MONTPELIER, Vt. — With a bill to clean up Lake Champlain and other Vermont waters awaiting the governor’s signature, a group devoted to preserving the lake is raising an alarm about a recent spate of sewage spills from municipal wastewater plants into its tributaries.

Problems occur when rain or melted snow, collectively known as storm water, infiltrate through old clay tile pipes or in other ways into sewage systems, which normally carry wastewater from homes, businesses and public buildings.

“Where combined sewers exist, water runoff from rain and snow-melt flows into the sewage plant and can cause too much volume for the facility to handle,” Lake Champlain International said this week. “When this happens, raw sewage and the water runoff overflows from the facility and into the nearby waterway.”

David Mears, the commissioner of the Vermont Department of Environmental Conservation, said municipal wastewater discharges are an ongoing concern for his department.

“We expect communities to do everything in their power to keep these from happening,” he said.

Mears said the legislation Gov. Peter Shumlin is expected to sign later this month was written to address what for Lake Champlain is a larger problem: runoff from farms, roads and other developed land.

Those sources have contributed the bulk of the phosphorus that has fed the blue-green algae blooms that have choked parts of Lake Champlain and some smaller bodies of water, Mears said. Outflows from municipal wastewater treatment plants contain about 3 percent of the phosphorus flowing into the lake, he added.

Mears said human health effects from bacteria like E.coli are a separate and distinct problem from phosphorus flows into the lake.

James Ehlers, executive director of Lake Champlain International, argued that too much forgiveness is built in to the state’s regulatory system for municipal sewage treatment plants. He pointed to the fact that seven of the 12 overflows reported between May 5 and June 1 were labeled “authorized” in the state’s reporting system, meaning allowed under state rules.

The biggest polluter among municipal systems during May was the city of Vergennes in western Vermont, which spilled a total of more than 237,000 gallons of combined storm and waste water in four episodes, said City Manager Mel Hawley. Vergennes straddles the Otter Creek, which flows into Lake Champlain.

Hawley said the city was under a state order to reduce the flows and had installed new monitoring equipment this spring so it could better measure the problem before deciding on a solution.

The state allows the city to have the overflows anytime there is more than 1 inch of rain in an hour or 2.5 inches in 24 hours, Hawley said. Both the city and state are looking for solutions. “It’s not as if we don’t care,” Hawley said.

Mears said the overflow incidents tend to spike this time of year due to spring rains and melting snow. He said the number of incidents reported in May “certainly wasn’t out of ballpark compared to what you’d typically see in the spring.”

Mears added that in most overflows storm water is a much larger part of the volume than wastewater.

Ehlers said he found that reassurance unconvincing. “That percentage is irrelevant if (sewage) is bubbling up in your street,” he said.

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