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Plastic Chamber Leach Fields

Plastic chamber leach fields can be substitutes for gravel beds.

Diagram of a plastic chamber leachfield shows a trench where open-bottomed plastic arched chambers rest. The chambers receive effluent from a septic tank and transmit it into the undisturbed soil under and around the chambers, where final treatment and disposal occurs.

Plastic chamber leach fields consists of trenches into which are placed open-bottomed plastic arched chambers that support the earth above and any applied loads. These chambers receive effluent from a septic tank and transmit it into the undisturbed soil under and around the chambers, where final treatment and disposal occurs. Chamber systems are easy to install, may be used wherever drainrock systems are appropriate, and--depending on state regulations and the type of chamber--may require significantly less space than a conventional drainrock system.

Chambers are formed from a series of arched, injection-molded plastic vaults that snap together. While products vary among manufacturers, a typical chamber is 20 to 40 inches wide, six feet long, and one foot high. Special end sections connect with feed piping, typically 4" PVC. The sides of each chamber have louvers to allow wastewater to seep into the surrounding soil. Because effluent flows freely into the space formed by the parallel rows of chambers, it spreads over much of the trench floor. In conventional systems, by contrast, effluent preferentially discharges from the first holes in the perforated pipes, creating biomat buildup and saturation near the entrance. No "masking" occurs from superimposed gravel, and the biomat at the floor of the chamber is fully in contact with ample oxygen. If effluent builds up within the chamber, some of it can escape through the sidewalls, which accounts for the increased effectiveness of chambers relative to gravel trenches. Narrower, higher chambers are available that substitute more side-wall absorption for less ground area. These designs typically require the same length of trench as a conventional system.

The effectiveness of chamber leach fields can be increased by using a dosage system. In this design, a small pipe with 1/8" diameter holes is suspended or supported on blocks within the vault, designed to evenly distribute the effluent. A holding tank with a filter collects effluent, which is pumped into the chambers when the tank is full by a small pump for about 3 minutes, typically about six times a day. This system distributes effluent evenly over the floor and walls of the chambers. Dosing may reduce the required depth of soil under the chambers.

Laboratory and field testing over the past fifteen years support the use of chamber systems as a viable alternative to gravel leach fields.


Affordability

Affordability: Because plastic chamber fields do not require gravel, there is no cost for gravel shipping and leveling. In addition, plastic chamber fields often do not require the same length trenches as conventional systems, saving cost on labor and machinery.

Environmental Performance

Environmental Performance: Leach fields are an effective way to distribute effluent from septic tanks to the surrounding soil to help supplement vegitation. Plastic chamber fields offer better distribution than typical drainrock systems by allowing for the lateral distribution of effluent, aside from the fact that not as much land must be trenched to provide space for them.


Easy

These systems are available from distributors throughout the United States and Canada, and have been installed and evaluated for over 15 years. Because leach chambers are substitutes for drainrock systems, so all the limitations that apply to conventional systems regarding the vertical distance to groundwater or an impervious layer, the depth of soil, and the type of soil, also apply to chambers (although as mentioned, trench length can sometimes be reduced for chambers).


Costs vary depending on size of pipe and manufacturer. Cost can range from less than a dollar per foot for 3" pipe to $70 per foot for 60" pipe. Additional hardware and setup equipment can increase these costs. However, because no gravel beds are required, costs will likely be less than typical leach fields.


Not Applicable


All states approve the use of chamber systems and some jurisdictions allow reduced size systems for this technology. Some states regulate on-site wastewater issues at the county level.


Not Applicable


Chambers are installed in level, flat-bottomed trenches. Chamber sections are designed to interlock to form a complete drainfield trench that includes an inlet plate and an end plate. Some manufacturers market a unit that permits curving the system to fit unusual terrain. Installation time can be reduced up to 50% compared to a gravel system.


Limited warranties vary depending on manufacturer, ranging from 1 to 10 years from date of installation.


Chambers eliminate the labor in placing tons of drainrock aggregate. Eliminating the equipment needed to spread the aggregate reduces undesirable compaction of the surrounding soil and disruption to nearby shrubs and trees. Chambers are clean, eliminating the problem of fine particles clinging to gravel. Most chambers stack, reducing the bulk that needs to be transported. Installers who have tried chambers often never go back to conventional gravel trenches. The typical cost is comparable to a gravel system of above-average cost. Many jurisdictions allow a reduction (often up to 40%) in drainage field length compared with a gravel system, when using the wide type of chamber. Observation ports can be added that allow inspection of the system for bio-mat buildup. Some jurisdictions require such ports.

Disclaimer: The information on the system, product or material presented herein is provided for informational purposes only. The technical descriptions, details, requirements, and limitations expressed do not constitute an endorsement, approval, or acceptance of the subject matter by the NAHB Research Center. There are no warranties, either expressed or implied, regarding the accuracy or completeness of this information. Full reproduction, without modification, is permissible.