2005-09-22_REVISION - M2000016 - Laserfiche WebLink

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Mr. Gregg Squire TETRA TECH RMC September 20, 2005 Page 2 Platte River only" was added to the discharge locations that are not located adjacent to the South Platte River. 2. Affected area has not been identified on the new Mine Plan maps. Please revise the maps to identify the affected area, per Rule 6.4.3(d). Please insure that all disturbances, including topsoil/overburden piles, are within the affected area boundaries. As noted in the prior adequacy review, "Since much of tlae site is located within the 100 year flood plain of the South Platte River and a flood analysis and flood control plan have not been submitted, the mining operation must remain a nzinimun: of 400 feet from the top of the riverbank. Both the Exhibit C -Mining Plan maps and the Exhibit F-Reclamation Plan maps must be amended to show the disturbance/affected area and `mining limits' boundaries a minimum of 400 feet from the top of the bank of the river. " This means that all topsoil/overburden piles must be at least 400 feet from the top of the bank of the river as well. Please revise the maps accordingly. The affected area boundary has been added to the Exhibit C plans. In addition, Note 10 has been amended to read, "Per Stipulation 1, prior to mining within 400' of the Platte River, Lafarge will submit a Bank Stabilization Plan; Flood Analysis; and Flood Control Plan to the DMG for approval. Mining within 400' of the South Platte River will not occur until the DMG has approved a Bank Stabilization Plan; Flood Analysis; and Flood Control Plan. Finally, a hatch pattern has been added to the plans to identify the area between the 200' and 400' offsets from the South Platte River. In the legend this hatch pattern represents areas where no mining will occur without DMG approval of a South Platte River Bank Stabilization Study. 3. Several topsoil/overburden stockpiles that flank Big Dry Creek and the Lupton Bottom Ditch are within the IOO year flood plain. Since they are near the edge of the flood plain, a full flood analysis may not be necessary to demonstrate they would not adversely impact the floodway in the event of a flood. If data can be provided that indicates the 100-year flood is shallow and low-velocity in these areas, this Wray be suff dent to allow them to be placed as depicted on the Mine Plan maps. Without these data, these piles must be relocated outside the flood plain. The stockpiles that flank Big Dry Creek and the Lupton Bottom Ditch are north of Weld County Road 10. In this area there is a detailed flood study] that includes a delineation of the floodway. The subject stockpiles are not located within the floodway, and therefore would not adversely impact the floodway. 4. As noted in the February 11, 2005 adequacy review as item 6. b), Note 1 on the maps must be removed as the Division cannot approve conceptual or approximate "cell locations and limit. " Any changes to a permit must first be approved by the Division through the Technical Revision or Amendment process. Note 1 on the maps has been removed. ~ FEMA Fooodway map Panel 0802660012, September 28, 1990, Weld County Colorado