2004-08-02_REVISION - M2000158 (3)

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ENVIRONMENT, IN G. nuousr z, zooa PARE 5 As we explained in the original permit review, gravel mines located in the floodplain of the South Platte River have had little impact on the floodplain's ability to carry floodwater. Under the this amendment the amount of gravel stored at any one time will have a very small footprint in comparison to the amount of hole created by mining of the two reservoirs. While there may be a large amount of gravel stockpiled in the flood- plain only that portion of the stockpile that would displace flood water needs to be accounted for. Below is the calculation for Longhorn Lake that will show there will be no increase flooding impacts. We will assume that the reservoir is full, leaving 18 inches of freeboard as this would be the worst case scenario. The hole between the natural ground level and the proposed maximum lake elevations on Longhorn Lake (approximately 113.39 ac., 1.5 feet deep) could absorb approximately 170.09 ac-ft (5,878,137 cu-ft) of flood waters that would enter the mine. Then if we assume that all of the material removed from the Lake area is still stockpiled on Bluff Lake (85 acres, average floodwater depth is 1.4 feet; flood elevation 4750 feet, average Bluff Lake ground elevation 4748.6 feet) then the stockpiles have a 119.0 ac-ft (5,183,640 cu-ft) foot print in the floodplain leaving a difference in our favor of 51 ac-ft. The property would actually retain more water than it does now, and will reduce the impact a regional flood would have on surrounding land. Once Sharkey's Lake is done the land will retain more since the reservoir area will increase but the stockpile footprint will not. Rule 6.4.12 Exhibit L -Reclamation Costs 10. So noted, let me know if there is anything I can do to help. Rule 6.4.19 Exhibit S -Permanent Man-Made Structures. 11. We maintain that the new wells were installed by the oiI companies with full knowledge that the gravel would be mined around them. This placed the wells within 200 feet of the mined area and Platte Sand & Gravel LLC should not have to worry about disturbing them now. It is apparent that they has no worry about our mining activities affecting the wells and gaslines since they were placed in the area the Board have approved for mining. It they had a concern then the wells would have been placed outside our mining envelopes that were clearly marked on the maps. We have a surface use agreement with Kerr-McGee the owners of the new wells that covers mining adjacent to the wells and pipelines. As for existing gasline we submitted a plan for mining within 200 feet of the structures that was satisfactory. However now that a slurry wall will be placed around the excavated area and a reservoir will be constructed we can reduce the setback needed to protect the lines. Within the reservoir area the mined slope will be worked 3:1 leaving a stable slope next to and within the setback.