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� Site Investigation and No Further Action Request Repo T� R&L Diesel Services, Project#051111 gW since 1954 2.0 SITE CONCEPTL AL MODEL 2.1 Source Area Evaluation F{ Site investigation work conducted by R&L and El indicates the primary source area is the properly abandoned waste oil UST. The February007 site investigation consisted of collecting one soil sample from beneath the UST and the March 2008 site investigation Fr consisted of collecting two vertical borings and two angle borings in the soil surrounding and beneath the former UST. FTPH-D was detected in all soil boring samples at a maximum concentration of 7,810 milligrams per kilogram (mg/kg) in B1 at 14 feet bgs an a minimum concentration of 399 mg/kg in B1 at 24 feet bgs. The highest concentrations of berizene, toluene, ethylbenzene, and total xylenes (BTEX)were detected in B1 at 14 feet bgs at concentrations of 2.55 micrograms per kilogram (ug/kg), 200 ug/kg, 97.3 ug/kg, and 407 ug/kg respectively. Total Petroleum Hydrocarbons as Gasoline (TPH-G) was not detected in any of the borings, and no analytes were detected at 44 feet bgs in B1. The chlorinated hydrocarbon (solvent) tetrachloroethylene (PCE)was detected in B1, B3 and B4, with a maximum concentration of 85.5 ug/kg in B1 at 14 feet bgs. The highest concentrations of TPH-D are found at shallower depths in B1 (7,810 mg/kg at 14 feet bgs and only 399 mg/kg by 24 feet bgs) but appear at greater depths in B2 and B3 (1,440 mglkg at 29 feet bgs in B2 and 4,580 mg/kg at 21 feet bgs in B3). The area of greatest impact was four feet north of the former UST (B1) and approximately 8 feet under the projected bottom of the former UST(B2). 2.2 Fate and Transport Analysis 2.2.1 Geology According to the United States Department of Agriculture Soil Conservation Service 1951 So#Survey of San Joaquin County, the soil at the site is the Stockton silty clay loam. This soil is found on basin floors in the Great Basin and Central Valley area at elevations of 20 to 70 feet above mean sea level. At the site the soil is 85% Stockton silty clay loarn, 4% Archerdale, 4% Cogna, 3% Hollenbeck and 4% Hardpan and fines. The soil is typically 12 to 60 inches deep, and a typical M1� profile for the area is silty clay loam to 12 inches bgs, c ay to 34 inches bgs, clay loam to 47 inches bgs, and cemented silty clay loams to 60 inches bgs. F1 According to the Department of Water Resources' (DWR's) Bulletin 118, Groundwater 1 Basin Number: 5-22.01, the Eastern San Joaquin Subbasin aquifers stem geology consists of Y 9 9Y Holocene alluvium and the Pleistocene Modesto and Riverbank formations topping the F! stratigraphy, both Quaternary deposits. The alluvium is a collection of unconsolidated gravel and sand in the fan areas, while the interfan areas are rimarily composed of silt, sand, and clay. The Modesto and Riverbank Formations are prec ominantly poorly consolidated gravel �� 2