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" ,...... /-. ...r::.. w NPDF{; Permit No. CO-0042161 Salinity Control Study Twentymile Coal Company 4.2.2 !Reduction of Salt Discharge by RO - Option 2 Option ~ would require an ROtreatment unit and a deep injection well for the disposal' of II reject f$ction of discharge, The construction of the RO treatment plant for this option is technically feasible, but it is not certain that an injection well capable of accepting brines 'at' the design r~te could be pennitted and constructed. An injection well permit would be required from Ee A. It is also uncertain whether the Dakota Sandstone would prove suitable for injectioniat a rate of 112 gpm, Further, the depletion of water by the RO reject fraction would require a surface water right, which might be difficult to obtain if it resulted in material damage to the quantity of water supplying a designated Alluvial Valley Floor. Cost esti!nates for this option were based on vendor quotes for major equipment items, Other costs were calculated using estimating methods outlined in cost estimation handbooks and design texts.. References included Means Site Work & Landscaoe Cost Data. 12th Ed,. RS. Means Cp. Inc., 1993, and Plant Design and Economics for Chemical Enl!ineers. 3rd Ed.. Peters atid Timmerhaus, 1980. The capital cost of Option' 2 is $3,794,000 with annual operatingicosts of $302,000, Capital and operating costs are itemized in Table 7, The optio/l would reduce salt loading by 1.53 tons/day or 558 tons/year of the estimated total of 668 tol\s/year, at a capital cost of $6,794 per ton over the first year and at an operating cQst of $541 per ton. Since the RO system is designed to treat to a 300 mg/l dischat.ge concentration, the cOncentration in Fish Creek below the discharge would approach 300 'mg/l during veJjy low flow conditions. The reduction in salt loads and concentrations in Fish Creek during sn6,wmelt runoff would not be measurable. Flow depl~tion in Fish Creek would be only 25% of that of Option I, but the 25% representS a large quan~ity of brine which requires disposal. The most significant difference between the first two pptions is the much higher operating oost for the RO treatment facility. The feasibility .of pennitting and constructing Option 2 facilities is essentially the same as for Option 1 ~ince both require deep disposal wells and depletion of water supplies. The feasibility bf disposing of the waste water brines from the treatment process is the primary technical o~stacle in Option 2. A deep injection well is the only practical disposal mode and it is uncertaiq whether a permit could be obtained or whether .the Dakota Sandstone would prove, suitable for disposal of the waste water brines , ~ AHA Filerwoe: 14SALC'Nl.DOC Page 28 11:59 AM 09rJ.9/95 ,L ~.