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PEA Work Plan Addendum Page 2 Former Haley Flying Service GPE Project 474.2 2.0 DATA COLLECTION This section describes the rationale and methods that will be used to obtain the samples and laboratory analytical information to be used in the completion of an addendum to the PEA. 2.1 Field Work Groundwater samples will be collected at six specific points on the subject site. Three points will be from borings to be installed through the south berm of an irrigation ditch that marks the north line of the site. Other borings will be located south, east and west of the contaminated area. The domestic water well will also be sampled, making a total of seven groundwater samples to be collected. 2.2 Sampling Strategy The regional direction of groundwater flow in this area is in a northerly direction, although the precise local direction of flow has not been determined. In an attempt to obtain representative groundwater samples in the down-gradient position, three of the borings will be installed on the south berm of the irrigation ditch. These positions will be northwest, north, and northeast of the area of the most intense pesticide contamination. These locations are also unlikely to exhibit high concentrations of pesticides in the soil, thus minimizing the risk of cross-contamination. To assure that a suitable groundwater sample has been obtained regardless of the actual direction of groundwater flow, additional borings will be installed south, east, and west of the area of major contamination, but at points sufficiently distant that shallow soil contamination will be minimal. The Geo-Probe soil borings (designated B-3 to B-8) will be advanced to a depth sufficient to penetrate the groundwater surface, and a sample of the shallow groundwater will be collected from each of these borings. In addition, a sample will be collected from the onsite domestic water production well. 2.3 Groundwater Sampling and Analysis Prior to installing the proposed soil borings, the required drilling permit will be obtained from the San Joaquin County Environmental Health Department. The Geo-Probe soil borings will be drilled using 1.5" outside diameter Geo-Probe drilling equipment owned and operated by RSI Drilling of Woodland, CA, a C-57 Licensed drilling contractor. The borings will be advanced to a depth sufficient to penetrate the groundwater surface (est. about 11 feet below grade). The domestic water well and borings B-3 through B-8 are shown on the detailed site sketch map (Figure 2). See the original Work Plan for information regarding soil boring and sampling procedures. After collecting the final soil sample and a groundwater sample, each boring will be filled to grade with Class G neat cement. 2937 Veneman Avenue, Suite B240 Geo-Phase Environmental Inc. Phone: (209)569-0293 Modesto, Ca 95356 Fax: (209)569-0295