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i Alternatives Al, A2, and A3 address removal of the soil source that contributes to the petroleum hydrocarbons detected in the groundwater at this facility Table 7 presents a comparison of the cost, mass removed, and cost per pound of TPH removed for each alternative in the October 2004 CAP and in this Addendum The most effective alternatives are Al, A2, and A3, as shown below Alternative Al A2 A3 ' Excavation Removal of Excavation 5' Into Excavation 14'-17'lnto TPH to 500 mglkg 14'-17' Watertable Laterally to Watertable Laterally out to Into Watertable MW-3 MW-3 Cost $254,500 to$298,500 $151,000 to $183,000 $276,300 to $322,500 Pounds TPH To [9 d) 11,300 lbs TPH(g+d) 10,200 lbs TPH(g,d) 11,600 Ibs TPH(g.dp Be Removed Cost per Pound of $22 4011b to $26 3011b $14 8011b to $18 00/1b $23 7011b to $27 7011b TPH(G-D) Removed TPH(g,d) TPH(g+d) TPH(g«d) Alternative A2 --Removal of soil at the soil/ground water interface and in the top 5 feet of the water table-- is the most cost-effective solution as the costs of shoring are avoided and the hydrocarbon mass removed is comparable to those alternatives with shoring The removal efficiency of Alternative A2 addresses the free product and petroleum material at the soil/water interface and contamination in the five feet of the water table Alternative A2 removes the mass reasonably accessible and provides the same remedial action time as the more expensive CAP ' Options, such as Alternatives 3, 4 and 5 The addition of calcium peroxide will provide an oxygen source to enhance degradation of the residual Alternative A2 is the most cost-effective with regard to cost per pound of TPH removed because Alternative A2 removes 87% of the TPH associated with Alternative Al or A3 at a much lower cost The driving factor in the cost difference between these options is primarily related to shoring costs Based upon this analysis, Alternative A2 is the recommend remedial action 20 R 1C0NTGRANIstock1onlCAKCAP ADDENDUM