Conventional Septic Systems in Arizona

Arizona Conventional Septic Systems

In conventional septic systems the water flows by gravity from the house to the septic tank then to the disposal system.  The disposal system is installed in soil where the water is treated by bacteria and other microbes along with physical filtering by the soil.

A conventional septic system is installed where there are no limiting conditions at the site or in the subsurface.  Conventional septic systems rely on the soil to provide treatment in addition to the septic tank.

In Arizona, there are four types of conventional septic disposal systems allowed under the state rules (A.A.C. R18-9-E302).

They are listed below:
1) Trenches.  The water from the septic tank drains into pipe with holes that is installed in aggregate rock or gravel.  The trench can be 1 foot wide to 3 feet wide and have up to four feet of the gravel below the pipe.  Filter fabric is installed on top of the gravel and pipe to keep the topsoil out.  Native topsoil is added over the top.  The advantage of trenches is the sidewalls and bottom absorb the water so less area is required than for a bed.  (add picture and link to trench entry)
2) Bed.  Instead of trenches, the pipes are laid out in a larger area, spaced 4 feet apart, in a bed of aggregate rock or gravel.  The gravel is at least 1 foot deep below the pipe.  Filter fabric is laid over the top of the gravel and pipe to keep the native soil cover out of the gravel.  The bed width varies from 10 to 12 feet.  (add picture and link)
3) Chambers.   Instead of rock and pipe, the chambers are black plastic units typically 3 feet wide, 4 feet long, and about 16 inches tall.  They are installed end to end the length of the trench with end caps.  The water from the septic tank flows by gravity in a pipe to the endcap and then dispersed into the chambers.  The chambers have some flexibility to bend and follow a curved hillside.  (add picture and link)
4) Seepage Pit.  Pits are drilled vertically into the earth similar to a drywell.  The drilled hole has a pipe with holes in it installed down the center to the bottom and aggregate rock or gravel fills the hole around the pipe.  Filter fabric is installed over the gravel to keep out the topsoil cover.  Pits are only allowed by the state rules if the site is in an area with valley sediment and alluvial fill and groundwater must be at least 50 feet below the bottom of the drilled pit.  The footprint for this type of system is small since the pits have a diameter of 4 to 6 feet.  (add picture and link)

The best septic system for a site is determined based on the size of the house or building, volume of wastewater, area available, soil texture and structure, and site constraints. (add links)

If soil conditions are limiting there are other types of disposal systems including Cap systems, Evapotranspiration Beds, Wisconsin Mounds, or advanced treatment like Engineered pads, Intermittent Sand Filters, Peat Filters, Textile Filters, Denitrifying Systems with Separated Streams, Aerobic Systems, and Constructed Wetlands.



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