ARCHIVED REPORTS_XR0004485 - Laserfiche WebLink

Home Browse Search

i 2003 4th Quarter Groundwater Deport Frontier Transportation - February 11, 2004 Page 2 through MW-7) to assess the extent of subsurface contamination beneath the site (See Figure 2, Site Layout Map) Soil samples were collected every five feet Laboratory analysis of soil samples identified no detectable concentrations of TPH-g, BTEX, or MTBE Groundwater samples were subsequently collected and results are tabulated in Table 1 In January 2000, BEII advanced two borings (B-5 and B-6), installed four additional groundwater monitoring wells (MW-8 through MW-11), and collected nine soil vapor samples for a soil vapor survey as part of an additional site assessment (See Figure 2, Site Layout Map for well locations) Soil sample analysis identified no detectable concentrations of petroleum ' hydrocarbons with the exception of boring B-6 Maximum contaminant levels in B-6 were identified 100 mg/kg as TPH-g, 2,343 [ig/kg as BTEX, and 10,600 gg/kg as MTBE at 10' bg Maximum soil vapor concentrations were identified at sample point V5 at 4' bg Groundwater ' samples were subsequently collected from all monitoring wells Results are tabulated in Table 1 In May 2002, BEII installed two additional groundwater monitoring wells (MW-12 and ' MW-13) screened from 30' bg to 40' bg Soil sample results identified maximum TPH-g, BTEX, and MTBE concentrations of 700 mg/kg, 115,000 gg/kg, and 25,000 p,g/kg in soil collected from MW-13 at 10' bg Soil concentrations attenuate by 99% at 15' bg No detectable TPH-g, BTEX, and MTBE were identified in MW-12 Also, monitoring well MW-3 was abandoned prior to excavation and removal of 325 tons of impacted soil and replaced by MW- 3R I In June 2003, BEII installed an additional groundwater monitoring well (MW-14) ' screened from 30' bg to 40' bg Soil sample results identified a maximum MTBE concentration of 1,020 gg/kg at 10' bg using EPA Method 8260B No detectable TPH-g and BTEX were identified in MW-14 9�q/y ewauf 0-1 hold, ,-:)+twu. vm 3.0) SITE GEOLOGYfHYDROGEOLOGY 1The site is located on the boundary of the Sacramento Valley and the San Joaquin Valley within the west-central portion of the Great Valley Geomorphic province of California The Great Valley has been filled with a sequence of older to younger alluvium of Pliocene to ' Holocene age which overlay sedimentary rocks of Cretaceous to Tertiary age These sedimentary units, in turn, overlay a crystalline basement of Paleozoic and Mesozoic metamorphic and igneous rocks The shallow subsurface geology in the site vicinity is a heterogeneous mix of 1 gravel, sand, silt, and clay(Reference Site Characterization Report, Twining Laboratories, October 16, 1996) BEII encountered predominantly clays with traces of interbedded sands from 1 0' to 25'bg during well advancement in January of 1998 1 i 1