HYDRO25740

• Permit No: C1981010
• IBM Index Class Name: Hydrology
• Doc Date: 2/7/1994
• Doc Name: RATIONALE FOR PUBLIC NOTICE
• Permit Index Doc Type: NPDES
• Media Type: D
• Archive: No

PART I
Page lh of 19
Permit No. CO-0032115
B. MONITORING REQUIREMENTS
4. Acute WET Testine-Outfalls 002. 005. 009. 011. 013 and 015 (continued)
(a) Testine and Reoortine Requirements (continued)
The permittee shall conduct each acute WET test in general accordance with
methods described in Methods for Measurine the Acute Toxicity of Effluents and
Receiving Waters to Freshwater and Marine Organisms, EPA/600/4-90/027 or the
most current edition, except as modified by the most current Division guidance
document entitled Guidelines for Conducting Whole Effluent Toxicity Tests.
The permittee shall conduct an acute 48-hour WET test using Ceriodaohnia sp.,
and an acute 96-hour WET test using fathead minnows. Acute tests will be
replacement static tests of a single effluent grab sample.
(b) Failure of Test and Division Notification
An acute WET test is failed whenever the LC50, which represents an estimate of
the effluent concentration which is lethal to SOX of the test organisms in the
time period prescribed by the test, is found to be less than or equal to 100X
effluent. The permittee must provide written notification of the failure of a
WET test to the Division, along with a statement as to whether the Preliminary
Toxicity Incident ("PTI")/Toxicity Identification Evaluation ("TIE")
investigation or accelerated testing is being performed (see next section).
Notification must be received by the Division within 14 calendar days of the
demonstration of acute WET in the routine required test. "Demonstration" for
the purposes of Parts I.8.4(b),(c),(d) and (f) means no later than the last
day of the laboratory test.
(c) Automatic Compliance Schedule Uoon Failure of Test
If a routine acute WET test is failed, the following automatic compliance
sched~ile shall apply. As part of this the permittee shall either:
(i) proceed to conduct the PTI/TIE investigation as described in Part
I.B.4.(d), or
(ii) conduct accelerated testing using the single species found to be more
sensitive.
If accelerated testing is being performed, the permittee shall provide written
notification of the results within 14 calendar days of completion of the
"Pattern of Toxicity"/"No Toxicity" demonstration. Testing will be at least
once every two weeks for up to five tests until 1) two consecutive tests fail
or three of five tests fail, in which case a pattern of toxicity has been
demonstrated or, 2) two consecutive tests pass or three of five tests pass, in
which case no pattern of toxicity has been found.
If no pattern of toxicity is found the toxicity episode is considered to be
ended and routine testing is to resume. If a pattern of toxicity is found, a
PTI/TIE investigation is to be performed. If a pattern of toxicity is not
demonstrated but a significant level of erratic toxicity is found, the
Division may require an increased frequency of routine monitoring or some
other modified approach.
Amendment 2 Issued Effective