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' III. Environmental Setting, Impacts, and Mitigations K Hydrology,Geohydrology,and Water Quality ' fall. Typically,the water table is at depths averaging 68 feet below the surface,but may fluctuate 13 to 23 feet seasonally,depending upon rainfall abundance(Kleinfelder, 1988). Groundwater flows in the project area are generally to the north. The groundwater gradient is also reflective of the weather cycles and pumping,with a steeper,north trending gradient in dry years and a more gentle, northeast gradient in wet years(Kleinfelder, 1988). The dry year gradient is apparently affected by greater drawdown in the area northeast of Stockton. Perched water may occur intermittently during the wet season,above relatively impermeable silts or clays in the sediment sequence(Kleinfelder, 1988). Hydrogeological data obtained from the adjacent Forward,Inc.Landfill site indicate that vertical and horizontal transmissivities are ' highly varied and there is substantial interconnection between upper and lower aquifers (Meinfelder, 1988). The development of a regional cone of depression east of Stockton,in ' response to pumping of agricultural and municipal wells,indicates the connectedness of the regional aquifers. No widely correlatable shallow aquifer sands,or silt and clay aquicludes(barriers)were observed, which reduces the ability to predict lateral groundwater flow or vertical ' interconnections. Groundwater tests associated with the adjacent Forward Landfill site determined that the rate of groundwater flow in the uppermost regional aquifer was in the range of 0.08 to 0.8 feet per day, which is a relatively high flow (Kleinfelder, 1991). Due to the heterogeneous nature of the Victor formation sediment units, aquifer properties,including conductivity and rate of flow are anticipated to vary by a factor of ten or greater,depending on location. In general,the available information suggests that the primary aquifer under the site is an unconfined aquifer within the Victor formation. Water Qty ' Groundwater The quality of groundwater in the vicinity of the Austin Road Landfill has been discussed in several reports on file with the City. The existing landfill has had a groundwater monitoring ' program since 1987,and there are thirteen monitoring wells(MWI through MW13)and two water supply wells on-site. Ten of the monitoring wells are down-gradient of the landfill (MW 1, ' MW4, MW6, and MW7 through MW 13) and three wells are located up-gradient(MW2,NIW3, and MW5). One of the water supply wells (WSW)has been decommissioned in compliance with III.K.8