Algae task force considers nutrients from septic tanks

Posted 8/10/19

FORT PIERCE — The Blue-Green Algae Task Force considered a human source of nutrient loads into Florida’s lakes and waterways at their Aug. 1 meeting. They reviewed the nutrient load from septic …

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Algae task force considers nutrients from septic tanks


FORT PIERCE — The Blue-Green Algae Task Force considered a human source of nutrient loads into Florida’s lakes and waterways at their Aug. 1 meeting. They reviewed the nutrient load from septic tanks and leaks and overflows from sewage systems.

Dr. Eb Roeder of the Florida Department of Health explained septic tanks are meant as individual wastewater systems where sewer service is not available. In Florida, septic tanks are permitted by the Florida Department of Health.

Traditional septic tanks are not designed to reduce any of the nutrient load in the waste. Florida septic tank regulations ensure the systems break down pathogens. Most of the treatment takes place in the drain field, he explained. The drainfield can reduce nitrogen by 10 to 50 percent, depending on the composition of the soil and the size of the drainfield.

“If you have private wells, that means you drink the groundwater that is under your lot, and thus under your septic system,” he said.

Florida law allows two 1,500 gallon-per-day (gpd) septic tanks per acre in areas where wells are used for drinking water.

Florida’s drinking water standard is based on 10 milligrams per liter of nitrate in the water, he said. One milligram is equal to 1,000 parts per billion; so drinking water could have up to 10,000 ppb nitrogen and still meet the FDOH standard.

Dr. Roeder said areas that do not rely on well water can have up to four 2,500 gpd septic tanks per acre. Florida currently has more than 2.4 million septic tanks. About 40 percent of septic tanks are in environmentally sensitive watersheds.

He said FDOH inspections are done to make sure the system is installed the way they are permitted. Construction permits are required for new systems, he said. “If you have a repair, you also need a new permit. Currently our standard for repair are less than new standards.”

In the 2018-2019 fiscal year, the Florida Department of Health issued 49,000 permits for new septic tanks, conducted 71,000 inspections and responded to 3,000 complaints.

He said Florida’s soil is not like other states. This was illustrated by a drainfield technology that came in, was approved, was used in large numbers and failed in large numbers. Testing on new technology is now required in Florida.

There are some areas in Florida where onsite systems do not work well enough. He said some counties now require more treatment or a larger separation between the drainfield and the aquifer. Probably the biggest example is the Florida Keys , where nutrient reduction treatment is required.

“New permits are driven by the economy,” Dr. Roeder said.

In 2004, Florida was averaging 40,000 new septic tanks per year. That number fell to about 20,000 per year when the real estate market fell. It is now back up to about 30,000 permits per year. Currently requirements for nutrient-reducing septic systems are only on new permits, and on small lots in areas of environmental focus.

In the future, the Basin Management Action Plans (BMAPSs) will require upgrades to a nitrogen reducing system when someone comes in for a repair permit, he continued. Dr. Thomas Frazer, Florida’s chief science officer, said with 1,000 people moving to Florida a day, the state continues to issue permits for new septic tanks.

He said they need to determine just how much nitrogen the septic tanks are contributing to the watersheds.

Dr. Roeder said the nitrogen is in the liquid that flows from the septic tank into the drainfield. He said pumping the tanks more often does not significantly reduce the nitrogen load into the watershed.

Dr. Michael Parsons said they need to determine the proportion of the nutrient load the septic tanks are contributing to the watersheds.

“If septic tanks are responsible for 30 percent of the nitrogen coming into the system, we need to target that,” he said.

Dr. James Sullivan said the nitrogen speciation is also important. “Even though ammonium might be smaller percentage of the total nitrogen, it could have a larger effect on the systems.

“Even if total nitrogen levels do not appear high, the amount of ammonium in the water could be a problem,” he said.

“I think as a society we need to think about the total cost of putting it in vs the cost of taking it out,” said Dr. Wendy Graham.

She said there will be a cost for putting in septic or sewage systems that prevent the high nutrient loads from entering the waterways. “Nobody is going to get this for free,” she said. “All of the free stuff is used up.”

Dr. Frazer said that in order to determine where the state should invest resources, they need data on the extent of the problems.

“Clearly there is a large number of failed systems,” he said.

Florida has 12 percent of the septic tanks in the whole country, noted Dr. Valerie Paul. “That’s staggering.”

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