by Marley Bice, MCRP '12
In light of the recent fire at New York City’s North River Sewage Treatment Plant which caused plant operations to cease for almost 48 hours and 360 million gallons of untreated wastewater to flow into the Hudson River, I hope people are starting to think more critically about what happens when it rains on the local Wal-Mart parking lot or what happens when you flush your toilet. In combined sewer system cities across the country, including New York City and Philadelphia, that rain water and waste water are funneled into the same pipe. In dry weather, the combined waters flow directly to the local water pollution control plant and all we have to worry about his how well that plant can actually clean that water and how much electricity it takes to run the plant. However, in wet weather (or when a fire outbreak causes plant operations to cease) this toxic mixture cannot be contained by the combined sewer system and the excess is piped directly into the local water body.
The alternative that cities that have developed more recently have implemented is a separate sewer system. In this system the stormwater and the wastewater are piped into separate systems so that sewage is always sent to the water pollution control plant and stormwater is always sent straight to the river. Unfortunately, it is a lose-lose situation. In dry weather, the combined system is better because it ensures that both forms of polluted water are treated. However, on average throughout the year, a separate sewer system is better because it prevents the most obnoxious and toxic forms of waste to always be treated.
In my opinion any sewer system of grey infrastructure needs to be combined with innovative green stormwater infrastructure that minimizes the amount of rain water that is sent to the sewer system. With our current technologies and knowledge, we are able to treat a large amount of stormwater with infiltration systems and strategic vegetation such as green roofs and rain gardens. Hopefully some day we will have similar sustainable methods of treating our sewage wastewater as well.
What can we do today? Decrease surface parking lots, increase tree canopy, create legislation and crediting systems to encourage private sector implementation of rainwater harvesting and green roofs, and teach our kids to respect the life-sustaining water cycle.