The site is located in the North Carolina Piedmont and is characterized by rolling topography and mostly well-drained residual clayey soils that have been weathered from metamorphic and igneous bedrock. The site is drained by the Cape Fear River dendritic tributary system. Rock underlying the site consists of metamorphosed granite of the late Proterozoic to late Cambrian Age. Megacrystic, well-foliated (granite), and locally containing hornblende describe the rock cluster. Bedrock at the site is typically shallow.
The unsaturated zone is infiltrated by precipitation and recharges the water table. Gravity led groundwater flows down slope and discharges as springs to perennial springs and rivers, usually within a distance of 3,000 feet or less. An underground pedestrian tunnel intercepts the water table and thus influences groundwater flow within the test area. Two sump pumps are used to dewater the tunnel.
Horizontal hydraulic conductivity is estimated to be 7.6 feet/day. The water table gradient in the central portion of the site is approximately 0.02 foot/foot. Average groundwater velocity is approximately 0.5 feet/day.
Targeted Environmental Media:
 Fractured Bedrock
The TCE plume extends approximately 900 feet west-northwest of the presumed source area.
Major Contaminants and Maximum Concentrations:
- Benzene-toluene-ethylbenzene-xylene (BTEX) (0 µg/L)
- Trichloroethene (2,600 µg/L)
- Pumping Tests
- Coring
Comments:
Estimated hydraulic conductivity = 4.7 X 10-4 cm/second; storativity = 4.1 X 10-3 centimeter per second.
Actual well pumping yields were lower than expected suggesting that actual aquifer conditions are more restrictive.
- Pump and Treat
- Soil Vapor Extraction
- Other (Air sparging)
Comments:
Active remediation operations have been ongoing for 10 years and have been effective in reducing BTEX. Emulsified Oil Substrate (EOS) is being used to remediate the TCE source area.
The first phase of EOS ran from June 29 to August 16, 2004. Approximately 12,180 pounds of EOS concentrate and 83,000 gallons of groundwater were recirculated during this phase. The second phase ran from September 10 to October 12, 2004. An additional 6,300 pounds of EOS concentrate and 80,000 gallons of groundwater were recirculated during this phase.
See results for further information.
An interim remedial goal was set to reach a TCE level of 536 µg/L groundwater within three years of the full-scale groundwater remediation implementation. The goal was based on achieving a 50% reduction in the average concentration of TCE in five monitoring wells from the 2001 preremediation average concentration of 1,072 µg/L.
Final remedial goal of achieving the North Carolina Groundwater Standards:
PCE = 0.7 µg/L
TCE = 2.8 µg/L
cis-DCE = µg/L
VC = 0.15 µg/L
The interim and final remedial goals for TCE have been achieved. The final remedial goals for PCE and cis-DCE have also been achieved; however, while VC concentrations are decreasing, they are not below the Standard.
EOS resulted in successful treatment of CVOCs. The two-step process effectively moved the emulsion throughout the targeted treatment area. At this site, it was possible to move EOS more than 20 feet from the injection points. Most of the water recirculation process was performed unattended and part of the EOS was gravity drained keeping labor and equipment costs low. EOS injection quickly created anaerobic reducing conditions.
References:
In Situ Bioremediation of Chlorinated Ethene DNAPL Source Zones: Case Studies
April 2007
The Interstate Technology & Regulatory Council Bioremediation of DNAPLs Team
Army Chemical Review - "New Technology Helps Mother Nature Expedite Cleanups" May and Skillman, 2005
http:www.wood.army.milchmdsdpdfsJul-Dec%202005Skillman2.pdf
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