Institute for Transportation

Recent research on the release of wood preservatives from
treated wood used in sensitive environments has not considered the potential contribution from construction residues. This study sought to develop leaching rate data for small construction debris and compare those to the release rate from treated wood itself. Western hemlock boards were pressure treated with chromated copper arsenate Type C (CCA-C), and then common construction tools were used to generate sawdust or shavings from those boards. These wood particles were then leached in deionized water, and the leaching rate was compared with that of solid wood samples cut from the same specimen. Release rate data from this study were also compared with those from endmatched samples that were leached in artificial rain in an earlier study. The release rates of copper, chromium, and arsenic from CCA-C treated chain saw sawdust, circular saw sawdust, and spade bit shavings were many times higher than from solid wood when samples were immersed in water. There was little difference in the release rates among the three types of shavings and sawdust, despite differences in their particle sizes. The rates of release from decking exposed to rainfall were many times lower than that of construction debris or solid wood continually immersed in water. These results show the importance of minimizing the amount of construction debris that is allowed to
enter the aquatic environment. However, example calculations
also demonstrate that if reasonable efforts are made to minimize release of construction debris, the contribution of these particles to the overall release of preservative from the structure will be minimal.