(1) A user may not introduce into a POTW any pollutants which cause pass through or interference.   These general prohibitions and the specific prohibitions in (2) of this rule apply to all non-domestic sources introducing pollutants into a POTW whether or not the source is subject to other national pretreatment standards or any national, state, or local pretreatment requirements.

(2) In addition, the following pollutants may not be introduced into a POTW:

(a) pollutants which create a fire or explosion hazard in the POTW, including wastestreams with a closed cup flashpoint of less than 140ºF or 60ºC using the test methods specified in 40 CFR 261.21;

(b) pollutants which will cause corrosive structural damage to the POTW, but in no case discharges with pH lower than 5.0, unless the works is specifically designed to accommodate such discharges;

(c) solid or viscous pollutants in amounts which will cause obstruction to the flow in the POTW resulting in interference;

(d) any pollutant, including oxygen-demanding pollutants (BOD, etc.) , released in a discharge at a flow rate and/or pollutant concentration which will cause interference with the POTW;

(e) heat in amounts which will inhibit biological activity in the POTW resulting in interference, but in no case heat in such quantities that the temperature at the POTW treatment plant exceeds 40ºC (104ºF) unless the department, upon request of the POTW, approves alternative temperature limits;

(f) petroleum oil, nonbiodegradable cutting oil, or products of mineral oil origin in amounts that will cause interference or pass through;

(g) pollutants which result in the presence of toxic gases, vapors, or fumes within the POTW in a quantity that may cause acute worker health and safety problems; and

(h) any trucked or hauled pollutants, except at discharge points designated by the POTW.

(3) A user has an affirmative defense in any action brought against it alleging a violation of the general prohibitions established in (1) (a) of this rule and the specific prohibitions in (2) (c) -(g) of this rule if the user demonstrates that:

(a) it did not know or have reason to know that its discharge, alone or in conjunction with a discharge or discharges from other sources, would cause pass through or interference; and

(b) (i) a local limit designed to prevent pass through or interference or both of them was developed in accordance with (4) of this rule for each pollutant in the user's discharge that caused pass through or interference, and the user was in compliance with each local limit directly prior to and during the pass through or interference; or

(ii) if a local limit designed to prevent pass through or interference or both of them has not been developed in accordance with (4) of this rule for the pollutant or pollutants that caused the pass through or interference, the user's discharge directly prior to and during the pass through or interference did not change substantially in nature or constituents from the user's prior discharge activity when the POTW was regularly in compliance with the POTW's MPDES permit requirements and, in the case of interference, applicable requirements for sewage sludge use or disposal.

(4) (a) POTW's developing POTW pretreatment programs must develop and enforce specific limits to implement the prohibitions listed in (1) and (2) of this rule.   Each POTW with an approved pretreatment program shall continue to develop these limits as necessary and effectively enforce these limits.

(b) All other POTW's shall, in cases where pollutants contributed by user(s) result in interference or pass through, and such violation is likely to recur, develop and enforce specific effluent limits for industrial user(s) , and all other users, as appropriate, which together with appropriate changes in the POTW treatment plant's facilities or operation, are necessary to ensure renewed and continued compliance with the POTW's MPDES permit or sludge use or disposal practices;

(c) Specific effluent limits may not be developed and enforced without individual notice to persons or groups who have requested such notice and an opportunity to respond.

(5) Where specific prohibitions or limits on pollutants or pollutant parameters are developed by a POTW in accordance with (3) of this rule, such limits are deemed pretreatment standards for purposes of 75-5-304, MCA, of the Montana Water Quality Act.

(6) If, within 30 days after notice of an interference or pass through violation has been sent by the department to the POTW, and to persons or groups who have requested such notice, the POTW fails to commence appropriate enforcement action to correct the violation, the department may take appropriate enforcement action.

(7) The board hereby adopts and incorporates by reference 40 CFR 261.21 (characteristics of ignitability) (July 1, 1991) . Copies of these materials are available from the Department of Environmental Quality, PO Box 200901, Helena, MT 59620-0901.