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Appendix C b the • Y boundaries of HAS, HA-9, the utility pole, and MW-3 The overburden area to removed and stockpiled for return to the excavation is estimated as 672 cubic yards—the same as in Alternative A2, however, in this alternative, shoring is included to a depth of 28 would cast between $85,000 and $95,000 Appendix C provides detailed information regarding this alternative Dewateringat a rate of IS gpm is included and the extracted water would be treated with carbon Prior to discharge to the City of Stockton sewer system Permits would be applied for this temporary discharge during excavation activities Costs for dewaterin are co other two alternatives and are between$21,800 and $37,500 g nsistent with the tThe soil removed (approximately 951 cubic yards) would be disposed of at a it This option includes the addition off 11 material equivalent to then volume taken off site d landfill An additional impediment to excavation is the 14 R by 20 ft concrete ated to be 6 in thickness that is partially over the excavation area Half of this pad w will ha�vetto 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 pole 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 poll is estimated to be between $2,000 and $2,500 Soil sampling, project oversight, and removal of monitoring wells are all additional activities included in the cost estimate The shoring cost of$85,000 to $95,000 is a large component of the total cost estimated at $276,000 to $322,000 depending upon the volume of soil and water removed The total mass of hydrocarbon'removed is estimated at 11,600 pounds of TPHd and TPHg This is slightly more than Alternative At and the costs are also higher by approximateI two percent Cost Per pound of TPH removed for this alternative is estimated to be between $23 73 and $27 70 Alternative A2 removes the soil source that has co m theributed soilcium peroxide will also enhathe nce The appearance of free is stable duct and addresses the area of highest TPH concentrations continue to slowly degrade over time and the addition of the calan ncle the degradation process The time to achieve compliance cannot be differentiated between these alternatives as all three are removing approximately 25 per cent of the total estimated mass of hydrocarbons This represents a conservative estimate as the dewatenng process will also remove some of the hydrocarbon mass present in the groundwater 6• SIJMMARi'AND RECOMMENDATIONS Residual petroleum hydrocarbons measured as TPHd and TPHg in shallow groundwater in con- tact with the limited residual petroleum in soil will likely remain above WQOs in a localized area for a long period of time Removing the source of free product can be accomplished cost effectively by selecting Alternative A2 and donducting activities at the low water tables in August/September 2005 R ICONTGRAMSIOCUOIACAKCAP ADDENDUM 19