PERMFILE105530

• Permit No: C1982056
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: Exhibit 44 NPDES Permit No. CO-0042161
• Media Type: D
• Archive: No

COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENV/RONMENT, Water Quality Control Division
Rationale -Page 7, Permit No. CO-0042/61
• c) Water Quality-Based Limitations
Total Recoverable Iron: The previous permit had a TR iron limitation of 0.5 mg/f that was derived in
conformance with antidegradation regulations. This limitation remains effective under anribacksliding
provisions of state and federal regulations.
Total Ammonia: The permittee has been required to monitor jot total ammonia at outfall 001 for several
years, but limitations have not been previously calculated. Appendix A to this rationale shows calculations
and resulting limitations for total ammonia, based on latest data. A comparison with effluent
concentrations, as shown in Table IV-1, indicates that the limitations are lower than the efJluem
concentrations; thus, limitations are necessary to protect classified uses. The Division acknowledges that
these limitations are extremely low, thus a long period is provided to plan and make any necessary changes
ro meet these [imitations. !t is expected that the ammonia comes from the domestic wastewater treatment
facility. The permittee will likely need to make changes to that facility in order ro meet the new [imitations.
Since the levels are so [ow and treating to obtain compliance may be difficult, it may be necessary jot the
permirtee to evaluate whether the facility can be made into a nondischarging facility. However, the course
of action is solely ar the permittee's discretion. The Division is only concerned that the limitations are met
beginning on the date they become effective.
d) Sa[iniN Re1tularions: In conformance with the Colorado River Sa/iniN Standards and section 61.8(2)([) of
the Colorado Discharge Permit System Re,¢ulations, the permittee shall monitor for total dissolved solids on
a quarterly basis. Samples shall be taken ar outfal1001, the e,~luenr discharge point to stare waters.
Salinity requiremems are included in Part /.B.2. oJthe permit.
• e) Whole Ellluent Toxicity (WET) Testing: For outfal1001, chronic WET testing is required. (See Part /.A. of
the permit.)
1) Purpose of WET Testing: The Water Quality Control Division has established the use of WET testing as
a method for identifying and controlling toxic discharges from wastewater treatment facilities. WET
testing is being utilized as a means to ensure that there are no discharges of pollutants "in amorous,
concentrations or combinations which are harmful to the beneficial uses or toxic to humans, animals,
plants, or aquatic life" as required by Section 31.11 of the Basic Standards and Methodologies for
Surface Waters.
2) /nstream Waste Concemration (TWC): Where monitoring or limitations jot WET are deemed
appropriate by the Division, chronic instream dilution as represented by the chronic IWC is critical in
determining whether acute or chronic conditions shall apply. For those discharges where the chronic
IWC is greater than (>) 9.1 `%, chronic conditions apply, where the IiVC is less than or equal !o (s) 9.1
acute conditions apply. The chronic /WC is determined using the following equation:
1WC = [Facility Flow (FF)/(Stream Chronic Low Flow (annual) + FF)J X J00`9o
The flows and corresponding /WC for the appropriate discharge point are:
Discharge Point Chronic Zow Flow, Facility Design Flaw, IWC,,. (96);;: ~;. s -'
i 30E3, (efs) . (cfs) ., a , ,,_,,,a
• The IWCjor this permit is 100',x, which represents a wastewater concentration of 100 effluent to 0%
receiving stream. Thus, chronic WET testing is applicable for this facility.