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I 9 ATC Associates Inc. YVATC 1117 Lone Palm Avenue, Suite 201 ( Modesto, California 95351 209-579-2221 A SS OCIATES INC . fax: 209-579-2225 Joaquin Subbasin is drained by the San Joaquin River and several of its major tributaries namely, the Stanislaus , and Calaveras , and Mokelumne Rivers. The San Joaquin River flows northward into the Sacramento and San Joaquin Delta and discharges into the San Francisco Bay. Annual precipitation within the Subbasin ranges from about 11 inches in the southwest to about 25 inches in the northeast. According to the United States Geological Survey (USGS) 7 .5-Minute Series Topographic Map of the Terminous , California Quadrangle ( 1978 edition , photo revised 1993) , the Site is located in Section 5 of Township 2 north , Range 5 east, Mount Diablo base and meridian , at an approximate elevation range of 2 . 4 feet above mean sea level (MSL) to 18 feet below MSL. Average depth to groundwater in the shallow water- bearing unit (Zone-A) over the last five years (June 2003 to June 2008) has ranged from 2 . 16 feet below top of casing to 1 .65 feet below top of casing . The depth to water variability across the site is due to the steep topographic slope from the top of the levee east towards MW-8 . Groundwater flow within the shallow water-bearing unit has been observed consistently to the east-northeast, away from the slough ranging from approximately 0 . 05 to 0 . 08 feet per foot or from 260 to 420 feet per mile . Table 2 summarizes the historic groundwater monitoring data . Regionally, groundwater typically flows away from the levees towards the lower lying areas and is influenced by tidal fluctuations. A primary use of surface water in the Delta region is irrigation of agricultural land , and is controlled by irrigation ditches found throughout the region . The western and southern margins of the site are located on an engineered levee that varies in width , but is approximately 55 to 85 feet wide in the vicinity of the study area . Along the landward edge of the levee , the ground surface elevation drops relatively sharply resulting in an elevation difference of approximately 17. 5 feet from the crest of the levee to a low lying area in the northeastern portion of the site in the vicinity of MW8 . The subsurface materials encountered during groundwater monitoring well installation activities conducted on the levee are similar and generally consist of a clay layer extending to a depth of approximately nine feet bgs that is underlain by silt and/or peat to approximately 19 feet bgs . A laterally extensive clay layer was encountered from approximately 19 to 22 . 5 feet bgs . Alternating layers of sand , clay, and silt were encountered to the terminal depth of MW13 at approximately 62 feet bgs. Inland from the levee , silt overlying a laterally extensive clay layer was encountered in the northern portion of the site in the vicinity of MW9 and MW11 . Silt, silty sand and peat overlying the laterally extensive clay layer were encountered in the southern portion of the site in the vicinity of MW12 and MW14 . This shallow laterally extensive clay layer was encountered at depths ranging from approximately 7 to 10 beet bgs and extended to depths ranging from approximately 15 to 20 feet bgs . A laterally extensive sand layer interbedded with clay and silt extending to depths of approximately 31 to 37 feet bgs was encountered beneath the laterally extensive clay layer. A deeper clay layer KIR 2009 WP for Pilot Testing.doc ATC Associates Inc, S\Enviromental\62514 — KIR ATC Project No. 54.62514.0001 Page 5