Phase I - Site & Soils Evaluation Inspection

A site/soils evaluation is a comprehensive investigation to determine the site suitability for the onsite wastewater treatment facility (OSWTF). This is a two-part investigation:
  1. Identify any limiting conditions which may affect the size, type and locations of the OSWTF.
  2. Evaluate the soils to establish Soils Absorption Rate (SAR).

Test Holes

Excavate thee test holes on the site-two in the proposed primary disposal area and one in the proposed reserve disposal area. The test holes must be 5 feet deeper than the proposed overall depth of the disposal field but at least 12 feet deep. Test hole width should be about 18 inches to 36 inches in width or about the width of the excavation bucket.  Test holes should not be drilled.


Stockpile the tailings from each of the test holes in two separate piles. The top half of the excavation must be placed closest to the hole and the bottom half of the excavation must be placed farthest from the hole. A total of six stockpiles should be at the site and available for inspection. Label each stockpile to indicate at what depth the material was excavated.

Conducting Evaluations

Maricopa County Environmental Services Division (MCESD) staff can conduct the site and soils evaluation for trench, chamber, or bed disposal. Arizona-registered engineers, geologists, or sanitarians (with prior MCESD approval) may also conduct the evaluations or percolation tests.

If the proposed disposal method is a seepage pit, the site evaluation and seepage pit performance test must be conducted by an Arizona-registered engineer or geologist. Site evaluations conducted by persons other than MCESD staff must be submitted on the ADEQ Site Investigation Report Form (PDF).

Construction Inspections

Final inspection requests must be accompanied by a completed Request for Discharge Authorization Form (PDF). A new or altered onsite wastewater treatment facility must receive a Discharge Authorization from the Department before operating the facility.

Advisory Inspection Upon Request

You may request an advisory inspection for a fee of $325 per property. The property must be under your ownership and the Department must have an active permit application on file.  To submit a request, send an email to the Maricopa Onsite Wastewater Systems Program with the address of the property, your contact information and when you would like to schedule the inspection.

Please allow at least 72 hours in advance for scheduling. We will respond to confirm your request and provide payment instructions. Please note that the fee must be received before the inspection can take place.