SITE HISTORY - Laserfiche WebLink

Home Browse Search

Tree WKW10 A LANGAN COMPANY i Request for Low-Threat Case Closure 6 June 2013 RWQCB case Pae 79 #391199 and#391162 420 and 423 N Madison Street Stockton,California Project 731589001 li Potential exposure pathways for groundwater include direct contact, ingestion, and inhalation. These pathways are not complete because dissolved petroleum hydrocarbons are estimated to extend approximately 140 feet downgradient, the nearest surface water body is upgradient and 350 to 400 feet away from the Sites, drinking water wells are greater than 2,000 feet away from the Sites and screened in deep aquifers over 200 feet bgs,•and the depth to groundwater., 16 to 18 feet bgs, is deeper than potential future construction trench work. Potential exposure pathways for vapor intrusion to indoor air from soil or groundwater exist for benzene, TPHg, and TPHd. This pathway appears to be complete at 423 N Madison for TPHg only, because benzene has not been detected in groundwater or soil. At Carando, benzene has been detected in groundwater, but not in soil. The pathway for benzene and TPHg vapor intrusion from groundwater to indoor air at Carando is potentially complete, though the exposure risk for vapor intrusion to indoor air is low because: • The residual concentrations of benzene (likely less than 46 pg/L due to biodegradation) in source area groundwater are an order of magnitude below the most recent Environmental Screening Level(ESL)for evaluation of potential vapor intrusion for commercial land use and fine to coarse subsurface soil type, 270 pg/L(RWQCB, 2013); • The source area is not beneath, or close to existing buildings; • Residual.concentrations of benzene in groundwater downgradient of the source area, and north of West Fremont Street, are estimated to be approximately 1 pg/L, which is two orders of magnitude below the ESL and would not be a concern for potential future trench workers; and. • The Site meets the LTCP criteria for vapor intrusion to indoor air exposure. The exposure risk for vapor intrusion to indoor air at 423 N Madison is low because: i • The source area is not beneath, or close to existing.buildings; and i i The Site meets the LTCP criteria for vapor intrusion to indoor air exposure. MASS REMAINING IN SOIL The mass of TPH remainingin soil at each site was estimated using soil sample results from 2004 and 9 P 2005. The TP•H mass in soil was calculated using the following equation: Hydrocarbon Mass (lbs) :Soil Volume (f t3) x Bulk Density (lbs Ift31 X Average Concentration (mg1kg) X (10-6kg/mg) i 4