(A) Type 3 modified mound systems. Type 3 Modified Mound Systems shall be designed to minimum requirements as follows:
(1) Pretreatment. The pretreatment component shall be dependent on the design soil treatment zone in accordance with the requirements of Table B.3 (Appendix B).
(2) Plowing and filling of soil treatment area. The soil treatment area shall be plowed in accordance with the requirements of § 171.142 and filled in accordance with the requirements of § 171.143. The fill material shall cover the entire basal area to a maximum depth of six inches. The sand must be placed prior to chisel plowing so it becomes incorporated into the original soil. All vegetation shall be cut to the ground surface and removed from the soil treatment area prior to placing the sand.
(3) Distribution piping. Distribution to and into the application bed shall be by low pressure pipe (LPP), which shall be installed in accordance with the requirements of § 171.102(F).
(4) Lift station. The lift station shall be sized according to Appendix C.
(5) Piping invert elevation. The invert elevation of the distribution piping shall be a minimum of 12 inches above original grade.
(6) Application bed area size calculation. The square footage of the application bed shall be equal to the projected daily flow in gallons per day divided by the loading rate of the coarse sand fill, one gallon per day per square foot (1.0 gpd/ft2) or 1.2 gpd/ft2, when an aerobic treatment unit is proposed for pretreatment.
(a) Seepage chamber application bed. Seepage chambers may be used in lieu of gravel for the application bed in accordance with the following:
1. The minimum inside width (MIW) of seepage chambers shall be calculated as follows:
(Linear Loading Rate/Sand
Loading Rate)/1.5 = MIW
2. The end caps of the chambers shall not be included in the length of the application bed.
3. The invert elevation of the distribution pipes shall be a minimum of six inches above the trench bottom with the distribution pipes mounted in the chamber in accordance with the manufacturer's specifications.
4. The perforations shall be located on top of the distribution lines.
5. Each distribution line shall have at least one perforation on the bottom, at either the proximal or distal end, to allow for drainage of the line. There shall be a concrete splash block of at least one square foot directly under the perforation to prevent erosion of the infiltrative surface.
6. There shall be at least one four inch diameter observation pipe installed in the length of each application bed. The observation pipe shall terminate at or above final grade.
(7) Soil treatment area size calculation. The square footage of the soil treatment area shall be equal to the projected daily flow in gallons per day divided by the assigned wastewater loading rate in gallons per day per square foot.
(8) Minimum length. The minimum length of the modified mound soil treatment area shall be limited by the maximum linear loading rate. The linear loading rate is equal to the projected daily flow in gallons per day divided by the total length of the soil treatment area in feet, and shall be limited as follows:
(a) Systems on soils in resource groups A or B shall be designed with a maximum linear loading rate of eight gallons per day per foot. A maximum of two basal areas may be connected perpendicular to the slope.
(b) Systems on soils in resource groups C, D or E shall be designed with a maximum linear loading rate of four gallons per day per foot. A maximum of two basal areas may be connected perpendicular to the slope.
(9) Laterals at different elevations. When laterals are at different elevations, a flow control valve shall be used to control the inline pressure of the laterals.
(10) Minimum gravel depth. The minimum depth of gravel in the modified mound soil treatment area shall be ten inches, with six inches of gravel beneath the pipe and two inches above.
(11) Minimum sand depth. The minimum depth of coarse sand fill material covering the soil treatment area shall be six inches.
(12) Minimum soil cover. The entire modified mound soil treatment component shall be covered with a minimum of eight inches of topsoil to support vegetative cover. Additional cover shall be placed over the application bed(s) as is necessary to shed storm water.
(13) Geotextile fabric cover. The application bed shall be completely covered with an appropriate geotextile fabric prior to the placement of topsoil.
(Ord. [Bd of Health Ord., Art. V], passed 11-12-1996; Ord. [Bd of Health Ord., Art. V], passed 11-12-2013; Ord. 17-0605, passed 6-13-2017)