WORK PLANS - Laserfiche WebLink

Home Browse Search

Site Assessment Report, Site Conceptual Model,and Site Investigation Work Plan R& L Diesel Services, 2417 West Lane, Stockton, California, 95205 2.0 SITE CONCEPTUAL MODEL 2.1 Source Area Evaluation Site investigation work conducted by R & L and Environeering, Inc. indicates the primary source area is the underground waste oil storage tank which was abandoned in place in 1988. Site investigation work consisted of one soil sample from under the UST taken in February 2007 and two vertical borings and two slant borings in the soil surrounding and under the former UST advanced in March 2008. Total Petroleum Hydrocarbons, as Diesel (TPH-D) were detected in all borings with a maximum concentration of 7,810 milligrams per kilogram (mg/kg) in 61 at 14 feet bgs and a minimum concentration of 399 mg/kg in B1 at 24 feet bgs. The highest concentrations of benzene, 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 depths of 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 mg/kg at 29 feet bgs in B2 and 4580 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 (62). 2.2 Fate and Transport Analysis 2.2.1 Geology According to the USDA Soil Conservation Service 1951 Soil 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 R & L location the soil is 85% Stockton silty clay loam, 4% Archerdale, 4% Cogna, 3% Hollenbeck and 4% Hardpan and fines. The soil is typically 12 to 60 inches deep, and a typical profile for the area is silty clay loam to 12 inches bgs, clay to 34 inches bgs, clay loam to 47 inches bgs, and cemented silty clay loams to 60 inches bgs. According to the Department of Water Resources' Bulletin 118, Groundwater Basin Number: 5- 22.01, the Eastern San Joaquin Subbasin aquifer system geology consists of Holocene alluvium and the Pleistocene Modesto and Riverbank formations topping the stratigraphy, both Quaternary deposits. The alluvium is a collection of unconsolidated gravel and sand in the fan areas, while the interfan areas are primarily composed of silt, sand, and clay. The Modesto and Riverbank Formations are predominantly poorly consolidated gravel with sand and silt. The thickness of these undifferentiated formations ranges to 150 feet. These deposits are moderate to highly permeable.