The NRDC issued this past week a new report titled “How to: Stormwater Trading Credit Programs.” The report begins:
When rain runs off impervious surfaces such as sidewalks, streets, and roofs, it collects a wide range of toxic pollutants, which are then dumped, usually untreated, into local waterways. With older “combined” sewer systems, the problem is exacerbated because stormwater pipes join with wastewater pipes, sending the polluted runoff and wastewater from sinks and toilets into our waterways. Many cities are taking steps to reduce stormwater runoff through largescale “green infrastructure” (GI) solutions, compelled in part by the Clean Water Act and in part by a desire to make cities more resilient, livable, and equitable. GI includes street trees, rain gardens, vegetated swales, porous pavement, and green roofs. These practices keep polluted stormwater on or near the site where the rain falls—and out of waterways—until it can be treated, evaporate back to the atmosphere, be used onsite, or filter into the ground to benefit vegetation and replenish groundwater supplies.
Most cities’ GI plans include modifications to existing paved space on public properties and in the public right-of-way such as streets and sidewalks. Private property, however, is also a substantial contributor to stormwater runoff, and satisfying water quality requirements will often necessitate controlling pollution from public and private property. In addition, stormwater management opportunities can be less expensive on private land than on public land. The most common and straightforward way for cities to realize some of the GI potential of private land is by requiring on-site stormwater retention as a condition of construction permit approval for projects above a certain size. The concept of “stormwater credit trading” typically arises within this context. Credit trading programs enable property owners who are subject to an on-site retention requirement to meet a portion of their requirements by Page 2 How To: Stormwater Credit Trading Programs nrdc buying stormwater “credits” from other property owners rather than building all needed GI on their own property. Credit trading programs are becoming popular because they introduce flexibility into cities’ on-site retention rules and, if designed correctly, credit trading programs can create equal or better water quality outcomes than a simple on-site retention requirement. The remainder of this paper will lay out some of the potential opportunities and risks presented by such programs. Continue reading . . .