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j As summarized in Table 5, the average concentration of TPH-as-gasoline in the upper cylinder would be calculated asfollo�ws: i Cd b, TPHg.average I_,(560+4.5+0)/3 Sample's = 188.2 ppm i ij Using the same assumptions described above, the mass of TPH-as-gasoline remaining } in soil following one year of SVE is as follows: TPHg mass= (25.132)ft3-sGRj(11.0 fb-seit)(188.2 Ib TPHg) w= 520 Ib TPH-as-gasoline s (ft sell) (106 Ib sea!) These mass.balance calculations indicate that SVE removed approximately 8,251 pounds of TPH=as-gasoline and all of the 28.9 pounds of benzene. This represents approximately 94% of the TPH-as-gasoline and 100% of the Benzene present prior to SVE ,: G Petroleum H drocarbon Mass Remainin in Groundwater.:. The remaining mass of MTBE in-groundwater is calculated using the flowing T assumptions: . Dissolved concentrations of MTBE are contained within an area estimated by a circle with a 60-foot radius centered on well MW-5; • The vertical extent of impacted groundwater extends from the groundwater surface at a depth of approximately 45 feet bgs to the groundwater-bearing sandy interval at a depth of approximately 75 feet bgs,k ' • 100% saturation throughout the 30-foot impacted interval * The calculated average'concentration of MTBE is uniformly distributed J,� . throughout the impacted volume of groundwater C • Average porosity of 0.35 .' • Unit weight of water of 62A poundslcubic foot • 1 µg11 (part per billion) = 1 pound MTBE/1 billion pounds of water I The average concentration of MTBE is calculated as follows using the groundwater' C analytical results from the fourth qudrter of 2005, and is the average of the five wells with concentrations above the reporting limit: MTBE average=(52.1+15.5+1.1:0+9.2+2.2)I5 = 18.0:µg11 Q