Impact of Wastewater Treatment Plant Effluent on Receiving Waters

This research examines the impact of Wastewater Treatment Plant (WWTP) effluent on stream water chemistry, and its relationship with changing seasonal discharge. Water samples were taken upstream and downstream of four plants in Central Vermont, before and after rainfall, and tested for dissolved inorganic compounds. Differences between concentrations of compounds during low and high flow were calculated by subtracting the average upstream values from the average downstream values. Contamination sources were determined by presence of elements during high versus low discharge days. Three plants showed no measurable differences between down and upstream sites, indicating WWTPs are not a source of contamination. During low flow, the Northfield downstream site showed higher levels of phosphorus and potassium, signaling WWTP effluent. The Barre and Waterbury upstream sites had higher concentrations of lead and arsenic during low flow suggesting a groundwater source. Additionally, road salt signals were found in several sites and indicate both groundwater and surface water sources. This study illustrates the importance of higher discharge levels to dilute stream contaminants. All the sites tested comply with Vermont water quality standards, however, it is important to note the potential for changing discharges in the future to negatively impact receiving waters.