2009-03-06_PERMIT FILE - C1981012A (6)

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COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENVIRONMENT, Water Quality Control Division Rationale -Page 27, Permit No. CO-0000906 which increased slightly. All other parameters for which permit imitations may be based on WQBELs are included in the permit as report only to collect data for future reasonable potential analyses. the 250 flow Note that based on historic Na data, the nity limay mit that is obtainable based on the h ?toric ata. tAa the perm?tteemcan control the However, the 900 gpm flow tier has a sodium rate of discharge during th pump down of the mine, the flow rate can be adjusted to meet the Na limit and thus the limitation is imposed immediately. Comment 4: Based on historical data, mine inflow rates average 150 to 200 gpm. Once the mine pools are pumped out, discharge rates should return to this level. Response 4: The 200 gpm rate corresponds to 0.29 mgd or 0.45 cfs. This will have a significant effect on the limitations for all nt an Response parameters based water quality sed on a tiered discharge rate, which will incorporate limitationslbased onea 200 gpm flow 6 standards or below, the permit is s being set up p b rate. Comment 5: Operation of the coal preparation plant requires make-up water and NECC has sufficient water rights to fulfill operational requirements of the_facility. The plant is scheduled to use mine water as make-up water for plant operation, diverting Purgatoire River water only when there is insufficient mine water to satisfy plant requirements. It is projected that during normal operation, Pond 001 will become a water storage pond with no discharge. Response 5: If/when Pond I becomes no discharge, and coverage will no longer be needed for this Outfall, the permit can be amended to remove Outfall 001. Alternately, the permittee may elect to keep this outfall covered in the permit in case discharge is needed in the future. Note that unless the pond is lined, this would be considered a discharge to groundwater and being mine water, this would likely fall under the jurisdiction of the Division of Reclamation Mining and Safety. Comment 6: The draft permit limitation for sodium (Na) is 142 mg/l based on a discharge of 6000 gpm (8.6 mgd) and the mass balance calculation using EC, SAR and the most sensitive crop of corn silage. Very little, if any, corn is grown in the Purgatoire Valley and NECC would request that alfalfa be used as the most sensitive crop. Also, since the limitation is based on the assimilative capacity of the Purgatoire River, a multi-tiered limit is requested based on the expected discharge rates from Pond 1 (discharge rates and potential limitations given). Response 6: Although alfalfa is the dominant crop, the Division must include all crops grown in the area in its consideration of the appropriate standards. According to information provided by the Farm Service Agency, irrigated water from the Purgatoire wheat and as the limiting o. River in this area is primarily sensitive crop lfwasadecrops, but termined totbte? corn (silage), it will remain also barley crops. As the most The permittee requested 5 different tiered levels of discharge for the Na and EC limitations. Division procedure is to include no more than 3 tiers within a given permit. The permit has been altered to provide these 3 tiers, which affects the limitations for Na and EC, and these tiers have been included as Outfalls 001A, 0018, 001 C, 009A, 009E and 009C. The tiers have been established at the maximum flow rate of 2500 gpm, for pumping out the mine (Outfalls 001A and 009A), 900 gpm as an intermediate flow rate (Outfalls 001B and 009B) and 200 gpm based on historic flows (Outfalls 001 C and 009C). Based on the 3r`r tier flow rate (200 gpm), the facility will not be exempt from a mixing zone study based on extreme flow ratios, and therefore a compliance schedule to perfrom a mixing zone study has been added to the permit. Andrew Neuhart August 27, 2008 0