ARCHIVED REPORTS_XR0004473 - Laserfiche WebLink

Home Browse Search

' Site Conceptual Model . Frontier Transportation June 30, 2003 ' Page 6 Dissolved TPH-m concentrations have remained non-detect at the site since September 2000, ' when the well cover was repaired BEH, therefore, has discontinued groundwater sample analysis for TPH-m at the site ' Laboratory analysis identified dissolved TPH-d in monitoring well MW-3 at a maximum concentration of 33,000 µg/L in January 2000, however it was reported as TPH-d and TPH-mr-- ' combined Since then, dissolved TPH-d concentrations in MW-3 have attenuated to non-detect in April, August, and November of 2001 -Groundwater analysis results from April 2002 identified dissolved TPH-d exclusively from MW-3 as 14,200 µg/L,The groundwater level in ' MW-3 dropped to its lowest recorded depth (10 72' bg) in April 2002 Monitoring well MW-3 was abandoned in May 2002 Replacement well MW-3R identified no detectable concentrations of dissolved TPH-d -No other detectable concentrations of dissolved TPH-d were identified from ' laboratory analysis in any of the wells, including MW-11 located in the former diesel UST excavation pit Groundwater analysis for TPH-d will continue to be performed at the site f ' Historical groundwater monitoring results have identified TPH-g concentrations above 1,000 µg/L in MW-1, MW-3, and MW-3R exclusively Maximum dissolved TPH-g concentrations were identified in March 1998 as 42,000 µg/l, in MW-3,which was the ' shallowest recorded groundwater depth in that well Since then, dissolved TPH-g concentrations have attenuated to a low of 100 µg/L"The last groundwater sample collected from MW-3 prior to abandonment detected dissolved TPH-g as 9,750 pg/L Monitoring well MW-3R identified a ' maximum dissolved TPH-g concentration of 3,790 µg/L in October 2002 Dissolved TPH-g concentrations in MW-1 have attenuated from 1,800 µg/L in August 1996 to <50 µg/L since ' January 2000 and has remained <50 gg/L -- Dissolved TPH-g over time was graphed for those wells (MW-1, MW-2, MW-3, MW- 3R, and MW-13) that demonstrate significant trends in contaminant concentrations Graphs of dissolved TPH-g concentrations over time are in Appendix E /An exponential regression line (black) is graphed in each figure to represent the reduction rate in each well, which is a first order reaction The exponential regression line was generated using Microsoft Excel using the equation y= ceh", where c and b are cons t� and ee is the base of the natural logarithm Low level dissolved TPH-g concentrations ( ��`V, 'were identified in monitoring wells MW-2 d uq-3 and MW-13, which have attenuated to <50 µig/L Based on the regression line, all five monitoringwells identified an overall attenuation of dissolved TPH- concentration Ail other g ' monitoring wells identified no detectable concentrations of dissolved TPH-g since December 1998 Laboratory analysis indicates that historically the dissolved TPH-g plume has been contained within the site boundaries Please see Appendix E for estimated plume extent using ' the maximum dissolved TPH-g concentrations from all sampling episodes