Handling Acid-Producing Material During Construction

Abstract

Environmental concern during construction has become a serious matter, especially regarding water quality. Earth materials weather rapidly when excavated and in some instances produce deleterious products. One such product is acid drainage (AD). Weathering of Precambrian metasedimentary rocks excavated during road construction in the Southern Appalachian Mountains is a classic example of AD formed in this fashion. Before the problem was recognized, aquatic life was decimated in several “blue ribbon” trout streams. In order to address the problem of how to handle acid-producing material during construction, the Federal Highway Administration initiated studies resulting in development of guidelines. The guidelines suggest procedures for detecting and evaluating potential AD problems and provide suggestions for handling acid-producing material without requiring post-construction mitigation. Geologic mapping is the basic tool for assessing AD potential in an area. However, in covered areas geophysical methods have been applied effectively to detect the sulfide minerals primarily responsible for AD production. To determine the bottom-line as to whether sulfidic material has the potential to generate AD the use of an Acid-Base Accounting analysis has proven successful. If construction encounters acid-producing material and the cost:benefit of the project permits, AD can be successfully abated by encapsulation of the material within specially designed embankments.