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Former Beacon Station No 12474 June 7,2005 Stockton California Results of Additional Groundwater Assessment • Site Physical and Hydrogeological Conditions The site is situated in the central portion of the Great Valley Geomorphic Province otherwise known as the Central Valley of California The Central Valley consists of two broad, topographically distinct, alluvial valleys the Sacramento Valley in the north and the San Joaquin Valley in the south These two valleys meet in the area of the inland delta formed by the confluence of the San Joaquin and Sacramento Rivers Stockton is situated in the northern San Joaquin Valley dust east of and adjacent to the San Joaquin/Sacramento River delta system Generally unconsolidated to poorly consolidated alluvial, fluvial and lacustrme deposits of Miocene to Holocene age comprise the upper portion of the stratigraphic sequence of the Great Valley province and are generally underlain by consolidated marine rocks Near surface sediments in the site area are generally Pleistocene to Holocene flood-basin deposits and Pliocene to Holocene alluvial and fluvial deposits Lithological data from soil borings indicate the site surface is underlain by interbedded sand, silt and clay as shown on the generalized geologic cross sections A-A' and B-B' (Figures 3 and 4) The Central Valley is divided into three hydrologic basins the northern Sacramento River Basin, the central San Joaquin River Basin, and the southern Tulare Lake Basin The city of Stockton is located within the San Joaquin River hydrologic basin Depth to groundwater at the site has fluctuated from 1998, rising from approximately 62 feet bsg to approximately 55 feet bsg in 1999 and falling to approximate 63 feet bsg in 2005 Historical groundwater monitoring data indicate that the groundwater gradient is generally less than 0 005 and the flow direction is variable During the most recent four quarters of monitoring, groundwater flows were northeast to southeast under gradients of 0 001 to 0 004 Evaluation of groundwater level data for first quarter 2005 indicate that groundwater table flow in the dispenser islands area varies from northeastward to eastward under a gradient of approximately 0 001 as shown on Figure 5 Evaluation of first quarter 2005 groundwater level data in the deep monitoring wells MW-13 through MW-17 indicate a southeasterly Addtn1GWassmnt Prosect No 1474 15 7 HORIZON ENVIRONMENTAL INC