Kure Beach Storm Water Outfall Experiment Shows Good Results
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view... (Pictured Above:) February 2006: Michael R. Burchell (At Right) of the NC State University looks on as town workers install a new infiltration system as part of a pilot program to mitigate storm water runoff through old ocean outfall pipes. | |||||||||
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By Willard H. Killough III
Managing Editor
mailto:editor@islandgazette.net
KURE BEACH - The Town of Kure Beach has long desired a way to eliminate 18 ocean outfall pipes that drain storm water runoff onto the beach and into the ocean.
In February of this year, the Town’s Public Works Department installed an underground alternative to the old outfall pipes near L. and M. Avenues along the oceanfront.
The alternative uses underground chambers to hold rainwater and allow it to filter through the ground instead of simply draining into the ocean.
After a summer of testing, the system has worked as planned with positive results.
The system was designed by the NC State University Department of Biological and Agricultural Engineering and paid for by the North Carolina Department of Transportation (NCDOT).
The new design is part of a pilot program to help mitigate or eliminate the discharge of storm water across the beachfront and into the ocean.
With every measurable rainfall, the state issues advisories to swimmers to stay 200 feet from all ocean outfalls due to the potential for non-point source pollution such as runoff from streets and other impervious surfaces.
The outfall pipes in Kure Beach carry runoff from all impervious surfaces including U.S. Highway 421 and other roads, parking lots, driveways, yards and rooftops.
Previously the Town considered diverting runoff from the pipes to a wetlands area on land owned by the U.S. Army as a buffer zone between the population and the neighboring Military Ocean Terminal at Sunny Point. Estimates for that plan proved too costly.
In February of this year, Michael R. Burchell, Ph.D. - Extension Assistant Professor/Water Quality at the NC State University’s Department of Biological and Agricultural Engineering - explained, “The system is designed to catch only the first half inch of rain fall,” during any event.
Burchell explained that once the underground infiltration pipes fill up, excess water would overflow into the old outfall pipe.
Burchell pointed out that most rainfall in the area is below half an inch with the exception of some summer storms.
The preliminary report delivered to the Town last month stated, “The Beaches Environmental Assessment and Coastal Health Act of 2000 (BEACH Act) requires states to monitor bacteria levels in recreational coastal waters. Increased levels of bacteria increase the potential for many illnesses to beach goers, so coastal towns are forced to post advisories or close beaches after many rainfall events, which potentially decrease tourism profits.”
The report states, “Storm water outfalls, common in many coastal towns, empty storm water and associated bacteria and other pollutants into the ocean or sounds. The NC Department of Transportation and the Town of Kure Beach wanted to reduce the amount of storm water entering their ocean recreational areas. Two storm water Dune Infiltration Systems were designed to divert a portion of the flow into the beach dunes. Sand filters have historically been successful in bacterial removal. The infiltration systems were constructed using commercially available open-bottomed infiltration chambers. Due to limited land area, the systems were designed to infiltrate 1.3 cm storms, which comprise approximately 80% of the rainfall events at the site.”
The report stated, “The watersheds of both sites were small ...and of mixed urban and residential land use. Water table measurements indicated a tidal influence, but approximately 2 m of sand was available for infiltration in the vertical direction."
The study offers a wealth of data obtained while monitoring the new system. The conclusion of the preliminary report states, “From background monitoring data, all but one measured rainfall produced storm water runoff with higher concentrations of fecal coliform then the state standard for swimable standards,” and that, “As seen from the first four storms after installation of the Dune Infiltration System, the amount of fecal coliform and enterococcus (state enterococcus standard is 104 CFU/ 100 ml for a single water sample (Dorman, 2004)) in the storm water runoff continue to be above the state standards. The storm water runoff from the first two months of storms have been successfully routed into the dunes, and it appears that the Dune Infiltration System thus far reduced the bacterial load being delivered to the ocean at these locations.”
The report stated, “The system most certainly reduced freshwater slugs with these pollutants from directly discharging to the ocean, reducing the potential for direct contact. More extensive monitoring and data collection is being executed in order to better understand the effects of the Dune Infiltration System on mitigating coastal storm water runoff.”
Burchell explained that of the 20 storms they analyzed so far, they only had overflow into the ocean on four occasions from the larger outfall pipe at M. Ave. and only for a brief period.
During Tropical Storm Ernesto, which was about a four-inch rainfall event over many hours with intensity less than what the system was designed for, all of the runoff was diverted into the dunes - nearly 200,000 gallons over a two-day period.
Burchell explained they will be watching closely for changes in the groundwater levels of bacteria near the system which does fluctuate at times, but is so far most often well below the state standards.
Councilman Mac Montgomery explained, “The Town Council strongly supports this joint venture as one that I believe will result in a new storm water management practice for the coast. This really shows what we can do when we work together with all available resources to solve our problems.”
The Storm Chambers are manufactured by HydroLogic Solutions, Inc. of Occoquan, Virginia.
According to their web site, (www.hydrologicsolutions.com) “The StormChamberTM system improves water quality through the same process as a septic drain field. A biomat of micro-organisms forms on the soil and stone underlying the chambers, which metabolizes pollutants and converts nutrients to non-contaminating byproducts.”
The StormChamberTM product was designed to allow municipalities to comply with the EPA Phase II storm water and Total Maximum Daily Load (TMDL) regulations.
HydroLogic Solutions developed the StormChamberTM as a management tool for the control of storm water runoff, sediment control, and nutrient removal, designed to overcome the deficiencies of older technologies.
The chambers maximize the benefits of storm water quality, storm water storage, and providing for recharge of groundwater supplies through infiltration.
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