Installation of EHCT for Treatment of Chlorinated Volatile Organic Compounds
Adventus installed 1 ton of EHC® into a trench and 3 tons of EHC® into an open excavation at a site that has groundwater contaminated with a mixture of chlorinated solvents.
Two areas of contamination were targeted for treatment. The first was a dissolved plume migrating from a source zone through a thin permeable soil unit overlying bedrock at approximately 12 feet below ground surface. The second was an open excavation containing groundwater, after contaminated soil had been removed. The site was contaminated with a large range of Contaminants of Concern (COCs) at both locations.
EHC® was selected for in situ treatment of the contaminants. Adventus recently adapted its patented combination of controlled-release solid carbon and zero valent iron (ZVI) particles to yield EHC®, a solid material for stimulating reductive dechlorination of otherwise persistent organic compounds in groundwater. Following placement of EHC® into the subsurface, a number of physical, chemical and microbiological processes combine to create strong reducing conditions that stimulate rapid and complete dechlorination of organic solvents and other persistent compounds.
A permeable reactive barrier (PRB) was constructed to intercept the dissolved groundwater plume. The PRB was constructed with an excavator by digging a 3-foot wide trench down to the top of the bedrock, followed by filling the bottom foot with a mixture of EHC® and sand. Only the bottom foot required filling because the groundwater table was less than a foot above the bedrock, and the permeable soil unit was also at this depth. The remainder of the PRB was backfilled with pea gravel.
To treat the excavation, the bottom 1 foot of the area was lined with sand and EHC®. The downgradient wall of the excavation was then lined with a 3-foot high, 3-foot wide bench of sand and EHC®. The 3-foot high bench would ensure that any water exiting the excavation at the downgradient side would come into contact with the sand and EHC® mixture.
This installation was completed in late February 2004. To monitor the effectiveness of the installation, wells were placed upgradient and downgradient of the PRB, as well as within and downgradient of the excavation. These will be sampled in June 2004 for volatile organic compounds. Total iron will also be measured to validate that the monitoring wells are hydraulically connected to the EHC® installation.
The installation was completed in less than 2 days.