Ever sunny and warm, Arizona continues to be one of the nation's fastest-growing states. But while the influx of aging baby boomers and new business is good for the economy, it requires water providers to be increasingly innovative to ensure supply meets demand. In a state that's mostly desert, this means going beyond asking residents to use brooms to sweep sidewalks and driveways, water early in the morning or evening, and make sure that sprinklers aren't spilling water into the street.

Located about 30 miles outside of Phoenix, Surprise, Ariz., is the second fastest-growing suburb of the state's largest city. Like much of the West, what was once a small farming town now encompasses almost 70 square miles of residential and commercial development. Anew home was built in Surprise every three hours in 2005, and, at that rate, population is expected to increase 72% by 2020.

In Arizona, water managers tasked with ensuring supplies meet future demand face a plethora of challenges beyond financing. The state Department of Water Resources, for example, places strict limits on how much groundwater utilities can draw, while the Department of Environmental Quality requires any water that's discharged back into aquifers to be Class B quality or better.

After assessing existing and possible future water sources in light of these regulations, as well as growth projections, the city's Water Services Department identified treated wastewater effluent as its primary source of renewable water. The department projects that, by 2020, almost half of the city's effluent—a total of 36,787 acre-feet/year—can be used for irrigation or to replenish groundwater supplies.

To generate that much effluent, the department is more than doubling its waste-water treatment plant's capacity, from 7.2 to 16.3 mgd, and building a network of wells, pipes, booster pumps, and filtration stations to treat and recharge the additional effluent. In anticipation of this $9.5 million upgrade, managers have been shoring up their capital-improvement budget with permitting and other revenues generated by the city's booming economy.

Making High Quality Affordable

Until now, the department has stored much of the plant's excess effluent in recharge infiltration basins. Given the price of land around Surprise and the basins' relatively low infiltration rates, the result of soil plugging due to total suspended solids composed mainly of organic materials, building more basins was not the most cost-effective option for storing and treating the expanded plant's excess effluent.

Local consultants proposed using vadose zone recharge wells instead. These wells treat effluent to higher quality levels than surface infiltration basins (for an explanation, see the sidebar below) and are so small that an entire cluster of the wells uses less space than the average recharge basin.

Since its development by the Scottsdale Water Resources Department more than a decade ago, other Arizona cities—including Glendale, Mesa, and Gilbert—are deploying vadose zone recharge well technology.