IN SITU REMEDIATION OF FRACTURED BEDROCK DNAPL SITES USING CHEMICAL OXIDATION

Bench-scale studies and field demonstrations were conducted for two fractured bedrock sites with a range of rock types, including shale, siltstone, and metagabbro. The permanganate demand exerted by the matrix, the potential for oxidant diffusion into the matrix, and the potential for mineral leaching were evaluated through bench-scale testing. The results of these studies demonstrated that permanganate destroyed PCE/TCE without adverse impacts to groundwater chemistry. Based on these results, field pilot tests have been completed.

At the first site, where TCE concentrations in groundwater are as high as 18 mg/L, pilot testing was planned based on the results of treatability studies as well as pre-design site characterization. An eight-week pilot test using continuous recirculation of site groundwater amended with up to 5 g/L potassium permanganate (KMnO₄) was implemented with the objective of assessing the impact of oxidant injection on TCE flux from DNAPL contained in the pilot test area. Field pilot results demonstrated that TCE was oxidized in situ and that the technology was implementable in the fractured bedrock media. At the second site, where PCE concentrations in groundwater are as high as 10 mg/L, sodium permanganate was injected to evaluate the efficacy of the technology. Oxidant was injected at concentrations up to 2 g/L for a period of 3 weeks followed by 4 weeks of groundwater recirculation without oxidant addition. Results, including chloride and PCE concentrations, indicated that DNAPL was destroyed during the pilot test.

Based upon the results of these pilot tests full scale in situ chemical oxidation (ISCO) remedies are currently being planned for both sites. Pre-design investigation activities will be used to evaluate the distribution and hydraulic characteristics of the source areas. The investigation activities will provide key data to be used during detailed design.

This paper will present the results of the bench-scale studies and the field pilot tests, and give an overview of the pre-design characterization and steps for detailed design of the full scale implementation. The ability of the ISCO technology to accelerate source remediation in fractured bedrock environments will also be discussed.