Mr. Macario received his B.S. in Civil Engineering from California State Polytechnic University, Pomona. His professional experience includes planning and implementation of complex environmental construction and remediation projects and providing technical support for CERCLA site characterization, management and closure within the municipal, commercial and federal sectors. His recent project emphases include construction management and quality control for large-scale field operations at sites impacted by 1,4-dioxane and PFAS contaminants.
1,4-Dioxane Treatment in Groundwater to Achieve Drinking Water Goals Using a Synthetic Sorbent Media Yuma, Arizona
Previous solvent spill and leaks at Site 1 in Yuma, Arizona resulted in chlorinated contaminants present in groundwater at approximately 80 feet below ground surface. The selected remedy in the ROD to treat the site chemicals of concern (TCE and 1,1-DCE) is groundwater recirculation. This system uses GAC to prevent further migration of these compounds at concentration greater than the drinking MCLs. Sampling of 1,4-dioxane, a contaminant not previously assessed at this site, was initiated by the Navy in 2012 at the request of the regulatory agency. A maximum concentration of 180 ?g/L was reported prior to initiation of the pilot study, greater than the U.S. EPA RSL for drinking water (0.46 ?g/L). A pilot study to treat 1,4-dioxane to below 0.46 ?g/L, TCE to 5 ?g/L, and 1,1-DCE to 6 ?g/L and was conducted using the existing 100-gpm groundwater recirculation system retrofitted with a synthetic media mobile unit. The pilot system diverted untreated groundwater directly from extraction wells, processed it through the synthetic media vessels, and then directed the treated groundwater through the existing GAC vessels to ensure compliance with the ROD. Unlike GAC, the synthetic media was regenerated onsite using superheated steam to restore its sorbent capacity. Groundwater samples were collected from influent and effluent sampling ports of the treatment vessels to evaluate the effectiveness. During the 11 contaminant loading and regeneration cycles over a period of approximately 4 months, a total of more than 3 million gallons of extracted groundwater was processed through both the synthetic media and the groundwater recirculation system. The study consistently demonstrated the ability to reduce 1,4-dioxane, TCE, and 1,1-DCE concentrations in groundwater. Pre-treatment influent 1,4-dioxane concentrations ranging from 1.5 to 2.1 mg/L were consistently treated to less than the laboratory detection limit of 0.084 ?g/L. All treated effluent concentrations for TCE and 1,1-DCE were below their respective laboratory reporting limits of 0.4 ?g/L throughout the entire treatment duration. Each steam regeneration cycle was effective in restoring the sorptive capacity of the synthetic media. 1,4-dioxane generated from the onsite steam regeneration cycles was captured, cooled, and condensed during the pilot study. The steam was vented to the atmosphere during regeneration in compliance with the Arizona air discharge requirements.