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Response to DRMS General Stormwater Comments — Cotter JD -9 Mine Drainage Design Plan <br />Cotter Corporation (N.S.L.) ( "Cotter ") submits this response to the February 22, 2013 letter from <br />Travis Marshall, Division of Reclamation, Mining and Safety ( "DRMS "), to Glen Williams, <br />Cotter. The DRMS' comments are in italics and Cotter's responses are in bold. <br />1. Page ESWMP -1, first paragraph. This paragraph discusses the settling ponds on <br />Monogram Mesa that are gravity drained through a series of pipes from uppermost to <br />lowermost pond. The text indicates that the ponds collect onsite precipitation and that <br />they are "designed with several inches of freeboard ". <br />a. It is not clear from photos 11, 13, and 15 in Appendix I of the "Materials <br />Containment Plan" whether there are berms around the settling ponds. Please <br />clarify whether or not the onsite precipitation collected in the settling ponds is <br />only direct precipitation on the ponds or does it also include some run -on <br />Stormwater. <br />There are existing berms around the settling ponds. Only the small amount of <br />direct onsite precipitation would collect in them, in addition to the mine water <br />pumped from the mine. Run -on from the surrounding area will be diverted away <br />from the ponds by the berms. <br />b. How is water managed in the lowermost pond? <br />The ponds will be designed at a later date to provide adequate capacity for <br />settling precipitate from the mine water, and providing for gravity <br />discharge of the mine water as well as the precipitation. The design will <br />incorporate a minimum of 12 inches of freeboard above the gravity outlet <br />pipe. This design will be forwarded as a Technical Revision prior to <br />resuming mining activity at the site. <br />c. Is "several inches of freeboard" in the lowermost pond sufficient to contain both <br />pumped groundwater and collected onsite precipitation? Please provide design <br />documents or an analysis to support your response. <br />See response to "b." above. <br />2. Page ESWMP -S, section 7.2. The NOAA Atlas 2, Volume III charts provided in the <br />attachments are illegible due to the small scale. Please state the specific design storm <br />depths used for runoff analyses for both the I 0-year and 100 year, 24 -hour events. <br />The 24 -hour design storm precipitation depths were taken from the NOAA Atlas 2, Volume <br />III and are: 1.90 inches for the 10 -year storm and 3.00 inches for the 100 -year storm. These <br />