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: August 4, 2006

Point of Contact:
Brad M. Stone
200 West Forsyth Street
Suite 800
Jacksonville FL 32202-4321 
Tel: 904-598-8900 
Fax: 904-598-8988
Email: bstone@
hdrinc.com

Municipal Solid Waste Landfill
Northern, GA


Hydrogeology:

The site is located in the Piedmont Physiographic Region of northern Georgia. Topography is dominated by steep uplands of northeast-trending, low, linear, parallel ridges. The predominant soils on the site are residuals from the weathering of underlying granite gneiss. Three primary geologic units have been identified. The residuum is the uppermost stratum (saprolite), ranging in thickness from 3 to 43 feet. It consists of predominantly fine-grained silt and clay formed in situ by the weathering of bedrock. The transition zone is a variable decomposed and highly fractured zone between the underlying competent bedrock and the overlying residuum. Particle size ranges from silts and clays to large boulders of unweathered bedrock. The bedrock is composed of variable forms of granitic gneiss, which are compositionally layered and moderately to well foliated. Fracture occurrence in bedrock is variable and generally diminishes with depth.

Ground water is typically encountered at the interface between the transition zone and bedrock. The direction of ground water flow is typically from topographic highs toward topographic lows; shallow ground water eventually discharges into streams.

Targeted Environmental Media:
  • - Fractured Bedrock

Contaminants:

Investigations indicated that low-level impacts from chlorinated volatile organic compounds (VOC) in shallow site ground water were limited to three small areas adjacent to the older clay-lined portion of the landfill.

Major Contaminants and Maximum Concentrations:
  • - 1,1-Dichloroethane (2 g/L to 33 g/L)
  • - 1,2-Dichloroethene (15 g/L to 100 g/L)
  • - Chloroethane (ND to 10 g/L)
  • - Trichloroethene (ND  10 g/L)
  • - Vinyl chloride (ND  2 g/L)
  • - Chloroform (4 g/L)
  • - 1,2-Dichloroethane (ND  4 g/L)
  • - Benzene (ND )
  • - Toluene
  • - Tetrachloroethene

Site Characterization Technologies:

No technologies selected.


Remedial Technologies:

  • - Bioremediation (In Situ)
    • Reductive Dechlorination (In Situ Bioremediation)
Comments:
The remedial approach selected at this site included injection of Hydrogen Release Compound (HRC) to accelerate natural attenuation of the contaminants in ground water. Three small pilot tests were implemented to evaluate the site-specific efficacy of the technology.

Injection wells were installed into the shallow bedrock with the tops of the screens set within the upper portion of bedrock. Monitoring wells were installed both upgradient and downgradient of the injection wells. Three injection wells were installed at two pilot test locations, GWC-5 and GWC-6. Six injection wells were installed at the third location, OW-3. The wells were installed in a line perpendicular to ground water flow. HRC was injected performed using a grout pump. A total of 807 pounds of HRC was injected at OW-3. At GWC-6, 324 pounds were injected, and 210 pounds were injected at GWC-5.

Remediation Goals:

None provided


Status:

Review of the monitoring data indicated no appreciable change in the concentration of VOCs at pilot test area GWC-6. Total VOCs increased in pilot test area GWC-5 because of the presence of acetone. The third pilot test area, OW-3, realized a substantial decrease in both chlorinated and petroleum-related compounds. Many of the compounds appeared to initially increase in concentration before they decreased to below target cleanup levels. Concentrations of vinyl chloride initially decreased and then increased. Approximately 1 year after HRC was injected, the initial results indicate success in reducing concentrations of VOCs in one of the three pilot test locations.

Performance monitoring is still under way.


Lessons Learned:

The variation of results at each pilot test location may be attributable to the local geologic heterogeneity or variations in remedial design. For example, slight differences were observed within the shallow bedrock between various pilot test areas during drilling, well development, and water level monitoring. The area that exhibited a reduction in the concentration of VOCs appeared to exhibit more interconnectivity between injection wells and performance monitoring wells than the other two pilot areas.

Additionally, the remedial design at the OW-3 area included a denser injection pattern with more HRC injected into the aquifer. The changes in geochemical indicators provide evidence for effectiveness of HRC to promote reductive dechlorination in the treatment area in the two pilot test areas that did not exhibit discernible reduction in VOCs. This evidence suggests that additional time may be needed to realize discernible reductions in concentrations of VOCs in these two pilot areas.

References:
Stone, Brad M.; Elizabeth A. Victor; Tracy A. Hughes; Edward Hood. 2003. Accelerated Bioremediation of Chlorinated Solvents in a Fractured Rock Aquifer. The Seventh International In Situ and On-Site Bioremediation Symposium, Orlando, Florida, June 2-5.

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