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- Remedial Action Plan Frontier Transportation June 17, 2004 Page 7 uN kk ll Extent of Impacted Soil (worst case)= 180 feet x 105 feet x 26 _feet thick (9 to 35' bgs)/27 C J /� � ft' = 18,600 yds' Extent of Excavated Impacted Soil (May 2002) = 30 feet x 30 feet x 5 feet thick/27 ft 3 ° = ' 170 yds' Extent of Impacted Deep Soil Left in Place = 18,200 yds' to 5,600_yds' - 170 yds3 = 18,030 yds' to 5,430 yds' Based on the soil sample results, it is estimated that 18,030 yd3 to 5 ,430 yds' of - - MTBE impacted soil remains in place (See Figure 6 for extent of impacted soil). The impacted soil exists primarily in heterogeneous clays and within the saturated zone. 1 Heterogeneous clays and saturated soil are the main factors limiting the effectiveness of - soil vapor extraction. Excavation would be the most effective remedial action based on site subsurface conditions. 5.0) IMPACTED GROUNDWATER Historical groundwater data has identified dissolved TPH-m in monitoring well MW-3 . Maximum concentrations of dissolved TPH-m were identified in MW-3 as 33 ,000 µg/l, in January 2000 using EPA method 8015 modified. In January 2000, the Jwell cover for MW-3 was observed as damaged and allowing oily surface water to infiltrate the well. BEII concludes that the damaged well cover caused the increase in TPH-m in MW-3 from November 1999 to May 2000. Dissolved TPH-m concentrations have remained non-detect at the site since September 2000, when the well cover was PIeS repaired. BEII, therefore, has discontinued groundwater sample analysis for TPH-m atye� 5 - the site. kyt,r � ,! Cdi v► 7n f�ry Laboratory analysis identified dissolved TPH-d in monitoring well MW-3 at a { tom 0 1 -' maximum concentration of 33 ,000 µg/L in January 2000, however it was reported as TPH-d and TPH-m 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 from MW-3 as 14,200 µg/L. The groundwater level in MW-3 dropped to its lowest recorded depth ( 10.72' bgs) in April 2002. Monitoring well MW-3 was abandoned in May 2002. Replacement well l MW-3R identified no detectable concentrations of dissolved TPH-d. No other detectable -I 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. Historical groundwater monitoring results have identified TPH-g concentrations iabove 1,000 µg/L in the area described by MW- 1 , MW-3 , and MW-3R. 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. Dissolved TPH-g '� J