Septic tank effluent is distributed in the mound through a series of perforated pipes buried in a layer of gravel or a chamber above the sand fill. Uniform distribution of the septic tank effluent is important in mound systems. Uneven distribution of septic tank effluent can result in localized overloading, short-circuiting through the mound, and even breakout at the side slope or toe of the mound near the overload.
Uniform distribution is achieved using a pressure distribution system. Pressure distribution systems should be carefully designed so that the volume of septic tank effluent flowing out of each hole is uniform across the system. 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 pressurizes the distribution network.
A pressure distribution network should be designed in accordance with Bulletin 829, Mound Systems: Pressure Distribution of Wastewater–Design and Construction in Ohio. This bulletin explains the dosing tank 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 designers, contractors, and health officials to properly design, construct, and inspect pressure distribution systems for mounds.
Pressure distribution systems for mounds consist of five components:
Bulletin 829 is available for purchase through your local OSU Extension office. The bulletin can also be found at www.ag.ohio-state.edu/~setll.