PERMFILE120159 - Laserfiche WebLink

Home Browse Search

• 4.8.1.2 Surface Drainage During Mining The following sedion discusses diversions and culverts which will be used to control runoff during the current permit tens. Since submittal of our original permit document er 1980, Trapper has submitted Technical Revision (TR-25) which altered design criteria for all future diversions and culverts. It has been agreed-to by the CMLRD that Trapper will not be required to after strudun~ which were constructed prior to the partial approval of TR-25 (Johnson and Pyeatt sediment con1ro1) September 5, 1988. Haul Road Culvert Sizino Haul road culvert sizes were determined using the 10-year, 24hour precipdation event predicting ma~d- mumflow rates. These mabmum flow rates and sizes were predicted through hydrobgic modeling tech- niques. The results are presented in Table 4.8-1. Some haul road culverts are placed in undisturbed drainages. Based on the Soil Conservation Service Curve Number Method for quantifying excess rainfall or runoff volumes, the formula shows undisturbed drainages yield no neatf from the approved 10-year, 24hour prectpttation event. In order to maintain proper drainage durug high snowmett or other exceptional events, the culverts in undisturbed areas were sized at eighteen (18) inches diameter. Table 4.8-1 presents the culvert sizing infornetion for existing and future haul road culverts. Table 4.8-1 a lists most non-haul road and au>aliary a,hrerts to ideMiry and quantify adverts within the active mining and reclamation area. Premine culverts installed outside of Trapper's active mining area are not shown in perntt tables or on the M51 maps. • The locations of all required culverts listed in both tables are shown on the Drainage end Sediment Con- trol Map (M-51). Actual future culvert loa3tbns may vary from those sham on Map M51. If so, the pro- axiures described in this sedion will be followed to ensure proper haul road culvert sizing and drainage continuity. Normal mining operations and weather conditions may require addttional culvert installations within pit areas (inctudes associated spoils) to provide environmentally sound aa~ss coridors across drainage poirrLs or to divert runoff to existing dreinageways. Culverts established wihin pit areas (often temporary installations for a short period of time) will not be shown on Tables 4.&1, 4.8-1 a, or M51 map and will not require Division approval prior to installation. Culverts established in these areas will be considered a Best Technology Curtentry Available (BTCA) predice wtth the intent of mrtrim¢ing erosional Impacts to Trapper's surtaaa water hydrology. '4-'ii'S • P~-~I _ __p~A~l~ 1995.._.