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http://www.rockymounttelegram.com/news/content/news/stories/2006/08/08/runoff.html
The brown toolbox on the nondescript grassy bowl in the Imperial Centre
parking lot could change the way developers across the state plan their
landscapes.
The roughly 400-square-foot stormwater runoff area – and its adjacent
shrub-and-mulch-covered twin – will be studied for the next year by
engineers at N.C. State University.
The research may lead to a change in state policies by proving that grass
can meet requirements to remove impurities from stormwater.
"We're just looking to see if grass is a suitable alternative," said Ryan
Smith, an extension engineer with the biological and agricultural
engineering department at N.C. State. "We found a certain pollutant
removal rate with the trees and shrubs, and want to make sure that the
grass will get similar pollutant removals."
Rocky Mount was chosen as the research site because it lies in the
Tar-Pamlico River Basin and was in the process of building the Imperial
Centre.
N.C. State paid the city $10,000 to change its stormwater runoff design
plans to include the two areas – called bioretention cells – for the
researchers to use.
"All their money paid was for how to align the basins that the stormwater
would sit in before it runs into the underground system," said Assistant
City Manager Peter Varney.
N.C. State is using about $40,000 of a grant from the Environmental
Protection Agency to complete the Rocky Mount project, Smith said.
Automatic water-quality samplers, housed in the toolboxes next to the
cells, will measure the performance of the two cells against each other.
A bioretention cell is one form of stormwater management, like retention
ponds and stormwater wetlands.
The N.C. Department of Environment and Natural Resources requires
developers who build on more than one acre to use approved stormwater
management forms to offset water pollution caused by development. The
requirements are fueled by pollution in the estuaries at the coast.
A bioretention cell is a low spot in the landscape that captures
stormwater. A pit under the ground contains plastic and a soil that's
designed to move water quickly and also promote plant growth. The cells
are similar to a sand filter, except with plant growth.
Cleaner water leaves the cell through pipes and flows off with the rest of
the area's stormwater. Approved bioretention cells require certain levels
of shrubs and mulch to help remove nitrates from the water.
"A lot of engineers would like to see the results of this (project,)"
Smith said. "It could be a cost-saving method or it could just be at a
given site the property owner prefers grass."
A similar project in Graham – using grass but not comparing it to shrubs
and mulch – has shown good results, Smith said. The grass has performed
well beyond state standards for pollutant removal, he said.
Robbie Davis, owner of Turn-Key Contractors in Rocky Mount, said his
company is intrigued by the project. Grass is cheaper to plant and
maintain than shrubs and mulch, and some areas that require bioretention
cells would look better if grass could be used.
"Any time where a developer is given choices on any regulation, it always
suits us better than rigid regulations," Davis said.
--John Ramsey
Rocky Mount Telegram
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