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Generally, the Division agrees with the assessment of increasing TDS concentrations <br />downstream of Seneca [I-W on Dry Creek. Possibly SCC was misled into believing <br />DMG had a concern with Yampa River salinity by the statement `'...the salinity suspect <br />level for the Yampa River Basin is l.0 millimhos/cm for specific conductance." While <br />this suspect level is indeed appropriate for the Yampa River water itself, it also applies to <br />all irrigation waters in the basin, regardless ojtrib:~tnry, except where site specific <br />exclusions have been stated in written Findings by the DMG. This includes Hubberson <br />Gulch. Division post-mining estimates of salinity in Hubberson Gulch indicate TDS <br />concentrations ranging from 1536-4366 mg/I for Hubberson Gulch at the 26 acre AVF <br />near site WSH7. Please provide estimates of water quality for this reach of Hubberson <br />Gulch, with supporting documentation of input data and methodology. Monthly <br />calculations are necessary over the period June-September due to irrigation usage. <br />Ultimately, the Division requires this information for vegetation productivity decrease <br />estimates in accordance with our procedure for assessing the degree of material damage. <br />In addition to salinity estimates, the group determined the appropriate TDS/EC ratio for <br />Hubberson Gulch to be approximately .70-.75. This should cleaz up any confusion when <br />converting values back and forth between TDS and EC. <br />Finally, I would recommend a minimum of monthly monitoring of any and all sites that aze in <br />the locality of AVF azeas, including direct measurement of the stream (WSH9) upstream of all <br />mining impacts on Hubberson Gulch. This had been our procedure at all significant mining <br />operations, excluding the Hayden Gulch Terminal, which I do not consider a significant <br />operation. Mike has appropriately asked SCC as part of this adequacy review to monitor the <br />upstream site on Hubberson Gulch, but SCC has apparently declined to this point. Any AVF that <br />would be potentially impacted or even AVF azea which are proposed not to be impacted to any <br />significant degree is required by the Rules to be monitored to prove it. Final water quantity and <br />quality determinations also require this monitoring over the operational and post-mining period. <br />CC: Larry Routten <br />Dan Hernandez <br />