U.S. EPA Contaminated Site Cleanup Information (CLU-IN)


U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

Fractured Bedrock Project Profiles

Last Updated: November 29, 2006

Point of Contact:
Elizabeth M. Rhine
30 Patewood Drive, Suite 155
Greenville SC 29615 
Tel: 864-987-3906 
Fax: 864-987-1609
Email: erhine@
arcadis-us.com

Former Groce Laboratory
Greenville County, SC


Hydrogeology:

The shallow geology consists of steeply dipping resistant units of partially weathered biotite schist extended up to 10 feet into saprolite, creating a series of small valleys and ridges in the bedrock topography. Hydraulic conductivity in the fractured bedrock ranges from 0.354 feet per day to 19.31 feet per day near the creek. Hydraulic conductivity in the saprolite aquifer is 0.34 feet per day.

Targeted Environmental Media:
  • - Fractured Bedrock

Contaminants:

A Phase II remedial investigation (RI) was conducted in 1999 to delineate the source, nature, and extent of contamination. Results indicated that ground water in the saprolite aquifer is contaminated by volatile organic compounds (VOC). Portions of the bedrock aquifer also have been affected as contaminants migrate downgradient from the saprolite aquifer.

Major Contaminants and Maximum Concentrations:
  • - 1,2-Dichloroethane (12 µg/L)
  • - 1,1-Dichloroethene (200 µg/L)
  • - 1,1,2,2-Tetrachloroethane (220 µg/L)
  • - 1,1,2-Trichloroethane (0 µg/L)
  • - Methylene chloride (0 µg/L)
  • - Carbon tetrachloride (0 µg/L)
  • - Benzene (0 µg/L)
  • - 1,2-Dichloroethene (3000 g/L)
  • - Tetrachloroethene (1000 g/L)
  • - Trichloroethene (4300 g/L)

Site Characterization Technologies:

  • - Vertical Chemical Profiling
    • Cluster Wells
  • - Pumping Tests
  • - Tracer (dye) Test

Comments:
In March 2003, a boring investigation was conducted to evaluate the variability of the bedrock surface in a pilot test area. Slug tests were conducted in February 2003 to better understand the hydraulic transmissivity in the bedrock aquifer.

During the pilot study, potassium bromide was added to the solution as a tracer to aid in estimating the in situ reactive zone (IRZ) and to evaluate vertical migration in the bedrock aquifer.


Remedial Technologies:

  • - Bioremediation (In Situ)
    • Reductive Dechlorination (In Situ Bioremediation)
Comments:
A pilot study using enhanced reductive dechlorination (ERD) was conducted to enhance mass degradation of chlorinated aliphatic hydrocarbons (CAH) in ground water by providing an organic carbon medium to stimulate bacterial activity. Blackstrap molasses was chosen as the carbohydrate source.

The pilot study which began in August 2003 was successfully completed in February 2004. During the pilot study, injections were made into both the saprolite and bedrock aquifers. However, because of the downward hydraulic gradient, the carbon migrated naturally into the bedrock aquifer and enhanced reductive dechlorination in the bedrock as well as the saprolite. Therefore, the full-scale remedy was designed to inject only into the saprolite, at a significant cost savings. The full-scale in-situ reactive zone was constructed and brought on line in August 2004. 117 saprolite injection wells were installed throughout the 9.6-acre plume, with injection rows spaced 18 months apart. Molasses injection began September 7, 2005. Initially, a 10 percent solution of blackstrap molasses was introduced into the saprolite aquifer.

Injections in the saprolite aquifer were initially conducted on a bi-weekly basis. As the TOC levels were established, the injection frequency was changed to monthly and then quarterly. To increase the distribution radius while keeping the carbon loading steady, the volume injected in each well increased to 1,000 gallons while the carbon loading decreased to 2.5%. Molasses was also blended with whey increase the retention time of the carbohydrates.

As of June 2006,
Remediation Goals:

The cleanup goals for this Superfund site are the maximum contaminant levels (MCL) as published in the record of decision (ROD). The MCL for PCE is 5 micrograms per liter (g/L).


Status:

By June 2006, fourteen injections were made into the saprolite aquifer. Analytical data show decreases in parent constituents in all saprolite and bedrock monitoring wells. The concentration of PCE has decreased from as high as 5.4 mg/L to non-detect in 6 out of 10 saprolite wells and from as high as 1 mg/L to non-detect in 7 out of 12 bedrock monitoring wells. TCE data exhibit a similar decrease from a high of 6.4 mg/L in the saprolite and 4.3 mg/L in the bedrock to non-detect in these same wells. Increases in daughter products have also been observed. Since full-scale start-up, cis-1,2-DCE concentrations ranging from non-detect to 0.05 mg/L at baseline to as high as 8 mg/L in saprolite and 2.4 mg/L in bedrock. As of June 2006, cis-1,2-DCE concentrations have started to decline in both saprolite and bedrock monitoring wells. Combined with a significant increase in methane and other indicator parameters, the findings indicate that the reductive dechlorination pathway will be driven to completion in both the saprolite and bedrock aquifers. Once the VOC concentrations have been reduced to 1 mg/L across the site, monitored natural attenuation will be the remedy to achieve the final clean-up goals for the site.


Lessons Learned:

Based on the success of the pilot study and the use of natural downward hydraulic gradients, the full-scale ERD system was installed in the saprolite. By taking advantage of the natural hydraulic gradient, significant cost savings were achived by avoiding the installation of costly bedrock injection wells. The carbon found the fractures (much like the original contaminants did), thus eliminating the need to define exactly where the fracture zones are located.

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