title: A five-year performance review of field-scale, slow-release permanganate candles with recommendations for second-generation improvements.
abstract: In 2009, we identified a TCE plume at an abandoned landfill that was located in a low permeable silty-clay aquifer. To treat the TCE, we manufactured slow-release potassium permanganate cylinders (oxidant candles) that had diameters of either 5.1 or 7.6 cm and were 91.4 cm long. In 2010, we compared two methods of candle installation by inserting equal masses of the oxidant candles (7.6-cm vs 5.1-cm dia). The 5.1-cm dia candles were inserted with direct-push rods while the 7.6-cm candles were housed in screens and lowered into 10 permanent wells. Since installation, the 7.6-cm oxidant candles have been refurbished approximately once per year by gently scraping off surface oxides. In 2012, we reported initial results; in this paper, we provide a 5-yr performance review since installation. Temporal sampling shows oxidant candles placed in wells have steadily reduced migrating TCE concentrations. Moreover, these candles still maintain an inner core of oxidant that has yet to contribute to the dissolution front and should provide several more years of service. Oxidant candles inserted by direct-push have stopped reducing TCE concentrations because a MnO2 scale developed on the outside of the candles. To counteract oxide scaling, we fabricated a second generation of oxidant candles that contain sodium hexametaphosphate. Laboratory experiments (batch and flow-through) show that these second-generation permanganate candles have better release characteristics and are less prone to oxide scaling. This improvement should reduce the need to perform maintenance on candles placed in wells and provide greater longevity for candles inserted by direct-push.
authors.affiliation: AirLift Environmental, LLC, 5900 N. 58th, Suite 5, Lincoln, NE 68507, USA; School of Natural Resources, University of Nebraska, Lincoln, NE 68583-0915, USA. Electronic address: mark@airliftenvironmental.com.
authors.forename: Mark
authors.initials: M
authors.lastname: Christenson
authors.affiliation: Department of Civil Engineering, University of Nebraska, Lincoln, NE 68583-0531, USA. Electronic address: annkambhu@gmail.com.
authors.forename: Ann
authors.initials: A
authors.lastname: Kambhu
authors.affiliation: School of Natural Resources, University of Nebraska, Lincoln, NE 68583-0915, USA. Electronic address: jamesreece10@yahoo.com.
authors.forename: James
authors.initials: J
authors.lastname: Reece
authors.affiliation: School of Natural Resources, University of Nebraska, Lincoln, NE 68583-0915, USA. Electronic address: scomfort@unl.edu.
authors.forename: Steve
authors.initials: S
authors.lastname: Comfort
authors.affiliation: Nebraska Department of Environmental Quality, Waste Management Division, Lincoln, NE 68509-8922, USA. Electronic address: Laurie.brunner@nebraska.gov.
authors.forename: Laurie
authors.initials: L
authors.lastname: Brunner
mesh_terms: D060587:Groundwater / Q000737:chemistry*; D016877:Oxidants / Q000737:chemistry*; D011196:Potassium Permanganate / Q000737:chemistry*; D014241:Trichloroethylene / Q000032:analysis* / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry; D018508:Water Purification / Q000295:instrumentation / Q000379:methods*
chemical_list: D016877:Oxidants; D014874:Water Pollutants, Chemical; D011196:Potassium Permanganate; D014241:Trichloroethylene
keywords: Chlorinated solvents; Permeable reactive barrier; Second-generation permanganate candles; Slow-release oxidants; TCE