Highway Construction Impacts on Corridor H Watersheds
This study objective was to evaluate potential impacts of highway construction on in-stream water quality of impacted areas by conducting water quality monitoring using a before-after-control-impact design. Corridor H, a four-lane highway, that runs through mountainous terrain in northern West Virginia has been under construction since 2001. This study focuses on evaluating two highway sections (Bismarck to Forman, and Forman to Moorefield) and their impacts on stream water quality in the Patterson Creek and Walnut Bottom watersheds. Grab samples were collected quarterly for 5 years before construction, during the construction, and 5 years after construction. Sampling started in 2002 for both watersheds and ended in 2018 for Patterson Creek and 2015 for Walnut Bottom. Reference sites, which were outside the impacted areas, were included to differentiate the impacts of construction from other environmental factors. Water quality parameters measured in the field included conductivity, pH, turbidity, and discharge while total suspended solids, alkalinity, acidity, sulfate, chloride, iron, calcium, magnesium, manganese, aluminum, nitrite, nitrate, ammonia, and phosphate were analyzed in the laboratory. Analysis of variance was used to determine if there were significant differences between construction phases.
There was no significant change in discharge between construction phases in either watershed. This is noteworthy because most water quality parameters are impacted by discharge dynamics. In addition, the study found little to no significant change in turbidity or total suspended solids after construction, however both parameters were higher during construction in Patterson Creek. This is notable since turbidity and total suspended solids are typically attributed to highway construction impacts.
Chloride, nitrate, and calcium were the parameters most impacted by highway construction. Chloride concentrations were 3.4 times higher in Walnut Bottom after construction. In Patterson Creek, monitoring sites that were adjacent to the highway had chloride concentrations that were 15 times higher while sites that were downstream of the highway were 5 times higher after construction. No change in chloride concentration was found at the reference site for Patterson Creek, but chloride concentrations at the reference site in Walnut Bottom increased slightly. The other sites that did not change were higher elevation sites with minimal exposure to the highway. These results may reflect leaching from the concrete used to construct the road surface.
Nitrate concentrations also increased after highway construction. All sites in both watersheds had higher nitrate concentrations after construction. The reference sites also increased but to a lower degree than the sites affected by the construction. Because the nitrate concentrations at the reference site increased as well, it is likely that other factors were affecting nitrate concentrations. However, since the post-construction concentrations were substantially higher at many sites, the increase is likely an impact of highway construction and may reflect decomposition of the former heavily forested lands that the highway runs through.
Calcium concentrations also increased modestly after construction. All Patterson Creek sites increased, including the reference site. Similarly, all sites in Walnut Bottom increased except the reference site. The higher calcium concentrations could be due to the leaching of gravel used in construction. There were no significant differences between construction phases for the remainder of the parameters.
This study has demonstrated that current practices were effective in maintaining total suspended solids loads and turbidity after construction. However, concentrations of dissolved constituents such as chloride, nitrate and calcium, were elevated in these two watersheds. The increased concentrations persisted throughout the five years of post-construction sampling, which acknowledges the presence of long term effects from highway construction in these two watersheds.