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Geosyntec3043 <br /> Gold Canal Drive,Suite 100 <br /> Rancho Cordova,CA 95670 <br /> PH(916)637-8048 <br /> consultants www.geosyntec.com <br /> Site Characterization Work Plan Second Addendum <br /> Date: 2 November 2018 <br /> To: Sid Sewalia, Central Valley Regional Water Quality Control Board <br /> From: Nicole Gotberg P.G., Geosyntec Consultants Inc. <br /> Scott Forbess P.E., Geosyntec Consultants, Inc. <br /> Subject: Site Characterization Work Plan Second Addendum, Former Occidental <br /> Chemical Corporation—Lathrop Facility <br /> Geosyntec Consultants, Inc. (Geosyntec) has prepared this Second Addendum to the Site <br /> Characterization Work Plan(Work Plan)on behalf of Glenn Springs Holdings, Inc(GSH), for the <br /> Former Occidental Chemical Corporation (OCC) Lathrop Facility (Site) in Lathrop, California. <br /> The Work Plan was submitted on 22 June 2018 and approved by the Central Valley Regional <br /> Water Quality Control Board (CVRWQCB) on 27 June 2018. Fieldwork for the Site <br /> Characterization work was initiated on 24 July 2018. An Addendum to the Work Plan was <br /> submitted to the CVRWQCB on 10 September 2018 documenting changes to the monitoring well <br /> design and proposing two additional borehole/monitoring well locations(Location 9 and 10). The <br /> CVRWCB approved the Addendum on 25 September 2018. This Second Addendum proposes <br /> three additional borehole/monitoring wells. <br /> Two additional borehole/monitoring wells are proposed to be installed between the Site and <br /> Lathrop Water District (LWD) water supply well LWD-8 at monitoring well clusters PW35 and <br /> PW36 (Figure 1). The existing deepest monitoring wells at the PW35 and PW36 monitoring well <br /> clusters are screened to 250 and 255 feet below ground surface (bgs), respectively. The Corcoran <br /> Clay was encountered at depths between 265 and 270 feet bgs at Locations 3, 5 and 8. There may <br /> be a 10- to 20-foot-thick transmissive zone above the Corcoran Clay that is not monitored by the <br /> existing monitoring wells at the PW35 and PW36 monitoring well clusters. We are proposing to <br /> drill a borehole near PW36 and, if the Corcoran Clay is encountered at a depth of 265 feet bgs or <br /> deeper, install a new monitoring well in the PW36 monitoring well cluster. Pending the sulfolane <br /> results and the depth at which the Corcoran Clay is encountered at PW36, a borehole and <br /> monitoring well to the Corcoran Clay may also be installed at the PW35 monitoring well cluster. <br /> engineers I scientists I innovators <br />