(1) Except as provided in (2) and (3), treatment and disposal of gray water must be by means of a wastewater treatment system that meets all of the requirements of this subchapter and applicable department circulars. Gray water reuse within a building or residence for uses such as toilet flushing is permitted without a permit under this subchapter, provided that the gray water is ultimately disposed of by means of a wastewater treatment system that is in compliance with this subchapter and applicable department circulars.
(2) Gray water may be used for irrigation as provided in (3). If a gray water irrigation system meets all of the requirements in (3), the system is not subject to the requirements of ARM 17.36.914, 17.36.916, and 17.36.918.
(3) Gray water that is collected separately from sewage flow and that does not contain industrial chemicals, hazardous wastes, or wastewater from toilets may be used for irrigation, if the following requirements are met:
(a) prior to installation, a gray water irrigation system must obtain a permit under this subchapter;
(b) gray water irrigation must be subsurface, using a collection and application system that is designed, installed, and used in accordance with Department Circular DEQ-4;
(c) as provided in 75-5-326, MCA, gray water may not be used to irrigate plants to be consumed by humans, and gray water systems may not be located in a floodplain, as defined in 76-5-103, MCA. For purposes of this rule, "plants to be consumed by humans" does not include nut and fruit trees;
(d) there must be a minimum vertical separation of four feet of natural soil between the point of gray water application and a limiting layer, as defined in ARM 17.36.912;
(e) gray water irrigation may not occur within:
(i) 100 feet of wells;
(ii) 100 feet of surface water;
(iii) 100 feet of a flood plain; or
(iv) two feet of a property line;
(f) gray water from kitchens may be used for irrigation only where a waste segregation system is used. For purposes of this rule, a "waste segregation system" consists of dry disposal of toilet waste by a method such as composting, chemical, dehydrating, or incinerator treatment, with a separate disposal method for gray water;
(g) if required under Title 76, chapter 4, MCA, and implementing rules, a gray water irrigation system must obtain subdivision approval from the department.
(4) Soil descriptions must be provided for each proposed gray water irrigation system. Soils must be described in accordance with Appendix B of Department Circular DEQ-4.
(5) Gray water irrigation systems with a design flow greater than or equal to 2,500 gallons per day must be designed by a professional engineer.
(6) The reviewing authority may require user agreements for systems that serve more than one user. The reviewing authority may require easements for systems that cross property lines.