A sophisticated $57 million water treatment plant under construction in northeastern Rhode Island will help clean up the Blackstone River, long considered one of the most polluted rivers in the U.S.

The City of Woonsocket is building the new facility, the largest public works project in its history, in compliance with an agreement with the State’s Department of Environmental Management (RIDEM) to end outfall discharges of the plant’s filter backwash water directly into the river. 
    
In complying with the agreement, the City chose to build a new water treatment plant that eliminates the need for a surface water discharge. The City of Woonsocket explained to RIDEM that upgrading or replacing the existing water treatment plant was also required as a result of the aging infrastructure present at the facility in addition to anticipated changes to the drinking water quality criteria.
    
Under a design, build and operate (DBO) contract with the City of Woonsocket, C.H. Nickerson & Company is constructing the plant, with AECOM Technical Services as the design engineer responsible for overall planning and guidance, while SUEZ will work with both firms for startup and operations. CDM Smith is the City’s consultant.
    
SUEZ will also operate the new water treatment plant and a raw water pump station under a 20-year, $44 million agreement with the City. In addition, the company is running the old plant until the new one is ready for operations.  

Problematic Outfalls
    
The 58-year-old existing facility, named the Charles G. Hammann Memorial Water Treatment Plant, uses flocculation, clarification, filtration, and disinfection to treat an average daily flow of 3.5 million gallons of raw water. Located at 1500 Manville Road, the plant operates three above ground sedimentation/filtration units, and two above ground 500,000 gallon clearwells.  An above ground backwash water tank is located across Manville Road, which supplies water to wash the three filters. And therein lies the problem. 
    
Filter backwash is discharged by three outfalls into the Blackstone River – under a permit from the state, of course, but there’s a deadline for this tied to the startup of the new plant.
    
RIDEM is concerned about those outfall discharges because the filter backwash water is subject to flow limits and water quality effluent limits that protect Water Quality standards. The discharges exit the plant through the outfalls, designated as 001A, 002A, and 003A, and enter the Blackstone River in a segment of the 48-mile river known technically as Water Body ID No. RI0001003R -01A. 
    
While the headwaters of the Blacktone River are in Worcester, Massachusetts, this particular segment of the river begins at the Massachusetts/Rhode Island boundary, runs through Woonsocket, North Smithfield, Cumberland, Lincoln, and ends in Central Falls where the Blackstone River reaches sea level and the Seekonk River begins. This location is the northernmost point of Narragansett Bay tidewater.

Health Concerns
    
Since the segment is classified as Class B1 according to Rhode Island Water Quality Regulations, its water is designated for primary and secondary contact recreational activities and fish and wildlife habitat. According to the EPA’s Water Quality Standards Handbook, primary contact classification protects people from illness due to activities involving the potential for ingestion of, or immersion in, water. Primary contact recreation usually includes swimming, water-skiing, skin-diving, surfing, and other activities likely to result in immersion. 
    
Secondary contact recreation classification is protective when immersion is unlikely. Examples are boating, wading, and rowing.
    
The attainment of the Federal and State Clean Water Act goals is measured by determining how well waters support their designated uses, and the Blackstone River has missed the mark for many years.
    
According to RIDEM’s List of Impaired Waters this segment of the Blackstone River does not support fish and wildlife habitat due to the presence of Cadmium, Eurasian Water Milfoil, Myriophyflum Spicatum, Lead, Non-Native Aquatic Plants, Dissolved Oxygen, and Total Phosphorus.
    
In addition, this waterbody segment is not supporting fish consumption since analyses of fish tissue show the presence of mercury and PCBs. Furthermore, this waterbody segment is not supporting primary and secondary contact recreational uses due to impairments associated with Enterococcus and Fecal Coliform. 

A River Most Polluted
    
The main causes of pollution lie with the river’s long history of industrial pollution which began in 1793 at Slater Mill in Pawtucket, Rhode Island, the site of the first textile mill.  This was followed by a long line of mills that took advantage of the water power and essentially used the river as an open sewer. 
    
As recent as 1990 the EPA called the Blackstone, "The most polluted river in the country with respect to toxic sediments."
    
RIDEM has taken firm steps over the past few decades to abate the pollution. As part of this, the department has sponsored comprehensive studies of the entire Blackstone River watershed including the 48-mile river and its Massachusetts and Rhode Island tributaries. 
    
Among their findings: 
•    Resuspension and movement of contaminated sediments, 
•    Headwaters defined by drainage from Worcester – the second largest city in New England – and its wastewater treatment facility, 
•    Multiple other wastewater treatment facility discharges, 
•    Storm water contributions from combined sewer outfalls, facilities and urban centers, 
•    And fluctuations in water levels due to hydropower operations – all create problems for this river system. 

Helping the Cleanup
    
The construction of the new Woonsocket treatment plant together with the elimination of the outfalls are a major step forward in helping to clean up the Blackstone River. The new treatment facility, designed for the Maximum Day flowrate of 7.0 mgd (million gallons per day), is located in south-central Woonsocket on a 20-acre site off Jillson Avenue. As part of the city-owned water system, the plant is operated by the Water Division under the Department of Public Works (DPW), headed by Steven D’Agostino. The Water Division’s service area includes the City of Woonsocket, and sections of North Smithfield and Cumberland, Rhode Island. It also serves customers in Blackstone and Bellingham, Massachusetts.

Construction Begins
    
According to John Finnegan, P.E., AECOM Project Manager, work crews broke ground at the new facility in late May 2018, with Steve Emmendorfer and John Mack serving as Nickerson’s Project Manager and Project Superintendent, respectively. Since the plant is situated on top of a hill comprised mainly of rock, drilling and blasting dominated early construction activity.
    
“The plant site is in a congested area with residences and an elementary school nearby,” said Andy Dufore, Division Manager for subcontractor Maine Drilling & Blasting. “Our blaster, Hoit Swaby, used Epiroc T-30s for drilling the rock, which was a very hard granite. He blasted about 27,000 cubic yards of rock during eight weeks of summer school vacation.”
    
Nickerson self-performed much of the earthmoving, but subcontracted J.R. Vinegro Corp. for crushing blasted rock to be used on site for building and road base construction.
    
The new two-story treatment plant and one-story administration area are housed in a single building with a total footprint of roughly 21,000 square feet. Insulated precast concrete panels with varying architectural finish supplied by Coreslab serve as both wall structure and cladding for most of the building exterior. The process function area takes up approximately 60 percent of the footprint and has a substantial reinforced concrete structural composition to withstand the pressure of deep massive concrete basins filled with moving water and chemicals. 

Advanced Design
    
As noted in the plant’s basis of design report, the treatment processes involve preoxidation, rapid mix coagulation, flocculation, dissolved air flotation (DAF), granular media filtration, and primary disinfection.
     
Raw water is first injected with chlorine dioxide and other chemicals and allowed sufficient contact time. Flow continues through two parallel concrete preoxidation basins, each 30 feet wide by 24 feet long, with a depth of 14 feet.  Two submersible mixers with a variable speed drives provide 15.5 minutes per train at maximum day flow. 
    
The water continues through a rapid mix basin with two stages each approximately 5 feet by 5 feet by 8 feet deep, where a coagulation chemical is added and mixed by vertical shaft mixers, with about 30 seconds of detention time provided. The coagulation process causes suspended particles to stick together and form larger particles. Water then enters three baffle- walled flocculator basins each measuring 18.5 feet by 14 feet by 14 feet deep, each equipped with four mixers. Flocculation is gentle stirring or agitation to encourage the particles previously formed by coagulation to agglomerate into larger masses called floc.
    
The treatment’s core process comes next, as water enters a train of three dissolved air flotation (DAF) basins measuring 17 feet by 18.5 feet by 14 feet deep. Two of these are online, while the third is a standby. This is where the floc formed previously is removed. In the DAF process, air diffusers on the tank bottom create fine bubbles that attach to floc resulting in a floating mass of concentrated floc. The floating floc blanket is skimmed from the surface and clarified water is withdrawn from the bottom of the DAF tank.
    
The final step in the treatment is the filtration process. The clarified water enters the granular activated carbon (GAC) filters that provide final polishing of the DAF clarified water to meet the state’s turbidity standards.  Four filters are provided, three for online work and one standby. Each of the reinforced concrete filters are approximately 25.5 feet long by 14 feet wide, and operate by gravity. Primary disinfection takes place before finished water is pumped to the city’s distribution system.
    
Construction of the massive treatment process components required more than 5000 cubic yards of concrete. Ready-mixed concrete was supplied by Cullion Concrete Company. Most of the concrete was pumped to the forming crews by Independent Concrete Pumping. In some instances in which a relatively small amount of ready mix was needed, a crane and concrete bucket were employed to place the material. Other major subcontractors and suppliers are listed in the accompanying sidebar.    
    
This project also involves major improvements to the piping at the City’s existing raw water blending chamber, a new raw water pumping station, finished water storage tanks, a new residuals management system, and interconnecting pipelines.
    
The entire project is on schedule to meet the December 2020 completion date.