As a member of a task force studying methodologies to mitigate the effects of flooding, I have found a general lack of understanding of the terms “retention” (indefinite/permanent storage of excess stormwater) and “detention” (short-term/temporary storage). Adequate surface and subsurface detention structures are effective in delaying the downstream impacts of instantaneous runoff of impervious surfaces.
— Charles E. Pound, president, Aqua Dredge Inc., Armonk, N.Y.
Editor's note: We thank Mr. Pound for his eagle eye: He noticed that the caption on page 46 incorrectly concludes that far fewer impervious parking lot islands exist than originally thought. Instead, far fewer pervious islands were mapped using remote-sensing techniques (see images).
In response to the“20 questions about sustainability” editorial (October 2010, page 7):
Public works professionals tend to be frugal and conservative, with a “show me first” attitude. We want to spend money only on tried and proven techniques.
Telling us to spend more now for a future benefit often becomes debatable, particularly when it's difficult to measure the anticipated results.
— Denis Knock, city engineer/director of public works, City of Des Peres, Mo.
With the advent of capitalism the world had apparently limitless resources, but man's ability to harvest them was limited.
Now we have limited resources but our ability to deplete or damage those resources is almost limitless.
My question(s): Is it time for a new political/economic model that rewards managing our world's natural cycles, not just greed and growth? Or can capitalism itself be managed to recognize the true worth of our resources?
— James Liubicich, PE, Burr Ridge, Ill.
Your questions are right on the mark.
Here in Contra Costa County, Calif., a ballot measure that would've added $10 — the price of a movie ticket — to annual car registration fees for local road, highway, and sidewalk expansion and maintenance was defeated.
What's particularly unfortunate is that our local population continues to expand, while the infrastructure to support it doesn't.
I wonder about the long-term economic costs if infrastructure increasingly hobbles — rather than facilitates — transport, public health, and quality of life. I worry that the voting public doesn't know or care about the big picture, only about the immediate impacts to themselves or their wallets. It's not the right way to build a sustainable, eco-friendly, or future-oriented national infrastructure.
Time will tell.
— Paul Davis, public relations director, Accela Inc.
I took the liberty of forwarding your 20 questions to a Towson University professor who teaches “sustainability.”
I established an internship there for environmental science students, and have learned more from them than they have from me. All of us in public works could learn what they are (and are not) being taught.
I hope they contact you. It would be interesting to get a young person's response to those questions.
— John Burnett, laboratory supervisor, Department of Public Works, Bureau of Utilities, Baltimore County, Md.
Editor's note: No word yet, but we'll keep looking.
We need a two-year engineering/public works retraining certification program in sustainability/green thinking. The program should be done through our community colleges. I know engineers who would be interested.
We'll help create the jobs of the future as we get retrained in more efficient engineering.
— Karin Hilding, senior project engineer, City of Whitefish, Mont.
Only when the right questions are asked and properly answered will the concept of sustainability truly progress.
More than a decade ago I heard a company talking up its recycling system on local radio, claiming the process filters sewer water into drinkable water. The show's guests said tests confirmed a bacteria rejection rate of 99.999%, and that these results were consistently reproducible.
When I called to ask if the recycled water had been tested for E. coli, they'd only say that the system's product was tested for all naturally occurring bacteria. I was cut off after asking for the virus rejection rate. I kept listening, though, and heard them admit that they'd never tested for virus rejection.
I guess the city council and county commissioners were listening too, because to this day no one's been able to get in front of either one without first answering one question: What's the virus rejection rate?
That's the type of smoke and mirrors I see from a lot of companies marketing to the “sustainability” niche. They talk the talk, but address safety-related questions by pointing to an irrelevant standard (like the normal environment and how safe it is).
It doesn't matter how safe the normal environment is, manmade systems must hold to a higher standard. Would you like to be the engineer at the water recycling plant that distributed Ebola or hepatitis B to households, restaurants, businesses, and schools?
— Thomas W. Kabis, BSG, MSE, general manager, GEO Consultants, Cedar City, Utah
In response to “How to go green by 2013” (October 2010, page 26):
The last page shows a cross section where a porous gutter collects and infiltrates water (see below image). We implemented a similar retrofit four years ago in an older, established neighborhood. The gutter plugs within a few weeks due to natural debris — blooms, seed pods, thatch, normal dirt, leaves. We expected the pervious surface to need cleaning once or twice a year, but to keep this system working requires more intensive efforts than that — which makes it unacceptable for future consideration.
Have you experienced a different result?
— Reid Wronski, PE, city engineer, City of River Falls, Wis.
Author Ted Blahnik, PE, of Williams Creek Consulting in Indianapolis, responds:
Regular street sweeping is necessary. Where there's an available storm sewer, we also install inlets for flood control in the event that the pervious concrete isn't adequately maintained and becomes clogged. Below are some additional considerations:
The pervious curb will clog without proper maintenance. The curb/ gutter provides pretreatment designed to capture solids prior to runoff entering the infiltration trench beneath the curb.Part of our pilot efforts is to project the type and frequency of maintenance needed. A June 2005 report conducted by Schilling Consultant Services for the Ramsey-Washington Metro Watershed District in North St. Paul, Minn., shows that maintenance costs per curb-mile range from $400/ year for quarterly vacuum sweeping to about $2,000/year for monthly mechanical sweeping. These are wide ranges that translate to about $2 to
For more information on street sweeping, click here.