Superfund Research Program
Improving the Treatment of Contaminated Aquifers by Developing Direct-Push Oxidant Candles with Pneumatic Circulators
Project Leader: Mark Christenson
Grant Number: R41ES022530
Funding Period: Phase I: September 2013 – June 2014
Water quality is one of the biggest issues related to public health in the United States. Few situations incite more public outcry than when a community learns that their drinking water has been tainted. Two of the biggest threats to groundwater quality in the U.S. are contamination from either chlorinated solvents or petroleum. Currently, there are an estimated 20,000 sites in the U.S. contaminated with chlorinated solvents. Many of these sites are remnants of releases that occurred 20 to 30 years ago. Left unattended, the size and scope of the problems associated with these spills have only become exacerbated with time. Likewise, leaking underground storage tanks (UST) containing petroleum are one of the leading causes of groundwater contamination in the United States. Of the 590,000 federally-regulated UST currently in the U.S., approximately 6,000 had confirmed releases in 2011.
In the past decade, significant efforts have been devoted to developing innovative remedial technologies to combat these environmental contaminants. One technology that is relatively mature is the injection of liquid oxidants into contaminated aquifers or in situ chemical oxidation (ISCO). There are two roadblocks to successfully implementing ISCO treatments. One is when contaminants are located in low permeable layers and these finer textured zones do not readily accept liquid injections. The other roadblock is when the aquifer is porous enough for liquid injections, but the cohesive properties of the chemical oxidant results in density-driven flow, thereby causing the oxidant to sink and not treat the desired target zone.
To address both problems, AirLift Environmental and the University of Nebraska developed slow- release oxidant-paraffin candles, that when inserted into low permeable zones, slowly dissolve and intercept the contaminant. To prevent the oxidant from migrating downward from the candles, pneumatic circulators were developed that aerate or release bubbles at the base of the candle and prevent the oxidant from sinking while greatly facilitating its horizontal distribution. AirLift Environmental and the University of Nebraska are designing and manufacturing slow-release oxidant candles with aerators tips that can be inserted into contaminated aquifers by direct push (i.e., no wells needed). This development will make it easier and less expensive to install slow-release oxidants and greatly increase its commercial appeal. The research is taking place in two stages where prototypes of direct-push candles are tested in a large groundwater flow model. Direct-push candles with circulators with the most promise are being scaled up and field tested by quantifying the ability of the oxidant candle system to vertically deliver oxidants evenly to 22-ft. monitoring wells in the field. Chlorinated solvents and petroleum products are clearly among the top groundwater contaminants worldwide. The innovation is specifically designed to provide a cost-effective and efficient technology to combat public water supplies impacted by these contaminants.