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COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENVIRONMENT, Water Quality Control Division Rationale -Page 1 Q Permit No. CO-0032638 observed toxicity is due to organism lethality. Only exceedance of the limitation specified in Part LA.1. will trigger the requirement for conducting the automatic compliance schedule ident~ed in Part LA.4. of the permid. Prior to and after the limitation becomes effective, if the toxicity is due to differences in the growth of the fathead minnows or the reproduction of the Cerfodaphnia, no immediate action on the part of the permittee 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.4 of the permit carefully. . The permit outlines the test requirements and the required follow-up actions the permittee must take to resolve a toxicity incident. The permittee should read, along with the documents listed in Part LA.4 of the permit, the Colorado Water puality Control Division Biomonitorfn¢ Guidance Document dated July I, 1993. This document outlines [he criteria used by the Division in such areas as granting relieffrom WET testing modifying test methods and changing test species. The permittee should be aware that some ofthe conditions outlined above may be subject to change if the facility experiences a change in discharge, as outlined In Part ILA.2. of the permit Such changes shall be reported to the Dn~fsion Immediately. 3. Stormwater: Stormwater from active or inactive cots[ mining operations that has been contaminated by contact with any overburden, raw material, intermediate products, finished products, byproducts or waste products located on the site of such operations is required to be covered by a Colorado Discharge Permit System (CDPS) permit in order to be discharged to State waters. This coverage must 6e obtained under a CDPS Stormwater Discharge Permit. Stormwater permitting issues for this facility will be handled separately by the Division's Stormwater Unit. 4. Economic Reasonableness Evaluation: Section 25-8-503(8f of the revised (June /985) Colorado Water Oualiry Control Act required the Division to "determine whether or not any or all of the 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 set forth in sections 25-8-I92 and 25-8-104." The Colorado Discharge Permit System Regulations, Regulation No. 6/, further define this requirement under 6/. l l and state: "Where economic, environmental, public health and energy impacts to the public and affected persons have been considered in the classifications and standards setting process, permits written to meet the standards may be presumed to have taken into consideration economic factors unless: a. Anew permit is issued where the discharge was not in existence at the time of the classification and standards rulemaking, or b. In the case of a continuing discharge, additional information or factors have emerged that were no[ anticipated or considered at the time of the classification and standards rulemaking." The evaluation for this permit shows that the Water Quality Control Commission, during their proceedings to adopt the Classificanbns and Numen'c Standards for Upper Colorado River Basin and North Platte River (Planning Region 12), considered economic reasonableness. Furthermore, this is not a new discharger and no new information has been presented regarding the class cations and standards. Therefore, the water quality standard-based effluent limitations of this permit are determined to be reasonably related to the economic, environmental, public health and energy impacts to zhe public and affected persons and are in furtherance ofthe policies set forth in Sections 25-8-102 and 104. Ifthe permittee disagrees with this finding, pursuant to 61.11(b)(ii) ofthe Colorado Discharge Permit System Regulations the permittee should submit all pertinent informatron to the Division during the public notice pertbd. B. Monitoring 1. Effluent Monitoring: Effluent monitoring will be required as shown in Tables VI-8 through V/-I ]. Refer to the permit for locations of monitoring points.