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MEMORANDUM • <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD • CENTRAL VALLEY REGION <br /> 3443 Routier Road, Suite A Phone: (916) 255-3000 <br /> Sacramento, CA 95827-3098 CALNET: 8-494-3000 <br /> To: Ms. Cori Condon From: Chris Foe <br /> Assoc. Engr. Geol Environ. Spec. t� <br /> DATE: 13 December 1996 SIGNATURE: <br /> Subject: TIEACTIVITIESATMARLEYCOOLING TOWER FACILITYINSTOC%TON, CA <br /> I have reviewed the proposed changes to Marley Cooling Tower's biomonitoring program. I agree with <br /> the proposed changes with one exception. S.R. Hansen recommends assessing metal toxicity by treating <br /> with a Bio-Rad AG50W-X2 column. I am not familiar with this resin but understand it to be a cation <br /> exchange column. Groundwater at the Facility is contaminated with chromium. Hexavalent chromium <br /> is the more toxic form and I have heard can be lethal to Ceriodaphnids at concentrations below 10 ppb. <br /> Hexavalent chromium should convert slowly to the trivalent form. Although I do not know the <br /> speciation of the element in the effluent,the reduction is consistent with the bioassay results. Of course, <br /> both tri and hexavalent chromium exist in surface water as oxyanions. I question whether the element <br /> would be effectively removed by a cation exchange resin. I suggest that S.R. Hansen undertake some <br /> control experiments to ascertain the toxicity of both chromium valences in the Facilities effluent and the <br /> efficiency of this column in removing the oxyanions. <br /> Please call me at (916)-255-3113 if you have questions. <br />