Monitoring the Distribution of a Groundwater Remediation Reagent in Fractured Bedrock with Water Quality Sondes

Remediation of contaminated groundwater is often a prolonged and expensive process from initial characterization to achieving remedial action objectives. Rapid assessment of the performance and effectiveness of remedial technologies can shorten the remediation process resulting in reduced costs, reduced contaminant exposure, and thus reduced corresponding risk. In this case study, a monitoring program was implemented to rapidly assess the migration of an in situ groundwater remediation technology applied to contaminated groundwater in shallow fractured bedrock under an active manufacturing building. Due to the manufacturing activities, access to the subsurface with vertical wells or other technologies was not practical, resulting in a limited understanding of the fate and transport of the contamination. To remediate the contamination, injection of a remediation reagent composed of fine particles of activated carbon was proposed. Due to the restricted access, the reagent would be injected along the perimeter of the building and up-gradient of the suspected source area. Initially, monitoring the effectiveness of the remedial solution was proposed to be through quarterly groundwater quality sampling of selected near-source down gradient wells. However, this approach would result in over one year of monitoring, analysis, reporting, and decision making to establish the effectiveness of the remediation. In an effort to accelerate the remediation process and avoid unnecessary delays, we deployed a network of water quality sondes and telemetry units to measure turbidity as a surrogate for the presence of the remediation reagent. Using the near real-time data, we rapidly demonstrated the limited and irregular distribution of the reagent to the target remediation zone (which was subsequently borne out by the groundwater quality sampling), and gained a better understanding of the groundwater flow system, thereby guiding future corrective actions and reducing delays in the remediation process.