3 Important Components to Consider When Installing Drainfields

These seven products can help ensure a successful, professional and long-lasting septic system drainfield installation

3 Important Components to Consider When Installing Drainfields
Puraflo Peat Fiber Biofilter from Anua

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Designing a drainfield can be complex; depending on the system, there are at least three key components you need to consider — storage media, a distribution device and chamber systems for an alternative approach. You also should have observation ports, access to clean the laterals if you have a pressure distribution system, and a nose for knowing the system you designed is odor-free and working properly. Here we take a look at some components to consider when installing drainfields:

1. Storage media 

Wastewater treatment might begin with a septic tank, but it takes a free-flowing discharge pipe and storage media to contain and control effluent flows to the drainfield. Common media include rock or a gravelless material, such as expanded polystyrene: 

  • The Q2 (Q squared where Q is flow) high-efficiency gravelless drainfield from Koi Environmental has interconnected pieces of expanded polymer, including expanded polystyrene, designed to maximize surface area and void space. The pieces are formed into strong, lightweight dimensional blocks 6 to 12 inches square and 5 feet long. The blocks weigh 2 1/2 to 5 pounds each, and can be stacked and cut for any dispersal system design. Design features optimize oxygen transfer and bacterial growth, allowing effluent to be channeled to the sidewall of the trench. Variable porosity of the individual pieces making up the blocks can be adapted to different soil types. Vertical channels enhance evaporation, and provision is made for aeration and heating through a channel in the bottom of the block. Insulation of the polymer improves cold-weather performance. 

2. Distribution systems 

Effluent also needs to be evenly distributed to the soil for proper treatment. “You need some kind of distribution device, whether that’s gravity through a distribution box (D-box), pump or siphon for discharge to a manifold,” says Bob Wright, P.E., co-owner of CHURCH Onsite Wastewater Consultants in Lakewood, Colo. 

“Even distribution over the field is critical to good treatment,” he says. “I prefer going with a pump because then I know I have distribution over the field.” 

Laterals assist in the distribution process, allowing the soil to do its work in the treatment process. Here are some distribution systems you might consider: 

  • Distribution boxes from Polylok/Zabel Environmental are available in 12- and 20-inch sizes, and accept 2-, 3-, 4- and 6-inch pipe. The 12-inch boxes come with stabilizing feet to anchor and prevent them from floating. They will accept risers to bring them to grade where necessary for convenient inspections.
  • The GSF Geotextile Sand Filter from Eljen Corporation provides advanced treatment and dispersal in the same footprint. The internal design provides sufficient void space to allow for aerobic conditions, while the Bio-Matt fabric promotes biological growth on its multiple surfaces. The fabric enhances system performance and keeps the biological growth away from the native soil, preserving the soil’s long-term acceptance rate. The unit’s lightweight and easy-to-handle modules allow for quick and convenient delivery and installation.
  • The Puraflo Peat Fiber Biofilter from Anua can be designed and installed as a combined treatment and effluent dispersal system. Treated effluent exits the modules via weep holes around the perimeter at the module base and flows into the dispersal system situated directly beneath. Available options include an in-ground or mounded pad. It features a small footprint and the ability to overcome site limitations such as seasonal high water tables, shallow soils or restrictive layers. Assistance is provided to designers and regulators on sizing and configuring the pad dispersal system.
  • The Spider Valve manifold assembly from Clarus Environmental allows the appropriate distribution of effluent when regulations require pressurized splitting or when small lots require lateral lines of unequal length. When combined with a pump, orifice diameters within the manifold may be modified to ensure no lateral receives more than its share of flow. The incoming line should maintain at least 3 feet of distal pressure to ensure equal effluent splitting. The assembly must be installed at the high point of the system, permitting the effluent to drain from the valve to the trenches. It is available in models that serve up to 10 laterals. The assembly should be installed level inside a 24- or 30-inch access riser with lid. 

3. Chamber systems 

Chamber systems offer an alternative to traditional media storage and distribution, especially when working with shallow installations. Here are a few selections to make the job easier: 

  • Quick4 Plus low-profile chambers from Infiltrator are optimal for shallow installations, providing maximum strength through center structural columns. At only 8 inches tall, they can be installed with as little as 6 inches of cover. They feature the Contour Swivel Connection that allows 10-degree turns, right or left. They come in easy-to-handle 4-foot lengths, and provide even distribution of effluent to the soil. They don’t require heavy equipment for installation, and can be configured in a variety of inletting options and heights.
  • The STF-BTBS bow tie pipe stand from Sim/Tech Filter Inc. is designed for use in chamber systems where the distribution piping is suspended above the soil. The stand is independent of the chamber, allowing pipe to be installed before chamber installation and before the squirt test is performed. The unit installs by a squeeze-and-release action that makes installation quick and easy. The stand can be installed on the pipe before placing in the trench, and is easily adjusted to any desired spacing. The stand stores flat. It is available to fit 1-, 1 1/4-, 1 1/2-, and 3-inch pipe. 

And don’t forget the observation ports. “It’s very important to be able to look into the field and see how ponding is being handled,” Wright says. “If you’re going to have a pressure distribution system, you want a way of cleaning it out to get rid of any biomat inside the laterals.” 

Finally, a properly working drainfield should pass the smell test, he says. “You really shouldn’t have odors if the drainfield is doing its job.” 

(All equipment listings from Onsite Installer Product Focus, May 2012 and May 2013.)


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