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A particular concern raised by the Division during the PR-2 review, was the potential that high salinity spoil water discharged from proposed South Taylor pit backfill areas into the West Fork of Good Spring Creek, would increase salinity levels on the main stem of Good Spring Creek, potentially causing material damage by significantly reducing forage production on irrigated fields on the Good Spring Creek alluvial valley floor. The potential for material damage was assessed by the Division, based on salt loading projections incorporating anticipated spoil discharge quantity, worst case projected spoil discharge salinity, and historic low flow discharge and salinity of Good Spring Creek, in selected upper and lower segments (see Section 2.05.6(3)(b)(iii) of permit Volume 12, and particularly Potential Surface Water Quality Impacts discussion on page R2-118). The projected worst case salinity for Good Spring Creek downstream of the West Fork confluence and upstream of Streeter Drainage confluence is 1192 mg/1 TDS (1.86 mmhos/cm conductivity). Projected worst case for lower Good Spring Creek, downstream of Streeter Drainage confluence is 1261 mg/1 TDS (1.97 mmhos/cm conductivity). The Division inserted the projected worst case salinity values from the referenced permit section for upper and lower reaches of Good Spring Creek into a material damage assessment formula listed in the Division's January 1988 material damage guideline document (A Description of the Material Damage Assessment Process Pertaining To Alluvial Valley Floors, Surface Water, Ground Water And Subsidence At Coal Mines). Based on available data for moderately sensitive species representative of the most sensitive forage species grown on the alluvial valley floor fields, projected yield declines range from 2.l % to 2.4% for upper Good Spring Creek, and from 1.1% to 1.3% for lower Good Spring Creek. The guideline document "suspect level" for initial determination of potential material damage is a 3% decline in productivity for an alluvial valley floor agricultural parcel. Based on this analysis, the Division has determined that the proposed operation will not result in material damage to the Good Spring Creek alluvial valley floor. Monitoring of spoil springs, alluvial aquifers on the West Fork and main stem of Good Spring Creek, and surface water in the West Fork and main stem will be conducted to verify that worst case salt loading projections are not exceeded. Details of Colowyo's water monitoring plan are found in Section B, Item III of this document and in Section 4.05 of the Permit. D. Specific Findings Required by Rule 4.24 1. The Division has determined that an alluvial valley floor exists within the affected or adjacent area. Therefore, the following findings are in order for the alluvial valley floors located in Wilson Creek and Goodspring Creek. Lower Elkhorn Creek is located outside the permit area and will not be affected by mining at Colowyo. A short segment of Jubb Creek passes through the northwest corner of the expanded permit area, but Jubb Creek is not within the affected area, is not hydrologically connected to the affected area, and will thus not be affected by mining at Colowyo. Proposed Decision and Findings of Compliance 4 May 2007 Permit Revision 02 Page 66