SITE HISTORY - Laserfiche WebLink

Home Browse Search

%Moll' For soil residual TPHD assuming 2707 in&,/kg, (2707 mf* g x 12( 1101' x 3,500 ft')— lb./6.8 gal. = 167 gal, TPHD Due to a calculation error revealed in this review, this, residual TPHI) and TPHG reported in the previous CSRNFAR are revised to the above estimated amounts. Benzene and.MTBE were not detected in the chemical analysiq of any soil sample so there is no Benzene or M.TBE residual soil contaminant. A 2003 reconnaissance groundwater sample at B-3 showed TPHG at 34,000 micrograms per liter (ug/1) and TPHD at 750,000 ug/l. However by August 2009 monitoring Tl1T-IG and TPHD were not detected in any monitoring well. including MW-2 adjacent to the B-3 location.. The TPHG and TP1-ID concentration changes are interpreted as being degraded from natural subsurface biologic degradation processes. However if a calculation estimate used the detection limit of 50 ug/1 in groundwater assuming an aquifer area of roughly 3,500 cubic feet, and an effective porosity of 25%, (50 ug/l x 0.25 x 3,500 W)-- 0.0004 gal. forTPHD and TPHG On that basis the estimate calculation of both TPHG and TPHD is essentially zero gallons. Neither Benzene nor MTBE was detected in any water sample and those residuals are also zero. 2.0 Presence of Chloroform and Dichlorodifluoromethane Wright notes that there was no petroleum fuel contamination in MW-3 for the three sample events. The monitoring,well sample analyses for VOCs have revealed very low levels of Chloroform and Dichlorodifluoromethane in the upgradient and down gradient monitoring wells, The UST contaminants from the Sixth Street source were TPHG and TPHD fuel, The area around Delta Disposal has historically been used for industrial/commercial and railroad use. Since these compounds are detected in the -up gradient and down gradient wells are about the some concentrations, they are interpreted to be from a regional and/or offsite source in groundwater. The highest levels of Chloroform and Dichlorodifluoromethane observed in 2003 are 2.6 and 4.5 ug/1 respectively. The reported concentration of Chloroform is below the current RWQCB Water Quality Goals Maximurn Contaminant Levels (MCLS, 2007 and 2009 revisions) of 80 ug/l. There is no MCL currently listed for Dichlotodifluoromethane. However, a Drinking Water Level of 1,400 ug/I is listed as a USEPA Integrated Risk Information System Reference .Dose, and the Suggested No Adverse Response Level of 1,000 ugil. 3.0 Soil Vapor Potential Risk Evaluation Wright performed the site assessment under EHD approved work plans, and prepared this CSR at the direction of a September 24,2009 EHD request. No soil vapor samples were taken during the work, and the CSR request was made on the basis of the existing investigation and Page 2 of 4