On Thursday, July 18, a large amount of water was released from the I-93 construction project. It flowed through a cross pipe under I-93, and then followed a stream channel down hill to a culvert under South Shore Road, adjacent to #46 South Shore Road. When it emerged from that culvert, it went straight into Canobie Lake. Eyewitnesses reported that the water was dirty and very smelly - it smelled like sewage. The flow was so great that the culvert couldn't handle it. The water rose behind the culvert, and flowed over the top of South Shore Road. Dave Blake, one of our CLPA directors, observed the incident and recorded videos. The incident occurred about noon. It was not raining at the time. The high flow condition continued for twenty or thirty minutes.
According to DOT officials the discharge was an accident. The input to the cross pipe had been deliberately plugged by the construction contractor, and water was building up in a wetland on the West side of I-93 for weeks. It was decided by DOT, DES and the contractor that the water was "natural", not affected by construction activity, and should be released in a slow, controlled flow. While a worker was attempting to do that, the pneumatic plug abruptly "let go" and blew through the pipe. The result was a fast, uncontrolled flow limited only by the capacity of the 24" diameter cross pipe.
The DES site monitor said the discharged water was dark from tannins and natural organic matter, and very smelly. But it was not contaminated with septic or sewage.
We believe this accidental discharge was a probable violation of water quality standards. No water samples were taken where the flow went into the lake. Therefore there are no numbers to document what the discharge may have been. But the high volume of water must have stirred up sediment all along its path, and delivered it to Canobie Lake. Sediment which would not have been transported under natural flow conditions was stirred up and delivered to the lake.