Excavation and trenching - South Dakota

South Dakota is under federal OSHA jurisdiction which covers most private sector workers within the state. State and local government workers are not covered by federal OSHA.

Underground utilities

Excavators must give prior notice of proposed excavations to South Dakota’s One-Call Notification Board so that the Board can notify operators of underground utilities to locate and mark their utilities to prevent damage, interruption of service, and injury to excavation workers. The rules are found at S.D. Codified Laws §§ 49-7A-1 through 49-7A-35.

Right to lateral and subjacent support

Each coterminous owner of land is entitled to the lateral and subjacent support which his land receives from the adjoining land, subject to the right of the owner of the adjoining land to make proper and usual excavations for purposes of construction, using ordinary care and skill, and taking reasonable precautions to sustain the land of the other, and giving previous reasonable notice to the other of his intention to make excavations.

Excavation requirements for septic tanks

The installation requirements for septic tanks include the following:

• Installed on a solid, level base, with access hole covers six inches to 12 inches below the finished grade. If the cover is airtight, equipped with a hasp, and kept locked to prevent unauthorized access, the cover may be shallower or above grade.
• Installed at a depth that provides adequate gravity flow from the building or facility sewer which meets the requirements of the South Dakota state plumbing code, § 20:54:11:09.
• Installed on undisturbed soil.
• If over-excavation occurs, it must be backfilled with sand to the correct elevation and compacted.
• Backfilling around the tank must be accomplished in a manner to prevent settlement and to prevent undue stresses on the tank and to the inlet and outlet pipes.
• When multiple tanks are used to obtain the required liquid volume capacity, the tanks must be connected in series.
• The interconnecting pipes between tanks must be at least 6 feet in length and unperforated.
• No more than four tanks in series are permitted to obtain the required liquid volume capacity.
• The first tank must not be smaller than any of the subsequent tanks in the series.
• All tanks must be located in an area which is accessible for the pumping of their contents.
• There must be no constructed building or facility of any kind covering any of the tanks.

Absorption trenches for small on-site wastewater systems

An absorption system (a system which utilizes absorption lines in trenches or beds to distribute wastewater to adjacent soils in an absorption field) must have at least two absorption trenches (a long, narrow excavation made in soil for the placement of an absorption line) 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 three feet.
• The bottom of the trench must be at least 18 inches below the ground surface, but the depth may not exceed four feet.
• The trench must 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 must be placed within each trench and run along the length of the trench.
• All absorption lines must have the ends capped.
• The fill material must be at least six inches deep below the bottom of the absorption line and 2 inches deep above the top of the line.
• The bottom of the trench must be uniformly graded to a slope from a minimum of 1/2 inch to a maximum of 4 inches per 100 feet.
• There must be at least 6 feet of undisturbed soil between trenches.
• A closed-loop absorption trench system must be level.
• To minimize sidewall compaction, trench excavation must be done with bucket equipment having side cutters or raker teeth.
• When the soil does not exceed the plastic limit, the trench walls and bottoms must be scarified before graded material is added.