Monday, February 20, 2017

WSSC Break Spills Millions of Gallons of Sewage

On February 9th 2017 a 20-inch pressurized sewer main at the at the Piscataway Wastewater Treatment Plant on Farmington Road in Accokeek ruptured; releasing millions of gallons of sewage into Piscataway Creek. The Piscataway Plant treats about 24 million gallons of wastewater per day. For about 10 hours almost half of all sewage reaching the plant was flowing to the creek as raw sewage until Washington Suburban Sanitary Commission (WSSC) workers were able to divert the flow into retention basins at the plant. Drinking water supplies were not impacted. 

Over the February 10th weekend, WSSC crews and contractors installed temporary pumps and bypass piping at the Piscataway Wastewater Treatment Plant. The bypass diverted the majority of the wastewater flow directly into the plant for treatment. The remainder of the flow was being pumped into retention basins on plant grounds will be treated at a later date.
from WSSC

WSSC crews continued their around-the-clock repairs. By the middle of last week the WSSC crews were able to reach an important milestone in the containment and repair process -they finished installing a second set of temporary pumps and bypass pipes, allowing all wastewater to bypass the break and be safely pumped into the plant for treatment. This means that wastewater is no longer being pumped into the on-site retention basins.

WSSC now has two sets of temporary pipes, each 2,000 feet in length, moving wastewater around the broken sewer main to the plant. A third set of temporary bypass pipes and pumps will be constructed and, if needed, put into service. It took several days to excavate the broken pipe for examination because it was located under a concrete-encased structure that contained approximately 120-feet of high-voltage lines. The electric lines were de-energized and the concrete encasement broken apart.

The 20-inch sewer main pipe is made of cast iron and is 52-years old. Experts analyzed the pipe late last week and determined that at least 60-feet of the 88 foot pipe needs to be replaced. A decision will be made on the remaining 28-feet of pipe after it is inspected. Given the costs in terms of environmental damage, and emergency response should push WSSC to replace the entire span of the pipe rather than see if they can get a few more years of service out of the 28 feet.
from WSSC

The replacement pipe was expected to be onsite this weekend. It will take at least a week to install all sections of the new pipe. WSSC has more than 5,500 miles of sewer mains throughout its service area. This pipe break last week and the growing number of drinking water and sewage breaks in the past couple of years serves to highlight the issue of aging infrastructure in the WSSC’s system and America. WSSC is in the middle of capital projects to replace 2,000 miles each of sewer and water mains.

Ideally, pipe replacement occurs at the end of a pipe’s “useful life”; that is, the point in time when replacement or rehabilitation becomes less expensive in going forward than the costs of numerous unscheduled breaks and associated emergency repairs; rather than waiting for a pipe to fail. Age alone, however, cannot always be used as an indicator of failure, but it is a good predictor in warm weather breaks.

In cold weather more pipes fail. There is a relationship between water temperature and pipe breaks. A sudden temperature drop provides a kind of shock to the pipes especially when the pipes are older. The recent warm weather punctuated by cold snaps may have contributed to the break happening now. Water temperature below 40 degrees Fahrenheit can also cause pipes to become more brittle, and break. That leads to increased pipe breaks in the winter, and why water utilities typically report their February number of breaks- when most breaks take place. For the last decade WSSC pipe replacement program has had more unscheduled emergency repairs in winter.

Remember WSSC’s water and wastewater systems are separate. This overflow did NOT affect WSSC’s drinking water.

No comments:

Post a Comment