NEW CASTLE COUNTY STORMWATER NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM (NPDES) PROGRAM
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Duffield Associates was retained to perform the monitoring requirements of New Castle County and the Delaware Department of Transportation's National Pollution Elimination Discharge System (NPDES) Permit. This includes "dry weather" inventory and monitoring of more than 3,500 stormwater outfalls in New Castle County for potential illicit discharges and "wet weather" monitoring and sampling of five (5) selected outfalls for pollutant loading estimates.

For dry weather monitoring, Duffield Associates' monitoring teams quickly assessed illicit discharges in the field by visual scanning and tracking and by review and knowledge of "upstream" sources. They "field determined" if a detected dry weather flow was indeed an illicit discharge or if it was a groundwater infiltration, a piped section of a stream or drainage channel, or if it was a discharge caused by a point source, such as irrigation of private/commercial property or an individual washing a car, etc. They did this by non-intrusive visual review of storm sewer manholes, catch basins and valley gutters. If the source of the discharge was not readily apparent, it was noted and more intrusive/extensive measures were implemented. Additional evaluation could include utilizing television inspections, smoke testing, dye and tracer implementation, forensic chemistry, sonic leak detection, and system location. This work includes not only problem identification but also design of corrective action.

Wet weather monitoring is performed during storm events, day or night, to collect samples of stormwater runoff from different land use types. The samples are analyzed for specific parameters and the data is utilized for pollutant loading estimates. Evaluation of the pollutant loading data is performed to determine potential pollutant reduction measures to be implemented in the watersheds and best management practices.

As part of this project, Duffield Associates developed and implemented a GIS system for customized data storage and analysis. The efforts began with the field survey of the outfalls, collecting data for locating pollutant sources, and uploading the data into the GIS database. The project concluded with developing customized analysis tools in accordance with the client's needs and providing the client with the complete GIS system and supporting documentation.