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Stormwater Management

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file icon Real Life Solutions to SUDShot! 04/20/2005
Authors
Alex Stephenson
Abstract
A novel integrated system providing ‘hard’ or engineered solutions to SUDS, Source Control and Rainwater re-use is described. The system is made up of several facets; a stormwater storage element (Stormcell
file icon PROTOCOL FOR ASSESSING SEDIMENT RETENTION IN STORMWATER TREATMENT CHAMBERShot! 07/26/2006
Authors
Kwabena Osei, Robert Andoh and Lisa Glennon
Abstract
In approving stormwater BMPs, regulators usually review sediment removal data as the basis for their decisions. One factor that is usually overlooked is the ability of a treatment device to retain captured material in the event of high flow rates. Lately, some agencies are requiring vendors to indicate washout prevention of their stormwater treatment systems. However, no standard protocol exists that measures how much of previously captured pollutant is resuspended and carried downstream of the treatment device during high flows.

This paper discusses an effective test protocol for evaluating the sediment retention efficiency of proprietary stormwater treatment systems. The sump of a full-scale treatment device is filled with a known mass of sediment or sediment tracer. The unit is run at steady-state for a specified duration that exceeds several multiples of its effective detention time. Repeated tests are undertaken at different flow rates and the amount of material retained in the device for each flow rate is determined. The sediment retention efficiency is then calculated based on a comparison between mass of material retained in the sump after running flows through the unit and the original mass of material deposited in the sump.

Test data using this protocol for different device configurations are discussed and this highlights the importance of chamber geometry and hydrodynamic regime on the sediment retention efficacy of stormwater treatment devices.

file icon Characteristics of urban run-off derived sediments captured by stormwater interceptorshot! 03/16/2007
Authors
M.G. Faram, K.O. Iwugo and R.Y.G. Andoh
Abstract
Sediment entrained in urban run-off is acknowledged as being an important carrier of pollutants. The paper reports on the physical and chemical characteristics of sediments captured by six installations of a proprietary interceptor device. The sites, located in the United Kingdom and the Republic of Ireland, were selected to represent a range of urban contexts. Particle D50 values were found to range from 7 to 112 mm, corresponding with ranges reported for stormwater ponds. Heavy metal and hydrocarbon concentrations were also found to vary, with the highest corresponding to the most established and heavily trafficked sites. Further to confirming the ability of the interceptor to remove contaminated sediments, useful insights are provided into the interrelation between sediment characteristics and site conditions. Keywords Heavy metals; hydrodynamic vortex separators; polycyclic aromatic hydrocarbons (PAHs); stormwater sediment; urban run-off.
file icon Evaluation of different configurations of stormwater treatment chambershot! 07/28/2004
Authors
David A. Phipps, PhD, Rafid M. Alkhaddar, PhD, James Dodd, Michael G. Faram, PhD, Pamela J. Deahl, P.E.
Abstract
With the objective of reducing the polluting impact of urban run-off on receiving watercourses, various proprietary treatment technologies have evolved, including ‘flow-through’ devices that are designed to intercept and store pollutants such as sediments and floatables for later removal and safe disposal. Frequently, the performance of chambers is stated in terms of ‘ability to remove pollutants from the inflow’, often at discrete flowrates. However, a parameter that is often overlooked is chamber ‘retention efficiency’, the ability of chambers to retain stored pollutants once collected. The paper presents the findings of both simulation and experimental studies of different designs of treatment chamber, focussing in particular on the ‘retention efficiency’ parameter. It is concluded that chambers in which the pollutants storage region is isolated from the main treatment area are likely to be most effective.
file icon Pollutants Washout - The Missing Dimension in Urban Stormwater Treatmenthot! 05/16/2007
Authors
R.Y.G. Andoh1, R.M. Alkhaddar , M.G. Faram and P. Carroll
Abstract
Several configurations of proprietary ‘flow-through’ stormwater treatment devices have evolved to address the need for compact and effective systems that remove sediment and other pollutants from stormwater runoff. Whilst a number of these systems have been the subject of several field monitoring and independent laboratory studies, differences between design methodologies, unit sizes and capacity, test protocols and site conditions in the field have made direct comparisons of results very difficult. Most studies to date have focused mainly on the pollutant removal efficiency (effectiveness) of these systems.

Though removal efficiency is a good indicator of a devices’ effectiveness in terms of separating pollutants from stormwater, particularly under low flow conditions, it does not provide a complete description of device efficacy especially in terms of its ability to retain previously captured pollutants under moderate or high flows. The phenomenon of ‘Washout’ defined as the tendency to re-suspend (re-entrain) and discharge previously captured pollutants is of particular importance in practice as stormwater treatment devices are typically maintained on an infrequent basis.

The paper describes results of work undertaken at Liverpool (JM) University to determine sediment retention performance of different stormwater treatment chamber configurations under controlled laboratory conditions that provides a true comparative assessment using identical testing protocols and methodologies. General conclusions drawn from the results include the observation that the phenomenon of “pollutants washout” from stormwater treatment chambers is very real and must be taken into account in system selection for practical application. The rate of stored pollutants washout was found to be extremely sensitive to chamber design with re-suspension and washout rates ranging from close to zero to close to 100 percent depending on device configuration, nature and type of flow modifying components and whether or not sediments are stored in isolated storage zones.

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