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ARCADIS <br />Mr. Daniel J. Arnold <br />Attorney <br />Denver Water <br />1600 West 12th Avenue <br />Denver, CO 80204 <br />Subject <br />Comment on monitoring plan for Schwartzwalder Mine (M- 1977 -300), Amendment 4 <br />Dear Mr. Arnold: <br />We have had an opportunity to review the monitoring plan issued by DRMS. A <br />concern that we have with "total carbon" analysis as opposed to "total organic <br />carbon" is that total carbon lumps organic carbon and inorganic carbon <br />(bicarbonate /carbonate) making it difficult to know exactly how much organic carbon <br />is present in the water. Organic carbon is an important parameter for tracking mine <br />pool remediation progress (to understand how well the organic carbon is being <br />degraded by native microorganisms in the pool). <br />We suggest collection of two water samples for total carbon analysis. One should be <br />acidified in the field, and one left unacidified. Acidifying drives all of the inorganic <br />carbon to CO (gas) that is then volatilized out of the sample. If both samples are <br />analyzed for total carbon, then subtraction of the acidified sample result from the <br />unacidified sample result will give "total organic carbon." Through this procedure, an <br />appropriate data set will be provided in order to evaluate organic carbon utilization, a <br />key aspect of the mine pool treatment process. <br />Sincerely, <br />ARCADIS U S., Inc. <br />Jeff Gillow, Ph.D. <br />Technical Expert - Geochemistry <br />Copies <br />Jason Kerstiens, ARCADIS <br />Imagine the result <br />ARCADIS U.S , Inc <br />100 Fillmore Street <br />Suite 200 <br />Denver <br />Colorado 80206 <br />Tel 303 316 6500 <br />Fax 303 316 6599 <br />www.arcadis - us.com <br />ENVIRONMENT <br />Date <br />April 17, 2013 <br />Contact <br />Jeff Gillow, Ph.D. <br />Phone <br />303 - 471 -3446 <br />Email <br />Jeff.Gillow @arcadis - us.com <br />Our ref <br />05600015.0000 <br />