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with Occidenta13. We snall fureher ass~e that afte= trea~~ent the water \-.. , en quality level is consistent with that of Table 4-5, with the possible ~ exception or organics contamination. It may be ~oted that no val~e has been 00 specified for the organic contaminants in the mine water because there is sL~ply no way or knowing at ~~is time what they migh~ be. For the relatively low TOS mine water with fluoride contami~at~on, ~~o processes prevent themselves as t~e most appropriate :or obtaining a high . 11 12 purity product: electrodialysis and reverse osmos~s ' . However, electro- dialysis will only separate those molecules which are in ionic fo~ in solution. Boron, for exanple, :equires that t~e solution ~H be about 8.5 to 9 to become ionic. In ge~eral elec~rodialysis also does not have a capabili~y for se?ara~ing soluble organic molecules. Reverse osmosis. on t~e other ~and, has a wocerat: capability :or separating soluble orgar.ic ~olecuIes, ~ut a veri poor ca~abilit: for se?d.!"ating boron frcm acidic waters~ It is onl'l at a quite high ~:i (~.. 9.3-10) that a 75\ rejection of boron is attained. Fluoride rejection is typically about 90~. Bot~ of the processes :equire a ~oderate to gOOG level ~: prefil:ration to :emove suspended solids whic~ will be conCained in ~~e ~ine ~aeer. The mine water is aL<aline ~~d electrodialysis ~ould requi~e pret:eat- me~t with sul=uric acid to prevent scali~q on ~~e ~embranes. Acid aceitio~ or chelating 3gents wauIe also ~e re~~ired :or ~e reverse osmosis system to prevent precipitation of salts~ We emphasize ~~at ~oth of ehe systems wculd pr~vide a product wit~ a lowe~ toeal dissolved solids t~an recui:~d :0: =isc~arge. As a rule, reverse osmosis would gi~e ~~e lowest T~S product wi~~ a t~~ical value for ~~e mine water considered of =~om 100-200 wg/l, while ~~e electro~ialysis produc~ mi~ht range frcm 200-400 rngjl. T~e5e values are illustrative only and are controlled by ~~e system economics. If total dissolved solids content were ~~e only dischar~e requirement to be met, then a sig~ificant reduction in tredtment cost could be achieved by treating only part of tne water anc blending it with ~~treated water =rom which only ~he suspended solids ha'le been re~oved. However, for the contaminar.t levels shawn in Table 4-6, it is not likely that ~~e discharge limi~s s?ecified i~ Table 4-5 could be met Nith blending. Of course, sgecific ?ollutan~ =e~aval might still be practiced whi~h ~culd enable blending. This decision is also an economic one. 9~,