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y <br />aCa2, <br />September 30, 1991 E N °1r <br />Mr. Robert A. Evans <br />Regional Water Quality Control Board <br />Central Valley Region <br />3443 Routier Road, Suite A <br />Sacramento, CA 95827-3098 <br />APPROVAL OF CORRECTIVE ACTION PLAN (CAP). AUSTIN ROAD LANDFILL. CITY OF STOCKTON <br />We are writing in response to your September 16, 1991, letter which approved the <br />CAP and asked the City to address several issues relating to it. We have <br />consulted with Emcon Associates (EMCON) on these issues and offer the following <br />responses to your comments. <br />Comment <br />A ground -water contour map constructed from ground -water levels measured on July <br />10, 1991, indicates the presence of a ground -water divide in which ground water <br />flows in both a northwesterly and northeasterly direction. The ground water <br />which contains the contaminated plume flows northeasterly. The City should <br />propose additional monitoring wells in the northwest corner of the landfill to <br />ensure that the volatile organic compound (VOC) plume is not spreading to the <br />northwest. <br />Response <br />The results of the Phase III HydroPunchTM program did not indicate the presence <br />of a VOC plume moving in a northwesterly direction. The CAP indicates that <br />ground -water levels will be measured on a monthly basis to assess whether the <br />ground -water divide occurs seasonally, or was a unique occurrence. Therefore, <br />no further action is proposed until water -level monitoring indicates a continuing <br />hydrogeologic condition. <br />Comment <br />The CAP did not discuss the reasons why wells MW -1, MW -3, and MW -4 were dry <br />during the July 1991 sampling event. Given the water table fluctuations and <br />future extraction well pumping, the City may need to drill additional wells to <br />adequately monitor ground water. <br />