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Phase I - Site and 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).

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.

Instructions for Site and 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.
  • To request an inspection, call 602-506-1787. Please have your permit number available.

For a complete description of the different types of conventional disposal, Phase I application requirements and procedures, and an application packet are required. Download the Phase I Site and Soils Evaluation Packet to obtain the information.

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