Tracing the Path of Stormwater
Polluted stormwater flows off of streets and yards into sinkholes where it disappears underground. Hydrogeologist Todd Kincaid learns where it ends up.
Audio Feature Transcript
Narration: More than 60 inches of rain fall in Tallahassee each year making Florida's capital one of the rainiest spots in the state. Rain flows off roofs, lawns, and streets into stormwater drains and ditches that carry it out of the city, out of sight and out of mind. but where do the water, and the pollutants that travel with it, go? Hydrogeologist Todd Kincaid Ph.D., working with the Florida Geological Survey and Florida Department of Environmental Protection, is trying to answer that question.
Todd Kincaid: We're here at Eight Mile Pond, which is near the southern most extent of the drainage of Lake Munson Slough, which drains the central part of Tallahassee. Surface water runoff from Tallahassee flows into Lake Munson Slough, which flows into lake Munson, which flows further downstream to Eight Mile Pond. It's overflowing its banks and draining down a creek to Ames Sink, which is the final destination where the water goes underground and recharges into the Floridan aquifer.
Narration: Kincaid and others are concerned that polluted Tallahassee stormwater is flowing into sinkholes, down into the Floridan aquifer and ultimately to Wakulla Spring where it can harm the spring ecosystem as well as darken the normally clear water.
Todd Kincaid: Surface water runoff through an urban area like Tallahassee will pick up any contaminants that are on the street or storm sewers, oils from the highways for cars, and any kind of chemicals that are leached out onto the land surface. So basically anything that gets collected into those storm sewers is getting delivered to Munson Slough, Eight Mile Pond and Ames Sink.
Narration: Kincaid moves on to Ames Sink, scouting it for an upcoming dye trace study. Located on private property about six miles north of Wakulla Spring, Ames Sink is the end point for water flowing through Munson Slough from Tallahassee. Green duckweed spirals slowly on the water's surface. Like a partially clogged drain, the water swirls and gradually disappears.
Todd Kincaid: It's just amazing to me that more people don't pay attention to features like this because it's so obvious that all of the surface water runoff is coming down at this point and going right down into the aquifer. This is all of the water that just yesterday and the day before was falling as rainfall over the city of Tallahassee.
Narration: A couple of weeks later Kincaid returned to release a non-toxic fluorescent dye into Ames Sink. He'll wait to see if the dye shows up at Wakulla Spring, located directly south of Ames Sink.
Todd Kincaid: We have water samplers set up at between 12 and 15 points throughout the basin so that we can hopefully see the groundwater tracer or the dye as it passes our water samplers, and then we will know where this water goes and how fast it travels through the groundwater system.
Narration: The foundation for this groundwater system is a shallow layer of limestone known as the Woodville Karst Plain extending south of Tallahassee to the Gulf of Mexico. The limestone layer is a virtual "Swiss cheese" of interconnected sinkholes, caves, and freeway-sized tunnels that carry water underground to springs like Wakulla Spring. This shallow groundwater system is also highly vulnerable to pollution.
Todd Kincaid: The Leon Sinks and Wakulla Cave systems account for more than 10 miles of passages underground that are in some places 100 to 200 feet in diameter, larger than a superhighway underground transporting water north to south from recharge areas to the spring discharge points. The other thing that makes the Woodville Karst Plain unique is that the aquifer is very shallow. It's basically right beneath your feet throughout the region. Every single stream throughout this basin disappears in a feature just like Ames sink. So we really need to understand where that water is coming from because anything that is in that water as illustrated by the beer can floating here in Ames sink is going to be transported down into the Floridan aquifer. It's going to mix with the water we drink and mix with the water that we swim in.
Narration: a few weeks after releasing the dye into Ames Sink, Kincaid reported that it had been detected at Wakulla Spring, confirming Tallahassee storm water was flowing there as well.
Todd Kincaid: We started to see some dye come through K tunnel at Wakulla Spring and then at about 18 to 19 days after the injection, the dye finally showed up at the Wakulla Springs basin. From this tracer test we can definitively demonstrate that the runoff water from Tallahassee from the southwestern one-third of the city flows directly to Wakulla, Indian and Sally Ward springs with a travel time of between two and three weeks.
Narration: Today at Wakulla Spring the popular glass-bottom boat tours are often cancelled because more frequent "dark water" days are caused by the influence of stormwater. Kincaid expects that his research will help clarify any doubts that people had about the connection between Tallahassee stormwater and Wakulla Spring. At the same time he hopes it will spur action to protect Wakulla's springshed and to restore clarity to the water.
Todd Kincaid: The Ames sink tracer test is very important because it reinforced what I believe people already knew which is that the runoff water flowing into these disappearing streams, particularly Ames sink, most likely flows to the biggest spring in the basin which is Wakulla Spring. I think now people can move forward with development and conservation approaches that they really knew should be implemented to begin. This tracer test can help to facilitate that because it provides the proof that Ames sink and the runoff water is connected to the major springs and natural resources that everybody collectively wants to protect in Wakulla County.