Stormwater Rule ResearchStormwater Rule Research

Healing Our WatersHealing Our WatersOctober 13, 2011October 13, 2011

Natural Resources Defense Council

• National non-profit membership group; 1.3 M members & online activists

• Founded in 1970• Mission: “to safeguard the Earth: its people,

its plants and animals, and the natural systems on which all life depends” and “to restore the integrity of the elements that sustain life – air, land, and water – and to defend endangered natural places”

Natural Resources Defense Council

• Staff of more than 400 lawyers, scientists, and technical experts

• 7 offices: New York; Washington, DC; Chicago; Montana San Francisco; Santa Monica; and Beijing

• MW Office (Chicago): opened in January 2007 to intensify NRDC’s advocacy efforts on water and energy policy in the Midwest (including Great Lakes issues and climate change)

NRDC: Rooftops to Rivers

Aurora, Illinois:•Saw Report approach to GI as a way to organize disparate planning documents•Brought in NRDC to identify potential projects and partners

Syracuse, New York:•Amended Consent Judgment for CSOs applied strictly grey infrastructure approaches•Community opposition to use of treatment plants pushes County to look for alternatives•NRDC report cited as convincing County GI could be a viable solution

NRDC: Rooftops to Rivers

What’s Next:•Updated report released later this fall•Updates on 9 cities profiled in 2006 + 5 new cities•Composite studies•Expanded economics and finance sections•New metric: how are cities doing?

Retention Standards

• Most effective standard to retain urban runoff & meet regulatory requirements?

• Retention: prevent conversion of precipitation to runoff discharging from a development site on the surface, from where it can enter a receiving water.

• Assessed 5 urban land use types (3 Res; 1 Retail Commercial; 1 Infill Redevelopment); each in a climate region on 2 soil types

Study Design

• 1st step: apply infiltrating bioretention (= no underdrain)

Study Design

• 2nd step: when the initial strategy could not fully retain post-development runoff, additional methods were applied, involving roof runoff harvesting & roof water dispersion.

• Assessed: reduction of average surface runoff volume, maintenance of pre-development groundwater recharge & water quality improvement

Results

• For the more highly impervious commercial retail and redevelopment cases, bioretention would retain about 45 percent of runoff & pollutants generated & save about 40 % of the pre-development recharge.

• Adding roof runoff management measures approximately doubled retention and pollutant reduction.

• Downside: little groundwater recharge

Results

• Retaining 90 percent of the average annual post-development runoff volume: most environmentally protective standard.

• Mtg this standard prevented 66-90 % runoff -- pollutant loading was also reduced for each soil type.

Results

• Retaining runoff produced by the 95th percentile, 24-hour precipitation event would yield equivalent protection on most soils.

• Also more consistent region to region than 85th percentile standard.

GI Works, is Good Policy, and is Enforceable

Results

• Standard 4: Diff betw post- & pre-development avg annual runoff volumes

• Standard 5: Diff betw post- & pre-develop runoff volumes for all events up to & incl 85th percentile, 24-hour precipitation event.

• Standards 4 and 5, inconsistent in retaining runoff and reducing pollutants; Standard 5 especially weak when pre and post development volumes converge.