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Expect Changes to Municipal Storm Water Systems

Expect Changes to Municipal Storm Water Systems. Harry Campbell, P.E. DWQ March 22, 2012. SW Causes Known Impacts to WQ. Urban stormwater identified as source of impairment (2004 WQ Report) SW Pollutants Sediments, nutrients, metals, temperature, trash, bacteria

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Expect Changes to Municipal Storm Water Systems

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  1. Expect Changes to Municipal Storm Water Systems Harry Campbell, P.E. DWQ March 22, 2012

  2. SW Causes Known Impacts to WQ Urban stormwater identified as source of impairment (2004 WQ Report) SW Pollutants Sediments, nutrients, metals, temperature, trash, bacteria Impacts beaches/swimming, fisheries, treatment of potable water SW Hydrologic Impacts Scour, flooding, reduced GW infiltration

  3. Pre/Post Development Hydrology 10% Surface Runoff 55% Surface Runoff 50% to Ground 15% to Ground

  4. SW a Growing Concern • ~800,000 acres being developed every year, growing to ~1.2 mil acres by 2040 • Impervious Surface from Development • Currently 100 mil acres; 25% is impervious • 16x more SW runoff Developed vs Undeveloped • Small increases of impervious can create large increases to watershed impacts

  5. MS4 Permit: Post Construction • 5th Min Control Measure (Long Term SW Management & Permanent SW Facilities) • Why New Rules? • Current approach unlikely to control SW’s contribution to waterbody impairment • Requirements leave a great deal of discretion to dischargers to ensure compliance 2009 NRC Report

  6. 2009 NRC Report: Urban SW Management in the U.S. • “A more straightforward way to regulate SW contributions to waterbody impairment would be to use flow or a surrogate, like impervious cover, as a measure of SW loading ….” • “Efforts to reduce SW flow will automatically achieve reductions in pollutant loading. Moreover, flow is itself responsible for additional erosion and sedimentation that adversely impacts surface water quality.”

  7. EPA to Promote/Require • Infiltration • Evapo-transpiration • Rainwater Harvesting Must Reduce Flow Volume

  8. EPA Proposed Permit Requirements • If disturbing 1 acre or more (& CPDS); must design, install, implement, and maintain SW control measures that infiltrate, evapo-transpirate, harvest SW. • Post-construction hydrology will not exceed pre-development hydrology in accordance with performance standards. **MS4 Permit Improvement Guide, by EPA**

  9. Is harvesting rainwater legal in Utah? • May 11, 2010 – SB 32 approved • You must register on DNR website • http://www.waterrights.utah.gov/wrinfo/faq.asp • Storage limited to 2 above ground 100 gal or 1 underground 2500 gal • Use limited to the same parcel of land owned or leased by rainwater collector.

  10. Current Volumetric Retention Standards • Montana (2009) – ½” • Wisconsin (2010) – achieve 60% to 90% of predevelopment volume based on impervious surface • West Virginia (2009) – 1”; no prior rain for 48 hours • Denver (2009) – (essentially) 1” • Anchorage (2009) – 0.52” no prior rain for 48 hours

  11. Description: Minimum SW to be retained Performance Standard: The site must be designed to prevent offsite discharge of the first 1” of rainfall from a 24-hour period preceded by 48 hours of no precipitation. Taken from West Virginia MS4 Permit SW STANDARDSEPA Proposed Example #1 Basis: Rainfall

  12. Description: Minimum storm size to be retained on site. Performance Standard: Design, construct, and maintain SW management practices so that rainfall events up to the 95th percentile do not discharge off the site. Employ SW management controls that effect infiltrate, evapo-transpire or harvest rainwater. The 95th percentile in SLC is 0.78” (SLC Airport, 1/1/80 to 1/1/10) Section 438, EISA Guidance www.epa.gov/owow/NPS/lid/section438/pdf/final sec438 eisa.pdf SW STANDARDSEPA Proposed Example #2 Basis: Rainfall

  13. 95th Percentile Calculation • 10 to 30 years of data (prefer 30) • 24 hour day (12 midnight to 12 midnight) • Delete all rainfall accumulations of 0.1” and less. • Perform 95th percentile function on Excel (or list accordingly from greatest to smallest – find 0.95 from bottom)

  14. 95th Percentile Atlanta, GA 1.8 Baltimore, MD 1.6 Boston, MA 1.5 Buffalo, NY 1.1 Burlington, VT 1.1 Charleston, WV 1.2 Coeur D’Alene, ID 0.7 Cincinnati, OH 1.5 Columbus, OH 1.3 Concord, NH 1.3 Denver, CO 1.1 Kansas City, MO 1.7 Knoxville, TN 1.5 Louisville, KY 1.5 Minneapolis, MN 1.4 New York, NY 1.7 Salt Lake City, UT 0.8 Phoenix, AZ 1.0 Portland, OR 1.0 Seattle, WA 1.6 Washington, DC 1.7

  15. Percentiles for SLC Airport 95th 0.78” 90th 0.59” 85th 0.49”

  16. Rainfall Frequency Spectrum for Minneapolis

  17. Description: Hydrologic Analysis Performance Standard: Design, const, and maintain SW management practices that preserve the pre-development runoff conditions following const. The post-const rate, volume, duration, and temp of discharges must not exceed the pre-development rates and the pre-development hydrograph for 1, 2, 10, 25, 50, and 100 yr storms must be replicated through site design and other approp practices. Defensible and consistent hydrological assessments and modeling methods must be used and documented. Section 438, EISA Guidance SW STANDARDSEPA Proposed Example #3 Basis: Recharge/Runoff

  18. Description: Ground water recharge requirement Performance Standard: Any major development project that disturbs (? acreage), must comply with 1 of the 2 following GW recharge requirements. Demonstrate w/ hydrologic and hydraulic analysis that the site maintains 100% of avg. annual pre-const GW recharge volume. that the increase of SW discharge volume from pre- to post-construction for the 2-yr storm is infiltrated SW STANDARDSEPA Proposed Example #4 Basis: Recharge

  19. Description: Limiting total impermeable surface or effective impermeable surface Performance Standard: Minimize total impervious cover resulting from new or redevelopment to <10% of disturbed land cover and/or limit total amount of effective impervious surface to no more than 5% of the landscape. SW STANDARDSEPA Proposed Example #5 Basis: Impervious Cover

  20. Incentives for New/Re Development EPA Proposed • The EPA has suggested incentives to development on: • Redevelopment sites • Brownfield redeveloped sites • High density (>7 units per acre) • Vertical Density, (floor/area ratio of 2 or >18 units/acr • Mixed use and transit oriented (w/in ½ mi of transit)

  21. Additional Requirements EPA Proposed • A site w/ reasonable potential for contamination of GW used for DW must provide treatment for associated pollutants. • Discharges to any surface or GW that is used for drinking water must comply w/ source protection. • Infiltration not allowed where soil contaminated • Projects that cannot meet pre-development hydrology may do off-site mitigation or payment in lieu

  22. Key Elements of the Proposed Rule • Establish performance standards for discharges from newly developed and redeveloped sites. • Require regulated MS4s to develop a program to address discharges from existing sites (retrofits). • Extend protection of MS4 Program.

  23. Current MS4 Program Applying the standard nationwide would create a level playing field for developers among municipalities and protect downstream communities from upstream development.

  24. EPA Rulemaking • Proposed Rules ??? • Final Rules Expected Nov. 2012

  25. Questions? Harry Campbell, P.E., CPESC 801-536-4391 hcampbell@utah.gov

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