Pollutants sometimes prevalent, but why?
By Greg Elias
The town of Williston has completed a four-month water testing program in Allen Brook. The results showed the water is polluted, but the cause is as muddy as the sometimes slow-flowing stream.
The tests indicated that parts of Allen Brook are consistently contaminated with high levels of E. coli. Two other types of pollutants were present in relatively low levels.
The source of pollution, however, remains a mystery. The only sure thing is that the problem gets worse when it rains.
“I think we can clearly say that some of the pollution problem we have in Allen Brook is related to stormwater runoff, which is what I totally thought based on the fact that the whole watershed is stormwater impaired,” said Carrie Deegan, the town of Williston’s environmental planner. “We definitely see some spikes in all of these parameters following rainfalls.”
The testing involved taking samples weekly during June, July, August and September from eight locations along Allen Brook. State laboratories analyzed the samples for E. coli, phosphorus and nitrogen.
E. coli contamination is common, the tests show. At five of the eight sampling sites – each in or near a residential area – levels exceeded the state’s strict standard of 77 colonies per 100 milliliters of water on at least 75 percent of the tests. At a sampling site on River Cove Road, every one of the 17 samples collected over the summer exceeded the E. coli standard.
But in rural areas near the southern headwaters of Allen Brook, E. coli numbers were relatively low. If farming was the cause, the tests could be expected to show elevated levels of E. coli and perhaps phosphorus in those areas, Deegan said.
Instead, with some exceptions, the highest levels of contamination were found along the more developed stretches. Many of those areas are in residential neighborhoods such as the South Ridge and Brennan Woods subdivisions. In some cases, Allen Brook literally runs through backyards.
That would seem to point a finger at homeowners as the main polluters, particularly those who use chemicals containing phosphorus or nitrogen to kills weeds or fertilize lawns. But the tests showed relatively low levels of those chemicals in areas of the stream near homes.
Residents’ dogs and cats, however, could be responsible for the high E. coli numbers, said Jim Pease, a biologist with the state Division of Water Quality. Cats and dogs defecate on driveways and streets, and the waste is washed into streams when it rains.
A recent study of the Lake Champlain watershed found that stormwater runoff was the major cause of pollution, particularly in developed areas, said Nicole Ballinger, communications coordinator for the Lake Champlain Basin Program, an organization whose mission it is to protect and restore the lake and its watershed. The study concluded that runoff in urban and suburban areas was quadruple that found near agricultural land.
Deegan said Williston’s testing program clearly shows that stormwater is a factor in how much pollution is present in Allen Brook. The highest levels of E. coli were recorded after storms.
For example, after a heavy rainfall in early July, testing recorded E. coli levels at six of eight sites that were literally off the scale – more than 30 times the state standard.
Allen Brook runs 11 miles through Williston. Beginning at Sunset Hill, it flows through Williston Village, bending north near Taft Corners and crossing Vermont 2A before it reaches its confluence with Muddy Brook near the Williston/South Burlington line.
Since 1992, portions of Allen Brook have been included on Vermont’s list of impaired waterways. The state has long known the stream’s health was hurt by stormwater runoff, but limited data was available on specific pollutants.
The tests likely indicate that most of the contamination is not related to any one source. That “non-point source” pollution is difficult to track, but it does point out the need for everyone, especially residents, to do their part in reducing it, Ballinger said.
“We all have to look at our own individual behavior,” she said.