Have you ever really thought about gas stations’ potential impact on the environment? How about the effect leaking gasoline can have on our soil and groundwater? I never did—until I started working for Environmental Resolutions, Inc. (ERI), an environmental consulting and engineering firm founded in Southern California in 1989.
In my first days at ERI, I learned all kinds of chemical names. Some, like methyl tertiary butyl ether (MTBE), I’d heard of; others, like benzene, tertiary butyl alcohol and a host of other chemicals found in gasoline, I hadn’t. As I got to know the environmental technicians, scientists, engineers and geologists at ERI, I began asking questions: What is our equipment for? How does it work? Are we helping the environment?
ERI manages the environmental monitoring and cleanup of more than 350 locations in the Western United States. The company assists clients with a variety of environmental concerns associated with pesticides, solvents, lead, asbestos and fuels. ERI has offices in Petaluma (where I work), Lake Forest and Ventura in California; Phoenix, Arizona; Tukwila, Washington; and Billings, Montana. One of the primary focuses of ERI is the cleanup of soil and groundwater at service stations and other petroleum hydrocarbon-related sites where gasoline and related constituents, like MTBE, have impacted the environment.
MTBE was first used in the 1970s as an octane booster. In 1990, after the Clean Air Act was passed, the amount of MTBE in California’s gasoline was increased in an effort to reduce air pollution. MTBE readily dissolves in water, which makes it extremely difficult to remove from groundwater, but small amounts can render a community’s groundwater undrinkable (due to its turpentine-like taste and odor). The EPA has added it to its list of “potential human carcinogens.” It can be tasted in water at about 20 parts per billion—that’s the equivalent of a thimble-full in an Olympic-sized swimming pool.
When gasoline is spilled into soil, it trickles down until it reaches the water below, where it spreads over the top, and is often carried along with the slow-moving groundwater flow. ERI has used several technologies at gasoline spill sites successfully. The most common method for removing small amounts of dissolved gasoline is called “pump and treat.” This method involves pumping the water out of the ground and through a carbon filter. The carbon filter absorbs and removes the gasoline from the groundwater, then the water is released to a storm drain or sewer district. Another method, called “soil vapor extraction,” removes gasoline by changing it into vapor, sucking it out of the ground and bringing it to the surface, where it’s either burned or filtered through carbon before being released into the atmosphere.
Unfortunately, these traditional methods aren’t always effective at removing MTBE, because carbon doesn’t absorb it very well. Passing water containing MTBE through a carbon filter will only remove small amounts, which means you need a very large volume of carbon to clean the water—which only replaces one environmental problem with another.
In 1998, researchers at the UC Davis first isolated a single-cell organism that eats MTBE as food. They named it the PM-1 microbe. These “bugs,” as they’re affectionately referred to by ERI employees, are found naturally in our groundwater, rivers, lakes and such (just not in high enough concentrations to take the MTBE out of a flowing creek on their own). ERI engineers and technicians worked with UC Davis scientists to develop a low-cost, portable bioreactor to effectively treat MTBE and other gasoline contaminants in groundwater. These bioreactors contain a concentrated number of microbes to eat the harmful chemicals, convert them to carbon dioxide and water, and eliminate the contamination.
In 1989, a large MTBE plume (approximately 1,600 feet long) was discovered in Sonoma County. An underground storage tank at a gas station in Healdsburg had leaked, releasing gasoline and MTBE into the soil. MTBE in the groundwater migrated away from the site and impacted 14 private drinking water wells. The standard techniques for removing it didn’t meet the county’s discharge requirements, because they couldn’t remove enough of the MTBE from the water.
ERI installed wells at the gas station in Healdsburg and pumped the impacted groundwater through underground piping to the bioreactor. The ERI bioreactor contains trillions of PM-1 microbes, which multiply on their own based upon the amount of MTBE and other “food” available to them. The higher the MTBE concentrations, the more bugs. Since these bugs are a native organism found in creeks, streams and lakes, they pose no threat to the environment.
The bugs live in a sand layer (much like their habitat in creeks) inside the bioreactor, and the groundwater is pumped into the bottom of the vessel. The extracted groundwater flows up through the sand layer where the MTBE and other gasoline components are eaten. Clean water collects at the top of the vessel. It’s then filtered through carbon before it’s released to surface water, a groundwater or municipal sewer system and back into the environment. Since 1998, it has processed 55 million gallons of groundwater and removed 354 pounds of MTBE from the groundwater in Healdsburg. The plume’s length has been reduced to approximately 37 percent. The number of impacted drinking water wells has been reduced to four.
Following the success of the Healdsburg bioreactor, ERI bioreactors have been deployed in five additional sites throughout Sonoma and Marin counties and 40 other locations throughout the United States. While the bioreactor may not always be the best solution, we believe that, for many groundwater contamination problems, it’s more effective than traditional technologies. And because less carbon filters are needed (which reduces waste), it’s environmentally friendly.
