Formatted Title
Pilot Testing a New Amendment Combination During Advancing Property Development
Background/Objectives
A former chemical manufacturing site in the southwestern US was impacted by chlorinated solvents discharged to the subsurface through daily operations. The property was sold to a developer and rapid demolition of existing site structures occurred and the site was ready for new building construction. A rapid investigation occurred using conventional soil and groundwater sampling aided by the membrane interface probe (MIP) that led to the development of a robust conceptual site model. With time of the essence, three target areas of the site were injected in a grid pattern with an all-in-one chemical oxidant using direct push technology. The goal was to achieve a gross mass reduction that could be further polished with other technology. With the loss of site access looming, an in situ chemical reduction (ISCR) approach was selected as the polishing technology.
Approach/Activities
After reductions of greater than 50% of the chlorinated mass post-oxidation event, and after allowing three months for subsurface conditions to return to background, a conceptual design was prepared to polish remaining mass. A critical aspect of the design was to have long-lasting remediation because site access would become limited and the monitoring well network would be reduced. A new combination of amendments was chosen based on three important treatment mechanisms: sorption, biodegradation, and abiotic reduction. The combination of amendments included a carbon-based sorptive media (PlumeStop®), a biodegradable wax (Aquifix™), a bioaugmentation culture (Bio Dechlor Inoculum - BDI®), and a sulfidated microscale zero valent iron (S-MicroZVI®). Not only was the amendment combination unique, but the compatibility of the individual components allowed them to be injected together. Because the site plume is greater than 150,000 ft2, the conceptual design focused on multiple injectable barrier rows arrayed perpendicular to the plume. Prior to full-scale implementation, a pilot test was completed as proof of concept. For the pilot test, direct injection of the amendments around an in-plume well was completed and monitoring of chlorinated compounds and geochemical parameters occurred for weekly and monthly time points over a four-month post-injection duration.
Results/Lessons Learned
A significant reduction in contaminant mass of about 75% occurred at the pilot test well within the first few weeks after injection. This presentation will show the progress during the duration of the pilot test and will also look at the design approach using a mass flux tool to target the injection intervals. Lessons learned from challenges working on site including artesian conditions will be shared.