(A) Type 4 at-grade systems. Type 4 At-Grade Systems shall be designed to minimum requirements as follows:
(1) Pretreatment. The pretreatment component shall be dependent on the design soil treatment zone in N accordance with the requirements of Table B.3 (Appendix B).
(2) Plowing of soil treatment area. The soil treatment area shall be plowed in accordance with the requirements of § 171.142. 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 soil treatment area 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 of the distribution lines shall be a minimum of six inches above original grade.
(6) Soil treatment area size calculation. The square footage of 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.
(7) Minimum length. The minimum length of the at-grade 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 12 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 six gallons per day per foot. A maximum of two basal areas may be connected perpendicular to the slope.
(8) 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.
(9) Minimum gravel depth. The minimum depth of gravel in the at-grade soil treatment area shall be ten inches, with six inches of gravel beneath the pipe and two inches above.
(10) Minimum soil cover over gravel. The gravel of an at-grade soil treatment system shall be covered with a minimum of 12 inches of topsoil to support vegetative cover. Additional cover shall be placed as is necessary to shed stormwater.
(11) Geotextile fabric cover. The gravel shall be completely covered with an appropriate geotextile fabric prior to the placement of topsoil.
(12) Other design requirements. Type 4 At- grade Systems shall comply with the provisions of the Wisconsin At-Grade Soil Absorption System Siting, Design, and Construction Manual as incorporated in Appendix A.
(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)