On March 18, the Florida Department of Environmental Protection launched a two-year pilot study at Ichetucknee Springs State Park in an effort to improve septic tank performance. In many areas, deep and sandy soils provide minimal treatment of nitrogen as it infiltrates to groundwater. As a result, septic tanks, especially in higher-density neighborhoods in vulnerable areas near springs, can contribute to elevated nitrate levels.
Nitrogen is a naturally occurring nutrient, necessary for the plants and animals living in surface waters. But excessive levels of nitrate, a form of nitrogen, can cause algal mats and depress oxygen levels, leading to an imbalance in the aquatic life of an ecosystem. This is the current case in many springs across Florida, where nitrate levels have been increasing for many years.
The Department has launched the pilot study because basic septic systems provide limited nitrogen removal. Placing a carbon source below a drainfield should provide additional nitrogen removal through microbial treatment. This expectation is supported by preliminary results of the Florida Department of Health’s ongoing study on septic system nitrogen reduction options. A passive technology, like the one being employed for the pilot study, offers the potential of an effective, low-cost means of reducing nitrogen loads from septic systems.
“Excessive nutrients are a problem to surface and ground waters in many areas in Florida,” said Drew Bartlett, DEP Deputy Secretary for Water Policy and Ecosystem Restoration. “This pilot project will give us useful information to better target nutrient reduction strategies and protect and restore our watersheds, particularly vulnerable spring systems.”
For the project, the Department is installing a new drainfield at the State Park Manager’s residence, which is currently served by a conventional septic tank and drainfield. The new drainfield will include an underlying reactive layer consisting of wood chips, a source of carbon.
The Department has worked closely with the Department of Health, the agency that regulates septic tanks in Florida, to meet its requirements. A diverter box will be installed to allow routing septic tank effluent back to the existing, conventional drainfield in the event of failure or needed modification of the new drainfield.
The Department will sample water quality quarterly to assess the effectiveness of the reactive wood-chip layer in nitrogen treatment and removal. We will also evaluate the construction cost and long-term viability of the reactive media. The pilot study is expected to last about two years, but we are optimistic that interim results will tell us much of what we want to know.