City considers nutrient trade plan with Invista nylon plant
By Lynn R. Parks
Throughout the Chesapeake Bay watershed, states, counties and municipalities are working out ways that they can meet a 2010 mandate from the U.S. Environmental Protection Agency that the amount of nutrients, primarily nitrogen and phosphorus, being dumped into the watershed be significantly decreased. In Seaford, where treated wastewater is deposited into the watershed's Nanticoke River, officials were concerned that because of the EPA order, the city would have to embark on a costly renovation of its wastewater treatment plant.
That renovation seems to have been put on hold, with a pending agreement between the city and the Invista nylon plant that would allow for "nutrient trading" between the two.
City manager Dolores Slatcher presented the proposed agreement to the city council at last week's meeting. By unanimous vote, the council agreed to allow the city to pursue the agreement. Final approval has to come from the state. The agreement will also come back before the city council for a final OK.
The city's wastewater treatment plant is currently permitted to treat 2 million gallons of waste a day. It treats about 1 million gallons of waste a day.
Slatcher told the council that under the EPA mandate, without an upgrade to allow it to remove more nitrogen and phosphorus from the waste, the plant's daily allowance would be decreased to 1.33 million gallons a day. That would hamper the city's efforts to attract more residents and businesses, she said.
But just down the river from the treatment plant, Invista, which also dumps treated waste into the Nanticoke, has a permit for 27,000 pounds of nitrogen a year more than it uses. Under the agreement, the plant could transfer that allowance to the city.
The amount of nitrogen going into the river wouldn't change, Slatcher said. But the city could buy some time before having to upgrade its treatment plant to meet the new standards.
On the other hand, Invista is interested in being allowed to dump 4 pounds of phosphorus per day more than it is permitted to do. Under the agreement, the city will transfer part of its phosphorus discharge permit to the plant.
"We may likely experience a higher chemical cost to meet our phosphorus limit," Slatcher wrote in a memo to council members.
But that will be less expensive than upgrading the treatment plant, she added.
The agreement would be good for five years, with an option to renew for another five years. Slatcher suggested to the council that the city should begin working on a design for a plant upgrade in 2019, to meet the EPA standards by 2025. By that time, the city will be allowed to discharge just 50 percent of its current nutrient load.
Slatcher said that delaying the plant upgrade to 2019 would also mean that the city would be able to pay off the loan that it took out for the most recent plant renovation. That loan will be paid off in 2017.
Under the EPA mandate, total nitrogen going into the Chesapeake has to be reduced by 25 percent. Total phosphorus going into the bay has to be reduced by 24 percent.
Pollution control measures have to be 60 percent completed by 2017, and totally in place by 2025.
"Actions will have significant benefits far beyond the Chesapeake itself, helping to clean rivers and other waterways that support local economies and recreational pursuits like fishing and swimming, and serve as drinking water sources," the EPA said in a December 2010 announcement of the mandate.
Nutrients are found in fertilizer as well as in animal waste. When they make their way into waterways, they encourage plant growth, just as they do when they are applied to farm land or home gardens. Microscopic algae in particular thrive in nutrient-rich water, especially in summer when the water is warm. The algae grow in the millions, forming large clouds of what is called a red tide or mahogany tide.
On bright sunny days, algae, like all thriving plants, give off oxygen through photosynthesis. But at night and even on cloudy days, the plants switch over to respiration, using up oxygen in the water and expelling carbon dioxide. They also die and the resulting decay consumes even more oxygen and generates toxic hydrogen sulfide.
Low oxygen, or hypoxia, leads to death among fish and shellfish. Scientists say that it also leads to reproductive problems in fish.
In addition, algae blooms block the sun from reaching bottom-growing sea grasses, which provide a nursery and breeding habitat for aquatic life.
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