DNAPLs present a remediation puzzle
By DAVID FLEMING
As the environmental industry and remediation technologies continue to mature and improve, and remediation companies gain more confidence in cleaning up sites, the more difficult sites are starting to be remediated.
Just a few years ago, these sites were thought of as impossible to clean. Recently, a resurgence of interest in the remediation industry has occurred in seeking more permanent solutions by deploying innovative technologies and remediation approaches for some of the most difficult soil and groundwater contamination problems.
Several new remediation technologies and cleanup approaches are showing promising results in the remediation of recalcitrant compounds including chlorinated volatile organic compounds (chlorinated VOCs) and semi-volatile, wood treating compounds. These compounds were traditionally used as solvents, degreasers and preservatives in heavy industrial manufacturing, dry cleaning and wood products industries.
These VOCs and semi-volatiles, being heavier than water, typically migrate downward through the soil column and pool on top of impermeable soil layers, like clay, to form Dense Non-Aqueous Phase Liquids (DNAPLs).
DNAPLs are a class of industrial chemicals that represent a major environmental problem in the industrialized world. Common DNAPLs include chlorinated hydrocarbon compounds such as carbon tetrachloride (CCL4), chloroform (CHCL3), trichloroethylene (TCE) and tetrachloroethylene (PCE).
If allowed to remain in the subsurface, DNAPLs will steadily dissolve and contaminate soil and groundwater for years. Many DNAPL compounds were first manufactured in the United States in the early 1900s and their subsequent use mirrored the economic growth of our country. Production quantities ranged from hundreds of millions, to billions of kilograms per year.
Historical use and disposal practices led to wide spread releases at thousand of locations nationwide and worldwide. According to a recent National Research Council study, three of the top 10 most frequently detected contaminants at hazardous waste sites are DNAPL compounds. Chlorinated compounds make up 99 percent of DNAPL found at contaminated sites.
The removal of DNAPL in situ (in place) is one of the remediation industry's toughest challenges. DNAPLs represent a major environmental problem at many Department of Energy, Department of Defense and private industrial facilities.
Chlorinated solvents were used by both government agencies and private business and released into the environment between 1950 and the early 1980s. To a lesser extent, these compounds are still being used and are periodically released into the environment. The Office of Management and Budget estimated that the federal government will spend between $234 billion and $289 billion on environmental remediation over the next 75 years at sites owned by DOD, DOE, Interior, Agriculture and NASA.
The ability to identify the location of and remediate DNAPLs is the subject of much debate. It was previously thought that the pump and treat technology could be used for DNAPL remediation. It is now widely accepted that pump and treat is not an effective remediation technology for DNAPL, but can provide contaminant plume control.
There are two schools of thought regarding DNAPL remediation. The first is that DNAPLs can not be fully remediated because it is very difficult to find and the cost for remediation is prohibitive. Therefore, it is argued, DNAPL remediation should not be attempted until further advances have been made. The second school of thought is that remedial technologies have advanced and costs have declined to the point where DNAPL remediation is technologically and economically feasible.
Dr. John Cherry, professor at the University of Waterloo in Ontario, Canada, is recognized internationally as an expert on DNAPL remediation. Dr. Cherry's premise is that it is very difficult or impossible to accomplish DNAPL remediation. He also believes that DNAPL remediation is too expensive and that there is no point in attempting remediation of DNAPL unless scientific trials are combined with the remediation.
In a recent telephone interview, Dr. Cherry said, "DNAPL remediation is like building a bridge across a river but you can't see to the other side because it is too foggy. We are attempting to remediate DNAPLs anyway so that we can pass on a cleaner environment to the next generations. By the time our children are grown, they can continue building the DNAPL bridge to the other side of the river."
"The money being spent on DNAPL remediation may be better used on schools," Dr. Cherry said.
Timothy Warner, Northwest operations manager for Terra Vac Corp., believes that DNAPL remediation is possible and that it makes economic sense. In fact, Warner has personally been involved in technology pilot tests at sites impacted by chlorinated DNAPL.
In these pilot tests, he employed chemical oxidation to remediate chlorinated DNAPL from VOCs and wood treating semi-volatiles. The DNAPL destruction rates were as high as 100 percent in some cases.
"While remediating DNAPL is more difficult than the traditional remediation of Light Non-Aqueous Phase Liquids (LNAPL) like gasoline, advances in the industry now allow for the cost effective remediation of DNAPL," Warner said. "New technologies, especially chemical oxidation, steam enhanced DNAPL vaporization, six phase heating, and surfactant flushing, are showing great results in reducing or eliminating DNAPL concentrations."
"Although remediation methods for DNAPL are not as refined or as frequently practiced as remediation methods for LNAPL, leaving DNAPL in place, while waiting for further advances in technology, exacerbates the problem and makes the subsequent remediation more difficult and cost prohibitive," Warner said.
For the past several years, government agencies and private firms have been focusing research and resources on the development of technologies and approaches for identifying and removing DNAPLs from the environment.
Some of the remedial technologies showing success and promising results for DNAPL remediation include: six phase heating, steam injection, dynamic underground stripping, chemical oxidation, dual extraction, soil flushing, in situ corona and radio frequency. Each of these technologies is conducted in situ and targets remediation of organic compounds in soil and groundwater.
Six phase heating (SPH) and corona technologies were developed at the Battelle Pacific Northwest Laboratories in Richland during the last several years. In situ corona is in the demonstration phase and will soon be commercially available. Six phase heating is currently being applied at Department of Defense and Energy sites as well as commercial industrial sites throughout the U.S. These technologies use electricity to destroy and steam strip contaminants in place.
In July 1997, Battelle Memorial Institute and Terra Vac Corp. formed a joint venture called Current Environmental Solutions, LLC (CES) to commercialize SPH and corona technologies. SPH has been demonstrated six times at government sites owned by the departments of Defense and Energy during the past four years. SPH is now being commercially applied on a full scale, on behalf of a Fortune 100 company, at a site in the Chicago area which has been impacted by chlorinated DNAPL underneath a building.
Chemical oxidation technologies using hydrogen peroxide and potassium permanganate have been commercially available for the past couple of years.
Dr. Richard Watts, professor at Washington State University in Pullman, and Terra Vac Corp. have been implementing in situ oxidation using hydrogen peroxide for several years. Dr. Cherry is conducting chemical oxidation research on DNAPL remediations using potassium permanganate as the oxidant of choice.
Steam injection was developed at the Lawrence Berkeley Laboratory in California. Dynamic underground stripping (DU) combines steam injection with electrical heating and has generated much interest in the industry for DNAPL remediation.
Steam injection is being implemented at a number of government and private sites to remediate DNAPL. This technology is showing promise at mobilizing heavier DNAPL compounds, such as creosote, as well as chlorinated DNAPL in permeable soils.
Surfactant flushing uses certain solvents and amines to flush contaminants including DNAPL from soil. Radio frequency (RF) was developed by the Illinois Institute of Technology Research Institute (IITRI) for remediation of DNAPL compounds. RF has shown positive results for soil remediation but is not as effective in groundwater. Microwave heating, which uses a higher frequency than RF, was developed by the Argonne National Laboratories, for remediation of organic compounds in soil. Microwave heating is also not effective at remediating compounds in groundwater.
The Interagency DNAPL Consortium (IDC), recently formed by the Department of Defense, Department of Energy, and the Environmental Protection Agency, is tasked with identifying successful technologies for DNAPL remediation, in soil and groundwater, at corresponding government sites. Last month, the IDC selected four in situ technologies for demonstration at an Air Force site in Cape Canaveral, Fla., that is impacted by chlorinated DNAPL.
The selected technologies include six phase heating, steam injection, chemical oxidation, and soil flushing. The field demonstrations are planned for September 1999. MSE Technology Applications, located in Butte, Mont., is managing this technology pilot project.
With site remediation, including DNAPL remediation, success or failure often depends upon the people who are implementing the technology and the approach they use in the field. Before decide to proceed with site remediation, make sure you do your homework and check company project references before proceeding with what could become a costly cleanup.
Additional information about remediation technologies is available on the internet at various government and privately operated websites. Two website are The U.S. Department of Environmental Management and Federal Remediation Technologies Roundtable. On the first website, choose the science and technology button at the homepage and it will take you to the innovative technology summary reports. On the second website, choose the 6th bullet, called Remediation Screening Matrix, on the left of the homepage.
David Fleming is an independent sales and marketing consultant, located in the Seattle area, representing firms that provide services and technologies to the environmental industry.
Copyright © 1998 Seattle Daily Journal of Commerce.