Is Drip Distribution Right for Your Site?

A drip system can be the solution for a wide range of difficult installation conditions
Is Drip Distribution Right for Your Site?
Drip systems are installed shallow and are ideal for sites with difficult, slow draining soils. (Photo courtesy of American Manufacturing Company)

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Drip distribution has been around for almost two decades. The first system of this type I was involved with was during a research and demonstration project looking at alternative systems for Minnesota around 2000. The system, in various forms, had existed long before then, mostly in Southern states or where irrigation was used extensively.

If you are unfamiliar with the concept, pretreated effluent is applied to soil through a series of tubes equipped with emitters that allow a small amount of effluent into the soil at a time. This allows the effluent to be distributed more evenly over a large area. In hot and dry areas of the country, a primary purpose of this method of application (aside from treating the wastewater) is to use the water efficiently to supply nutrients to plants while treating and removing pathogens and bacteria in the soil. This is consistent with the “keep it shallow” principle that you often hear me talk about. The most permeable, most biologically active zone and the best placement for both treatment and acceptance is at or near the soil surface.

Because of these characteristics, drip distribution is used in places where conventional trench systems are not suitable or where steep slopes or heavily forested areas make it difficult to install trenches, mounds or at-grade systems. So it can be used to solve problems such as shallow bedrock or a high water table and slowly permeable soil conditions. They are also often used in seasonal applications such as at resorts and golf courses. All of this sounds much like the laundry list of problems we face in Minnesota and elsewhere, so it potentially has broad applications.

A drip distribution system has four main parts and some additional must-haves, from my perspective. The parts are: a pretreatment device, a pump tank, a filtering and flushing device, and the distribution tubing. The pretreatment device depends on specific manufacturers’ requirements for their proprietary product and any deviation from these requirements will void any guarantees or warranties, so it is important the service provider be familiar with not only state and local requirements but also the manufacturer’s recommendations.

One product on the market only requires a septic tank in front of the pump tank ahead of the headworks for the drip distribution part of the system, which includes the final filtering devices before the effluent goes into the tubing in the dripfield. Other products require aerobic treatment before being delivered to the pump tank. The main concerns here are plugging the filters or, worse yet, plugging the emitters in the tubing. In both cases it is important to have good filtering devices that deliver a very solids-free effluent to the tubing emitters.

A high head pump is needed for this application. The tubing typically operates at pressures of 15-20 pounds per square inch.

The filters remove particles larger than 100 microns. Some filters have automatic cleaning systems. Flushing capacity and the total dynamic head are important design features that ensure effluent passes through the emitters in the tubing. Even with good filtration there will be growth in the tubing, which can cause plugging. This is why most systems have a flushing system built in to prevent emitter plugging. The flushed water is delivered back to the septic tank.

In my opinion, the additional components or aspects that are needed are pump controls and a panel that provides for time dosing and metering the flow to prevent overloading the system.

About the Author 
Jim Anderson is connected with the University of Minnesota onsite wastewater treatment education program and is an emeritus professor in the university’s Department of Soil Water and Climate. Send him questions about septic system maintenance and operation by email to kim.peterson@colepublishing.com

This article is part of a series on drip distribution:



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