1. (1) When part of a discharger's process wastewater is not being discharged into state waters or contiguous zone because it is disposed into a well, into a POTW, or by land application thereby reducing the flow or level of pollutants being discharged into state waters, applicable effluent standards and limitations for the discharge in an MPDES permit must be adjusted to reflect the reduced raw waste resulting from such disposal. Effluent limitations and standards in the permit must be calculated by one of the following methods:

   1. (a) If none of the waste from a particular process is discharged into state waters, and effluent limitations guidelines provide separate allocation for wastes from that process, all allocations for the process must be eliminated from calculation of permit effluent limitations or standards.

   2. (b) In all cases other than those described in (a), effluent limitations must be adjusted by multiplying the effluent limitation derived by applying effluent limitation guidelines to the total waste stream by the amount of wastewater flow to be treated and discharged into state waters, and dividing the result by the total wastewater flow. Effluent limitations and standards so calculated may be further adjusted under 40 CFR Part 125, subpart D, to make them more or less stringent if discharges to wells, publicly owned treatment works, or by land application change the character or treatability of the pollutants being discharged to receiving waters. This method may be algebraically expressed as:

      P =

      E x N T

      where P is the permit effluent limitation, E is the limitation derived by applying effluent guidelines to the total waste-stream, N is the wastewater flow to be treated and discharged to state waters, and T is the total wastewater flow.

2. (2) Section (1) does not apply to the extent that promulgated effluent limitations guidelines:

   1. (a) control concentrations of pollutants discharged but not mass; or
   2. (b) specify a different specific technique for adjusting effluent limitations to account for well injection, land application, or disposal into POTW's.
3. (3) Section (1) does not alter a discharger's obligation to meet any more stringent requirements established under ARM 17.30.1342, 17.30.1343, and 17.30.1344.
4. (4) The department adopts and incorporates by reference 40 CFR Part 125, subpart D, which is a series of federal agency rules setting forth criteria and standards for determining eligibility for a variance from effluent limitations based on fundamentally different factors (FDF).

Authorizing statute(s): 75-5-201, 75-5-401, MCA

Implementing statute(s): 75-5-401, MCA

History: NEW, 1989 MAR p. 2060, Eff. 12/8/89; TRANS, from DHES, 1996 MAR p. 1499; AMD, 2020 MAR p. 1879, Eff. 10/24/20; AMD, 2024 MAR p. 257, Eff. 2/10/24.