PERMFILE139367

• Permit No: C1981013
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: Exhibit 22 NPDES Permit Part 2
• Media Type: D
• Archive: No

COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division
Rationale - Page 6. Permit No. CO-0033367
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DISCUSSION: (Cont.)
C. Internal Monitoring
Due to the elimination of discharge point 001, monitoring for two domestic
wastewater parameters, BOD and TSS, will be required at the WWTF influent
and effluent, in addition to the combined effluent, to determine if the
WWTF is operating properly (in compliance with state effluent regulations
which apply to domestic wastewater treatment plants). (The permittee has
been performing this monitoring, but the requirement has not been spelled
out clearly in the permit.) This internal monitoring point shall be
designated as discharge point 045. For TSS and BOD, monitoring only is
required at 045; no numeric limits will apply at this time. However, the
numeric flow limit will apply at 045.

D. Total Residual Chlorine (TRC)
The TRC limit for 004 is based on the WQS for the Purgatoire. An instream
limit of 0.003 mg/1 is allowed. Due to the estimated acute low flow for
the river being 0.646 MGD, a mass balance equation Ss applied and a limit
of 0.035 mg/1 calculated. (Since this limit is below the approved
detection limit of 0.05 mg/1, the permittee shall report "less than the
detection limit,", as appropriate.) This replaces the limit in the
original permit of 0.5 mg/1, which was based oa the SES. This change is
due to the increased flow limit for 004, the change in location for the
WWTF discharge (004 instead of 001), and the use of a different system of
low flows by the Division. TRC monitoring Sa required at 004 only, and
not at 045.
The new TRC limit is stricter than the previous limit; however, due to the
increased treatment provided by Pond 004, no problems are eapected in
meeting the limit.
E. Total Suspended Solids
The State Effluent Limitation Regulations dictate that where Federal
Effluent Guidelines saint they shall take precedence over SES. This is
the reason for selection of BPT-based TSS limitations for all of the
discharge points.

F. Fecal Coliform
Fecal coliform is a common contaminant in domestic wastewater, and is
therefore limited for 004. The limit for fecal coliform ie based on the
State Fecal Coliform Policy. An instream WQS limit of 2000 org/100 ml is
allowed. Due to the estimated low flow for the river being 1.62 MGD, a
mass balance equation results in a limit of 56,000 org/100 ml. Since this
is greater that the State Fecal Coliform Policy maximum of 6000/12000
org/100 ml, the stricter limit is used. (This limit therefore remains the
same as in the original permit.)