This bulletin examines the dosing chamber and distribution system that convey the septic tank effluent into the mound for treatment and disposal. The discussions on design and construction are intended to enable health officials and contractors to design, construct and inspect pressure distribution systems for mounds. Uniform or even distribution of the septic tank effluent is especially important in mound systems. Uneven distribution of septic tank effluent can result in localized overloading and short-circuiting through the mound. Surface seepage in one area of a mound, as shown in Figure 3, may be caused by uneven distribution.
Uniform distribution is achieved using a pressure distribution system.
Pressure distribution systems are carefully designed so that the volume of septic tank effluent flowing out of each hole of the distribution pipe is nearly identical. The pipe diameters and hole diameters must be carefully sized to achieve uniform distribution. A pump placed in a dosing tank is used to deliver the septic tank effluent into the mound and pressurize the system. The steps to design and construct the five components of a pressure distribution system will be presented in this bulletin. To illustrate the steps, an example pressure distribution system for a mound will be presented in the series of figures, calculations and tables that follow this introduction.