Company to pay $270,000 for ‘largest mussel kill in the state’
A fertilizer spill in Dubuque in June 2020 killed hundreds of fish and mussels in Bee Branch Pond. (Photo by Tom McCarthy)
A large agricultural company will pay nearly $270,000 in fines and restoration fees for its June 2020 fertilizer spill that killed hundreds of fish and clams in a Dubuque pond near the Mississippi River, according to the Iowa Department of Natural Resources.
The majority of that money will be used to replenish the mussel populations of Bee Branch Pond, which is the terminus of a watershed that Dubuque has transformed in the past decade with more than $100 million of projects to mitigate flooding and to create a recreational, waterfront green space in the heart of the city.
On June 18, 2020 — about a week after the creek that feeds the pond was stocked with 2,500 juvenile mussels — someone at Gavilon Grain reported the spill of up to 1 million gallons of liquid nitrogen that overflowed from a storage tank.
Gavilon employees had been transferring the fertilizer between two tanks, each of which had a capacity of 2 million gallons.
“It happened at the end of the staff’s shift at night,” said Tom McCarthy, a senior environmental specialist for the DNR who investigated the spill. “They forgot to flip off the switch or tell somebody to check it.”
An estimated 432,000 gallons of the fertilizer overcame two containment barriers and flowed to a stormwater drain in a parking lot that empties into the pond.
Dubuque city officials closed gates between the pond and the Mississippi River to help contain the spill, and Gavilon erected a berm of sand and blocked storm drains.
Heavy rains about a week after the spill led to a subsequent contamination of the pond when stormwater apparently absorbed leftover fertilizer in the pavement of the parking lot, McCarthy said.
It took about three weeks for the presence of nitrates and ammonia in the pond’s water to return to normal levels. In the meantime, more than 606 fish and 181 mussels died, according to the DNR’s kill assessments, and that represents “only a percentage” of the dead creatures.
“This was a huge amount of fertilizer,” McCarthy said. “That’s the largest mussel kill in the state that I’m aware of.”
Gavilon has since installed a system to detect future leaks.
“After a release of fertilizer in June of 2020, Gavilon immediately began working with the Iowa Department of Natural Resources to identify and limit the environmental impact to the local water ways,” the company told Iowa Capital Dispatch in a prepared statement. “This agreed resolution will allow the IDNR to restock impacted wildlife. Gavilon remains committed to being a responsible corporate citizen.”
Gavilon is an international grain merchant with a headquarters in Omaha, Nebraska. It also sells fertilizers and other products.
McCarthy confirmed that Gavilon complied with his mitigation requests promptly and “put a lot of time and effort into it.”
The DNR’s Oct. 25 settlement agreement with Gavilon includes the largest payout McCarthy is aware of for a fish kill in Iowa, and it was fueled by the large presence of mussels in Bee Branch Pond because of its proximity to the clam-laden Mississippi.
The pond is seeded with mussel larvae by fish that swim through the gates between the waters with the larvae attached to their gills and fins, an evolutionary trait of mussels that allows their upstream spread.
The pond is part of Dubuque’s Bee Branch Creek Greenway, which is about a mile long and has a recreational trail and an outdoor amphitheater, among other features. The creek is popular for urban fishing, and there are plans to make the pond more accessible to anglers, McCarthy said.
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