LOW-PRESSURE DOSED DRAINFIELDS – GIVING THE WHOLE DRAINFIELD A DRINK OF EFFLUENT
ABSTRACT: Onsite residential and commercial sewage facilities depend on the soil to provide final treatment of wastewater before it is dispersed back into the environment. One means of maximizing the soil’s potential to renovate wastewater is to provide uniform distribution of septic tank effluent across the whole drainfield. A gravity conventional system can only place effluent at the beginning of the trench and uniform distribution does not occur until ponding starts to develop within the trench. With a low-pressure dosed drainfield (LPDD), a small diameter pipe (typically 1.25” diameter) that has small diameter perforations every 60” is used to apply the effluent along the entire length of the trench with each dose of the system. In Texas, LPDD systems are considered nonstandard disposal systems (§285.33(d)(1)). However, this alternative disposal system should be evaluated for sites with limited soil depth. The required trench depth and vertical separation over rock is less than what is required for conventional gravity systems. This session will focus on the hydraulic design of a low-pressure dosed drainfield. Guidance will be provided in the determination of orifice size and spacing, pipe diameters and overall system layout. This session will finish by designing a pump and control system for the LPDD.
JOHN R. BUCHANAN, PH.D., P. E., Associate Professor, Biosystems Engineering & Soil Science, The University of Tennessee, Institute of Agriculture
John Buchanan is a Registered Professional Engineer, State of Tennessee, and specializes in the design of Drip Distribution of treated effluent. He is a former President of the Tennessee Chapter of the Soil and Water Conservation Society, a member of Tennessee Onsite Wastewater Association and the National Onsite Wastewater Recycling Association. When John is not teaching class at the University, he is involved nationally in the advancement of adult education in the Onsite Wastewater community.
