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GeoStrategies <br /> September 4, 1997 <br /> Ms. Margaret Lagorio, Supervisor <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> P.O. Box 388 <br /> Stockton, California 95201-0388 <br /> Subject: Response to letter of August 26, 1997, Regarding Installation of Groundwater <br /> Monitoring Well MW-9 at Former Unocal Station No. 0187, 437 East Miner, <br /> Stockton, California <br /> Ms. Lagorio: <br /> On August 19, 1997, GeoStrategies (GSI) installed one off-site groundwater monitoring well (U-9) <br /> downgradientof the subject site. Installation of this well was originally proposed ir\GSI Report No. <br /> 7827.21-1, Work Plan to Install An Offsite Groundwater Monitoring Well (dated March 3, 1997). <br /> This Work Plan proposed installing the well with the screened interval extending from 25 to 55 feet <br /> below ground surface (bgs). San Joaquin County Environmental Health Division (SJCEHD) issued <br /> a well installation permit#13207 with the condition that the well have no more than 20 feet of screen. <br /> This permit condition was inadvertently overlooked by GSI, and the well was installed with 30 feet <br /> of screen as proposed in the Work Plan. This letter is to clarify Ms. Meays' response at the time of <br /> the well/grout inspection and our rationale for the 30-foot screen interval. <br /> On the afternoon of August 19, 1997, Ms. Meays was informed in the field of the well construction <br /> details and she requested verification of the depth to the bentonite transition seal in the well boring <br /> prior to placement of the grout seal. Ms. Meays allowed the driller to grout the well knowing the <br /> well was constructed with 30 feet of screen. Had Ms. Meays requested.GSI and the drillers to <br /> rebuild the well with only 20 feet of screen, this could have easily been accomplished immediately. <br /> Since Ms. Meays did not make this request in the field, GSI assumed the well construction was <br /> acceptable to SJCEHD. <br /> Subsequent to installation of well U-9 and inspection of the grout seal placement, SJCEHD issued <br /> the subject letter indicating Unocal had failed to comply with permitting requirements. GSI left a <br /> voice mail message with Ms. Meays on August 28, 1997, asking to discuss options for resolving this <br /> situation. Ms. Meays returned our call on September 2, 1997. She indicated the site had been turned <br /> over to the District Attorney and declined to discuss options for resolution via telephone, and <br /> informed GSI that any concerns should be in writing. <br /> A technical rationale for the 20-foot screen interval permit condition was not provided by SJCEHD <br /> at the time the permit was issued. GSI's decision to install 30 feet of well screen was based on field <br /> observations and historical monitoring data from the site. We believe that installation of 30 feet of <br /> screen is warranted at this site based on the following conditions: <br /> d:%w=1\782r7\1cWa <br /> 3164 Gold Camp Drive, Suite 240 Rancho Cordova, CA 95670 (916) 631-1314 • Fax (916) 631-1317 <br />