The site is composed of a thin layer of sand and fill overburden (approximately 1 meter thick), which lies on top of sedimentary rock. Approximately 14 to 24 meters below ground surface is dolomitic limestone overlying granite. The limestone is moderately fractured along horizontal and sub-horizontal bedding planes and is relatively non-porous. Within the bedrock lies the ground water table. Ground water flow is to the south.
Targeted Environmental Media:
 Dense Non-aqueous Phase Liquids (DNAPLs) - Fractured Bedrock
Major Contaminants and Maximum Concentrations:
- Trichloroethene (175,000 µg/L)
- Chloride (614,000 µg/L)
No technologies selected.
- Chemical Oxidation (In Situ)
- Pump and Treat
Comments:
In 1992, a ground water pump and treat system was installed in order to mitigate plume migration. Though operated for 15 years, concentrations of TCE up to 20% of the pure-phase solubility remained in the source zone. To oxidize the remaining TCE, 40,000 liters of 2.5% by weight potassium permanganate was injected into the source zone. Carbon and chlorine isotopes were used to monitor the oxidation rates.
TCE levels decreased below the method detection limit within 1 week; however, rebound occurred by the fifth week. Within the source zone, rebound was slow and resulted in significantly lower TCE levels by week 34 of the project. Outside of the source zone, TCE concentrations equal to pre-injection concentrations or higher were found by week 34. Chloride concentrations found in areas where permanganate was observed after injection increased by less than a factor of four. Chloride concentrations at week 34 were found to be elevated at some points and decreasing at others. In areas where permanganate remained, chloride levels were elevated.
Not identified in the reference cited.
Not identified in the reference cited.
Carbon isotopes can be used to determine TCE oxidation dynamics within fractured bedrock and diffusion from the rock matrix. It can also be used to identify how ground water displacement from the injection process alters TCE concentrations.
References:
Helsen, Jordi, Aravena, Ramon, Zhang, Min, Shouakar-Stash, Orfan, and Burns, Leanne. Assessment of TCE Oxidation by KMNO4 using Stable Carbon and Chlorine Isotopes at a Fractured Bedrock Site. Presented at the 2007 U.S. EPANGWA Fractured Rock Conference: State of the Science and Measuring Success in Remediation. Portland, ME. September 24-26, 2007.
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