Black Lagoon: Strain on damaged dam drained

BULLWORK OF DEMOCRACY EXCLUSIVE COVERAGE: The Black Lagoon is a contaminated man-made pond near the corner of Maple and Walker streets in Marlborough, Mass. For more than a century, petroleum-product spills have plagued properties on a mile-long stretch of Maple Street. Toxins from those spills now rest uneasily in The Black Lagoon, mingled in massive silt deposits that pose a threat to the nearby Sudbury Reservoir.

RELIEVING PRESSURE: The water level at The Black Lagoon has lowered at least a foot since state workers removed the floodgate from the putrid pond's damaged dam on Feb. 19. /Christopher Cheney photo

In a move apparently prompted by the dilapidated condition of The Black Lagoon's concrete-and earthen dam, state workers removed the floodgate from the damaged structure on Friday.

On Thursday, Bullwork of Democracy reported that an architect and an engineer believe natural forces and years of neglect have structurally compromised the dam. Also on Thursday, Bullwork Editor Christopher Cheney called the Office of Dam Safety at the Department of Conservation and Recreation, the state agency responsible for maintaining the dam and surrounding property. A voice mail message, which raised concern about the condition of the dam and requested comment, was left at the safety office. The message was not returned, and DCR officials have not responded to several other requests for comment.

On Friday, two DCR trucks with at least five workers were at The Black Lagoon for about 30 minutes, a neighboring property owner said. The workers spent most of their time at the dam but also walked along the pond's shoreline, the homeowner said.

LET LOOSE: Water gushes over The Black Lagoon's floodgate on Feb. 20. /Christopher Cheney photo

The concrete portion of the dam shows several signs of wear and tear, including a destroyed wooden-plank gate in the floodgate's spillway as well as cracking and chipping of the main spillway dam, which is the largest concrete element of the structure. The structural integrity of the earthen portion of the dam is clearly in doubt.

In addition to heavy tree growth in the packed-earth portion of The Black Lagoon's dam, there is a washout at least four-feet-wide on the back side of the dam. The washout, which has exposed the top of the earthen dam's steel pilings, extends at least eight feet down the side of the dam's western stone-and-mortar abutment.

PHOTO GALLERY: Dam observations on Feb. 20 include washout on the earthen portion of the structure and oil slick in main spillway

EROSIVE FORCE: Water has evidently washed over the earthen portion of The Black Lagoon's dam in the past, eroding a gash in the back of the structure along the western abutment of the main spillway. Steel pilings at the center of the earthen dam's crown appear to have held off a more serious washout. "It could be catastrophic. It certainly needs to be addressed as soon as possible," says a longtime Connecticut highway engineer who reviewed these images. /Christopher Cheney photos and bullworkofdemocracy illustration

CONTAMINATION: With The Black Lagoon's floodgate removed, the main spillway is dry, with the exception of an oily ooze leaking from the floodgate spillway. /Christopher Cheney photos and bullworkofdemocracy illustration

PETROLEUM-BASED: In photo below, a six-foot-long slick of oily ooze flows down the middle of the main spillway at The Black Lagoon's dam.

INFILTRATED: The earthen portion of The Black Lagoon's dam is overrun with trees and brush on both sides of the structure. /Christopher Cheney photo