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upgradient reclaimed surface mine areas and routes it around the Area 1 Basin to Pond D, so wazer cornributions from run-on are sinularly negligible. For design dewatering purposes, the contribtuion from incident precipitazion for the Probable Maximum Precipitation (PMP) event (131 inches over 24hours) is 5.6 acre-feet, or approxrmately 4.4 percent of pond capacity and slightly over 1-foot of depth with the pond neaz its maximum design water level With a capacity of 250 gpm, the Area 1 Basin pumping station can discharge the accumulated precipitation from the PMP over a period of approximately 5 days. Contributions from and Management of Mine Water Dischazge Flows -Mine water inflows pumped from the mine are piped to the surface at either Site 109 or the Fish Creek Borehole (Site 1 I5). From either of these locations, the water can be piped to either the Area 1 Basin or the Million-Gallon Tank. Water pumped from the Area 1 Basin can be routed to the: 1) Prep Plant, 2) Mine water recycling line, and/or 3) Pond D for discharge to Foidel Creek. Water routed from the Area 1 Basin to either locations 1 or 2, above, is piped to a de-sander, located at an old well site. A return line from the de-sander allows back-flush water to be returned to the pit. The location of these lines is shown on Map 24 of the PAP. The ability to discharge directly into Foidel Creek will be dictated by downstream water quality in Trout Creek, whether or not the Fish Creek Borehole is discharging, and the rate of discharge. Pond D serves as the treazment facility for discharge poirt[ 005 (Site 84) under ®PS Pemtit CO-0027154. Any discharge from the Area 1 Basin will be treated in Pond D to meet applicable effluent limitations under this CDPS Pemut, before being released to Foidel Creek An overflow channel has been constructed az the lowest topographic point on the Area 1 Pit highwall, and conforms to applicable requirements for temporary diversions under Rule 4.05.3. Designs for the overflow channel are provided in Table 51, Overflow Channel Specifications, of the PAP. The DEPOSITS model (Ward et. al 1979) was used to determine the capacity and effectiveness of Sedimentation Pond D to handle inflows fmm all tribrtary sources, during a 10-year, 24-hour precipitation event. The output from the DEPOSITS model is included in Exhibit 28, Deposits Model Output, of the PAP. Several assumptions were made in calibrating the DEPOSITS model First, it was assttmed that two sourt:es of water will be tributary to Pond D: drainage from the upgradient spoils through Ditch D-3, and discharge from the underground mine through Ditch D-2. The inflow to the pond from these sources was assumed to fill the impoundment to the sediment storage level; thus dead storage was set equal to the pem~anent pool volume. Second, it was assumed that the runoff from the design event will enter the pond from all tributary areas simultaneously, without regazd to lag time due to diversion. These assumptions make the flood muting and sedimentation analyses rrrore conservative. The inflow hydrognph calculated bythe DEPOSITS model is derived by applying the 10-year, 24hour SCS Type II storm and the SCS unit hydmgraph to derive the runoff response. The outflow hydrograph is derived by calculating the cumulative volume in the pond and applying stage-storage relationships to detemvne head on the decant orifice, which is used in the orifice equation to derive the discharge. The outflow seditnern-graph is derived by applying the variable rates of inflow and outflow to determine detention time, and appl}dng represernative patticle size distributions to Stokes' Iawin an iterative analysis. The output from the DEPOSITS model shows that the average effluetn concetnration from Pond D of Total Suspended Solids ('ISS) is 20.7 mg/L This u in compliance with the average monthly effuern limitation for TSS set in the GDPS pemrit. Based on this analysis and monitoring records for pI-~ total iron, total manganese, oil and grease, and other pazameters, the effluent limitation set for discharge point 005 (Site 84 in CDPS Pemri[ 00-0027154 are expected to be met. Therefore, either operation of the Area 1 Basin as a temporarywater storage basin or coal wore disposal area will not compmmise the existing sedirrrent control plan and will not degrade surface water qualiry. Water Ri¢hts -Beneficial use of mine water discharge from both Site 109 and the Fish Creek Borehole (Site 115) is pemutted under weer rights filings, File Nos. 12593 through 12595 and TC~'s Plan of Augrr~ntation, as amended (Case No. 90CW99). TR 05-47 Ex8V-3 Revised - Mazch 2005