South Dakota Administrative Rules
Title 74 - Department of Environment And Natural Resources
Article 74:53 - Water supply and treatment systems
Chapter 74:53:01 - Individual and small on-site wastewater systems
Section 74:53:01:35 - Requirements for an absorption trench

An absorption system shall have at least 2 absorption trenches of approximately equal length. The length of a trench with gravity flow may not exceed 100 feet, the width of a trench may not exceed 3 feet. The bottom of the trench shall be at least 18 inches below the ground surface, but the depth may not exceed 4 feet. The trench shall be constructed with a fill material consisting of washed gravel, crushed stone, slag, or clean bank run gravel ranging in size from 1/2 inch to 2 1/2 inches in diameter. An absorption line shall be placed within each trench and shall run along the length of the trench. All absorption lines shall have the ends capped. The fill material shall be at least 6 inches deep below the bottom of the absorption line and 2 inches deep above the top of the line. The bottom of the trench shall be uniformly graded to a slope from a minimum of 1/2 inch to a maximum of 4 inches per 100 feet. There shall be at least 6 feet of undisturbed soil between trenches. A closed-loop absorption trench system shall be level. To minimize sidewall compaction, trench excavation shall be made with bucket equipment having side cutters or raker teeth. When the soil does not exceed the plastic limit, the trench walls and bottoms shall be scarified before graded material is added.

General Authority: SDCL 34A-2-93.

Law Implemented: SDCL 34A-2-20.