In this study, a PCSWMM model is established to mimic the existing conditions and retrofit scenarios of a pilot project “Green Streets” in Lakeview area, Mississauga, Ontario. The landuse within the catchment is a Medium Density Residential; detached and semi-detached, townhouse dwellings within a density range of 30-57 units per net residential hectare, the houses’ roofs are not connected to the drainage system. The streets are covered by asphalt pavement, interspersed with concrete sidewalks and driveways. The model is developed from the photogrammetric data and AutoCad maps representing the studied area with the use of a GIS tools. The entire area is divided into six subcatcments that range in size from 0.52 to 2.72 ha. Two monitoring stations are used to characterize individual rainfall during both storm and non-storm periods. Flow meters are installed into selected manholes measuring flow using continuous level loggers and v-notch weirs. Peak flows and total runoff volumes are set as the objective functions for water quantity. The calibration is done for five single storm events and verification for other four single storms. The calibration focused on estimating the parameters introduced in the developed model. To determine these parameters, an order of priority is established for finding a global optimal solution. The ``Green Streets`` retrofit project was highly successful in enhancing the infiltration, detention and evapotranspiration processes to reduce stormwater runoff volumes and peak flows.