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Year # Samples Min. TDS Max. TDS Ave. TDS <br />1979 21 2080 3850 2948.1 <br />1980 37 700 3320 2626.8 <br />1981 22 456 2920 2608.5 <br />1982 17 324 3320 2863.1 <br />1983 24 520 4400 2757.9 <br />Incident Precipitation and Run-on -The surface area of the Area 1 Basin is only approximately 5.1 acres, so <br />water contributions from normal incident precipitation are negligible (0.77 ac-ft fora 10-year, 24-hr event or <br />0.61 percent of pond capacity). An upgradient diversion ditch (Ditch D-3) intercepts any surface runoff from <br />upgradient reclaimed surface mine areas and routes it around the Area 1 Basin to Pond D, so water contributions <br />from run-on are similarly negligible. For design dewatering purposes, the contribution from incident <br />precipitation for the Probable Maximum Precipitation (PMP) event (13.2 inches over 24-hours) is 5.6 acre-feet, <br />or approximately 4.4 percent of pond capacity and slightly over 1-foot of depth with the pond near its maximum <br />design water level. With a capacity of 250 gpm, the Area 1 Basin pumping station can dischazge the <br />accumulated precipitation from the PMP over a period of approximately 5 days. <br />Contributions from and Management of Mine Water Discharge Flows -Mine water inflows pumped from the <br />mine aze piped to the surface at either Site 109 or the Fish Creek Borehole (Site 115). From either of these <br />locations, the water can be piped to either the Area 1 Basin or the Million-Gallon Tank. Water pumped from the <br />Area 1 Basin can be routed to the: 1) Prep Plant, 2) Mine water recycling line, and/or 3) Pond D for dischazge to <br />Foidel Creek. Water routed from the Area 1 Basin to either locations 1 or 2, above, is piped to a de-sander, <br />located at an old well site. A return line from the de-sander allows back-flush water to be returned to the pit. <br />The location of these lines is shown on Map 24 of the PAP. The ability to dischazge directly into Foidel Creek <br />will be dictated by downstream water quality in Trout Creek, whether or not the Fish Creek Borehole is <br />discharging, and the rate of discharge. Pond D serves as the treatment facility for dischazge point 005 (Site 84) <br />under CDPS Permit CO-0027154. Any discharge from the Area 1 Basin will be treated in Pond D to meet <br />applicable effluent limitations under this CDPS Permit, before being released to Foidel Creek. An overflow <br />channel has been wnstrncted at the lowest topographic point on the Area 1 Pit highwall, and conforms to <br />applicable requirements for temporary diversions under Rule 4.05.3. Designs for the overflow channel aze <br />provided in Table 51, Overflow Channel Specifications, of the PAP. <br />The DEPOSITS model (Ward et. al 1979) was used to determine the capacity and effectiveness of <br />Sedimentation Pond D to handle inflows from all tributary sources, during a 10-yeaz, 24-hour precipitation <br />event. The output from the DEPOSITS model is included in Exhibit 28, Deposits Model Output, of the PAP. <br />Several assumptions were made in calibrating the DEPOSITS model. First, it was assumed that two sources of <br />water will be tributary to Pond D: drainage from the upgradient spoils through Ditch D-3, and dischazge from <br />the underground mine through Ditch D-2. The inflow to the pond from these sources was assumed to fill the <br />impoundment to the sediment storage level; thus dead storage was set equal to the permanent pool volume. <br />Second, it was assumed that the runoff from the design event will enter the pond from all tributary azeas <br />simultaneously, without regazd to lag time due to diversion. These assumptions make the flood routing and <br />sedimentation analyses more conservative. <br />The inflow hydrograph calculated by the DEPOSITS model is derived by applying the 10-yeaz, 24-hour SCS <br />Type II storm and the SCS unit hydrograph to derive the runoff response. The outflow hydrograph is derived by <br />calculating the cumulative volume in the pond and applying stage-storage relationships to determine head on the <br />decant orifice, which is used in the orifice equation to derive the discharge. The outflow sediment-graph is <br />derived by applying the variable rates of inflow and outflow to determine detention time, and applying <br />representative particle size distributions to Stokes' Law in an iterative analysis. <br />The output from the DEPOSITS model shows that the average effluent concentration from Pond D of Total <br />Suspended Solids (TSS) is 20.7 mg/l. This is in compliance with the avemge monttily effluent limitation for TSS <br />TR07-59 Ex8V-3 02/27/07 <br />