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2 . HYDROGEOLOGY When the five monitoring wells were installed, depth to ground- water was recorded at between 47 and 50 feet (GTI 1986, 1987) . A piezometric map prepared in June 1987 (Figure 3 ) indicated that the groundwater flowed downgradient toward the northeast (GTI 1987 ). The wells have been gauged frequently by FA since 30 October 1987, and gradient directions calculated from these data agree with the earlier work by GTI. A consistent and nearly flat gradient indicates flow to the northeast ('Fable 1 ) . One anomaly in this weekly gauging series occurred during the 11 January 1988 gauging; depth to water in monitoring well 2 decreased 0.57 foot from 30 December 1987 to 11 January 1988. Gradient calculations d which took this change into account indicated .a southwest L gradient, which has not been reproduced since. ti A geologic cross--section is graphically presented for this site (Figure 4 ) . This cross section was based on well logs available 4'. for the five monitoring wells installed by GTI. The geologic section includes interbedded sands, silts, and clays. They are heterogeneous formations which are both laterally and vertically discontinuous fluvial deposits. The principal aquifers at the site. are sand a,nses with some silt s &, and clay, and clay lenses with sand .and silt. Each has a vari- able- thickness. Maximum thickness of the sand lenses is 20 feet; r ij the minimum thickness is less than l foot. The sand lenses aver- } age .perhaps 10 feet in thickness. The clay lenses range in thickness from 25 feet to as little as 1 foot or less, but aver- age-thick n.ess is in the range of '15 to 20 feet.. Hydraulic conductivities yri]1range. from .0.0002 'm/dayto as high as 12 m/day (Todd 1980 ). On average, .the hydraulic conductivity will _ be closer to the lower end of the range of values, because the clay-rich formations dominate the lithology below the water table. tj e25/71050/txt 2 '. •tit.'-.. ..