The Connecticut Water Company’s (CWC) Mackenzie Water Treatment Plant (WTP) provides drinking water to the towns of Clinton, Guilford, Madison, Old Saybrook, and Westbrook in Connecticut. Raw water manganese (Mn) concentrations typically peak during mid-summer (exceeding 2.0 mg/l) when the dissolved oxygen levels create anoxic conditions, resulting in over-bottom manganese concentrations which negatively impact water treatment.


The GZA team was retained to engineer a retrofit of the intake structure, which draws water from the shallow Kelseytown Reservoir via a single near-bottom intake where summer manganese concentrations are particularly problematic. The measured source water supply reservoir experienced manganese levels as high as 4.5 mg/l in the water column during summer anoxic conditions in the bottom waters.


Partnered with Dr. Robert Kortmann of Ecosystem Consulting Services (ECS), the GZA/ECS team designed and installed a baffle to fully enclose the intake pipes on all four sides with an open top to draw water from the surface layers rather than from the mid-depth or over-bottom waters.  The GZA/ECS team also ensured all regulatory permitting was submitted and approved for the project.


After installation of the baffle, the Mackenzie WTP raw water intake experienced dramatically lower manganese concentrations – below 0.5 mg/l – during the entire summer. These concentrations are significantly lower than what was measured in the reservoir and what was historically measured in the raw water intake. As a result of better raw water quality coming into the treatment plant, water treatment costs and operations were significantly improved.