Laserfiche WebLink
22 <br />The proposed DWDA #2 storm water management above, around and on the waste <br />pile was evaluated for a 100 year, 24-hour storm event. The results indicate that the <br />management system already in place for the site will safely pass the storm with the <br />recommendation that the berms and ditches are field verified to be constructed as <br />designed. The storm water routing near the DWDA #2 is shown on Figure 2e. The <br />runoff above (North) is diverted through Ditch D-11 through culvert C-30, ditch D-1, <br />culvert C-26, and ditch D-32 to the river. This is shown in Figure 2e. Exhibit 39 <br />Sediment Design Specification- Development Waste Disposal Area demonstrates that <br />the existing ditches are appropriately sized to carry the storm water above the <br />DWDA #2. <br />The DWDA #2 runoff is routed through a small catchment into culvert C-13 and to <br />pond 007. The engineering evaluation of the DWDA #2 is included as Exhibit 39 <br />Sediment Design Specification- Development Waste Disposal Area. As part of TR - <br />60 the DWDA #2 was expanded to the west in order to gain more storage area for <br />development waste. The drainage area evaluated for TR -60 is 5.1 acres and includes <br />the DWDA #2, and a small portion of the haul road north of the pile that will flow <br />into Ditch D-12. The 100 years, 24-hour storm precipitation is 4.2 inches. SedCad <br />calculates the peak flow to be 15.58 cfs with 1.47 acre-feet of total runoff. The <br />required ditch size to convey that flow is a trapezoidal channel of bottom width 3.0 <br />ft, height of 1.5 ft, side slopes of 1:1 and a minimum slope of 1%. Existing ditches <br />are of this recommended size and shape. The minimum pipe diameter needed to <br />convey the 100 -year, 24-hour peak flow to pond 007 is 24 inches. The existing <br />culvert is 24 inches. The pipe installation should have a minimum of 1.2 feet of <br />material from the top of the pipe to the top of the bank (i.e. the lowest point on any <br />top of berm/top of bank around the DWDA #2 shall be no less than 1.2 feet above the <br />top of the 24 inch outlet pipe. <br />A small area exemption has been established for a material storage area and <br />associated activities located south of sediment pond 7 due to its location outside of an <br />area where runoff will be routed to a sediment pond. Berms and a silt fence provide <br />alternative sedimentation control for this area. The design of the silt fence is included <br />Exhibit 19(17). This SAE area is shown on Map 11 Sheets 1, 2 and 3. <br />The cut slopes above the upper diversion ditch at the Bates Portal fall under Rule <br />4.05.2(4), which states in part; for the purposes of 4.05.2, "disturbed area" shall not <br />include those areas in which only diversion ditches sedimentation ponds, other <br />treatment facilities, or roads are installed in accordance with the performance <br />standard requirements of this Rule. The cut slopes will be covered with a straw <br />blanket and seeded since there is concern the slopes may contribute suspended solids <br />to stream flow or runoff outside the permit area. The straw blanket will be <br />maintained until vegetation is established. <br />An erosion estimate was done for the proposed DWDA #2 and as a result, a small <br />sediment basin of 250 cubic yards is recommended if no cover management is <br />practiced on the DWDA #2. The sediment basin should be installed at the inlet to the <br />culvert, the entire volume of which is below the pipe invert. The sediment basin will <br />Section 2.05 RN -6 10/17/2016 <br />