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which excavated an area of 1,340 ft2 The total volume of soil removed is 1,254 yd of which 672 yd is clean overburden that can be re-used and 672 yd will be taken off site for disposal ' Costs are similar to Alternative Al for dewatering, treating, and discharging water from the excavation to the City of Stockton sewer system Removal of water in the excavation will allow any floating or dissolved hydrocarbon material to be removed during the excavation process A tcarbon system will be used to treat the water prior to discharge to the City of Stockton Sewers The primary difference is the elimination of shoring due to a shallower depth of excavation, i e 17 feet versus the 28 feet in Alternative Al Additionally, we would propose the addition of calcium peroxide to provide an additional oxygen source for continued degradation of the remaining petroleum residuals The addition of calcium peroxide is estimated to cost $3,400 and will improve degradation rates An additional impediment to excavation is the 14 ft by 20 ft concrete pad, estimated to be 6 in ' thickness that is partially over the excavation area Half of this pad will have to be removed to allow excavation Costs for removing the concrete pad are estimated to be between $1,000 and ' $2,000 The power line and power poll that lay adjacent to the excavation area will also need to be removed for safety purposes The cost of removing the power line and power pole is estimated between $2,000 and $2,500 This option will result in the removal of the soils contributing to the free product historically detected in MW-2 as well as the petroleum concentrations reported in MW-3 and MW-4 Removal of floating hydrocarbons through dewatenng plus removal of soils in the former tank excavation eliminates a source area Expanding the excavation to MW-3 at the soil/groundwater interface removes additional TPH material The use of a petro-trap in MW-2 has shown that the ' residual material is limited and this proposed option will capture both the saturated soils with the highest concentrations and the water containing floating residual The highest TPH concentrations on site occur at a depth of 20 feet near MW-2 Efforts will be made to remove ' these soils using excavation practices without shoring The seasonal water table is lowest in late August and early September and this would provide an extra 1 to 2 feet of depth into the water table for the excavation In addition, the excavation will be managed by phasing the excavation, ' such that the entire area is not open at one time to minimize sloughing into the excavation of adjacent soils ' The costs for this alternative are estimated at $1.47,000 to $180,000 depending upon the quantity of soil removed The TPH mass removed by this option is estimated at 10,200 lbs Although the soil removed is only 74 per cent of what is removed in Alternative Al, the TPH mass removed is ' 93 percent of that alternative Cost per pound of TPH removed for this alternative is estimated to be between $14 82 and $17 96 53 Alternative A3 Extend excavation laterally to MW-3 and vertically extend to a depth of 28 feet Alternative A3 is similar to A2, however, the depth of the excavation is extended to 28 feet to reach the soil concentrations detected in MW-2 The excavation is defined in Figure A3 in ' 18 R 1CaNTCRAN\Stockton\CAP\CAP ADDENDUM