Pneumatic Fracturing and In-Situ Chemical Oxidation Project
 | A bulk chemical tank was
used to feed H2O2 to ARS crew |
During November 2002, ARS completed a field pilot test demonstrating chemical oxidation at an active government facility located in the Southeastern United States. The project scope consisted of integrating Pneumatic Fracturing and the injection of Fenton's Reagent to address DNAPL source contamination within both the unsaturated and saturated zone at the site.
The site, a former drum storage area, contains TCE soil and groundwater concentrations ranging up to hundreds of thousands of ppb, with the probability that DNAPL is present in the groundwater. The heterogeneous geology consists of a tight silty clay (unsaturated zone) overlying a gravel, chert, clay layer (saturated zone) above limestone bedrock. Using three injection wells in a triangular pattern around two existing monitoring wells, Pneumatic Fracturing was first applied to create an interconnected fracture network and increase the bulk permeability of the formation. The enhanced fracture network served to optimize the reagent injection, improve contact between the target contaminant and the injected chemicals and allow for better pH adjustment control in the subsurface.
Once the Pneumatic Fracturing was complete, ARS injected phosphoric acid to decrease the in situ pH below 4 SU to facilitate the Fenton's reaction. The acid was injected using a combination of ARS' Liquid Atomized Injection (LAI) process and hydraulic methods. Once the pH was lowered, injection of hydrogen peroxide commenced. In total, approximately 8,600 gallons of hydrogen peroxide at concentrations ranging from 5 - 12 % were effectively emplaced within the unsaturated and saturated zones.
Three post injection rounds of groundwater sampling have shown TCE concentrations decreased by 50 to 75% in the two target monitoring wells. Soil sampling is planned for the site to assess treatment of the unsaturated zone. ARS' Pneumatic Fracturing and chemical injection delivery method for chemical reagents is ideally suited for difficult geologic formations.
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