State of the Planet

News from the Columbia Climate School


Students Advise County on Permeable Pavement

During a site visit to the Pratt Institute, students checked out a permeable pavement parking lot with rain gardens.
During a site visit to the Pratt Institute, students checked out a permeable pavement parking lot with rain gardens.

By Emily Mei Lau

In the face of population growth and urban development, ensuring sustainable sources of water and managing stormwater runoff becomes increasingly challenging. One such rapidly developing area is New York’s Rockland County, bordered by Orange and Westchester counties and New Jersey.

Rockland is home to Columbia University’s Lamont-Doherty Observatory and has a population of nearly 300,000 people. Its current population growth has put additional stress on the county’s water supply, and continued land development has increased the impervious surface area contributing to increased stormwater runoff. As stormwater runoff increases, so does the risk of flooding in low-lying areas and the contamination of nearby waterbodies with surface pollutants. Moreover, impervious surfaces prevent rainfall from infiltrating into the ground and recharging the aquifers.

To address these concerns, Rockland’s Water Task Force began looking into green infrastructure techniques—typically plantings of trees, shrubs and grasses on roofs, sidewalks or other areas—that could simultaneously reduce stormwater runoff and facilitate aquifer recharge.

Permeable pavement emerged as a promising solution. Although it falls under the category of “green infrastructure,” permeable pavement itself does not have a vegetation component. Instead, it has pores that allow rainfall to infiltrate through the surface and into the soil, which then filters the water. In short, permeable pavement turns the otherwise impervious surface of roads, parking lots and sidewalks into pervious ones that can still be used for walking, biking and driving.

Lamont-Doherty has already installed a permeable pavement parking lot, and Rockland, in partnership with the Stevens Institute of Technology, has recently identified a parking lot at Rockland Community College for installation. The Water Task Force is still in the early stages of exploring possible green infrastructure projects and is in the process of scouting out other possible locations.

At Pratt Institute during a site visit, from left: Emily Lau, David Bigio, Katie Homa, Jenny Olsen, Tara Mohtadi and Zoe Berg.
At Pratt Institute during a site visit, from left: Emily Lau, David Bigio, Katie Homa, Jenny Olsen, Tara Mohtadi and Zoe Berg.

This semester in the Capstone Workshop for Sustainable Development, I had the opportunity to partner with Rockland’s Water Task Force on a project looking into the feasibility of implementing permeable pavement. In researching and evaluating relevant design, legal and financial concerns, my student group produced four main deliverables over the course of the semester: a list of site selection recommendations for permeable pavement based on the requirements from the NYSDEC Stormwater Manual; an overview of permits and regulations required for installation; a list of federal and state grants for which Rockland can apply in order to finance the installation; and a fact sheet to educate municipal leaders and the community about permeable pavement.

An important part of the design is the site selection. Places with heavy truck traffic and debris are not optimal for permeable pavement, as the former would wear out the pavement and the latter would clog the pores. Additionally, while permeable pavement itself can melt snow faster than most regular pavement, traditional de-icing techniques of applying sand and salt cannot be used since they lead to clogged pores and possible contamination of the groundwater. Snow plow trucks are also out of the question, since they can easily tear up the surface.

If improperly maintained, the pores of permeable pavement can clog, rendering it ineffective in staunching runoff.
If improperly maintained, the pores of permeable pavement can clog, rendering it ineffective in staunching runoff.

Thus, cold weather storm events pose a challenge to permeable pavement, but areas such as mall and school parking lots have been identified as optimal sites, because they are low-traffic areas that are not critical for travel. They also have the added benefit of having large surface areas.

In terms of legal concerns, installing permeable pavement necessitates developing a Stormwater Pollution Prevention Plan for the municipality to ensure that the site meets the design requirements delineated in the New York State Stormwater Design Manual. Additionally, if the site exceeds 1 acre, then a permit for stormwater discharges must be applied for. Municipalities, however, have the ability to reduce the area that would warrant the permit to enforce stricter regulations. While the additional permitting may seem like a barrier, the regulations help guarantee that the installation is done correctly and without compromising water quality standards.

The biggest barrier to installation, however, is funding. Permeable pavement is about double to triple the cost of normal pavement and requires the additional maintenance of annual vacuuming. The life of permeable pavement can extend for about 20 years, which is comparable to asphalt, if maintained properly (biannual vacuuming to maintain porosity). Yet in terms of benefit, the positive outcomes are less quantitative and more qualitative: reducing flooding, mitigating stormwater runoff, and recharging the aquifers.

So far, Rockland is interested in installing permeable pavement in public areas and plans to apply for federal and state grants that are relevant to clean water and stormwater management. They have identified financing options through the Environmental Protection Agency, Department of Environmental Conservation, and the New York State Environmental Facilities Corporation. There are also community partnerships that can encourage the collaboration of various stakeholders and lower the cost of installation.

In addition to these three central concerns, an important component of encouraging green infrastructure initiatives is educating municipal leaders and the general public about these options. Permeable pavement is not the only green infrastructure with promising results: bioswales, green roofs and rain gardens are just a few others with the potential to mitigate stormwater runoff and increase rainfall infiltration. The variety of green infrastructure practices ensures that there are numerous and flexible options for every place, and oftentimes, these practices work best when combined with one another.

“These green infrastructure practices can allow us to meet a triple bottom line because of their economic, social and environmental benefits. This student project inspired us to scale up our efforts to install these techniques throughout the county,” said Patricie Drake, Rockland’s Water Task Force coordinator.

The task force is planning to share our work with the Planning Department and continue disseminating the fact sheet to educate the community about permeable pavement. Although it is too early to have a definitive idea of the widespread impact of permeable pavement, innovative thinking in places such as Rockland can help pioneer the way for others.

Emily Mei Lau is an undergraduate English major with a concentration in sustainable development. This piece is a summary of the work done by her and five other undergraduate students in the Capstone Workshop in Sustainable Development. The course is a requirement for all students in the Sustainable Development Program and is designed to provide them an opportunity to partner with outside clients and work on real-life projects over the period of one semester.




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