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Water Quality Control Division <br /> Addendum to Rationale <br /> Permit No. : CO-0000396 <br /> • Page 2 <br /> III. OUTFALLS 001 THROUGH 018: <br /> The Environmental Protection Agency recently promulgated Best Available <br /> Technology Economically Achievable (BAT) guidelines. As a result, <br /> precipitation-related limitations now exist for discharges from surface <br /> areas. <br /> This new regulation will not affect outfalls #002, 003, 004, or 005 <br /> because they discharge directly from underground mines (settling is <br /> provided by sumps within the mines) . The existing limitations for these <br /> four outfalls will remain unchanged (this applies to #019 also) . <br /> However, outfalls #001, 006, 007, 008, 009, 010, 011, 012, 013, 014, 015, <br /> 016, 017, and 018 are affected by the new regulation. <br /> This amendment will change the effluent limitations for these fourteen <br /> outfalls to conform with the BAT guidelines. EPA requires that all <br /> facilities achieve compliance with BAT by July 1, 1984. It is Division <br /> policy to incorporate BAT as permits are renewed or reopened for other <br /> reasons. Therefore these changes will be made in this permit now in <br /> order to meet the statutory deadline. <br /> • Under the new BAT regulations, up to three different sets of limitations <br /> can apply to a discharge point depending on meteorological conditions. <br /> During dry weather (periods of no precipitation) one set of limits is <br /> applicable. During wet weather (periods of precipitation less than the <br /> 10 year - 24 hour event) another set of limits may be applicable, at the <br /> option of the permittee. Finally for precipitation events in excess of <br /> the 10 year - 24 hour event only pH and oil and grease limits apply. <br /> However, the burden of proof for the occurrence of such an event rests <br /> with the permittee. <br /> Dry weather limitations are shown in Table 2 below. <br /> Table 2 <br /> Parameter Limitation <br /> Flow (MGD) (Monitor) <br /> Total Suspended Solids (mg/1) 35/70 <br /> Total Iron (mg/1) 3.5/7.0 <br /> Oil and Grease (mg/1) 10.0 <br /> pH (s.u.) 6.5/9.0 <br /> Salinity (Monitor) <br /> Wet weather limitations are applicable to discharges during periods of <br /> . precipitation. <br />