Water Matters!

So this past month, I spent a good chunk of my time preparing a presentation for the St. Louis University speaker series “Water Matters.” This series is the companion to a fall series entitled “Energy Matters,” and is comprised of [very early] morning sessions on five consecutive Wednesdays. The series was structured such that the first session addressed global issues, and then each successive session focused in more narrowly—giving a comprehensive picture of water issues that ranged from worldwide problems to those in your backyard. I had the opportunity to speak at the third of these series, entitled “The Challenges We Face, What We Can Do and Why We Should Do It,” which addressed metropolitan issues.

One glance at my AmeriLog this past month and you’ll see that I spent a good chunk of my time working on this presentation. There were two reasons for this: one, I was doing a slightly different presentation that required a good deal of research and number crunching; and two, I was terrified of sounding like an idiot in front of a crowd of professionals.

Needless to say, both reasons were enough motivation to put in a lot of effort! The presentation I gave was very cool (if I do say so myself), because my coworker and I attempted to quantify the financial benefits of installing a green roof or pervious concrete.

The reason we chose these two types of green infrastructure was because they are the only types for which the St. Louis Metropolitan Sewer District (MSD) lessens the impervious surface fee. This recent—and controversial—fee imposes a monthly charge on your impervious surfaces. Right now, the fee stands as $0.12/100 square feet, however it will more than double over the next four years to $0.29/100 square feet. The purpose of this fee is not only to encourage people to reduce their impervious surfaces, it’s to give MSD the money they need to put in place their Long-Term Control Plan, which will work to address the combined sewer overflows in St. Louis. Either way, this fee is good news for water quality.

In light of this fee, and the various other benefits of installing a green roof or pervious concrete, I presented a case study of a “big box” in Chesterfield. For a variety of reasons, I had much more success calculating the cost/benefit of a green roof rather than pervious concrete, however I believe my research also turned up some important benefits of the latter.

As it turns out, if this store were to install what’s referred to as an “extensive” green roof (which has only a few inches of soil, as opposed to an “intensive” green roof, which has greater benefits but is far more expensive), this store would see a significant net benefit. I used very rough numbers, but I was able to calculate that over 40 years, the life of the green roof, the store would save over $170,000 on impervious surface fees. Furthermore, the store would over $100,000 on energy—and that’s not taking into account that energy prices will likely increase. The store would also save on the cost of replacing the conventional roof, since green roofs extend the life of roofs because they protect from damaging UV rays and wind. In sum, the store would see nearly $300,000 in savings, beginning around year 27 after installing their green roof.

Pervious concrete was a little trickier, because the cost of installing the concrete depends heavily on the site. However, after speaking to several contractors, I was able to ascertain additional monetary benefits that the store would see if they were to put in pervious. First off, pervious concrete does not require a connection to the storm sewer system, which can be quite costly. In addition, the current BMP is to build a stormwater detention basin on the site, which either requires the developer to purchase additional property or reserve some property they would otherwise build on or pave. With pervious, however, developers get the most cost-effective use of their land, because they are not required to build a detention basin. Pervious concrete has a longer lifespan than asphalt, and also saves tenants money on deicing their parking lots (because pervious lots use roughly 75% less salt). Finally, our case study would see over $120,000 in savings on their impervious surface fee over the life of their pervious parking lot! In fact, every contractor I spoke to said that even though pervious concrete is more expensive up front, the costs end up being a wash.

Overall, we discovered that pervious concrete and green roofs are good for the wallet AND good for the environment! One more reason why both types of green infrastructure should be utilized more. And if they contractors I spoke to are right (which I’m inclined to believe they are), that’s exactly what’s going to happen.

Happy spring, everyone!