ADDING SMALL-SCALE MICORWATERSHEDS TO YOUR STORMWATER IDDE TOOLKIT

Contaminated stormwater runoff and illicit connections are leading contributors to water quality problems in this nation's surface waters. Even though regulations have been in place for many years regarding the treatment and disposal of municipal and industrial waste streams, the majority of drainage systems flow untreated into the nation's surface waters. The NPDES Phase II program requires six minimum control measures (MCMs) for proper implementation of the program requirements. One of these MCMs, Illicit Discharge Detection and Elimination (IDDE), can be difficult to integrate into existing Municipal Separate Stormwater Systems (MS4s) without significant expenditures in both manpower and equipment.The Small Scale Microwatershed (SSMW) Method of watershed management applies GIS technologies to quickly identify, eliminate, and manage pollution within an MS4. The SSMW method began in the suburban community of Acton, MA based on a long term surface water sampling program. Rooted in GIS capabilities, the SSMW method starts with the surface water sampling locations, which overlay a parcel base map, and then adds other layers, including topography, surface water features, wetland features, and the digitized map of the MS4. Once the final map is produced, the Small Scale Microwatersheds (SSMWs) can be defined by the parcels that directly impact each sampling point.The SSMWs are not cumulative and are viewed as individual units within the overall watershed or sub-watershed. The sampling points provide baseline data and a jumping off point for IDDE programs. Simply, the SSMW can be defined as the drainage area impacting a particular sampling point.Although the initial program is based on surface water sampling locations because of a previous program designed to track septic system problems, the sampling points could also be drainage outfalls or other drainage structures. The actual sampling point depends on the main pathway for storm water (drains or streams), the topographic and land use features of the SSMWs, as well as access and other pragmatic concerns.