The mound system is a soil absorption system constructed above grade that uses sand fill to enhance septic tank effluent treatment before the wastewater is dispersed to the natural soil at the site. Sites not suited for a conventional subsurface soil absorption system may be suitable for a mound system. Detailed information on mound systems is presented in Bulletin 813, Mound System for On-site Wastewater Treatment: Siting, Design, and Construction in Ohio. Copies of Bulletin 813 are available through Ohio county Extension offices or on the website setll.osu.edu.
This bulletin examines the dosing tank and distribution system that convey the septic tank effluent into the mound for treatment and dispersal. The discussions on design and construction are intended to enable engineers, soil scientists, sanitarians and installers to design, construct and inspect pressure distribution systems for mounds.
Septic tank effluent is distributed in the mound through a series of perforated pipes buried in a layer of gravel above the sand fill (Figure 1) or in chambers set on top of the sand fill. A pump placed in a dosing tank is used to deliver the septic tank effluent across the top of the sand fill in the mound. Pressure distribution systems for mounds consist of five components: 1) lateral pipes with equally spaced shielded holes drilled into the top of the pipe; 2) manifold and main connected to the laterals; 3) dosing tank to collect septic tank effluent to be pumped to the mound; 4) pump to pressurize the system; and 5) controls and power supply to operate the pump.
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Figure 1. Mound system components.
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. A shaded example across the bottom of the pages will help illustrate the steps.