ToolBase.org logo
The Home Building Industry's Technical Information Resource

Back to Standard View
Search TechnologiesAbout Technology Inventory
 
Browse by Building System


Symbol Legend
Adobe Acrobat Reader required for PDF documents

PDF documents require the free Adobe Reader.


All PDF documents open in a new browser window. Close the browser window to return to the site.

Pressurized Leach Field Dosing

In this technique, effluent is delivered to the leach field in intermittent doses by a pump.

In this technique, effluent is delivered to the leach field in intermittent doses by a pump. See figure 1. in Texas A & M university fact sheet on Pressure leaching fields. The effluent is pumped under pressure through small-diameter piping (typically 1" diameter with 1/8" holes), which if properly balanced will deliver the effluent evenly over the entire leach field. See Figure 2 in Texas A & M university fact sheet on Pressure leaching fields. Dosing should be thought of as a technology that can be advantageously combined with many secondary treatment and leach field designs, rather than as a specific product or system. A closely related technology, Drip Irrigation Leach Field, is described in another article in this Technology Inventory.

Below the ground surface, a supply pipe leads to distribution pipes that are covered with geotextile fabric. Clean out valves lead from the distribution pipes to the ground surface. Surface drainage is off to the side.

Dosing has desirable features, and can be used in some cases to rehabilitate a failed leach field. In all dosing systems, leachate is collected from the primary or secondary treatment unit in a dosing tank, typically 30 to 60 gallons, containing a pump. When the dosing tank level reaches the high water float switch, the pump discharges the leachate into the distribution piping until the effluent level reaches the level of the low water float switch. See CAD details in Pump chamber diagram in Low-Pressure Dosing Systems fact sheet.

Given that a typical 3-bedroom home generates about 360 gallons of waste a day, the system will cycle on the average every two to four hours. Between cycles, the drain field "rests" with positive results for the maintenance of the aerobic micro biota on the floor and walls of the leach field.

If the distribution piping is under pressure, a properly balanced system will distribute leachate evenly over the field, enhancing its effectiveness, lessening the chances of anaerobic biomat buildup, and reducing the extent of soil saturation. Studies show that pressurized dosing significantly improves leach field performance.


Environmental Performance

Pressurized systems distribute effluent more evenly, allowing better absorption into the earth and less buildup of anaerobic biomat around the perforated pipe in the leach field.


Easy

The need for a pump, pump chamber, effective filter, and water-tight piping raise the first cost and maintenance cost (the pump draws very little electric energy). Like any pump-operated system, a reliable source of power is required, and an electrician may be needed to hook up the pump. Routine maintenance is necessary to ensure the proper functioning of these systems. Regular monitoring and maintenance of the system is required; lack of maintenance is a sure precursor to failure.


In an area where a standard system would cost from $1,800 to $4,000 to install, a small, simple pressurized system might cost from $3,500 to $5,000. Added maintenance cost will also be incurred.


Costs of running the system is not siginificantly higher than a standard distribution system. However, the importance of regular maintenance might be more costly than a regular system.


Pressurized dosing systems are widely accepted, and are required by some jurisdictions for certain soil conditions. As usual with new technology, the local official may not be familiar with the concept, but these barriers are being overcome as systems become more commonly used. Some jurisdictions may allow the systems on an experimental basis, with monitoring.

A database including references to state by state sanitary code requirements is located at: www.nesc.wvu.edu/nsfc/nsfc_regulations.htm.


Not Applicable


In a typical pressurized dosing system installed within a plastic chamber leach field (see Plastic Chamber Leach Field in this Technology Inventory), 4" PVC piping will be elbowed up at the end of each trench. These elbows are capped, with a hole drilled in the cap the same size as those in the distribution pipe. The system is filled with water, and the pump is run to check that the "squirt height" in each trench is even. Such a test may need to be performed with the field exposed, in the presence of an inspector. This test can also be used as a periodic check on system clogging and the need for cleaning.

Because of the small size of the orifices, an effective effluent filter system is needed, of the reusable cartridge type. A control panel and an elapsed time counter are essential accessories. The pump chamber (as well as the septic tank) should have easily accessible access risers with child-proof and slip-resistant lids. The piping should be arranged to drain by gravity.


Not Applicable


Dosing, especially pressurized dosing, significantly improves the operation of a drain field, and extends its life. Pressurized fields may be located above the level of the septic tank. It may be possible to rehabilitate a failed field with pressurized dosing. Some jurisdictions require a pressurized dosing system for shallow soils, or for very coarse soils where distributing effluent over the entire field area can reduce the rate at which the effluent soaks into the porous soil.

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.