(A) General. Type 1 and 2 soil treatment trench systems shall be designed to the minimum requirements as follows:
(1) Pretreatment. The pretreatment component shall be required based upon the design soil treatment zone in accordance with the requirements of Table B.3 (Appendix B).
(2) Distribution. Distribution to the soil treatment trench may be by serial distribution using drop boxes and header pipe, manufacturer approved chamber connections, or by equal flow distribution. Piping and distribution device size and material shall comply with the requirements of §§ 171.160 through 171.168.
(3) Lift station. Lift stations, if required, shall be sized in accordance with the requirements of Appendix C.
(4) Distribution piping. Distribution into the soil treatment trench shall be by perforated pipe. No perforation shall be located closer than three feet to the proximal end of the soil treatment trench.
(5) Piping invert elevation. The invert elevation of the distribution pipe shall be a minimum of six inches above the trench bottom.
(6) Soil treatment area size calculation. Only the trench bottom area shall be used in calculating the required soil treatment area. The square footage of trench bottom area shall be equal to the projected flow in gallons per day (gpd) divided by the assigned wastewater loading rate in gallons per day per square foot.
(7) Maximum trench length. The maximum trench length shall be 100 feet from the distribution device. All trenches connected to an equal flow distribution box shall be of equal length.
(8) Maximum trench width. The maximum trench width shall be 36 inches; the minimum trench width shall be 12 inches.
(9) Trench separation. Trenches shall be separated by a minimum of four feet of undisturbed soil.
(10) Minimum gravel depth. The minimum depth of gravel in the soil treatment trench shall be 12 inches, with six inches of gravel beneath the distribution pipe and two inches above. Gravel shall not be placed closer than 12 inches to the distribution device.
(11) Soil cover over trenches. The maximum depth of soil cover over the top of a soil treatment trench shall be 24 inches. The minimum depth of soil cover over the top of a soil treatment trench shall be six inches.
(12) Low pressure pipe distribution. When distribution in a Type 1 or 2 system is by low pressure pipe, the applicable requirements of § 171.102(F) and this section shall apply.
(a) The soil loading rate may be increased by up to 10% above the original soil loading rate found in Table B.2
(b) No perforation shall be located closer than five feet to the proximal end of the soil treatment trench.
(c) The invert elevation of the distribution line shall be a minimum of six inches above the trench bottom.
(d) The square footage of trench bottom 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.
(e) The maximum trench width shall be 24 inches; the minimum trench width shall be 12 inches.
(f) Trenches shall be separated by a minimum of four feet of undisturbed soil.
(g) The minimum depth of gravel in the soil treatment trench shall be ten inches, with six inches of gravel beneath the pipe and two inches above.
(h) Gravel shall not be placed closer than 24 inches to the manifold trench.
(i) The design of the pressure distribution network shall be in accordance with the requirements of Design of Pressure Distribution Networks For Septic Tank-Soil Absorption Systems as incorporated in Appendix A.
(13) Seepage beds. Seepage beds shall be sized at one and one-half times the required trench soil treatment area.
(14) Seepage chambers. The soil treatment area per lineal foot for soil absorption components using seepage chambers shall be calculated by multiplying the average inside width of the chamber times an equivalency factor of 1.5. For example:
(a) Using a chamber with an average inside width of 24 inches, the soil treatment area per lineal foot would be calculated as:
24 in x 1 ft/12 in x 1 ft x 1.5/lineal ft = 3 ft2/lineal ft
(b) For a system that requires 600 feet2 of soil treatment area, 200 lineal feet of chamber would be required using 24-inch chambers (600 ft2/3 ft2/lineal foot = 200 lineal feet).
The trench bottom area of end caps may be included in the minimum required soil treatment area.
(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; Ord. 24-1005, passed 8-13-2024)