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May 24, 2001 <br />Project 077.43451.270 <br />Mr. Marty Hartzell <br />Regional Water Quality Control Board (RWQCB) <br />Central Valley Region <br />3443 Routier Road, Suite A <br />Sacramento, California 95827-3098 <br />Re: Aquifer Test Report -Clarification <br />Former Chevron #95775 <br />301 West Kettleman Lane <br />Lodi, California <br />Cleanup and Abatement Order No. 5-00-704 <br />Dear Mr. Hartzell: <br />SECOR <br />International Incorporated <br />SECOR International Incorporated (SECOR), on behalf of Chevron Products Company <br />(Chevron), has prepared this clarification to the Aquifer Test Report, dated March 30, 2001. <br />This letter has been written in response to a telephone conversation between Mark Trewartha <br />of SECOR and Marty Hartzell of the RWQCB, on March 7, 2001, regarding certain <br />parameters used within the aquifer test report. <br />Data Analysis — Aquifer Thickness <br />As stated in the report, the computer program AgtesolvTM was used to assist with the aquifer <br />parameter analysis. The AgtesolvTM analysis was performed using the assumption that the <br />pumping wells were partially penetrating, and the saturated thickness of the aquifer was 445 <br />feet. The saturated thickness of the aquifer is based on Municipal well construction details <br />provided by the city of Lodi. <br />During our telephone conversation, you inquired as to why SECOR used a saturated aquifer <br />thickness of 445 feet and not the saturated thickness of aquifer based on the depth of the <br />pumping well used for the aquifer test. Based on communications with Aqtesolv <br />representatives, the thickness of the aquifer used to evaluate aquifer test data should be <br />entered as the actual saturated thickness of the aquifer and not the saturated thickness of the <br />aquifer to the depth of the pumping well. The effects of conducting a pump test from <br />partially penetrating wells are accounted for when applying a solution (i.e., Theis, Neuman, <br />etc.) to the data. Partial penetration is determined from comparing the aquifer thickness data <br />and the extraction well data input into the program. SECOR used a saturated thickness of <br />1225 Pear Avenue, Suite110, Mountain View, CA 94043 650.691.0131 650.691.9837 Fax www.secor.com <br />