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water-bearing formations in Eastern San Joaquin County are the Mehrten, Laguna, Victor, and alluvial deposits. The Groundwater Management Plan notes that the regional groundwater flow patterns have been significantly altered since pre-development conditions: Groundwater was used for agriculture in the Central Valley starting around 1850, prior to which time the groundwater system was in a state of hydrologic equilibrium (Williamson, et. al., 1989). Under equilibrium, or steady-state conditions, groundwater flowed from the natural recharge areas along the perimeter of the valley towards the low areas along the San Joaquin River. The natural groundwater and surface water discharge was through the Delta westward to San Francisco Bay. Under pre-development conditions groundwater gradients within San Joaquin County were likely similar to the topographic gradient, or around 0.00 12 ft/ft. Beginning in 1850 the development of groundwater for agriculture expanded rapidly. Within the Central Valley, irrigated agriculture has grown from less than 1 million acres around the turn of the century, to an estimated 7 to 8 million acres at present. Within eastern San Joaquin County, an estimated 800,000 of/yr of groundwater was being extracted by 1993. In Bulletin 118-80, DWR designated the Basin as `critical overdrafted'. [A] significant cone of depression [exists] east of Stockton. Regional groundwater flow now converges on this low point, with relatively steep groundwater gradients (0.0018 feet/feet) westwards towards the cone of depression, and eastward gradients from the Delta area on the order of 0.0008 feet/feet. The eastward flow from the Delta area is significant because of the typically poorer quality water. 2. Vicinity and Site Near-Surface Geology and Hydrogeology The State Water Resources Control Board's online GeoTrackerTM database (www.geotracker.swrcb.ca.gov) identified the closest LUST site with available online soils and groundwater data as the H& H Engineering and Construction (H&II) facility at 212 Industrial Drive, the western adjoining property to the subject site. From more than 20 borehole logs recorded on the H&H site, cross-sections were constructed illustrating that the predominant soil types from ground level to a depth of 55 feet are silts and clays (from low to high plasticity). Discontinuous stringers and lenses—to a maximum thickness of 9 ft—of silty or clayey sand were identified in five of the boreholes. In the three boreholes in which permanent monitoring wells were constructed, the depths to first encountered groundwater ranged from 33.4 to 33.8 ft bgs. Static water levels after development ranged from 30.70 to 32.05 ft bgs, indicating semi-confined or confined conditions. Static water levels over the period that the wells were active (1998 to 2007) fluctuated by almost 10 ft—e.g., in MW-1, the minimum depth to water was 26.89 ft while the maximum depth to water was 36.61 ft. The available online data also indicate a general northeasterly direction of groundwater flow at that site (toward the northwest portion of the subject property). The soils beneath the site are interpreted to be alluvial/fluvial deposits that are the result of flood events and overbank deposits from local sloughs. The predominant soil type is bioturbated (roots and burrowing), very dark brown and gray clayey silt to the drilled depth of 50 feet bgs. These soils contain caliche in the form of blebs and stringers but not as a well- indurated and thick layer. Almost all of the soils are oxidized to a brown or reddish brown color as a coating. Sand-sized soils are rare but tend to exist around 26 to 28 feet bgs if they are present. Above the sand,the clayey silts are yellow brown in color.