Water Treatment Process

The Tewksbury Water Treatment Plant is an independent water treatment and distribution system. It can combine with the Lowell and Andover water distribution systems as alternatives. The treatment plant capacity is 7 million gallons per day.

Water Source: The Merrimack River is a class ‘B’ river which makes it suitable for recreational uses and drinking water supplies. The Tewksbury Water Treatment Plant is located at the northeast corner of Town of Tewksbury between the Merrimack River and River Road and uses the Merrimack River as its water source.

Treatment: A pump station is used to lift river water up to the main facility. The river intakes are installed approximately 14 feet under the water surface and are equipped with 1/8” (3mm) screens to prevent debris from entering the treatment system. The Tewksbury Water Treatment Plant uses a multiple barrier approach to treating the raw water before it becomes potable drinking water. In case of a failure of one or more treatment barriers, the water is still potable and the public is protected.

Initial-treatment: Chlorine Dioxide is added at the pumping station to disinfect the water and oxidize organic material, which may cause color, taste, and odor. Chlorine Dioxide is also capable of oxidizing iron and manganese to insoluble forms for easy removal.

  1. Coagulation: Alum is introduced into the partially treated water to precipitate and adsorb the suspended particles and the colloidal materials to form ‘flocs particles’. High speed mixers provide agitation to ensure uniform distribution of raw water and chemicals used for coagulation.
  2. Flocculation: Low speed mixers provide the gentle agitation to allow suspended particles and colloidal material to attracted to generate larger floc particles.
  3. Sedimentation: The Sedimentation Basins allow the large, heavy floc particles to settle to the bottom of the basin. Clarified water rises to the top and is sent to the filter through underground pipes.
  4. Sludge: Sludge is drawn out from the sedimentation basins through sludge collection hoppers. The sludge is then discharged to the sludge storage tanks. Sludge pumps lift the sludge to a vacuum filter de-watering system. This system greatly reduces the volume of sludge and dries it to about 30% solids. The sludge cake is then collected in a 30 yard dumpster which is then trucked to an out of state triple-lined landfill.
  5. Filtration: Pretreated clarified water from the sedimentation basins is carried into four Automatic Backwash Filters (ABF) that contain 36” of granular activated carbon (GAC) on top of 12” of sand.  After passing through the filter media, the filtered water then flows to the Contact Chamber

Finished Water: Four chemicals are added into the filtered water for final treatment: Sodium Hypochlorite (bleach) for disinfecting the water, Potassium Hydroxide for adjusting the water pH, Hydrofluorosilicic acid which supplies fluoride for consumers’ dental protection, and Zinc Orthophosphate to prevent leaching of lead and copper from consumers household piping.

Distribution: The treatment plant has four finished water pumps totaling 600 electric horsepower. These pumps are used to move the now potable drinking water into the distribution system. In the distribution system, there are two 1-million-gallon drinking water storage tanks, which are used to store and to distribute the finished water to individual households and businesses.

Certified Laboratory: The Tewksbury Water Treatment Analytical Laboratory is certified by the State of Massachusetts to perform a variety of drinking water quality analyses such as Total Coliform, Fecal Coliform, and E. coli. Laboratory analyses will control the treatment of water and ensure the quality water discharged to our consumers.

Drinking Water Quality Control: Samples from the finished water are monitored every four hours for pH, turbidity, chlorine residual, and fluoride, tested weekly for bacteria, quarterly for Trihalomethanes (THM’s), Haloacetic Acids (HAA5) and Volatile Organic Compounds (VOCs), and annually for Inorganic’s, Nitrate, Nitrite, Radionuclides, Secondary Contaminant’s and Synthetic Organic Compounds (SOC).  All the monitoring processes are used to ensure the highest drinking water quality to your tap.