Facing stricter state and federal regulations for the land application of biosolids more than two decades ago, officials in Boise, Idaho, decided they could save ratepayers money by going into the farming business instead of giving away the byproducts of the city's two wastewater treatment plants.

Before the new regulations, the city was spraying its biosolids (at 2 percent solids) on private lands, giving local farmers first-come, first-served access. Since 1993, Boise has applied biosolids to cropland it owns, harvesting the crops for sale to livestock operations and dairies in southwestern Idaho.

Thanks to favorable commodity prices, the city's Twenty Mile South Farm in 2011 posted record revenues of $2.79 million from sales of crops that include mainly alfalfa hay, corn for silage and winter wheat. Operating and maintenance costs were $2.27 million. Revenue from crop sales helps keep sewer rates down and will support investments in wastewater treatment plant upgrades needed to comply with phosphorus limits in the city's new NPDES permits.

Heading off conflict

City leaders were worried about public concerns over the earlier land application program, according to Ben Nydegger, biosolids program manager for the Wastewater Treatment Division. In particular, they felt that continuing to work with contract farmers would lead to more complaints and potential conflicts with neighbors.

"In the late 1980s and early 1990s, as urbanization was taking place in Treasure Valley, we were getting more questions and concerns from citizens in the subdivisions encroaching on land traditionally used solely for agriculture," Nydegger says. "Boise was one of the fastest-growing cities in the nation during that period."

At the time, farmland was still readily available and reasonably priced. When the U.S. EPA adopted its 503 regulations in 1993, Boise was adding belt filter presses and launching its own farm enterprise with the purchase of a 2,300-acre farm 20 miles south of town. Today, the city is awaiting state Department of Environmental Quality approval to apply its dried biosolids on a spread that has grown to 4,000 acres.

Two sources

The Boise Public Works department operates two wastewater treatment plants. The Lander Street plant, which serves the older part of the city east of the Boise River, was built in 1950 and is permitted for 15 mgd. The West Boise plant, permitted for 24 mgd, was built in 1976. The plants handle a combined average of 28-30 mgd, and operators have some ability to divert flow from one plant to another, if necessary.

The city produces 24,000 to 27,000 wet tons per year of biosolids from its two belt filter presses (Andritz-Ruthner CPF 2.8 SMX-S8) at West Boise. The biosolids from Lander Street are piped under the Boise River to West Boise for pressing.

The biosolids enter the presses at about 2 percent solids and are dried to 12 to 14 percent solids before being transferred to the farm. The pressed biosolids are hauled on three commodity trailers pulled by two Kenworth T800 semi-tractors. The city ships 15 to 19 loads per week, an average of 450 to 550 wet tons.

Preparing for application

On arrival the biosolids are weighed and off-loaded into one of five bunkers, where they are stored until application. The bunkers, covering a total of 3.5 acres, have concrete- or asphalt-lined bases and have Eco Block concrete walls.

To handle the biosolids in the bunkers, the farm staff uses a 2007 Case 921E loader, a 2010 Caterpillar 930H loader, a 2011 Caterpillar 420E backhoe loader, and a 1994 Dresser 525 loader. Most material is spread in spring before planting and in fall after harvest. The bunkers provide six to seven months of storage capacity.

The Boise plants treat the biosolids to Class B quality. Team members test the material for metals, nutrients, pathogens and fecal coliform at least six times a year. "On average, we test eight to 10 times per year," says Nydegger. "From every fifth truckload, we take a handful, and the samples are composited." The composite samples are tested at the Public Works department laboratory downtown.

To the soil

The farm has four spreader trucks: a 2007 Mack CV-713 Granite, a 2010 International 7600, a 2009 International 7600 and a 2004 Kenworth T800. All have Kuhn Knight Pro-Twin Slinger Boxes. When all four trucks are in use, farm workers can apply 30 to 40 loads per day.

Nydegger says the city has faced minimal resistance to its biosolids operation. The farm abuts Bureau of Land Management property on one side, and the few neighbors are dairies.

The farm primarily grows alfalfa hay, corn for silage and winter wheat. Other crops can include oats, rye grass and triticale, a hybrid of wheat and rye. The city has experimented in recent years with planting a double crop of triticale with corn to gain more productivity.

Field work at the farm is handled with help from seven tractors, two swathers, two windrowers, three balers and a sprayer. To deal with the area's semi-arid climate, the farm has an extensive irrigation system with 22 quarter-mile center pivots distributing water pumped from an aquifer 300 feet below the surface. There are also hand lines, corner lines and wheel lines to cover areas the center pivots don't reach. The harvest at the farm has "come a long way with the installation of the irrigation," says Nydegger.

Looking toward expansion

The city is careful to avoid disrupting markets in its corner of Idaho. "We're a large enough producer that we could set the market for feed, so we are very, very transparent about our operation," Nydegger says. "We use pricing data to keep our prices current with the market." Ranchers and dairy farmers seeking stability in their feed supplies convinced the city to sell its products on three-year contracts, and there are producers waiting to get those contracts.

The farm operation has been a winning proposition for Boise. "We can use the sale of our crops — our commodities — to offset the cost of managing our biosolids," Nydegger says. "And with the higher commodity prices we've seen in recent years, it's been a boon to the city."

Boise has used some revenue from the farm to help maintain and upgrade the wastewater treatment facilities, reducing the burden on customers. One planned upgrade involves modifications to meet lower phosphorus limits in the city's new NPDES permits.

Until recently, Boise was operating under NPDES permits last renewed in 1999, before the city acquired a neighboring 1,620-acre farm in 2000 and added another 280 acres in a 2008 land swap. The EPA did not re-issue the city's permits in 2004 or 2009, so the terms of the 1999 NPDES permits remained in effect under administrative extensions.

The old permits mapped the original farm and defined it as the city's site for biosolids application. The new permits issued Aug. 1 do not address biosolids application. "Therefore, once we get Idaho DEQ approval of a Biosolids Management Plan for the entire Twenty Mile South Farm, we should be able to apply on the entire farm," Nydegger says.

Expanding the site

The approval of the BMP is a state requirement that Nydegger tackled after the new NPDES permits were issued. He included the original farm, plus a 1,620-acre parcel (the Watkins addition) and a 280-acre parcel (the Nicholson addition) in the application for the updated BMP.

"DEQ had previously approved a BMP for the original farm site and the Watkins property in February 2004, but we were not allowed to apply on the Watkins site because of the definition of our land application site in the 1999 NPDES permit," Nydegger says.

The additional application area should come in handy as Boise tackles the challenges posed by stricter phosphorus limits. The city is considering a chemically enhanced pretreatment (CEPT) process in which ferric chloride is added to the wastewater to precipitate phosphorus. That would increase Boise's biosolids volume.

The revenue from the additional commodity sales will help Boise if the city finds it necessary to invest in major changes to the wastewater treatment system. As the city looks forward, one option on the table as it makes plans to meet the December 2018 deadline for compliance with the final limits in the new NPDES permits is to decommission the older Lander Street plant and expand the West Boise facility to handle all treatment.

For now, however, Nydegger's focus is on the future operations of the Twenty Mile South Farm and all 4,000 acres he expects to have available for biosolids application. It has been more than a decade since the Watkins farm was added to the city's spread, and Boise's farm workers have yet to apply the first truckload of biosolids to that land. "It's been a long process," Nydegger says. "But we can see the light at the end of the tunnel."