Last Thursday afternoon, a section of one of Westwood’s main sewer lines along Clapboardtree Street, just north of Washington Street, collapsed. The line carries sewage to the Mass Water Resources Authority trunk line.
The resulting blockage caused sewage to back up in the system and ultimately to overflow into nearby Purgatory Brook. The Westwood Department of Public Works (DPW) discovered the problem at about 3PM, and by midnight had set up a system of pumps to collect the sewage and pump it around the blockage and back into the sewer, ending the overflow to the Brook.
The DPW estimates that about 500,000 gallons of sewage discharged to the brook before the bypass was up and running. For a sense of scale, picture one (very unpleasant) Olympic-sized swimming pool. Obviously, a sewer discharge like this is never a good thing, particularly on a small stream like Purgatory Brook, which has a trout population. Thankfully, the Westwood DPW seems to have moved quickly to remedy the situation.
That said, this incident is another reminder of how infrastructure maintenance is critical to protecting the purity of our water. Unlike potholes and other more obvious problems that are visible and which generate resident complaints, sewer and drain infrastructure all across the watershed is all but invisible, making it much easier to overlook, especially when budgets are tight. That’s why it is so important to ensure that all of our DPWs have the resources they need to do their jobs properly. We understand that the Westwood DPW is now making plans to reinforce this section of sewer with a plastic liner, later this year.
On the positive side, if Westwood were going to have a sewer overflow, this was a good time to do it. Purgatory Brook is flowing vigorously right now, with rain runoff and cold snow melt. This should help flush contaminants out of the system relatively quickly and beyond the potential influence of riverside drinking water wells, downstream. As an added bonus, the cold should kill off most of the pathogens.
One of the biggest threats posed by such a spill is that the sewage could spur an explosion of bacterial decomposition and algae blooms, consuming all the available oxygen in the water and producing a fish kill. But again, the cold weather is on our side, suppressing both algae and decomposition, and because cold water naturally holds more oxygen in the first place. Had the spill occurred in the heat of summer, when stream flow is sluggish, the water hotter, dissolved oxygen levels much lower, and summer recreation happening, the consequences would have been significantly worse.
This also is an example of the kind of stream impact which is aggravated by the existence of so many small, old, dams (more than 117 in all) and poorly designed culverts around the watershed. The dams and culverts break-up stream habitats and prevent fish from being able to swim away to a safer area when something like this happens. Unnecessary dams also slow down water flow and decrease oxygen levels, thus further reducing the resilience of the entire ecosystem.