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ay:cb <br /> i I II I II IIII III <br /> III III United States Department of the Interior 999 <br /> U.S.GEOLOGICAL SURvjy <br /> Water Resources Division <br /> 402 Rood Avenue. Room 223 � -1 � 77- <br /> Grand Junction. Ca 81501 - /-7 <br /> (970) 245-5257 <br /> /April 4, 1996 <br /> ivtr Davy Holm <br /> Director <br /> Colorado Department of Public Health and Frnironment <br /> 4300 Chary Creek Drive South <br /> Deaver,CO W222 <br /> Den Dave: <br /> This note is the follow up to my commeru made at the March Mee" of the Animas Stake <br /> concerning the u n f the American Tunnel and the mobs;Tza�.o-n d <br /> PH grew than 1717 .""`."-�'-'•_._�."�."M,�TM » U ( es°rptr`�of selected metals at <br /> Above a pH of about 8,you can get substantial desorption of Arsenic from hydrous iron oxide.Anything <br /> that is usually an anion will tend to desorb as pH Sues up.If bicarbonate or carbonate is used to raise the <br /> PH,certain metals(i.e.Copper and bead)may riot cme out of solution.This is becaase the cubm ate <br /> tends to complex some metals and that prevents them from sorbing. <br /> If the waters are anoxic or have tow dissolved oxygen and if most of the iron is not present as ferric iron <br /> them may not be mucb precipitation of hydrous iron oxide.Aluminum hydroxides could preei <br /> above a pH of about 5,which may result in some metal attenuation.There arc some differences in the pH <br /> interval and sorption affinity for metal sorption onto iron versus aluminum hydroxide.Without sorption, <br /> the pH needed to precipitate metals as metal hydroxides would be about pH 4 or 10 <br /> 'this infowatiou is based on my recent conversations and written communication with Karhteen Smith of <br /> am USGS.If you need further information please Contact me at extension 3014 or Kathleen at 303.236- <br /> 5788. <br /> S' rely <br /> von Guerard = <br /> Cc:KathI=Smith.USGS Denver,CO <br />