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• MEMORANDUM • CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD • CENTRAL VALLEY REGION 3443 Routier Road, Suite A Phone: (916)255-3000 Sacramento, CA 95827-3098 CALNET: 8-494-3000 To: Karen Bessette From: Robert Reeves Project Manager Geologist DATE: 6 July 1995 SIGNATUR : Subject: IRRIGATION WELL INSTALLATIONAT 26101 S. CHRISMANROAD NEAR DEFENSE DISTRIBUTION REGION WEST(DDR 99 TRACY,SAN JOAQUIN COUNTY. I have reviewed a letter by Dennis C. Noble, representing Anthony Trains, requesting that we review a permit for construction of an irrigation well at 26101 S. Chrisman Road. It is my understanding that the Trains wish to construct an irrigation well that would pump approximately 250 gallons per minute (gpm) at a depth of 160 feet below ground surface (BGS). The irrigation well will be used to drip irrigate a 10 acre parcel bordering the western perimeter of DDRW Tracy. My review focused on determining if the proposed irrigation well could affect the proposed remedial design or the contaminant plume (PCE and TCE plume) at DDRW Tracy. I reviewed the following technical documents: Pre-Design Data Report for Operable Unit 1, February 1995 (Sections 1,2, 3 and Attachments A and B) Well Monitoring Program Quarterly Monitoring Report, October 1994 Sampling Round Well Monitoring Program Quarterly Monitoring Report, August 1994 Sampling Round Background: Tracy has identified four hydrostratigraphic units in the Upper Tulare Member of the Tulare Formation: the Above Upper Horizon( 0 to 25 feet BGS), the Upper Horizon( 25 to 60 feet BGS), the Middle Horizon(75 to 105 feet BGS)and the Lower Horizon(110 to 170 feet BG). The Corcoran Clay is found at 220 feet BGS and is the regional confining layer between the Upper Tulare Member and the Lower Tulare Member of the Tulare Formation. Isopach maps presented in the Pre-Design Report (February 1995), show several well-defined paleochannel deposits in the Upper Horizon and Middle Horizon. Although the isopach maps do not extend west of DDRW Tracy, it is likely that the paleochannel deposits found beneath DDRW Tracy also extend beneath the subject property. Geologic cross sections show four well defined water bearing zones that also extend beneath the subject property and are present at depths ranging from 25 to 170 feet BGS.