Due to continuing property development in the area much of the Pennichuck Brook Watershed has transformed from wooded areas and farmland into residential and commercial districts with a large amount of impervious area. The result has been increased runoff and pollutant loadings to the chain pond water supply system operated by Pennichuck Water Works. The new EPA Storm Water Management Model (SWMM) Version 5.0.006a was used to assess the condition of this watershed. Utilizing the aquifer sub-model the SWMM model was calibrated to the Pennichuck Brook Watershed. Due to the large volume of precipitation percolating into the ground, the aquifer component was necessary to determine groundwater flow to surface waters. Stream gaging stations were set up and streamflows were measured to develop stage discharge curves for each of the nine gaging stations throughout the watershed. Water level data loggers were installed at these sites where stream levels were recorded from September 29, 2005 through May 4, 2006. These levels were converted into continuous streamflow records that were subsequently used in model calibration and validation procedures. Problems encountered in this project included heterogeneities in the aquifers and heterogeneities in the precipitation neither of which were modeled due to lack of sufficient data. Additionally, there were several gaps in the streamflow records as a result of wildlife interference and datalogger batteries failing. The calibrated SWMM model provides a reasonably accurate model for predicting runoff and streamflow in this watershed. The coefficients of determination

were 0.50 and 0.86 for the model calibration and validation, respectively. On average the model predicted lower streamflow rates and volumes than were observed in the field most likely due to inter-watershed groundwater flow.