1. Session 6A: Permeable Pavement

2. From the Rooftop to the Bay, March 9 -11, 2010 Photos: Chesapeake Bay Program Permeable Pavements Permeable Interlocking Concrete Pavers (PICP) Pervious Concrete (PC) Porous Asphalt (PA)

3. From the Rooftop to the Bay, March 9 -11, 2010 Photos: Chesapeake Bay Program Pavement Sizing and Design The depth of the stone reservoir layer (base) is set by four factors: –Structural load –Soil infiltration rate –Maximum drain time –Design storms stored or infiltrated May or may not have underdrain, depending on infiltration rate Cross-section specifications different for each kind of pavement (PC, PA, IP)

4. From the Rooftop to the Bay, March 9 -11, 2010 Photos: Chesapeake Bay Program Underdrain Sump Design Source: Hunt and Collins, 2008

5. From the Rooftop to the Bay, March 9 -11, 2010 Photos: Chesapeake Bay Program Stormwater Science Due to high surface infiltration rates: –Reduce runoff quantity –Lower peak runoff rates –Delay peak flows Even in applications with underdrains PPs can effectively reduce concentrations of heavy metals, TSS ( Nutrient removal capabilities less understood

6. From the Rooftop to the Bay, March 9 -11, 2010 Photos: Chesapeake Bay Program LID PracticeLocationRunoff ReductionReference Pervious Pavement *ONT99 Van Seters et al (2006) Pervious Pavement *PA94 Traver et al (2006) Pervious Pavement *FRA98 Legret and Colandini (1999) Pervious Pavement *NC100 Bean et al (2007) Pervious Pavement *NC95 to 98% Collins et al (2007) Pervious Pavement *WA97 to 100 Brattebo and Booth (2003) Pervious Pavement *CT72 Gilbert and Clausen (2006) Pervious Pavement *UK78 Jefferies (2004) Pervious Pavement #NC38 to 66 Collins et al (2007) Pervious Pavement #PA25-45 Pratt et al (1989) Pervious Pavement #NC66 Bean et al (2007) Pervious Pavement #UK53 Jefferies (2004) Pervious Pavement #MD45 to 60 Schueler et al (1987) Pervious Pavement #Lab30 to 55 Andersen et al (1989) Runoff Reduction Estimate45# to 75* * no underdrain collection # underdrain collection

7. From the Rooftop to the Bay, March 9 -11, 2010 Photos: Chesapeake Bay Program Table 1: Summary of Stormwater Functions Provided by Permeable Pavement Stormwater FunctionLevel 1 DesignLevel 2 Design Annual Runoff Reduction 45%75% TP Removal 1 25% TN Removal 1 25% Channel Protection Moderate. May be able to provide some or all within the reservoir layer Flood Mitigation Partial. May be able to provide some in the reservoir layer 1 Change in event mean concentration (EMC) through the practice. Actual nutrient mass load removed is the product of the removal rate and the runoff reduction rate and will be higher than these percentages, as calculated using the Runoff Reduction Spreadsheet Methodology. Sources: CWP and CSN (2008) and CWP (2007).

8. From the Rooftop to the Bay, March 9 -11, 2010 Photos: Chesapeake Bay Program Comparative Properties of the Three Major Permeable Paver Types Design FactorPorous Concrete (PC) Porous Asphalt (PA) Interlocking Pavers (PICP) Scale of Application Small and Large Scale Applications Micro, Small and Large Scale Applications Paver Thickness 5 to 8 inches3 to 4 inches3 1/8 inches Design Permeability 10 feet/day6 feet/day2 feet/day Construction Cost $ 2.00 to $6.50 sf$ 0.50 to $1.00/sf$ 5.00 to $ 10.00/sf Min Batch Size ~ 500 sfNA Longevity20 to 30 years15 to 20 years20 to 30 years Colors/TextureLimited Range of Colors and Textures Black or Dark Grey Color Limited Range of Colors and Textures Other IssuesAvoid Seal CoatingSnowplow Damage

9. From the Rooftop to the Bay, March 9 -11, 2010 Photos: Chesapeake Bay Program Design Scales for Permeable Pavers Design Factor Micro-ScaleSmall-ScaleLarge-Scale Suitable PaverPICPALL Reservoir SizeSome or all of the RRv or WQv Full WQv, and as much of CPv and design storms as possible External DA?NoYes, Impervious cover up to twice the permeable paver area may be accepted Observation WellNo Yes Underdrain?RareDepending on soilsBack up underdrain

10. From the Rooftop to the Bay, March 9 -11, 2010 Photos: Chesapeake Bay Program Construction Each Paver Type has a different construction sequence –PC: Cover and Cure for a week –PP: Cast in Place –PICP: Manually or mechanically installed (up to 5000 sf/day)

11. From the Rooftop to the Bay, March 9 -11, 2010 Photos: Chesapeake Bay Program Permeable Pavers in the right situation

12. From the Rooftop to the Bay, March 9 -11, 2010 Photos: Chesapeake Bay Program Permeable Pavers in the wrong situation Source: Bill Hunt, NCSU

13. From the Rooftop to the Bay, March 9 -11, 2010 Photos: Chesapeake Bay Program

14. From the Rooftop to the Bay, March 9 -11, 2010 Photos: Chesapeake Bay Program Design Choices: Hotspots and Snowmelt

15. From the Rooftop to the Bay, March 9 -11, 2010 Photos: Chesapeake Bay Program INFORMED OWNERS Maintenance agreements should also note which conventional parking lot maintenance tasks must be avoided: sanding re-sealing re-surfacing power washing snow plowing and dumping Signs should be posted on larger parking lots to indicate their stormwater function and special maintenance requirements.

16. From the Rooftop to the Bay, March 9 -11, 2010 Photos: Chesapeake Bay Program ActivityAction Inspect surface for signs of surface clogging. Schedule a vacuum sweeper (no brooms or water spray) to remove deposited material. Inspect the structural integrity of the pavement Replace or repair affected areas, as necessary. Check inlets, pretreatment and flow diversion for sediment buildup and structural damage. Remove sediment or repair affected areas Inspect CDA for any controllable sources of sediment or erosion Stabilize CDA Measure drawdown rate in observation well storm > 0.5 in. Standing water after 3 days = clogging problem. Replace or repair affected areas.

17. From the Rooftop to the Bay, March 9 -11, 2010 Photos: Chesapeake Bay Program Overall Design Guidelines Infiltration designs reduce more runoff than underdrain designs Stable CDA (100% IC) Do not site near disturbed areas Design on Flat Slopes Maintenance Agreements

18. From the Rooftop to the Bay, March 9 -11, 2010 Photos: Chesapeake Bay Program Addressing common Myths How often do these need to be maintained? How much do they cost? What happens at the end of the design life? Do you need a certified installer?