For information only to provide results of a recently completed feasibility study.

Flagstaff Water Services is evaluating how to secure and provide a safe reliable water supply to meet the future needs of Flagstaff's growing population.  One possible water supply may be to purify reclaimed water to produce drinking water at one or both of the City's two water reclamation plants for either direct or indirect potable reuse.  This presentation provides the results of a recently completed feasibility study conducted by Brown & Caldwell Engineering.  The purpose of the study was to evaluate the challenges and determine the capital & operations and maintenance costs from an "inside the fence" perspective on what it would take to add an advanced treatment process at either water reclamation plant.  Additionally, a public outreach effort was undertaken to get a preliminary idea of the public's acceptance of purifying reclaimed water to produce drinking water.

Arizona recently adopted some pilot regulations that became effective in January 2018 to open the door for direct potable reuse.  The pilot regulations allowed for the possibility of treating reclaimed water to drinking water standards on a temporary basis, but only if it is purified thru an advanced treatment process.  The rule contains an interim provision to allow pilot studies until ADEQ drafts a final rule that will include the specific requirements for treating reclaimed water to drinking water standards.  
 
Potable reuse is nothing new.  Indirect potable reuse has been taking place ever since potable water has been mixed with wastewater.  Indirect potable reuse uses environmental buffers, such as a groundwater aquifer or dilution into surface water.  Either indirect potable reuse alternative requires further treatment to assure the water meets potable drinking water standards. 
 
Direct Potable Reuse uses an advanced treatment process and multiple barriers to microbial and chemical contaminants to produce highly purified potable drinking water. 
 
Two alternative treatment trains were evaluated for this study which include:
• Alternative 1 – Reverse Osmosis (RO) -based treatment train; and
• Alternative 2 – Ozone/ Biologically Aerated Filter (O3/BAF), non-RO based treatment train.
Each alternative was evaluated for design production rates determined by the City Water Services Division which include the following phases:
• Phase 1 - 6 million gallons per day (mgd);
• Phase 2 – 10-mgd; and
• Phase 3 – 14-mgd.
 
Phase 3 is the maximum build-out capacity for either facility. Each alternative treatment train was also evaluated at the two water reclamation plants; Wildcat Hill and Rio de Flag. Individual treatment process design criteria were developed for each alternative under each phase and modeled on both sites to understand the spatial requirements of each alternative. This study focused on the feasibility of implementing advanced-treated water augmentation to supplement the City’s potable water supply for direct potable reuse.