Septic tanks a major threat to lagoon
New research by Harbor Branch scientist Brian Lapointe shows that septic tanks on the barrier island are flooding the Indian River Lagoon with nitrogen that is feeding algae blooms and killing marine life.
“Sewage is probably the biggest source of pollution in the estuary,” says Lapointe, who presented his findings for the first time at the recent county lagoon symposium put on by District 3 Commissioner Tim Zorc. “The septic tanks are a severe environmental problem," says Vero Beach Mayor Craig Fletcher.
The damaging effects of nutrient pollution in the lagoon came to the fore in the past two years as algae blooms fed by excess nitrogen and phosphorous killed most of the seagrass in the county, decimating fish populations and harming marine mammals.
Until now, attention focused on nutrients entering the lagoon in fertilizer-laden storm-water runoff.
Now it seems sewage may be an even bigger problem than excess fertilizer.
There are more than 900 septic tanks on the island within the city of Vero Beach, and more than 80 percent of them were installed prior to 1983 when state regulations required only a six-inch separation between groundwater and the bottom of septic drain fields and allowed systems to be built within 25 feet of the lagoon.
Hundreds of additional septic systems in island neighborhoods outside city limits, from Ambersand to the south county line, are feeding nitrogen and other pollutants into groundwater that flows into the lagoon.
Lapointe uncovered the mass sewage pollution using a method he pioneered that pinpoints the source of nitrogen.
Starting in May 2011, he and colleagues Laura Herren and David Debortoli collected macroalgae, a fancy name for seaweed, at 20 points along the lagoon, including three locations in Indian River County.
“We took the macroalgae back to my lab at Harbor Branch and cleaned it up and dried it and powdered it and then analyzed it for carbon and nitrogen content,” Lapointe says.
Seaweed consumes nitrogen in lagoon water as food, absorbing it into its tissue. By comparing the ratio of a nitrogen isotope called N-14 with an isotope known as N-15 in the powdered seaweed, Lapointe determined a majority of the chemical came from human waste, not fertilizer.
Lapointe took a second set of samples after the 2011 rainy season and found even higher levels of sewage nitrogen.
“We found a very strong chemical signal of sewage pollution along the length of lagoon, with the highest levels in Indian River County.
“At the end of the rainy season the IRC lagoon had an average reading of nine parts per million, which is what you would get if you tested at the mouth of a sewage treatment outfall. The measurements were off the chart.”
The city tried to get rid of septic tanks on the island in 2007, according to Rob Bolton, the Water and Sewer Department director.
“We had a potential a grant from the state for seed money and did some preliminary design for sewers in the affected neighborhoods,” he says.
Septic tanks in the city portion of the island are concentrated in Silver Shores, Bethel Isle, Central Beach north of Beachland Blvd., Old Riomar, South Beach and the canal streets along 17th Street.
The city paid engineering firm Camp Dresser & McKee $40,000 to do initial design and cost estimates for installing sewers on streets in those subdivisions.
CDM came up with an estimate of $14 million that would have been split between the city and residents, with residents receiving low-interest state loans to pay their $7,500-per-household share of the cost.
“The loans would have been paid back in quarterly installments over a 10-year period,” Bolton says.
The project faltered when islanders refused to support it.
“We needed the support of 60 percent of residents by state law and we didn’t get it,” Bolton says. The city polled 845 island homes with septic systems and received 520 replies that went 4-to-1 against the improvements.
Mayor Fletcher says the public and political atmosphere in regard to the lagoon has changed drastically since 2007. “People are much more aware, acutely aware, of how bad the problems are,” he says. “It is possible we would get support for putting in sewers if we polled residents now.
“I would support any program that would get these neighborhoods off of septic and on to sewers.”
“I stand ready to assist the city council and the county commissioners in any way I can, as I have in many other counties,” says Lapointe.