“By increasing the amount of high-quality reclaimed water that they deposit back into the aquifer, city utilities accrue ‘water credits' they can ‘spend,' to draw ground-water during system emergencies or supply shortages or as demand rises with population, much like a bank account for water,” says Floyd Marsh, water resources manager and practice leader for the Phoenix office of Lockwood, Andrews & Newnam Inc.
“This is the most efficient and cost-effective way to recharge water into the underground system,” says Kinga Stanek, senior project manager at Surprise's Water Services Department.Connecting Treatment to Filtration
Surprise is installing the wells in phases in conjunction with the treatment plant's expansion so the amount of additional treated water matches the water department's discharge capacity. Between now and 2011, a cluster of 32 wells—along with pipelines, filtration systems, booster pump station modifications, and an electrical instrumentation control system that's integrated with the plant's existing SCADA system—will provide an estimated recharge capacity of 10 mgd.
Each well will be 48 inches in diameter and drilled to 180 feet. Since ground-water lies 300 to 500 feet below the surface, water from the wells will trickle through more than 120 feet of sand, clay, gravel, and silt—a process known as water polishing—before it reaches the aquifer.
“Permitting agencies see this as a real advantage because of the additional treatment that the water undergoes,” says Stanek.
To maximize space, the wells will be placed in a rectangular formation with each located 100 feet from the other, a configuration that allows replacement wells to be constructed in between when an individual well fails to perform over time.
The closed-loop design will recharge reclaimed wastewater by:
- Diverting it into two temporary storage basins with a combined capacity of 15 million gallons
- Sending the reclaimed water into a set of pipelines using booster pumps
- Filtering out sediments, suspended solids, and organic matter through a filter system connected to the pipelines
- Injecting the filtered water through vadose zone recharge wells
- Discharging the material backflushed from the filter system into a nearby sewer line, where it will be returned to the plant for recycling.
The department's long-term goal is to build a second recharge facility at the city's recreation campus, located four miles from the wastewater treatment plant.
If all goes according to plan, operators working at the 5-mgd facility may rub shoulders with members of the Texas Rangers Major League Baseball team, who travel to Surprise each year for spring training at the half-acre park.
— Srinivasan is a technical writer for Houston-based engineering consulting firm Lockwood, Andrews & Newnam Inc.