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I <br /> EKV. <br /> RECOVED <br /> ENSR International <br /> 10411 Old Placerville Road <br /> ENVIRONMENT HEALTH suite 210 <br /> pERMIT/SLWCES Sacramento, CA 95827-2508 <br /> January 12, 2005 (916)362-7100 <br /> FAX (916)362-8100 <br /> www ensr com <br /> IMr James Barton <br /> Regional Water Quality Control Board <br /> Central Valley Region <br /> 11020 Sun Center Drive, Suite 200 <br /> Rancho Cordova, CA 95670 <br /> RE Monitoring Well Installation Report <br /> Former Unocal Facility No 5098 <br /> 5400 and 5606 Pacific Avenue, Stockton, California <br /> Dear Mr Barton <br /> ENSR Corporation (ENSR) was authorized by Union Oil Company of California (Unocal), to <br /> conduct an additional hydrogeologic investigation at the subject site (Figure 1) The <br /> investigation was conducted in response to the Regional Water Quality Control Board, Central <br /> Valley Region (RWQCB) request for additional work to further assess the groundwater gradient <br /> and the downgradient and cross-gradient extent of petroleum hydrocarbons constituents in <br /> groundwater in units C and D This report provides the results of the hydrogeologic investigation <br />' conducted on November 16 and 17, 2004, that Included the installation of two groundwater <br /> monitoring wells (Figure 2) The work was conducted in accordance with ENSR's Work Plan to <br /> Evaluate Potential SVE/AS System Enhancements and Additional Well Installation within the Deeper <br /> Aquifer Units dated November 3, 2004 The RWQCB approved the workplan to install the <br /> proposed monitoring wells, with conditions, as specified in RWQCB letter dated November 5, <br /> 2004, a copy of the RWQCB letter is included In Attachment A <br /> Permits <br /> Well permits were obtained from San Joaquin County Environmental Health Department <br /> (SJCEHD) Copies of the permits are included in Attachment B <br /> Soil Borings and Sampling <br /> On November 16 and November 17, 2004, a geologist from ENSR observed Cascade Drilling, <br /> Inc of Rancho Cordova, California, who advanced soil borings MW-31 and MW-32 to <br /> approximate depths of 90 feet and 103 feet below ground surface (bgs), respectively The <br />■ oorings were advanced using a truck mounted onii rig witn is l/4-incn aiameter nohow stem <br /> augers The soil borings were completed as groundwater monitoring wells MW-31 and MW-32 <br /> The locations of the monitoring wells are shown on Figure 2 <br /> Soil samples were collected from MW-31 and MW-32 using a split spoon sampler at a minimum <br /> Iof 5-foot Intervals and at changes in lithology to the total depth of each boring <br /> • J IProiects1069401509B-2931WorkinglReports15098 Well Installation Report doc <br /> ICelebrating 35 Years rf Excellence in Envaonmental Services <br />