Town officials are investigating after a recent malfunction at the Scituate Waste Water Treatment Plant discharged roughly 930,000 gallons of partially treated effluent into the storm drains in the North River.

The April 27 incident didn’t create any danger to the public drinking water supply, but did force a temporary closure of shellfish beds in the North and South rivers and forced town staff to make some changes at the plant, Kevin Cafferty, Scituate’s public works director, said.

“We’ve already taken precautions to fix this and to ensure it doesn’t happen again,” he said.

For one, he said, plant staff monitored all operational systems on Friday and through the weekend to make sure the facility functioned properly and didn’t cause further discharges. Staff also added a new Secondary Control and Data Acquisition Controls logic to the plant to prevent future failures, he said.

The discharge was traced to a power fluctuation that happened Wednesday evening and was discovered by plant staff Thursday morning.

The fluctuation caused a surge in the power system, which in turn shut down a Programmable Logic Controller or “Brain” for the secondary treatment process, Cafferty said.

The controller’s shutdown caused the clarifiers to discharge the grey water, an effluent that has been treated through the first of three processes in the plant, Cafferty said. Because it only went through the primary cycle, the water had higher nitrogen and bacteria count than typical outflow when it was discharged, he said.

Town officials are continuing to investigate what may have caused the power fluctuation, Cafferty said. While there have been lesser incidents of discharge, the clarifiers have never shut down before, he said.

“Unfortunately, problems like this can happen,” he said.

Samantha Woods, executive director of the North and South Rivers Watershed Association, called for a more timely public response when these problems arise. She said the association only heard of the discharge through “unofficial channels” on Friday, which she noted was two days after the release of the primary-treated effluent.

The organization sent its own notification Saturday via email. The town issued a news release from Cafferty about the plant discharge on Monday afternoon and posted a notice on the town’s website shortly after.

People could have gone shellfishing on kayaks or fishing during the weekend without knowing about the discharge or its potential impact, Woods said. She noted the harbormaster and shellfish warden were out patrolling, but an announcement and postings would have reached a wider audience.

“This is the public’s waterway and they have a right to know,” Woods said. “Whether there’s a public health impact or no public health impact, they should be notified either way. They have a right to know, and immediately.”

Cafferty said there’s a protocol when an issue arises and the town followed it. That included notifying the Division of Environmental Protection, the Environmental Protection Agency, and the Division of Marine Fisheries as soon as the issue was discovered, and waited for their response before spreading the word. Town officials also notified Scituate’s board of health, shellfish warden, harbormaster and selectmen.

“The town remained in contact with each agency during the response,” he said.

He added, however, that the town's response would have been altered as needed, such as if this involved raw sewage or happened July 4 weekend.

This plant discharge only caused the shellfish bed closure, and didn’t enforce swimming or fishing restrictions, Cafferty added.

The shellfish beds will be closed for at least seven days and that closure could continue for up to 21 days, Cafferty said. The Division of Marine Fisheries will sample the water next week to determine when they can be reopened, Katie Gronendyke, state spokeswoman, said.

Plant staff already samples the plant’s discharge every day to comply with permits and will follow any necessary protocols from the Division of Marine Fisheries, Cafferty said.

Eventually, the discharged effluent will wash out to the ocean.

“It takes several tidal cycles for it to be removed,” Woods said.

Follow editor Kristi Funderburk on Twitter @kfunder