Rochester and Dover Wastewater Treatment Plant Upgrades Reduce Nitrogen Levels in the Great Bay Estuary to Historic Lows

City of Rochester
John Storer, Director of City Services
31 Wakefield Street
Rochester, NH 03867


Tuesday, Feb. 7, 2017

Contact: John Guilfoil
Phone: 617-993-0003

Rochester and Dover Wastewater Treatment Plant Upgrades Reduce Nitrogen Levels in the Great Bay Estuary to Historic Lows

ROCHESTER — Director of City Services John Storer is pleased to announce that through a joint effort, the Rochester and Dover wastewater treatment facilities have implemented several voluntary measures to dramatically reduce the amount of nitrogen being released into the Great Bay estuary.

In 2009, the New Hampshire Department of Environmental Services recommended that a 0.3 mg/L Total Nitrogen concentration throughout the estuary was necessary to protect ecological resources, particularly eelgrass.

For the past five years, communities of the Great Bay Municipal Coalition (GBMC), which include Rochester and Dover, have implemented cost-effective measures to ensure the protection of Great Bay estuary resources. This included an independent review of the estuary in 2014 that recommended testing the effect, if any, of the eelgrass response to nitrogen level reductions in Great Bay, and, in turn, to look at other factors that may be the cause of impacts to eelgrass.

Although GBMC has challenged the scientific basis of the New Hampshire Department of Environmental Services’ recommendation, Rochester and Dover have invested millions of dollars in a series of significant voluntary actions to decrease nitrogen in their wastewater treatment facilities. This has resulted in historically low levels of nitrogen in Great Bay. For the period of 2012 through 2015, water quality data indicates that the average Total Nitrogen concentration at Adams Point in Great Bay was below 0.3 mg/L

“We understand that in the 1990s there was a high presence of eelgrass in the estuary, but the current collective nitrogen levels from municipal treatment plants are less than 50 percent of what they were in the ‘90s,” Storer said. “If eelgrass is not flourishing now, when there is a historically low level of nitrogen in the estuary due to our voluntary efforts, other factors like disease, temperature, salinity, herbicides and storms should be investigated as possible causes of eelgrass impact before additional nitrogen reduction efforts are implemented.”

In Rochester, since 2011, the wastewater treatment plant cut its nitrogen production by 80 to 85 percent through innovative initiatives. These include:

    • A nutrient control plan that identified sources of nitrogen and outlined strategies for remediation. (Approximately $95,000)
    • Voluntary contributions in 2016 to the Piscataqua Region Estuaries Partnership in support of programs for the estuary. This includes collecting and presenting on data that protects and improves the water quality and overall health of Great Bay. ($27,000)
    • Replacement of aeration basin diffusers — created an efficient system for mixing oxygen into the water, which enhances the microbial process to better ensure clean water is sent into the bay. ($200,000)
    • Ongoing automation upgrades to improve efficiency in the wastewater treatment plant’s operational controls. ($315,000 to date)
    • Annual budget costs due to electricity consumption, lab testing, river monitoring, labor, equipment, etc. ($100,000)

Additionally, moving forward, Rochester is in the process of completing:

  • Aeration basin upgrades for more efficient mixing zones. ($200,000)
  • Analyzer upgrades that provide real-time notifications of nitrogen levels and reductions inside the treatment center. ($53,000)
  • A storage and feed system for acetic acid (similar to pickle juice) that is used to remove nitrogen from the water. ($1.2 million)

“Whether eelgrass will rebound due to these water quality improvement remains unknown, as numerous factors influence eelgrass health,” Storer said.

In 2011, Dover also committed to voluntarily begin the process of upgrading its wastewater treatment plant to reduce nitrogen from its discharge. A facilities management plan, completed in March 2013, identified the most efficient means to implement nitrogen removal, which included $3 million in upgrades to Dover’s treatment plant.

In August of 2015, the upgrades were completed and since then nitrogen has been reduced by 75 to 80 percent in Dover.

“Water quality monitoring in the estuary has shown a dramatic drop in nitrogen levels in recent years,” said Dean Peschel, Dover’s environmental consultant. “Due to improvements undertaken by the cities of Dover and Rochester, the 2016 Total Nitrogen levels in the Great Bay estuary are expected to be well below the 0.3 mg/L Total Nitrogen value.”

Peschel also noted that three more treatment plants that discharge to the Great Bay estuary will be coming online with new facilities in the next few years, and nitrogen levels are expected to be even lower.