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• Initially, the reported laboratory pH values which were below the 6.5 s. u. tugger level were 5.8 (11-19991, 6.2 (11-99), 6.3 (12-1999). and 5.9 s. u. (1- 2000). This occurred dunng and immediately following the initial start up period (October 1999) for she treatment system. All field pH values that have been reported have been greater than 6.5 s.u. Outside laboratory analysis tend to he less than the field measured pH. The two Feld measured pH values for January 2000 were 6.98 and 7.3 s.u. Also, held pH data at the downstream stations RS-2 and RS-5 were well in compliance with the pH standard (RS-2 values were 7.95 s.u. to 8.5 s.u.during 10-1999 through 1-2000: and RS-5 pH values ranged from B.OS to 8.4 s.u. during 10-1999 through 1-2000). Since the time just after the initial scan up period (or the Irea[ment system (November 1999 through January ?000), all pH values in the discharge have been in compliance with the pH trigger level range. A. Baffle Mountain Resources, /nc. (BMR/) Comments, May 1, 2000: These carunents and the Division's responses are given in sequential order beginning wilt [he permit and jolloxRng through to the rationale. /. Part 1 - EJJiuent Limitations -Discharge Point OOIa, OOIb, and OOIc a. There is no evidence provided by BMRI, or in the Division's records, that support the development and imposition of effluent limitations or monitoring requirements for three parameters. ~ Specifically, those are x•eak acid dissociable (WAD) cyanide, rnercurv and silver. Based ors the history of the jaciliry, and the data in the records, there is no reasonable potential to discharge any of these constituents. Mercury is clearly discussed in the rationale. Additional discussion regarding cyanide and silver are included in this comment. These parameters should all be addressed in a similar fashion within the permit and rationale. 71Jat is, [hey shou/d be eliminated jrom the ejJluent limits list and from the monitoring and reporting requirements. /n the alternative, ijthe Division chooses to retain the monitoring and reporting requirements, then the parameters should be eliminated upon a 6-month demonstration period ajnon-detects. Cyanide is included ostensibly because it was part of the beneflciation process at the mine. However, the description of the project clearly identifies that the cyanide x~as used only in the mill process, which was designed to contain and route any upset conditions to the lined tailings jaciliry. Furthermore, at no time in the operational history of the BMR! San Luis Mine were any materials associated with the cyanide process ever returrsed to the West Pit. Therefore, there is no reasowble potential for cyanide to occur in any ajthe sources associated x2th this discharge permit. Similar to the discussion jot cyanide and mercury, silver has generally not been detected a! canflnned values greater than the analyrical detection limit in the contributing wastewater sources, the treated discharge, or instream monitoring samples. Response: The Division has reevaluated the existing data jar Jltese three parameters. For both mercury and cyanide, no detectable levels have occurred in the wastewater sources, discharge, or in the Rilo Seco in the vicinity immediately above or below the backf~lled West Pit discharge location. The Division does concur that there is no reasonable potential jar these m~o parameters to occur. Thus, mercury has been added to the list of sis monthly samples to be monitored in Part /.B.3. ojthe permit. The Division is requiring semiannual monitoring jar WAD Cyanide jrom the 00! ouffalls jar a tx~o year period, along with submission of instreatn data for WAD Cyanide located downstream of the discharge (RS-2) to verify that no cyanide continues to be detected. For silver, since detectable concentrations have been previously found in the wastewater sources at levels above the proposed chronic permit limitation, the same limits and monitoring will apply jar silver.