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A S S O C I A T E S I N C to the project site area. Instead, the site and the surrounding parcels rely on site wells to satisfy their water needs. The City does not currently have an aquifer or wellhead vulnerability program in place for the project site area. In January 1997, at the request of the PHS/EHD, Smith Technology conducted a groundwater receptor survey which included a search of the DWR groundwater well construction logs to identify any groundwater wells located within one half-mile of the site. The search revealed thirteen wells located in the vicinity of the site. The well locations are shown on Figure 5. A review of the nearby well locations reveals that the on-site well is the closest groundwater receptor to the plume (within approximately 100 feet crossgradient of the plume). A completed Water Well Drillers Report of the on-site domestic well, which was recently obtained from MR, reveals the well is constructed of 6 5/8-inch diameter steel casing. The wells' total completion depth is 139 feet bgs with perforated casing extending from 130 feet to 139 feet bgs. A 100-foot cement grout sanitary seal extends from the surface to 100 feet below grade. As previously mentioned, clay is present from 22 to 51 feet bgs; gravel from 51 to 70 feet bgs; clay from 70 to 131 feet bgs; and gravel from 131 to 139 feet bgs. The second nearest groundwater receptor is located approximately 330 feet southeast, generally crossgradient of the site's former UST locations. A completed Water Well Drillers Report of this domestic well (Figure 10, well 12) indicates this well is constructed of 6-inch diameter casing. The well's total completion depth is 95 feet bgs with perforated casing extending from 65 feet to 70 feet bgs. A 50-foot cement grout sanitary seal extends from the surface to 50 feet below �. grade. A log of the well's borehole indicates the lithology includes sand from 18 to 24 feet bgs; clay from 24 to 46 feet bgs; alternating gravel and sand units from 46 to 90 feet bgs; and clay from 90 to 150 feet bgs. This lithology is generally consistent with soil encountered during drilling at the site. Further examination of DWR well construction logs of wells within 2,000 feet indicate that none are screened in the predominantly sandy water-bearing unit present at approximately ± 10 feet to ±20 feet bgs. This sandy unit appears to be laterally continuous across the well survey area and as mentioned previously, is a horizontal preferential flow path for groundwater beneath the site. Additionally, the clay unit observed underlying the sand appears to be continuous, unfractured, confining strata extending across the study area. Although this underlying clay, which appears to have a thickness of± 25 feet, would be expected act as a physical barrier against contaminants migrating vertically from above the overlying sand strata. Utilizing the geophysical analytical results of soil samples collected from the upper sand strata Smith Technology previously evaluated the flow rate of groundwater beneath the site. Using a native state effective water conductivity of 4.55 x 107' cm/s and a hydraulic gradient at the site of 0.003 ft/ft, it was estimated that dissolved petroleum hydrocarbons in the upper sand strata would travel 4.69 ft/year by advection alone. Using this value, the estimated time for the hydrocarbon plume to reach the on-site domestic well (the nearest groundwater receptor) is 20 w:V S 122Veports\Request for NFAdoc 6 r