ARCHIVED REPORTS XR0008697 - Laserfiche WebLink

Home Browse Search

a July 6, 2001 Page 2 The piping was removed and soil samples were collected at the direction of Mr Michael Infurna of SJCPHS/EHD Additional excavation and sampling was completed on April 15, 1999 to remove the unidentified piping discovered on April 8, 1999 Over-excavation in the southern portion of the site was terminated to protect the structural integrity of the station canopy supports Following removal of the former station canopy, canopy footings and kiosk, additional over- excavation was completed on June 1 and 2, 1999 An additional 960 tons of soil were removed to a maximum depth of 31 feet bgs Over-excavation was terminated when the structural integrity of the sidewalk was endangered and groundwater was encountered Groundwater was encountered during additional over-excavation activities at a depth of approximately 31 feet bgs One water grab sample was collected from the excavation The grab water sample contained elevated TPH-g and BTEX concentrations Four groundwater monitoring wells (MW-1 through MW-4) were installed on December 9 and 10, 1999 at the locations shown on Figure 2 The wells were screened from 5 feet above to 15 feet below the current water level Initial depth to water in MW-1 was 36 feet, therefore, the well was set at 50 feet bgs Groundwater rose to approximately 30 feet bgs after well completion Groundwater sampling events identified low intermittent concentrations of benzene and MtBE Four Geoprobe borings (GP-1 through GP-4) were completed on July 20 and 21, 2000 at the locations shown on Figure 2 The borings encountered petroleum hydrocarbon impacted soil as well as groundwater at depths of approximately 50 to 60 feet bgs Following this investigation IT recommended onsite soil sampling below 60 feet bgs for vertical delineation and installation of deeper level monitoring wells for assessment of groundwater impacts Three on-site groundwater monitoring wells were installed in November 2000 to depths of 80 feet bgs to delineate the vertical extent of groundwater impacts These deep monitonng wells were sampled in January 2001 and in April 2001 as part of the quarterly groundwater monitoring program Samples collected from wells MW-5 and MW-6 contained dissolved TPH-g and BTEX during both sampling events, the sample collected from MW-7 did not contain detectable petroleum hydrocarbons in the April 2001 event Geologic cross-section A-A', located in Attachment A, depicts subsurface conditions identified in the November 2000 well installation program PROPOSED SCOPE OF WORK This assessment is proposed to further define the extent of deep groundwater impacts at 80 feet bgs The scope of work proposed for this investigation will include the installation of three monitoring wells Proposed monitoring well locations are based upon data collected in previous investigations, an east to southeast groundwater gradient, and the results of the two prior sampling events of the deep monitoring wells ffCOAMMn+on ti SAC IN 1sacDP120011PRAPJ81828800 laa doc-0011t 1 Rev 0, 07/06/01 (01000000) ° I