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I U t,.~eo r~~ ._.. ._I.yyl vJy•~fHl'I rKUI'I ilO.i 447 '(~f4b r.u~ ~~; order to meet the Environmental Protection Agency'8 and the Colorado Department o£ Health's water quality standards when the Cash mine is dewatered, the Gold Hill Mining Company has ~ commissioned the construction of a water treatment plant. Th; s water treatment plant was desL•7 'd by t!;e Environmental . Services Division of ENV Incorporate; 716 West 14th Street, Long Beaoh, California. Using water ~u:rples of the Cash mine water, their staff has designed a water treatment plant that will meet the Environments! Protection Agency's and the State of Colorado's limits for discharging mine water into the e~- vironm•: `:. An application for a National Pollutant Discharge ~! Elimi~f: ion System Permit to Discharge the Cash mine water `~ will as filed concurrently with tho Colorado Mined Land Rer,'1•-yr±.on Soard Mining and Reclamation Permit. ':' will be pumped out of the Cash mine by using four _td diaphragm pumps in series. These pumps will de- ._. ~: mine workings at a rate of 30 gallons per minute of :~e« nr.• 43,200 gallons per day over 24 hours. A flow re- stt:ctinq valve on the inlet to the first treatment tank will assurE t~iat the flow doer not exceed 30 gallons per minute and Upset the water treatu,~.:z~ system. :'hr, first tank of the treatment system :.; designed to precipi- *ute the metals contained in the mine water as insoluble hy- c?roxi.des and Sulfides. Automatically controlled caustic addi- tion will keep the pH around B.0 to ~.5. A pH probe in thin tank will sense the hydrogen ion (H ) concentration in ttiF ~:ank, dnd add caustic (NaOH) until the concentration corres- ^n~s to a pH of 9.5. The metals will fall out as insoluble ~~~dro:ides due to the addition of this caustic. Since pimple caustic addition is insufficient to remove enough :petals to meet the Federal Environmental Protection Agency's dnc7 tP',e :•~ater Quality Control Division of the Colorado Depart- n~en-:. c' lth's eater quality ~;tandards, sodium hydroxide and scd• .de will be added to precipitate the remaining met- f.L~- iuble sulfides. The addition of this sulfide pre- r,;_L ~-~.;-::.: unit will allow this water treatment plant to eas- :.ly meet the Environmental Pratection Agency's and the '.olorado Department of Health's limits with at least a 10 fold safety factor. The sulfide addition will be automatically Con- trolled much like the caustic addition. The sulfide probe will sense the sulfide concentration and the unit will add sodium sulfide until the sulfide concentration becomes appre- ciable. A concentration of 0.5 mq/1 will mean that dll of the metal sulfides Yrave grecipitated, because the previously added sulfides have combined with the metal ions and precipitated them. An increasing sulfide concentration will indicate that there are no more metal ions to precipitate and unused sulfide has built up in solution. • 1n addition, Dearborn 421 Anionic Polymer and seed sludge will _ be added to aid in the formation of large metal hydroxide- ,'~y';•xlfide sludge particles. This will allow the sludges to set- s;le more easily, and result in a clearer efflgent. A three-compartment settling tank has been designed.to give a 45 minute rete}Ltion.ti:me;--which will allow the sludge to set- `~~~ .tO.xlfe -bottom of. the tank with a 15 minute safety factor.' :`he tank will have hopper bottoms with clear water flowing from one tank to the next through a hole in the baffles. The sludge will be drawn o£f the bottom of the settling tanks dnd the clarified water passed to the final tank. Tn this final tank, another p}t control unit using hydrochloric -acid will Power the p}I to the 6.5-7.0 range. This will lower. the p[{ ko within the Environmental Protection Agency's limits -for discharcle t.o 6.0-9.0 and cause any remaining sulfide to berome hydrogen sulfide gas which bubbles out of solution. T}ic treated w~tc?r will qo to the environment and the hydrogen -i`,~,= s r ' i '! ~t