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Ms. Patricia Vellines 8188.001.002 The Trails of Manteca October 25, 2012 WORKPLAN FOR SOIL AND GROUNDWATER ASSESSMENT Page 2 Previous environmental activities performed by Terra Search identified elevated concentrations of total petroleum hydrocarbons as gasoline (TPHg), diesel (TPHd), volatile organic compounds (VOCs), and polychlorinated biphenyls (PCBs) in soil and groundwater adjacent to an above- ground storage tank (AST) in 2005. The 2005 Phase 11 report is not available; however, based on excerpts from the subsequent excavation report, it appears that two borings (B-3 and ASTI)were advanced within the footprint of the excavation, prior to the excavation occurring. TPHg and PCBs were detected in soil at concentrations up to 350 and 7 mg/kg. Concentrations detected in groundwater were as follows: TPHg (2,000 ug/1), TPHd (500,000 ug/1), TPHmo (190,000 ug/l), 1,2,4-trimethylbenzene (8.1 ug/1). In 2008, approximately 315 tons of diesel-impacted soil was excavated to a depth of eight feet, which appears to have encompassed borings B-3 and ASTI. The soil was disposed at an offsite landfill. It appears that the excavation was backfilled with soil from onsite without geotechnical observation. Confirmation soil samples collected from the sidewalls and base of the excavation exhibited no significant impacts. No further investigations were conducted to address the remaining soil and groundwater impacts. SCOPE OF WORK The intent of this workplan is to further characterize the soil and groundwater impacts associated with the former AST. Prior to commencing field services, we will obtain approval of this workplan from RWQCB-Region 5 and the appropriate boring permit(s) will be obtained from San Joaquin County. SOIL SAMPLING Soil samples will be collected on a grid pattern around the AST area. A total of 10 soil borings will be advanced to an approximate depth of 25 feet below the ground surface (bgs) in the locations shown in Figure 2. Soil samples will be retrieved within continuous Geoprobe®acetate core liners measuring 4 to 5 feet in length. The soil cores from each boring will be logged by an ENGEO Environmental geologist or engineer under the direction of a licensed Professional Engineer. Specific soil samples will be collected for laboratory analysis by cutting a 6-inch portion of the Geoprobe® soil core liners corresponding to the respective desired sampling depth. The sample sleeves will be sealed using Teflon sheets secured by tight fitting plastic end caps. Upon collection of samples, a sample label will be placed on the sample and include a unique sample number, sample location, time/date collected, laboratory analysis, and the sampler's identification. Sample locations and depths will be as follows: • At the boring proposed within the center of the excavation footprint, soil samples will be collected at 11, 16, and 25 feet bgs. If elevated PID readings are recorded at 25 feet, the boring will be advanced further until PID readings indicate that no impacts are present, and a fourth soil sample will be collected at this depth. Three soil samples will be submitted to a State certified laboratory for analysis of TPHg and VOCs by EPA Test Method 826013; TPHd and TPHmo by EPA Test Method 801513; and silica gel by EPA Test Method 3630.