This layer indicates which areas contribute sanitary and storm water flow to a CSO overflow point. Areas are broken down by NPDES Outfall Number. The data source is DWW.cso_basin_plgn_pv. The layer continues to be updated as new information about the CSO system becomes available and as modifications to the system are completed. The boundaries in this layer were created and updated for purposes of developing a hydrologic and hydraulic computer model. The model was used to estimate CSO control volumes and develop CSO control alternatives. Estimation of control volume and alternative analysis did not require a parcel level of detail, so it is expected that the boundary is not always correct at the parcel level. In addition, the CSO basin boundary shapefile reflects both the sewer basin AND the drainage basin tributary to the overflow point, and these two basins do not always line up cleanly. This layer reflects the best compromise between the two boundaries.Updates as needed.