2009-01-23_REVISION - C1980007 (3)

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photography, surface water flow measurements, piezometer water level • measurements, and visual inspections. The monitoring frequency for each structure or feature is designed to span the pre-subsidence to post-subsidence time period. XVI. Concurrent Surface and Underground Mining 1. This section does not apply to the West Elk Mine. XVII. Operations on Alluvial Valley Floors MCC has performed a detailed reconnaissance investigation for alluvial valley floors (AVFs). During the investigation, MCC identified several areas within or adjacent to the mine plan area which may meet the geomorphic criteria of alluvial valley floors. Alluvial deposits were identified along Minnesota Creek, the Dry Fork of Minnesota Creek, Sylvester Gulch, and the North Fork of the Gunnison River. Based on MCC's reconnaissance, and the Division's field inspections, the Division designates the following three areas as alluvial valley floors: 1) North Fork AVF - North Fork of the Gunnison River downstream from Gribble Gulch, 2) Minnesota Creek Main Stem AVF - The alluvial deposits of the main stem of Minnesota Creek extending from the north section line of Section 17, T14S, R90W, downstream to the North Fork of the Gunnison, 3) Minnesota Creek Lower East Fork AVF - The alluvial deposits on the lower East Fork of Minnesota Creek, extending from the upper limit of mapped alluvial • deposits in Section 9, T14S, R90W to the confluence with the main stem of Minnesota Creek. Mining will not occur in these AFVs. MCC's monitoring, as described below, will provide sufficient information for the Division to determine that the requirements of 4.24.4 (1)(a), (b), and (c) are being met. North Fork AVF - Oxbow Mining monitors North Fork surface water immediately downstream from the headgate of the Fire Mountain Canal (site NF-3). This site is within a subirrigated portion of the modern-day alluvial valley, approximately 2 miles upstream from the agriculturally productive North Fork AVF. Data from site NF-3 enables identification of material damage to the quantity and quality of water supplying the North Fork AVF. MCC's contribution to impacts can be identified from MCC's monitoring of its CDPS outfalls, approximately 2.5 miles upstream from NF-3. Significant inputs from the West Elk Mine would occur only from the part of the mine that is upstream from Somerset, as the Lone Pine Gulch area no longer has a pumping site and has been Phase II bond-released. Minnesota Creek Main Stem AVF - MCC financially supports the USFS monitoring station that is located on this AVF. This station and MCC's monitoring upstream from the AVF would enable identification of material damage to the quantity of water supplying the AVF. Material damage to water quality would not be expected because the mine does not propose to discharge mine water to this drainage. 52