Winchester, MA Water Treatment Facility



Background

The Town of Winchester obtains its drinking water from two separate sources, from the town's reservoirs located within the Metropolitan District Commission (MDC) Fells Reservation off of South Border Road and from the Massachusetts Water Resources Authority (MWRA) through connections on Ridge and Forest Streets.

In 1992, the federal Safe Drinking Water Act (SDWA) mandated that drinking water from surface supplies, such as Winchester's, be treated and filtered before distribution to customers. To bring the town's water into compliance with federal and state drinking water standards, it was voted at the 1993 Winchester Town Meeting to authorize funds for the design and construction of a water treatment plant and other water system improvements.

In October 1993, the town retained the services of Camp Dresser & McKee Inc. to design and provide engineering services during construction of the water treatment plant and associated water system improvements. Designs were completed and the project was advertised for construction bids in the summer of 1994.

Facility

The 2 million gallon per day (mgd; expandable to 3 mgd) water treatment plant is designed to meet increasingly stringent government standards. To ensure that these standards are met, the facility uses state-of-the-art water treatment processes. Raw water flows by gravity from the South Reservoir through the intake/screen structure where it is screened to remove larger, suspended material before flowing to the Raw Water Pump Station. The raw water is pumped via a 12-inch ductile iron transmission pipeline to the plant by one of two pump units and undergoes the following processes.

The Processes

At the plant, the raw water passes through a diffuser assembly and static mixer where chemicals may be added to assist in the treatment process. Alum and polymers may be added to aid in coagulation/flocculation; sodium hypochlorite may be added for disinfection, and sodium hydroxide may be added for pH control.

After chemical addition and mixing, the water flows up through adsorption clarifier units and then down through granular activated carbon/sand filters into the filtered water pump units. In the adsorption clarifier, the chemically treated water flows up through a coarse plastic media. The chemicals that have been added to the water surround the dirt particles and make them sticky, allowing adherence to the adsorption clarifier media. Flow passing the adsorption clarifier will contain some fine particles that are then removed by filtering

To guard against bacterial growth in the distribution system, sodium hypochlorite is added to the filtered water for primary disinfection. A small amount of fluoride is also added to prevent tooth decay. The filtered water is pumped to the one million gallon baffled prestressed concrete storage tank for release into the distribution system. Before release into the system, sodium hydroxide is added to the treated water to reduce corrosiveness.

After the adsorption clarifiers and filters have been in use for a number of hours, the media becomes clogged with chemically treated particles and must be cleaned by backwashing. The adsorption clarifier is scoured with air and water. The filters are washed with air and clean filtered water. The dirty water is collected and pumped to two alum residuals lagoons where the solids are allowed to settle out and surface water is decanted and recycled to the plant.

Fully Automated Plant

The plant is fully automated, allowing operation with minimal supervision and unattended operation during nights and weekends.

The water treatment plant has demonstrated the ability to provide superior water quality that will serve Winchester's needs for many years.

Construction

The Town of Winchester accepted bids for construction of the water treatment plant on September 8, 1994. On October 1 1, 1994 the town entered into an agreement with the lowest bidder, Methuen Construction Company, Inc. of Methuen, Massachusetts. The completed project cost of $6,442,000 included the construction of a raw water pumping station, a 2 million gallon per day (MGD) water treatment plant, a 1 million gallon (MG) clear water storage tank, two residuals lagoons, modifications to the Risley Road pumping station, improvements to the North Reservoir pumping station, transfer piping to allow the transfer of raw water to the South Reservoir, connections to the existing water distribution system, and all associated engineering and administrative costs.

The facility became operational in June 1996, on schedule