What the New Stormwater Rule Means for Erosion Control

EPA’s new stormwater rule is scheduled to be released late this year; it’s an update to the national stormwater regulations now in place. If you’re not working directly for a municipal stormwater program, what will the changes mean for you?

At the StormCon conference in Anaheim, CA, in August, Jeremy Bauer, an environmental scientist with EPA, gave us an overview of the rule’s highlights. Although the rule will have little direct effect on construction-site erosion and sediment control practices-its primary focus is on post-construction runoff-it will have far-reaching effects on water-quality practices and possibly on the locations where much of our work is performed. For anyone working in the construction arena, the provisions of the new rule will likely mean that we’ll see more green infrastructure measures incorporated from the start of a project, and we may also see more redevelopment work and retrofitting of existing sites rather than development of new sites.

Green Infrastructure
EPA has been moving for a few years toward adopting green infrastructure practices-also called low-impact development or LID practices-and many cities and counties have followed suit. Green infrastructure aims to retain stormwater onsite, mainly through infiltration (via bioswales, rain gardens, pervious pavement), detention, rainwater harvesting, and vegetation to encourage evapotranspiration. The new stormwater rule encourages integrating green infrastructure into project design.

The rule will quantify performance standards for new development and redeveloped sites, requiring them to detain a certain amount of runoff. New developments on federal property are already required, under Section 438 of the 2007 Energy Independence and Security Act, to retain runoff from the 95th percentile storm; the rule will apply similar standards to residential, commercial, institutional, and industrial sites.

Bauer noted that the rule allows site-specific variations. For example, if soil and climate conditions in a particular area generally result in only 80% of runoff being retained on an undeveloped 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. 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.

A Break for Redevelopment
An important element of the new rule-lacking from many previous stormwater regulations-is the distinction between new development and redevelopment. Many developers find it easier to meet stormwater requirements-particularly those involving green infrastructure, which usually requires some open space-on greenfield sites. It is usually less expensive to build on an empty lot than to work within the constraints-space, underground utilities, existing impervious cover, and so on-of an already-developed neighborhood. However, to encourage redevelopment, which has many environmental benefits over building on pristine land farther from an urban center, the new rule will in some cases hold redevelopment sites to a lower retention standard.

Retrofitting
The rule also requires municipal stormwater programs 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; -municipalities can define milestones, which will be evaluated periodically.

Extending the Program
The rule will extend the coverage of the national stormwater 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.

After the proposed rule is released, EPA will accept and respond to public comments, and the final rule will be issued in November 2012.