Concrete Progress: The Parking Lot That Doubles as a Sponge

Concrete Progress is an ongoing series of columns by Peter Brewitt devoted to exploring America’s infrastructure. It is part of Orion’s Reimagining Infrastructure project.

In most places, when it rains, water bounces off roofs and sweeps across blacktop, gathering litter, motor oil, and sediment. Modern landscapes are pretty thoroughly paved over, so this is a problem nearly everywhere people live: an acre of pavement yields five times the runoff of an acre of woodland—the pollution rushes down sewers and floods into lakes and rivers. If there’s too much, sometimes sewers overflow, or basements flood. Such runoff is one of America’s biggest water pollution problems of the twenty-first century, and not just in cities like Seattle and New York, but in places like Monona, Iowa (the location of the video) as well.

Monona is a village of about 1,500 people in the rolling prairie of northeastern Iowa, along the Wisconsin border. It prides itself as the “Garden City of Iowa,” full of rural scenery and outdoor recreation. Among its star attractions is an aquatic center, built in 2007, where you can do everything from sliding down a water slide to enjoying an artificial geyser (yes, really) to swimming laps. It’s in the southwestern corner of town, just above Silver Creek, in the Turkey River watershed. Before they paved the gravel parking lot last year, Mononans saw that rainstorms washed sediment into the water. This seemed unfortunate, the aquatic center hurting the aquatic environment. They didn’t want to continue the problem by covering the lot in conventional blacktop, so they turned to permeable pavement.

Permeable pavement works by simulating the action of ordinary soil. It contains spaces to absorb rain water, and let it drain, at a gradual pace, through the dirt and into the groundwater—a kind of natural(ish) hydrology with the convenience of sturdy pavement. There are several kinds; Monona used pavers that fit together like, as the local paper said, “Tetris pieces.” Under the ordinary-looking concrete surface are layers of stones and gravel, which slow and filter the water, letting it recharge aquifers and reach lakes and rivers free of surface pollutants. I’ve heard some concerns about how permeable pavement performs in freezing temperatures, but a study in New Hampshire (a state that knows all about freezing temperatures) found that permeable pavement needed 75 percent less salt and did not form black ice in winter. You do have to spray it out a few times a year to keep sediment from clogging the pores.

The problem is, permeable pavement is several times the cost of conventional pavement, and while some of that cost may be recouped in the long run, a town of 1,500 people is not likely to have a spare $260,000 (such was the cost) lying around. So, in Monona, a coalition of town representatives, state agencies, regional NGOs, and local businesses worked with the Clean Water State Revolving Fund (SRF) to solve the problem.

The SRF is one of the few signs that the federal government can adapt with changing infrastructural needs. When the Clean Water Act passed, back in 1972, one of its most important programs was a massive national effort to fund the construction of publicly owned sewage treatment works. Many American communities did not use any biological sewage treatment at all; it was a different, grosser world. But after a few decades, the sewage problem was just about solved—a classic example of a big, old-school infrastructure program. Instead of washing its hands of clean water, the federal government turned the treatment works fund into the SRF. Today, the SRF provides $5 billion a year in low-interest loans to states looking to help their communities with water quality projects, like Monona’s parking lot. It’s given out more than $100 billion and helped realize tens of thousands of projects. In the specific case of the aquatic center, Monona had already taken out a larger loan to work on wastewater improvements, and was able to channel the interest they would have paid on that loan into the parking lot.

As more and more cities take responsibility for their water quality, permeable pavement use is growing quickly. We may, perhaps, look back on the days of hard pavement and stormwater runoff the way people today look at 1960s sewage treatment. If you have any permeable pavement insights or experience, I would love to read about them in the comments.

Peter Brewitt has wondered about infrastructure ever since a flood kept him away from three days of kindergarten. A professor of environmental studies at Wofford College, he is devoted to understanding how people decide to restore and remake their environments.


  1. Vision like this gives me hope in the midst of a growing sense of environmental doom. Bring it on, brilliant folks who are dreaming outside the box! Creative think tanks of unencumbered (profit minded) visionaries will save the planet as best as possible. Here’s to a future born of love, passion and a commitment to functional solutions.

    We need a new flag and a global pledge. Here’s mine so far:
    “I pledge allegiance to the Earth, the lovely planet of my birth, and to the biodiversity upon which it stands. One planet under our Sun, with stewardship and consideration for all. “

  2. I can’t imagine permeable concrete having much practical use due to the fact that it is so much more expensive AND has to be thoroughly ‘sprayed out’ (whatever that is) several times per year. Perhaps his only practical value is in some parking lots in northern climates due to its needing less deicing salt and its resistance to performing black ice.

  3. It only seems more expensive because not all of the true costs of regular concrete are being taken into account – only the immediate monetary costs.

  4. When you consider the benefits of recharging the aquifer, reducing storm water infrastructure, eliminating combined sewer overflows (in the 772 cities where this is a serious contributor to water pollution), reducing erosion and siltation, not to mention a reduction in icing and salt use, the increased costs of permeable asphalt, concrete, and unit pavers, and their maintenance becomes quite reasonable. We will be making this switch eventually, particularly considering increased storm events. We might as well get started now. Thanks for bringing it to our attention.

  5. Good article. Porous pavemnts have their place along with structural soil (developed and patented by Cornell University) for urban trees.
    Experience has shown that porous pavement formulation, hading and installation is tedious. The manufacturer must thoroughly clean the facilty before preparing so the cost is more for the shutdown of production. This wouldn’t be a problem with a dedicated plant in large urban areas with ongoing projects, One other concern is flooding that causes sediments to clog the porous pavements, so these pavements are not recommended for floodplains.

  6. This was used somewhat frequently here in Colorado about 40 years ago, fell out of favor for all the reasons given.
    An outlet controlled retention basin is far lower cost and easier to maintain.

  7. These are some great points. Kenneth, it is true that up-front costs are a challenge for permeable pavement as well as for many other environmental innovations, but the overall cost-benefit balance, listed by Carol, make it a strong choice for lots of municipalities and other entities that aren’t required to show short-term profits – and that are responsible for the landscapes and waterways around the concrete. Thomas, I’m glad to say that crushed concrete is indeed used for some permeable pavements. Thanks to everyone for reading.

  8. Peter: good article! The deep and steady snow loads this winter in Massachusetts have caused my town to consider giving up on its two new porous parking lots. Truck plowing was too difficult. Would like to hear if others had this trouble, and what the solutions are; maybe a snowblower or sidewalk plow instead?

  9. Hey Pete,
    Did you know that Arana Gulch’s bike and ped trail finally got built in the urban greenbelt connecting the east side and midtown in Santa Cruz? It opened late last year and features permeable pavement paths, one of the environmentally protective design features meant to encourage the native tarplant. Another measure is the presence of grazing cattle. The endangered tarplant delayed the project for 20 years. Finally, through some serious compromise between NGOs, local government and citizen groups, the project moved forward and I think by all counts is a success. The not-too-obtrusive improvement in cross town connectivity via active transportation options also enables less mobile folks to explore green space safely and comfortably. Enjoying the series! Cheers!

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