The Collaborative has “sentinel” monitoring sites on the New Haven River in Bristol and downriver near Middlebury at Halpin Road. ACRWC also samples for bacterial pathogens at Bartlett Falls due to its heavy use by the public in the summer. The long-term trend of E.coli readings may indicate slightly increasing levels. E. coli counts in the New Haven River generally are close to the state standard, but rise to high levels during periods of high flow and runoff, greatly exceeding the standard for swimming waters. One pattern that has emerged is an increasing trend in E.coli with distance downstream from Bristol to just below the confluence with the Muddy Branch in New Haven.
Turbidity levels in the New Haven River increase downstream but are generally low and below the state standard. However, at times of high flow and runoff, turbidity levels reach very high levels, greatly exceeding the state standard near its mouth. Phosphorus concentrations in the New Haven River are generally low, increasing downstream as do turbidity levels, indicating that phosphorus in the river is mainly associated with suspended sediment. There is currently no Vermont water quality in-stream standard for phosphorus.
Total nitrogen concentrations in the New Haven River have proven to be low and well below the Vermont State Standard for nitrate.