2019-01-17_REVISION - C1982056 - Laserfiche WebLink

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submission 23. The proposed passive water treatment system design submitted to be included in Exhibit 49EE indicates that the target TDS removal goal is not achievable with a constructed wetland system that includes the 6MN Reservoir as a final polishing pond even with the maximum and minimum expected flows of 375 and 75 gpm. Proposed revised page 2.05-153 indicates that the passive water treatment system will reduce TDS with associated reductions in EC and that discharge from the 6MN reservoir will be managed to keep EC levels below downstream material damage thresholds. Please explain in detail how the discharge will be managed to keep EC levels below the material damage threshold as the design appears to indicate that this will not be possible? Text relative to EC is still present without explanation, even though this system is not proposing to discharge please explain in detail how EC will be managed. This paragraph also quotes the reduction of iron as 21% but the design report states 20%. Please verify the accuracy of this data. Response: The referenced discussion of hydrologic impacts has been reviewed and revised to reflect that discharge to Fish Creek is not planned and to update the projected concentration levels after treatment. TDS limits are generally based on practical limitations for livestock watering use. Accepted livestock watering thresholds (EPA and CSU Extension Service) show TDS levels of up to 5,000 mg/l are "Satisfactory for livestock...", and up to 7,000 mg/l "Can be used with reasonable safety for dairy and beef cattle, for sheep, swine, and horses." Projected TDS concentrations after treatment are on the order of 3,500 to 4,800 mg/l, dependent on system flow. While discharge to Fish Creek is not currently planned, the projected constituent concentrations after treatment would generally meet applicable effluent standards. Copies of the revised text and supporting materials accompany these responses for replacement in the PAP. 24. The flow rate and water quality of Trout Creek below Fish Creek can be affected by discharges at site 109, 115 and proposed future discharges from the 6MN Reservoir. TC proposes to revise page 2.05-155 to indicate that Site 109 has not discharged in some time; however this site has not been decommissioned to the Division's knowledge and could potentially be utilized. Pages 2.05- 154 through 156 discusses detailed plan to adjust the flows at either site 109 and 115 in order to meet the applicable Sulfate standard on Trout Creek. Based on a review of Exhibit 51 and the passive water design, the sulfate level discharged from the 6MN Reservoir after treatment could potentially have sulfate levels that could exceed the sulfate level discharged at Site 115. There is no discussion about how TC will coordinate the discharge at sites 109 (potentially), 115 and the 6A41V reservoir to comply with the sulfate standard. Please either explain how this will be done or provide justification why it is not necessary. If no water supply uses are in place along lower Trout Creek below the confluence of Fish Creek please verify this. No longer applicable to this revision as discharge is not being proposed. 25. When the 6MN Reservoir is discharging please explain why increased monitoring along Trout Creek is not necessary as it is when Site 115 and/or site 109 is discharging? No longer applicable to this revision as discharge is not beingproposed. Items from 2nd Adequacy Review Letter CPW's letter identified three recommendations. The first recommendation pertains to water discharge that may impact Fish Creek that this project is specifically designed to address. Given this, the Division does not have any additional requests based on this comment. The second recommendation is for Twentymile Coal, LLC. (TC) to ensure the treatment ponds do not trap wildlife and prohibit wildlife from exiting each pond. The third recommendation requests that TC preclude the use by livestock in all wetland areas that are created as a result of this project. Given the second two recommendations, please address the following items: