1987-12-01_PERMIT FILE - C1981017 (278)

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Water Quality Control Division Addendum to Rationale Permit No. : CO-0000396 Page 3 • III. OUTFALLS 001 THROUGH 018: (Continued) For discharges caused by precipitation less than or equal to the facility's 10-year, 24-hour event, the permittee has an option. A settleable solids limit of 0.5 ml/l may be met instead of the total suspended solids limit of 35/70. Additionally, the total iron limitation does not apply during precipitation-caused discharges. Precipitation-related limits are shown in Table 3 below (for events less than or equal to the 10-year, 24-hour event). Table 3 Parameter Limitation Flow (MGD) (Monitor) Oil and Grease (mg/1) 10.0 pH (s.u. ) 6.5/9.0 Salinity (Monitor) Settleable Solids (ml/1) 1/ 0.5 Total Suspended Solids (mg/1) 1/ 35/70 1/ The permittee may opt to meet the settleable solids limitation in lieu • of the total suspended solids limitation. For discharges greater than the 10-year, 24-hour event, the permittee has a second option. The settleable solids and/or TSS limit does not apply to events greater than the 10-year, 24-hour event. Depending on facility geography, it may be easy to sample a discharge point but difficult to read a rain gauge. Therefore, the permittee is given the option of waiving documentation for storm exemption, thereby agreeing to comply with the settleable solids and/or TSS limit. Table 4 below shows limitations which, at a minimum, apply to all discharges caused by precipitation greater than the 10-year, 24-hour event. Table 4 Parameter Limitation Flow (MGD) (Monitor) Oil and Grease (mg/1) 10.0 pH (s.u.) 6.5/9.0 Salinity (Monitor) It shall be the responsibility of the permittee to demonstrate the applicability of any alternate effluent limitation. Thus, the permittee must provide evidence that the alternate limitations are applicable. • This evidence shall be in the form of written documentation attached to the applicable discharge monitoring report.