By John Menatti
Contaminated soils under a former gas station are heating up—literally. For the first time in Utah, an innovative technology called Electrical Resistance Heating (ERH) is being used to clean up soil and water contaminated by gasoline leaks from underground storage tanks (USTs). DEQ is assisting in this cutting-edge cleanup effort by providing funding from its Petroleum Storage Tank (PST) Trust Fund.
Underground tanks, especially older tanks that have become
corroded, can release gasoline into subsurface soils and ground water. In this particular instance, leaking gasoline from USTs at a former gas station in Millcreek Township, Salt Lake County, contaminated soil and groundwater to a depth of approximately 50 feet. Excavation—the typical remediation for these kinds of leaks—was not feasible because the contamination was so deep, the soils were clayey, and the station was located close to buildings and streets.
An environmental consultant for the developer of the property proposed a new, in-situ (in-place) remediation technology to remove the volatile organic compounds (VOCs) below the former gas station. This remediation technology, known as ERH, uses electricity to heat the subsurface soils and ground water to the boiling point of water, converting the VOCs in the soils and ground water from a liquid to a vapor that is then removed by a soil-vapor extraction (SVE) system. We had heard that this technology had been used successfully in Montana and New Mexico, so we approved its use at the property.
Here’s how ERH/SVE works:
Large electrodes are placed in vertical arrays around the site. Electrical current passes through the soils between these electrodes and flows through moisture in the pores in the soil.
The resistance from the soil to the electrical current generates heat, turning the VOCs into vapors.
As the gasoline in the subsurface evaporates, SVEs draw these vapors to the surface through extraction wells. The volatized gasoline vapors are then directed to a thermal oxidizer, where they are burned.
The ERH/SVE system was installed in Spring 2013, and the subsurface electrodes were energized in November 2013. By February 2014, the subsurface gasoline- soil contamination and ground water had been heated up to about 200 degrees Fahrenheit, and the SVE system was removing gasoline vapors and burning them in a thermal oxidizer under a Division of Air Quality (DAQ) permit.
Here is what the heating process looks like:
The white areas are the highest temperatures. As you can see, the soils heated up quite rapidly over a two-month period.
The electrodes will be d-energized in September and October 2014. It will take about three to four months for the soil to cool down after the electrodes are turned off. Soil and groundwater samples will then be collected to confirm that the site has been cleaned up to DEQ standards and contamination is gone. After we confirm that the site meets these standards, we will issue a No Further Action (NFA) letter which will free up the property for development.
Learn more about DEQ’s UST program or underground storage tanks. If you would like to find out if there have been any cleanups or releases from tanks in your neighborhood, visit our Interactive Map.
I am the manager of the PST Trust Fund in the Division of Environmental Response and Remediation (DERR). I am a Utah-licensed Professional Geologist, hold a Master of Science and Technology degree in environmental science (2007) from the University of Utah and a Bachelor of Science degree in soil science (1980) from California Polytechnic State University. I like to play golf and hike in the mountains during the summer, and snowboard during the winter. I also enjoy spending time with my 10-year old grandson.