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monitored at the site. <br /> The sedimentary formations underlying the Victor formation have many productive <br /> confined aquifers. In order to develop adequate flow, most of the agricultural <br /> irrigation wells in the area are at least 500 feet. The unconfined aquifers are <br /> recharged by rainfall and local stream infiltration. Rivers, reservoirs and surface <br /> runoff along the slopes of the western Sierra Nevada Foothills recharge the deeper <br /> confined aquifers. <br /> 3.7.4 GROUNDWATER FLOW DIRECTION AND GRADIENT <br /> The groundwater surface and gradient are measuretl at'*ei-ousting Forward`an'd <br /> Austin Road landfills in a network of groundwater monitoring wells. The location <br /> of the wells is depicted on Figure 7 and discussed in Section 7.2.2. Data from on- <br /> site monitoring wells indicates that the groundwater.gradient generally.Aopes.lo <br /> the north-northeast, in agreement with the regional trend. The groundwater <br /> gradient is also reflective of the weather cycles and pumping;`with a steeper, north <br /> trending gradient in dry years and a more gentle, northeast gradient in wet years. <br /> The dry-year gradient is apparently affected by greater drawdown in the area <br /> northeast of Stockton. The development of,,a regional cone of depression,east.of <br /> Stockton, in response to pumping of agricultural and municipal wells, indicates the <br /> connectedness of the regional aquifers. <br /> Fluctuations in monitoring well groundwater elevations and gradient follow the <br /> seasonal variation in rainfall, indicating that infiltration of rainfall has an effect. <br /> Perched water may occur intermittently during the wet season, above relatively <br /> impermeable silts or clays in the sediment sequence. <br /> According to the information compiled over the last several years, groundwater <br /> gradients have varied from 0.15 -0.53 percent consistently to the northeastand <br /> have remained fairly stable with an average of about 0.2 to 0.3 percent. <br /> 3.7.5 HYDRAULIC CONDUCTIVITY AND GROUNDWATER VELOCITY ESTIMATES <br /> To assess the insitu hydraulic conductivity of the uppermost aquifer underlying the <br /> existing Forward Landfill, slug tests were performed in four wells during 1991 by <br /> Kleinfelder as part of the RCRA Facility Investigation for the closed Class I area. <br /> The selection of the four wells for slug tests was based on the following criteria: <br /> Forward Landfill JTD 3-12 <br /> L:\AI lied\2000.193\Reports\finaljtd:Sec-3.0:08/20/01 <br /> BRYAN A.STIRRAT&ASSOCIATES <br />