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Aquifer materials logged, to the total depth of the borings, appear homogenous horizontally and grade vertically from silty clay to medium-grain sand near the bottom of the wells The lower extent of the aquifer is not known The saturated horizon occurs under unconfined conditions Groundwater elevations have been measured at the site since April 1989 The calculated groundwater gradient has ranged from 0 002 to 0 0005 ft/ft during the observation period The flow direction has remained fairly constant toward the northwest The depth to groundwater has ranged from 23 87 to 27 68 feet Groundwater elevations cycle seasonally with the lowest groundwater elevations being observed in May and June and the highest recorded elevations occurring in November and December Estimates of hydraulic conductivity (K) were made in July 1991 from rising-head tests performed in wells MW-2, MW-3, and MW-5, and ranged from 3 673 X 104 to 4 327 X 10-3 ft/min, respectively Estimates of flow were made from the individual K values and were 0 05, 0 58, and 6 04 gallons per minute (gpm), respectively ("Final Remediation Plan" (FRP), Aegis, 1992) Because of the limited amount of data collected, hydrogeologic conditions are considered to be homogenous and isotropic The thickness of the saturated horizon has not been defined and is considered to be 8 feet, or equal to the thickness of the water column in the wells An average hydraulic conductivity of 2 16 feet per day based on the three K values from the slug tests is used in the model Porosity of 25 percent is assumed, based on the logs of the sod borings Infiltration due to irrigation is not quantified and evaporation exceeds natural infiltration To provide a conservative estimate of capture zone, the infiltration rate is considered to be zero NUMERICAL MODEL Data and assumptions presented in the conceptual model were inputed to the numerical computer model Attachment A is a log of the numerical model Due to the limited amount of data collected, shallow groundwater and anticipated low yield from well MW-1 B, the domain of the model was defined as an area 500 by 500 feet with the site placed in the center The grid for the model consists of 63 rows and 64 columns with the grid spacing at the edge of the domain to be one square per 10 feet The grid density was increased in the area of the site to one square per 5 feet to increase detail of the model (Figure 3) Boundary conditions were set as constant head nodes Head measurements were extrapolated to the boundaries of the site from water data collected on October 21, 1991 (Figure 2) The first simulation performed was a calibration simulation for head distribution with the pumping well MW-1 B turned off Figure 4 indicates the head distribution predicted by "Flowpath" under non-pumping conditions A comparison of measured head distributions (Figure 2) and the predicted head distributions (Figure 4) indicate a reasonable match The figure also indicates anomalies due to conflicts between the numerical model and domain boundaries are limited to areas beyond the boundaries of the site