Although technologies favored for use in the decentralized concept can produce effluent of sufficient quality to meet discharge limits in many situations, regulatory authorities everywhere frown upon the concept of a multitude of small discharges. While it can be argued that this perspective is questionable – I've often said, not completely tongue-in-cheek, that the real point of so-called “regional” wastewater plants was to gather this stuff together in one place where it can REALLY do some damage – soil dispersal will doubtless remain the norm for on-site/small-scale “waste” water systems. It is important, therefore, to have a thorough understanding of just what happens to effluent when it enters the soil system. It does not go “away”—which seems to be the focus of soil dispersal system “design” in many quarters. There is no “away”. Wherever it goes, the water remains in some part of the hydrologic system. Thus, there is no such thing as a “disposal” system—that word should be stricken from the lexicon of the wastewater management field. All “disposal” fields are really dispersal systems, and the aim of their design should be to provide optimum conditions for the required treatment to be accomplished in the soil system. This demands evaluation of the ability of the receiving soil to provide whatever additional treatment is required of any effluent-derived water that may percolate to join environmental waters. The soil dispersal system is also an opportunity to utilize the treated effluent as reclaimed water, providing beneficial irrigation, to provide a reuse benefit that defrays demands on “original” water sources. Papers in this menu review those issues.

Soil Treatment Mechanisms

A review and discussion of the mechanisms by which “waste” water is treated in the soil system to assimilate or eliminate pollutants before any water which percolates reaches a limiting condition—a point where essentially no further treatment can be expected before the water enters groundwater or daylights in seeps to join a surface watercourse. This information is used to analyze how dispersal mechanisms can be designed to take best advantage of whatever soil resources are available. This paper was originally written in 1994 as an input into the Washington Island project. The State of Wisconsin asked me to redraft it for distribution by them as an instructive document for designers in the state.

Decentralized Reuse with Subsurface Drip Irrigation Fields

Subtitled “Issues and Opportunities”, this paper is the proceedings paper for a presentation at the 2008 NOWRA annual conference. It reviews design and operation of subsurface drip irrigation (SDI) dispersal systems to serve as a beneficial reuse system, and also how it would function as a “drainfield” during times when insufficient matric potential is available to hold all the water routed to the field in the root zone. Treatment performance and O&M issues are reviewed. The paper closes with discussions of regulatory issues that must be resolved in order to be able to maximize the use of SDI as a reuse system.

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