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Frequently Asked Questions

    • Most OSWTFs include a septic tank, which digests organic matter and separates floatable matter, such as grease and oil, and solids that settle in the tank, from the wastewater. Soil-based systems discharge septic tank effluent (liquids) into a series of perforated pipes or chambers buried in a disposal field or pit designed to slowly release effluent into the soil. Alternative systems may use pumps or gravity to trickle septic tank effluent through sand, organic matter (e.g. peat, sawdust), constructed wetlands, or other media to remove or neutralize pollutants, such as disease-causing pathogens, nitrogen, phosphorous, and other contaminants. Some alternative systems are designed to evaporate wastewater or disinfect it prior to discharging it into the soil.
    • Most system failures are related to inappropriate design and poor maintenance. Soil-based systems (with a drain field) may have been installed at sites with inadequate or inappropriate soils, excessive slopes, or high ground water tables. These conditions can cause hydraulic failures and water resource contamination. Failure to perform routine maintenance can cause solids or greases and oils in the tank to migrate into the drain field and clog the system. The easiest way to ensure the longevity of your septic system is to routinely pump the tank every three (3) to five (5) years, not dump unapproved products into the system, and clean the effluent filter inside the tank every six (6) to twelve (12) months.
    • The following items should not be put into the septic disposal system:
      Hair Combings Cleansers Cigarette Butts
      Coffee Grounds Solvents Condoms
      Dental Floss Fat, Grease, Oil Gauze Bandages
      Disposable Diapers Paper Towels Waste Oils
      Kitty Litter Paints Pesticides
      Sanitary Napkins Varnishes Photographic Solutions
      Tampons Thinners

      Do not dispose of non-biodegradable materials with wastewater through drains and toilets as they displace storage volume of the septic tank and will upset the biological activity occurring in the tank.

    • OSWTFs that are properly planned, designed, sized, installed, operated and maintained can provide excellent wastewater treatment. However, systems that are sited in densities that exceed the treatment capacity of regional soils or are poorly designed, installed, operated, or maintained may cause problems. The most-documented problems involve contamination of surface and ground waters with disease-causing pathogens and nitrates.
    • Yes. Private water well Notice of Intent (NOI) permit applications, for properties up to five (5) acres, are available at our office, through Arizona Department of Water Resources (ADWR), or through your drilling company. The application must be filled out completely and accurately, including well driller information. All required documents and fees must be submitted to MCESD. Once the well site inspection is completed, all documents will be forwarded to ADWR for final processing of the well permit.
    • You and your neighbor must contact the Maricopa County Environmental Services Department to obtain the necessary permits and instructions to install a new system on your own lot.

      If a lot split occurs and the OSWTF no longer meets any minimum setback requirement, the system must be relocated. Additional inspections, plan reviews and fees may apply.

      If a lot split had taken place prior to your ownership and the property line now cuts through the existing OSWTF (or the neighbor’s OSWTF), splitting the system between the two lots, the issue then becomes a legal matter. In these cases, it is recommended that you contact legal counsel or your real estate agent to obtain advice on how to rectify the situation. In most cases, each lot will be required to install an OSWTF.
    • An alternative system is any type of septic system other than a septic tank using gravity to convey effluent for disposal into trenches, beds, chambers, or pits. Typical alternative systems include aerobic system, cap system, sand lined trench, intermittent sand filter, Wisconsin mound, composting toilet, peat filter, textile filter, pressure distribution, subsurface drip irrigation, and Ruck system. Alternative OSWTFs must be designed by and stamped with the seal of a Professional Engineer (P.E.), registered to work in the state of Arizona and with expertise in the on-site wastewater field.
    • See for the current approved list of alternative components allowed in the state of Arizona. These components may be used alone or with other components in an alternative septic disposal system. This list is provided by the Arizona Department of Environmental Quality (ADEQ). Maricopa County may have additional requirements or restrictions. You may contact the MCESD OSW Engineer for additional questions regarding these types of systems.
    • No. Only an alternative system requires an engineer to properly design, select and lay out the onsite system. Conventional systems may be designed by the homeowner or any other party authorized by the owner provided all requirements listed in the Arizona Aquifer Protection Permit Rule and the Maricopa County Onsite Wastewater guidelines are observed and satisfied.
    • Yes. All changes must be identified on the newly-submitted, revised site plans with the date of the revision clearly marked on all submittals. Recalculations of the size of the septic system, site plan revisions and additional soils testing may be required, at which time a second plan review must take place before the permit is issued.
    • Yes. Any proposed changes to the septic system that occur after permit issuance will require an additional plan review. New or revised site plans and/or recalculations must be submitted and approved prior to construction. Additional fees will apply.

      Undocumented changes observed during the construction inspection will result in costly delays, additional procedures, and, potentially, additional fees. MCESD encourages all applicants to spend a little extra time planning the project, keep up to date on any changes that do occur throughout the project, and notify the proper authorities of such changes as soon as possible.
    • Yes. The same procedure applies as for a construction inspection. You may designate that it is a partial inspection on your requests. Indicate which components of the system are to be inspected.
    • Leach rock for OSWTFs must be cleaned, washed aggregate with a screened diameter of ¾ to 2 ½ inches and a void space of 30%.
    • The tank should be installed on a six (6) inch bed of pea gravel or sand to maintain stability. This is required when the tank is installed where jagged or large rocks are present. Access openings on the tank must be brought to within six (6) inches of finished grade. If tanks are installed such that the top of the tank is greater than twelve (12) inches below finished grade, MCESD-approved inspection risers (concrete or dual-wall corrugated polyethylene) are required. Tanks deeper than twenty-four (24) inches are required to have a reinforced lid. The top of the tank shall not be greater than sixty (60) inches below finished grade.

      Native soil can be used to backfill the tank excavation as long as there are no jagged or large rocks in the mix that could damage the tank during or after backfilling. If jagged or large rocks are present, the soil must be screened to remove the potentially damaging rocks prior to backfilling.

      The inlet t-baffle and in-line effluent filter at the outlet end of the tank must be easily accessible for maintenance and cleaning. Ensure that the inlet t-baffle can be easily reached and the effluent filter can be pulled up through the smaller inspection port on the top of the tank. If not properly aligned, the larger inspection plugs will need to be removed for routine maintenance.
    • Distribution boxes (d-boxes) must be level, set on a firm foundation and placed in the correct direction. One opening is one (1) inch higher than the remaining openings; this is the inlet side of the d-box. Attach the inlet end of the d-box to the septic tank by a solid pipe at least two (2) feet in length. Pipes must extend into the d-box one (1) inch and be level, secure, and watertight. Once approval to backfill has been granted, seal the d-box lid so that it is watertight. All connections outside of the disposal field must be watertight!
    • Disposal field risers shall be brought to within six (6) inches of finished grade or higher. Disposal pipes that are deeper than twenty-four (24) inches will require a minimum of SDR 35 or equivalent pipe. Trench bottoms and disposal pipes must be level!
    • If your septic system is not functioning properly, contact a plumbing or septic specialist. If one component of the system (tank or disposal) has failed, an Alteration permit to replace that component will be required. If both the tank and the disposal field have failed, a new OSWTF must be installed.
    • It may be possible to use the existing septic system with a new house. See Minor Plan Review for more information.
    • MCESD can only release building permits for unincorporated areas. The building permit will be released when the OSWTF is approved for construction. Building permits will be released after plan review has been completed. Construction in incorporated areas may have different requirements. Contact the appropriate building department for more information.

Please contact the Onsite Wastewater Program at with any questions or concerns you may have.