=== Features of ABR Systems ===
When adequately reinforced, ABR systems may be installed under driveways, parking areas, play grounds or other open spaces. The tanks are usually constructed completely underground with manholes or access ports as the only protrusions. ABRs, being passive systems requiring no electricity to operate, are truly low-cost technologies. However, ABRs, while more efficient than septic tanks, will still require secondary treatment to provide a quality of effluent suitable for discharge. Secondary treatment may be in the form of soils treatment (leach trenches if soils are adequate), constructed wetlands, sand or media filtration. Some designers will combine ABRs with mechanical treatment such as sequencing batch reactors to provide a highly treated wastewater effluent. Visit our [[Sequencing_Batch_Reactors|page on sequencing batch reactorsSequencing Batch Reactors]] for more information on these systems.
=== The Tank ===
'''Hollow block construction.''' Contractors should first prepare the site by excavating the tank hole to the proper depth plus extra depth to accommodate bedding material, typically 1/4 to 1/3 meter of compacted sand, gravel or aggregate base. Forms are set on top of the bedding material and vertical rebar installed at every other block. Once the floor is poured and set, the block-laying may proceed. Contractors will mortar the blocks in place and use bond beams with horizontal rebar every other row. When all of the blocks are laid, the cells will be filled with grout and allowed to harden. Due to the many joints, some plastering or sealing with tar or mortar on the tank inside is usually required. In high groundwater areas, sealing the outside of the tank to prevent infiltration is beneficial.
'''Poured-in-place tank construction.''' For larger projects, or systems that must support heavy loads, pouring concrete as a monolithic structure is often preferable to concrete blocks. Poured-in-place tanks are started in the same manner as block tanks: first excavate the tank hole with extra depth for bedding material then install the forms and rebar as per the specifications. Baffles and transfer pipes are also set using forms. Note that for extra load-bearing capabilities, thickened columns and slabs are often used. When the forms and steal are in place, pour the concrete and allow it to harden. Concrete will harden to about 90% of its total strength after 7 days, unless additives are used to quicken the hardening. Such concrete mixes, called high-early, may be used when backfilling must be accomplished quickly.
=== Leak Testing and Backfilling Procedures ===
#Backfill the rest of the way with clean soil and manually compact as above. Mound soil slightly around the tank to shed surface water and to avoid ponding of surface water over the tank.
#Check the soils over the tank frequently. Over the weeks or months after tank installation, some soils settling will occur. Fill depressions or fissures as soon as possible.
''NOTE: As soon as possible after the tank has hardened, add water to the tank and begin the backfilling procedure. This provides weight that can counteract buoyancy forces. This is especially important in areas where groundwater is high or surface waters can fill in tank holes.''
''[[Primary Treatment MethodsAnaerobic Baffled Reactor (ABR) 1| Back to Primary Treatment MethodsAnaerobic Baffled Reactor (ABR) 1]]''
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