17.30.1107    DESIGNATION PROCEDURES: SMALL MS4S

(1) For purposes of this rule, "designation" means a determination by the department that an MS4 is subject to the permit requirements of this subchapter.

(2) The department shall designate an MS4 other than those identified in ARM 17.30.1102(23) if a discharge from the MS4 results in, or has the potential to result in, exceedances of water quality standards, including impairment of designated uses, or has other significant water quality impacts, including habitat and biological impacts.  In making a designation under this subsection, the department shall:

(a) consider whether the MS4:

(i) has discharges to a listed impaired waterbody that is on the most recent 303(d) list;

(ii) has high growth or growth potential;

(iii) has high population density;

(iv) is contiguous to an urbanized area; and

(v) is a significant contribution of pollutants to surface waters; and

(b) place a high priority on evaluating small MS4s that have a combined permanent and seasonal population of over 10,000, as determined by the latest decennial census by the United States census bureau plus the number of commercially advertised bedroom accommodations that will allow for an overnight stay, as listed through the chamber of commerce, or any local resort or property management company.

(3) The department shall designate an MS4 other than those identified in ARM 17.30.1102(23) if the MS4 contributes substantially to the pollutant loadings of a physically interconnected municipal separate storm sewer that is a regulated small MS4 under these rules.

(4) The department may designate an MS4 other than those identified in ARM 17.30.1102(23) pursuant to the criteria in ARM 17.30.1105(1) (e) or (f) .

(5) The department may designate discharges from municipal separate storm sewers on a system-wide or on a jurisdiction-wide basis.  In making its designation the department may consider the following factors:

(i) the location of the discharge with respect to surface waters;

(ii) the size of the discharge;

(iii) the quantity and nature of the pollutants discharged to surface waters; and

(iv) other relevant factors.

(6) Upon petition, the department may designate an MS4 under the appropriate criteria in these rules.  The department shall make a final determination on a petition to designate a small MS4 within 180 days after receipt of the petition.

(7) An MS4 may petition the department to reduce the census estimates of the population served by the MS4 to account for storm water discharges to combined sewers, as defined in 40 CFR 35.2005(b) (11) , that are treated in a publicly owned treatment works.  In municipalities in which combined sewers are operated, the census estimates of population may be reduced in proportion to the fraction, based on estimated lengths, of the length of combined sewers over the sum of the length of combined sewers and municipal separate storm sewers.  The MS4 shall submit the MPDES permit number associated with each discharge point and a map indicating areas served by combined sewers and the location of any combined sewer overflow discharge point.

(8) The department may re-evaluate its designation of an MS4 if circumstances change or if new information becomes available.

(9) The department may waive the permit requirements of this subchapter for an MS4 identified in ARM 17.30.1102(23) if the MS4 demonstrates to the department that the MS4 has existing storm water quality control programs that are equivalent to the six minimum control measures set out in ARM 17.30.1111.

(10) The department may waive the permit requirements of this subchapter for an MS4, which would otherwise be regulated because it is located within an urbanized area, if the MS4 serves a population of under 1,000 and both of the following criteria are met:

(a) discharges from the MS4 are not contributing substantially to the pollutant loadings of a physically interconnected regulated MS4; and

(b) storm water controls are not needed for the MS4 based on wasteload allocations that are part of an EPA-approved or established TMDL that addresses the pollutants of concern.

(11) The department may waive the permit requirements of this subchapter for an MS4, which would otherwise be regulated because it is located within an urbanized area, if the MS4 serves a population of between 1,000 and 10,000 and both of the following criteria are met:

(a) the department has evaluated all surface waters, including small streams, tributaries, lakes, and ponds, that receive a discharge from the MS4 and has determined that storm water controls are not needed based on wasteload allocations that are part of an EPA-approved or established TMDL that addresses the pollutants of concern or, if a TMDL has not been developed or approved, an equivalent analysis that determines sources and allocations for the pollutants of concern;

(i) for purposes of this subsection, pollutants of concern include biochemical oxygen demand (BOD) , sediment or a parameter that addresses sediment (such as total suspended solids, turbidity, or siltation) , pathogens, oil and grease, and any pollutant that has been identified as a cause of impairment of any water body that will receive a discharge from the MS4; and

(b) the department has determined that current and future discharges from the MS4 do not have the potential to result in exceedances of water quality standards, including impairment of designated uses, or other significant water quality impacts, including habitat and biological impacts.

(12) The department shall at least once every five years review all waivers granted under this rule to determine whether any of the information required for granting the waiver has changed.  The department shall consider a petition to review a waiver if the petitioner provides evidence that the information required for granting the waiver has substantially changed.

(13) The department may designate an MS4 for which the permit requirement is waived under this rule if circumstances change or new information becomes available.

History: 75-5-201, 75-5-401, MCA; IMP, 75-5-401, MCA; NEW, 2003 MAR p. 219, Eff. 2/14/03.