Decommis­sioning & De­contamination (# 84)

Utility facility Undergoes Extensive Remediation

Environmental remedial actions have proven to be a significant, multi-year undertaking at a location where a municipal utility provider in the southeastern United States has operated for decades. Historically, electrical equipment-including transformers-was cleaned and serviced at the site, resulting in the release of fuels, industrial solvents, metals, and polychlorinated biphenyls (PCBs).

Releases of these constituents caused source areas with dense non-aqueous phase liquids (DNAPL) from solvents, widespread PCBs in soil and sediment, and groundwater impacts at the site.

Golder has provided assessment and remediation services for several years at the still-active facility. Given the complexity of site impacts, the technical continuity of ongoing consultant involvement has provided value to our client, as we have negotiated solutions with the state regulatory agencies and worked closely with site personnel to minimise disruption of site activities.
A feasibility study prepared by Golder recommended a phased risk-based corrective action strategy. The remedial program has included DNAPL removal, soil and sediment source area removal and capping, and groundwater monitoring. An engineered "cap", or paved surface that has been installed, will actually increase the area for on-site operations after the remediation is completed.

For the DNAPL source removal, Golder designed and constructed a turnkey innovative remedial system, consisting of an in-situ thermal conductive heating (TCH), multi-phase extraction and soil vapour extraction system. Use of the TCH remedy resulted in greater source reduction in an expedited timeframe over conventional technology, with an estimated 50 percent cost-savings versus excavation and off-site disposal of the hazardous material. An added benefit is that the increased subsurface heat triggered enhanced bioremediation of the groundwater in the source area.

For removal of PCB-impacted soils, a large-diameter auger (LDA) approach was used to excavate deep soils in a tight work area, constrained by an off-site manufacturing facility. Use of LDAs, rather than a conventional sheeting and excavation approach, reduced remedial costs and minimised risks of impacts to the off-site facility.

Following a groundwater monitoring program to evaluate the effectiveness of the DNAPL and soil source removal actions, Golder will implement groundwater remedial actions as needed. This will reduce the presence of chlorinated volatile organic compounds and arsenic in groundwater and control risks of off-site plume migration.