ARCHIVED REPORTS XR0006976 - Laserfiche WebLink

Home Browse Search

i 7.0 SUMMARY AND DISCUSSION 71 Summary ' • The subject site is an undeveloped parcel situated in a primarily industrial area of south Stockton The site was previously used for a heavy equipment maintenance and fueling facility • Subsurface petroleum hydrocarbon impact was discovered in 1986 when a UST failed a tightness test All USTs and fuel delivery equipment were removed from the property between 1987 and 2000 • Soils beneath the site appear to consist of strata of primarily fine-grained material ' interbedded with strata of primarily sandy material These strata appear laterally continuous across the site The current interpretation does not suggest these strata are providing a preferential pathway for the vertical migration of impact ' • Depth to groundwater beneath the site has been measured at depths ranging from approximately 37 feet bgs (1987) to 81 feet bgs (1992), and may have been as low as ' approximately 105 feet bgs in 1979 Groundwater levels are currently measured at approximately 50 feet bgs Originally, groundwater flow was predominantly toward the south and southeast (1990 to 1992) By 1999, flow was toward the northeast ' • The lateral extent of impact in soil beneath the site has been adequately characterized, and appears limited to the immediate vicinity north of the warehouse Impacted soils ' were remediated by excavation and SVE The lack of hydrocarbons in the SVE influent at the time it was shut down, and the very low concentrations reported for samples from confirmation boring B-17, suggest that virtually all the residual vadose zone impact has ' been removed An estimated 13,400 pounds of TPHG has been removed via excavation and SVE ' • Dissolved hydrocarbon concentrations (TPHG, benzene, and MTBE) in wells MW-13 and MW-14 appear to show a generally decreasing trend Benzene and MTBE concentrations in groundwater are currently below laboratory detection limits The ' lateral and vertical extent of this impact appears to be adequately characterized Less than 50 pounds of dissolved TPHG are estimated to remain beneath the site ' • The vertical extent of impact appears to be adequately characterized except in the vicinity of CPT 8 The lateral extent of impact has been adequately characterized except east of CPT-5 and east and southeast of CPT-8 Additional assessment in this area is warranted i • There do not appear to be any complete pathways for exposure to the dissolved hydrocarbons remaining beneath the site i 1 K ITeiche&Slocl i.n 1031Reportslscm 04-2006 doc Page 13 5TKATU5 1