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Lor Xiong [EH] From: Sewalia, Siddharth@Waterboards <Siddharth.Sewalia@waterboards.ca.gov> Sent: Tuesday, April 9, 2019 9:46 AM To: Nicole Gotberg Cc: Srinivasa Varadhan; Chris Christensen; Randy Dockery; Ian.Richardson@ghd.com; Scott Forbess; Smith, Roger;John.Buyers@ghd.com; Meeks, Steven @Waterboards Subject: RE: Former OCC Lathrop well EW-18B Hi Nicole, I do not see any problem using the damaged well EW-18B as a piezometer during the remedy. However, you must confirm that the measured water level represents the water bearing zone you want to measure and water is not entering the well from other zones. Eventually,you would need to destroy this well.Therefore, you must look into different options to properly abandon this well. If the County is concerned about not properly sealing the well due to sand at the bottom,you must look into methods to clean the sand out (recirculating?) before you could pressure grout the damaged well. In Summary, we concur with the proposed use of the damaged well as a piezometer during groundwater remediation. Thanks, Sid Sewalia Water Resource Control Engineer California Regional Water Quality Control Board, Central Valley Region 11020 Sun Center Drive, Suite 200 Rancho Cordova, CA 95670 Phone: 916.464.4658 From: Nicole Gotberg<NGotberg@Geosyntec.com> Sent: Monday,April 08, 2019 3:28 PM To:Sewalia, Siddharth@Waterboards<Siddharth.Sewalia@waterboards.ca.gov> Cc:Srinivasa Varadhan <SVaradhan@Geosyntec.com>; Chris Christensen <cchristensen@greggdrilling.com>; Randy Dockery<rdockery@greggdrilling.com>; Ian.Richardson@ghd.com; Scott Forbess<SForbess@Geosyntec.com>; Smith, Roger<Roger_Smith@oxy.com>;John.Buyers@ghd.com Subject: RE: Former OCC Lathrop well EW-18B Sid, San Joaquin County will not allow extraction well EW-18B at the Former Occidental Chemical Corporation Lathrop Facility which has a damaged well screen that allows sand to enter the well casing,to be destroyed by pressure grouting. As outlined in the letter proposing the well destruction methods (see email below), due to the EW-18B well design and location, pressure grouting is the only viable well destruction method.Therefore, we propose leaving the damaged EW-18B well in place for the duration of the remedy and using it as a piezometer to measure water level responses to pumping at the EW-18B replacement extraction well.The replacement extraction well will be located approximately 25 feet from the damaged EW-18B well and will be screened over the same depth interval.The County has asked for concurrence from the Central Valley Regional Water Quality Control Board to use the damaged extraction well as a piezometer. Could you please let me know if you approve of using the well for this purpose. 1