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Site Assessment Report 1022 Frontage Road C A M B R I A Ripon, California • December 16, 2005 propane tank, a 4,500-gallon oil water separator, a truck scale, and a drainage pond A site plan showing the general layout and relative locations of site features is included in Figure 2 22 Regional Geology and Hydrogeology The site is located within the San Joaquin Valley Groundwater Basin(Basin No 5-22) The Modesto, Riverbank, and Turlock Formations, as well as Recent Alluvium are the primary sources of groundwater production within the San Joaquin Valley Groundwater Basin 2.3 Local Geology and Hydrogeology Soils encountered during drilling consist primarily of interbedded sand,silty sand, sandy silt,silt,and clay to a total explored depth of 60 ft bgs(boring B-18) Saturated silty sand is encountered across the site at depths between 25 and 35 feet bgs The shallow groundwater aquifer is detected within this silty sand bed Boring and well construction logs detailing the subsurface findings are included in Appendix B Since May 1998, groundwater monitoring activities have been ongoing at the site Since 1998, the groundwater table has decreased in elevation from approximately 15 ft bgs to as deep as approximately 27 ft bgs The decrease in the groundwater table elevation is presumed to be related to groundwater pumping at nearby municipal and domestic wells On NgNember 15,2005,groundwater tf 17`Dd flowed away from the source area toward the southwest ando ast at gradients ranging between approximately 0 0008 and 0 0MVft/ft(Figure 3) Arose diagram on Figure 3 represents the historical groundwater flow directions Since 1998, the groundwater flow direction has varied significantly with groundwater flow predominately toward the west and north "The varied groundwater flow direction is likely due to the flat groundwater gradient observed at the site and nearby groundwater pumping On April 1, 2005, Cambna had all the monitoring wells and related site features resurveyed and a revised site plan is presented on Figure 2 24 Sensitive Receptors In 2003,Advanced GeoEnvironmental,Inc (AGE)of Stockton,California conducted a well survey to identify any domestic,municipal,irrigation,or monitoring wells within a 2,000-foot radius of the site The well survey identified one municipal well and several domestic wells within the search radius The municipal well is located 750rwest of the site and is screened from 170 to 195 ft bgs, with . additional screened intervals below this depth Well DW-1 is located onsite near well MW-8 and is screened from 160 to 200 ft bgs Well DW-1 is used to operate the truck wash onsite A domestic or 2