I don't know about standard procedures, but based on experience, I'd suggest something like the following:
- delineate and characterize catchment
- isolate like areas (partially separated, converted combined, separated, possibly in some cases by land use)
- identify and isolate areas with potentially large sources of extraneous flows (e.g. flat roof connections)
- monitor flows at d/s end of isolated area from early spring (just before snow melt, if applicable) for a period of 3 to 6 months
- analyze data to characterize extraneous flows for different types of events (likely will see highest flows for low intensity, long duration/moderate to high volume events) and different types of inputs (foundation drains, direct inflows, infiltrations) through hydrograph separation
- compare results against typical parameters for various types of catchments in your region
- review CCTV tapes, and use monitoring data to determine where more inspection is required
- identify priorities for flow removal, system rehabilitation and more detailed investigations based on monitoring and inspection results (you may want to consider modelling techniques to better understand processes and performance under critical conditions, and to better define priorities)
