Traces of coronavirus in Mass. wastewater tick down for one region, up in another

The MWRA's Deer Island Sewage Treatment Plant is seen from Spectacle Island in Boston Harbor.Lane Turner/Globe Staff

The amount of coronavirus found in wastewater at the Massachusetts Water Resources Authority’s Deer Island treatment plant ticked downward for the northern section of the MWRA system, which includes Boston, but were slightly higher for the southern section, new data show.

The latest tests, which were conducted up until Monday, come after levels last week reached their highest recorded since the pandemic began.

The seven-day average of virus detections appears to have begun leveling off for both sections.

Similar to other metrics in Massachusetts, the wastewater tests show a peak in the spring, with the virus levels appearing to dip and flatten off over the summer, and an acceleration that appears to have begun in October.

The pilot program looks for SARS-CoV-2 RNA copies per milliliter of wastewater. Officials are hoping the tests can serve as an early warning system for virus surges.

The data come as Massachusetts began a statewide rollback of its reopening plan on Sunday, and after officials in Boston, Brockton, Lynn, Newton, and Somerville announced Monday they were reverting to more restrictive phases of the state’s reopening plan amid rising coronavirus cases in the state.

The latest wastewater figures from the Mass. Water Resources Authority.MWRA (Custom credit)