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08i31i00 THII 13:32 NA.i permit, thue are no numeric limitations proposed for Outfall 002, except for provisions expressed in TR-26 and TR-28 (with Tft-28 not yet approved.) Since these documents were simply incorporated by reference into the permit, EPA does not have sufficient information from the permit rationale to conclude that the conditions of'[R-26 and the yet to be approved TR-28 will ensure protection of water quality standards in the Rito Scco. EPA suggests that the Division evaluate the conditions of TR-26 and TR: 28, that will ensure compliance with water quality standards, and inwrporate numeric limitations and appropriate monitoring into the permit and rationale for the permit. One possible alternative approach to ensure water quality standards aze rnet through discharges from Outfall 002 would be to require installation of a monitoring well which intercepts a representative flow of the seepage which directly enters the Rito Seco, and impose limitations at that location along with monitoring conditions to ensure compliance tan be demonstrated. To demonstrate representativeness of the monitonng and compGana location, the Division should cleazly de5ne the [ateraland vertical extent of the seepage front and fully explain where all the seepage sre (is) located wiUt respect to the geologic formations at the site, i.c, in the alluvium, etc." EPA believes the Division has defined the seepage front (Outfa11002) as requested, however, the extent of the seepage front encompasses a much wider vertical anc'. lateral extent than EPA envisioned in review ofthe previous draft permit and discussions with CDPIIE and Aattlc Mountain Resources, Inc, Because of the complex hydrogeologic conditions of the area, EPA does not believe that water Level monitorirte in one monitoring well (BF-4) and its relation to the proposed elevation "trigger" of 8583 ft. amsl, is sufficient to demonstrate the presence or absence of a discharge to the Rito Seco along such a large seepage front. In addition, the basis for the proposed elevation "trigger" is not explained in the rationale for the draF permit. If you have any questions concerning EPA's general comments or specific technical issues, please contact Bruce Kent of the Pelmits Team directly at (303)312-6133. mcerely, 1 Debra H. Thomas, Permits Team header Water Program Office Of Partnerships and Regulatory Assitance cc~ Susan Nachtrieb, CDPHE Don Halmer, CDPI~ Dan Robertson, Operations Manager Batrle Mountain Resources, Inc.