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ARCADIS Ms. Lori Duncan <br /> March 20, 2009 <br /> Petroleum hydrocarbons have not been detected <br /> in water samples collected from the <br /> Y P <br /> domestic well located near the northern property boundary. Summary tables of <br /> historical soil analytical results are provided in Attachment 1. Historical boring <br /> locations are included in Attachment 2 <br /> Regional Geology <br /> The Stockton area is underlain to a depth of approximately 150 feet below grade by <br /> Holocene age alluvium and the Victor Formation, which is comprised of <br /> unconsolidated Quaternary age deposits. These formations are heterogeneous <br /> consisting of laterally discontinuous lenses of sand and gravel with varying amounts <br /> of sand and silt interstratified with units of clay and silt. <br /> Hydrology and Hydrogeology <br /> Surface water bodies present in the vicinity of the site include Morman Slough, <br /> located approximately 3,000 feet to the north, and Walker Slough located <br /> approximately 6,000 feet to the south. <br /> During the third quarter 2008 groundwater monitoring event, the groundwater flow <br /> direction was toward the southwest at an approximate horizontal hydraulic gradient <br /> ranging from 0.001 to 0.003 feet per foot(ft/ft). Depth to water.(DTW)measurements <br /> show groundwater levels at approximately 60 feet bgs. The most recent groundwater <br /> monitoring data can be found in ARCADIS' Third Quarter 2008 Groundwater <br /> Monitoring Report, dated February 18, 2009 <br /> I <br /> Temporary Groundwater Monitoring Well Installation <br /> Between January 6 and 16, 2009, Cascade, under the supervision of ARCADIS, <br /> advanced one soil boring(SB-2) and installed a temporary monitoring well to. <br /> evaluate the vertical extent.of petroleum hydrocarbon impacts to soil and <br /> groundwater near groundwater monitoring well MW-1 (Figure 1). <br /> C <br /> �+ Soil Boring <br /> Prior to drilling, SB-2 was hand cleared using an air knife and hand auger to a <br /> minimum depth of 8 feet 1 inch (utility clearance depth) bgs. The boring was <br /> advanced using a combination of rotary and sonic technologies to a total depth.of <br /> f approximately 150 feet bgs. <br /> 6.1 <br /> Page: <br /> \larcads sWfticedata%SacamantoCAIEtMCHEVROM30907516 DeliverableskRepatsWuessmenl Addendum\Tex*09075 Site Assessment Addendum Report_282910950.doc 3/7 <br />