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COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division <br /> Rationale - Page 2. Permit No. CO-0000396 <br /> APPLICABLE RULES & REGULATIONS: (Continued) <br /> Table 1 shows a comparison of applicable limitations: <br /> Table 1 <br /> Parameter SES WQS BPT BAT <br /> PH, s.u. 6.0 - 9.0 6.5 - 9.0 6.0 - 9.0 N/A <br /> Oil and Grease, mg/1 10 N/A N/A N/A <br /> Total Suspended Solids, mg/l 30/45 N/A 35/70 N/A <br /> Total Recoverable Iron, mg/1 N/A 1.0 3.5/7.0 3.5/7.0 <br /> Settleable Solids, ml/1 N/A N/A N/A 0.5 <br /> EFFLUENT LIMITATIONS, RATIONALE AND MONITORING FREQUENCIES: <br /> As discussed previously, WQS based iron limitations apply to this outfall. The <br /> Federal Effluent Guidelines offer relief from BPT and BAT limitations for TSS <br /> and total iron when discharges are caused by precipitation, but this does not <br /> apply to WQS based limitations, which normally apply at all times. <br /> WQS-based limitations can be exempted for discharges caused by precipitation <br /> greater than the 10-year, 24-hour event, in this specific case because such <br /> discharges would contain a greater proportion of surface runoff than mine <br /> water. Additionally, discharge would occur during periods when the receiving <br /> stream volume is greater than the 7-day, 10-year low flow. Table 2 below shows <br /> limitations chosen and their rationale: <br /> Table 2 <br /> Monitoring <br /> Parameter Limitation Rationale Frequency <br /> pH, s.u. 6.5 - 9.0 WQS Weekly <br /> Oil and Grease, mg/l 10 SES Weekly <br /> Total Suspended Solids, mg/l 1/ 35/70 4/ BPT Monthly <br /> Total Recoverable Iron, mg/1 2/ 1.0/2.0 4/ WQS Monthly <br /> Settleable solids, ml/1 3/ 0.5 BAT Monthly <br /> l/ The permittee may be exempted from compliance with this parameter when <br /> discharge is caused by precipitation (subject to burden of proof <br /> requirements). <br /> 2/ This parameter applies to discharge not caused by precipitation and <br /> discharges caused by precipitation less than or equal to the 10-year, <br /> 24-hour event. <br /> 3/ The permittee may comply with limitations for this parameter instead of <br /> TSS when discharge is caused by precipitation (subject to burden of proof <br /> requirements) . <br /> 4/ 30-day average/daily maximum limitations respectively. <br />