SWMM Groundwater Infiltration Modeling for Hartford, Connecticut

The Metropolitan District’s collection system experiences occasional sanitary sewer overflows (SSO) in sewers serving the communities of Newington, West Hartford, Windsor, and Rocky Hill, Connecticut. In August 2006, a Consent Decree was issued to the District by the United States Environmental Protection Agency in conjunction with the State of Connecticut to address these SSOs. CDM developed and calibrated models for the Newington, West Hartford and Windsor systems based on meter data collected in spring 2005. The models were used to complete capacity assessments of the systems and develop facilities plans to address capacity issues. Preliminary capacity analysis was completed in early 2008. Results computed by the models, especially for large storm events, did not always match the expected system response based on the District’s understanding of their system. To confirm the models were developed appropriately and to identify possible model enhancements, an independent review was conducted in May 2008. Completing reliable long-term simulations to establish return periods and size SSO mitigation facilities appropriately was a primary recommendation. Most improvements to the model validation completed to-date have focused on tuning groundwater parameters to enable reliable long-term simulations. PCSWMM.NET’s Sensitivity-based Radio Tuning Calibration tool was used to calibrate groundwater parameters to achieve reasonable goodness of fit with long-term groundwater levels at a nearby USGS well. The 2005 calibration data were supplemented with fall 2008 flow metering.