Green is the new Gray — The Next Phase of Infrastructure
There are so many modern technologies and infrastructures to be grateful for these days — with the spotlight currently on those leading to the development of multiple effective vaccines for COVID-19. Though this disease is far from being eradicated, investing in sound infrastructure that defends human health and public safety will always be an ongoing process. To give an example of a disease that modern infrastructure eradicated, think of cholera — an illness caused by a bacterium that flourishes in dirty water. This is not an illness most people in the United States have any experience with. The widespread use of modern water and sewage treatment systems pretty much eliminated the water-related spread of this bacteria.
In fact, wastewater infrastructure is a huge part of why city living can be the way it is today. Before it’s widespread use, cholera was a common epidemic thought to be caused by the “miasma” of foul air around unmanaged garbage, animal manure, and human waste in the streets. Though the reality was that bad bacteria was flowing freely into people’s drinking water, the idea to keep the sickening gases away from people by building underground wastewater systems worked doubly. By having a system below the soil to channel waste and storm waters out of the city and away from drinking wells, public health in cities like early New York and Philadelphia was greatly improved.
Above the soil, other city infrastructures changed to accommodate these new waste and stormwater systems. Streets were made wider and straighter, and were paved over so that waste could be washed down the drain more easily. Parts of the land that collected fetid water were also paved to prevent a source of “miasmic gases”, which allowed industry and housing to expand. Miasma theorists also advocated for the development of city parks to act as a source of fresh air in a densely urban place. As more infrastructure improvements were made, more people were able to safely live in relatively close quarters, and cholera eventually met its demise in the United States.
As will always be the case, when old problems are solved, new problems are made. In the cities of today, there is too much water going into the underground water infrastructure and not enough going into the soil. This can cause groundwater depletion and a host of other issues. Many cities have both a combined sewer system and a municipal separate storm sewer system — the combined sewer collects both sewage and stormwater to send to a wastewater treatment plant, and the municipal storm sewer collects only stormwater to send directly back to streams and rivers. Water that flows into the storm sewer system often comes loaded with the pollution, chemicals, and trash that builds up on the city’s paved and impermeable surfaces. And when intense rainfall occurs (as it will more frequently as the climate changes), the combined sewer is overwhelmed and ends up discharging both stormwater and raw sewage into natural waterways.
The problem of combined sewer overflows caused by overwhelming rain events can be solved by improving the capacity and treatment infrastructure of existing wastewater treatment plants. However, it comes with a big initial investment and a high annual cost of maintenance. The pollution that accumulates in stormwater directed into waterways has no single source and therefore can be a challenge to reduce.
A low cost, widely beneficial solution to these issues can be found in the use of green infrastructure. But what exactly does that term include? Broadly defined, green infrastructure includes “all natural, semi-natural, and artificial networks of multifunctional ecological systems within, around, and between urban areas at all spatial scales”. Green roofs, rain gardens, and porous pavement can be part of the artificial network inside of the city, while constructed, semi-natural, or fully natural systems like wetlands can be used to retain and treat dirty runoff outside the city lines. Best-management practices for agriculture and forestry can also be included as ways to reduce non-point source pollution.
The investment objective of both green and gray infrastructure is to reduce the expected loss from natural and human disturbances in a way that both minimizes the cost of meeting that objective and also maximizes any benefit to the public. To compare the two types by what they are used for, take coastal flooding as an example. In order to prevent a coastal flood, sea walls, levees, pumping facilities, dikes, and floodways can be build. Green infrastructure that would also minimize damage from the same events include restored mangrove areas, dunes, and wetlands.
Though comparisons are helpful, the two are not meant to exist as mutually exclusive; gray infrastructure is already present and functioning, so green infrastructure can be used to help “lighten the load”, making gray infrastructure last longer and work more effectively. And while gray infrastructure depreciates in value over time, green infrastructure often appreciates as it grows into maturity or practice. By reducing the amount of capital investment needed for gray infrastructure for cost of operation, maintenance, updates, and expansions, an investment in green infrastructure would seem to pay for itself.
That being said, there currently is no consistent and accessible methodology to compare the green and the gray yet, which makes it tough for investment managers to choose green. Green infrastructure is generally considered riskier, because of the relative new-ness and the higher susceptibility to climate change, floods, fires, droughts, insect damage, and other uncertainties. But gray infrastructure is subject to damage from most of the same factors, as well as other unique sources of risk. It is also easier to mitigate the risk to green infrastructure by “doubling up” and using a multi-barrier approach, like installing a network of rain gardens instead of just one.
Something that comes close to a consistent method and cost-benefit analysis for green infrastructure is the guide published by the Center for Neighborhood Technology called “The Value of Green Infrastructure”, and the numerous case studies of different successful projects funded by the Environmental Protection Agency. The guide bases the framework of benefits in eight categories: water, energy, air quality, climate change, urban heat island, community livability, habitat improvement, and public education.
Lancaster, PA is a great example of a successful city-wide project in using green infrastructure. As one of the many cities in the United States with a combined sewer overflow system, Lancaster and the surrounding areas can end up discharging up to 750 million gallons of untreated wastewater and stormwater into the nearby Conestoga River annually due to intense rainfall events. Managing this problem with gray infrastructure alone would have cost $250 million (in 2011).
By developing a 5- and 25-year green infrastructure plan, the city predicted to spend between $77 million (if the construction was tagged onto pre-planned maintenance projects) and $141 million (if the construction was tackled independently) reducing the average annual stormwater runoff by 1.053 billion gallons a year. This was a significant budget reduction, in the pursuit of systems and projects that would only improve over time and provide a wide variety of social and economic benefits, in addition to environmental and development benefits.
An example of green infrastructure on a much larger scale can be found by looking at the source of New York City’s drinking water supply: the watershed of the Catskills. The mountainous, mostly rural area of the Catskills Mountains is the largest unfiltered water system in the United States, protected by the NYC Watershed Memorandum of Agreement, guiding environmental protection and significantly reducing water treatment costs. As it has for many hundreds of years before, ice melt from the mountain is naturally filtered by the land, made possible by these careful land conservation and management practices. It enters a system of nineteen reservoirs to supply the huge water demand of New York City — 1.2 billion gallons daily.
A filtration plant large enough to clean the City’s water supply would cost over $6 billion to build and $650 million (in 2006 dollars) to maintain annually. By instead investing in best waste mitigation and ecosystem preservation in upstate New York, the City spends an average of only $167 million a year (in 2006 dollars, again) in maintenance and improvement costs to the watershed system. Farmers are compensated for improving the water quality of their run off. Resident septic tanks are fixed and replaced at no cost to the homeowners. Forests are managed to ensure that ecosystem services are maximized. Money saved there could be allocated to improving the aging water infrastructure within the city.
It is a challenge to find any failed examples of green infrastructure, but the spread of the benefits needs to be considered. As in the example with New York City’s water supply, millions of people benefit in the form of clean drinking water and city budget savings from the land management in the Catskills region. However, the many people who live in this region can make the case that restricting development and industry on this land systematically deprives communities of economic opportunity, and that the costs of clean water should be paid by those who enjoy it. Not to mention that entire communities were forced to vacate and relocate because the city had bought out the land to create reservoirs. Entire graveyards had to be exhumed to be reinterred where they wouldn’t be underwater.
Is economic sacrifice for an agricultural region worth creating safe drinking water for the largest city in the United States? And is the investment in green infrastructure one that is demonstrably good? A better system of benefit-cost analysis, based on a framework that can accommodate the differences between regions, would make it easier for city officials to decide to make the jump. Of course, case studies like that in Lancaster could lead to the inclusion of green infrastructure as an improved choice during planning in those regions. More studies that track different metrics are needed as well. These could be anything from the reduction in nutrients in run off instead of just the volume mitigated, to the frequency of pedestrian traffic before and after an installation occurs.
As climate change continues, new challenges will arise for city planners, scientists, gardeners, and engineers. Many more disciplines will have to work together to bring about safe and secure places to live. Society has seen the outcome of allowing wastes to go unmitigated — and while we may be avoiding cholera epidemics now, the current pandemic has opened up a larger discussion of how to make cities more livable and resilient. By combining newer green infrastructure techniques with established gray infrastructure, cities can improve in a wide variety of ways, from an improved social safety to a healthier surrounding environment. These changes are cost effective, and the sooner they happen, the more value they will add to the spaces we live in.
