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' Aquifer Testing Work Plan • • <br /> Formerrth GroBroadway <br /> Facility <br /> 1905 North Broadway Avenue - <br /> ' Stockton,California - <br /> Sierra-Pacific Project No. 94-055.05 <br /> ' 3.0 ENVIRONMENTAL SETTING <br /> 3.1 Geology and Stratigraphy <br /> The site is located in the northern part of the San Joaquin Valley in an area underlain by several thousand <br /> ' feet of terrestrial and marine sedimentary rocks. The northern San Joaquin Valley has been a lowland <br /> ' area subject to marine intrusion, flooding, and incremental sedimentation for millions of years. The <br /> uppermost 200 feet of sedimentary strata consist of Pliocene,Pleistocene,and Holocene sediments. The <br /> ' sediments are mixed-fluvial sediments, dominated by medium-grained sands and silts. Thin beds of <br /> clayey sand and sandy-clay are abundant, but no laterally-continuous aquicludes have been identified <br /> ' within the uppermost 200 feet of sediments. <br /> ' The dominant subsurface lithology at the site is brown silty-sand,with little or no coarse sand and gravel. <br /> Near-surface soils are classified SM or SC under the Unified Soil Classification System(USCS). Soil <br /> ' types vary between boring locations,with some locations being substantially more clayey than others. <br /> The most complete stratigraphic (soil) section was observed at an off-site monitoring well (MW-7), <br /> ' where continuous core was collected and described from the surface to about 150 feet below ground <br /> surface (bgs). <br /> 1 <br /> Several soil borings were advanced,and soil samples collected and tested,to characterize contaminated <br /> ' soils which remain in situ at the two former evaporation ponds. Soil borings were advanced in the <br /> former Brea (north) evaporation pond area. Soil borings were also advanced in the former PureGro <br /> ' (south)evaporation pond area. Results of these soil sampling programs provide a better understanding <br /> of the nature of the sediments and agricultural-chemical contamination at the site. <br /> ' Yellowish-brown, clayey-sand (SC)with little or no coarse sand and gravel is the dominant lithology <br /> from 20 to 35 feet below ground surface (bgs). Clay content generally increases with depth. Well- <br /> graded sand and gravel (GW)with little or no fines was intercepted from about 48 to 51 feet bgs. The <br /> permeable sand and gravel sequence is underlain by a thin layer of reddish-brown clayey-gravel (GC). <br /> SIERRA-PACIFIC GROUP 3 <br /> t <br />