Type 4 At-Grade Absorption systems shall be designed to minimum requirements as follows:
A. Pretreatment shall be by septic tank, sized for the projected design flow, or by a Class I aeration device sized for the projected design flow. If a septic tank is utilized, it shall be augmented by an effluent filter.
C. Distribution to and into the absorption area shall be by low pressure pipe (LPP) distribution. LPP network piping shall be as specified in this section and in § 8.04.540.
E. The invert of the distribution lines shall be a minimum of six (6) inches above the original soil surface.
F. The effective length of the absorption area is the actual length of the aggregate along the contour. The effective width on sloping sites is the distance from the distribution pipe to the downslope toe of the aggregate and on level sites it is the width of the aggregate.
G. The square footage of absorption area shall be equal to the projected flow in gallons per day (GPD) (200 gallons per bedroom for residential properties, and per Table II for non-residential properties) divided by the assigned soil loading rate in gallons per day per square foot (See column six (6) of Table 1).
H. The soil loading rate is determined by the most restrictive permeability within 24 inches below the aggregate in moderate soils, 36 inches below the aggregate in moderately rapid soils and 48 inches below the aggregate in rapidly permeable soils.
I. The minimum length of the at-grade domestic wastewater absorption area parallel to the site contour 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 absorption area in feet, and shall be determined per column 7 of Table 1.
J. The minimum depth of gravel in the at-grade absorption area shall be twelve (12) inches, with six (6) inches of gravel beneath the pipe and a minimum of two (2) inches above.
K. The gravel of an at-grade soil absorption system shall be covered with a minimum of twelve (12) inches of topsoil to support vegetative cover. Additional cover shall be placed as necessary to shed stormwater.
L. The gravel shall be completely covered with a geotextile fabric prior to the placement of the topsoil.
M. The soil cover shall extend a minimum of five (5) feet beyond each side and end of the aggregate to tie the system into the existing soil surface. Multiple Type 4 systems may be utilized to provide the total seepage area required for a specific application. The minimum separation distance between the aggregate of multiple Type 4 systems shall be six (6) feet.
N. Observation ports are optional.
O. Separation distances from Type 4 systems to structures, water wells, bodies of water; etc. shall be measured from the closest portion of the aggregate.
P. Type 4 at-grade systems shall meet all requirements of all other applicable sections of the Ordinance and shall comply with the provisions of Wisconsin At-Grade Soil Absorption System Siting, Design, and Construction Manual as incorporated in Appendix A.
(Ord. O-201711-51-031, passed 11-14-2017)