(1) A permittee that has not been assigned a whole effluent toxicity limit because of attaining the performance standards described in WAC 173-205-050 (2)(a) or 173-205-120(1) will not be required to conduct a new effluent characterization in accordance with WAC 173-205-050(1) unless the department determines that:

(a) The permittee has made changes to processes, materials, or treatment that could result in an increase in effluent toxicity.

(b) A municipal sewage collection and treatment system has experienced the addition of any new source as defined in 40 C.F.R. 403.3(k) that belongs in any industry category identified in 40 C.F.R. Part 403, Appendix C and cannot demonstrate that the new source is nontoxic or that the pretreatment program and local limits are adequate to control toxicity from the new source.

(c) The average dry weather flow volume has changed by ten percent or more due to changes in plant processes, production changes, or increases in the number of users. Changes in flow volume due to water conservation measures would not indicate a need for a new characterization unless this resulted in a final effluent containing a higher concentration of potentially toxic pollutants.

(2) It is the responsibility of the permittee to demonstrate to the department's satisfaction that no change has occurred to the facility which would cause or increase effluent toxicity.

(a) The permittee must make this demonstration as soon as possible after any change listed in subsection (1) of this section has occurred but under no circumstances later than the time of application for permit renewal.

(b) Toxicity testing by the permittee shall be accepted as a demonstration that such facility changes have not increased effluent toxicity providing that the department has approved the number and types of toxicity tests performed.

(c) The department may accept other demonstrations that toxicity has not increased based on other scientific disciplines such as chemistry.

(3) An increase in effluent toxicity is assumed to have occurred and a new effluent characterization shall be required if toxicity in excess of a performance standard has been demonstrated during:

(a) Toxicity testing conducted in accordance with WAC 173-205-030(8); or

(b) Toxicity testing conducted in response to a rapid screening test as required by WAC 173-205-120 (2)(d).

(4) A permittee does not need a new effluent characterization for acute or chronic toxicity if the discharge is being routinely monitored for compliance with a whole effluent toxicity limit using species rotation. This determination only applies to the type of toxicity (acute or chronic) covered by the whole effluent toxicity limit.

(5) A permittee may be required to further characterize effluent toxicity if a new toxicity test method has been approved pursuant to WAC 173-205-050 (1)(d) that, in the opinion of the department, should replace one of or supplement an existing toxicity test in the permit because it:

(a) May be more sensitive to effluent toxicity; or

(b) Has a closer ecological or taxonomic relationship to receiving water species.

(6) Only the new toxicity test method is needed for effluent characterization in the case of a new toxicity test being approved.