Digester: boon or bane for water quality?

Michelle Monroe

By Michelle Monroe

Executive Editor

The Facts

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ST. ALBANS — Will a proposed manure digester for St. Albans Bay reduce the amount of phosphorous entering the bay?

That’s the question at the heart of concerns raised about the project by the St. Albans Area Watershed Association (SAAWA) and questions posed by the Agency of Natural Resources.

Last week, project developer Green Mountain Power temporarily suspended its application before the Public Service Board (PSB) for a certificate of public good in order to develop a response to those concerns and questions.

The proximity of the project to Jewett Brook, an impaired waterway is a concern, as it what will happen to phosphorous removed from the manure, according to Marli Rupe, Agricultural Water Quality Specialist for the Agency of Natural Resources (ANR).

A third concern, cited by both Rupe and Deputy Secretary of Agriculture Diane Bothfeld, is the documentation required to make certain the promised phosphorous reductions are achieved.

GMP and the farmers in the project will need to keep accurate records of how much phosphorous is in the digestate – the liquid left after the manure has gone through the digester – when it is spread on the fields. The agencies will also want to know where it was spread, the levels of phosphorous in those fields, what crops are grown on the fields and the yield, explained Rupe.

Both the farmers and GMP have indicated a willingness to provide that detailed accounting, said Rupe.

“That way we’ll be able to see how the phosphorous is managed,” Rupe said Friday. “If it’s managed the right way, it has the potential to reduce phosphorous… getting into the bay.”

GMP’s proposal calls for manure on two farms in St. Albans Bay, the Bourbeau and Bess-View farms to pipe manure to the digester site leased from Bess-View. In addition, manure from a third farm would be trucked to the site.

Between them, the three farms have 2,000 milking cows, Bothfeld testified.

Another reason for the detailed accounting is making sure those cow numbers don’t increase, according to Bothfeld, who wrote: “The Agency needs to have confidence in the records of imported material from each farm in order to ensure that herd increases are not occurring on the farms beyond the permit limit. From a public perception standpoint, there appears to be a financial benefit to the participating farm and Green Mountain Power in the farm increasing its herd size.”

In a letter to the PSB, SAAWA expressed concern the digester will lead to more cows on those farms. Currently, farms cannot add cows if they do not have a means for dealing with the resulting manure, such as the land base necessary for spreading.

With the digester taking manure, SAAWA fears the farmers will add cows.

“Historically, improvements to ‘manure handling’ have not resulted in improved water quality – they have resulted in more cows and, therefore, more corn and more water problems,” wrote SAAWA. “A digester in the watershed will institutionalize industrial farming in our watershed, and any move to reduce the number of cows in our watershed will now, after the installation of the digester, become more difficult. It is clear that fewer cows are key to water quality health.”

“It’s moving things in the wrong direction,” said SAAWA President Steve Cushing. “It has the potential to really increase the amount of phosphorous going into the bay.”

While a digester may remove phosphorous from manure, it doesn’t address the issue of land use and agricultural practices, Cushing pointed out. Cornfields, for example, are a leading source of phosphorous.

Instead, the digester may result in “promotion of an activity that is hurting water quality in the bay the most,” said Cushing.

He added the problem is not agriculture, but a model of agriculture that results in runoff. Cushing pointed to another farm in the watershed adjacent to an impaired waterway, the Reynolds farm, as not harming water quality. The Reynolds farm, which is organic, does not have the kind of bare fields found on nearby conventional farms, he noted.

Josh Castonguay of GMP said the goal will be to remove 70-80 percent of the phosphorous from the manure before returning it to the farmers for spreading. Castonguay indicated GMP will have the ability to alter the phosphorous content of the manure based upon the nutrient needs of the fields where the digestate will be spread.

According to Rupe’s testimony, 39 percent of the fields owned by the three farms have either high or very high phosphorous levels already.

Castonguay suggested the ability to spread digestate with very low phosphorous levels on those fields would result in a reduction in phosphorous levels in those fields over time.

“Limiting the runoff is also key,” he said, indicating cover cropping and other practices would still be needed to reduce the amount of phosphorous getting into the lake. In addition, GMP is investigating ways to potentially help the farmers in acquiring manure injectors.

“The farmers that are part of this system will also have to take more responsibility,” said GMP spokesperson Kristin Carlson. “We want this to be a model. We also want the these farms to be model farms.”

The phosphorous removed by the digester will be part of a solid cake. Where that phosphorous goes will be key to reducing the total phosphorous within the watershed, explained Rupe.

Where that phosphorous will go is a question GMP is still exploring, according to Castonguay, including shipping it to areas of the country which are deficient in phosphorous.

A concern of both ANR and SAAWA is the proximity to Jewett Brook and Black Creek Swamp.

“Any release or spill of manure or digestate beyond a de minimus amount that reaches the wetland or brook would have an adverse impact on water quality. Manure spills can lead to ammonia toxicity. Ammonia is highly toxic to aquatic life and is a leading cause of fish kills,” Rupe wrote in her testimony.

“There’s a history of these things that have had spills,” said Cushing.

Rupe expressed confidence GMP will ultimately produce a satisfactory plan for containing spills, stating, “I have no doubt they can figure it out.”