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COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division Rationale; Amendment No. 2 -Page 2 Permit No. CO-0038776 V. DJSCUSS/ON OF AMENDMENT: (Continued) From the MSDS sheets (which are included in the permit Jile), toxicity data jot aquatic life shows [hnt most of the chemicals that are used to this jaciliry are not considered very toxic to aquatic life. For example, the aquatic toxicity data from the MSDS sheets was ar follows: Nalco 7883 = 360 ppm jot the 96 hour static acute LC50 to Rainbow Trout, and 420 ppm jar the 96 hour static acute LC50 to Bluegill Sunfish; Nalco 7888 = 300 ppm jot the 96 hour static acute LC50 to Rainbow TY~out ("slightly toxic"), 360 ppm jot the 96 hour static acute LC50 to Fathead Minnow ('slightly toxic J, and greater than 1000 ppm for the 48 hour static acute LCSO to Daohnia g ('essentially non-toxic"); Zyme- Flow = 71 mg/1 jot the 96 hour static acute LC50 to both the Fathead Minnow and the Stickleback Mittrtow. However, the tonicity data for Nalco 8852 indicates that this chemical ins very tonic to aquatic life: Nalco 8852 = 0.47 ppm jot the 96 hour static acute LC50 to Rainbow Trout, and 0.90 ppm jot the 96 hour static acute LC50 to Bluegill Sunfish. The Division has previously indicated to the perrtdttee that this product is considerably more toxic to aquatic life, and tha[ other less [azic chemicals should be used instead of Nalco 8852. Since a spill of the Nalco 8852 product could result in fish kills instream, the permittee should be very cautious in the use and storage ojrhis product. The permittee has indicated that they are aware ojthese concerns, and this is the primary reason why other chemicals have been selected jot treatment at this facility. The chemicals (Nalco 7883 Liquid, Nalco 7888 Clarification Aid, and United 657 Zyme-Flow) used as settling agents at this facility are typically used in al! six sedimentation ponds on site. A site map wns submitted with the October 14, 19931etter which shows the locations where the potential flocculation stations could be set up or are added at a point prior to the senling ponds. Typically, the cherrdcals are added via a drip barrel in the ditch above sediment traps which are prior to the senling ponds. Chemical addition is designed so that the solids will senle out in the sediment traps rather than in the ponds. No flocculation points occur at or near the discharge points. The dosage requirements vary depending on the total flow, the overall effects desired, and total percent solids in the water to be treated. 7ypicn(ly, the produce are applied for thin slurry thickening and clarification, spec flca(ly ro settle Lora! suspended solids prior to discharge. The dosages of the applications range from 0, l to 25.0 ppm, depending on the produce in use. According ro the perm(ltee, the concentrations of the product expected to be in the ponds would be minimal or undetectable due to the (urge vo(urne of water contained in the ponds. As indicated in the letter dated October 14, 1993, two of the existing sediment ponds will be mad fled (one of which will be reloca[ed), but the dtscharge points will remain in their currently permi[ted locations. These ponds are MB-3 (outjall OOSJ and MB-2(R) (oujal[ 004J. The permittee also indicated that recently a DMG technical revision has been approved for a project involving patois MB- 6 atui MB-2(RJ. The pond MB-6 (outfnl[ OIOJ will eventually be taken out of service and replaced by pond MB-2(RJ, possibly as early as November 1993. However, autfall 010 will not be deleted from the perttut until a !ales time when the facility changes have been made, since this pond presently exists and could potentially discharge. Thus, deletion of outjall 010 will be handled as n later nmendrttettt, after ate perntinee has notified the Division of these final changes. The pernuttee also indicated that the mine 'process" thnt has changed recently Ls the installation oj(ongsvall mining equipment in the mine. A correction was mule on page /k of the permit under Part LB. 10 to spech~ that chronic WET testing it only applicable for otttfnlls 011 and 012, ns s,~as previously indicated on page 14 of the renewal rntionnle. Since changes were made to the permit, mui there is n change of chemicals that nre used nt the facility, public notice requirements nre applicable jot this amendment. Dan Nalrner October 20. 1993