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CLEARWA.�" TER iEnv,.oRm�n,ar5�.�«es 1 The mass of post-remediation TPHg remaining in the soil can be estimated assuming that the contaminated soil has a cylindrical shape with the height of 15 feet and a radius of 6 feet (Figure 4) using the following equation M(TPHg) _a (r)z (h) p (TPHg avg) where, r= radius = 6 ft h = thickness = 15 ft p = density = assume 100 lbs / W TPHg avg = 220 ppm or 0 00022 unitless (average TPHg concentration at CBI) M(TPHg)_Tc (6 ft)2(15 ft) 100 lbs /ft3 (0 00022) = 37 lbs Residual Mass of TPHg in soil = 37 lbs This calculation indicates that approximately 37 lbs of TPHg remain in the soil following remediation versus the 5,050 lbs which was present prior to remediation This indicates that the SVE/AS system was effective at removing more than 99% of the gasoline from the soil column beneath the site ® In groundwater, pre-remediation levels of TPHg were as high as 150,000 fig/L in MW-2 Separate-phase hydrocarbons were observed as sheen and or droplets in purge water from wells MW-1 and MW-2 on several occasions prior to remediation Post-remediation levels of dissolved-phase contaminants have dropped steadily over time Water samples from all wells except MW-1 and MW-2 have been non- detect for all hydrocarbons for several quarters of sampling Results from the most recent sampling event show that only low levels of dissolved-phase gasoline remain in samples from MW-1 (550 fig/L TPHg), and MW-2 (65 gg/L TPHg) Additionally, recent monitoring results indicate that benzene was only detected in one well, MW-1, at a concentration of 2 6 pg/L MTBE was the only Fuel Oxygenate detected and was only detected in two wells, MW-1 (78 fig/L) and MW-2 (6 3 fig/L) Conclusions and Recommendations At the time of UST removal in 1988, gasoline concentrations soil beneath the USTs were reported to be X10,000 mg/kg Following investigation activities, it was estimated that approximately 5,050 lbs of TPHg resided in the vadose prior to remediation Additionally, SPH had been observed intermittently in the areas of MW-1 and MW-2 Maximum pre-remediation dissolved-phase TPHg, benzene, and MTBE concentrations were 150,000 pg/L, 9,400 pg/L, and 3,800 fig/L, respectively Operation of SVE/AS system from November 1998 to September 1999 resulted in a dramatic reduction of contaminants beneath the site Based on system operation data, it was estimated that 7,377 lbs of TPHg were removed from the subsurface during remedial efforts • ZB107C Conf Borings/GWMR 1Q00 6 March 27, 2000