PERMFILE61538

• Permit No: C1980005A
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Doc Name: NPDES PERMIT
• Section_Exhibit Name: TAB 7 APPENDIX 7-5
• Media Type: D
• Archive: Yes

COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division
Rationale - Page 7. Permit No. CO-0000221.
VI. TERMS AND CONDITIONS OF PERMIT •
Table VI-4 -- Effluent Limits - 008
Parameter Limit Rationale
Flow, HGD Report a/ NA
TSS, mg/1 35/70 b/ New Source Performance Standards
Total Recoverable Iron, mg/1 6.0 d/ New Source Performance Standards
Total Recoverable Iron, mg/1 1.0 a/ Water Quality Standards
pH, s.u. 6.5-9.0 c/ Water Quality Standards
Oil and Grease, mg/1 10 d/ State Effluent Regulations
Total Dissolved Solids, mg/1 Report d/ Salinity Regulations
Whole Eff. Toxicity, Ac ute Report See Discussion, VI.A.S
whole Eff. Toxicity, Ch ronic Report See Discussion, VI.A.S
Table VI-5 -- Effluent Limits - 009, 010
Parameter Limit Rationale
Flow, MGD Report a/ NA
T55, mg/1 35/70 b/ New Source Performance Standards
Total Iron, mg/1 3.0/6.0 b/ New Source Performance Standards
pH, s.u. 6.5-9.0 c/ Water Quality Standards
Oil and Grease, mg/1 1C d/ State Effluent Regulations
Settleable Solids, ml/1 ~0.5 e/ Eff. Limits for Precip. Even!
Total Dissolved Solids, mg/1 Report d/ Salinity Reaulat ions
a/ 30 Day Average
b/ 30 Day Average/Daily maximum
c/ Minimum-Maximum
d/ Daily Maximum
e/ Effective during periods of precipitation less than or equal to the 10-year, 24-hour
precipitation event for this facility, subject to burden of proof requirements as
described in permit.
f/ The acute toxicity limit is exceeded if (1) a statistically significant difference in
mortality (at the 95~ confidence level) is observed for either species between the
control and the identified IWC, or (2) a species mortality in any dilution of effluent
(including 1008 effluent) exceeds 508.
1. Water Ouality Standard Based Effluent Limitations:
a) pH: For pH, the limits are set directly from stream standards.
b) Iron: Amass balance equation is usually used to determine the effluent
concentrations for those parameters whose limitations are based on the
Water Quality Standards (WQS). However, the mass balance equation
relies on a low flow for the receiving waters in the calculation. Since
discharge is expected from this facility only in the event of a
precipitation event, there is insufficient data to use a mass balance
equation. Therefore, any applicable Water Quality Standards (WQS) a~
applied directly to the effluent. For this facility, discharge poin
004 and 008 discharge to a stream with WQS for Iron, and so at these two
points the WQS for Total Recoverable Iron of 1.0 mg/1 ie applied, ae a
30 day average. The daily maximum limit for Iron is based on BAT.