PERMEABLE PAVEMENTS. Have been around for a long time, but are poised for a resurgence

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1 PERMEABLE PAVEMENTS Have been around for a long time, but are poised for a resurgence

2 Three Broad Types of Pavers PC: Porous Concrete PA: Porous Asphalt IP: Interlocking Concrete Pavers

3 The depth of the stone reservoir layer (base) is set by four factors: Structural load Soil infilration rate Maximum drain time Design storms stored or infiltrated Source: Hunt and Collins, 2008 Figure 1: A Permeable Pavement System Can Be Designed With or Without an Underdrain May or may not have underdrain, depending on infiltration rate

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5 Table 1: Summary of Stormwater Functions Provided by Permeable Pavement Stormwater Function Level 1 Design Level 2 Design Annual Runoff Reduction 45% 75% Total Phosphorus 25% 25% Removal 1 Total Nitrogen Removal 1 25% 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).

6 Table 7 Suggested Annual Maintenance Inspection Points for Permeable Pavements Activity The drawdown rate should be measured at the observation well for three days following a storm event in excess of 0.5 inch in depth. If standing water is still observed in the well after three days, this is a clear sign that that clogging is a problem. Inspect the surface of the permeable pavement for evidence of sediment deposition, organic debris, staining or ponding that may indicate surface clogging. If any signs of clogging are noted, schedule a vacuum sweeper (no brooms or water spray) to remove deposited material. Then, test sections by pouring water from a five gallon bucket to ensure they work. Inspect the structural integrity of the pavement surface, looking for signs of surface deterioration, such as slumping, cracking, spalling or broken pavers. Replace or repair affected areas, as necessary. Check inlets, pretreatment cells and any flow diversion structures for sediment buildup and structural damage. Note if any sediment needs to be removed Inspect the condition of the observation well and make sure it is still capped Generally inspect any contributing drainage area for any controllable sources of sediment or erosion

7 Comparative Properties of the Three Major Permeable Paver Types Design Factor Porous Concrete (PC) Porous Asphalt (PA) Interlocking Pavers (IP) Scale of Application Small and Large Scale Applications Small and Large Scale Applications Micro, Small and Largee Scale Applications Paver Thickness 5 to 8 inches 3 to 4 inches 3 1/8 inches Design Permeability Construction Cost 10 feet/day 6 feet/day 2 feet/day $ 2.00 to $6.50 sf $ 0.50 to $1.00/sf $ 5.00 to $ 10.00/sf Min Batch Size ~ 500 sf NA Longevity 20 to 30 years 15 to 20 years 20 to 30 years Colors/Texture Limited Range of Colors and Textures Black or Dark Grey Color Limited Range of Colors and Textures Other Issues Avoid Seal Coating Snowplow Damage

8 The profile and stone specifications for the underground cross-section of each kind of paver is different (PC, PA, IP)

9 Permeable Pavers in the right situation

10 Permeable Pavers in the wrong situation

11 The Three Design Scales for Permeable Pavers Design Factor Impervious Area Treated Typical Applications Most Suitable Paver Reservoir Size External Drainage Area? Micro-Scale Pavers Small-Scale Pavers Large-Scale Pavers 250 to 1000 sq. ft to 10,000 sq. ft. More than 10,000 sf Driveways Sidewalks, Walkways Court Yards Plazas Fire Lanes Road Shoulders Spill Over Parking Plazas IP ALL ALL Infiltrate or detain some or all of the RRv or WQv No Parking Lots with more than 40 spaces Infiltrate or detain full WQv, and as much of CPv and design storms as possible Yes, Impervious cover up to twice the permeable paver area may be accepted Observation Well No No Yes Underdrain? Rare Depending on soils Back up underdrain

12 Permeable Pavement Source: Cahill Associates Difference

13 Overflow Options

14 Pavers w/ permeable joints Uncompacted soil subgrade over optional geotextile No. 8 bedding material No. 57 stone base for water storage No. 2 stone subbase for water storage

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16 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.

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19 Design Choices: Hotspots and Snowmelt

20 Design Choices: 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)