Solving the Solvent Problem: Part 2 of a 2-Part Series
by Walter Mugdan
In Part 1, I explained that a large variety of chemical solvents were concocted over the past two centuries. They are integral to nearly every industrial enterprise, but many of them are dangerous to your health if you ingest or inhale them. Among the most common is PCE or “perc,” which is a probable human carcinogen. The most common use of perc is as dry cleaning fluid. In the past, many dry cleaners simply dumped their used perc on the ground, contaminating both soil and groundwater. EPA’s “Superfund” list of the worst toxic waste sites in the country is littered with former dry cleaning facilities.
One of these Superfund sites is located in Nassau County, just a stone’s throw from where I live in Queens County. I’m in the Little Neck part of Queens; and the former Stanton Cleaners sites is a half mile away in Great Neck. When Stanton dumped its used perc down the drain, it contaminated the groundwater below. This is bad enough under any circumstances, but here it was particularly dangerous, because Stanton was only about 300 yards away from a Great Neck drinking water supply well. To make matters even worse, perc vapors from the contaminated groundwater were getting into nearby homes and a synagogue.
The Stanton site was added to the Superfund list in 1999 and EPA installed a “pump-and-treat” system. This is one of the ways that we use to solve our solvent problems. Contaminated groundwater is pumped up to a small building at the back of the dry cleaner’s parking lot. There it’s treated to strip away the perc, and returned clean to the ground. More than 200 million gallons have been treated to date at the Stanton site.
As a precaution, a treatment system was also installed at the drinking water well; and vapors are now vacuumed from the soil before they can reach homes and other buildings. (The current dry cleaning operation – a different company, though still using the Stanton name – has state-of-the-art equipment to prevent perc from entering the ground.)
Over the past three decades, we’ve developed a variety of techniques for solving solvents problems. In a “pump-and-treat” approach like the one used at Stanton, the contaminated groundwater is cleaned by passing it through a carbon filter or an air stripper (in which air is blown through tiny water droplets, stripping away the contaminants). Alternatively, various in situ techniques can be used to clean the groundwater in place. Other chemicals that react with the solvents to form harmless substances can be added to the groundwater; or nutrients can be added to stimulate microbes that degrade the solvents.
For contaminated soil, one approach is simply to dig it up and truck it off-site for disposal at a secure, licensed facility. The most common alternatives involve heat treatment and soil vapor extraction (SVE). Both work on the principle of separating the solvents from the soil by evaporating them, followed by capture and treatment of the chemical gases or vapors. SVE is the approach used at Stanton. Perforated pipes are driven into the contaminated soil and a vacuum is applied, which causes the chemical contaminants to evaporate. The vacuum draws the chemical gases through carbon filters where they are captured; later the carbon is sent away for treatment or disposal. SVE uses far less energy than a heat treatment process and is considerably less expensive. Sometimes adding nutrients to stimulate microbes can also work in soil.
So here’s the bad news: there are lots of places contaminated with dangerous solvents, and cleaning them up is very expensive. But here’s the good news: we’re getting much better at cleaning up the messes we’ve made. In summary: Solvents — we can’t live without them (literally), and we’re finally learning how to live better with them.
About the Author: Since 2008 Walter has served as Superfund director for U.S. EPA Region 2, managing the region’s toxic waste cleanup, emergency response and brownfields programs. For the previous six years he was director of the region’s air, water, hazardous waste and environmental review programs. He joined Region 2 in 1975 as a staff attorney doing air pollution enforcement work. From 1991 to 2002 he held various supervisory positions in the region’s legal office, culminating as Regional Counsel. In his private life he heads a small, local conservation group in northeast Queens. He enjoys bicycling, kayaking and hiking; and since 2010 he has been moonlighting as an Executive Producer (read: source of funding) for his daughter’s nascent career as an independent film maker.
Editor's Note: The opinions expressed in Greenversations are those of the author. They do not reflect EPA policy, endorsement, or action, and EPA does not verify the accuracy or science of the contents of the blog.