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~ o en *'" salinity Standards (APPENDIX A) and in Section I of the Intercepted Groundwater Policy (APPENDIX C). 2. Water Treatment Svstem to Reduce Salinitv in the Discharqe Stream Currently at the La Plata Mine, there is no treatment of mine pit water or other outfall waters for reduction of salinity concentration, Among the technological alternatives for reducing salinity, reverse osmosis is generally acknowledged to be the most economical treatment. In order to adequately treat mine pit waters to reduce salinity toward a no-salt discharge and in a timely manner to allow for mine operation in the dewatered pit for a majority of the year, a water treatment system to handle maximum mine pit flows of 132,117 gallons per day is provided, A reverse ~smosis treatment system with a capacity of 150,000 gallons per day is a suitable scale for processing this volume of mine pit water. An unlined surge storage reservoir will be required t~ contain pit water prior to treatment, in order to provide for dry operating conditions in the pit. Additionally, a gravity filtration pretreatment will be provided prior to the reverse osmosis treatment to remove suspended particles to prevent fouling of the reverse osmosis membranes. The process flow for the reverse osmosis treatment is described in FIGURE 4 for maximum conditions, Maximum cond~~igIL~ccount for processinSL of 148 acre feet per ~. Reverse osmosis removes 95 percent of salt in one pass. Water recovery through reverse osmosis is 75 percent, According to this process analysis, the one pass treatment of the mine pit water removes 1311 pounds of salt per day, resulting in 61 pounds of salt per day remaining in discharge water, 9 j; ;<,<'-"; _ ",.:",_. ~-- ~i;~< ~;-' _ ;:;'<"_