MWRA State of Boston Harbor report

MODEL PREDICTIONS OF EFFLUENT DILUTION
COMPARED TO MONITORING RESULTS

Model predictions of effluent dilution at Bay outfall

A: AVERAGED COMPUTER MODEL PREDICTIONS OF EFFLUENT DILUTION. These maps, generated by USGS before the outfall was built, show dilution contours from the harbor and bay outfall locations. The harbor model shows a large area of highly concentrated effluent centered in the harbor but spreading east and south, into Massachusetts Bay and south of Boston. In comparison, the bay outfall has a small patch of effluent centered around the diffuser, with dilution rapidly increasing away from the outfall.

B: AMMONIUM CONCENTRATIONS, A GOOD TRACER OF EFFLUENT, WERE MEASURED WHILE THE OUTFALL WAS AT DEER ISLAND, AND AFTER THE BAY OUTFALL WENT ON-LINE. The pattern of ammonium concentration agrees well with the model, giving scientists and engineers confidence that we understand how the outfall is functioning. A lesser area is affected, and ammonium levels in the harbor have decreased dramatically.