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SEPTIC SYSTEM INSPECT DIAGNOSE REPAIR
SEPTIC CARE INSTRUCTIONS
SEPTIC D-BOX INSTALL REPAIR
SEPTIC DRAINFIELD FAILURE DIAGNOSIS
SEPTIC DYE TEST PROCEDURE
SEPTIC FAILURE SIGNS
SEPTIC INSPECTION & TEST GUIDE
SEPTIC LIFE EXPECTANCY
SEPTIC SUPPLIES & PARTS
SEPTIC SYSTEM DESIGN ALTERNATIVES
SEPTIC SYSTEM DESIGN BASICS
SEPTIC SYSTEMS, HOME BUYERS GUIDE to
SEPTIC SYSTEM SAFETY WARNINGS
SEPTIC TREATMENTS & CHEMICALS
SEWAGE BACKUP PREVENTION
SEWAGE EJECTOR / GRINDER PUMPS
SEWER GAS ODORS
SEWER LINE REPLACEMENT
SINKHOLES, WARNING SIGNS
SOAKAWAY BED FAILURE DIAGNOSIS
SULPHUR & SEWER GAS SMELL SOURCES
TOILETS, INSPECT, INSTALL, REPAIR
TRAPS on PLUMBING FIXTURES
TREATMENTS & CHEMICALS, SEPTIC
VIDEO GUIDES: Septic Videos
WATER CONSERVATION MEASURES
WATER SOFTENERS & CONDITIONERS
WATER SUPPLY & DRAIN PIPING
WATER, WELLS, WATER TANKS: TESTING GUIDE
WASHING MACHINES & SEPTIC SYSTEMS
WASTEWATER TREATMENT BASICS
WINTERIZE A BUILDING
This article defines, illustrates, and explains the operation of alternate bed (or alternating bed) septic systems, a variation on dosing systems for septic system effluent final treatment and disposal. We explain how alternating bed septic drainfields work, how the fields are switched, and how often they are alternated or switched.
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While alternating bed septic systems are not complicated and are discussed here as a septic design alternative, the concept - manually or automatically switching effluent disposal between two or more collections of drainfield trenches - is similar to septic dosing systems in concept. Readers of this article should also see GRAVITY/SIPHON DOSING SYSTEMS and also PRESSURE DOSING SYSTEMS. Page top image shows a sketch of a basic septic system design using gravity dosing, with effluent flowing from a septic tank to a dosing chamber and from there to a drainfield. Image: Indiana state health department.
What is an alternating bed septic system?
Alternating bed septic system designs are intended to decrease hydraulic overloading of septic drainfield soils by switching effluent distribution between two or more sets of septic drainfield trenches.
The alternating drainfield areas may be uniformly interspersed (alternating individual septic drainfield lines) or they may be parallel in the same area, or they may even be in completely different physical areas on a property. The layout choice for alternating septic bed systems depends on the space available as well as soil characteristics.
In the U.S., some states such as Massachusetts, define alternating bed systems as a design intended to provide a backup septic capacity: "
Alternating Bed Systems - Also known as an alternating leachfield. An absorption system designed with a backup absorption field for use while the primary absorption field rests."
How Far Apart Are the Alternating Septic Bed Drainfield Trenches and Leach Lines?
The answer is, it depends: on
How is Effluent Dispersal Switched Between Alternating Septic System Beds
Alternating drainfield designs are used most often on flat sites and in combination with a programmable or timed automatic distributing valve, but they may be operated manually.
Our friend and associate Victor Faggella reports a long-standing and traditional alternating septic bed design at which the property owner simply opened the distribution box for his drainfield and periodically switched a plug from one set of drainfield pipes to the other. (See SEPTIC D-BOX INSTALL REPAIR)
An example of a floating outlet design for dosing systems and that can be adapted to alternating bed septic system designs to handle dosing type septic system effluent disposal can be seen in animation at Rissy Plastics FLOUT floating outlet for septic effluent dispersal.
How Often is Effluent Distribution Switched Between Alternating Septic Beds
Sometimes installed as a retrofit where an existing septic drainfield is failing, the contractor may make a backup absorption field, adding the ability to route septic tank effluent to either field.
The "backup" septic drainfield is used while the primary field is rested and allowed to recover through biological activity. In this design septic drainfields or leaching beds are often alternated every 6 months. We recommend that the alternation dates be shifted so as to avoid always using the same field during the wettest months of the year.
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Frequently Asked Questions (FAQs) about septic dosing systems and alternating bed septic system designs
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Technical Reviewers & References
Septic Effluent Dosing System Designs, Products and Suppliers
Some basic information about handling septic effluent follows.
How and When Septic Effluent is Moved Through a Septic System
Septic effluent is distributed to a system final treatment and disposal using either gravity methods (which depend on terrain slope) or pressure methods (which use a pump to move effluent to its destination treatment and disposal area).
Methods For Septic Effluent Distribution Using Gravity Systems
Design Manuals for Septic Systems
Onsite Wastewater Disposal Books