A. Pavers: solid concrete pavers that fit together with slight gaps

B. Granular Fill: gaps in pavers are filled with a small granite chip to allow water to pass through

C. Setting Bed Aggregate: 2 inch layer of clean, crushed, 3/8″ stone (ASTM No. 8)

D. Filter Aggregate: 4″ layer of 3/4″ – 1″ of clean, crushed stone (ASTM No. 57)

E. Storage Aggregate: 12″ layer of 1.5′ to 3″ clean stone (ASTM No. 2) This depth may vary depending on necessary storage volume.

F. Subdrain: Perforated subdrain tile ensures the system never stays saturated

G. Fabric: high-flow geotextile fabric

H. Existing Soils: soils under the rock layer

Things to consider during design and construction:

In situations with slopes, include baffles (walls used to control water elevation within the system) to slow the water down. Geotextile fabric is often used as a baffle. while our intention is to slow it down to prevent flooding during large-volume rainfall. Design the baffles to create a slope of 1% or less to prevent uneven ponding. Place the baffles so the downstream baffles takes on overflow from the upstream baffle.

Design Considerations:

Permeable paver systems can be designed to address a variety of rainfall events. 

Rate or inflow must be considered to avoid overwhelming the practice. 

Include features to bypass large rainfall events such as increased pavement area, increased subsurface storage, and/or surface intakes for emergency overflow. 

If designing a treatment train with multiple interconnected paved surfaces, each section needs to treat at least 30% of WQv class (measurement of water volume capacity) requirements to avoid overwhelming any one area of pavers.

The practice should be constructed at least 2 feet above the seasonal water table, or built with a waterproof liner if needed.

Our Learned Lessons: 

• Compaction of rock aggregate is critical to practice function
• Concrete edge restraints must be provided around the perimeter of permeable pavement systems.
• Install pavers 1/2″ above the edging to allow for settling.
• Avoid staging of landscaping materials like soil or mulch as tracking sediments onto the permeable pavement surface during construction can cause clogging and reduce practice efficacy
• Erosion and sediment control practices should be used to protect the rock aggregate and pavers until contributing drainage area is stabilized. The joins of these pavers will need to be vacuumed out in order to function properly.
• Regularly inspect the pavers and blow off any grass clippings after mowing 
• Leaf litter and other tree debris must be removed from the pavers on a regular basis to prevent clogging of joints.
• Prevent application of winter sand with signage and education. Use alternate de-icing products that do not harm the environment

Installation:

Step 1: removal of concrete and site excavation

Step 2: installation of perforated subdrain tile

Step 3: Leveling and compacting aggregate

Step 4: Laying pavers

Step 5: Add edge restraints

Maintenance:

Develop a maintenance plan and inspect pavement routinely

Ensure pavers infiltrate water during rain events (no ponding or runoff)

Pavers should be cleaned with a vacuum truck on a scheduled basis to avoid plugging

Sand should not be used on pavers, like in the wintertime, because it plugs the joint spaces

Remove built-up dirt, leaves, grass, and other organic material

Stabilize surrounding soil immediately to prevent sediment from moving onto pavers

Avoid staging of landscape materials like mulch or soil on pavers

Joint material should be regularly refilled or replaced.