Featured Research

from universities, journals, and other organizations

Building The Right Barrier Stops Spread Of Deadly Pollutants

Date:
March 27, 2000
Source:
Johns Hopkins University
Summary:
Engineers create model to help design safer, more cost-effective sub-surface barriers to water-borne pollutants.

Underground water, tainted with toxic chemicals, is on the move. How do you stop the contaminants from polluting nearby wells? One new method is to throw a barrier of iron filings in front of the deadly flow. In theory, as the water passes through this wall, the pollutants will react chemically with the iron, leaving only harmless compounds in the water.

This permeable reactive barrier technology, in use for less than a decade, promises to be a highly effective pollution control tool. But environmental engineers at The Johns Hopkins University have found that cleanup crews may be making crucial miscalculations in designing these pollution neutralizing walls. To correct this problem, researchers William A. Arnold and A. Lynn Roberts have prepared a new mathematical model that should lead to safer and more cost-effective barriers. They presented their findings Sunday, March 26, at the national meeting of the American Chemical Society in San Francisco.

Pollution cleanup barriers must be designed properly to keep cancer-causing chemicals away from drinking water supplies. Each project can cost more than $1 million, most of which pays for the materials. "If you build these barriers too thin, you won't get complete treatment of the contaminated water," Arnold explained. "But if you build them too thick, then you're using two or three times more iron than you need, and you're greatly increasing the cost of the cleanup. This also limits the number of sites where you can use this technology because it's difficult to place thick barriers in front of pollutants located at large depths."

While preparing his doctoral thesis at Johns Hopkins, Arnold studied the chemical reactions that take place when certain contaminants collide with iron filings. Roberts, an associate professor in the Johns Hopkins Department of Geography and Environmental Engineering, collaborated on the research as Arnold's thesis advisor.

The pair focused on chlorinated ethylenes, suspected cancer-causing chemicals commonly found in dry cleaning solvents and de-greasing solutions. Through improper disposal at military and industrial sites, these deadly chemicals have seeped into underground water supplies and begun to migrate. Robert Gillham of the University of Waterloo in Canada developed the permeable reactive barrier technology about nine years ago as a way to de-toxify such plumes before they contaminate nearby drinking water supplies. Generally, the process calls for digging a trench to the level of the contaminated water. Workers then pour in tons of iron filings to form a permeable wall, usually one to six feet thick, that should remove toxins as the water moves through it. This method is now being used in full-scale and pilot projects at more than two dozen groundwater contamination sites in the United States and other nations.

To study the effectiveness of this process, Arnold and Roberts set up lab experiments at Johns Hopkins that mimicked the chemical reactions taking place in the field, but at an accelerated rate. They discovered that chlorinated ethylene molecules must compete for access to a limited number of sites on the iron surfaces where reactions can take place. "So at higher concentrations of pollution, there is more of this competition, and the reaction occurs more slowly," said Arnold, who, after receiving his Ph.D. at Johns Hopkins, became an assistant professor of civil engineering at the University of Minnesota. "At lower concentrations, the reaction takes place more quickly."

He and Roberts developed a new mathematical model that incorporates such variations. "We found that it's crucial that you know the exact concentration of the pollution, and you must use the correct mathematical model when you calculate how wide to build these barriers," Arnold said. "Our new model requires a lot more experimental data, which means you have to do a lot more preliminary testing in the lab. But if we can design these barriers more accurately, they will operate more effectively and more economically."


Story Source:

The above story is based on materials provided by Johns Hopkins University. Note: Materials may be edited for content and length.


Cite This Page:

Johns Hopkins University. "Building The Right Barrier Stops Spread Of Deadly Pollutants." ScienceDaily. ScienceDaily, 27 March 2000. <www.sciencedaily.com/releases/2000/03/000325104026.htm>.
Johns Hopkins University. (2000, March 27). Building The Right Barrier Stops Spread Of Deadly Pollutants. ScienceDaily. Retrieved August 29, 2014 from www.sciencedaily.com/releases/2000/03/000325104026.htm
Johns Hopkins University. "Building The Right Barrier Stops Spread Of Deadly Pollutants." ScienceDaily. www.sciencedaily.com/releases/2000/03/000325104026.htm (accessed August 29, 2014).

Share This




More Earth & Climate News

Friday, August 29, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Killer Amoeba Found in Louisiana Water System

Killer Amoeba Found in Louisiana Water System

AP (Aug. 28, 2014) State health officials say testing has confirmed the presence of a killer amoeba in a water system serving three St. John the Baptist Parish towns. (Aug. 28) Video provided by AP
Powered by NewsLook.com
Scientists Have Figured Out Why Rocks Move In Death Valley

Scientists Have Figured Out Why Rocks Move In Death Valley

Newsy (Aug. 28, 2014) The mystery of the moving rocks in Death Valley, California, has finally been solved. Scientists are pointing to a combo of water, ice and wind. Video provided by Newsy
Powered by NewsLook.com
Big Waves, Minor Flooding from Hurricane

Big Waves, Minor Flooding from Hurricane

AP (Aug. 27, 2014) Thundering surf spawned by Hurricane Marie pounded the Southern California coast Wednesday, causing minor flooding in a low-lying beach town. High surf warnings were posted for Los Angeles County south through Orange County. (Aug. 27) Video provided by AP
Powered by NewsLook.com
Calif. Quake Underscores Need for Early Warning

Calif. Quake Underscores Need for Early Warning

AP (Aug. 26, 2014) Researchers at UC Berkeley are testing a prototype of an earthquake early warning system that California is pursuing years after places like Mexico and Japan already have them up and running. (August 26) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins