The site includes fractured bedrock aquifers and overlying unconfined aquifers in saprolitic soils. The shallow, saprolitic soils have a low hydraulic conductivity.
Targeted Environmental Media:
 Fractured Bedrock
Dissolved phase chlorinated solvents were identified in both the fractured bedrock aquifers and the overlying, unconfined aquifers in the saprolitic soils.
Major Contaminants and Maximum Concentrations:
- Halogenated VOCs (var)
No technologies selected.
- Bioremediation (In Situ)
- Reductive Dechlorination (In Situ Bioremediation)
Comments:
Direct push borings and a pressure pulsing technology were selected to deliver an emulsified vegetable oil (EVO) substrate to form a reactive barrier.
Historically, remediation has been achieved at the site by using sodium lactate substrate as an electron donor for reductive dechlorination of chlorinated solvent plumes. The sodium lactate is introduced into the contaminated plumes through arrays of 77 injection wells. However, in areas where contamination is present in shallow saprolitic soils, effective delivery of a substrate is difficult due to the low hydraulic conductivity of the soils. In June 2011, a pilot-scale study was conducted at this closed municipal solid waste landfill in Central, Virginia to assess the effectiveness of using direct push borings and pressure pulsing technology to deliver an EVO substrate into shallow groundwater in saturated soils with a low hydraulic conductivity. Multiple direct push borings were completed in the pilot study area using a Geoprobe 6620 DT (Geoprobe). The substrate was injected under pressure through the existing hardware of the Geoprobe at target depths of 34 to 28 feet below ground surface with the assistance of a Primawave pressure pulsing technology. An EVO substrate was chosen as the electron donor because it was predicted to last longer in the environment (when compared to the use of a sodium lactate substrate). During the study, 250 gallons of an EVO substrate and about 4,500 gallons of dilution water were injected into eleven borings in an array spanning approximately 100 feet on each side. An effective coverage of substrate injections was achieved in the study area through the use of numerous direct push borings in the array.
Not documented.
The pilot study has been completed. The pressure pulsing technology allowed average injection rates that were approximately 40% faster than those achieved without the use of the technology. Additionally, the occurrence of ýday-lightingý (substrate extruding from the boring during an injection) was observed to be less frequent when the pressure pulsing technology was applied.
With increased injection rates and more efficient distribution of dilute substrate through the saprolitic soils, it appears that the contaminated groundwater present in the saprolitic soils of the study area was well inoculated with the EVO substrate effectively creating a reactive barrier in the native soils.
Reference:
Nash, S., et. al. 2012. ýCase Study: Use of Pressure Pulsing Technology to Aid in the Development of a Subsurface Treatment Barrier." 8th International Conference Remediation of Chlorinated and Recalcitrant Compounds. May 21-24.
|
