Theme: 02. Assessing Remediation Effectiveness

Topic Area: 02h. Optimizing Remedial Systems

Formatted Title:

Effective Use of Analytical Tools to Reinvent the Project Strategy

Background/Objectives:

Historical operations at a former manufacturing site in South Carolina included the use of volatile organic compounds (VOCs), primarily trichloroethene, and releases from impacted site soils and groundwater. Investigation and remediation of VOC impacted soil and groundwater has been ongoing since 1986. Activities are currently being performed in accordance with a consent agreement.

In 2017, the responsible party implementing the environmental remediation changed following a merger and acquisition, and WSP was retained as the consultant. WSP initiated an audit of the remedial approach after the project transition to 1) confirm the strategy met the requirements under the consent agreement, and 2) evaluate ways to optimize the strategy into a practically minded solution.

Approach/Activities:

The approach included a comprehensive evaluation of 30 years of site groundwater and soil data, as well as meetings with the regulatory agency, the facility, and local subcontractors. Potentially feasible remedial alternatives were identified, which expedited progress towards remedial goals at a lower cost while still meeting the requirements under the consent agreement. Data gaps were identified to confirm the feasibility of alternatives recommended in the evaluation.

With regulatory approval, WSP initiated efforts to collect additional biological, chemical, and geotechnical soil and groundwater data in 2018 to fill data gaps and confirm recommended remedial optimizations. The additional soil quality data, including discrete interval sampling, revealed that the extent of VOC-affected soil was 95% less than previously characterized using qualitative techniques. Therefore, with regulatory approval, WSP implemented a revised remedial approach for soil, which consisted of a small ‘hot spot’ excavation instead of the previously recommended large-scale soil vapor extraction system. Based on the extent of onsite affected groundwater, WSP evaluated whether the groundwater treatment system operations could be reduced or modified. A temporary shutdown in 2021 was implemented to evaluate non-pumping groundwater conditions, which demonstrated that only two of the seven pumps wells were required for full hydraulic capture. With the scaled down pumping network, operational savings in labor, materials, and utilities were realized. Optimizations in the groundwater monitoring program were completed in 2017 and again in 2022 following regulatory approvals, including (1) a 70% reduction in monitoring locations (from 232 to 89 locations) to eliminate vertical and horizontal redundancy in sampling locations, and (2) sampling method modifications from a labor-intensive purge method to a no-purge method, where technically appropriate. WSP also performed groundwater modeling to determine the predicted distribution of VOC-affected groundwater in 30 years, proving that the groundwater containing VOCs at concentrations above the criteria, supporting monitored natural attenuation as an effective long-term remedy for groundwater.

Results/Lessons Learned:

Focusing on the practical objectives, alternatives continue to be identified which significantly reduce cost, risk, and timeline while adhering to the requirements of the consent agreement. Over $1M in initial savings have been achieved, with additional $1M in savings in the long-term cost projections.

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Pamela Robertson