August 2012, Vol. 24, No.8

Has it been 100 years already?

Why rare storms occur so frequently and what to do about it

Feature 1 art.jpg William S. Gonwa

Many people wonder why their cities have experienced so many X-year (fill in the blank for X) recurrence-interval storms recently. The public has a hard time believing authorities when they report the third 10-year recurrence-interval storm in 7 years. In fact, sometimes, the authorities don’t understand it themselves.

Do the statistics experts who develop precipitation frequency estimates really know what they are talking about? It turns out that, yes, they do.

Three potential reasons exist for this perceived higher-than expected frequency of rare storms. Numerical testing shows a 71% to 700% increase in the perceived frequency of rare storms attributed to these reasons. Read full article (login required) 


Making stormwater retrofits pay

Creating a market for stormwater retrofits to harness self-interest, leverage river protections, and promote sustainable development in the District of Columbia

Feature 4 art.jpg Brian Van Wye

In a highly urban area such as Washington, D.C., vast impervious surfaces shed massive volumes of stormwater every time it rains. Stormwater retrofits that retain stormwater onsite have the potential to make D.C. “spongier,” that is, more closely mimicking a natural area where rainfall is captured by vegetation and soaks into the ground. However, getting retrofits installed to serve the 43% of D.C.’s land area that is impervious is a difficult challenge. The majority of this impervious surface achieves little or no retention, is not required to retrofit, and does not have financing available to support a retrofit.

Against this backdrop, the D.C. Department of the Environment (DDOE) drafted revised stormwater management regulations with a new requirement for regulated development projects. DDOE also saw the potential for a win–win between regulated projects and the vast areas of D.C. that need stormwater retrofits and soon embraced two key ideas: allowing regulated projects to achieve a portion of their obligation offsite makes fiscal and environmental sense and a private market that pays dividends to property owners for retrofits may optimize these benefits and yield additional ones. Read full article (open access) 


Tracking bacteria to find pollution sources

An integrated watershed approach to improve water quality 

Feature 6 art.jpg Ting Lu, David Wendell, Donald Linn, Biju George, MaryLynn Lodor, and James Parrott

The Metropolitan Sewer District of Greater Cincinnati (MSD) operates and maintains a collection system of more than 4828 km (3000 mi) of pipe covering an area of more than 1036 km2 (400 mi2). Wet weather flows cause about 53.4 million m3 (14.1 billion gal) of combined wastewater to overflow into local waters each year.

Within these overflows, fecal microorganisms are a major source of surface water pollution. In fact, water quality evaluations conducted between 1999 and 2004 for Hamilton County — one area served by MSD — show that fecal bacteria are the sole pollutant of concern during both dry and wet weather.

But measuring only the concentration of fecal bacteria sheds no light on where the pollution originates. To help solve that problem, MSD, in conjunction with the University of Cincinnati, is conducting a watershed-scale biomonitoring assessment project that includes state-of-the-art microbial source tracking (MST).

This research fits within MSD’s integrated watershed approach to improve water quality. The data collected by more incisive testing will help identify the source of the fecal bacteria and guide the development of more targeted combined sewer overflow fixes. Read full article (login required) 


Evolving reclamation

40 years of innovation in total reuse in the Fountain Hills, Ariz., Sanitary District

Feature 7 art.jpg Doug Kobrick and Ron Huber
The Fountain Hills (Ariz.) Sanitary District provides wastewater services to Fountain Hills, a community northeast of Phoenix with approximately 23,000 residents. Because there is no access to a regional wastewater system or to natural water sources for discharge, total reuse of reclaimed water, or zero discharge, has been necessary in Fountain Hills since the community was founded in the 1970s. The district’s current reclaimed-water system includes an advanced water treatment facility (AWTF) that performs microfiltration, several aquifer storage and recovery wells, and a distribution system that serves golf courses and parks. Expanding this system to meet the community’s needs as it has grown has been the result of persistence and prudent innovation on the district’s part. During the past decade, more than 19 billion L (5 billion gal) of water have been reused via the Fountain Hills system. Read full article (login required) 


Operations Forum Features

Getting more out of the same old pipes

The South Bend, Ind., combined sewer overflow regulator automation program

Feature 3 art.jpg Timothy Ruggaber, Patrick Henthorn, and Richard Radcliff

The City of South Bend, Ind., is implementing a real-time control system to better use the city’s existing conveyance and treatment capacities. The city has automated nine of its combined sewer overflow (CSO) regulators. This change will enable the collection system to self-adapt to the inherent variability of rainfall.

The result is that flow that normally would have overflowed now is captured and treated at the wastewater treatment plant (WWTP). The city completed several successful test exercises during actual storms in 2011 and implemented full automation in spring 2012. These control sites will reduce the city’s annual overflow volume by more than 800 million L (215 million gal), or 23%, simply by using existing pipes better. Read full article (login required) 


Intelligent real-time solutions for stormwater management

The key to navigating shifting weather trends

Feature 2 art.jpg Carmen De Miguel and Jim Foerster

The increasing intensity and frequency of rainfall patterns, combined with increasingly violent storms, are prompting public works officials to take stock of their stormwater management systems and revise long-term strategies.

While each municipality, region, or district must determine its own strategy to mitigate street flooding, optimize wastewater treatment plant operations, and reduce combined sewer overflows (CSOs) based on its unique infrastructure and topography, the execution of each strategy depends on a common principle: a capable, state-of-the-art monitoring system that provides instant access to critical information. Read full article (login required) 


Achieving ultralow phosphorus concentrations

Coeur d’Alene, Idaho, tests a tertiary membrane filter demonstration pilot system

Feature 5 art.jpg Karen Bill, Mario Benisch, Haley Falconer, Marie-Laure Pellegrin, H. Sid Fredrickson, Casey Fisher, Ben Carleton, JB Neethling, and David Clark

The City of Coeur d’Alene (Idaho) Wastewater Treatment Plant (WWTP) may be required to treat its wastewater to a seasonal 0.050 mg/L total phosphorus (TP) effluent limit under a future National Pollutant Discharge Elimination System permit. To determine the most satisfactory technology for the job, the city conducted two pilot programs that ultimately identified a tertiary membrane filter (TMF) system as a reliable technology for reaching the anticipated permit limit.

Success in a small-scale pilot program under controlled conditions promoted a larger-scale 2-year demonstration under real-world conditions, including variable flow rates, plant staff operation, automated controls, and on-line measurements. Read full article (login required) 


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