Mound Systems or an evapotranspiration system may be required when the percolation rates or high water table don't allow for an absorption system to be installed. Mounds and evapotranspirtation systems may be designed for gravity or pressure flows in accordance with the following criteria:
(1) Plans and specifications shall be submitted to the secretary by a registered professional engineer or licensed plumber for review and approval of any individual or small on-site mound or evapotranspiration system prior to construction; NOTE: The county where the system is installed may allow only an engineer to design the system.
(2) Mound and evapotranspiration systems shall not be constructed on sites located in a flood plane. Mound systems shall not be constructed on sites located on bedrock or on soils with percolation rates of 120 or more minutes per inch or 3 or fewer minutes per inch at a depth of 12 inches below the sand layer of the mound. Mound or evapotranspiration systems may not be located on natural slopes exceeding 12 percent under any soil percolation rate conditions. When a mound or evapotranspiration system is located on a slope, no buildings, driveways, other surface or subsurface obstructions, or future construction is permitted within 30 feet of the system on the down gradient side while the system is being used. The systems shall be located in open areas with maximum available sunshine. The area surrounding the systems shall be graded to provide for diversion of surface runoff water;
(3) The mound or evapotranspiration system may be constructed only upon undisturbed naturally occurring soils. The bottom of the system bed shall be excavated to a depth from 8 to 12 inches below the ground surface and shall be completely level. The system may be round or rectangular;
(4) The mound system shall be constructed so that the minimum distance between the seasonal high groundwater table and the invert elevation of the distribution system is 4 feet;
(5) The required bottom area of the bed shall be calculated on the basis of a recommended or design application rate with respect to the soil percolation rate. For mound systems receiving less than 1,500 gallons of wastewater per day, an application rate of 0.6 gallons per square foot per day shall be used when the percolation rate is from 60 to 120 minutes per inch and an application rate of 0.83 gallons per square foot per day shall be used when the percolation rate is 3 or more but less than 60 minutes per inch. For mound systems receiving 1,500 or more gallons of wastewater per day, the application design rate shall equal the soil percolation rate plus the seasonal evapotranspiration rate.
2009 Rapid City Business of the Year !
R. Chris Howie & Darin R. Howie
