2010-02-15_HYDROLOGY - M2007044 - Laserfiche WebLink

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The resegmentation of the San Miguel mainstem into segments 3a and 3b is warranted because water quality differs above and below Marshall Creek and significantly different aquatic life habitat is attainable above and below this point. Because of the influence of Marshall Creek, water quality in the San Miguel is significantly different below their confluence. There was evidence that habitat limitations in the mainstem are significantly more pronounced above Bear Creek(downstream of Marshall Creek)due in part to rechannelization as the result of Idarado's operations and due to lower stream flows. The mainstem has been resegmented at Marshall Creek rather than Bear Creek because there was evidence that habitat limitations on the mainstem between those two creeks are largely correctable. The resegmentation of Ingram and Marshall Creeks into segments 6a and 6b is warranted by the significantly different current water quality of those two streams Idarado proposed the establishment of additional sub-segments on the San Miguel mainstem and of separate segments for several additional tributaries which currently are grouped together as part of segment 2. The additional mainstem resegmentation appears unnecessary at this time. While there is evidence of some variations in water quality and habitat in this stretch,they do not appear substantial enough to warrant further resegmentation. Also, there is not enough differences to warrant, separate segmentation for the other tributaries. Moreover, it is not apparent that further resegmentation would have significantly different regulatory impacts on potential affected entities. Classifications: Retention of the existing classifications is warranted by the evidence submitted. Marshall Creek and Ingram Creek retain their current cold water aquatic class 2 designation because of the evidence that they currently are, and are likely to remain, habitat-limited. No parties challenged this classification. The other segments at issue retain their current cold water aquatic life class 1 designations. For the mainstem of the San Miguel, below Bear Creek all parties agreed that the class 1 designation is appropriate. From Bear Creek upstream to Marshall Creek,there was evidence of some degree of current habitat limitations, as well as water quality limitations on aquatic life. The Commission believes that any habitat limitations are correctable within a twenty year period. For new segment 3a above Marshall Creek,there was some evidence that flows in this stretch are very limited, creating a significant habitat limitation. However,there was other evidence that there are substantial flows in this segment for significant parts of the year, adequate to support a variety of aquatic life. For the other tributaries that were not resegmented or reclassified, there was some evidence that habitat limitations may be a significant factor on these streams, due primarily to flow and gradient conditions. However, the Commission does not believe this evidence was substantial enough to warrant reclassification. Moreover, it is not apparent that reclassification of these tributaries would have significantly different regulatory impacts on potentially affected entities. Standards: The revised metals standards for segments 3a, 3b, 6a and 6b have been adopted because the information currently available indicates that the more stringent levels should be attainable within a 20-year period. All parties agreed that significant improvement in water quality will occur as a result of the changes that will be implemented due to the legal actions that has been instituted under the Comprehensive Environmental Response, compensation and Liability Act (CERCLA). At a minimum„ the cleanup plan proposed by Idarado Mining Company will result in some water quality improvement. The standards are consistent with levels found to be achievable by the Record of Decision prepared by the State in the CERCLA action. 26