In Situ Chemical Oxidation Remediation Pilot Study Of A Karst Bedrock Aquifer Contaminated With Chlorinated Solvents

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A pilot study to evaluate an innovative in situ treatment technology was implemented at Letterkenny Army Depot, Chambersburg, Pennsylvania, for a limestone bedrock aquifer contaminated with chlorinated solvents. This technology destroys VOCs in groundwater, utilizing a network of injection points to deliver a solution of hydrogen peroxide (50%), catalysts, and surfactants. The chemical reaction generated by this solution creates a hydroxyl radical, which is extremely effective in oxidizing complex organic compounds. The organic hydrocarbon contamination is rapidly oxidized by the hydroxyl radical to carbon dioxide, oxygen, and water.

This pilot study was the first to evaluate this technology in a high-flow karstic limestone aquifer. Extensive geophysical logging, packer testing, and discrete sampling were conducted to evaluate the fracturing and hydraulic properties of the bedrock for the injection design. Extensive on-site and downgradient monitoring was conducted during the pilot study to evaluate the effectiveness of this technology.

The limestone aquifer had maximum total VOC concentrations of 114 mg/L. Chlorinated compounds composed over 94% of the VOCs in the aquifer. The most prevalent VOC detected was 1,2-dichloroethene at 64% of the total chlorinated VOCs detected. Treatment was targeted at depths of 30 to 80 feet below ground surface within the source area. Over 12,000 gallons of 50% hydrogen peroxide were injected into the limestone aquifer over a 3.5-day period. The post-injection sampling results indicate that the estimated mass of total chlorinated VOCs destroyed was approximately 2,000 pounds.

The pilot study results indicate that this innovative in situ remediation technology can effectively lower chlorinated solvent concentrations in source areas located within a limestone bedrock aquifer.

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