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<br /> <br />• potential pollutants. Given this situation, it may be difficult to determine whether any <br />changes to water quality between the existing upstream and new downstream stauon are <br />solely the result of mining-related impacts or if they reflect other factors. <br />Oxbow proposes to maintain and continue sampling the existing downstream station NF-2 <br />as a water quality reference point in order to provide some basis for differentiating between <br />mining-related and ocher water quality effects. Monitoring of NF-2 may be discontinued in <br />the future if warranted. The monitoring discussion in Section 2.05.6 has been revised to <br />reflect these changes. Please see accompanying revisions. <br />2.05.6(6) Subsidence Survey, Subsidence Monitoring and Subsidence Control Plan <br />66. On page x of the TR 291ntroduction, the applicant states: <br />Potential environmental impacts associated with ongoing mining operations and the <br />phased mine expansion activities include:...... " <br />2J Indirect surface disturbance due to mining-related ground subsidence. Given the depth of <br />mining, surface subsidence effects are negligible and have not nor are they expected to <br />adversely impact any renewable resources." <br />Further, on revised page 2.05-46, the applicant states that the implementation of longwall mining <br />will increase coal recovery factors form approximately 50% to as high as 75% overall. <br />• However, the application presents only vague generalizations implying that the character and <br />magnitude of subsidence will not change signifcantly. The applicant will have to provide <br />more plan specific projections of subsidence anticipated to result from the implementation of <br />longwall mining, as depicted on Drawing No. 5-0078. Will the magnitude of maximum <br />subsidence change? Will the timing of subsidence occurrence change? :Yfost importantly, will <br />the subsidence symptoms expressed at the surface, including ground surface cracking, <br />hydrology implications, or landslide rejuvenation be expected to change? <br />7Tie applicant does commit to the continuation of visual inspection for any significant variance <br />form previous subsidence projects. " However, the applicant should be more specif c about the <br />style and frequenry of visual inspections and reports to be completed. <br />Response: Agapito & Associates is presently completing a preliminary subsidence <br />evaluation based on Oxbow's proposed longwall mining plans and existing site geologic <br />information. The purpose of this evaluation is to determine the extent (angle of draw) of <br />anticipated mining-related ground subsidence and to assess the potential effects of <br />subsidence relative to both overlying mine workings and surface topography and features. <br />On receipt, the preliminary subsidence evaluation report will be submitted to the DMG for <br />review and insertion as Appendix J-1, Sanborn Creek Mine -Preliminary Longwall <br />Subsidence Evaluation. Appropriate summary statements and references have been added <br />to Section 2.05.6. <br />The subsidence monitoring measures outlined for the Sanborn Creek Mine (refer to page <br />• 2.05-60) remain applicable for the proposed longwall mining operations. Please see <br />accompanying revisions. <br />