The New Stormwater Rule

EPA’s long-anticipated stormwater rule is close to being released. At StormCon 2011 in Anaheim, CA, in late August, Jeremy Bauer, an environmental scientist with EPA’s Office of Wastewater Management, gave a presentation outlining the rule. At the time of the conference, the rule was undergoing agency review and was expected to be released to Congress in September, but that deadline has reportedly been extended to December 2. Once the proposed rule is published, there will be a public comment period–typically 60 days. The final rule is scheduled to be issued on November 19, 2012.

Key elements of the rule’s approach include integrating green infrastructure into project design, viewing stormwater as a resource, and generally slowing the flow of runoff to allow more infiltration, which will not only reduce the volume of runoff but also the amount of pollutants reaching receiving waters. The rule will emphasize “cost-effective, flexible, and demonstrated” solutions and will build on innovation, Bauer said, which means that it won’t disrupt existing successful programs, but instead will try to bring others up to their level of performance.

The rule quantifies performance standards for new development and redevelopment sites based on a specific storm (the 95th percentile storm, for example). These standards will apply to residential, commercial, institutional, and industrial sites and to roads, but not to federal properties, which are already required, under Section 438 of the 2007 Energy Independence and Security Act, to retain runoff from the 95th percentile storm.

Bauer emphasized that the rule will recognize equivalent state programs already in place. It also allows variations based on site-specific analyses; for example, if soil and climate conditions in a particular area generally result in only 70% of runoff being retained on a predevelopment site, the rule won’t automatically require developed sites to retain a greater percentage. However, in such cases treatment of the additional runoff may be required. In response to a question from the audience about calculating the amount of runoff retained, Bauer said that EPA is assuming designing for a “dry antecedent”–that is, a single storm, rather than conditions in which ponds are partially full or soils partially saturated from a previous storm.

Recognizing that there may be space and other constraints on redevelopment sites, and also that redevelopment has environmental benefits compared to developing greenfield sites, the rule holds redevelopment sites to a lesser standard.

The rule also requires MS4s to develop plans to address discharge from existing sites through retrofits. This portion of the rule applies to municipal, not private, property, and there will be some flexibility. This portion won’t apply to CSO (combined sewer overflow) communities that are already required to reduce runoff volume, but the agency hopes others can draw on the research and experience from those communities.

No specific techniques are mandated by the rule, although some now-standard practices–reducing impervious cover, harvesting rainwater for onsite use, promoting infiltration through rain gardens, swales, and other means, and using green cover to increase evapotranspiration, infiltration, and interception–are encouraged.

Finally, the rule will extend the protection of the MS4 program. The US currently has about 6,700 municipal separate storm sewer systems (MS4s), Bauer noted, and these cover about 2% of the country’s land area. Although that area contains a large portion of the population, considerable development falls outside it, such as new development on the margins of MS4s and the thoroughfares connecting them, and some of these areas will be considered for coverage.

During his StormCon presentation, Bauer emphasized that the final 2012 rule must be a natural outgrowth of comments received, and he noted that EPA is required by law to read and respond to all comments, saying “You can have a real impact on the final rule.” Some of the components–the emphasis on green infrastructure, for example–seem to align with recommendations by various groups such as American Rivers (a summary of that group’s work on the stormwater rule is available on its website), but other aspects may not go as far as some had hoped: Retrofit requirements won’t apply to private property, for instance, and the rule as it’s being proposed does not include a requirement for monitoring water quality, although Bauer acknowledged that changes will be considered depending on the comments EPA receives.