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3-11 infiltration. Rivers, reservoirs and surface runoff along the slopes of the western base of the Sierra Nevada Foothills recharge the deeper confined aquifers. Wells in the area are used primarily to supply water for agricultural and domestic purposes. Of the facilities in the area, the CYA and the Northern California Women's Facility north of the Forward Landfill both have wells that are thought to be used to supply drinking water. 3.7.4 Groundwater Flow Direction and Gradient The groundwater surface and gradient are measured at the Forward Unit and Austin Road Unit in a network of groundwater monitoring wells. The locations of the wells are depicted on Figure 8 and discussed in Section 7.2.1. During the 2012 monitoring year, groundwater flow was generally directed to the north and northeast with an average hydraulic gradient of 0.002 ft/ft (Water Quality Monitoring Report, Fourth Quarter 2012/Annual, GLA, 2013). Fluctuations in monitoring well groundwater elevations and gradient follow the seasonal variation in rainfall, indicating that infiltration of rainfall has an effect. Perched water may occur intermittently during the wet season, above relatively impermeable silts or clays in the sediment sequence. 3.7.5 Hydraulic Conductivity and Groundwater Velocity Estimates To assess the insitu hydraulic conductivity of the uppermost aquifer underlying the existing Forward Landfill, slug tests were performed in four wells during 1991 by Kleinfelder as part of the RCRA Facility Investigation for the closed Class I area. The selection of the four wells for slug tests was based on the following criteria: ♦ Spatial representation of the Forward Landfill site (horizontal) -one shallow well on the southern side and two shallow wells on the northeastern side of the landfill were tested. ♦ Spatial representation of the upper aquifer (vertical) -one deep well, MW -10, was tested for comparison with the three shallow wells. ♦ Sufficient submergence of the well filter pack to allow the greatest possible vertical displacement of water during slug insertion/withdrawal. The four wells chosen were sufficiently deep that the filter pack around and above the perforated section was submerged on the test date. Testing previously attempted in April 1990 was unsuccessful due to the small vertical changes in water elevation that were achieved as the slug displaced water into the unsaturated filter pack. Based on the slug tests, hydraulic conductivities in the shallow wells appear to range from 2 x 10-2 to 2 x 10-3 cm/sec (57 to 5.7 feet per day [ft/d]). These results are consistent with Forward Landfill SWT Engineering Joint Technical Document - April 2014 z:\projects\allied waste\forward\five year permit rvw 2013\jtd-5 yr pr 2013\text\sec 3_final.doc