February 11, 2009
Professor wages unrelenting war against erosion, water pollution
For those science warriors who introduce new methods to control water pollution, it’s a battle of sorts out there, and it’s raging.
And a soil scientist in North Carolina State University’s College of Agriculture and Life Sciences is on the front lines.
Research shows that the top polluter of our state’s waterways is sediment -- any particles that water can move and eventually deposit -- and the resultant turbidity that wash down from construction sites, farms and eroding stream banks. Not phosphorus, not nitrogen, but sediment, which can contain both of those pollutants and many more.
“Our lakes and streams typically turn brown after rains, illustrating that sediment and turbidity pollution is the biggest challenge to water quality,” says Dr. Rich McLaughlin, associate professor and Extension specialist in the college’s Soil Science Department.
“Sediment,” he says, “is the most common pollutant affecting North Carolina’s waterways, impacting a range of aquatic organisms, reducing reservoir capacity and hurting their aesthetic value. In many areas, the major source can be construction sites, including roadway projects, which have erosion rates a hundred times greater than farmland.
“In fact,” McLaughlin notes, “the U.S. Environmental Protection Agency recently proposed rules that require runoff from many construction sites to be treated so they are nearly free of turbidity before release.”
The 200-page EPA draft document that proposes those rules, including a new minimum water-quality standard for construction sites of 30 acres or more, comprises some of McLaughlin’s research, such as his development of a technique that uses polyacrylamide (PAM) to rapidly settle clay particles by bonding with them. PAM is a water-soluble, synthetic polymer commonly used in various water treatment processes, including municipal water supplies and wastewater, and as a food processing aid.
While current stormwater Best Management Practices (BMPs) effectively handle larger sediment particles, they usually aren’t as effective at trapping smaller silt, clay and organic particles, McLaughlin says.
“Speed is essential when you are trying to clean a deluge of stormwater before it leaves a construction site and flows into the watershed,” he says in a recent Soil Science Department newsletter. “PAMs are now used on less than 5 percent of North Carolina’s construction sites each year, but we hope to increase their use to 100 percent by teaching methods to all practitioners in the state.”
McLaughlin works at the Sediment and Erosion Control Research and Education Facility at N.C. State University’s Lake Wheeler Field Laboratory. With funding from the North Carolina Sedimentation Control Commission, McLaughlin developed the facility along with colleague Dr. Greg Jennings, Biological and Agricultural Engineering Department professor and Extension specialist. They, with Extension associates Jan Patterson and Scott King, also developed required certification courses for state Department of Transportation contractors and engineers involved in erosion and sediment control practices. Patterson and King teach most of the workshops.
Opening new fronts on the war on erosion, after developing new techniques at Lake Wheeler, McLaughlin and his research team apply them to construction projects around the state.
In a recent project with DOT in western North Carolina, his team demonstrated how to bring turbidity down to levels acceptable for sensitive trout stream waters. Study sites included two road paving projects near Lenoir in Caldwell County and one north of Boone in Watauga County, where researchers compared new erosion control techniques to “standard” DOT erosion control designs: mostly rock checks and small sediment-trapping basins.
Each study site included the installation of a drainage ditch adjacent to the road, where DOT had placed control measures to reduce the sediment amount discharged from the site.
“We portioned these ditches into experimental sections, each one hydrologically distinct from the others by the periodic placement of drainage culverts that run under the road, discharging stormwater off the project site,” McLaughlin says.
The study evaluated two things: how well alternative new “check dams,” composed of cylindrical fiber or plastic mesh bags filled with either straw or coconut-husk “coir” fibers slowed stormwater flow, and the effectiveness of adding granular PAM to these new BMPs.
PAM can be manufactured in a variety of charged forms to be cationic, anionic or non-ionic (neutral), but each is intended to increase the particle binding that occurs in treated water. This significantly increases the sedimentation rate by increasing the sediment particles’ sizes.
“Most applications involve the anionic PAM because it is non-toxic to aquatic organisms, so in this study we used anionic APS 705, which has been approved for stormwater treatment by the N.C. Division of Water Quality,” he says.
The study results indicate a significant advantage in using the new sediment control systems, particularly those with PAM added.
“Overall,” McLaughlin says, “we can capture 99 percent of the sediment with all the systems in place except PAM, but turbidity will still be high. Add the PAM in the right way and the turbidity can also be reduced by more than 90 percent.”
McLaughlin recommends that the new sediment BMPs be more widely used by the DOT on similar roadway improvement projects, particularly in areas adjacent to sensitive habitat waters.
DOT listened to McLaughlin’s reports from the field and lab. The department is starting to use the fiber check dam system instead of rock in ditches. The proven combination of fiber dams and PAM is likely to be applicable to other construction sites, and could lead to significant reductions in stormwater impacts on adjacent streams and lakes, he says.
Also, based in part on one of McLaughlin’s research projects, the state Department of Environment and Natural Resources now uses his porous baffled skimmer sediment basin design as its new standard of practice. And a current state Department of Transportation project near High Point has effectively employed all of McLaughlin’s approaches.
How much does it cost to deploy these new techniques?
While it’s not easy to compare cost estimates per device among the various BMPs, the new BMPs are not significantly more expensive than standard BMPs, based on overall average costs, McLaughlin says.
“The differences for each project,” he says, “would likely be less than a few hundred dollars, very small in comparison to the total project costs.
“It also appears that the new BMPs are a reasonable substitute to the standard BMPs with regards to their overall water storage volume capacity,” McLaughlin adds, “as their calculated storage volumes for the project sites were equal to or exceeded those of the standard BMPs.
“We’re working with some large developers interested in using this strategy,” McLaughlin says in the newsletter. “I believe it could have a profound impact in North Carolina because it makes good environmental and business sense.”
And that means significant advances in the scientific war on water pollution.
For sedimentation and turbidity fact sheets by McLaughlin and his team, go here:
-- Art Latham
Posted by Art at February 11, 2009 11:05 AM