Barrier to Groundwater Contaminants Developed

N M TECH HYDROLOGISTS CONTINUE RESEARCH ON SUBSURFACE BARRIER

SOCORRO -- An extremely efficient, as well as relatively inexpensive, subsurface barrier material developed by a New Mexico Tech research hydrologist is being tested at an Oregon university research facility as a pollutant filter which potentially could trap most common groundwater contaminants.

At the Oregon Graduate Institute of Science and Technology (OGI), New Mexico Tech hydrology professor Robert S. Bowman, Tech graduate student Stephen Roy, and their OGI research colleagues have set up a pilot-scale demonstration of an innovative groundwater remediation method which employs a permeable barrier formed of surface-modified zeolites (SMZ). Zeolites are a group of minerals ordinarily used in water softening and as an adsorbent material in everyday "kitty litter."

In previous studies, Bowman found that when treating zeolites with the surface-active agent HDTMA--a chemical commonly used in manufacturing mouthwashes and hair conditioners--the surfactant tended to coat the surface of the cage-like minerals, leaving the internal pores of the zeolites open for ion exchange and other mechanisms which retain different types of organic and inorganic pollutants.

The low-cost surface-modified zeolites can then be used as a subsurface permeable barrier to limit the spread of mobile pollutants in contaminated soils, protecting downstream aquifers as it filters the flow of groundwater -- and significantly reducing environmental cleanup costs.

Barrier material made of treated zeolites, Bowman estimates, costs about 25 cents a pound to produce at current market prices.

At the OGI Large Experimental Aquifer Program (LEAP) site, Bowman and his research collaborators have set up a six-foot-deep barrier made up of 13 tons of surface-modified zeolite in the center of a swimming pool-sized tank to test the filtering efficiency and other possible applications of the material.

The remainder of the 10-by-10-yard-wide, concrete-lined tank is filled with beach sand and an array of small, plastic tubes from which the researchers can draw groundwater samples from 81 different locations and levels within the tank during the ongoing experiment.

At the LEAP site, groundwater contaminated with low concentrations of chlorinated organic compounds and metals is being pumped into one end of the small-scale aquifer and is being allowed to flow passively through the SMZ barrier.

"This phase of our research is basically a simulation of what would be taking place at, say, a Superfund site or other groundwater contaminated area," Bowman points out. "If it's successful, then the next step would be to install an SMZ barrier at an actual field site."

Bowman has found that the treated zeolites are particularly effective in trapping groundwater contaminants such as perchloroethylene, an organic solvent commonly used by dry cleaners and other businesses, and chromate, a liquid used in the chrome-plating industry, which is normally difficult to treat once it reaches aquifers.

New Mexico Tech graduate student Steve Roy says that preliminary research shows that groundwater remediation with SMZ permeable barriers is an effective technology which also is easy to maintain.

"The idea is that it's passive," Roy explains. "You can put a SMZ barrier in place, turn around, and walk away. There's very little operation and maintenance involved."

One of the largest producers of zeolites in the United States is the St. Cloud Mining Company, which maintains a zeolite mining operation in Winston, N.M., about 35 miles northwest of Truth or Consequences.

Major funding for the SMZ barrier pilot-scale demonstration study at the LEAP site at OGI is provided by the U.S. Department of Energy.

-NMT-

(George Zamora)