Fractured Bedrock Characterization and Remediation at Former Fort McClellan
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Project Objective

The former Fort McClellan in Anniston, AL served as a DOD training facility from 1917 until 1999. At the legacy Landfill 3 at McClellan, chlorinated solvent impacts extend up to 250 feet below ground surface into a fractured bedrock aquifer adjacent to a fault zone.

Geosyntec’s Scope of Services

Geosyntec was tasked by Matrix Environmental Services (MES) with conducting a pre-design investigation for fractured bedrock to refine the hydrogeologic conceptual site model (CSM), improve understanding of contaminant fate and transport, and aid in remedial design and implementation. Surface geophysical tools were utilized to identify subsurface anomalies (i.e., potential preferential flowpaths) at the partially weathered bedrock interface. Pneumatic slug testing was conducted at existing monitoring wells to generate hydraulic conductivity data to better understand groundwater flow and mass flux. Sonic drilling was utilized to generate high-quality soil and rock cores. Sonic boreholes were further analyzed using borehole geopshyical tools and packer testing to develop hydraulic profiles, identify flow zones and chlorinated solvent concentrations, and understand fracture intervals and orientation. These data were used to inform the design and installation multi-port (FLUTe) bedrock wells. Data generated from the additional characterization efforts, along wth existing chemical, lithological, and hydrogeological data, were compiled into 2-D and 3-D data visualizations to design and optimize the planned in-situ bioremediation remedy.

The detailed pre-design investigation resulted in a reduction of the biobarrier length to approximately 400-ft, a significant change and cost savings compared to the conceptual biobarrier design which was nearly a quarter-mile in length. The biobarrier design was supported through bench scale treatbility studies, a monitored natural attenuation (MNA) evaluation for the downgradient plume, and permitting the injection through Alabama Department of Environmental Management’s (ADEM’s) underground injection control (UIC) program. Flexible remedial design goals which focused on mass flux reduction, instead of absolute numerical criteria, allowed for remedy optimization.

The resulting field implementation consisted of injecting emulsified vegetable oil (EVO) and a pH buffer. In addition, implementation included injection of the KB-1® Plus bioaugmentation culture, which was specifically formulated for the treatment of both chlorinated ethenes and ethanes as well as acidic environments (pH down 5).

Notable Accomplishments

Geosyntec’s detailed pre-design investigation resulted in a streamlined biobarrier design representing significant cost savings for the client. Post-injection performance monitoring indicates (i) development of geochemical conditions necessary for successful biological reduction, (ii) chlorinated solvent concentration declines, and (iii) over 90% reduction in mass flux. Groundwater data collected from the Site indicates that biologicial treatment and mass flux reduction continues.

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Project Summary

  • Location: Anniston, Alabama
  • Client: Matrix Environmental Services, LLC
  • Project Practice Areas: Contaminated Sites
  • Type of Facility: Landfill Facility
  • Services Provided: Conceptual Site Model Development; Fractured Bedrock Characterization; Laboratory Treatability Testing; Groundwater Remedy Design and Optimization; Permitting; Remedy Implementation; Coordination with ADEM
  • Type of Work: Modeling & Remediation
  • Governing Regulation: State and Local