Idaho cities look to irrigation to keep sewage out of river

Ken Windram frequently hears flattering remarks about the 55-acre grove of hybrid poplar trees grown by the Hayden Area Regional Sewer Board.

During the summer, the trees provide a green oasis on the windswept Rathdrum Prairie. In fall, they shed showers of gold leaves.

Aesthetics are a side benefit. The poplars are cultivated for their sponge-like roots. During the summer, the poplars and adjacent fields of alfalfa and orchard grass soak up 1.2 million gallons of treated wastewater daily, said Windram, the sewer board’s manager.

The irrigation keeps the effluent out of the Spokane River, where it would nourish noxious algae blooms. Instead, the nutrient-rich wastewater helps fertilize crops.

Hayden’s system could become a prototype for other Idaho cities. Irrigating 4,000 acres on the prairie with treated wastewater might help solve the long-term sewage disposal needs of Post Falls, Hayden and Rathdrum, according to the Rathdrum Prairie Wastewater Master Plan, which looks 40 years into the future.

By 2055, the cities’ populations could quadruple to 180,000 residents, according to some projections. Even if the growth occurs at a more moderate pace, the towns still will be dealing with millions of gallons of additional sewage, said Paul Klatt of J-U-B Engineering, author of the master plan commissioned by the three cities and Kootenai County.

As new residents go about their daily lives – showering, flushing toilets, laundering clothes and washing dishes – they’ll each produce about 73 gallons of sewage a day.

“It’s the most expensive water you’ll ever irrigate with or discharge into the Spokane River,” predicted Klatt.

And federal discharge regulations are tightening for the Spokane River, which is already overtaxed from phosphorus during summer months. Permits for new discharges into the river are likely to require millions of dollars in upgrades to existing treatment plants.

Irrigating crops with treated wastewater is a partial solution, said Terry Werner, Post Falls’ public works director. Removing the city’s pipe from the Spokane River isn’t feasible, because the sprinklers can only be turned on during the growing season, he said. But diverting some of the wastewater for irrigation takes pressure off the river during the summer, which is when most of the water quality problems occur, Werner added.

Between them, the cities of Post Falls and Rathdrum own about 900 acres of farmland on the prairie. In the next six months, Werner said, Post Falls will apply for a water reuse irrigation permit from Idaho Department of Environmental Quality.

The water from city sprinkler heads must be absorbed by crops. Treated wastewater can’t seep beyond the plants’ root zones or it might contaminate the Spokane Valley/Rathdrum Prairie Aquifer, which provides drinking water for more than 500,000 of the region’s residents.

“The bottom line is that there can’t be any degradation,” said John Tindall, a DEQ engineer. “We have to protect the drinking water.”

Open-space advocates endorse the idea of irrigating with wastewater. It may be the only way to preserve agricultural ground on the rapidly developing Rathdrum Prairie, said Bob Flagor, administrator of the Kootenai-Shoshone Soil and Water Conservation District.

“If that’s going to be the last 4,000 acres on the prairie, I’ll take it,” Flagor said. “If that’s going to allow a few people to continue farming, I’ll take that, too. It will allow my grandkids to see what I grew up with, and what I love.”

Flagor, who grew up in the Sacramento Valley, counts the Rathdrum Prairie among his favorite landscapes. He often drives the back roads to Spokane, appreciating the sights of center-pivot irrigation systems and hawks hunting the remaining open fields.

“One of my simple pleasures is watching a hawk nail a vole. I’m awed by how acute their eyesight is,” Flagor said. “Once the subdivisions and roads go in, you don’t see that anymore.”

A 2003 study estimated that 10,000 acres of open space remained on the Rathdrum Prairie. Kootenai County’s new comprehensive plan steers future housing development to the prairie, saying the flat ground is among the best suited areas for growth, according to a draft of the plan, which will guide land-use decisions over the next 20 years.

If the cities decide to expand their water reuse programs, they’ll have to compete with developers for ground. That’s one of the drawbacks of the plan, Werner said.

“It’s getting harder and harder to find large acreages out there,” he said, and prices are climbing, too.

Land on the Rathdrum Prairie costs roughly $30,000 per acre, according to estimates in the wastewater master plan. So purchasing an additional 4,000 acres would cost around $120 million.

Flagor said cities could stretch their money by buying development rights. Private farmers would still own the property, but deed restrictions would require keeping the land for growing crops.

Federal funds to purchase development rights on ranch and farmland are available through the Natural Resource Conservation Service, which is part of the U.S. Department of Agriculture. The land has to meet criteria, said Bob Bartholomew, assistant state conservationist for the conservation service in Boise. But parcels on the Rathdrum Prairie might qualify for funding under two programs, he said.

One program buys development rights on farms and ranches threatened by suburban growth. A government or nonprofit agency must put up matching money to tap the federal funds, Bartholomew said. Another program, aimed at saving native or nonnative grasslands, doesn’t require a local match.

The Hayden sewer board bought the land for the poplar farm in the mid-1990s. It owns 472 acres near the Coeur d’Alene Airport and grows trees and crops on about 300 acres.

A weather station at the site tracks humidity, soil moisture and precipitation. During the irrigation season, the sprinklers are adjusted throughout the day, so the crops don’t get over-watered. DEQ regulates the operation as part of protecting the aquifer.

“It’s not just a matter of throwing the seeds out there and turning on the irrigation water,” said Windram, the sewer board’s manager. “There’s a lot of management involved.”

When soil moisture and weather conditions don’t allow the sprinklers to run, the wastewater has to be stored for another day. And the sprinklers can’t be turned on until the plants actually start growing. Some years, the crops need watering by mid-April. Other years, they’re basically dormant until June.

“As a wastewater guy, I’ve got to become a part-time farmer,” Windram said. “I’ve got to get rid of that water, but I can’t irrigate if it’s raining.”