Posts Tagged ‘chlorinated hydrocarbons’

Electrical Resistance Heating (ERH) White Paper

June 9th, 2013

When chlorinated hydrocarbons, such as dry cleaning fluids and industrial solvents, are released into the environment, they migrate downward until they reach groundwater. Because they are heavier than water, they continue sinking through the aquifer until they find a layer of tight soil where they form pools of pure product. As these solvent pools slowly dissolve into the groundwater, they feed large contaminant plumes capable of impacting human health and the environment well down gradient of the impacted site.

These solvent pools are often found at depths of over 30-feet below ground surface and 20-feet below the water table, making them impossible to access using conventional remediation technologies. For example, the shoring and dewatering requirements for soil excavation and disposal at these depths represent insurmountable safety, engineering, and cost challenges. grs-3Phase-Diagram

Electrical Resistance Heating (ERH) is an aggressive in situ remediation technology that can simultaneously treat the solvents found in saturated and unsaturated soil, groundwater, and pools deep below the groundwater table. ERH is often used to clean sites where other technologies have had limited success. Using ERH, even large sites can be remediated quickly and completely. The technology is so robust that it can return highly contaminated groundwater to drinking water quality.

Developed for the US Department of Energy, ERH takes power from standard utility lines and applies it to electrodes placed in a grid pattern across an impacted site. As the subsurface resists this application of electricity it is heated to the boiling point of water producing steam and contaminant vapors. Installed to the maximum depth of contamination, ERH systems can heat to over 100-feet below grade.

During ERH, pools of solvents located below the water table are boiled first and this large contaminant mass is quickly removed from the subsurface. Next, steam formed in the subsurface starts driving contaminants out of soil and groundwater. As steam tries to escape from the subsurface, it sweeps contaminants to the recovery wells where they are collected and carried to the surface for treatment.
At the surface, steam and contaminant vapors are condensed into water, liquid contaminants, and cool contaminate vapors. Liquid contaminants are collected for recycling while condensate water and contaminant vapors are treated prior to release to the local sewer system and the atmosphere.

ERH can be applied in flowing gravel aquifers, heterogeneous glacial tills, and tight clays. It can treat fuel hydrocarbons, chlorinated solvents (dry cleaners), and polycyclic aromatic hydrocarbons (PAHs) such as creosote and coal tar. It can be safely used under roads, parking lots, and occupied buildings without disruption of traffic or occupancy. GRS would be happy to review any site for the use of ERH, and an easy to use site evaluation tool can be found on our web site.