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By Benjamin Weinryb Grohsgal

One of the benefits of the profusion of new kinds of data collection and analysis taking place in cities across the US today is that it makes possible monitoring and evaluation of a much broader set of interventions than ever before. These include the technology-driven interventions one might expect, but also include novel low-tech approaches that may deliver much more per dollar spent. The latter may have been less attractive in the past because of the difficulty of proving their efficacy. Refining and improving low-tech solutions without a steady flow of information was akin to taking shots in the dark and hoping for the best - particularly problematic when attempting to scale piloted solutions to the citywide level or replicating them elsewhere.

Philadelphia is leading the way with the comprehensiveness of its low-cost green infrastructure approach.

For example, the Green City, Clean Waters program in Philadelphia is a city-wide low-impact development approach to mitigating the city’s combined sewer overflows (CSO). The program integrates very low-tech interventions like rain barrels and street trees with very high-tech data collection and analysis. The city is addressing a problem faced by many others that began before the 1950s: a CSO system wherein there is no physical division between stormwater and the sewer system responsible for wastewater coming from homes and businesses. This means when a big storm rolls in, the system becomes overwhelmed, stormwater and wastewater mix, and a toxic effluent is discharged into waterways, degrading the environmental quality for both plants and animals as well as citizens who may live or recreate near these rivers and streams. For this reason, and rightly so, the EPA ruled in 1994 that cities must fix this problem. However, because this is an unfunded mandate that can cost cities nationwide upwards of $50 billion over the next 20 years, most cities put the project on the backburner. A few undertook massively expensive infrastructure projects to build huge underground pipes and storage tanks to hold stormwater and then slowly treat it before discharge. Chicago built the largest tunnel reservoir system in the world, in addition to some green infrastructure, at a cost of about $3.6 billion. Many cities haven’t been able to build suitable plans to finance such massive projects, and while such an approach fixes the CSO problem, it does little to improve the environment above-ground.

Big data analysis and a profusion of sensors spread within the city’s sewer system provide this vital piece of the puzzle, lending some big-technology insights to what is a purposefully low-tech, low-impact approach to attacking the CSO problem.

Philadelphia took a decidedly different approach: making the city as a whole more permeable. By increasing the citywide capacity to naturally absorb rainfall, the city can ensure that excessive stormwater doesn’t enter the system at levels that would strain its capacity. This is much cheaper both in initial construction costs (estimated to be a quarter the cost of a traditional approach) as well as operations, maintenance, and electricity costs. The program also aims to improve quality of life above-ground, mitigating the heat-island effect, reducing pollution, beautifying streets, and creating entry-level jobs. But with such a sundry approach, proving success and evaluating the effectiveness of different interventions - whether they be rain swales or permeable concrete - takes a little more creativity than required for more traditional high-tech big-infrastructure approaches.

Luckily, big data analysis and a profusion of sensors spread within the city’s sewer system provide this vital piece of the puzzle, lending some big-technology insights to what is a purposefully low-tech, low-impact approach to attacking the CSO problem. Since the program’s conception, an extensive and quantitative evaluation plan has been in place. Philadelphia pulls data from sensors throughout the system (originally purposed just to warn departments and citizens of overflows) to see if the approach is really working, and also conducts health quality tests in various bodies of water to check if there is a substantive long-term impact. Real cost comparisons can be made between different elements of the program, allowing the city to adjust its plans over time and maximize the returns of each program dollar spent. The program also creates a valuable store of data to develop best practices for other cities looking to replicate the approach. Philadelphia is leading the way with the comprehensiveness of its low-cost green infrastructure approach. Many cities are waiting for clear answers before addressing the long-overdue requirement to mitigate for their CSO systems, so Philadelphia’s data-driven strategy is vital for making this low-tech solution viable on a nationwide scale. Data analytics need not only be rooted in tablet apps and data portals - sometimes it can leverage the most low-tech policy of all.

Topics: Infrastructure

About the Author

Benjamin Weinryb Grohsgal

Benjamin Weinryb Grohsgal is a joint MPP/MUP candidate at the Kennedy School and the Graduate School of Design at Harvard.

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