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noted that topsoil salvage must be completed in advance of mining assuming that the pit slopes will slough as depicted in the foregoing illustration so that topsoil is not lost by sloughing into the pit (Rule 3.1.9(1)). The proposed reGamation plan includes recreation as a post mining land use and swimming beaches are spec~cally mentioned. The Operator should be aware of the requirements of Rule 3.1.5(7) that slopes shall be no sleeper than 5h : 1v throughout the area proposed for swimming. The application should designate areas where swimming beaches will be constructed or at least provide a material volume estimate for creating a certain number of acres of 5h : 1 v slopes so that the reclamation cost for the additional backfilling can be incorporated into the bond. The application provides no specifics on topsoil and overburden stockpile configurations and locations. The Division recognizes that the Applicant is making a commitment to concunent reclamation that will minimize the amount of topsoil and overburden that will be stockpiled at any given time. However, since the pit is in the floodplain the Division is concerned with the stability of the topsoil and overburden piles during a flood event. The Applicant should provide additional information on the stockpiles including an estimated maximum volume of topsoil and overburden to be in stockpile at any time during the life of the operation. The Applicant should further commit to stockpiling material away from areas where the deepest and highest velocity flooding can be expected and should align the stockpiles as windrows with the direction of floodwater flaw paths. Review of Flood Insurance Rate Maps (FIRM) for the mine area would be useful in this regard. The application specifies 200 foot setbacks from the existing topof-bank of the South Platte in certain sections of the mine reach, and 300 foot setbacks from the existing centerline of the river in areas where mature trees are growing. It is noted in the memo prepared by Tom Schreiner dated 2I16I01 that there is insufficient information in the application to evaluate the adequacy of these setbacks; the same memo requests that the Applicant provide flood water elevation information. Legible copies of the FIRM through the mine reach would facilitate the Division's review. It was observed during the Division's preoperational inspection of the proposed S 8 H Mine that sections of the riverbank through the mine reach are subject to active erosion and bank cutting. The Applicant is careful to specify that the proposed setbacks are based on the current position of the river. The application indigtes that encroachment of the river on the pit as a result of bank cutting is likely to occur over time. The Division recognizes that the Applicant is not responsible for the cement bank cutting, that stabilization of the riverbank is not the Applicant's responsibility, and that stabilization may even have an adverse effect on the dynamics of the stream system. However, rf the river eventually cuts into the gravel pits, adverse impacts to the riverbanks upstream and downstream may result, impacts that would not occur'rf the pits were not excavated. The Urban Drainage and Flood Control District, which regulates the South Platte River south and west of the S 8 H Mine, has determined that 400 foot setbacks from the topof-bank are adequate to protect the integrity of the river without mitigation required. The Applicant may want to increase the setbacks to 400 feet or provide an analysis of potential flooding impacts and a plan far mitigation as discussed in Tom Schreiner's 2116/01 memo. If flood mitigation plans are to be prepared, they must specifically address the potential for erosion of the lateral berms that will carry gas/oil pipelines during mining and following reGamation. Reference: Urban Drainage and Flood Control District, "Technical Review Guidelines for Gravel Mining Activities," December 1987. c:\vrindows\personaf~,S 8 H Mine.doc • Page 3