HYDRO29812

• Permit No: C1981041
• IBM Index Class Name: Hydrology
• Doc Date: 6/8/1992
• Doc Name: RATIONAL FOR PUBLIC NOTICE POWDERHORN COAL CO
• Permit Index Doc Type: NPDES
• Media Type: D
• Archive: No

COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division
Rationale - Page 14. Permit No. CO-0027146
VI. TERMS AND CONDITIONS OF PERMIT
A. Effluent Limitations (continued)
5. Whole Effluent Toxicity (WET) Testing (continued)
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 fi.rsc four quarters of
eescing show no pattern of toxicity.
Purpose of WET Testing: Section 6.9.7 of the Regulations for the
State Discharge Permit System (6.1.0), passed by the Water
..... Quali.cy Control Commission (WQCC), 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 co ensure Chat there are no discharges
"in amounts, concentrations or combinations which are harmful co
the beneficial uses or toxic co humans, animals, plants, or
aquatic life" as required by Section 3.1.11 (1)(d) of the Basic
Standards and Methodologies.
Chemical analysis of effluent has provided only a partial
evaluation of the potential impact a discharge could have on the
receiving scream. Also, chemical analysis cannot evaluate the
synergistic or antagonistic eEfecc of compounds. There are also
compounds for which an accurate or reproducable method of
chemical analysis has not yet been developed, as well as
compounds which are just beginning co be evaluated for toxic
effects. WET testing will provide a more comprehensive means of
evaluating the toxicity of a discharge than could otherwise
currently be accomplished.
Instream Waste Concentration (IWCI: As a condition of the
permit, the permictee will be reeuired co conduct routine
monitoring for acute toxicity. Acute toxicity occurs when there
is a staciscically significant difference in the mortality
observed, for Ceriodaohnia sp. (water flea) and fathead minnows,
between Che control and env efflu=_nc concentration. Should
acute toxicity 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 100X effluent) exceed 507., the permictee is required
co 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 (FF1 K 100
Stream Low Flow (annual) + FF