Case Study | Geology-Based Design Results in Remediation Cost Avoidance

Case Study

Geology-Based Design Results in Remediation Cost Avoidance

A groundwater remediation system at Eglin Air Force Base was not meeting performance based remediation objectives. Environmental Sequence Stratigraphy (ESS) — an innovative geology focused approach for mapping subsurface conditions and contaminant distribution — refocused the remedy, improved performance and resulted in an estimated 10-year timeframe reduction in life cycle costs.

Challenge

Eglin Air Force Base in Okaloosa County, Florida, had implemented a groundwater extraction and treatment system to remediate tetrachloroethylene (PCE), a chlorinated volatile organic compound often found in groundwater as a result of a history of solvent use. Our client was contracted by the Air Force to execute performance based remediation of the chlorinated solvent groundwater plume.

The design for the original groundwater pump-and-treat remediation system was based on a conceptual site model (CSM) that was developed using standard data interpretation techniques. The remediation goal was to reduce contaminant concentrations to the groundwater cleanup target levels (GCTLs) and close the site within five years by 2020. After two years of operation, contaminant mass removal rates indicated that the remediation system would not achieve performance goals until 2032, over a decade longer than originally estimated.

The Air Force recognized the need to optimize the remediation system to achieve project goals within an acceptable time frame. A successful optimization strategy would require an improved understanding of the subsurface, particularly heterogeneities that were limiting the ability of the pump-and-treat system to efficiently remove contamination. Contaminant occurrence and migration pathways needed to be defined to refocus groundwater extraction efforts, increase contaminant mass removal rates and achieve remediation milestones.

165%

increase in contaminant mass removal

year reduction in remedial operations

Solution

Our team applied ESS, a technical approach recognized by the U.S. Environmental Protection Agency and the U.S. Air Force as a best practice in developing CSMs for complex contaminated groundwater sites. This approach focuses on the geology and understanding depositional systems that formed the subsurface to accurately define the subsurface heterogeneities and permeability architecture, which is the primary control on fluid migration and contaminant distribution and transport. Equipped with ESS enhanced CSMs, remediation professionals are able to design more effective groundwater treatment systems that achieve project goals in less time, at significantly lower cost.

Our team applied the geology-based ESS approach by examining the existing subsurface data and applying scientifically proven stratigraphic analysis. The analysis incorporated knowledge of the regional geology and depositional environment to identify and correlate genetically related lithology units (or lithofacies), resulting in a more refined understanding of the site’s stratigraphic connectivity.

Detailed geologic cross sections and maps were constructed to define the 3D hydrostratigraphic units that controlled contaminant transport and storage. The ESS framework was then used to evaluate groundwater elevation data and contaminant chemistry data to target the location of additional groundwater extraction wells and maximize the extraction of impacted groundwater and contaminant mass removal.

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Results

This approach improved the subsurface CSM, allowing the Air Force to better understand the fate and transport of groundwater contaminants to establish optimum extraction well locations based on the geologic conditions at this site. The ESS analysis identified and mapped an intermediate clay layer that proved to be key in targeting and designing new groundwater extraction well location and screened interval beneath the clay (see Well #1).

The second new extraction well (Well #2) also targeted stream channel features identified by the ESS analysis. The new extraction wells were brought online without increasing the overall capacity of the pump-and-treat system. Thus, a significant increase in contaminant mass removal was achieved without increasing operational costs (see Before ESS and After ESS graphics).

Implementation of the recommendations and enhancements to the 3D fate and transport model resulted in a shorter estimated timeline to site closure. Comparison between the original and optimized performance curves reveals cost avoidance and shows that the system should achieve GCTLs by 2022 — 10 years earlier than the system performance prior to applying ESS. This relatively small investment in analysis and data interpretation helped produce significant project life cycle cost savings, substantial risk reduction and the ability to meet remediation performance goals on a timely basis.

Project Stats

CLIENT

Bhate/U.S. Air Force

LOCATION

Eglin Air Force Base, Okaloosa County, Florida

Challenge

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Solution

Results

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