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Based on the slug tests, hydraulic conductivities in the shallow wells appear to range from 2 x 10.2 to 2 x 103 cm/sec (57 to 5.7 feet per day [ft/d]). Aquifer pumping tests completed by Camp Dresser McKee Inc. (1999) and groundwater modeling by Herst & Associates/ Andrews Environmental Engineering ([HA/AEE], 2001) indicate that the hydraulic conductivity of deeper well aquifer materials in the area is significantly higher (250 ft/d [0.088 cm/sec]) than was measured in the slug & bail test results. CH2M Hill also conducted aquifer pumping tests on the north side of the Austin Unit of the FL and calculated a hydraulic conductivity of 875 gallons per day per square foot (0.04 cm/sec). The higher values obtained from pumping tests are consistent with values listed in the literature (Driscoll, 1986) for medium-to coarse-grained sands and appears to most closely approximate the types of materials encountered within water-bearing zones in the deeper monitoring wells at the site. Using the conservative hydraulic conductivity value selected by HA/AEE (250 ft/d), an average groundwater gradient of 0.001 ft/ft, and an estimated effective porosity of 0.25, the calculated average linear groundwater velocity at the site is: v= [(K)(h/I)]/n = [(250 ft/d) (0.0025)] / 0.25 = 2.5 ft/d Where: v =velocity (ft/d) K = hydraulic conductivity (ft/d) n = effective porosity h/I = gradient 2.7.6 REGIONAL WATER QUALITY The San Joaquin hydrologic basin has experienced overdraft for many years. In the Central San Joaquin Irrigation District, which encompasses FL, water levels have dropped approximately 70 feet since the 1940s. Declining water levels_- - -- ----- - throughout the Stockton area have induced the eastward movement of poor- quality water from the delta sediments. Migration of these saline waters had impacted groundwater as far east as Stockton at the time of a 1981 study by the ® U.S. Geological Survey (USGS) (San Joaquin County Flood Control and Water Conservation District, 1990). The San Joaquin County Flood Control and Water Forward Landfill-Project Description 2-12 BRYAN A.STIRRAT S ASSOCIATES ):\Allied\Forward\2007.0018 Lateral Expansion\Reports\Prof Descrip\021308 Final Proj Des\Sec 2.doc:2/13/2008)