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A sustainable parking lot? It can be done

Permeable pavement, a green parking solution

In big cities like Toronto, pavement often covers much of the landscape, especially parking lots. That means when it rains, water runs off the pavement, bringing contaminants along with it. Permeable paving technology merges science and design to allow surface water to infiltrate back into the ground.

So, why is this important? There are a few reasons. When water infiltrates back into the ground, it’s diverted from the stormwater management system. This is good for the environment and for the pocket book. How?

It improves water quality. Because these systems deal with the first flush from rain events, they capture oil, gas, and fine particulates. Research has proven that microorganisms within the base layer digest the hydrocarbons, effectively treating the typical volumes entering the system from parking lots. This makes permeable systems a valuable part of the stormwater treatment train.

It can cut short-term costs. These systems offer a viable solution to minimize the need for traditional hard infrastructure (pipes, detention/retention ponds), which typically add costs and needed space to a project. When water hits the permeable surface, it’s intercepted and infiltrates back into the ground. Because the water is intercepted before it can reach a pipe, there’s less need (if any) to even have the pipes. What’s more, allowing the runoff to infiltrate the base course has the potential to reduce the need for stormwater management facilities on a site – an especially important factor in areas where land has a premium value. Permeable paving systems are also a good consideration for sites with aging infrastructure, where reducing the stormwater load can potentially extend the life of the system.

It can cut long-term costs. When exploring permeable paving systems, it’s important to look at life cycle costs. These include the initial investment capital to purchase the system, cost savings through the reduction in hard infrastructure, potential cost savings based on intensified land use, and long-term maintenance costs. Land intensification is a critical factor for most sites. Property owners can achieve significant financial returns if the required land for storm water management treatment facilities can be reduced on a site to allow for that land to be developed through adding a permeable system within the parking area. These reductions in traditional costs can potentially offset the additional costs associated with a permeable paving system.

Permeable paving systems also have different maintenance requirements from traditional paving. Because permeable paving can only function if water can flow through the system, annual cleaning and vacuuming of the surface is essential. This removes any fine material trapped in the joints and on the surface, and helps maintain the permeability of the system. The summer maintenance costs are typically offset by the reduction in salt required for winter de-icing as water infiltrates into the system before it can freeze and become a slipping hazard.  Plowing and snow removal are still required throughout the winter months but Sand cannot be used for maintenance of a permeable system as it plugs up the joints limiting infiltration.

It’s sustainable. Permeable paving is eligible for LEED® points under the sustainable sites, water efficiency, materials and resources, and/or innovative design. But the benefits go well beyond LEED®. Research continues to prove that these systems are not only viable in cold weather climates but are becoming an increasingly common part of our landscape.

Tim McCormick, OALA, CSLA, is a senior landscape architect with Stantec and the team lead for landscape architecture in our Kitchener office. Tim specializes in arboriculture, green infrastructure, and sustainable landscape design.

Porous pavement at Park and Ride lot, MTO Campbellville

Permeable paving systems are also a good consideration for sites with aging infrastructure, where reducing the stormwater load can potentially extend the life of the system.

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