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_ COLORADO DEPARTMENT OF PUBLIC HEALTHAND ENVIRONMENT, Water Quality Control Division Rationale -Page 6, Permit No. CO-0038342 Discharge Point Chronic Low Flow, Facility Design Flaw, ~,C (/) 30E3, (cjs) (cfs) 002 0 0.0077 100% The IWCfor this permit is 100%, which represents a wastewater concentration of 100% effluent to 0% receiving stream. iii. Chronic WET Monitotinr: Although coal mine drainage at some facilities has shown significant toxicity, this outfall has not shown significant toxicity in any recent test, so the permtttee will be required to conduct routine monitoring for chronic toxicity using Ceriodaphnia sp. and fathead minnows. The results of the testing are to be reported on Division approved forms. The permittee will be required to conduct two types of statistical derivations on the data, one looking for any statistically significant difference in toxicity between the control and the effluent concentrations and the second identifying the ICzs, should one exist Both sets of calculafions will look at the full range of toxicity (lethality, growth and reproduction). If a level of chronic toxicity occurs, such that there is a statistically signiftcant difference in the lethality (at the 95% confidence level) between the control and any effluent concentration less than or equal to the In-stream Waste Concentration (IWC) and if the ICzs < the IWC, the permittee will be required to follow the automatic compliance schedule identified in Part LA of the permit, if the observed toxicity is due to organism lethality. If the toxicity is due to differences in the growth of thefathead minnows or the reproduction of the Ceriodaphnia, no immediate action on the part of the permitee will be required. However, this incident, along with other WET data, will be evaluated by the Division and may form the basis for reopening the permit and including additional WET limits or other requirements. iv. General Information: The permittee should read the WET testing section of Part LA. of the permil carefully. The permit outlines the test requirements and the required follow-up actions the permitiee must take to resolve a toxicity incident. The permittee should read, along with the documents listed in Part LAf the permit, the Colorado Water Quality Control Division Biomonitorinr Guidance Document.dated July I, 1993. This document outlines the criteria used by the Division in such areas as granting relief from WET testing, mod~ing test methods and changing test species. The permittee should be aware that some of the conditions outlined above may be subject to change tf the facility experiences a change in discharge, as outlined in Part ILA.2. of the permit. Such changes shall be reported to the Division immediately. v. Outfall 001: Outfa11001 does rsot receive a significant volume of toxic or industrial wastes and, in accordance with Section 61.8(2)(b)(i)(B) of the Colorado Dtscharge Permit Svstem Regulations, Regulation No. 61, the discharge does not have the reasonable potential to cause, or measurably contribute to, an excursion above any narrative standards for water quality. Therefore, WET testing is not a requirement for this outfall. However, the Division reserves the right to reopen the permit to include WET testing, should facility conditions change or tf new information becomes available. 3. Stormwater: Stormwater dischazge permits are required for active and inactive coal mining facilities as covered under Standard Industrial Classification (SIC) Code 12. Division records indicate that Central Appalachia Mining, LLC has coverage for Stormwater discharges from the McClave Canyon Mine under a General Stormwater Discharge Permit, number COR-040098. Stormwater permitting issues for this mine will be handled separately by the Division's Stormwater Unit, although this permit may be reopened at a later date to incorporate Stormwater provisions, if deemed appropriate 4. Economic Reasonableness Evaluation: Section 25-8-503(8) of the revised (June 1985) Colorado Water puality Control Act required the Division to "determine whether or not any or all ojthe water quality standard based effluent limitations are reasonably related to the economic, environmental, public health and energy impacts to the public and affected persons, and are in furtherance of the policies setforth in sections 25-8-192 and 25-8-104." The Colorado Discharge Permit System Regulattons, Regulation No. 61, further define this requirement under 61.1 ]and state: "Where economic, environmental, public health and energy impacu to the public and affected persons have been considered in the classifications and standards settingprocess, permits written to meet the standards may be presumed to have taken into consideration economic factors unless: bast Revised: 6/9/2004