Unraveling the Nitrate Mystery
A new study looks at Tallahassee's Southeast Farm in an attempt to identify sources of nitrates that may harm spring ecosystems.
One of the chief threats to spring ecosystems in Florida is increasing nitrate levels in the water. Nitrates that are introduced by humans into the environment are byproducts of municipal sewage treatment and disposal, residential septic systems, agricultural and residential fertilizer use and livestock farms. One new study looks at Tallahassee's Southeast Farm and Wastewater Reuse Facility in an attempt to identify sources of nitrates that may threaten springs.
At the Southeast Farm and Wastewater Reuse Facility, 17 million gallons of treated Tallahassee wastewater are sprayed on crops that "recycle" most nutrients like nitrates and phosphorus in the water. However, some are concerned that nitrate-laden wastewater entering the aquifer at the farm may harm Wakulla Spring.
Most of Tallahassee's sewage and wastewater is treated at the Thomas P. Smith Water Reclamation Facility, which is located in southwestern Tallahassee near the airport. The wastewater is then pumped eight miles to the Southeast Farm and Wastewater Reuse Facility on Tram Road.
The 2,160-acre Southeast Farm is located in an area where the aquifer is shallow and vulnerable to pollution on the land surface. Unabsorbed nitrates, a by-product of wastewater treatment and fertilizer use, filter down into the Floridan Aquifer and flow south toward Wakulla Spring. Nitrates in very small amounts can upset the balance of fragile spring ecosystems by promoting algae and invasive weed growth.
Randy Bond, manager of the Southeast Farm complex, inspects one of the center pivot irrigation systems spraying wastewater on bermuda hay. Bond is responsible for overseeing the daily operation of the irrigation system at the farm to ensure that 17 million gallons of wastewater is disposed of daily on crops.
"The water is being treated in the city's two treatment plants, the Thomas P. Smith and the Lake Bradford Road plants. Once the water goes through those treatment processes, the clean water is piped to me around Capitol Circle, eight and a half miles away, and it's brought into my facility," says Randy Bond. "From here we do a little more screening on it and then send it out through a distribution system to the 16 different center pivots. The main crops are coastal Bermuda hay and corn for cattle feed."
Hal Davis, at left, a hydrologist with the US Geological Survey, is coordinating a study to evaluate the flow of wastewater from Southeast Farm through the Floridan Aquifer. Here, Davis explains the scope of the project to Michael Bascom, administrator of the Florida Department of Environmental Protection's Springs Initiative.
"We are trying to determine where the water that leaves the sprayfield property is going to. So what we intend to do is come down about a mile south of the sprayfield to install six wells. The nitrate-laden water leaving the sprayfield leaves it at about 150 feet below land surface," says Hal Davis. "So we are setting a wide bracket in our monitoring wells to try to intercept that contaminant plume, and we'll sample the wells as we drill them to try to determine exactly where we intersect the water. We'll sample those for the wastewater treatment series a sampling series that the USGS came up with. It tests for about 75 parameters that are typically in sprayfield water. They include fragrances, caffeine and other things that the USGS has determined are typically in sprayfield effluent. If you can pick up those you know that we've picked up the sprayfield water."
The wastewater flow study is a cooperative effort between the USGS and the City of Tallahassee. Koren Taylor, at left, coordinator of Tallahassee's Aquifer Protection Program, meets with Hal Davis to review placement of new monitoring wells for the study.
"In 2002 the Northwest Florida Water Management District published a report cataloging nitrate sources in the area that contributes to the Wakulla Spring springshed, and the sprayfield was one of the potential sources of nitrate loading," says Koren Taylor. "When that study came out there were a lot of questions relating to the water coming from the sprayfield, and we realized we didn't have a lot of good answers. That's when we decided to partner with the USGS and work with them to do a study to find out where the water is going once it leaves the sprayfield."
Randy Bond inspects corn growing at Southeast Farm. Bond says that the sprayfield complex is an efficient way to manage Tallahassee's wastewater, but adds that water conservation by citizens and business is critical if the city is to minimize its impact on the environment and keep costs downs.
"If you quit producing it we'll quit trying to find ways to get rid of it. When I started in this business 30 years ago, the average person in the United State used 100 gallons of water a day. In Tallahassee that figure is up to 160 to 175 gallons of water a day. All that water has to go somewhere," says Randy Bond. "You still have to find a way of getting rid of it. This is one of the best ways that Tallahassee has found to deal with it. We have a very good site for this type of operation. It's very sandy soils. It can take a lot of water. It can grow crops. The crops are here to take up the nutrients left in the water. If we didn't use crops to do it, we would use dollars to do it. And by that I mean you have to come up with a different treatment process to take the nutrients out that these crops take out. All of that costs money. Technology today can do anything you are willing to pay for. Your tax dollars pay for this system. If they didn't pay for this system, they'd be paying for another system. Any other system that we've looked at can almost double the cost of the operation."