Using Ice Surfaces to Decrease the Impact of a Remediation Project

Eagle River Flats is an estuarine salt marsh located on Fort Richardson, AK. It has been the main impact area for artillery training for over 60 years. In 1990, large reported waterfowl die-offs (>1,000 ducks/year) were attributed to white phosphorus residues in ponded and marsh areas from the detonation of military smoke munitions. A remediation strategy of temporary draining of contaminated ponded areas followed by capping of isolated locations was specified in the Record of Decision (RoD) by site regulators in 1998. Remediation by pumping of the ponded areas was carried out from 1997 until 2007, when the initial remedial action objectives were met. Many small, isolated locations remained contaminated, however, resulting in continued low rates of waterfowl mortalities. Capping these sites was thus required by the RoD to prevent waterfowl access to the contaminant. Our strategy was to conduct capping operations over the frozen salt marsh to reduce costs, minimize environmental impact, and improve safety while working in an active impact area. By mid-February, there is sufficient ice, continuous cold temperatures, and daylight to conduct operations. The process requires an unexploded ordnance technician to sweep the access routes and sites prior to plowing to expose the ice surface. Two days are allowed to freeze up and strengthen the roads. Geotextile is then laid at the pre-marked capping locations and a layer stone is piled over the Geotextile as capping material. When the ice melts in the spring, the stone is kept consolidated by the geotextile, settling over the contaminated area and isolating it from waterfowl. A test capping operation in 2007 was successful. A full-scale capping operation was carried out in February of 2008. The number of ducks killed by white phosphorus poisoning fell from 35 in 2007 to eight in 2008. The corresponding median mortality rate for the overall duck population fell from 0.9% to 0.3. Ground surveys of the treatment area indicated no adverse environmental impact. Further work was conducted in March of 2009 to address the remaining contaminated areas and to conduct minor maintenance. All capped areas have been sampled along their periphery to ensure completeness of coverage.