This story was originally produced by the New Hampshire Bulletin, an independent local newsroom that allows NHPR and other outlets to republish its reporting.
It was a Monday in February with a low of 7 degrees and an average day temperature of 22.9 when Merrimack Station fired up its two boiler units, going online as it typically would to feed the electric grid as an intermittent resource.
But that day, the Bow coal plant — the last of its kind in New England — failed a required stack test, results returned in April would later show. The Department of Environmental Services alleged the plant’s particulate matter emissions exceeded national standards by more than 70 percent.
Stack tests measure pollution emissions subject to the requirements of the Clean Air Act, a federal mechanism to protect public health. In this instance, particulate matter, also known as soot, contains inhalable microscopic solids or liquid droplets that can cause serious health problems. Studies have linked long-term exposure to premature death in people with heart or lung disease, and it can aggravate asthma and respiratory functions.
DES later determined that Merrimack Station, owned by Granite Shore Power, operated out of compliance with the particulate matter emission rate limit of the U.S. Environmental Protection Agency’s Mercury and Air Toxic Standards for a total of 114 hours, or 4.75 days, after the failed Feb. 27 stack test.
According to an analysis of DES records by the Bulletin, February’s stack test was the first one Merrimack Station has failed dating back to 2000. But in recent years, there have been a slew of other reported permit deviations, state records show.
DES warned Granite Shore Power on May 23 that operating either of its primary coal-fired units prior to a successful performance test would “constitute an excess emission and a deviation from permit conditions.” But by then, the plant had already operated for a stretch between February and March, and would soon again in July.
In a letter sent later in August, DES told Granite Shore Power that it had determined one or more of its permit breaches met the criteria of a federally reportable violation, which can result in a variety of consequences from the EPA such as fines and litigation.
DES documents show the department determined in August that Merrimack Station operated out of compliance for a total of 114 hours since its failed February stack test. (Screenshot) “A failed stack test is usually pretty significant,” said Raymond Walters, field operations manager for DES’ Air Resources Division Compliance Bureau.
Meanwhile, Granite Shore Power contests that it has fixed the issue that resulted in elevated particulate matter readings in February, saying that excess emissions did not occur as a result. Asked by the Bulletin how its findings match up with DES’ claim of violations, Granite Shore Power said, “This discussion is pending awaiting the completion of a retest.”
In mid-October, Merrimack Station attempted another stack test with the goal of coming into compliance. But that didn’t go as planned, either. That test was abandoned after one of the plant’s two boilers malfunctioned. The second retest has been rescheduled for Nov. 30 and Dec. 1.
It is unknown if DES has taken any action since its August letter. Thomas Guertin, air compliance programs manager for DES, said he wasn’t able to speak about ongoing or in-process enforcement actions. Once completed, those actions are available to the public in OneStop, an online database maintained by DES.
“A compliance determination can be complex, particularly in this case since both state and federal rules are applicable,” Guertin said. “NHDES usually waits until it has all the facts before making a determination. One fact that we do not yet know, for instance, is whether or not (Granite Shore Power) passes the repeat stack test.”
Failed February test and October retry
Walters said stack tests are federally required for particulate matter and hydrogen chloride. They are planned events that are coordinated between the state, plant owner, and a third party that conducts the test, to make sure pollution control equipment is functioning as it should.
Stack tests can take anywhere between six and 12 hours. For Merrimack Station, which currently operates very intermittently as a “peaker resource” at less than 10 percent capacity, Walters likened a stack test to “starting up a car that you haven’t run for two months.”
DES received the test results and final report from the Feb. 27 stack test in late April, showing Merrimack Station was out of compliance with particulate matter standards. By that time, the plant had already operated from Feb. 27 to March 1.
DES documents show the February stack test exceeded the particulate matter emissions standards by 73.3 percent. But in a related report, Granite Shore Power stated that all air pollution control parameters had been within normal operating conditions during the test and the cause of the failure “could not be determined.”
Despite warning Granite Shore Power that any additional operation would be a permit deviation, Merrimack Station operated again from July 4 to 8 in order to complete a required ISO-New England annual summer claim audit.
DES records show the parties met virtually on July 13 to discuss the continuing violations and Granite Shore Power’s plans to “determine the causes of the failed stack test, the schedule for the retest, and GSP Merrimack’s plan going forward to mitigate future violations.”
In a statement to the Bulletin this week, Granite Shore Power said the issue with the February stack test was “failed mist eliminator tray sections” in the scrubber that resulted in post-process mist, ultimately impacting particulate matter and hydrogen chloride values. Each of the mist eliminator trays, which reduce pollutants that gases may carry, and in turn, improve plant emissions, have since been replaced, the company said.
The failed stack test did not result in any excessive emissions, Granite Shore Power contended, but it did not directly address the DES allegations that it operated out of compliance for 114 hours.
Merrimack Station was scheduled for a retest on Oct. 18, an opportunity to come into compliance with particulate matter standards, but the test didn’t happen. Granite Shore Power said one of the boilers tripped offline “due to an unrelated boiler tube leak.”
Montrose Air Quality Services, the company performing the compliance testing, did not respond to a request for comment. But a copy of its test plan obtained by the Bulletin shows the intent was to conduct three, 120-minute test runs of both coal-fired cyclone utility boilers (Merrimack 1 and Merrimack 2) to determine particulate matter and hydrogen chloride emissions.
Montrose’s plan details the pollution control equipment in place at Merrimack Station. The two boilers have two electrostatic precipitators for reduction of particulate matter, and a selective catalytic reduction system to reduce nitrogen oxide emissions. They also have continuous emission monitoring systems (CEMS) that measure for carbon dioxide, nitrous oxide, and sulfur dioxide.
The stack gases from both operating units combine to enter a wet limestone-based desulphurization system, also known as a scrubber, designed to reduce mercury and sulfur dioxide emissions, and another continuous emission monitoring system is located on the 445-foot-tall common stack. The documents note a new system was recently installed to monitor mercury emissions in accordance with national standards.
Catherine Corkery, senior regional organizing representative for the New Hampshire Sierra Club, learned of the Oct. 18 stack test malfunction after inquiring with DES. She said the gist of a stack test is “all about protecting public health.”
“That really raises our concerns, not only about that day, but about the future operations of this facility,” she said. “We’re really concerned about it. We will be asking our members and supporters to watch on Nov. 30 and Dec. 1 and to take pictures and to be on the lookout in case there is another failure. And we hope that there isn’t.”
Of significance to Corkery is that following the failed Febrary test, Merrimack Station, as noted by DES, no longer qualifies for “LEE status” (Low Emitting EGU), which means it must conduct performance tests more frequently now, once per quarter. Previously, Merrimack Station had qualified for LEE status based on stack testing conducted from 2015 through 2017.
“I think one of the bigger issues here is this is getting more and more expensive,” Corkery said. “These are the really large issues that are looming in the future of this plant.”
On Oct. 19, the day after the abandoned stack test, Corkery photographed emissions exiting from Merrimack Station’s smoke stack, signaling the plant was running. DES was able to confirm that the EPA was on site that day, but the department did not know why.
A request to EPA’s Region 1 revealed that the agency’s Land, Chemical and Development Division had a field visit on Oct. 19 “to talk about their operations,” a spokesperson said. It was not a compliance visit.
Other Merrimack Station permit deviations
Violations that allegedly occurred following the failed February stack test join a slew of other reported permit deviations that happened this year and in 2022, according to compliance reports and other state documents. Those include:
- For approximately 27 days in 2022, Merrimack Station experienced mercury emissions above the 30-boiler operating day rolling average limit when using a single sorbent trap monitoring system for all hours of operation including startup and shutdown.
- On Jan. 15, 2022, Merrimack Station experienced nitrogen oxide emissions above the daily limit of 11.5 tons.
- On Dec. 15, 2022, and February 3, 2023, Merrimack Station experienced nitrogen oxide emissions above the daily rate limit of 0.22 lb/MMbtu.
- On Feb. 24, 2023, Merrimack Station exceeded the opacity (smoke/dust) standard on four occasions.
- On July 7, 2023, Merrimack Station exceeded the nitrogen oxide startup limit by 11 tons, or 98.2 percent.
In its 2023 on-site compliance report, which was done before the results of the failed stack test, DES recommended several actions “to maintain facility compliance with operating, monitoring and recordkeeping requirements,” including boiler operation that prevents exceedances, timely equipment audits, and preventative and corrective maintenance, among others.
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