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a YWGEPS OESGNplS(ri6uIANIS Zones 1 and 2 are located above the historical high water table and will not be discussed in detail Zone 3 vanes in thickness from 10 to at least 25 5 feet. Zone 3 is composed of a relatively permeable sand and contained the water table aquifer in 1989 Zone 4 is composed ' of a silt with clay and sand lenses Because of the finer sediments of Zone 4, Zone 3 is more permeable than Zone 4 Zones 3 and 4 do not appear to be separated by a hydraulic barrier 2.2.2 Hydrogeology and Groundwater Conditions Eleven monitor wells have been installed at the site. Two wells were abandoned due to low ' water levels, currently eight wells are part of the regular monitor well network. The majority of the wells are screened in Lithologic Zone 4 The water levels in the monitor wells have been ' measured periodically since 1989 Histoncal groundwater elevations are presented in Table 2. In 1988, groundwater beneath the site was encountered at a depth of approximately 25 feet bgs (-15 feet msl) in the Zone 3 sand. Monitor wells MW-1, MW-2 and MW-3 were completed in this zone with screened intervals from approximately 21.5 feet to 45 5 feet bgs Between 1989 and 1991 due to drought conditions water levels dropped by as much as 26 feet Because MW-2 ' and MW-3 went dry, they were replaced by deeper wells MW-2A and MW-3A By 1991, drought conditions caused a drop in groundwater elevations to a low point of approximately - 37 8 msl, which coincided with Zone 4 The aquifer is considered to be an unconfined water table aquifer which is hydraulically connected with Zone 3 sand The two zones are essentially parts of the same unconfined aquifer in which the water table elevation fluctuates according to the amount of regional groundwater recharge Since 1991, groundwater elevations have rebounded to approximately -22 feet rnsl 2.2.3 Flow Direction and Gradient Regionally, groundwater flows east-northeast toward a large groundwater depression approximately eight miles east of the site (WESTON, 1992) Based on groundwater contour ' maps prepared for site quarterly monitoring reports, groundwater flow beneath the site is toward the north-northeast in a trough-shaped pattern Figure 5 is typical of the site groundwater flow patterns observed at the site Typically, the groundwater gradient in the center of the trough is ' 0 002 to 0 003 foot/foot (ft/ft) as measured between wells MW-2A and MW-7 Groundwater gradients on the sides of the trough are typically 0 01 ft/ft ' 2.2.4 Hydraulic Conductivit Hydraulic conductivities of Zone 4 were estimated using slug tests collected in October 1991 ' (WESTON, 1992) The calculated hydraulic conductivities are presented in Table 3 LTR0JECTMANIOQMASALTI0NPL 8