Wisconsin Administrative Code › Department of Natural Resources › NR 100-199 - Environmental Protection - General › Chapter NR 106 - Procedures For Calculating Water Quality Based Effluent Limitations For Point Source Discharges To Surface Waters › Subchapter II - General Procedures for Effluent Limitations › Section NR 106.09 - Whole effluent toxicity data evaluation and limitations

Current through June 24, 2024
(1) DATA
				  EVALUATION. Data evaluation procedures are specified in the whole effluent
				  toxicity test methods specified in s.
				  NR
				  219.04, Table A. In the event of a WET test failure,
				  facility specific requirements shall be established in the WPDES permit which
				  specify required follow-up actions.
(2) ACUTE WHOLE EFFLUENT TOXICITY.
(a) Except as provided in par. (c), the
				  department shall establish acute whole effluent toxicity limitations to ensure
				  that substances shall not be present in amounts which are acutely harmful to
				  aquatic life in all surface waters including the mixing zone and effluent
				  channel as required by s.
				  NR
				  102.04(1).
(b) To assure compliance with par. (a), a
				  whole effluent toxicity test may not result in a statistically valid LC 50 less
				  than 100% with the following tax as pecific exposure periods:
1. 48 hours for aquatic invertebrate
				  organisms (including
Ceriodaphnia dubia)
;
2. 96 hours for aquatic vertebrate organisms
				  (including fathead minnows (
Pimephales promelas
));
3. Any other exposure period deemed
				  appropriate by the department for a specific test organism.
(c) If a zone of initial dilution
				  is determined appropriate in accordance with the provisions of s.
				  NR
				  106.06(3) (c), whole effluent acute
				  toxicity limitations determined by this subsection shall be adjusted such that
				  the effluent meets the following condition. The adjustment shall insure that
				  after dilution of the effluent with the receiving water at a concentration
				  equal to 3.3 times the percent dilution value calculated through application of
				  the zone of initial dilution, the test solution of effluent and receiving water
				  shall not produce a statistically valid LC 50 less than 3.3 times the percent
				  dilution value determined through application of the zone of initial dilution
				  with the exposure periods as provided in par. (b).
(d) If, in the judgment of the department,
				  the statistical interpretation methods used to test for LC 50 are not
				  appropriate for a specific data set, empirical interpretation methods may be
				  used to determine the significance of an effect.
(e) Acute whole effluent toxicity limits
				  shall be expressed as 1.0 TU a unless an AMZ is approved in which case these
				  limits shall be expressed as a value that is 100 divided by the AMZ. Compliance
				  with an acute whole effluent toxicity water quality-based limitation shall be
				  determined by comparing the TU a endpoint from each toxicity test to the
				  limitation. Pursuant to s.
				  NR
				  106.08(6) (d) acalculated LC50 that
				  exceeds 100% is set equal to zero.
Note:
A toxicity reduction evaluation study is
					 not always required in the event an acute WET limit is imposed in a
					 permit.
(f) Whole effluent
				  acute toxicity limitations shall be expressed in permits as daily maximum
				  limitations.