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• COLORADO DEPARTMENT OF HEALTH <br />Water Quality Control Division <br />Amendment to Rationale - Page 2 <br />Permit No: CO-0032638 <br />FACILITY DESCRIPTION: <br />Outfall 003 is the only outfall affected by this amendment. Outfall 003 <br />and corresponding sedimentation pond ~F003 serve an area in which active <br />mining no longer takes place. The last coal was removed from the area in <br />August, 1982. The pit has been backfilled and graded and except for a <br />small area, top soiled and revegetated. <br />APPLICABLE RULES AND REGULP.TIONS: <br />Federal BPT (Best Practicable Control Technology) and BAT (Best Available <br />Technology Currently Achievable) recently promulgated specify the <br />following effluent limitations for reclamation areas: <br />TABLE 1 <br />Parameter BPT BAT <br />• pH (s.u.) 6.0 to 9.0 N/A <br />Settleable solids (ml/1)* 0.5 0.5 <br />* This parameter does not apply to discharges caused by precipitation <br />greater than the 10-year, 24 hour event (or equivalent snowmelt <br />volume). <br />State Effluent Standards (SES) dictate the imposition of an Oil and Grease <br />limitation of 10.0 mg/1 for all discharges not otherwise limited. <br />Additionally, State Water Quality Standards (WQS) dictate a pH limitation <br />of 6.5 to 9.0 s.u. This supersedes the BPT limitation for pH shown in <br />Table 1. <br />Because discharge will be intermittent and will normally occur only during <br />precipitation events (periods when receiving water flows will be high) no <br />water quality standard-based effluent limitations are appropriate other <br />than pH. <br />EFFLCE'dT LIMITATIONS, RATIONALE AND h10NTTGRI`:C REQUIRE7(ENTS: <br />The proposed effluent limitations for outfall 11003 are shown in Table 2 <br />• below, as are the rationale for [heir choice and [he monitoring <br />frequencies. <br />