity of the tank cavity (AGS Letter Report 86091-6, dated <br /> August 3, 1986) ; it is our understanding that Beacon has had a <br /> preliminary feasibility study conducted at the site and plans to <br /> complete the vapor-extraction system. A vapor-extraction system <br /> should reduce the concentrations of volatile contaminants in the <br /> soil around the vicinity of the tank cavity, and may effect a <br /> reduction of dissolved contaminant concentrations in the ground <br /> water underlying the site. We recommend that the vapor- <br /> extraction system be implemented and the effectiveness of the <br /> "'� system in reducing contaminant concentrations in <br /> ground water be <br /> evaluated. We also recommend `.hat more direct methods of ground- <br /> water remediation be evalua,ed. If aquifer parameters at the <br /> site are fi:vcia:,le, periodic purging of relatively large volumes <br /> of water (several hundred to 4,000 gallons) conducted in <br /> conjunction with the quarterly monitoring, may effect a <br /> satisfactory interim remediation measure by reducing contaminant <br /> concentrations and confining contaminated -ground water to the <br /> site. Prior to commencing periodic purging, a pump test should <br /> be conducted at the site to allow evaluation of the effectiveness <br /> and cost--efficiency of such a program. We also recommend that <br /> quarterly monitoring at the site be continued; the next sampling <br /> event has been tentatively scheduled for the week of March 6, <br /> 1989. <br /> as <br /> 4 <br />