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SECTION 4.0 SITE INVESTIGATION ACTIVITIES s ' Fairgrounds, located east of the Shop 10 site According to Mr Clark, "the two private wells at the mobile home park were closed a couple of years ago," and "the fairgrounds may have had [private] wells " The locations and existence of wells on the San Joaquin County Fairgrounds could not be ascertained with available records at Clark Well, but their locations are estimated to have been more than 500 feet from the District 10 sites (Clark, 2000) The closed mobile home ' park wells were located a distance greater than 500 feet from Shop 10 Clark Well provided copies of well logs and pumping rates (where available) for the local, public ' and private wells in the vicinity of the Shop 10 site Well logs available through Clark Well and the California Water Service Co indicated general stratigraphy consisting of a clay layer extending from the surface to approximately 40 to 63 feet bgs, intermittent sand and clay from 63 to 75 feet bgs, a clay layer from approximately 75 to 190 feet bgs, followed by layers of sand and gravel Available water quality information for the two wells on the Clark property, and for the ' California Water Service Well No 46-01 collected indicated that concentrations of the constituents of concern (TPH-g, BTEX, and MTBE) were below the respective detection limits Water quality data from the Clark Well was collected in 1988 and 1989, and data from the California Water Service Company was collected in 1999 Water quality data for the mobile home park wells were not available Available information is included in Appendix D Based on the results of the local well survey, there do not appear to be any private or public wells within 500 feet of the property boundaries of Shop 10 Based on the review of groundwater ' sampling data for wells on the Shop 10 site, the dissolved petroleum hydrocarbon plume does not appear to have migrated to these public and private wells ' 4.2 GROUNDWATER SAMPLING AND ANALYSIS ' URSGWC conducted vertical groundwater sampling and analysis in three wells (MW-13, MW- 14, and VM-2) at Shop 10 on April 7, 1999 The objective of the groundwater quality monitoring and sampling was to collect discrete samples vertically within the developed wells to assess the vertical extent of petroleum hydrocarbons Discrete groundwater samples were collected at five depths within the water column of MW-13, ' three depths in MW-14, and two depths in VM-2 The discrete samples were collected without immediate prior purging of groundwater from the wells The sample depths were (1) within ' approximately the top 2 feet of the water table, and (2) at approximately 10 foot intervals below the water table thereafter to the maximum depth of the well Samples were collected using the KabisTM H sampler for 4-inch wells (MW-14 and VM-2) and KabisTM I for the 2-inch well (MW-13), as described in Appendix B The discrete samples at each depth were collected in three 40-milliliter vials (40-mil VOAs) The 40-mil VOAs are screwed into the bottom of the stainless-steel lid on top of the KabisTM sampler Groundwater fills into each vial via stainless- steel sample ports located on top of the KabisTM sampler lid As long as the KabisTM sampler S 1PROJ141040100041SHOP10lSHOP10SA.00C 4-2 Uf1S Greiner Woodward Clyde