Delaware Public Media

Study shows heavy rain contaminates ocean off Rehoboth

May 15, 2018

Results from a state-mandated study coinciding with Rehoboth Beach’s ocean outfall project show heavy rains contaminate the city’s stormwater outfalls and by extension the nearby ocean.


The study done by engineering firm GHD shows Rehoboth’s stormwater has high levels of a bacteria called enterococcus when it drains into the ocean - just six hours after heavy rain. Results from the city's stormwater outfalls on streets like Maryland Ave. showed the stormwater had between 2,000 – 5,000 colony-forming units per 100 milliliters in that six-hour period. GHD’s recommendation was 60 cfu/100 mL. 

High levels of this bacteria can originate from things like bird droppings. According to DNREC’s Recreational Water Program, “Enterococcus does not cause illness, it is used as a fecal indicator for other species of harmful bacteria or viruses that may be associated with feces, especially if they originate from human sources.”

According to the GHD study, the bacteria levels dissipate significantly within 24 hours, roughly to 60 – 75 cfu/100 mL. Within 48 hours, it has basically fully washed away.

The 24-hour results make some ocean conservationists, like the Delaware chapter of the Surfrider Foundation, wonder why the city isn’t putting up swimming advisory signs after a major storm event.

“It’s a public health issue,” said Gregg Rosner, the group’s conservation chair. “People should avoid water contact. Other beaches in the United States have posted signage.”

A storm drain warning sign.
Credit Gregg Rosner / Delaware Surfrider Foundation

Rosner lived in California for 10 years, where he said “no swimming” signs were posted during these types of events. He says he’s also been to beaches in North Carolina and Florida that have them.

In August 2017, officials from the Department of Natural Resources and Environmental Control found high levels of bacteria near Rehoboth Ave., prompting a recreational swimming advisory that lasted less than 24 hours. The city cautioned residents on social media.

Rehoboth Mayor Paul Kuhns says he worries signs like what Rosner is referring to would scare beachgoers and tourists. But the city is working on other measures to stop the bacteria from building up over time in the storm sewers.

“We have the catch basins that we clean fairly often in town, but maybe we clean them a little bit more often,” Kuhns said. “Maybe we work with the community to make sure things aren’t going into the storm sewers from their yards.”

Kuhns says the city could also work with businesses in town to make sure they’re maintaining grease traps.

When asked what he thought about the study results, Kuhns said some of them were “a bit disturbing.” But it makes city officials think about what sort of action individuals can take – like maintaining their cars.

“The oil that drips on the roads gets washed in via rain, goes into the storm sewer and then adds to it,” Kuhns said.

DNREC and the EPA required Rehoboth to do this stormwater study to understand what is in the city’s stormwater as part of the city’s ocean outfall project.

Rehoboth's ocean outfall project goes online June 1 - the same day they are mandated to stop discharged treated wastewater into the Lewes-Rehoboth Canal.