2002-03-13_REVISION - M1988044 - Laserfiche WebLink

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appear to be close to those maxima. Further examination of that will be done later when fully reclaimed land is examined for a release request. In reclaiming such a mining pit as those produced in the upland area, a double ended approach is used. If the pit bottom is in excess of 25 feet below the original surface then backfilling is done to bring the pit bottom up to very neaz that elevation. However, the backfilling does not address the pit side slopes and highwalls. Those aze then reduced by cut and fill. In essence, a dozer is used to cut the top of the slope or wall and push that material into the pit followed by blending of the bottom of the slope with the more level pit bottom. Where drainages extend through the mining area, the grading modifies the reclamation topography to allow a reconnection of the drainage. Although this approach tends to create a slightly lazger disturbance than was originally there, it has the advantage of creating a more stable top of the slope out of native material rather than creating the entire slope out of fill. This approach tends to reduce the amount of erosion that might occur before the vegetation becomes fully developed. The final step in this process is spreading topsoil over the graded land. Because the amount of soil salvaged is sometimes greater than the amount that needs to be replaced, sometimes more soil is replaced than the six inch requirement. Although exact measurements of the volume of material in the various overburden and topsoil stockpiles were not done, due to the extreme difficulty of making such measurements accurately, estimates were made based on the estimated average height of the stockpile and the amount of land the stockpile covers. The values on the maps appear to indicate high precision, which is not the case. The values shown on the maps are the values derived from the estimation process and were not rounded. Such an approach often underestimates the volume by a considerable amount, but the amount of error lazgely depends on the precise geometry of the pile. Piles that have a more regular geometry generate more accurate estimates than piles that are basically windrow piles with considerable irregularity. A cross-check can be obtained by determining how much soil should be stockpiled based on the area from which topsoil should have been removed. Unfortunately, that approach also generates considerable error because a considerable amount of soil can be contained in very small piles surrounding such features as water storage and settling ponds and other minor disturbances. Soil from these areas are often not placed in the large general stockpiles because such small disturbances are often more easily reclaimed by simply pushing the adjacent berm material back over the shallow excavation. On this site a fine example is the freshwater pond excavation (Area M1). This pit was not excavated for sand, but rather to store cleaner water. The material removed from the pit, which is mostly soil with some overburden-like material, surrounds the pit on all sides except the north. To move, stockpile elsewhere, and then replace the material would greatly increase the cost of reclaiming the 0.58 acre disturbance (including the stockpiles). It is better to simply leave it as a berm around the excavation and then push it all back into the hole when the disturbance is reclaimed. The amount of soil and overburden removed is considerable but is not accounted for in the inventory of overburden and topsoil. In effect, the inventory only includes the well distinguished stockpiles and not the minor stockpiles. It is estimated that about 63,000 cubic yards (actual estimate is 62,996 cu yds) of overburden is in the major stockpiles. In addition there is about 40,000 cubic yazds (actual estimate is 39,701 cu yds) of soil. The two primary mining pits (Areas MS and M6) potentially need to be reclaimed with the backfill- slope cutting-topsoiling process. However, azea MS has a maximum depth of about 7 feet and therefore does not actually need to be backfilled. Area M6 has a maximum depth of about 25 feet, but averages about 16 feet. Therefore, Area M6 would not require more than minimal backfilling, if any at all. After estimating the volume of each of the two pits that might be backfilled, but actually don't need to be, it was determined that Area M6 could be reduced to a depth of about 9 or 10 feet below the original land surface. This is less than half of the required maximum. To topsoil all of the disturbed area, assuming only the measured topsoil stockpiles were used and all of every identified disturbance is actually disturbed, neither of which is an accurate representation, approximately 58,000 cubic yards of soil would be needed. It is estimated that the lazge stockpiles of soil amount to 40,000 cubic yazds. But because not all land within each identified zone would need to be Page 6 of 8