Administrative Rules of Montana
Department 17 - ENVIRONMENTAL QUALITY
Chapter 17.36 - SUBDIVISIONS/ON-SITE SUBSURFACE WASTEWATER TREATMENT
Subchapter 17.36.9 - On-Site Subsurface Wastewater Treatment Systems
Rule 17.36.912 - DEFINITIONS

(1) "Absorption bed" means an absorption system that consists of excavations greater than three feet in width where the distribution system is laid for the purpose of distributing pretreated waste effluent into the ground.

(2) "Absorption trench" means an absorption system that consists of excavations less than or equal to three feet in width where the distribution system is laid for the purpose of distributing pretreated waste effluent into the ground.

(3) "Bedrock" means material that cannot be readily excavated by hand tools, or material that does not allow water to pass through or that has insufficient quantities of fines to provide for the adequate treatment and disposal of wastewater. The term does not include gravel and other rock fragments as defined in Department Circular DEQ-4, Appendix B.

(4) "Cesspool" means a seepage pit without a septic tank to pretreat the wastewater.

(5) "Commercial unit" means the area under one roof that is occupied by a business or other nonresidential use. A building housing two businesses is considered two commercial units.

(6) "Department" means the Montana Department of Environmental Quality.

(7) "Drainage way" means a course or channel along which storm water moves in draining an area.

(8) "Experimental system" means a wastewater treatment system for which specific design standards are not provided in Department Circular DEQ-4, DEQ-2, or this subchapter.

(9) "Failed system" means a wastewater treatment and/or disposal system that no longer provides the treatment and/or disposal for which it was intended, or violates any of the requirements of ARM 17.36.914.

(10) "Floodplain" means the area adjoining the watercourse or drainway that would be covered by a flood that is expected to recur on the average of once every 100 years or by a flood that has a one percent chance of occurring in any given year. The floodplain consists of the floodway and the flood fringe, as defined in ARM Title 36, chapter 15.

(11) "Gray water" means wastewater that is collected separately from a sewage flow and that does not contain industrial chemicals, hazardous wastes, or wastewater from toilets.

(12) "Ground water observation well" means a well installed for the purpose of measuring the depth from the natural ground surface to the seasonally high ground water.

(13) "Holding tank" means a watertight receptacle that receives wastewater for retention and does not, as part of its normal operation, dispose or treat the wastewater. The term does not include surge tanks used in a gray water irrigation system if the system meets the requirements of ARM 17.36.919.

(14) "Impervious layer" means any layer of material in the soil profile that has a percolation rate slower than 240 minutes per inch.

(15) "Individual wastewater system" means a wastewater system that serves one living unit or commercial unit. The term does not include a public sewage system as defined in 75-6-102, MCA.

(16) "Limiting layer" means bedrock, an impervious layer, or seasonally high ground water.

(17) "Living unit" means the area under one roof that can be used for one residential unit and which has facilities for sleeping, cooking, and sanitation. For example, a duplex is considered two living units.

(18) "Multiple-user wastewater system" means a wastewater system that serves or is intended to serve more than two living units or commercial units or a combination, but which is not a public sewage system as defined in 75-6-102, MCA. In estimating the population that will be served by a proposed residential system, the reviewing authority shall multiply the number of living units by 2.5.

(19) "Municipal" means pertaining to an incorporated city or town.

(20) "Percolation test" means a standardized test used to assess the infiltration rate of soils, performed in accordance with Appendix A in Department Circular DEQ-4.

(21) "Piped water supply" means a plumbing system that conveys water into a structure from any source including, but not limited to, wells, cisterns, springs, or surface water.

(22) "Pit privy" means a pit that receives undiluted, non-water-carried toilet wastes.

(23) "Replacement system" means a wastewater treatment system proposed to replace a failed, failing, or contaminating system.

(24) "Reviewing authority" means a local board of health or local health officer, as those terms are defined in 50-2-101, MCA, or their designees.

(25) "Sealed pit privy" means an enclosed receptacle designed to receive non-water-carried toilet wastes into a watertight vault.

(26) "Seasonally high ground water" means the depth from the natural ground surface to the upper surface of the zone of saturation, as measured in an unlined hole or perforated monitoring well during the time of the year when the water table is the highest. The term includes the upper surface of a perched water table.

(27) "Seepage pit" means a covered underground receptacle that receives wastewater after primary treatment and allows the wastewater to seep into the surrounding soil.

(28) "Septic tank" means a wastewater settling tank in which settled sludge is in immediate contact with the wastewater flowing through the tank while the organic solids are decomposed by anaerobic action.

(29) "Shared wastewater system" means a wastewater system that serves or is intended to serve two living units or commercial units or a combination of both. The term does not include a public sewage system as defined in 75-6-102, MCA.

(30) "Site evaluation" means an evaluation to determine if a site is suitable for the installation of a subsurface wastewater treatment system.

(31) "Slope" means the rate that a ground surface declines in feet per 100 feet. It is expressed as percent of grade.

(32) "Soil profile" means a description of the soil strata to a depth of eight feet using the United States Department of Agriculture (USDA) soil classification system method in Appendix B, Department Circular DEQ-4.

(33) "Subsurface wastewater treatment system" means the process of wastewater treatment in which the effluent is applied below the soil surface or into a mound by an approved distribution system.

(34) "Variance" means the grant, pursuant to ARM 17.36.922, by the reviewing authority of an exception to the minimum requirements set out in this subchapter or Department Circular DEQ-4.

(35) "Wastewater" means water-carried wastes. For purposes of these rules, wastewater does not include storm water. The term includes, but is not limited to, the following:

(36) "Wastewater treatment system" or "wastewater disposal system" means a system that receives wastewater for purposes of treatment, storage, or disposal. The term includes, but is not limited to, all disposal methods described in Department Circular DEQ-4.