Pecan Water Reclamation Facility Expansion | 2023 WWD Top Projects

When EPCOR acquired the San Tan water and wastewater service area in January 2021, it identified necessary improvements that would cost more than $136 million. Of those improvements, EPCOR chose to prioritize a $21.7 million expansion for the Pecan Water Reclamation Facility (WRF).

An expansion of the Pecan WRF was one of the service area’s most urgently-needed infrastructure investments. The previous utility owner had received a consent order in 2018, which cited capacity expansion and other improvements as ways to address the area’s deficiencies by December 2022. The Arizona Department of Environmental Quality had designated EPCOR as an interim operator, overseeing plant operations and compliance.

EPCOR took on the task of implementing the improvements. It selected the team of MGC Engineering and GHD under a design-build procurement method. The goals of the improvements were to expand the Pecan WRF’s biological nutrient removal (BNR) and water reuse capacity from 3 million gallons daily (MGD) to 4 MGD; replace influent and odor control systems; and improve resiliency and operations/maintenance at the facility.

The project’s limited footprint presented a challenge to the improvement project’s goals.

The existing WRF utilized three BNR treatment plants with Aero-Mod technology, each with 1 MGD capacity. The expansion added an additional 1 MGD plant (Plant 4) to expand that capacity.

The project teams overcame challenges of keeping the plant operational during the expansion work, developing in a constricted footprint, and maintaining the environmental integrity of the site.

“At times, navigating a limited site footprint and congested corridors, it felt as if we were rebuilding a car while driving it, requiring the removal of portions of existing assets while reconstructing with new larger and more robust materials,” said Gary Whitten, senior project manager at GHD. “All this without disturbing daily operations.”

The available site footprint required portions of existing assets be removed while rebuilding the new, larger materials — but without disturbing the operation of existing assets.

The project’s limited footprint presented a challenge to these goals. The facility’s site was surrounded by congested utility corridors, a 115 KV electrical power transmission line, a major county arterial, Queen Creek wash, and residential developments. The available site footprint required portions of existing assets to be removed while rebuilding the new, larger materials — but without disturbing the operation of existing assets. The Pecan WRF stood on a reclaimed water recharge site, and the surrounding infiltration ponds and recharge wells impacted soil quality.

For example, the Plant 3 blower building needed to be demolished to make adequate space for the improved BNR reactor. This required Plant 3 blowers to be set up in a temporary enclosure to maintain process air flow. Then, those blowers were placed in a new building with new blowers. GHD designed helical piles to support the new building under impacted soil conditions.

The project successfully increased BNR treatment capacity from 3 MGD to an average daily capacity of 4 MGD, capable of producing Class A+ reclaimed water.

The project also replaced and upgraded the site’s influent pumping station (IPS), and the preliminary screening and grit removal. It added a new distribution box to split flow and load evenly to each of the four BNR reactors, and added new odor control and building additions along with extensive site and drainage improvements.

Excavation and construction of the new IPS required MGC to install and maintain a temporary bypass pumping system. This temporary system was used to bypass and feed all four plants individually 24/7 for 8 months while the new distribution box was being connected.

The expansion to the Pecan WRF was fully complete by early 2022. The project successfully increased BNR treatment capacity from 3 MGD to an average daily capacity of 4 MGD, capable of producing Class A+ reclaimed water. The additional improvements to the site’s IPS, headworks and general site also increased peak flow capacity to 12 MGD.

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