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Hydrogeologicaily, the site is within the Sacramento-San Joaquin Delta subregion of the greater Central Valley aquifer system. Based on .groundwater data obtained from a previous investigation at the site (Geological Technics Inc., 2001), groundwater is at approximately 20 to 24 feet below ground surface (bgs). Although groundwater flow direction and gradient are not known at the site, based on available information it expected that groundwater flow is generally west toward the San Joaquin River, approximately 5.5 miles to the west (DWR, San Joaquin District, 2003). 2.3 Potential Sensitive Receptors According to the Department of Water Resources ,Central Region (DWR-CR), there are 1-4 active _ production wells and 22 monitoring wells located within a one-mile radius of the site. Information that the DWR-CR could release regarding the wells is summarized in the following table. Townsilp Range Number of `Well Use Approximate Depth {feet} Section TI S/R7E Section 31 " 3 Monitoring >50 T1 S/R7E Section 31 1 Domestic >200 T1 S/R7E Section 32 1. Monitoring 350 to 425 T1 S/R7E Section 32 1 Public Supply 350 to 425. LI T2S/R7E Section 6 8 Monitoring 15 to 35 T2S/R7E Section 6 7 Domestic 150 to 200 T2S/R7E Section 6 2 Irrigation 150 to 300 T2S/R7E Section 5 10 Monitoring -30 T2S/R7E Section 5 2 Domestic 150 to 250 T2S/R7E Section 5 1 Irrigation" >300 Exact location, distance from the site and well.construction details.were not available, Accor_ding to -the DWR-CR, written authorization from the well owner is required to release any further information. L .The DWR-CR also recognizes seven wells that have been either backfilled or abandoned, and one Pacific Gas & Electric well installed to provide cathodic protection to product lines within a one- L mile radius of the site. 2.4 Environmental Site History Geological.Technics Inc. (GTI) performed a geoprobe investigation at the site on August 16, 2001, obtaining soil and groundwater samples. A complete report of this investigation was not made available to WPI, however figures and tabulated analytical data of the investigation were reviewed. L During the GTI geoprobe investigation, soil samples were collected at approximately 15 feet in four locations, GP-1, GP-2, GP-3, and GP-4 (Figure 2). Grab groundwater samples were collected in each of the geoprobe borings at depths ranging from 20 to 24 feet bgs. L 116O W. Yosemite Avenue (at Union Road), Manteca, CA 2