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 17.36.914 - WASTEWATER TREATMENT SYSTEMS - TECHNICAL REQUIREMENTS

Current through Register Vol. 13, July 5, 2024
(1) Except as provided in ARM
				17.36.916, all wastewater
				treatment systems must be designed and constructed in accordance with the
				applicable requirements in ARM
				17.36.913 and in Department
				Circular DEQ-4.
(2) Department
				Circular DEQ-4, 2023 edition, which sets forth standards for subsurface sewage
				treatment systems, and Department Circular DEQ-2, 2016 edition, which sets
				forth design standards for public sewage systems, are adopted and incorporated
				by reference for purposes of this subchapter. All references to these documents
				in this subchapter refer to the editions set out above. Copies are available
				from the Department of Environmental Quality, P.O. Box 200901, Helena, MT
				59620-0901.
(3) Wastewater
				treatment systems must be located to maximize the vertical separation distance
				from the bottom of the absorption trench to the seasonally high ground water
				level, bedrock, or other limiting layer, but under no circumstances may this
				vertical separation be less than four feet of natural soil. For elevated sand
				mounds constructed in accordance with Department Circular DEQ 4, the depth of
				the key may be included as part of the separation distance between the
				infiltrative surface and a limiting layer.
(4) A replacement area or replacement plan
				must be provided for each new or expanded wastewater treatment system.
				Replacement areas and plans must comply with the requirements of this
				subchapter.
(5) A site evaluation
				must be performed for each wastewater treatment system. As determined by the
				reviewing authority, the site evaluation may include the following:
(a) soil descriptions for proposed wastewater
				treatment systems. Soil descriptions must be based on data obtained from test
				holes within 25 feet of each wastewater treatment location. Test holes must be
				at least eight feet in depth unless a limiting layer precludes digging to eight
				feet;
(b) percolation test results
				within the boundaries of the proposed wastewater treatment system; and
(c) if the applicant or the
				reviewing authority has reason to believe that ground water will be within
				seven feet of the surface at any time of the year within the boundaries of the
				system, the applicant must provide data to demonstrate that the minimum
				separation distance required by (3) between the absorption trench bottom and
				the seasonally high ground water level can be maintained. The reviewing
				authority may require the applicant to install ground water observation wells
				to a depth of at least eight feet to determine the seasonally high ground water
				level. The applicant shall monitor the observation wells through the seasonally
				high ground water period. Measurement must occur for a long enough period of
				time to detect a peak and a sustained decline in the ground water
				level.