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~ STATE OF C~LORADO - Roy Romer, Governor Patti Shwayder, Acting Executive Dnector Dedicated to protecting and impror•ing she health and environment of the people of Colorado x300 Cherry Creek Dr. S. Denver, Colorado 80222-1530 Phone (3031 692-2000 Mazch 22, 1995 Laboratory Building a 210 E. 11th Avenue Denver, Colorado 80220-7716 i30J1691-4700 Mr. John E. Hardaway Manager, Environmental Affairs Cripple Creek and Victor Gold Mining Company P.O. Box 19! Victor. CO 80860 ~ epr0 4F', e cF • ~ . ~ ~ ~ ~~ r6 ~ Colondo Department of Public Hnlth and Environment Re: CDPS Permit No. CO-0024562 -Carlton Tunnel Flow Monitoring, Roosevelt Tunnel Permitting Dear Mr. Hardaway; The Water Quality Control Ditision has reviewed your nvo letters, both dated January l7, I995, which addressed issues raised by the Division regarding: l) the need for an etlluent flow monitoring dcvzce at the outfall from the settling ponds which treat [he flow from the Cazl[on Tunnel, and 2) the need to include the dischazge from the Roosevelt Tunnel in the permit [hat already is required for the Carlton Tttnnel. For the reasons listed below, vve have determined that the permit must be amended to include requtrements related to both of these issues. Carlton Tunnel Flow Monitontie In your letter of January 17. 1995, the most significant azglunent against the installation of an effluent flow monitoring device is the purported lack of space within which to locate such a dev~cc. This must be further documented, with consideration given to the possibility of constructing reconfigured outlet works and the use of devices that will satisfy the requirements of limited space. In order to avoid the installation of a new flow measurement device at the outlet from the treatment ponds. it will be necessary to conclusively demonstrate, through scientific analyses, that the e.isting flow measurement device is accurate to within 10% of the actual flow coming out of the ponds, even during dry weather conditions. Along with the addressing the issue of whether or not a new effluent flow measurement device is necessary, it may be necessary to reexamine the appropriate flow monitoring frequency, for either influent or effluent flows. Without more detailed data, showing the variability of the flow at the existing Flow station. the Division may require continuous monitoring at the existing influent monitoring location, as instantaneous monitoring is ordinarily only allowed where Flow variation is minimal -such as at the outlet of a pond treatment system. With respect to your concerns about maintaining homogeneity with historic records, i[ appears that the most important reason for maintaining homogeneity would be [o be able [o detect trends in the flowrate from the Ttuuiel. The analysis of trends m the flowrate from the Tunnel would be useful in the identification of the causes for such trends and the control oCTunnel Flowrates. Therefore, since measuring flows at the outlet from the ponds may mask such trends, the agree that it may be necessary for CC&V to continue to measure flow at the existing location. Still, the determination of permit effluent limits and the monitoring of compliance with those limits must be based upon the flow being discharged to the receiving stream. Therefore, it may be necessary to perform monitoring of both influent and ef3luent flows. The need for such monitoring and the specification of appropriate monitoring frequencies will depend upon the resWts of the analyses described above.