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JO DEPARTMENT OF PUBLIC HEALTHAND ENVIRONMENT, Water Quality Control Division - Page 7, Permit No. CO-0034142 The IWC for Phis permit is 23. 8%, which represents a wastewater concentration of 23.8% e~fuent to 76.2% receiving ~ dream. Thus, chronic WET testing is applicable for this facility. 3) Because of the potential for toxicity in these discharges, as demonstrated by the existence ofineials in the discharges, as well as WETmonitoring resulu at other coal mining facilities, the Division believes there is reasonablepotentialtor the discharge to interfere with attainment of applicable water quality classifications or standards. Because of this condirion, the chronic limitation has been incorporated into the permit and becomes e,~"ective immediately. The permittee u required ro conduct routine monitoring. The resulu of the testing are So be reported on Division approved forms. The • permittee will be required to conduct a staristieal derivation on the data, looking for any statistically signfcant difference in toxicity between the control and the eJjluenr concentrations. This se[ of calculations will look at the full range of toxicity (lethality, growth and reproduction). !f a level of chronic toxicity occurs, such [hat there is a statistically significant difference in the lethality (at the 95% confidence level) between the control anti any effluent - concentration less than or equal to the Instream Waste Concentrafion QWC), the permittee will be required io follow the automatic compliance schedule identified in Part I.B of the permit, if the observed toxicity ir,due to organism lethality. Only exceedance of the limitation specfied in Part LA.3. will trigger the requirement for conducting the automati2 compliance schedule ident fled in Part I.B. of the permit. If the toxicity is due to di,{Jerences in the growth of the fathead minnows or the reproduction of the Ceriodaphnin, no immediate acrion on the part ojthe permittee will be required. However, this incident, along with other WET data, will be evaluated by the Division and may joint the basis for reopening the permit and including additional WET limits or other reguiremenu. 4) Generallnformation: ThepermitteeshouldreadtheWETrestingsectionsunderPartl.A.4.oflhepermitcarefully. The permit outlines the test reguiremenu and the required follow-up actions the permittee must rake to resolve a toxicity incident. Thepermitree shouldread, along with the documenu.listed in Part I,A.4.a. of the permit, the Colorado Water OuoliN Control Division BiomonitorinR Guidance Document. dated duly I, 1993. This document outlines the criteria used by theDivision in such areas asgran~ing relieffrbm WET testing, mod~ing test methods andchanging resrspeeies. The permittee should be aware that some of the conditions outlined above may be subject [o change if [he facility experiences 6 change in discharge, as outlined in Part ILA:Z. of [he permit. Such changes shall be; reported to the Division immediately: 4. Stormwater Evaluation: Stormwaterfrom active or inactive coal mining operations that has been contaminated by contact with any overburden, raw material, intermediate produce, finished produce, byproducu or wasteproducu located on the site ofsuch operations is required to be covered by a Colorado Discharge Permit System (CDPS) permit in order [0 6e discharged to State ivarers. This coverage maybe obtained under either a CDPS Industrial Wastewater Discharge Permit or a CDPS Stormwaler Discharge Permit. For facilities .that have individual CDPS permiu for discharge of process water, any applicable stormwaterprovisions can then 6e included in individual CDPSpermiu. The individual p¢irtiit for discharge of process water for the Eagle Mine, CDPS permit (No. CO-0034142), contains stormwater provisions that differ from the provisions of the process water portion, and are laid out in Part I.D.? of the permit. Under the terms of the combined individual permit (CO-G034142), RAG Empire Eagle Mine will be authorized fo discharge stormwater associated with industrial activity into waters of the State of Colorado.. The terms and conditions of this permit, as related to stormwarer discharges, include: a. Segregation ofStormwarer Discharges: All discharges covered by the stormwaterportion of this permit shall be composed entirely ofstormwater (except as discussed at Part LD.1.d.2 of the permit). Stormwater, whiek mixes with process water, is subject to process water controls. Discharges from sources other Than stormwater must be addressed by theprocess water controls in this CCPSpermit. b. S[ormwater Management Plans (SWMPs): The purpose of a SH'bIP is to identify possible pollutant sources tc stormwater and to set out best managementpraerices that, when implemented, will reduce or eliminate anypossiblr water quality impacu. A SWMP must be maintained for the Eagle Mine in accordance with good engineering .practices. (A registered engineer need not complete ilieplan.) The Dgvision has a guidance document available a preparing a SWMP. Theplan identifies potential sources ofpollurion (including sediment), which may reasonably be expected [o offer the quality of stormwa[er discharges associated with mining or remediarion operations. In addition, the plc describes practices which will be used to reduce the pollutanu in stormwater discharges from she mining c remediarion operation, and to assure compliance with the terms and conditions of this permit. Facilities mu implement the provisions of their SWMP as a condirion of this permit.