Iron Oxide Deposits on Highway Construction Projects

The New Hampshire Department of Transportation (NHDOT) has determined that rock fill material placed in wet areas can release iron to surface water, resulting in hydrated iron (ferric) oxide compounds with red-orange microbial deposits in drainage ways adjacent to highways. Naturally occurring bacteria commonly catalyze iron reactions, and their cellular material is found in the precipitate as a biofilm. The ferric iron compounds and associated microbial deposits accumulate in drainage ways, are aesthetically unappealing, and can result in adverse environmental impacts to the water body and highway structures. Iron deposits in surface water downstream of roadways constructed with rock fill are a continuous construction and maintenance challenge for NHDOT (Fowler and Minichiello, 1977). When iron transport occurs after roadway construction, the expected duration and factors controlling the event are not immediately clear, complicating plans for remediation. Moving forward, NHDOT would like to use more quantitative methods based on geochemical characterization and common road construction scenarios in order to determine rock-use suitability and to reduce iron fouling from construction. Restricting specific combinations of rock type (mineralogy) and interactions between the rock and certain hydrogeologic settings may improve water quality at roadway construction sites. There are many factors affecting iron fouling, and accounting for all of them at every construction site is cost prohibitive. Measurements made and tested through modeling in this project will be used to determine the propensity for iron fouling for each parameter. This will help to develop a subset of primary measurements needed to make general predictions at new sites.