Stormwater Quality Management

1
Stormwater Quality Management

• Road School 2005
• Purdue University
• West Lafayette, Indiana
• Speaker Ted Blahnik, P.E.

2
AGENDA

• Session I (90 minutes)
• Water Quality Volume
• Water Quality Peak Flow
• Water Quality Budget
• Break
• Session II (90 Minutes)
• Example Design

3
History of Stormwater Regulation

• 1972 Passage of the Clean Water Act
• 1990 EPA enacted Phase I of the NPDES stormwater
  regulations
• 1999 EPA enacted Phase II the NPDES stormwater
  regulations

4
Purpose of the Regulations

• Minimize extent and duration of disturbed soil
  exposure
• Protect off-site and downstream locations
• Decrease exit velocities
• Implement a thorough ongoing inspection,
  maintenance and follow-up program

5
New Stormwater Management Regulations

• 1 acre of disturbance activities requires Rule 5
  Permit (Acreage can vary under Rule 13 -MS4)
• Weekly erosion control inspection log
• Post construction best management practices for
  stormwater quality

6
Municipal Separate Storm Sewer Systems (MS4s)

• Urbanized areas with a populations lt100,000
• Every MS4 develops their own regulations
  according to the Phase II requirements

7
Rule 5 Permit

• For all areas outside of a MS4
• Required for any land disturbance 1 acre or
  greater
• Post construction BMPs required
• SWPPP are reviewed by the local IDNR and/or SWCD
• Permits are issued through IDEM

8
Post-Construction Pollutants

• Sediment
• Nutrients
• Bacteria
• Oil and Grease
• Road Salts
• Thermal Pollution
• Trash

9
What is a Stormwater BMP?

• According to EPA an urban stormwater BMP is a
  "technique, measure or structural control that is
  used for a given set of conditions to manage the
  quantity and improve the quality of storm water
  runoff in the most cost-effective manner."

10
Classification of BMPs

• Manufactured or Proprietary Technologies
• Hydrodynamic Separator Systems
• Filtration Systems
• Inline Filtration Systems
• Catch Basin Inserts - Long Term/Short Term
• Exterior Treatments
• Stormwater Underground Storage Tanks
• Sediment Containment Devices

• Natural BMPs
• Constructed Wetlands
• Bioretention Systems
• Swales
• Filter Strips
• Rain Gardens
• Green Roofs
• Designed Structures
• Porous Pavement
• Infiltration Basins/Trenches
• Detention Basins
• Retention Ponds (Wet Ponds)

11
Water Quality

• Management Requirements
• Check the ordinances
• Local or state may have prescriptive requirements
• IDEM and/or USACE prohibit untreated point
  discharges to waters of the state
• Water quality volume (WQv)
• standard benchmark for treatment volume

12
Water Quality

• Local and State Ordinances
• Rule 5
• Requires stormwater quality (generic)
• Rule 13
• Requires post construction stormwater BMPs
• Some counties / MS4s have regs
• IDNR publishing state regs soon

13
Water Quality

• USEPA stated goal 80 TSS removal
• TSS Used as a Surrogate for Other Pollutants
  Based on Pond and Wetland BMP Data
• Design Guidance Based on Research Conducted
  Primarily outside midwest
• Big green book (MWCOG, 1987)

14
Water Quality

• To calculate mass removal, we need
• Treatment Volume
• Influent Concentration
• Effluent Concentration

15
Water Quality Volume

• Water Quality Volume (WQv)
• Conceptually Captures Either
• first-flush of runoff (typically considered 1
  rain)
• 90 storm frequency

16
Water Quality Volume

• Water Quality Volume Method (MWCOG, Schueler,
  1987)
• WQv P x Rv x A
• 12
• WQv Water Quality Volume (ac-ft)
• P inches of rainfall
• A Area (acres)
• Rv volumetric runoff coefficient
• Rv 0.05 0.009 I
• I percent impervious cover

17
Water Quality Volume

• Estimating P
• Default values (Typically 1)
• Storm frequency analysis (Minton, 2002)
• Indianapolis 90 UTL 1.3 in
• Ft. Wayne 90 UTL 1.1 in

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Water Quality Volume

• Estimating I
• Default values (Ogden, 1990)
• Vegetated 1
• 0.5 residential units per acre 6
• 1.0 residential units per acre 12
• 2.0 residential units per acre 30
• Apartment complex 60
• Commercial 75
• Industrial 90
• Project specific takeoffs

19
Water Quality Volume

• Estimating Rv
• Controlling Urban Runoff A Practical Manual for
  Planning and Designing Urban BMPs
• Metropolitan Washington Council of Governments,
  1987
• Thomas Schueler, Author

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Water Quality Volume

• WQv P x Rv x A
• 12
• Rv Volumetric Runoff Coefficient
• Driscoll (1983) computed Rv from 50 sites across
  nation
• MWCOG omitted 7 due to small sample size, added
  4, and recomputed 1 to account for base flow
  interference
• 44 sites used in MWCOG NY 9, DC 8, CO 5, IL 5,
  WI 4, MA 4, MD 3, WA 2, NC 2, CA 1, NH 1

21
Water Quality Volume

• WQv P x Rv x A
• 12
• Rv Volumetric Runoff Coefficient
• Schueler transformed Median Rv for each site to
  Mean Rv using
• (Median Rv)SQRT(1 Cv2)
• Where Cv Coefficient of Variation
• No Cv or derivation of Rv presented for 8 sites,
  but mean Rv included in regression analysis
• Mean Rv for data point 20 (CO4, Asbury Site)
  miscalculated as 0.99 Corrected value 0.26

22
Water Quality Volume
23
Water Quality Volume
24
Water Quality Volume
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Water Quality Volume

• WQv P x Rv x A
• 12
• Rv Volumetric Runoff Coefficient
• Regression of 44 Rv values as presented
• Rv 0.049 0.0088 I (R2 0.71)
• Regression of 44 Rv values with CO4 corrected
• Rv 0.018 0.0092 I (R2 0.85)
• Regression of 36 Rv values similarly derived
• Rv -0.001 0.0095 I (R2 0.88)

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Water Quality Volume

• This manual was prepared with the goal of
  describing the state of the art in urban runoff
  control and focuses on the Washington D.C. area.
  As with any emerging field, significant gaps
  remain in our understanding, and more research
  and experience must be gathered.This manual is a
  first approach towards this goal, and it is hoped
  that the informatin it contains will be expanded
  and refined in the coming years. T. Schueler
  in Preface to 1987 MWCOG manual.

27
Water Quality Volume

• WQv assumes soil type, climate, topography, and
  vegetated cover have no influence on runoff
  volume
• In summary, this method yields
• Runoff from impervious areas 95 P
• Runoff from pervious areas 5 P
• The majority of this data was first published in
  1983, and most recently updated in 1987.

28
Water Quality Volume

• Over 116 sites are currently being studied in the
  USEPA stormwater database.
• Over 170 references published since 1987 are
  cited in Municipal Stormwater Management (Debo
  and Reese, 2002)

29
SHORT BREAK

• 10 MINUTES PLEASE

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Water Quality Loading

• Sediment
• Nutrients
• Bacteria
• Oil and Grease
• Road Salts
• Thermal Pollution
• Trash

31
Water Quality Loading

• TSS loads by Land Use (lb/ac/yr)
• Commercial 1000
• Parking 400
• HDR 420
• MDR 190
• LDR 10
• Freeway 880
• Industrial 860
• Park 3
• Construction 6000
• Source Horner, et al. Fundamentals on Urban
  Runoff Management, Terrene Institute and USEPA,
  1994

32
Water Quality Loading

• TSS Concentration Method (NURP Data)
• Median TSS 67 to 101 mg/L pending land use
• Total annual rainfall (Indiana) 36 inches
• 90 of storms are assumed at or below WQv
• Annual WQv per impervious acre
• (90 x 36 in) x 0.95 / 12 2.85 ac-ft per acre
• TSS load 532 to 802 lbs/ac (app. 4 to 7 cf per
  ac)
• BMP retention (assumed 80) 4 to 5 cf per yr
  per ac

33
Water Quality Loading

• TSS Concentration Method (USEPA data)
• 115 sites, 1536 events
• Mean TSS 272 mg/L
• Total annual rainfall (Indiana) 36 inches
• 90 of storms are assumed at or below WQv
• Annual WQv per impervious acre
• (90 x 36 in) x 0.95 / 12 2.85 ac-ft per acre
• TSS load 1944 lbs/ac (app. 16 cf per ac)
• BMP retention (assumed 80) 14 cf per yr per ac
• Source USEPA stormwater database, March 2003

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BREAK
35
BMP Design

• Its all about the WQv
• Youve got to account for it somewhere
• 3 available opportunities
• minimize impervious surface
• detain in collection areas
• Treat whats left (if any) in storage systems

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WQv Minimization

• Minimize impervious surface
• Vegetated or porous pavement islands in parking
  lots
• Gravel v. paved shoulder on roadways
• Reinforced turf or other porous pavement in very
  low traffic areas (emergency and maintenance
  access roads)
• Calculate as pervious surface in WQv

37
WQv Minimization

• Porous or Grass Pavers
• Not cheap (3 to 6 per square foot in large
  quantities)

38
WQv MinimizationPorous Pavement Strips

• Typical areas Road Shoulders, Sidewalks, and
  Parking Islands
• Assume as pervious surface in WQv calculations
• Photo Perkiomen Watershed Conservancy

39
WQv Collection Systems

• Minimize pipeflow
• Eliminate or reduce curbs
• Linear filter strips (overland flow) off parking
  and roadways
• Collect overland flow in swales
• Include detention in swales
• Keep swales well-drained with proper slope and/or
  underdrains
• Provide maintenance access for sediment and trash
  removal

40
WQv Collection Systems

• Interception and Infiltration Strips with
  Detention
• Gravel level spreader required for influent
• should abut adjoining impervious service or be
  placed at toe of influent slope
• 0 grade
• Recommended interim 6 high permeable gravel
  berms parallel to slope every 1 ft drop in grade

41
WQv Collection Systems

• Interception and Infiltration Strips with
  Detention
• 2 to 6 slope
• Design to drain within 24-hrs through underdrains
  or orifice control
• Check and maintain freeboard requirements for
  safety

42
WQv Collection Systems Interception and
Infiltration Strips with Detention
Parameter Impervious Surface Areas Impervious Surface Areas Impervious Surface Areas Impervious Surface Areas
Maximum inflow approach length (ft) 35 35 75 75
Filter strip slope (max 6) lt2 gt2 lt2 gt2
Filter strip minimum length (ft) 10 15 20 25
43
WQv Collection Systems Interception and
Infiltration Strips with Detention
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WQv Collection SystemsDetention Swales

• Elevated outlet
• Check freeboard requirements for allowable
  staging height
• Side slopes 31 or less steep, 61 preferred if
  planted with trees
• Minimum base width of 2 feet
• Channel slope 1 w/o underdrains
• Channel slope 0.3 w/ underdrains

45
WQv Collection SystemsDetention Swales

• Detention Swales
• Appropriate vegetation required for setting
• Salt tolerant at roadside
• Intermittently wet or submerged conditions to
  staging elevation
• Size low flow outlet control for lt 24-hr drain
  time
• Size high flow weir for staging above WQv to
  prevent backwater flooding
• May require maintenance points for sediment
  removal

46
WQv Collection SystemsDetention Swales
47
WQv Collection SystemsDetention Swales

• Recommended Vegetation
• No-mow turf (fescue hybrid) for traditional
  landscapes
• Native wet to dry mix for prairie or natural
  landscape
• Tree and shrub species should be tolerant of
  poorly drained soils, and may not be appropriate
  where vehicle safety is an issue
• All species should be salt tolerant if planted
  roadside

48
WQv Collection SystemsDetention Swales

• No-mow Turf

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WQv Collection SystemsDetention Swales

• Native Grasses
• Photo Little Blue Stem

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WQv Collection SystemsDetention Swales

• Wet and Mesic Trees
• Photo Hackberry

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WQv Collection SystemsDetention Swales

• Salt Tolerant Species
• Photo Fox Tail Barley

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WQv Collection SystemsDetention Swales

• Inlet Protection
• Rock
• Concrete
• Porous or turf pavers
• Outlet Control
• Pipe
• Weir
• Agri-drain structure
• Underdrains

53
WQv Storage Systems

• Minimize maintenance requirements
• Oversize basins to account for long-term sediment
  accumulation, with or without a forebay (75 of
  removed TSS can be expected to settle in primary
  basin)
• Negotiate removal of forebay or other
  pretreatment if primary sediment storage can be
  shown in primary BMP

54
WQv Storage Systems

• Minimize maintenance requirements
• Specify low maintenance vegetation native
  species or no-mow turf grass adapted to
  anticipated hydrologic conditions
• Calculate water budget to ensure permanent pools
  can be supported by watershed and/or groundwater
  recharge

55
WQv Storage SystemsForebays et al.

• Placed at end of collection systems containing no
  pretreatment for TSS
• Designed to store 5 to 10 of WQv
• Up to 25 of suspended sediments may settle in
  the forebay, catch basin, or other sediment
  pretreatment unit
• Post construction volumes can be expected to
  equal 1 to 4 cf per year per acre of watershed

56
WQv Storage SystemsForebays et al.

• Forebays may not be necessary where ponds are
  designed with adequate long term sediment storage
  capacity
• Regulations may require them, whether or not the
  pond has adequate storage, unless pretreatment is
  provided for coarse sediments (swirl chambers,
  e.g.)

57
WQv Storage SystemsPond Systems

• Dry ponds, wet ponds, wetlands, and other large
  basins
• TSS removal most effective when basin is at least
  0.5 of watershed size
• Adjustable outlet control recommended for
  manipulation after placement

58
WQv Storage SystemsPond Systems

• Outlet Control Agri-drain Type Systems

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Session II Coming Up

• Example Storm Water Quality Design Calculations

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Contact Information - Indiana

• WILLIAMS CREEK CONSULTING, INC.
• Babeca Building
• 919 North East Street
• Indianapolis, Indiana 46202
• 317/423.0690 p.
• 317/423.0696 f.
• P.O. Box 5606
• Lafayette, Indiana 47904
• 765/477.6170 p./f.