On-Site Wastewater Treatment Facility, formerly known as a septic system or individual sewage disposal system. This is a treatment facility installed to treat and dispose of wastewater, predominately of human origin, generated at the site. The treatment facility may consist of a conventional septic tank or alternative, engineered treatment unit, each using subsurface effluent disposal. The generated design flow is less than 3000 gallons per day.

Aggregate/Leach Rock

Clean, graded hard rock, volcanic rock, or gravel of uniform size, ¾ to 2-½ inches in diameter, with 30% or more void space. Washed or prepared to be free of fine materials that will impair the absorption surface performance. Has a hardness value of three or greater on the Moh's Scale of Hardness (can scratch a penny).

APP Rule

Aquifer Protection Permit Rule.


Any room that has:
  • Floor space of at least 70 square feet
  • Ceiling height of at least 7 feet
  • Electrical service and ventilation
  • Closet or area where closet can be constructed
  • At least one window capable of being opened and used for emergency egress
  • Method of entry and exit into the room which allows it to be considered distinct from other rooms in the dwelling to afford a level of privacy customarily expected for such a room

Design Flow

Daily rate of flow of wastewater for which a facility is designed, in gallons per day (gpd).

Disposal Field

There are two designated disposal fields. One is the primary area designated for construction of the permitted OSWTF. The other is the reserve area set aside for future use, if the primary disposal area should fail.

Effective Depth

Effective Depth (ED) or sidewall absorption area. The depth of the area of sidewall absorption in the disposal field. In trenches and beds, this is the distance between the horizontal, perforated disposal pipe and the bottom of the disposal field.

For trenches, the ED can be one, two, three or four feet deep. For beds, the ED can be one, two or three feet deep. For seepage pits, this is the distance between the incoming pipe to the pit and the bottom of the pit.

Minimum Effective Depth

Minimum ED for a pit is ten feet and the maximum is five feet less than the depth the seepage pit performance test was conducted. In chamber technology installations, it is the distance between the bottom of the louver (top arch) and the bottom of the disposal trench.

Fixture Unit

The number designated by the Universal Plumbing Code to specific plumbing fixtures to express the rate of flow of wastewater from these fixtures.

Limiting Conditions/Limiting Factors

Any feature or condition at the property or within 200 feet outside of the property which may impact the location of the proposed OSWTF and the reserve disposal area.


Maricopa County Environmental Services Department, delegated authority for the Arizona Department of Environmental Quality for Maricopa County OSWTF's.


Notice Of Intent to Discharge. This is the application to construct the OSWTF. The NOID Packet is the application plus all supporting documents required by the APP Rule.

Overall Depth

This is the total depth of the installed disposal field from the top of finished grade to the bottom of the disposal field. The maximum overall depth of the disposal field is five (5) feet less than the depth of the test holes.

Perc Rate

Percolation Rate is the rate of fall, in inch per minutes, of clear water seeping into the ground during a standardized testing procedure. An educated soils analysis can estimate the percolation rate of the soil.