Remediation of Metals
Duncklee & Dunham has undertaken an innovative remedial action project to address metals contamination in the shallow and intermediate groundwater at an industrial facility. Metals contamination in groundwater represents one of the more difficult remediation scenarios because metals do not degrade and have limited capacity to attenuate under normal aquifer conditions. Our staff has extensive experience in the assessment and remediation of metals and other inorganic soil and groundwater contamination resulting from agri-chemical, electronics, plating and coating, wood treatment and mining operations.
Although the existing groundwater plume is still confined to the client’s property, 3D groundwater fate and transport modeling verifies that groundwater metals contamination will ultimately exceed regulatory standards at the facility boundary if left unabated. These metals continue to be released to the groundwater from a centralized soil source area. Metals in the groundwater beneath these source area soil act as a source for the strengthening plume.
The objective of the program is a unified remedy for both the current groundwater plume and the future release of additional metals contamination from the source area. Duncklee & Dunham’s senior staff, working with nationally recognized geochemical and groundwater modelers and treatability experts developed a unified strategy to address the existing groundwater plume and the continuing source area. The treatability-study results and the data from a groundwater assessment using a hydraulic-profiling tool equipped with a groundwater sampling system, and an extensive monitoring-well network were used to refine the groundwater model. These data helped to overcome heterogeneity in the hydrostratigraphic units at the site and adjust the remedial approach based on site-specific attenuation-capacity properties of the saturated zone, which were then used to design and implement a groundwater-extraction system that targeted select zones of the groundwater plume that maximized its efficiency.
Duncklee & Dunham also designed a remedial approach to address the source-area soil contamination by assessing the natural attenuation capacity of the unsaturated zone to evaluate the ability of these soils to mitigate the migration of metals to the water table. We calculated site-specific remediation goals that represented a metal concentration that would exceed the attenuation capacity of underlying soil and eventually leach to groundwater. We evaluated various remedial options and ultimately selected a metals-stabilization method by way of in situ soil blending. This remedial method allowed for treatment of soil on-site and substantial savings related to disposal costs. The treatability-study results allowed Duncklee & Dunham to increase the remedial goals, reduce the amount of soil that required treatment by approximately 50% while being protective of human health and the environment. This remedial approach amounted to a cost savings of over $600,000 when compared to conventional dig-and-haul methods for soil remediation. This is another example of Duncklee & Dunham’s intent and ability to use innovation and creative thinking to find effective solutions to serious environmental challenges.
Duncklee & Dunham responded to releases of propylene glycol and water at a solar-panel field in Robeson County, North Carolina in 2012. A mixture of propylene glycol and water is used as a heat-transfer agent by the solar panels, which supply energy for use at an adjacent industrial plant. Duncklee & Dunham reported the release to the Fayetteville Regional Office of NCDENR, who told us they would not add the site to the Inactive Hazardous Sites Inventory if we completed the assessment remediation within three months. We calculated a proposed Interim Maximum Allowable Concentration in groundwater for propylene glycol and submitted it to NCDENR, which accepted this concentration one month later. We used this IMAC to calculate a protection-of-groundwater preliminary soil remediation goal. Within a month, NCDENR approved our calculations and established this PSRG. We completed our report and submitted it to the Fayetteville Regional Office within the timeframe allotted. NCDENR did not add this site to the IHSI.