Low Impact Development and Stormwater Management in Pennsylvania Catherine Chomat, P.E. F. X. Browne, Inc Brian Oram, PG Wilkes University Dr. Robert Traver, P.E. Villanova University

Impacts of Stormwater Runoff on Aquatic Ecosystems

Impacts of Stormwater Runoff on Aquatic Systems Historical Perspective EPA 2000 Water Quality Report Water Quality-Ecosystem Impacts

Wastewater Treatment Since 1970… STP Construction$239 Billion STP Operations$234 Billion EPA Needs Survey $84 Billion Needed for new STPs for year 2008

Wastewater Treatment Populations Served by STPs million people million people From 1972 to 1988… 4000 new sewer systems 2000 new STPs

Wastewater Treatment 1988:Less than 1% of U.S. Population discharges untreated wastewater Meeting Effluent Criteria Industrial93% Municipal87%

Summary of Quality of Assessed Rivers, Lakes, and Estuaries

Leading Causes and Sources* of Impairment in Assessed Rivers, Lakes and Estuaries

Development Activities Site Clearing and Grading Tree Removal Loss of Natural Depressions (Storage) Loss of Topsoil/Humus Loss of Pervious Area/Percolation Increase in Impervious Area Increase in Runoff

Development Impacts on Water Quality 1. Watershed Hydrology 2. Stream Geometry 3. Degradation of Aquatic Ecosystems 4.Pollutant Export During Construction 5.Pollutant Export After Site Development

Impervious Cover as an Indicator of Stream Health (Schueler 1995) CharacteristicSensitiveDegradingNon-Supporting Percent Impervious Cover 0% to 10%11% to 25%26% to 100% Channel StabilityStableUnstableHighly Unstable Water QualityGood to ExcellentFair to GoodFair to Poor Stream BiodiversityGood to ExcellentFair to GoodPoor Pollutants of ConcernSediment and temperature only Also nutrients and metals Also bacteria

1. Watershed Hydrology 1. Reduced Infiltration 2.Increased Peak Discharges 2-5x Predevelopment 3.Increased Volume of Runoff Moderately Developed – 50% more runoff 4.Decreased Time of Concentration “Time Runoff Reaches Stream” as much as 50% lower 5.Increased Flooding Frequency & Severity Bankfull conditions: Natural…Once every 2 years Developed…3-4 times per year 6.Reduced Base Streamflow Due to Loss of Groundwater 7.Higher Runoff Velocity

Changes in Hydrology Due to Development

Hydrology Changes Due to Development

Parking Lot vs. Meadow ParameterParking LotMeadow Runoff Coefficient Time of Concentration (minutes) Peak Discharge (cfs) 2-Year Year Storm Runoff Volume (cu. ft.) 3, Runoff Velocity 2-Year Storm (fps) 8 1.8

COMPARISON OF RUNOFF VOLUME BETWEEN UNDEVELOPED AND DEVELOPED CONDITIONS STORM FREQUENCY (years) 24-HOUR RAINFALL (inches) ESTIMATED RUNOFF (inches) Undevel. Devel. RUNOFF AS PERCENT OF RAINFALL Undevel. Devel %21% %33% %46%

2. STREAM GEOMETRY 1.Channel Widening Developed Area Streams: 2 to 4 times original size Streambank Erosion Increased Pollutant Loads 2.Increase in Floodplain 3.Undercut Streambanks 4.Siltation of Stream Stream Bedload Substrate Changes (Biota Changes)

Physical Impacts of Impervious Cover

3.DEGRADATION OF AQUATIC ECOSYSTEMS 1.Cumulative Effects Scouring Sedimentation Velocity Streamflow Organic Matter - Biochemical Oxygen Demand Dissolved Oxygen Nutrients Toxics Chlorides

3.DEGRADATION OF AQUATIC ECOSYSTEMS 2.Temperature Increase in % Impervious  Increases Temp. Adverse Impact on -Algae -Macroinvertebrates -Fish

Temperature % Impervious Area

3.DEGRADATION OF AQUATIC ECOSYSTEMS 3.Fish and Macroinvertebrates – Decrease in …Diversity …Populations …Clean Water Species Increase in Pollution Tolerant Species

URBAN RUNOFF POLLUTANTS Sediments Nutrients Bacteria Organic Matter Hydrocarbons Metals Toxic Chemicals Chlorides 3. Degradation of Aquatic Ecosystems

SEDIMENTS Produced by:Construction Erosion Developed Area Erosion Washoff Streambank Erosion Problems:Turbidity Reduced Light Penetration Clogging of Gills/Filters (Fish & macroinvertebrates) Reduced Spawning Habitat Destruction Nutrients Metals Toxics Metals and Phosphorus Attach to Sediments

NUTRIENTS Nitrogen (TN, NH 3, NO 3, Organic-N) Phosphorus (TP, PO 4, SRP) Eutrophication of Lakes, Impoundments & Large Rivers PROBLEMS: Excessive Algae and Aquatic Weeds Dissolved Oxygen Depletion Taste & Odor Problems Fish Kills Loss of Recreation Toxins Increased Water Treatment Costs

Wet vs. Dry Weather

Stream Hydrograph Total Phosphorus Concentrations

Stream Hydrograph Total Suspended Solids Concentrations

BACTERIA Always Found in Urban Runoff Often Exceed Health Standards More Developed – More Bacteria Older Developed – More Bacteria Special Problem Areas: Combined Sewer Areas Sewer Overflow Areas

ORGANIC MATTER Biochemical Oxygen Demand (BOD) of Stormwater Runoff is High Causing: Decreased Dissolved Oxygen Stressed Aquatic Life Fish Kills Older, highly impervious areas – Highest BOD

Dissolved Oxygen in Stream 0.4 Inches of Rain

HYDROCARBONS Oil & Grease – Hydrocarbons Sources: Parking Lots Roads Gas Stations

METALS Toxic Affect on Aquatic Life Impact on Drinking Water Common Metals Lead Copper Zinc Caveats: 1. Only soluble form is toxic and available for biological uptake 2. Some are attached to sediment

TOXIC CHEMICALS NURP Studies: Scan of 120 Pollutants Small concentrations – no real problem Great Lakes – Contaminated Sediments Limited Data Base, Need More Data for Suburban, and Urban Ateas

CHLORIDES Snowmelt: 2,000-3,000 mg/L Chlorides  Soluble  Streams High Levels: Toxic to organisms

4. POLLUTANT EXPORT DURING CONSTRUCTION Soil Erosion Tons/Acre/Year – Uncontrolled 10 Times Agriculture and Developed Land

5. POLLUTANT EXPORT AFTER DEVELOPMENT A. Impervious Area Washoff Dryfall & Wetfall Up to 90% Washoff Constituents Sediments Metals Nutrients Sources Buildings, Roofs, Pipes Pet Droppings Vegetative Matter Litter Debris “THE LAND TAKES A SHOWER”

5. POLLUTANT EXPORT AFTER DEVELOPMENT B.Older Community – More Impervious Household Add-Ons C.Causes On-Site and Streambank Erosion

Unit Area Loads Total Phosphorus Load Use lb/ac/yr Forest0.1 – 0.35 Developed0.4 – 3.5 Commercial0.5 – 1.6 Agriculture0.36 – 1.52

Ultimate Concern Runoff Volume Velocity in Stream Streambank Erosion

Our Ultimate Goal