2011-06-10_HYDROLOGY - C1981022 - Laserfiche WebLink

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Outfall 012 - Pond B The pond discharge valve was opened on 5/09/2011 at 0800 hrs during the storm and outflow sampled at 0800 hrs. The valve was closed on5/10/2011 at 1000 hrs. The manually operated headgate valve was opened to insure necessary capacity and stability of the pond during the extreme inflow event. The data indicates a TSS of 74 mg/l, which nearly otherwise met the daily maximum requirement of 70 mg/l. However, since the discharge is a result of rainfall induced inflow it is appropriate to waive the primary TSS effluent limit and claim the alternate effluent limit for Settleable Solids (SS) instead. The analytical results for SS indicated <0.1 ml/l/hr which is well below the 0.5 ml/l/hr requirement. Receiving Streams Although not required, it is often useful to compare the pond discharges to local receiving streamflow to assess any potential for impacts. On April 19, 2011, Oxbow had sampled local streams in accordance with the stream monitoring programs of our CDRMS Mining and Reclamation Permit. Oxbow completed this sampling program at the start of spring runoff conditions. The quality and quantity of runoff in the local streams on April 19, 2011 reflect the early spring runoff conditions, which due to above normal snowpack, predict a record 2011 runoff volume. We have included a Table 2 to provide a comparison between the pond discharge and the local streams condition. Clearly, the pond discharges exhibit vastly better water quality than that found in the receiving streams. Overall, Oxbow is pleased that the ponds functioned as designed and in accordance with the approved CDRMS designs and the CDPS Permit. No other issues were encountered during May 201 L If you have any questions or comments, please contact me at (970) 929-5806. Sincerely, James A. Kiger Environmental Manager Attachments Xc: Mr. Mike Bouley, CDRMS Jim Cooper, OMLLC Files • Page 2