The Great Pond Water Treatment Plant was originally constructed in 1935 and supplies approximately 90% of Weymouth’s water demand. While the existing facilities at the Great Pond WTP had undergone several upgrades and improvements over many years, and had an increased hydraulic capacity of about 8.0 MGD, concerns existed about the overall reliability of the facility to efficiently and consistently produce high quality drinking water.
Due to episodes of unacceptable water quality at the existing facility and observations made by WTP staff indicating a degradation of filter performance and efficiency for several filters, The City of Weymouth retained the services of Environmental Partners in 2004. EP was selected to perform a treatment pilot study for the review of alternative treatment technologies and provide the eventual design and construction of a new Water Treatment Facility, to ensure that water met or exceeded existing and anticipated future drinking water standards and regulations.
EP provided piloting, conceptual planning, and final design of a new state-of-the-art 8.0 MGD surface water treatment plant. To best meet the City’s needs, EP completed two separate pilot studies, each running for two seasons of testing in both cold water and warm water conditions. The first task of the pilot study was to set objectives to meet existing and future drinking water regulations and standards. After an assessment of the quality of the Great Pond water supply, it was determined that new facilities must have the capability of meeting certain requirements for both cold water and warm water conditions. These requirements included the removal of source iron and manganese, to levels below Secondary Standards; removal of low-density particulates, to reach compliance with the Enhanced Surface Water Treatment Rule (ESWTR); removal of organic matter to decrease production of distribution system disinfection by-products, to meet the Stage II Disinfection/Disinfection By-Product Rule requirements; elimination of objectionable tastes and odors; disinfection compliant with CT requirements of the ESWTR; and corrosion control for compliance with the Lead and Copper Rule.
To meet these objectives, EP developed a scope of work to evaluate alternative high rate solids separation processes, and water quality goals were established to compare and evaluate the performance of the pilot treatment systems. EP monitored the performance of the pilot system daily, including collection of water samples. Evaluation of the results of this pilot study indicated that a combination of pre-oxidation with potassium permanganate, coagulation/flocculation, dissolved air floatation (DAF), intermediate ozonation, deep-bed biologically activated GAC filtration, and chlorine for secondary disinfection offered the highest operational flexibility, reliability, water quality, and the lowest projected costs for the new WTP. It was determined that the project would consist of construction of the new Water Treatment Facility, after which the existing facility could be demolished, and the site restored.
Immediately upon recognizing the need for a new plant, Environmental Partners worked with City officials on an extensive site analysis and selection process, resulting in the location of the new facility adjacent to the existing Great Pond WTP. EP also assisted the City in successfully applying for and securing a commitment for a $35,000,000 low interest State Revolving Fund loan. EP managed the loan and completed design level services, including architecture, water processing and engineering, geotechnical and civil site analysis, and structural and MEP services.
Site work and construction began in late 2008, and was completed in September 2010. The new treatment process, based on preliminary investigations conducted during pilot testing activities, included connection to an existing upgraded raw water intake; conventional dissolved air floatation followed by ozone disinfection; accommodation of either granular activated carbon filtration or powdered activated, carbon/membrane filtration; and gaseous chlorine secondary disinfection. Upon completion of construction and commissioning of the new facility, demolition of the existing plant commenced. The work consisted of demolition of the main building of the existing facility and associated structures which included a Trac-Vac building, sodium bicarbonate silo, underground CT tank for contact water, below ground reinforced concrete sedimentation basins, and cutting and capping of existing utilities below normal grade. Demolition began in May 2011, and was completed in September 2011. Cost estimating, budgeting, and cost control were critical elements for the project’s success, ultimately leaving the City with leftover funds when the project was finished. In addition, superior cost control measures and construction oversight resulted in project change orders less than 1% (0.9% change orders).
Environmental Partners coordinated the site preparation, facility construction, lagoon decommissioning contractors, and the demolition of the existing facility including final site restoration and landscaping which was completed in May 2012. Selective demolition items took place in the existing 30-foot deep raw water pump station at the pond shore, immediately adjacent to the old intake structure, which had to remain in full operation throughout this project.
Throughout the duration of this complex project, Environmental Partners was able to present the City with original solutions that overcame specific challenges and exceeded expectations. At the time of completion, the New Great Pond WTP was only the second of its kind in MA to use the combination of DSF, intermediate ozonation, and biologically activated carbon filters for the production of drinking water. Despite the novelty of this technology, disinfection by-products had been reduced by 35% within the first few months of operation, compared to the previous facility. EP was also able to reduce schedule and cost for the City by dividing the project into five separate contracts, which allowed the City to hire specialized Contractors for distinct phases of the project. While this strategy enhanced both project quality and cost competitiveness, it also added complexity to construction when EP successfully coordinated multiple independent contractors while maintaining ongoing production of drinking water for the City.
In 2011, EP was awarded an ACEC/MA Engineering Excellence Silver Awards in recognition of the work completed.