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algebraic approsimatians. The basic components of the equations are: 1) ayuifer characteristics; 2) the rate of ground ,eater tlaty; 3) canceutra[iou of dissolved solids; 4) values of kongitudinal and transverse dispersivity; and 5) retardation factors [o account for ion exchange, solute absorption and radioactive decay. Aquifer characteristics are determined frasn pump tests attd drill hole data presented earlier. The rate of gmund water Fln,v is calculated from the average permeability and potentiometric gradient within the overburden aquifer in this area. Concentration of dissolved soils for tltese tests was measured tfirougft column leaching studies as shown in Figure 9, Predicted Leachate Concentration, Energy Mute No. I. Dispersivity is a parameter tr•ttich is difficult in ateasure in the field and must be assumed. Dispersivity is the ratio of solute dispersion to flow vebcity. As the saline water leached from the spoils enters [he aquifer, a "plume" of solute. spreads through the aquifer in the direction of ground water flow. As the pSmne moves through the ayuifer, the dissolved solids are diluted, diffused and ahsorbed by physical and chemical interaction with the natural ground water The greatest effect on dispersion in aquifers associated with rani strata is the heterogeneous nature of the farntation. The lithology aF the Williams Fork Formation is variable, dispiayistg many facies changes, pinc}t-outs and thin sandstone leases. Groutxi tenter movement in such an aquifer is non-laminar, thus absorption and diffusion of highly saline water is enltartced. Lostgitudinal dispersivity is measured in the direction of ground water flow; transverse dispessivity is measured iu a lateral direction. The measurements, calculations and assumptions discussed above were used in a predictive analysis to atndel the d+str[bution of a plume of saline water emanating from rite Energy Mine No. 4 into the Twentymile Park ground water basis. The OSM Plume Management Model (1981) was used to estimate concentrations of total dissolved solids (TDS) in milligrams per liter above baseline concentration after 50 years of solute intrusion. The results in Figure I1, Predictive Analysis -TDS Concentrations After SO Years, show concentrations to be diluted to acceptable levels of TDS concentration. The disturbed area is tributary to Sedimentation Pond D, as Shawn an Map 24, Surface Facilities. Pond D serves as the treatment faci)ity for discharge point Oi15 (Site 84) under NPDES Permit C©-OOZ7fj4. A system of diversion ditches delivers water to Pond Q from the underground and surface mining operations. As ssated previously, the Area 2 Pit receives water from surface runoff and infiStration from reclaimed spots upgradient. In addition, backfilling operations necessary for reclamation and waste rock disposal displace water itt the ptt, causing an overflow at the final highwaSl. The overflow has been directed into Prntd D through a designed chaattel. 5ufficieut freeboard has been provided to handle rates of flow higher than the desist flow of 0.8 cfs. The drainage from the Area 2 Pit will be treated in Pond b to meet the eft~uent }imitations applicable under the Sv`PDES Permit issued to C;YCC, before being released fa Foidei Creek. The overflow channel has been constructed at the kowest tapogsaphic point on the highwafl, and conforms to the requirements for temporary diversions set forth in Ru4e 4.05.3. Designs for the overflow channel are given in Tahfe 51, Overflow Channel Specifications. i'he DEPOSITS model (Ward et. ai f979) was used to determine the capacity and effectiveness of Sedimentation Pond ll tc hartdfa inflows from ail tributary sources, during a iQ-year, 24-hour precipitation event. The output from the DEPOSiT5 ntodel is given in Exhibit 28, Depasits Model Output. Several asswnptions were made in calibrating the DEPOSITS model. First, it was assumed that ttvp peremual sources of water will be tributary to Pottd D: drainage Prom tlta upgradient spoils through the overflow channel, and discharge from the underground mine through Ditch D-2. The inflow to the pond from these sources was assumed to fiN she impoundtttettt to the sednnent storage level; thus dead srorage was set equal to the permanent poo! volume. Second. it was assunted that the runoff from the design event sviSi enter the pond from all tributary areas siatnitanenu>ty, without regard to lag time due to diversion. These assumptions make the flood matins acrd sedimentation analyses more conservative. The inflow hydrograph calculated by the DEP©S1TS nrodei is derived by applying the l0-year. 2d-hour SCS Typc fl ston« and the SCS «nit hydrograph to derive the runoff response, The outflow hvdro~raph is derived 6y calculating the cumutative volume in the pond and applying stage-storage relationships to determine head on the 1,ttt 97-I j4 2,Qj-96 Revised 9(4t9?