Seaford wastewater treatment plant to prepare for sea level rise

By Lynn R. Parks

According to a 2012 state analysis, four wastewater treatment plants in Delaware will be affected by sea level rise. One of those is in Seaford.

At the recent Seaford City Council meeting, Judy Schwartz, engineer with George, Miles and Buhr, presented the results of a state-mandated study on what the city has to do to prepare the treatment plant, which sits on the edge of the Nanticoke River, for higher water. Sea level rise, as well as stronger and more frequent storms, are some of the consequences of climate change.

"The state is encouraging municipalities to plan for rising waters and an increase in floods," Schwartz said.

The other cities in which wastewater treatment plants are threatened are Delaware City, Port Penn and Lewes. But Seaford, part of the Chesapeake Bay Watershed, faces a problem that those cities don't, Schwartz said.

According to the National Oceanic and Atmospheric Administration (NOAA), waters are rising twice as fast around the Chesapeake Bay as they are worldwide. The global rate of water level rise right now is 1.8 millimeters a year; in the bay watershed, it's 3.6 millimeters a year.

That is because, Schwartz said, in addition to the level of the water coming up, the land in the watershed is subsiding.

Scientists have suggested a couple of causes for the land subsidence. Some say that humans around the watershed are pumping out so much groundwater that aquifers are compacting, allowing land above them to settle. Alternatively, a study published in the August issue of "GSA Today," a journal put out by the Geological Society of America, suggests that subsidence is simply the land settling back down to where it was before the last ice age. The study says that 12,000 years ago, a large slab of ice to the north of the bay pushed down the land on which it was lying, pushing up the ground to the south and creating what scientists call a forebulge. With the ice long gone, that bulge is now smoothing out.

Whatever the cause, Seaford and other communities in the bay watershed will have to deal with the consequences. "Locally, land subsidence is projected to worsen the effects of sea level rise," Schwartz said. "We are really under a double threat."

Predictions of the extent of global sea level rise vary. The International Panel on Climate Change, set up by the United Nations, predicted in its latest report (2013) that on average, ocean levels worldwide could be up to 1 meter higher by the end of this century. Other reports say that seas could be as much as 2 meters higher than they are now.

In its 2012 study, the Delaware Sea Level Advisory Committee examined three scenarios that could occur by 2100: sea level rise of half a meter, of one meter and of a meter and a half (nearly 5 feet).

Schwartz told the city council that with a half-meter rise in the level of the Nanticoke River, there wouldn't be much change in the coastline near the wastewater treatment plant.

With a one-meter and a 1.5-meter rise, water would flood the park at the city boat ramp and would come up onto Nanticoke Avenue, the access road for the treatment plant.

Schwartz's study also looked at how the plant would be affected by storm-related flooding. Even with just a half meter of sea level rise, a flood could threaten essential structures of the plant, including the primary pumping station and the chlorine tank.

Schwartz said that as the city plans for the next 30 years at the plant, there's no need to consider moving it away from the river.

"We have options for mitigating the risks, to make the plant more flood resilient," she said. In the long term, however, the city might want to look at resituating the plant inland, she said.

Danielle Swallow, a planner with the Delaware Coastal Program, was at the city council meeting. She praised the city for the work it is doing.

"I really applaud Seaford for improving the resiliency of important pieces of its infrastructure," she said.

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