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Type II Work Plan - Addendum <br />UXO Construction Activities and Soil Removal Action <br />Preliminary Assessment/Site Investigation Update <br />California Army National Guard Facility <br />Stockton, California <br />Contract No. GS-00E-007L/Task Order W91238-05-F-0084 <br />Version 2.0 <br />1.3 TOPOGRAPHY <br />The CA ARNG facility is located in the central portion of the Sacramento Valley at an elevation <br />of 16 to 36 feet above sea level. The facility is nearly flat and has been graded and modified to <br />promote surface drainage. Catch basins collect rainwater for flow north through underground <br />pipes into the adjacent airport storm water system. Eventually, surface drainage is to Little John <br />Creek, a water course oriented east to west approximately 1.5 miles north of the Site. Little John <br />Creek flows into French Camp Slough and eventually into the San Joaquin River. <br />Soils beneath the Site consist of fine sands and silt/sand mixtures to a depth of approximately 50 <br />feet below ground surface (bgs). One exception is the OMS area where soils comprised of clayey <br />silt with localized areas of sandy silt and silty clay may be encountered. <br />A geophysical survey performed during May 2006 (Appendix B) identified two distinct layers <br />beneath the subject area at the CA ARNG facility. Electrical resistivity testing identified a <br />surficial soil/fill layer varying in thickness from 10 to 20 feet. This layer is underlain by more <br />resistive, coarser grained sediments. <br />1.4 CLIMATE <br />The climate of San Joaquin County is characterized by hot, dry summers and cool, moist winters <br />(USDA 1992). The average monthly temperature in Stockton is about 77 degrees Fahrenheit (F) <br />in July and about 45 degrees F in January. Rainfall averages vary from 8 to 12 inches per year in <br />the areas south of Stockton to 18 inches per year north of Stockton. About 90 percent of the total <br />annual rainfall occurs between November and April. Stockton has an average of about 184 clear <br />days, 75 partly cloudy days, and 105 cloudy days annually. <br />104700.4965.300 Page 1-3 April 2007