Tufa Precipitation and its Effect on Drainage of Interstate Highways in Northeastern Ohio

Calcareous tufa has been observed occluding drain outlets and catch basins as well as covering slopes at 124 localities in Cuyahoga, Portage, Summit, and Medina counties in northeastern Ohio. Regional geologic studies, hydrogeologic studies, and geochemical analyses have been employed to identify the source and mode of origin of the material which prevents highway drainage systems from functioning properly. No correlation was found between regional geologic and hydrogeologic conditions analyzed. Geochemical analysis of water collected from subbase drain outlets and of an array of construction materials leads to the conclusion that slag, when used as a subbase material, is sufficiently soluble to affect the pH of drainage water and to provide the calcium deposited as tufa. Solution of calcium hydroxide in slag in the subbase elevates the pH of drainage water above 10.3 and produces an environment in which CaCO₃ can be precipitated.

The problem of tufa deposition will continue in northeast Ohio as long as slag is used as a subbase material. However, careful maintenance of the highway surface to reduce the amount of water entering the drainage system through edge joints and cracks in the pavement will significantly reduce the magnitude of the problem.