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dibromide (EDB)at concentrations up to 110 and 2.1 gg/L, respectively No additional subsurface investigation work has been conducted at the site since 2007, although an additional groundwater sampling event was conducted by the CVRWQCB in 2010,which reported the presence of TPH-G and MTBE in groundwater at relatively low concentrations. Analytical results of the groundwater sampling event are included in Appendix A. Figure 3 presents the concentrations of TPH-G, Benzene, and MTBE reported for this event. Based on the potential that the dissolved hydrocarbon plume has migrated off site beneath Oro Street,the following scope of work has been prepared from discussions during our meeting with the CVRWQCB and from available site data to move the site towards consideration for site case closure. 2.0 PROPOSED TASKS Winzler& Kelly proposes to advance one soil boring, install two groundwater monitoring wells, and install two soil gas monitoring points with up to six soil samples collected from each boring for analytical purposes, in order to define the vertical and horizontal extent of petroleum hydrocarbon impacted soil. The top of casing elevation for the new groundwater monitoring wells installed at the site will be surveyed relative to mean sea level. The horizontal location of the new monitoring wells will also be surveyed with high precision utilizing global positioning system equipment. The attached Figure 2 shows the locations of the proposed soil borings/monitoring wells. 2.1 PRE—FIELD ACTIVITIES Prior to initiating the drilling and sampling activities, each proposed boring location will be marked with white paint and Underground Services Alert(USA)will be notified at least 48 hours before the field event, in order to clear subsurface utilities. A private underground locating company will also be utilized to clear each drilling location. A soil boring and well construction permit will be obtained from the San Joaquin County Environmental Health Department(SJCEHD). A City of Stockton encroachment permit shall be obtained for the installation of the proposed off-site monitoring wells. Additionally, the SJCEHD and the CVRWQCB will be notified of the proposed field activities at least five days in advance. 2.2 DRILLING AND MONITORING WELL CONSTRUCTION ACTIVITIES Drilling will be performed utilizing-a truck mounted hollow-stem auger drill rig. The two monitoring well borings will be sampled every 5 feet utilizing a California split-spoon sampler. Drilling and sampling equipment will be decontaminated before and after each use using a steam cleaner. Soil cuttings and decontamination rinseate will be stored in labeled, Department of Transportation approved 55-gallon steel drums, pending evaluation of disposal options. The two monitoring wells are proposed to be drilled to a depth of approximately 80 feet bgs, dependent on where depth-to-groundwater is encountered. Each well will be constructed using 2-inch diameter polyvinyl chloride (PVC) casing with a 20-foot long section of 0.020-inch factory slotted screen extending from a depth of approximately %kq 80 feet bgs in each well (or 5 feet above and 15 feet below the groundwater surface). The well annulus will be packed with#2/12 or equivalent sized Lonestar sand from the total depth of the boring to at least 6 inches above the screened interval, followed by 2.0 feet of hydrated bentonite chips and a neat cement sanitary seal to within 6 inches of the ground surface. The surface of each well will be completed with a traffic- rated well box set in concrete, and a lockable expanding well plug with lock. Proposed well 03009-10016-37020 3 WINZLER&KELLY August 2011