2009-05-07_REVISION - M2000158 - Laserfiche WebLink

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CIVIL RES`VURCES,LLC ENCINF_f RS & PLANNERS April 16, 2009 Mr. Jared Ebert Division of Reclamation, Mining & Safety 1313 Sherman Street, Room 215 Denver, Colorado 80203 RE: DRMS Permit No. M-2000.158 - Platte Sand & Gravel; Technical Revision 5 - Mining Sequence & Reclaimed Storage Configuration Dear Mr. Ebert: Platte Sand & Gravel, LLC. requests a Technical Revision to Permit M-2000-158 to allow for modification of the mining sequence and reclaimed storage configuration, A site location map is included as Figure 1. This letter describes the proposed modifications to the currently approved plan. Mining Sequence The site is currently permitted for nine lakes with a 69 acre maximum disturbance area at any given time as indicated in Technical Revision No. 4 (TR-4) dated April 3, 2006 (changed from originally 35 acre maximum disturbance area). There is no specific mining sequence for the approved reclamation permit, however the bond basis considers mining in only two lakes (Sharkey's Lake and Longhorn Lake). Portions of Sharkey's Lake have already been mined as shown on Figure 2a. A slurry wall was constructed to control the inflow of groundwater during mining and limit the alluvial groundwater impacts in the area. This Technical Revision proposes that the slurry walls be constructed in advance of mining and that the overburden be removed from within the revised Pond layout footprint as shown on Figure 3. The modified mining sequence is only an operational consideration and will not have additional offsite impacts. Reclaimed Storage Configuration The revised reclaimed storage configuration does not increase the limits of disturbed area currently included in the approved permit as shown on Figure 2b. The proposed overburden embankment is fully contained within the current mine limits with the western limit of the proposed embankment alignment set based on preliminary hydraulic modeling of the floodway limits associated with the South Platte River within the project reach. Modeling results are summarized in Attachment A. The proposed embankment fill is located within the FEMA recognized 100-year floodplain and therefore a formal submittal will be made to request approval of the proposed fill activities and an associated map revision as necessary. Refer to Figure 3 for the proposed reclamation layout. The proposed modification(s) to the reclaimed storage configuration will allow the site to be more economically reclaimed by reducing the net square footage of slurry wall lining required and also by incorporating the overburden into the site reclamation plan. The overburden is deemed non-economic material and therefore is unlikely to be sold offsite thereby requiring the material to be incorporated into on-site reclamation plans. The proposed plan includes using the overburden to construct an embankment around the perimeter of the revised pond configurations. The berming has the added benefit of creating additional above grade water storage capacity. All final design of the above grade storage will be completed per the requirements of the State Engineer's Office, Dam Safety Branch as required by the Rules and Regulations for Dam Safety and Dam Construction. 323 FIFTH STREET • P.O. eax 680 • FREDERICK, 00 80530 • PHONE (303) 833-1 41 6 • FAx (303) 833-2BSO