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4-4 <br />RO is a membrane process in which a solvent (water) is forced to flow from a stronger solution <br />(concentrated salt solution) to a weaker solution (water only) using pressures above the <br />solvent's osmotic pressure. The weaker solution or permeate will be essentially salt (TDS) free <br />' and will be discharged through the existing permitted outCalle. The stronger solution will <br />become more concentrated in TDS as the water is forced out. As the stronger solution <br />increases in TDS concentration, the pressure required to force the water out increases <br />' proportionally. Therefore, to maintain operational efficiency and coat effectiveness of the <br />treatment process, the concentrated stronger solution will require periodic purging. The <br />purged materiel must then be properly managed (e.g., on-site treatment or off-site treat- <br />ment/disposal). <br />1 <br />Based on data presented in Table 1, when mine water is being discharged, it is anticipated that <br />' the concentrated stronger solution would require purging when the TDS concentration <br />approached 25,000 milligrams per liter. This concentration corresponds to a purge stream of <br />' approximately 12,200 gallons per day and 2,600 pounds per day TDS loading for the two <br />current discharges and a total of 25,300 gallons per day and 5,200 pounds per day TDS loading <br />' for all three discharges. Management of the purged streams can then be effectively managed <br />on site utilizing natural or assisted methods similar to those described in Sections 4.4.3. and <br />4.4.4. <br />The major work activities associated with this management alternative include the following. <br />• Construction of equalization surface impoundments. <br />• Construction of a facility to house the RO treatment system. <br />• Installation of three independent RO units. <br />• Installation of prefiltere for each of the RO unite. <br />• Installation of support piping and pumping systems. <br />• Construction of evaporation impoundment or installation of <br />evaporation equipment. <br />' 4.4.1.2 Effectiveness <br />The technical basis and approach for this alternative have been fully documented and could <br />be accomplished using readily available, although custom fabricated, equipment end the <br />' existing sedimentation impoundments. The effectiveness of RO treatment for removal of <br /> <br />