Creosote retention levels of timber highway bridge superstructures in Michigan’s Lower Peninsula.

Acknowledgments Environmental concerns about preservative bleeding (or migrating) from timber bridges have increased in recent years. This preliminary study examined the creosote retention levels at six timber highway bridges in Michigan’s lower peninsula during the summer of 2000. Several test core samples were removed from the bridge superstructures (four bleeders and two controls) and were evaluated for creosote content in the laboratory. Results from three of the four bleeder bridges indicated high creosote retention levels between 36 and 52 lb/ft (576.7 and 833 kg/m) after several years in service. The authors extend appreciation to the following people for their valuable contributions to this project: Dan Sikarskie and Roger Rasmussen (retired) of the Huron Pines Resource Conservation and Development Council (Grayling, Michigan) for coordination of fieldwork and assistance with gathering initial treatment process information; Dan Foster and Stan Lebow of the USDA Forest Service, Forest Products Laboratory, for technical assistance with fieldwork and laboratory analysis procedures; and Carlito Calil, Jr., of the University of Sao Paulo at Sao Carlos (Brazil) for assistance with fieldwork. We also acknowledge the assistance of the following organizations for permitting access to their bridges and providing background treatment documents for this study: Missaukee County Road Commission, Alcona County Road Commission, Crawford County Road Commission, Otsego County Road Commission, and the U.S. Fish and Wildlife Service—Shiawassee National Wildlife Refuge.