Tests shows high bacteria levels in Allen Brook
By Greg Elias
Brian Connelly wades into Allen Brook and dips a clear plastic container into the water. Connelly, a summer intern with the town, collects the first of several samples he will take from various places along the stream.
It’s a sunny day on the cusp of summer. Birds chirp as red maples sway in the breeze. The site, at the end of a dirt road outside of Williston Village, seems far away from the bustle of Taft Corners.
It’s hard to believe that a stream flowing through such an unspoiled setting could be polluted. But recent tests showed that Allen Brook has elevated levels of the bacteria E. coli and other contaminants.
Samples taken earlier this month from sites nearer to residential areas produced E. coli levels so high that they were literally off the scale, although those results were not replicated in later tests.
The town of Williston earlier this month began a water testing program to assess the health of Allen Brook. The program, a partnership between the Williston Conservation Commission and the Vermont Agency of Natural Resources, involves collecting weekly samples from eight sites.
Results after three weeks of testing showed widespread E. coli contamination. The first samples collected on June 5 showed E. coli counts exceeding the state’s strict standard of 77 colonies per 100 milliliters of water at all eight sites. Samples at three sites – each close to residential areas – showed levels of at least 2,419 colonies per 100 milliliters, more than 30 times the state standard. The actual number may have been higher because the levels exceeded the test’s limits.
Two subsequent weeks of testing showed more moderate levels that still mostly exceeded state standards. The June 12 samples showed the stream surpassed the E. coli standard at five of eight sites, albeit at generally lower levels. The June 19 testing indicated high E. coli levels at six of eight sites, with most levels rising from the previous week.
Allen Brook meanders through Williston for 11 miles. 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 the state’s list of impaired waterways. The state has long known the stream’s health was hurt by stormwater runoff caused by Williston’s extensive development over the past two decades, but had little concrete data on specific pollutants.
Allen Brook is considered a Class B waterway that should be suitable for “aquatic habitat, boating, swimming.”
In fact, swimmers rarely if ever take a dip in Allen Brook, which is mostly too shallow for recreational use. But the town does get calls from people who wonder if it is OK for their children and pets to play in and around the stream, which runs near an elementary school and several subdivisions.
“We’ve got kids playing in the brook, dogs playing in the brook,” said Carrie Deegan, Williston’s environmental planner. “Is it safe? We don’t know.”
Neil Kamman, an environmental scientist with the state Agency of Natural Resources, said “it is way too early” to know what, if any, dangers the water poses based on the limited testing conducted so far. But he said to be cautious, residents should stay away after rain washes potential pollutants into the stream.
“You might not want kids to be in there a day or two after it rains,” he said, adding that most of the time there is “absolutely no threat” to children and pets playing near the stream.
E. coli is a type of bacteria commonly found in the intestines of animals and humans. Tests showing E. coli in a stream or lake indicate the potential presence of waterborne pathogens that can make people sick.
The likelihood of that happening is expressed in terms of probabilities. Swimmers who enter water with Vermont’s highest allowable concentration of E. coli stand roughly a 3 in a 1,000 chance of developing a gastrointestinal illness, according to the state.
State standards for E. coli are considerably stricter than those of the U.S. Environmental Protection Agency. The EPA standard is 126 E. coli per 1,000 milliliters of water.
The testing program also looks for the presence of phosphorus and nitrogen. Phosphorus levels exceeded the state standard in some cases, with just the first week’s data available. Nitrogen levels fell well below the standard for the first round of testing.
Data still inconclusive
The data from the first three weeks of testing comes with caveats. Kamman emphasized that the numbers are only preliminary, with just the first week of data confirmed by the state. The plan is to test all summer, and he said the season-long results will provide a clearer picture of the pollution problem.
The numbers can vary greatly in streams depending on rainfall and other variables. Those sky-high E. coli numbers from the first round of tests, for example, came from samples taken after two days of heavy rain, Kaamen said.
That spike, however, could be a useful indicator of what is polluting the stream, Deegan said. If replicated in future tests that follow rain, high numbers could point to land-based sources of pollution rather than waste from waterfowl and beavers.
Deegan said the town has no plans to post areas with elevated E. coli levels. She hopes to eventually publicize test results on the town’s Web site, but that may not happen this summer because the site is being overhauled.
Finding the source
It is possible that the testing will show that Allen Brook is no longer impaired and the state can take it off its list, Deegan said, but she considers that unlikely.
Instead, the tests could help pinpoint which areas need the most help and suggest solutions, Deegan said. For example, if E. coli levels are consistently high at one testing site, the town and state may be able to identify its source, such as a failing septic system.
It is more likely, however, that the pollution sources will be tough to trace to a single, correctable source, Deegan said. In that case, she hopes the program at least will help educate residents about threats the stream faces.
“People need to see the results – it’s a kick in the rear,” she said. “They need to say this is way out of control, it’s not what we want to see in our environment.”
For weekly updates on the Allen Brook water tests, visit www.anr.state.vt.us/dec/waterq/cfm/volmon/index.cfm and click on Williston Conservation Commission. For more information about what the numbers mean and testing locations, contact Deegan at firstname.lastname@example.org or 878-6704.