HYDRO23023

• Permit No: C1981020
• IBM Index Class Name: Hydrology
• Doc Date: 4/22/1991
• Doc Name: RATIONALE FOR PUBLIC NOTICE
• Permit Index Doc Type: NPDES
• Media Type: D
• Archive: No

COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division
Rationale - Page 8. Permit No. CO-0040827.
VI. TERMS AND CONDITIONS OF PERMIT
a) Purpose of WET Testing: (Cont.) effects. WET testing will
provide a more comprehensive means of evaluating the toxicity ~~E
a discharge than could otherwise currently be accomplished.
b) Instream Waste Concentration (IWC): As a condition of the
permit, the permittee will be required to conduct routine '
monitoring For acute toxicity. Acute toxicity occurs when there
is a statistically significant difference in the mortality
observed, for Ceriodaphnia sp. (water flea) and fathead minnows,
between the control and any effluent concentration. Should
acute tonicity be detected in any effluent concentration less
than or equal to the Instream Waste Concentration (IWC) or
should a species mortality in any dilution of effluent
(including 100% effluent) exceed 50%, the permittee is required
to conduct a series of timely tests to identify and ultimately
eliminate or treat the toxicant. The IWC is determined using
the following equation:
IWC = [Facility Flow (FF)/(Stream Low Flow (annual) + FF)j X 100%
Using the facility design flow of 0.5 MGD and the acute stream
low flow (1E3) of 0 MGD, the IWC for the permittee is therefore
100%, which represents a wastewater concentration of 100%
effluent to 0% dilution water.
c) Chronic $iomonitoring: The determination as to whether or not
an individual facility must conduct chronic WET testing is
dependent upon the ratio of the chronic stream low flow (30E3)
to the design flow of the wastewater treatment plant, as well as
the receiving waters classifications. Since the receiving
waters are not classified as Aquatic Life Class 1, or Class 2
with inorganic and metal numeric standards, chronic WET testing
is not required at this time.
d) Waiver of Requirements: Industrial facilities having simple
effluents of consistent quality, which can be totally
characterized chemically, may request a full or partial waiver
of WET testing for the remainder of the life of the permit,
subject to Division approval, if the first four quarters of
testing show no pattern of toxicity.
The permittee should read the WET testing sections of Part I.A. and
I.B. of the permit carefully, and should note that the test methods
for the toxicity tests are described in detail in the Division
guidance document, Guidelines for Conducting Whole Effluent
Toxicity Tests. This document should be read thoroughly prior to
commencing [he required WET testing, to ensure that the permittee
is aware of the various test conditions that could affect the test
results (e.g., sample holding time).