WORK PLANS - Laserfiche WebLink

Home Browse Search

(2) Upgradient reported that the release had been stopped and the source(s)of hydrocarbons in the vadose zone had been removed or permanently contained. The UST and dispenser had been removed, and the residual hydrocarbons were restricted to the silt bed that underlies the site to'a depth of more than 25 feet. Silt beds typically have fairly low permeability, and diesel has limited mobility in soil. Hence,the contaminants were effectively contained. (3) Upgradient explained under item 2 above, that it was unlikely that groundwater had been or will ever become impacted because the soil at the site is generally silty and there is at least a 15-foot buffer zone of clean soil between the estimated high groundwater level and the residual soil petroleum hydrocarbon mass. (4) Upgradient also concluded that no significant tisk to human health and safety existed or is anticipated to exist. A sensitive receptor survey was conducted and the nearest potential receptor was identified as ST&E's own well,which is approximately 300 feet from the UST location. The ST&E locomotive shop parcel is several acres in size, and is surrounded on all sides by even larger industrial properties and the ST&E.freight yard. The area is not zoned for residential use. Upgradient concluded that the risk of public exposure is very low.Upgradient therefore concluded that the residual diesel contamination within the UST excavation posed no significant threat to public health. Upgradient(1999)recommended site closure but that request was denied jointly by the California Regional Water Quality Control Board(RWQCB) and PHSEHD. Upgradient subsequently submitted a fate and transport model for hydrocarbon contamination to PHSEHD in 2001 in an attempt to justify closure. The results of this transport model suggested that impact to groundwater at depths of 40 to 45 feet bgs might likely occur within several years of the release(1980's). The data contained in the report actually suggested a groundwater problem likely existed. However,the Upgradient document concluded that actual field conditions were not coincident to modeled conditions. Main5DWnvironmenWA15T61Workplan\Workplan)1192007,wpd 10 I�F