ARM 17.36.320
ARM 17.36.320. SEWAGE SYSTEMS: DESIGN
Cite as Mont. Admin. R. 17.36.320
(1) All components of subsurface sewage treatment systems must be designed and installed in accordance with department Circular DEQ-4. As indicated on Table 2 of this rule, public systems and multi-user systems with design flows greater than or equal to 2500 gallons per day must be designed by a registered professional engineer.
(2) A minimum separation of at least four feet of natural soil must exist between the infiltrative surface or the liner of a lined system and a limiting layer, except that at least six feet of natural soil must exist on a steep slope (15% to 25%) .
(3) The proposed subsurface sewage treatment area must include an area for 100% replacement of the system. Unless a waiver is approved by the department pursuant to ARM 17.36.601 , the replacement area must meet the same requirements as the primary area. If the replacement area is not immediately adjacent to the primary area, or if the department indicates to the applicant that it has reason to believe that site conditions for the replacement area may vary from those for the primary area, the applicant shall submit adequate evidence of the suitability of the replacement area.
TABLE 2
ALLOWABLE SYSTEMS, REQUIREMENTS
YES - Systems that are allowed
NO - Systems that are not allowed
DEQ-4 System
Public:
> 5000 gpd
(1) (7)
Public or Multiple-user:
Ā³ 2500 gpd and
Ā£ 5000 gpd
(2) (7)
Public or Multiple-user:
< 2500 gpd
(3)
Individual/Shared:
(6)
Standard Absorption Trench
NO
NO
YES
YES
At-Grade Systems
NO
NO
YES
YES
Gravelless
YES
YES
YES
YES
Deep Trench
NO
NO
NO
YES
Elevated Sand Mound
YES
YES
YES
YES
Evapotranspiration (ET) Systems
NO
NO
NO
NO (5)
ET-Absorption
NO
YES
YES
YES
Intermittent Sand Filters
YES
YES
YES
YES
Recirculating Sand Filters
YES
YES
YES
YES
Recirculating Trickling Filters
YES
YES
YES
YES
YES - Systems that are allowed
NO - Systems that are not allowed
DEQ-4 System
Public:
> 5000 gpd
(1)
Public or Multiple-user:
Ā³ 2500 gpd and
Ā£ 5000 gpd
(2)
Public or Multiple-user:
< 2500 gpd
(3)
Individual/
Shared:
(6)
Chemical Nutrient Reduction;
Aerobic Sewage Treatment Systems
NO (5)
NO (5)
NO (5)
NO (4) (5)
Pressure Distribution
YES
YES
YES
YES
Sand-lined Absorption Trenches
NO
YES
YES
YES
Experimental Systems
NO (5)
NO (5)
NO (5)
NO (5)
(1) Public systems with design flow greater than 5000 gallons per day (gpd) .
(2) Public or multiple-user systems with design flow greater than or equal to 2500 gpd and less than or equal to 5000 gpd.
(3) Public or multiple-user systems with design flow less than 2500 gpd.
(4) Means of securing continuous operation and maintenance of these systems must be approved by the reviewing authority prior to DEQ approval.
(5) May be allowed by waiver, pursuant to ARM 17.36.601 .
(6) Individual or shared commercial sewage systems that have a design flow greater than 700 gpd shall be considered multi-user.
(7) Must be designed by a professional engineer.