Sunday, April 18, 2010

Growing Technology that Grows

Runoff from construction sites has long been a major factor in polluting our rivers and lakes. The EPA has even issued a new rule requiring all construction sites over 10 acres to reduce runoff to about 100-times lower than is typical of their discharge.

Luckily, research out of NC State University shows how a remarkable polymer can be used to reduce runoff from road construction up to 98% from current methods.

Professor R.A. McLaughlin, professor S.E. King, and professor G.D. Jennings are taking advantage of a remarkable polymer called polyacrylamide (PAM). PAM is a water soluble, synthetic polymer that expands when it comes into contact with water.

So, when it rains, PAM dissolves into sediments from runoff, causing tiny sediments to literally expand and settle. Not only does this stop the sediments from polluting a river or lake, but it also creates a physical barrier that slows runoff.

When used in conjunction with fiber check dams (FCDs) consisting of straw wattles and coir logs, construction companies might actually have a chance of meeting the DOT’s requirements.

Construction companies’ current method of using rock check dams are highly ineffective and even more expensive than McLaughlin et al.’s method of using the fiber check dams with PAM.

This research has major implications in a nation where 45% of rivers and streams in the United States are “impaired for their intended use, with sediment and siltation as the leading cause,” according to a study the EPA did in 2002.

When water has high levels of particles due to sedimentation, it is called turbid water, and high levels of turbidity in drinking water can protect disease-causing bacteria from ultraviolet sterilization, which when drank can cause nausea, vomiting, and dizziness. And, long-term drinking of turbid water can lead to gastrointestinal diseases or death.

McLaughlin et al. tested three different systems for controlling erosion at two roadway projects undergoing construction in the North Carolina mountains from June 2006 to March 2007. The team marked off three experimental sections next to each other at the first roadway project, and two experimental sections at the second roadway project.

The first experimental section of the first roadway was treated using the standard technique used by construction companies:

“[Rock check dams] are narrow sediment traps in the ditch along with rock check dams,” McLaughlin said.

The team treated the second experimental section of the first roadway with fiber check dams (FCDs) consisting of straw wattles and coir logs.

And the team treated the third experimental section of the first roadway using fiber check dams with granulated PAM added to each. The PAM is granulated rather than liquid so that when it rains, it dissolves into the soil and thickens the barrier of the dam, as well as weighs down the sediments.

The team compared the three systems by measuring the turbidity, or the amount of sediments, in the water.

Turbidity is measured in nephelometric turbidity units (NTU). The EPA requires turbidity for construction companies be less than 280 NTU. At site one, the average turbidity values for the storm-water runoff was 3,913 nephelometric turbidity units (NTU) for rock check dams. However, the Fiber check dams with PAM’s average turbidity values were only 34 NTU.

"Because we did this research before the rule was issued, we have good confidence that we can train the industry to attain the turbidity goal following key elements we have determined are necessary based on our research," McLaughlin said.

McLaughlin et al. published their research, titled “Improving construction site runoff quality with fiber check dams and polyacrylamide,” in the Journal of Soil and Water Conservation 64(2):1444-154.

No comments:

Post a Comment