nonpoint source pollution · morgantown, wv npdes monongahela river. 3/29/2019 3 ... csos and high...
TRANSCRIPT
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National Pollutant Discharge Elimination System (NPDES)
• Part of the Clean Water Act of 1972, the NPDES permit program controls water pollution by regulating point sources that discharge pollutants into waters of the USA
• Point sources are discrete conveyances such as pipes or man‐made ditches
• Individual homes that are connected to a municipal system, use a septic system, or do not have a surface discharge do not need an NPDES permit
• Industrial, municipal, and other facilities must obtain permits if their discharges go directly to surface waters
• In most cases, the NPDES permit program is administered by authorized states
http://cfpub.epa.gov/npdes/
Nonpoint Source Pollution
• Remember…?
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Point Source Pollution
Ohio river
Acid water from an abandoned underground mine is being discharged from this point
source into a major stream
(photo: Jeff Skousen)
Morgantown, WV NPDES
Monongahela River
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Morgantown, WV NPDES
Deckers Creek
Combined Sewer Overflow
• Systems designed to collect rainwater runoff, domestic sewage, and industrial wastewater all in the same pipe
• Most of the time, combined sewer systems transport all of their wastewater to a sewage treatment plant
• During periods of heavy rainfall or melting snow, however, the volume of wastewater going into the pipes can exceed the capacity and excess wastewater empties directly into nearby streams, rivers, or other water bodies
• Typically found in older cities
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CSOs and high and low flow
Dry Weather Flow Wet Weather Flow
Spatial distribution of CSOs in the USA
EPA Region 3Mid‐Atlantic
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http://w
ww.efc.unc.edu/publications/pdfs/001_C_C
SO.pdf
CSOs in Appalachia
Stormwater Management Planning
‐ Runoff
‐ National Pollutant Discharge Elimination System (NPDES)
‐Municipal Separate Storm Sewer Systems (MS4s)
‐ Combined Sewer Overflow (CSOs)
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Stormwater
• Water that reaches the landscape as a result of precipitation
• Development activities can increase the amount and velocity of water reaching streams and rivers– This causes an increase in overland flow
– Resulting in greater magnitudes and peak flows on streams
• Impacts of increased overland flow can cause:– Flooding
– Accelerated stream channel erosion, including real property damage
– Reductions in water quality
– Degraded wildlife habitat
Stormwater
Most precipitation reaching the ground is disposed of in 1 of 4 ways:
– Interception• Storage of water above ground by vegetation and is returned to atmosphere by vaporization
– Infiltration• Precipitation absorbed directly by the soil
– Depression storage• Precipitation collected in small topographic depressions
– Overland flow• Precipitation that is not captured by the previous three, and runs off the surface
• This is stormwater
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Hydro Cycle
Interception
Distribution of Precipitation
E
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Components of Interception
= gross precipitation
= canopy interception
= throughfall
= stemflow
= litter interception
grossP
cI
tP
stP
lI
Interception: Storage of water above ground by vegetation and is returned to atmosphere by vaporization
Relative changes to overland flow with soil type and vegetation on sloping ground
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Forest removal and floodingIs there a direct relationship between timber harvesting and changes in
stream channel stability that can show empirically that forest removal increases flooding?
• One philosophy, removal of vegetation reduces interception & evapotranspiration, resulting in higher flows – Higher flows exert more energy on the stream channel system, which accelerates channel degradation– Models available that predict the % of a watershed that can be harvested without altering channel
stability
• A second philosophy suggests that accelerated channel degradation depends upon major wet‐mantle floods, which result from storms that occur after the soil mantle becomes saturated– Because soils are saturated regardless of the presence or absence of vegetation, these floods are
unaffected by timber removal– Channel systems have evolved to withstand normal fluctuations in energy levels– While timber removal may increase annual and seasonal flows, even increased flows during a
normal year are not sufficient to break down a channel's armor layer and initiate movement of the substrate
• Both philosophies have merit, but which is dominant depends upon a region's climate, soil type, and topography.
From, “Timber harvesting and flooding”, Scott Hess Journal of Soil and Water Conservation March 1984 vol. 39 no. 2 115‐117
Summary on Forestry and Flooding
• Current thinking on flood causes...– Clearcutting on small watersheds (low order)
– 1‐5 year return period storms
– Rain on snow on clearcuts, partial cuts
• Otherwise…– Forest cutting alone does not necessarily cause flooding
– Forest floor, soil disturbance
– Roads
– BMPs
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Overland Flow
• Overland flow usually:
– Increases with slope
– Decreases with soil organic content and particle size
– Increases with impervious ground cover
– Decreases with vegetative cover
• Coefficients of runoff are determined for particular surface materials, soils, and uses
Overland Runoff Transport
• Overland flow
– Sheet flow
– Rill flow
– Gullies
http://geography.sierra.cc.ca.us/booth/Physical/chp16_fluvial/fluvial1_overland.htm
http://www.duluthstreams.org/understanding/impact_impervious.html
These lead to erosion and then, sedimentation…
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Coefficient of runoff table example
http://proceedings.esri.com/library/userconf/proc95/to250/p2464.gif
Computing Runoff
• Rational Method – combines the following:
– the coefficient of runoff, with– the intensity of rainfall, and– the area of the watershed
Q = A • C • I• Where:– Q = discharge in cubic feet per second
– A = area of watershed in acres
– C = coefficient of runoff
– I = intensity of rainfall in inches per hour
Q is the peak streamflow
(discharge) for one rain
storm at the mouth of the watershed
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Design Storm
• When planning for stormwater, you must decide on a threshold amount of rainfall (in/hour) to represent “I” in the rational method equation
• This is the Design Storm (event)
• You must choose on local rainfall records for intensive storms of short duration which occur once, on average, of some T (time)
– Once every 10 years ~ the 10 yr. event
– Once every 25 years ~ the 25 year event
Design Storm
• Most adopted stormwater ordinances require post construction runoff from all developed sites not to exceed pre‐development for a design storm
• Design storms vary among ordinances, generally;– 100 year storm
• there is a 1 in 100 or 1% chance that a storm will reach this intensity in any given year
– 50 year storm
• there is a 1 in 50 or 2% chance of occurring in a year
• Software programs (sometimes simply spreadsheets) exist to perform these calculations– TR 55
– Mechlinberg
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Stormwater Regulation• A Municipal Separate Storm Sewer System (MS4) is a system that is
required of Urbanized Areas (UAs)
• An urbanized area is a land area comprising one or more places ‐‐central place(s) ‐‐ and the adjacent densely settled surrounding area ‐‐urban fringe ‐‐ that together have a residential population of at least 50,000 and an overall population density of at least 1,000 people per square mile.
• Urbanized Areas constitute the largest and most dense areas of settlement
• UA calculations delineate boundaries around these dense areas of settlement and, in doing so, identify the areas of concentrated development
Stormwater RegulationThe regulatory definition of an MS4 is:
a conveyance or system of conveyances (including roads with drainage
systems, municipal streets, catch basins, curbs, gutters, ditches, man‐made channels, or storm drains):
– (i) Owned or operated by a state, city, town, borough, county, parish, district, association, or other public body (created to or pursuant to state law) including special districts under state law such as a sewer district, flood control district or drainage district, or similar entity, or an Indian tribe or an authorized Indian tribal organization, or a designated and approved management agency under section 208 of the Clean Water Act that discharges into waters of the United States
– (ii) Designed or used for collecting or conveying stormwater
– (iii) Which is not a combined sewer; and
– (iv) Which is not part of a Publicly Owned Treatment Works (POTW) as defined at 40 CFR 122.2
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Green Infrastructure
• An approach to wet weather management that claims to be ‘cost‐effective, sustainable, and environmentally friendly’
• Green Infrastructure management approaches and technologies infiltrate, evapotranspire, capture and reuse stormwater to maintain or restore natural hydrologies
• “low‐impact design”
Urbanized Areas (UAs) and additional MS4 Communities
‐ Urbanized Areas (UA) ‐Municipalities meeting MS4 2004 ‐population criteria for Phase II
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Urbanized Areas (UAs) and additional MS4 Communities
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Providence, RI CSO mitigationNarragansett Bay Commission
Photo: Peter Goldberg, 2004
Providence, RI CSO mitigationNarragansett Bay Commission
Photo: Peter Goldberg, 2004
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Providence, RI CSO mitigationNarragansett Bay Commission
Photo: Peter Goldberg, 2004
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Stormwater Mitigation
“Urban Wet Weather” Discharge
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3 Rivers Wet Weather
• Ten Principles of Green Infrastructure
• Connectivity is the key.• Context Matters.• Green infrastructure should be grounded in sound science
and land‐use planning theory and practice• Green infrastructure can and should function as the
framework for conservation and development.• Green infrastructure should be planned and protective
before development. • Green infrastructure is a critical public investment that
should be funded up front.• Green infrastructure affords benefits to nature and people.• Green infrastructure respects the needs and desires of
landowners and other stakeholders.• Green infrastructure requires making connections to
activities within and beyond the community.• Green infrastructure requires long‐term commitment. • (from Benedict, M.A. and E.T. McMahon, 2006 Green
Infrastructure: Linking Landscapes and Communities. Island Press, Washington, D.C., pp37.)
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Types of activities that require Erosion and Sedimentation Plans (E & S)
• Earth disturbances greater than 5,000 square feet but less than acre must submit a written Erosion and Sediment Control Plan to the permitting authority– 5000 square feet is about 1/8 of an acre– PA Code § 102.4. Erosion and sediment control requirements
• Any disturbance associated with the use of Chapter 105 General Permit (GP) (stream crossing, wetland disturbance, pond dredging etc.), or one acre and greater disturbance must have an Erosion and Sediment Control Plan developed and then reviewed by permitting authority
PA Code § 102.4. E & S Control Plan components:
1. The existing topographic features of the project site and the immediate surrounding area
2. The types, depth, slope, locations and limitations of the soils
3. The characteristics of the earth disturbance activity, including the past, present and proposed land uses and the proposed alteration to the project site
4. The amount of runoff from the project area and its upstream watershed area
5. The location of waters of this Commonwealth which may receive runoff within or from the project site and their classification pursuant to Chapter 93
6. A written depiction of the location and type of perimeter and onsite BMPs used before, during and after the earth disturbance activity
7. A sequence of BMP installation and removal in relation to the scheduling of earth disturbance activities, prior to, during and after earth disturbance activities
8. Supporting calculations
9. Plan drawings
10. A maintenance program which provides for inspection of BMPs on a weekly basis and after each measurable rainfall event, including the repair of the BMPs to ensure effective and efficient operation
11. Procedures which ensure that the proper measures for the recycling or disposal of materials associated with or from the project site will be undertaken in accordance with this title
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Stormwater Management Techniques
• Silt Fence
• Detention Ponds
http://www.newgarden.org/stormwater.htm ‐ Landenberg, PA
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http://www.newgarden.org/stormwater.htm ‐ Landenberg, PA
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Stream Discharge