The Connecticut Water Company’s (CWC) Mackenzie Water Treatment Plant (WTP) draws water from the Kelseytown/Killingworth Reservoir System.  Historically, the WTP has had difficulty with raw water manganese (Mn) peaks during summer months. Manganese is released from sediments as an anaerobic respiration byproduct when anoxic conditions occur over the water-sediment interface at depth.


The elevated summer manganese concentrations (>2.0 mg/l) have impacted raw water intake water quality and the water treatment process. The CWC sought to better understand contributing factors.


Partnered with Dr. Robert Kortmann of Ecosystem Consulting Services (ECS), the GZA/ECS team designed and conducted a focused manganese monitoring program to identify contributing factors of manganese formation in the raw water sources and to complete predictive modeling of concentrations based on the identified factors. The GZA/ECS team monitored the reservoir system from early summer through early fall. In addition to the field sampling program, five miniDOT dataloggers were deployed in the reservoir to measure several parameters at a higher frequency. Results were reported weekly to the CWC in spreadsheet and trend indicating format to provide feedback and opportunities for adjustments in the water treatment process during the monitoring time period.


The analysis of the data collected from the monitoring program revealed several parameter relationships that were instructive in helping the water company identify sources of manganese in the reservoir system, enhance their treatment process, and focus their future monitoring of raw water sources.  Especially evident were the changes in manganese concentrations in the Kelseytown Reservoir due to daily temperature fluctuations and anoxic conditions in the reservoir’s mid-depth .