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6ETTLER-RYAN INC. <br />49 <br />February 9, 2000 [Fa&'ED <br />Mr. Harlan Knoll <br />San Joaquin County Environmental Health Division <br />P.O. Box 2009 <br />Stockton, CA 95201-2009 <br />Subject: Addendum to GRReportNo.346408.06, Work PlanjorMonitoring Welllnstallation (dated <br />November 11, 1999), at Former Chevron Station #9-5775,301 West Kettleman Lane, Lodi, <br />CA. <br />Mr. Knoll: <br />Underground storage tanks (USTs) and dispenser islands were removed in August 1998. Based on <br />compliance soil sampling, the eastern portion of the UST pit was excavated to 22.5 feet below ground bgs, <br />but the confirming sample from the base of this area contained 2,300 ppm of TPHg, 4.1 ppm of benzene, and <br />330 ppm of MtBE. Four groundwater monitoring wells (MW -1 through MW -4) were installed in January <br />1999 to assess groundwater impact. To further assess impact in the unsaturated zone in the vicinity of the <br />former UST pit, GR prepared the subject Work Plan for installation of vapor extraction wells (VE -1 through <br />VE -4), soil borings (SB -1 through SB -3), and additional an groundwater monitoring well (MW -5). This <br />work was performed in in December 1999, and will be reported separately. <br />Data from the December 1999 drilling event indicate that groundwater in deep well MW -5 had been <br />impacted. At the request of Chevron Products Company, GR proposes to install one 2 -inch diameter <br />shallow groundwater monitoring well (MW -6) in the vicinity of well MW -5 to assess conditions at the water <br />table. Groundwater is expected to be encountered at approximately 55 feet bgs, and the well will be screened <br />from 45 to 65 feet bgs. A proposed well construction detail is attached. Proposed location of this well is <br />shown on Figure 2. <br />GR also proposes to install one 4 -inch diameter groundwater extraction well (EX -1) in the former UST pit <br />to facilitate future removal of impacted groundwater. This extraction well will be screened from 53 to 65 <br />feet bgs. Proposed well construction details are attached. Proposed location is shown on Figure 2. <br />The wells will be installed by V&W Drilling (C57-720904) under existing SJCEHD permit #018004. Soil <br />samples from the borings will be collected, handled, and analyzed as described in the subject Work Plan. <br />The proposed scope of work is scheduled to be implemented on February 17, 2000, under the direction of <br />Stephen J. Carter, R.G. <br />346408.07 <br />6747 Sierra Court, Suite J • Dublin, California 94568 • ( 9 2 5 ) 551-7555 <br />