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c• Subject Predictions of Well Yield, Cone of Depression, Radius of Influence, Capture Zone and Particle Tracking Moore Petroleum, Inc. 1399 East Yosemite Avenue, Manteca, California At the request of the Central Valley Regional Water Quality Control Board, a hydrogeologic model for the site was prepared to determine the radius of influence, drawdown, yield, and capture zone at a specified pumping rate from well MW-1 B, located at the subject site It has been proposed to pump groundwater from beneath the site to capture and control dissolved hydrocarbons in groundwater Based on a conceptual model derived from field data and background information,the two-dimensional horizontal aquifer computer simulation, "Flowpath," was selected to perform numerical analysis of the aquifer beneath the site (Flowpath 3 02, Waterloo Hydrogeologic Software, Franz, T and Guiger, N 1990) The conceptual model was used to guide input to the numerical model Several numerical solutions were obtained from the numerical model by varying pumping rates and comparing the results to field data to achieve model calibration Once model predictions of head dad not exceed possible head distributions as defined by field data, analysis of head distributions, velocity calculations and particle tracking was performed Because the amount of field data is relatively limited, refinement of the model can be performed as more data is collected CONCEPTUAL MODEL The surface of the site is predominantly paved The area surrounding the site to the north and east is paved Unpaved areas to the west and south of the area are irrigated landscaping Storm sewers provide drainage from the paved areas and transmit runoff into a lined ditch approximately 1,000 feet north of the site (Figure 1) Average annual precipitation in the area is approximately 17 inches per year (Department of Water Resources Bulletin 130-85, May, 1988) Evaporation exceeds infiltration in the area of the site The nearest surface water is an intermittently used, lined, irrigation ditch located approximately 300 feet south of the site Wells in the area are predominantly for domestic and irrigation uses, with screened wto intervals beginning at depths exceeding 100 feet A search within a quarter mile of the site did not indicate the existence of any such wells ("Problem Assessment Report," Aegis, 1991) Description of the hydrogeologic setting is based on logs of six, on-site, 10-inch-diameter sod borings drilled to an approximate depth of 35 feet (Figure 2) The sod borings were converted to 4-inch-diameter PVC wells, screened with 0 020 inch slots from approximately 15 to 35 feet The gravel pack of each well consists of #3 grade Lonestar sand ("Problem Assessment Report" Aegis, 1991)