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1* 4.5 Site and Area Lithology *,y According to BC, the subject site is located in the San Joaquin Valley which is a north -south trending�.j�' ha basin bounded by the Sierra Nevada Mountain Range to the east and the Coast Ranges to the West' `� Within the Stockton area the valley floor consists of Quaternary age alluvial sediments deposited by the01 ,`r�� San Joaquin River and its tributaries Soil hthology in the Stockton area includes sands, silty sands, silts, ` clayey silts and clays The site lies at an elevation of approximately 25 feet above mean sea level Sediment deposition in the area has produced nearly horizontal topographic features in the vicinity of the site Soils encountered beneath the site during the previous assessment activities consist of inter -bedded alluvial deposits, including clays, silts, sands, and fine gravels 4.6 Area Hydrology and Hydrogeology According to BC, the San Joaquin River is the major surface drainage within the Stockton area of the San Joaquin Valley The river flows approximately 40 miles from its point of origin, in the central San Joaquin Valley to Suisun Bay Groundwater in the valley flows west, from the Sierra Nevada Mountain range, - fnd mast rcm- the Coastal :angcs, toYaaid,, the ec itei of the dailf'y, a,-11 tL O'1_1L°Tll Valley Delta area The general groundwater flow direction in the Stockton area is reportedly to the northwest, towards the Stockton Divertion Channel, and exists at approximately 50 to 100 feet bgs Shallow groundwater is considered unconfined and has been designated as a beneficial water use unit Groundwater is used for farming and ranching (irrigation of crops and watering of farm animals), municipal and industrial water supply, and as a drinking water supply for the general public The San Joaquin River is located approximately 4 miles southwest of the site However, the nearest body of surface water, a water transportation and irrigation canal, is located approximately 3/2 mile northeast of the site Within the last 10 years groundwater beneath the site has risen from approximately 80 to 50 feet bgs. 5.0 RECENT SITE CHARACTERIZATIONS In accordance with the ATC Workplan For Additional Assessment, dated December 21, 2001, ATC installed five groundwater monitor wells (MW -13 through MW -17), three dual completion vapor extraction/air sparge wells (VEAS-1 through VEAS-3), and one groundwater extraction well (EX -1) on- site for the purposes of additional assessment and conducting pilot study activities The wells were drilled and installed from December 9 through 20, 2002 The installation and assessment associated with the drilling of groundwater monitor wells MW -13 through MW -17, remediation wells VEAS-1 through VEAS-3, and groundwater extraction well EX -1 was presented in the ATC Additional Site Assessment Report dated February 12, 2003 The ATC workplan was approved by Mr Harlan Knoll of the San Joaquin County Public Health Services, in a letter received by ATC on May 22, 2002 A copy of the approval letter is included as Appendix A — Regulatory Correspondence Appendix B outlines Standard EZ 100966 CAP S \EZ Serve\F-Z 1009661Reports1100966CAP 5 ATC Associates Inc ATC Project No 43 25827 0026