A geochemical assessment of highway construction through sulfidic rocks

This research attempted to evaluate the impact of highway construction through sulfidic rock on the water chemistry of streams draining the construction site. The Tellico Plains to Robbinsville Scenic Highway crosses the mountains between Tellico Plains, Tennessee and Robbinsville, North Carolina encountering the sulfide mineral bearing rocks of the Late Precambrian Ocoee Supergroup. Portions of the highway were built prior to widespread knowledge of the adverse environmental impacts associated with road construction in sulfidic rocks. As a result, streams draining these sections of highway suffered the effects of Acid Drainage (AD). Since that time, road construction practices have improved and construction methods were developed to abate AD created by highway construction. This study evaluates the effectiveness of these construction methods at maintaining favorable water quality. This investigation is divided into three parts: 1) Surface water chemistry was investigated in both streams draining watersheds containing the highway and streams with no possible influence from the road. 2) A geologic investigation was performed (mapping and collection and analysis of rock samples) to provide better understanding of the geologic contribution to water chemistry, and 3) Mineral coatings on outcrops and in streams, a possible indicator of AD conditions, were sampled and identified to provide information on possible AD sources and the chemical processes occurring near them. Although the Tellico Plains to Robbinsville Scenic Highway is constructed through bedrock which exhibits locally abundant sulfide mineralization, data collected during this study indicates that AD-abating methodology applied during road construction has been effective at minimizing adverse chemical alterations to the surface water in the study area. For most parameters measured statistical analysis of the water chemistry data indicates that there is no difference between streams draining watersheds containing the highway and streams not associated with the road. Widespread geologic influences on the water chemistry are not observed in the study area. Although mineral coatings characteristic of AD conditions are found, their extent is limited to sulfide mineral-bearing outcrops with abundant water. With the exception of one stream sample point, mineral coatings are absent from the stream sample points used in this study. In conclusion, data collected for this study indicates that the Telhco Plains to Robbinsville Scenic Highway does not adversely impact surface water draining the construction site.