Perspectives Online

A Sandy Solution - Extension experts' efforts to slow storm water will make ocean cleaner for swimmers.

Kure Beach
Photo by Art Latham

The drill was getting old: Every time it rained more than a sprinkle or two, officials warned swimmers to stay 200 feet from 18 large storm-water drain pipes that line the shore along Kure Beach.

Rainfall meant potentially dangerous bacteria and other pathogens flowed from U.S. 421, which parallels the seashore at this New Hanover County family beach town. Rains also washed contaminants from town streets, parking lots, driveways, yards, rooftops and other impervious surfaces. The resultant polluted water exited through drainpipes called ocean outfalls onto the beach and into the Atlantic Ocean.

A water-quality research team led by College scientists is working to make warning signs like this one at Kure Beach a thing of the past. Their method uses sand to filter storm water before it reaches the ocean.
Photo by Art Latham
That situation prompted Dr. Bob Holman, an environmental operations engineer with the state Department of Transportation, to ask Kure Beach officials to seek a solution from N.C. State University water-quality researchers.

Drs. Bill Hunt and Mike Burchell of N.C. State's College of Agriculture and Life Sciences responded and are the resultant experiment's co-principal investigators. Hunt, assistant professor and North Carolina Cooperative Extension urban water-quality specialist, and Burchell, Cooperative Extension assistant professor for water quality, are in the College's Biological and Agricultural Engineering Department.

"Bacteria that enter the swimming areas increase the potential for many illnesses to beach-goers," says Burchell, "so coastal towns must post advisories or close beaches after many rainfalls. Reducing this risk would protect both human health and tourism profits so vital to these communities."

If the experiment Hunt and Burchell launched earlier this year at Kure Beach's L and M streets proves successful - and preliminary data indicate it will - soon significantly less storm-water runoff may flow into the ocean from outfall pipes. And since outfalls that empty storm water into the ocean or sounds are common in many coastal towns, the Kure Beach experiment's results could benefit our state's entire coastal area and beyond.

A close look at this stretch of beach (top) reveals calibration access pipes of the Dune Infiltration System (top-middle and bottom middle). Engineer Tiffany Bright (bottom) calibrates rainfall and other data, with assistance from Dr. Mike Burchell (right), CALS Department of Biological and Agricultural Engineering, and Sonny Beeker (left), Kure Beach Public Works Department.
Photos by Art Latham
As part of the experiment, a Dune Infiltration System (DIS) - designed by Burchell and his colleagues, paid for by the state DOT and installed in February 2006 - uses large underground chambers to pass storm water beneath the dunes, where it then filters through the sand instead of draining directly into the ocean.

"We divert storm water, infiltrating it over an area beneath the dunes that's about 500 square feet at site L and 900 square feet at the larger site, M," Burchell says. "That water then moves toward the groundwater rather quickly, laterally toward the ocean, increasing the sand's filtering capacity, to areas larger than that immediately beneath the filtering system. This greatly dampens the storm water's flow to the ocean and bacteria concentration."

The DIS seems to be working well. "Sand filters have been successful historically in bacterial removal," he says.

"The bacteria we measure for are indicator organisms for other potentially pathogenic organisms," Burchell says. "We measure bacteria levels from the storm water in a vault as it enters the DIS. We then measure the groundwater concentrations near the system for bacterial content and compare the two levels."

Tiffany Bright completed her CALS master's thesis based on the experiment. Bright, recently hired by a New York City engineering consulting firm, presented project data to scores of engineers at the second annual Low Impact Development Conference in Wilmington in March.

The system, Bright explained, catches only the first half-inch of rain, which works because most area rainfall is under that amount, except for some summer storms and hurricanes. When the underground infiltration pipes fill up, excess water overflows into the original outfall pipe; this happened in only five of the 25 measured storms. But during Tropical Storm Ernesto in 2006, with a four-inch rainfall scattered over many hours, all runoff still was diverted into the dunes: about 200,000 gallons over two days. And the system diverted 97 percent of all storm water from the two watersheds involved into the dunes.

The DIS uses a commercially available open-bottomed pipe called a Storm ChamberT manufactured by HydroLogic Solutions Inc. of Occoquan, Va. "Because this is a unique application of his product, company owner Bob Maestro came out to the site, provided the chambers at reduced cost and has been interested in the results," Burchell says.

"While the amount of measured fecal coliform and enterococcus in the storm-water runoff continues to be above the state standards," he says, "it appears the DIS is reducing the bacterial load delivered to the ocean at both locations, thus reducing the indicator bacterial concentrations in the storm water by 97 percent when compared to groundwater samples taken following storms."

That's good news - good enough to generate a second grant, this one from the UNC Water Resources Research Institute.

Checking out the DIS are (from left) Mac Montgomery, Kure Beach mayor pro-tem, Beeker, Bright and Burchell. Early indications have shown the system reducing bacterial concentrations in storm water by 97 percent when compared to groundwater samples.
Photo by Art Latham
"This grant is to continue monitoring at the site and to more closely examine the fate and transport of the bacteria beneath the dunes," Burchell says. "We'll do this through a more-intense study of the groundwater hydrology beneath the system, including sampling around it to determine if bacteria are residing around it, to be sure we can recommend this system safely for more widespread use.

"Though our groundwater results look good," he says, "we want to do a more detailed study with the WRRI grant we received to assess where these bacteria reside between storms, and, when they are trapped within the sand matrix, how long can they survive.

"We want to be sure we understand the mechanisms of the fate and transport of bacteria beneath the dunes," Burchell says.

But Tim Fuller, Kure Beach mayor, and Mac Montgomery, mayor pro tem, already are eager to install more chambers. Burchell, town officials and DOT's Holman also are considering the design of another system to take care of a few more outfalls south of the existing system, near the Kure Beach Pier.

Burchell says the project couldn't have happened without help of Sonny Beeker, Kure Beach's Public Works Department, who supervised site installation work; David Nash, Extension area agent for coastal management, who harvested and provided American Beach Grass and helped guide plantings; John Nelms, Carolina Beach greenhouse manager, and Tim Owens, Carolina Beach town manager, who donated about 1,250 sea oats; and J.D. Potts, state Division of Environmental Health's Shellfish Sanitation and Recreational Water Quality Section, whose staff analyzed bacteria from collected storm and groundwater