Philadelphia Stormwater Management Criteria: What Are the Neighbors Doing? - A Peer City Comparison

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1 Philadelphia Stormwater Management Criteria: What Are the Neighbors Doing? - A Peer City Comparison S. Randall, C. Marjoram & M.J. Vanaskie Pennsylvania Stormwater Management Symposium, Villanova University October 13, 2005

2 Why is Philadelphia changing their Stormwater requirements? Act 167 Planning Process NPDES Permits TMDLs Quality of Life Water quality CSO Reduction Reduce Flooding River City Initiative

3 Broader Stormwater Program Objectives Maintain Groundwater Recharge Maintain W-Q Prevent Channel Erosion Manage Overbank Flooding Manage Extreme Events Infiltrate 1.0 inch Remaining Volume from 1 1 Total from IMP Area 1-yr, 24hr Detained, released 24hrs Release Rates 2,5,10 yr events Release Rates 25, 50, 100 yr events New requirements Existing Ordinance Objectives

4 Program Provides Additional Benefits Streamlines development process for developers and the City Encourages tree credits and city greening Captures and treats over 75% of all stormwater as opposed to first flush. Protects drinking water supply. Protects investment in stream restoration. Assists us in complying with State and Federal regulations.

5 Who are the Neighbors and What do we ask them? Selecting Cities: Peer attributes Inclusion in Building Industry Association of Philadelphia Report (October( October 2004) Comparing Criteria: Earth disturbance thresholds New versus redevelopment Sizing Criteria: Flood Control, Channel Protection, Water Quality Collecting Data: Web city searches (Manuals, Regulations, and Ordinances) Follow-up telephone interviews with city and county staff members

6 Peer Cities Atlanta, Atlanta, GA Baltimore City, MD Baltimore County, MD Boston, Boston, MA Chicago, Chicago, IL Cincinnati, OH Detroit, Detroit, MI Milwaukee, WI Minneapolis, MN New New Jersey (State) New New York City, NY Portland, OR Prince Prince Georges County, MD Seattle, Seattle, WA Washington DC Wayne Wayne County, MI

7 Earth Disturbance threshold 5,000 sq ft threshold: Atlanta, GA (5,000 sq ft of impervious area for single residences only) Baltimore City, MD SE PA/ Philadelphia (Darby-Cobbs Watershed) Seattle, WA (5,000 sq ft OR 2,000 sq ft impervious) Washington, DC More Restrictive (< 5,000 sq. ft): Atlanta, GA (All hotspots and development not for single family residence) Portland, OR (all mechanized earth disturbance) Seattle, WA (2,000 sq ft impervious)

8 Earth Disturbance threshold (Cont d) Less restrictive (>5,000 sq ft): Chicago, IL (15,000 sq ft) Cincinnati, OH (6,000 sq ft) SE PA / Philadelphia Detroit, MI (1 acre)** New Jersey (1 acre)** New York City / State (1 acre) Milwaukee, WI (increase impervious by 0.5 acres or 1+ acre site) Minneapolis, MN (1acre) ** State requirements

9 New vs.. Redevelopment Atlanta, GA Baltimore City, MD Baltimore County, MD Chicago, IL New Jersey (State) New York City / State Prince Georges County, MD SE PA / Philadelphia

10 Sizing Criteria: Channel Protection Volume Slowing the flow to prevent: Scour and erosion Overbank flow Channel destabilization Different volumes and rates: Site specific 1-year / 24-hour 2-year / 24-hour Specified rate (i.e cfs/acre)

11 Channel Protection Volume Site specific or no minimum Washington DC Cincinnati, OH Minneapolis, MN Detroit, MI Chicago (15% targeted reduction)

12 Channel Protection Volume Design Storm Atlanta Prince Georges County, MD Baltimore City, MD Baltimore County, MD New York State SE PA / Philadelphia Wayne County, MI Boston New Jersey* Portland, OR 1-year design storm detained for 24-hours 1.5-year design storm released over 40-hour 2-year storm detained for 24-hours 2-year peak proposed = 50% of existing peak * State guidelines communities may not be less stringent.

13 Channel Protection Volume Specified release rate Milwaukee, WI 2-year pre = post (0.15 cfs/acre) Seattle, WA (0.2 cfs/ac under 25-year / 24-hour design OR 0.15 cfs/ac under 2-year 2 / 24-hour design

14 Sizing Criteria: Water Quality Volumes City Less More Washington, DC Detroit, MI Portland, OR in. 0.5 in in. Baltimore, City; Baltimore County, & Prince Georges County, MD Boston, MA* Minneapolis, MN SE PA/Philadelphia Seattle, WA Atlanta, GA 0.5 in. OR in. 1.0 in. 1.0 in. 1.0 in in. 1.2 in. New Jersey State NY City / State Milwaukee, Chicago, Detroit, & Cincinnati 1.25 in in. No minimum requirement

15 So What are Philadelphia s s Stormwater Requirements? Earth Disturbance threshold: 5,000 sq ft Darby-Cobbs Watershed 15,000 sq ft New vs. Redevelopment: Redevelopment with criteria exemptions Sizing Criteria: Water Quality Volume: 1 1 of rainfall over DCIA within limits of earth disturbance Channel Protection Volume: Control and release 1-1 year 24-hour storm (~ 2.7 inches) from DCIA within limits of earth disturbance Flood Control and Management Districts

16 Summary We are within the range of volume and peak requirements compared to peer cities. Our stormwater objectives are well within national, regional and local expectations for stormwater management requirements.

17 For more information on stormwater management in Philadelphia visit:

18 Thank You Questions? Christine Marjoram Philadelphia Water Department 1101 Market Street 4th Floor Philadelphia, PA