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u u <br /> Ms. Margaret Lagorio, SJCEHD November 30,2007 <br /> Work Plan for Additional Assessment Project No.2033-15688-01 <br /> 15688 Harlan Road, Lathrop, California <br /> Page 4 <br /> three discrete water-bearing zones during the period January 1997 to March 2007. From <br /> these borings, it appears that generally fine-grained soils (logged as ML and CL), with <br /> several laterally continuous coarser-grained zones (logged as SP and SW), are present <br /> beneath the site vicinity, from ground surface to the maximum depth explored of 75 <br /> feet bgs. <br /> Three distinct water-bearing zones (known as Sands A, B, and C) have been encountered <br /> beneath the site vicinity. Sand A is encountered at about 5 to 8 feet bgs and is <br /> approximately 3 to 10 feet in apparent thickness; Sand B is encountered at about 25 to 35 <br /> feet bgs and ranges in apparent thickness from 7 to 18 feet; Sand C is encountered at <br /> about 50 to 65 feet bgs and is 15 to 25+ feet in apparent thickness. Historically, static <br /> water levels in wells constructed within Sands A and B average about 8.9 feet bgs. <br /> During the most recent monitoring event in September 2007, depth to water was <br /> measured at about 11 to 12 feet bgs. Historically, groundwater flow beneath the site <br /> vicinity has been dominantly northeasterly(with northerly and northwesterly variations). <br /> PROJECT APPROACH / RATIONALE <br /> The objective of this work plan is to evaluate the extent of petroleum hydrocarbon- <br /> impacted soil and groundwater associated with the former USTs and to determine a <br /> groundwater flow direction and hydraulic gradient. To meet this objective, Stratus <br /> proposes the advancement, sampling, and logging of three exploratory soil borings at the <br /> site to first encountered groundwater (anticipated at a depth of about 10 feet bgs) and the <br /> conversion of each borehole to a groundwater monitoring well (MW-1 through MW-3). <br /> Well MW-1 will be located in the former source area. Wells MW-2 and MW-3 will be <br /> located in an area about 20 feet north and northeast, respectively, of the former USTs in <br /> assumed downgradient directions (based on historic flow directions at the adjacent Joe's <br /> Truck Plaza). These locations were also selected to provide an adequate triangulation <br /> area for flow direction and hydraulic gradient calculations. The location of the fire <br /> hydrant will be used as a point of reference for locating the proposed wells. <br /> All three borings will be continuously cored and logged to determine the depth to water- <br /> bearing Sand A, and the depth to the underlying fine-grained soil separating Sand A from <br /> Sand B, if present. Soilsamples for laboratory analyses will be collected from borings <br /> MW-2 and MW-3 at depths of approximat .lv . and 10 feet bQs, to evaluate whether <br /> impact is present in the vadose zone (assumed about 0-7 feet bgs) and within the capillary <br /> fringe (based on expected fine-grained soil, assumed about 7 to 11 feet bgs). Skil <br /> samples for chemical analvicec will not be collected in saturated groundwater conditions <br /> within Sand A (assumed 11+ feet bgs) since, at the termination of each boring, permanent <br /> monitoring wells will be constructed. hi addition, soil samples for chemical analyses will <br /> K:Voe's Truck Plaza\Work PlansVoe's Truck-SOUTH PARCEL-WP for Site Assessment 11-30-07.doc 9TPATU5 <br />