ARCHIVED REPORTS_XR0002565 - Laserfiche WebLink

Home Browse Search

• ASSOCIATES I NC . iThe highest concentrations are present at approximately 15 feet bgs. The estimated lateral extent of soil impacted by petroleum hydrocarbons is shown on Figure 3. Cross sections showing the extent of vertical contamination was created and the location of the cross sections are shown on Figure 4. The cross sections are shown on Figures 5 and 6. ' Utilizing the most recent analytical data from Table 1, ATC performed mass balance calculations to determine the estimated soluble mass of soil contamination remaining in soil. The total soluble mass of TPH and BTEX remaining in soil is approximately 233.2 kg and 32.5 kg, respectively. ' Mass balance calculations are included in Appendix E. ' 4.2 Groundwater Conditions Groundwater was not encountered during field subsurface investigation activities. However, based ' on San Joaquin County, Flood Control and Water Conservation District data (Spring 1997 Report) groundwater is estimated to be present at approximately 55 feet bgs. Regional groundwater flow direction has been reported to be easterly (Spring 1997 Report). This groundwater flow direction is consistent with a former ATC project site (1994 to 1996) located approximately 2,000 feet east-southeast of the subject property and a current ATC project located one mile west, which exhibit easterly gradients. ' 5.0 DISCUSSION The following paragraphs summarize the results of the subsurface investigation performed at the project site. The soil analytical data indicates that petroleum hydrocarbon analytes have not impacted the capillary fringe soils or the groundwater in the vicinity of the former USTs. 1. The vadose zone is estimated to be from approximately 0 to 55 feet bgs and generally ' consist of poorly drained soil. This soil consists of clay, silt and some sand deposited during flood stages of major streams; in the delta area including mud, muck, loam and sand. Permeability is slow in the "Jacktone" soil. Available water capacity is moderate. The rate of water intake in irrigated areas is 0.1 inch per hour. Apparent fill material consisting of silty sand (SM) was observed in the upper 10 to 15 feet of soil borings SB1 and SB4. 2. Groundwater is estimated to be present at approximately 55 feet bgs. Regional groundwater flow direction has been reported to be easterly (Spring 1997 Report). This groundwater flow direction is consistent with former and current ATC project sites located in the vicinity. ' w:1943041rcportsklosure.doc 4