A user shall have an affirmative defense to an enforcement action brought against it for noncompliance with the general prohibitions in §§
67A-5 and
67A-6 of this chapter if it can prove that it did not know, or have reason to know, that its discharge, alone, or in conjunction with discharges from other sources, would cause pass-through or interference and that either:
A. A local limit exists for each pollutant discharged and the user was
in compliance with each limit directly prior to, and during the pass-through
or interference; or
B. No local limit exists, but the discharge did not change substantially
in nature or constituents from the user's prior discharge when
THTMA was regularly in compliance with its NPDES permit, and in the
case of interference, was in compliance with applicable sludge use
or disposal requirements.