ARCHIVED REPORTS_XR0004476 - Laserfiche WebLink

Home Browse Search

t20023 d Quarter Groundwater Report Frontier Transportation ' 1102-194 November 26, 2002 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 fsamples were subsequently collected and results are tabulated in Table I ' 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 µg/kg as BTEX, and 10,600 µg/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 l 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 milk', 115,000 pg/kg, and 25,000 pg/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 t 3.0) SITE GEOLOGY/HYDROGEOLOGY The site is located on the boundaryof the Sacramento Valle and the San Joaquin Valle Y q Y 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 gravel, sand, silt, and clay (Reference, Site Characterization Report, Twining Laboratories, October 16, 1996) BEII encountered predominantly clays witli traces of interbedded sands from 0' to 25' bg during well advancement in January of 1998 1 - 1 First subsurface water was encountered at depths from l F to 12' bg during tank removal and monitoring well installation at this 'site in 1995 and 1996 Since then, shallow subsurface water has been encountered beneath the site between 6' and 10' bg Data collected in October of 2002 identified the flow of groundwater in a generally western direction beneath the site (See