ARCHIVED REPORTS_XR0006155 - Laserfiche WebLink

Home Browse Search

Closure Report -Chevron Station#9-1848 January 18, 1999 depth of 24 feet bgs Eight soil samples were submitted for analyses Petroleum hydrocarbons were not detected in any of the eight soli samples analyzed Four grab groundwater samples were collected from the soil borings and submitted for analysts Petroleum hydrocarbons were not detected in any of these samples Data from this investigation are presented in GR's Limited Subsurface Investigation Report, dated October 28, 1997 Soil chemical analytical data are presented in Appendix A-3, and soil boring locations are shown on Figure 3 Quarterly Monitoring and Sampling Quarterly monitoring and sampling began in July, 1991 Historical groundwater monitoring and chemical analytical data are summarized in Appendix B Available historical potentiometric maps are included in Appendix C Since the installation of wells C-1 through C-3, TPHg has been detected in wells C-1 and C-2 at concentrations ranging between 58 and 5,300 ppb Benzene has also been detected in the groundwater samples from wells C-1 and C-2 ranging in concentrations from 0 62 to 100 ppb • Low concentrations of methyl tert-butyl ether (MTBE) have also been detected in well C-1 ranging between 3 9 and 7 8 ppb MTBE has also been detected in well C-2 over the last ten sampling events ranging in concentrations between 52 and 2,100 ppb The highest concentration of MTBE confirmed by GC/MS analysis has been 650 ppb in well C-2 TPHg and benzene concentrations have been detected only sporadically in groundwater samples from well C-3 since July 1991 MTBE has never been detected in well C-3 During the most recent monitoring and sampling event (August 10, 1998), depth to groundwater was measured between 11 62 and 12 40 feet below top of the well casing Groundwater flow was to the northeast at a gradient of 0 002 ft/ft Previous quarter data indicates a variable groundwater flow direction at gradients between 0 0007 to 0 01 ft/ft RATIONALE FOR CLOSURE All former gasoline USTs, hydraulic lifts, hydraulic fluid tanks, grease traps, waste-olI tank and remote fill lines have been removed or replaced Concentrations of TPHg and benzene remain in the soil only in the vicinity of the former gasoline UST pit, the associated product Iines, and the present gasoline UST pit Two soil samples analyzed from the well borings contained minor concentrations of TPHg and benzene The soil sample collected from well boring C-1 at 19 5 feet bgs contained TPHg(2 0 346392 M-0 3