Plant upgrade leads to sewer expansion project

Facing a state consent order to comply with the Clean Water Act (CWA), Scituate, Mass., recently completed extensive upgrades to its wastewater treatment plant. In addition to allowing the town to meet strict nitrogen discharge limits, the $14 million project opened the door for a much needed sewer expansion.

Settled on the south shore of Massachusetts, Scituate has 17,860 residents, most of whom have private septic systems. In 1995, the state revised its subsurface disposal regulations, and, as a result, many of the oldest septic systems were classified as posing a public health or environmental threat. Compounding the problem, the town’s wastewater treatment plant, built in the 1970s, discharged high levels of nitrogen and bacteria to receiving waters, which had resulted in a 1987 federal moratorium on new residential and commercial sewer connections.

The town already had begun planning a facility upgrade when it received the CWA consent order in 1996. It needed to expand plant capacity from 1 million gallons per day (mgd) to 1.6 mgd, and it needed to upgrade treatment processes to reduce biological oxygen demand, total suspended solids and nitrogen.

Working with Cambridge, Mass.-based CDM, the town finalized the project design in June 1997, and upgrades got under way in April 1998. The town implemented energy-efficient, fine-bubble aeration in two existing aeration basins. It also installed a third aeration basin, a new secondary clarifier (there now are three), and aerobic selectors at the front end of the aeration system to optimize settling and improve effluent quality.

The town modified existing treatment processes to include denitrification and ultraviolet disinfection, and it added a supervisory control and data acquisition system to automate operation. In addition to making those changes, it constructed facilities for effluent reaeration and emergency effluent storage; installed an intermediate pump station, new influent screens and pumps; and constructed a new administration area and laboratory.

Plant expansion was completed in 2000, while treatment upgrades and construction continued through March 2002. Project costs were covered, in part, by a state revolving fund grant.

Since the project’s completion, Scituate has embarked on a multi-phased effort to reduce groundwater and sump pump infiltration in the sewer system. As a result of that work and the plant upgrade, the federal government has partially lifted the sewer moratorium.

Today, the town is designing the first two phases of sewer expansion that ultimately will connect most of Scituate’s residences to the town’s sewer system. “Now that treatment modifications are completed, we can start solving the town’s problems,” says Town Administrator Richard Agnew.