17.36.319 GRAY WATER REUSE
(1) This rule applies to gray water reuse on subdivision parcels that are subject to review, or that have been approved, under Title 76, chapter 4, MCA.
(2) Except as provided in (3) and (4), treatment and disposal of gray water must be by means of a wastewater treatment system that meets all of the requirements of this chapter and applicable department circulars. Gray water reuse within a building or residence for uses such as toilet flushing is permitted without review, provided that the gray water is ultimately disposed of by means of a wastewater treatment system that is in compliance with this chapter and applicable department circulars.
(3) Gray water may be used for irrigation as provided in (4). If a gray water irrigation system meets all of the requirements in (4), the system is not subject to the requirements of subchapter 3.
(4) 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 have a permit from the local health department;
(b) gray water irrigation must be subsurface, with 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 within 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 of four feet of natural soil between the point of gray water application and a limiting layer, as defined in ARM 17.36.101;
(e) unless a waiver is granted by the department, the following horizontal setback distances must be maintained. Gray water irrigation may not occur within:
(i) 100 feet of wells;
(ii) 100 feet of surface water;
(iii) 100 feet of a floodplain; 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) gray water irrigation systems in subdivisions may not be installed unless approved under Title 76, chapter 4, MCA. If a system complies with (4)(a) through (e), review under Title 76, chapter 4, MCA, is not required if the system serves:
(i) a parcel that has a previous certificate of subdivision approval issued pursuant to Title 76, chapter 4, MCA, if no other changes to the certificate are proposed, except that review under Title 75, chapter 6, MCA, is required before a public wastewater system is modified to include a gray water irrigation system; or
(ii) a parcel that, when created, was exempt from review under Title 76, chapter 4, MCA, because it was served solely by municipal facilities, as defined in 76-4-102, MCA.
(5) Subdivision applications must contain descriptions of the soils within 25 feet of proposed gray water irrigation areas. Soils must be described in accordance with Appendix B of Department Circular DEQ-4. Each test hole must be keyed by a number on a copy of the lot layout or map with the information provided in the report.
(6) 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.
(7) The department may require user agreements for systems that serve more than one user. The department may require easements for systems that cross property lines.
(8) If an existing gray water irrigation system is present in a proposed subdivision, the department shall review the adequacy of the system for the proposed use and the capability of the system to operate without risk to public health and without pollution of state waters. Existing systems must comply with state and local laws and regulations, including permit requirements, applicable at the time of installation.