2003-06-10_REVISION - M1977342 - Laserfiche WebLink

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As a further check on the sufficiency of the cover soil volume proposal for tree island construction, DMG has examined aerial photographs of the impoundment area taken prior to and during the construction of the tailing dam. These photos show that the tailing basin had several distinct stands of trees surrounded by large areas of treeless open meadow. This pre-mining condition supports the use of tree islands for reclamation. The pre-mining treed areas show sparse to moderate stands over approximately 41 percent of the tailing basin (see enclosed photo). This is substantially more tree coverage than the 46 acres of tree islands under consideration through the amendment AM-004 application. However, Henderson's commitment to plant trees and shrubs on all other affected land in accordance with the plan in the original permit, even though the historic aerial photos show patchy tree cover in a number of the areas subsequently affected by Henderson, tends to counterbalance the diminished tree cover proposed for the tailing impoundment. Also, the additional cost to be incurred by Henderson bringing in the additional soil to construct the tree islands will assure that viable tree cover will succeed on the tailing, whereas research and direct experience over the past 30-years (since the original reclamation plan was conceived) shows that without the additional soil cover, tree plantings on the tailing would have little chance of success. In this regard, the tree island plan is an upgrade from the previously approved plan. Although fewer trees will be planted under the tree island plan, more trees will survive and grow to maturity than if the originally approved plan were implemented. The following revised and new cost estimating spreadsheets were generated relative to the revised reclamation plan for the tailing impoundment. The new spreadsheets are enclosed. Task 09e: The schedule for topsoil salvage from the tailing basin is such that there will be a deficit of soil in stockpile at the Henderson Mill that will diminish year by year as additional soil is salvaged and as the inundated area increases in size. In order to meet the permit requirement to spread 6-18 inches of soil over the tailing at the time of reclamation, soil must be bonowed from the tailing impoundment perimeter once the stockpiled soil is exhausted. The spreadsheet for task 09e as completed on 5-21-02 estimated the cost to borrow 875,467 cubic yards of soil from a 181 acre pit. For creation of the tree islands, an additional 166,667 cubic yards of borrow soil will be required (total of 1,042,134 cubic yards) and the borrow pit must be enlarged to 227 acres. The estimated cost for task 09e dropped from $1,343,054 to $1,333,125 even though the volume of soil to be borrowed and spread was increased for the more recent estimate. The reason for the drop is that labor and operating costs for earthmoving decreased substantially during the period of time between the two estimates. Task 09f: A new cost was estimated for finish grading of the soil borrow pit considering the increase in size from 181 acres to 227 acres to provide the additional soil needed to construct the tree islands. The estimated cost for this task went from $16,216 to $ 18,871. Task 09i: A new tree and shrub planting cost was estimated for the tailing impoundment considering the limitation to planting only on the tree islands and the increased size of the soil borrow pit requiring tree and shrub planting. The estimated cost for this task went from $1,822,685 to $489,348.