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u <br />~ ins <br />, .-.x - _ <br />LABORATORY DIVISION <br />1475 PINE GROVE ROAD <br />P.O. BOX 774018 <br />STEAMBOAT SPRINGS, CO 80477 <br />April 29, 1986 <br />Mr. Rick Mills <br />Colorado Yampa Coal Company <br />29588 Routt County Road #27 <br />Oak Creek, Colorado 80467 <br />Dear Rick: <br />1303)879-6260 <br />TELEX 510-100-3880 <br />I enjoyed talking with you on the telephone last week. As <br />you requested, the following is information regarding the <br />method detection limit for analyzing mercury in water. <br />• <br />ACZ INC. is using the United States Geological Survey (USGS) <br />Method I-2462-78 for determining mercury in water. The <br />instrument used is an automated atomic absorption <br />spectrophotometer (cold vapor procedure) which is able to <br />detect mercury down to .0002 mg/1 mercury in water. In <br />comparison, the EPA Method 245.2 (automated cold vapor <br />technique) and the USGS method, which we are now using, are <br />virtually the same. <br />These procedures, as well as the EPA approved manual cold <br />vapor methods, are very accurate and precise but lack the <br />sensitivity to detect mercury in water at concentrations <br />below .0002 mg/1 with any confidence. we have attempted to <br />"fine tune" our mercury procedure to obtain lower detection <br />limits without success. At this time, using EPA approves: <br />procedures to obtain a mercury detection limit of .00005 mg/1 <br />as listed in your NPDES permit is not possible. <br />If you have any questions or require additional information, <br />please do not hesitate to contact me. <br />Sincerely, <br />ACZ INC. <br />~~1~/~~~ <br />Ralph V. Poulsen <br />Laboratory Director <br />• RVP:ju <br />