Senior Engineer / Geologist
Fritz Krembs is a Senior Engineer / Geologist with Trihydro Corporation. He has a MS from the Colorado School of Mines, and is a registered P.E. and P.G. His work experience includes conceptual site model development, remedy selection, and implementation/optimization of in-situ groundwater remediation technologies.
FLASH POSTER PRESESNTER - Oxidative and Reductive Treatments
In-Situ Ozone Treatment for 1,4-Dioxane in Confined Aquifer
1,4-dioxane is present in a locally-confined aquifer at an active solvent transfer center in Puerto Rico. The groundwater flow direction is influenced by off-site production wells and a buried sand-gravel paleochannel. While other co-contaminants are present in groundwater at the site, 1,4-dioxane is the key regulatory driver because of its recalcitrance and mobility in the subsurface. This paper presents the details of remediation technology evaluation of this emerging contaminant in a challenging site setting.
Technology screening for 1,4-dioxane treatment in this setting has been evaluated with a combination of desktop/literature study and site-specific bench testing. The treatment scenario that was selected was a reactive barrier installed at the leading edge of the 1,4-dioxane plume. The first round of technology screening was documented in a draft Interim Corrective Measures Study (ICMS) submitted in late 2013. At that time, use of in-situ chemical oxidation (ISCO) with ozone had been documented in laboratory and field-scale studies performed by others. During the regulatory review period, researchers working on behalf of the Environmental Security Technology Certification Program (ESTCP) demonstrated that permanganate, unactivated persulfate, and permanganate combined with persulfate had the potential to treat 1,4-dioxane under some conditions. A site-specific bench test was conducted in 2015 to evaluate the ability of permanganate and persulfate to successfully treat 1,4-dioxane at this site.
Laboratory and field-scale studies have demonstrated that ISCO with ozone can successfully treat 1,4-dioxane. The draft ICMS outlined the conceptual design of an ozone-based ISCO system to be installed in multiple phases at the leading edge of the plume. There are challenges associated with ozone sparging at this site, including lack of power source in the immediate vicinity of the treatment zone, the possible need for venting of gases from the locally-confined treatment zone, and permitting requirements associated with permanent construction in this area.
Based on promising interim results published by ESTCP researchers, site-specific bench testing was performed to evaluate 1,4-dioxane treatment with permanganate and persulfate. Bench testing was conducted in batch reactors and evaluated: three oxidants (permanganate, persulfate, and permanganate + persulfate); low, medium, and high oxidant concentrations; and low and high initial 1,4-dioxane concentration over a period of 14 days. The results indicated that 1,4-dioxane treatment was feasible with each of the oxidant evaluated. However, relatively high oxidant concentrations were required to attain substantial treatment. In addition, oxidant consumption was high, suggesting high natural oxidant demand (NOD). Therefore, while bench testing suggested that 1,4-dioxane treatment with permanganate and persulfate was technically practicable at this site, because of the large treatment zone and relatively high NOD, ozone appears to be the oxidant that will be carried forward to the field scale. Construction of the ozone system is scheduled for the summer of 2016, and monthly performance monitoring data will be presented in this paper.