17.36.310 STORM DRAINAGE
(1) The applicant shall submit a storm drainage plan in accordance with department Circular DEQ-8 to the reviewing authority.
(2) Storm drainage plans must be prepared by a professional engineer and must comply with the requirements in ARM 17.36.314 if the subdivision application proposes either of the following:
(a) six or more lots; or
(b) a lot proposed for use other than a single living unit with greater than 25 percent impervious area.
(3) A storm drainage plan must include a maintenance plan for all drainage structures. The maintenance plan must describe the drainage structures, provide a maintenance schedule, and designate the entity responsible for performing maintenance. The reviewing authority may require the applicant to create a homeowner's association or other legal entity that will be responsible for maintenance of storm drainage structures and that will have authority to charge appropriate fees. The maintenance plan must include easements and agreements as necessary for operation and maintenance of all proposed storm drainage structures or facilities.
(4) The applicant shall obtain an easement if the reviewing authority determines the easement is needed to allow adequate operation and maintenance of the facilities. The easement must be filed with the county clerk and recorder at the time the certificate of subdivision approval issued under this chapter is filed. The easement must be in one of the following forms:
(a) in writing signed by the grantor of the easement; or
(b) if the same person owns both parcels, shown on the plat or certificate of survey for the proposed subdivision.
(5) The reviewing authority may exempt the requirements of (1), (2), and (3) for subdivisions located entirely within a first-class or second-class municipality, as described in 7-1-4111, MCA, or within a Municipal Separate Storm Sewer System (MS4) general permit area, as defined in ARM 17.30.1102, if:
(a) the applicant submits to the reviewing authority a letter of consent from the municipal or MS4 entity on a form provided by the department; and
(b) the municipal or MS4 entity either accepts the stormwater into a municipal storm water system or requires the applicant to comply with municipal or MS4 storm water drainage design standards.
(6) If material will be displaced or added within a delineated floodplain, the applicant shall provide evidence that the floodplain permit coordinator has been notified and that appropriate approvals have been obtained.
(7) If applicable, the applicant shall obtain an MPDES permit for storm water discharges, pursuant to ARM Title 17, chapter 30.
(8) Storm water that reaches state surface waters must be treated prior to discharge if the reviewing authority determines that untreated storm water is likely to degrade the receiving waters.
(a) minimum treatment of storm water consists of removal of settleable solids and floatable material. The reviewing authority may require more extensive treatment if deemed necessary to protect state waters from degradation;
(b) plans for the treatment facility must be approved by the reviewing authority.
(9) The department may grant a waiver from any of the requirements in this rule pursuant to the provisions of ARM 17.36.601.
History: 76-4-104, MCA; IMP, 76-4-104, 76-4-125, MCA; Eff. 12/31/72; AMD, Eff. 11/4/73; AMD, Eff. 11/3/75; AMD, Eff. 5/6/76; AMD, 1977 MAR p. 746, Eff. 10/25/77; AMD, 1984 MAR p. 1027, Eff. 7/13/84; TRANS, from DHES, 1996 MAR p. 1499; AMD, 2002 MAR p. 1465, Eff. 5/17/02; AMD, 2003 MAR p. 221, Eff. 2/14/03; AMD, 2014 MAR p. 2098, Eff. 9/19/14; AMD, 2018 MAR p. 1588, Eff. 8/11/18.