Site & Soils Evaluation

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

Who Can Conduct 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).

Instructions for Site & Soils Evaluation

  • Three test holes (two in the primary disposal area, one in the reserve disposal area), excavated to a minimum depth of 12 feet, are required.
  • Soil removed from each test hole is to be stockpiled in two separate piles, with material from the top half of each excavation placed closest to the hole. A minimum of six stockpiles must be presented at the site.
  • Request an inspection by contacting the Onsite Wastewater Systems Program. Have the permit/tracking number and address available and provide any special instructions or requests (e.g. call to meet at site, gate code).

Applications & Instructions


Descriptions of the different types of conventional disposal methods, detailed instructions for preparing for site and soils evaluations, application instructions and forms and online Permit Application Submittal instructions can be found on the Forms and Applications page.