An article in the Summer 2011 issue of Runoff Rundown, which is published by the Center for Watershed Protection, proposes that “illicit” stormwater and wastewater discharges from local governments may be underreported and that identifying and correcting these discharges may be a more cost-effective method of reducing nitrogen and public health risks than more expensive bioretention retrofits.

Although the Center’s data is admittedly limited, what it shows is rather astonishing- based on Center case studies in the mid-Atlantic, illicit discharges can represent a significant portion of overall pollutant loads in urban watersheds, including loads from stormwater.  …

Because much of the storm sewer system is hidden underground, many of these discharges go undetected unless there is an obvious, major break in a pipe. In one Maryland County, for example, officials reported an unusually low number of illicit discharges along an approximately 10-mile long urban stream. However, by making some simple updates to the techniques of detecting illicit discharges, we found over 180 new outfalls that were never shown on the mapping (an average of one previously unidentified outfall per 300 feet).  …

 If these discharges are fixed, the County should be able to meet State bacterial standards for recreation at least during dry weather. We conservatively estimate that the flow from these outfalls also generates about 24 lbs of nitrogen and 0.8 lbs of phosphorus per day. On an annual basis, these loads are equivalent to the nitrogen in stormwater runoff from 560 acres of impervious cover, and the phosphorus generated by 140 acres of impervious cover.  At an estimated average cost of about $10,000 per repair, removing these discharges would cost the County $300,000.  By comparison, it would cost over $50 million to achieve the same nitrogen reductions and over $7 million to achieve the same phosphorus reductions using bioretention retrofits.  [Citations omitted]

The article argues for the use of updated detection methods and more rigorous field inspection to identify illicit discharges and suggests that local governments that fix illicit discharges should be given credit by the United States Protection Agency towards meeting their Chesapeake Bay Total Maximum Daily Load nutrient reduction goals.