BRATTLEBORO -- When some local rivers and streams showed significantly elevated E. coli levels earlier this summer, officials attributed the results to rainfall.
But even after an extended dry period drove down bacterial counts in most waterways, the Williams River remains a trouble spot that may warrant further investigation.
"Adjacent land use, contributing tributaries and other possible watershed characteristics will need to be scrutinized to help determine the possible source of impacts contributing to the elevated E. coli counts," said Laurie Callahan of Southeastern Vermont Watershed Alliance.
Alliance volunteers have been testing every two weeks for E. coli, which is found in fecal matter and can cause gastrointestinal illness and other health problems.
Two rounds of sampling in June each showed more than half of the organization's testing sites with E. coli levels greater than 235 organisms per 100 milliliters of water, the governmental threshold for "suitability for swimming."
But Callahan has noted that there was significant rainfall prior to each of those tests. Precipitation can wash E. coli into streams.
Rainfall also may have affected results for the association's July 25 samples.
A dry August, though, seems to have kept bacterial levels low. On the West River, for example, all eight test sites were well within suitable-swimming standards for both the Aug. 8 and Aug. 22 samples.
Three sites on Saxtons River also were in the clear for both August tests, as were two sites on Whetstone Brook and the Indian Love Call site on the Rock River above the Route 30 bridge.
After a relatively clean report on Aug. 8, however, the Williams River again showed elevated numbers of E. coli last week. Three sites, all in Chester, exceeded safe-swimming levels -- below the wastewater-treatment facility (291), Rainbow Rock swimming hole (291) and above the Middle Branch of the Williams River confluence (462).
Two other Williams River sites were labeled suitable for swimming: Sampling at the Missing Link Road Bridge in Chester produced a 225 E. coli level, while Rockingham at Bartonsville Bridge scored 118.
Nearly exceeding the governmental swimming standard -- but remaining just below it with a score of 229 -- was the Middle Branch of the Williams River in Chester.
"All of SeVWA's 2012 sites along the Williams River have had E. coli values above the ‘suitable for swimming' standard this season, at times regardless of rainfall impacts," Callahan wrote in a memo accompanying last week's test results.
The alliance's last full round of testing for 2012 is scheduled for Sept. 5. The organization's reports are available at https://sites.google.com/site/vtsevwa.
Mike Faher can be reached at email@example.com or 802-254-2311, ext. 275.