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Scientists Experiment with Bioreactors to Address Pollution from Bay Region’s Springs

There’s not much that seems special about the water gurgling out of the ground at Peyton Yancey’s farm in Virginia’s Shenandoah Valley. It is clear and cool. At times, the area around the spring is full of salamanders. Last year, it attracted nesting geese.

“This is Smith Creek right here — the origin story,” said Kurt Stephenson, as he knelt by the remains of the springhouse foundation.

The spring is, indeed, the starting point of a 35.5-mile waterway that flows to the North Fork of the Shenandoah River.

Along the way, the rivulet is joined by other creeks and springs as it drains more than 100 square miles of forests and farmland. It also gathers nutrients — nitrogen and phosphorus — from those areas, much of which will eventually work its way to the Chesapeake Bay. There, they contribute to algae blooms and poor water quality.

But part of the “origin story” at the spring is that Smith Creek is polluted with high levels of nitrogen before it even begins, much of which likely originated many miles away and many years ago.

“What is coming out of this spring, on average, is about 16,000 pounds of nitrogen a year,” said Stephenson, a Virginia Tech professor of agricultural economics.

That, he noted, is nearly three times as much as the amount discharged annually from the Strasburg wastewater treatment plant farther down the Shenandoah Valley, which serves about 7,000 people.

The spring’s water went untreated until four years ago when an underground bioreactor was built on the farm. Now, about 20% of the spring water is diverted through a white plastic pipe to a buried bed of wood chips. About a quarter of the nitrogen that flows into the pipe is removed before the water is returned to Smith Creek.

After years of monitoring and tinkering with the device, Stephenson and colleague Zach Easton, a Virginia Tech professor of engineering, think bioreactors could be installed at many springs throughout the Bay watershed.

The spring on the Yancey farm is only the tip of the iceberg when it comes to nitrogen bubbling out of the ground. The U.S. Geological Survey has identified 1,034 springs in Virginia, Maryland, Pennsylvania and West Virginia — not all in the Bay watershed — and has monitored nitrogen concentrations at 644 of them.

Stephenson and Easton calculate that those monitored springs pump out more than 13,000 pounds of nitrogen a day, or around 4.9 million pounds a year — more than the 2.9 million pounds discharged from the District of Columbia’s Blue Plains Wastewater Treatment Plant, by far the largest treatment plant in the watershed.

The actual amount would almost certainly be higher if nitrogen data was available for all of the sites. Further, the USGS figures don’t include all of the springs in the Bay region: Easton recently found an additional 600 listed in a Virginia database.

“It’s a big potential contribution [of pollution], and we’re probably only scratching the surface of the total,” Easton said. “They’re all over the place. These are only the ones that have been identified by state and federal agencies.”

Treating spring discharges with bioreactors wouldn’t solve the Chesapeake’s nutrient problem but, with the region needing tens of millions of pounds of additional nitrogen reductions to meet cleanup goals, it could help.

The idea is gaining traction. Virginia’s Bay cleanup plan calls for achieving 300,000 pounds of nitrogen reductions annually using bioreactors at springs. Officials estimate that would require about 100 installations, with several slated to go in this year.

The state is supporting ongoing research by Easton and Stephenson to help devise a program that could encourage landowners to install bioreactors. Other states are showing interest as well, Easton said.

Attacking a long-standing problem 

It is a way to address at least a portion of the “legacy” nitrogen in the Bay watershed.

Much of the nitrogen in streams does not run directly off the land. Instead, it seeps from farm fields or septic systems into the soil until it reaches groundwater. Then, it moves — often great distances — until the groundwater intersects the bottom of a stream or emerges at a spring. That journey can take years, even decades.

Treating legacy nitrogen is difficult and often impossible. In places, the roots of a mature forested stream buffer can reach far enough to pull some of it out of the water table, but most evades management actions.

Groundwater that gurgles out of springs is different, though. It often contains significant amounts of nitrogen and is concentrated at a specific point, almost like a pipe out of the ground. That presents a unique opportunity to capture the water and treat it with bioreactors.

Bioreactors are a relatively simple technology. A trench is excavated, lined and filled with wood chips. Then water is piped in.

Carbon in the wood chips provides fuel for microbes that break down nitrogen in the water, transforming it to nitrogen gas that eventually escapes to the atmosphere, where it makes up most of the air everyone breathes.

Bioreactors themselves are nothing new. They’ve been around for several decades in Canada and the Midwest, mostly to treat water from drain tiles under farm fields before reaching drainage ditches.

About a decade ago, they started to be used in the Bay region, mainly on the Eastern Shore, to treat farm tile drainage systems and, in some cases, ditches.

Drew Koslow, a former Choptank Riverkeeper in Maryland, worked with farmers on some of the first installations and later helped with bioreactors in Virginia, where he met Easton.

Easton had installed a bioreactor at a Virginia Tech test site outside Blacksburg in 2015, which was the first attempt in the region to use the device on a small spring.

Impressed with that potential, Koslow, then working with the nonprofit Ridge to Reefs, joined the Virginia Tech researchers and others to secure roughly $70,000 for a larger spring project.

Ultimately, the U.S. Department of Agriculture’s Natural Resources Conservation Service helped to identify the spring on the Yancey farm. The Yanceys were willing partners, having participated in several NRCS conservation projects on their 225-acre, fourth-generation farm.

“The water is clear and cool and looks just beautiful,” Koslow said of the spring, which pumps out about a half-million gallons a day on average. “Yet it’s got that pretty heavy nitrate load, really discharging like a wastewater plant.”

No one knows where that originates.

The area is underlined by karst geology where water flows through a maze of cracks, caverns and gaps in limestone rock before it emerges, often many miles from where it entered.

Built in 2020, the project included the design, engineering and construction of the 50-by-150-foot bioreactor with a 2-foot layer of wood chips topped with 6 inches of soil — along with the piping needed to carry the water, spread it through the reactor and return it to the stream. It reduces the amount of nitrogen flowing downstream by about 1,200 pounds a year, with the potential to reduce more.

It requires little maintenance and is expected to last for about 15 years, when the carbon from the wood chips will be fully consumed. At that point, the chips will need to be replaced.

Although it has high upfront costs, Stephenson and Easton estimated that the nitrogen removal cost over the life-span of the bioreactor is only $8–$12 a pound.

That’s roughly the same or less than the cost of many other agricultural nutrient reduction practices, and it’s significantly less than the costs of installing most urban stormwater controls. Unlike some practices, like planting nutrient-absorbing cover crops, it does not need to be repeated each year.

“It’s a tool that shows good promise for treating a source of nitrogen that has been otherwise untreatable,” Easton said.

Paying for performance

Despite the potential, landowners are not flocking to install bioreactors. On Maryland’s Eastern Shore, only a handful have been installed in tile drainage systems, even though the state helps farmers with the expense, which can help pay for costly tile repair and maintenance.

Bioreactors on springs, by contrast, usually provide no direct benefits to the landowner. The nitrogen emerging from springs — unlike that found in tile drains and ditches, which originated on adjacent fields — often comes from someplace else, so landowners essentially are paying to clean up someone else’s pollution.

But Easton and Stephenson say there is a way to make bioreactors more appealing: Pay landowners for the amount of nitrogen removed.

Most nutrient reductions on farms are achieved through programs that pay landowners a portion of the cost to use “best management practices,” such as cover crops, streamside buffers and fencing to keep livestock out of streams.

The nutrient reductions from those practices can vary widely from place to place, and it is often unclear if they are performing as well as anticipated.

That’s created more interest in “pay for performance” systems, in which someone is paid for actual nutrient reductions — not assumptions about how a practice might perform.

Stephenson and Easton say that spring bioreactors are ideal candidates for pay for performance because the nitrogen removal is easily measured. They have established a monitoring system at the Smith Creek site that provides regular measurements of the water and nitrogen going in and out.

It shows that such near-constant monitoring is largely unneeded. The percentage of nitrogen removed remains mostly unchanged, regardless of other factors such as flow, Easton said. So only periodic sampling may be required to determine how much nitrogen is removed, and how much to pay a landowner.

Easton and Stephenson are also looking for ways to get even better results. In December, they placed a pond liner and sandbags around the spring box to better trap the water and push more through the pipe to the bioreactor. At a cost of roughly $300, it doubled the flow — and greatly increased nitrogen removal.

“That’s an example of an incentive that a pay-for-performance type program would offer,” Easton said. “You could double your load removal and also double your ‘income’ from the project.”

Still, bioreactors are no silver bullet for the Bay’s nutrient problem. They require willing landowners and the right site characteristics. There needs to be enough slope to allow water to flow downhill to and through the bioreactor and then drain into the stream.

The amount of the spring water that can be treated is also limited; state guidance only allows half of the flow to be diverted.

“You’re always going to be limited by landowners, you’re always going to be limited by the landscape and where you could actually build one,” said Kevin Tate, director of conservation with the Alliance for the Shenandoah.

The nonprofit organization has funding from the National Fish and Wildlife Foundation to install two bioreactors.

But, Tate cautioned, while it’s part of the solution, “it’s not going to fix everything.”

Bioreactors don’t resolve the core problem: Too much nitrogen is being put on the landscape, which eventually leads to elevated concentrations at springs. And bioreactors don’t provide additional benefits as other on-farm practices do. Cover crops can help improve soil health, for instance, while forested buffers improve the aquatic health of streams.

“Bioreactors are very pointed to this nitrogen issue,” Tate said. “I know that’s something we need to solve, but I don’t want to redirect all of our focus on that when we could be gathering tons of other benefits from the other types of best management practices out there.”

Original Source: Bay Journal