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COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENVIRONMENT, Water Quality Corurol Division Amendment No. 5-Rationale. Page 6, Permit No. CO-0000132 If a level of chronic toxicity occurs, such that there is a statistically significant di, fference in the lethality (at the 95 % conftdence level) between the control and any effluent concentration less than or equal to the Instream Waste Concentration (IWC) and if the ICu < the IWC, the permittee will be required to follow the automatic compliance schedule identified in Pan I.A.S. (c) of the permit, iJthe observed toxicity is due to organism lethality. /f the toxicity is due to differences in the growth of the fathead minnows, no immediate action on the pan 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 permi[ and including additional WET limits or other requirements. 4) General Information: The permittee should read the WET testing sections under Pan I.A.S. of the permit carefully. The permit outlines the test requirements and the required follow-up actions the permittee must take ro resolve a toxicity incident. The permittee should read, along with the documents listed in Part I.A.S. (a) of the permit, the Colorado Water Otu:liN Control Division Biomonitoring Guidance Document dated July 1, 1993. This document outlines the criteria used by the Division in such areas as granting relief from WET testing, modifying test methods and changing test species. The permittee should be aware that some of the conditions outlined above may be subject to change if the facility experiences a change in discharge, as outlined in Part /I.A.2. of the permit. Such changes shall be reported to the Division immediately. B. Monitoring 1. Effluent Monitoring: Effluent monitoring will be required as shown in Table VI-3. Refer to the permit for the location of the monitoring point. Table VI-3 -Monitoring Requirements Parameter .: Measurement Frequency Sample Type Flow, MGD Weekly Total Suspended Solids, mg/P Momhly Totallron, mg/? Momhly Oil and Grease, mg/P Weekly pH, s. u. Weekly Total Dissolved Salids, mg/P Quarterly /nstantaneous or Continuous Grab Grab Visual a/ In-situ Grab a/ a/ IJa visible sheen is noted at any time, a grab sample shall be collected and analyzed for oil and grease. The results are to be reported on the DMR under parameter 03582. Additional Monitorinx: The permittee submitted copies of several analyses of wells in the vicinity and current mine water outfall number 011. However, there is no way to monitor the new outfal1015 at this time since discharge has yet to commence. The Division must review analytical results of speciftc parameters from the actual discharge before determining whether additional limitations and/or conditions are required. The permit will require that six grab samples be collected on a monthly basis beginning on commencement of the new discharge. The parameters are total recoverable arsenic, total recoverable cadmium, dissolved iron, and dissolved manganese. As soon as the results of all six analyses are available to the permittee, the results shall be tabulated in a letter and submitted to the Division. The predicted due date for submission of this compliance item is September 1. 2000. If sampling is delayed for reasons beyond the petmittee's control, such as a period of no discharge within the designated sampling period, the permittee shall notify the Division in writing, indicating the reason for the delay and the adjusted projected submission date.