Visitors making their way along the Neponset Greenway this spring may have wondered why there is a new above-ground pipe running along the trail. It’s part of an ongoing project helmed by the Massachusetts Water Resources Authority (MWRA) to repair an aging sewer system in the neighborhood.

The sewage artery in question is MWRA’s Dorchester Interceptor Sewer, an approximately 6,500 foot-long brick structure built in 1895-1896. The Dorchester Interceptor conveys flows from MWRA’s Neponset Valley Sewer, as well as directly connected service areas in Boston and Milton, and discharges its flows to the Boston Water and Sewer Commission (BWSC) owned and operated “BWSC Dorchester Interceptor” that carries flows to MWRA’s Columbus Park Headworks.

Recent internal inspections have revealed many structural and non-structural deficiencies in the 120-year-old sewer, prompting a rehabilitation project.

Several segments of the MWRA Dorchester Interceptor, which runs parallel to the Neponset Trail and the high speed Mattapan Trolley line, had progressed from cracked to broken since previous inspections. In addition, numerous areas of heavy root intrusion and light to heavy water infiltration also exist.

Temporary “bypass piping” has been laid down along that route while construction crews work on the 19th-century era sewer system. The project, which began last October after the contract was awarded to engineering firm CDM Smith, is expected to last 18 months.