NATO Advanced Research Workshop
Riverbank Filtration Hydrology: Impacts on System Capacity and Water Quality
Outline:
Background of Riverbank Filtration
General Approach of Conference
Proceedings Published by Springer in Cooperation with NATO Public Diplomacy Division.
Samorin-Cilistov (near Bratislava),Slovakia Republic
Workshop Objective: The objective of this workshop is:
• to bring together public water supply scientists actively working on the chemical, biological, and physical processes of riverbed clogging;
• to document current data on the impact of riverbed clogging on the quantity and quality of water supply produced from riverbank filtration systems; and
• to elucidate methods to quantify the riverbed clogging process through monitoring and modelling.
Steve Hubbs, Louisville Water Company (retired), 3715 Hughes Road, Louisville, Kentucky 40207 USA email: stevehubbs@bellsouth.net
Chittaranjan Ray, Assistant Professor Dept. of Civil & Env. Engineering, Univ. of Hawaii, 2540 Dole Street, Honolulu, HI 96822 USA e-mail: cray@hawaii.edu
Igor Mucha, Professor and President, Ground Water Consulting, Ltd., Koliskova 1, 84105 Bratislava 4, Slovak Republic, e-mail: imu@gwc.sk
Philippe Bavaye, Associate Professor, Cornell University, Ithaca, New York
Peter Engesgaard, Professor, University of Denmark, Copenhagen
Thomas, Grischek, Professor, University of Applied Sciences Dresden, Germany
Steve Hubbs, Vice President (retired) Louisville Water Company, Louisville, KY
Wolfgang Macheleidt, Specialist, University of Applied Sciences, Dresden
Jordi Martin, Hydrologist, Barcelona Waterworks
Igor Mucha, Prof. and President, Groundwater Consulting, Bratislava, Slovak Republic
Chittaranjan Ray, Associate Professor, University of Hawaii at Manoa
Dave Schafer, Consultant, Dave Schafer and Associates, USA
Jurgen Schubert, Engineer Emeritus, Dusseldorf Waterworks, Germany
Bernhard Wett, Professor, University of the Innsbruck, Austria
Background of Riverbank Filtration (RBF)
Riverbank filtration (RBF) is a process for producing drinking water. River water is induced to flow through riverbed soils to pumping wells located on the banks of the river. During the passage of this water through the riverbed and aquifer, dissolved and suspended contaminants as well as pathogens are removed due to a combination of physical, chemical, and biological processes. The concept of RBF began in 1870’s in Germany, and it is a common water production technology in Europe. In the industrial regions of Europe, RBF is used as a pre-treatment technology preceding more advanced treatment operations. In the United States, RBF systems have been operating for about half a century, and often provide the only treatment other than chlorination and fluoridation prior to consumption. According to a conservative estimate, potential exists for 67 million people to be served by riverbank filtration in the US. Increasing concern regarding the impact of surface water contamination is driving many utilities to seek a higher quality of source water, and many are investigating riverbank filtration.
While the filtrate from RBF systems is of higher quality than most source waters, the quantity and the quality of the filtrate can vary depending on the hydrogeologic setting, source water quality, and river dynamics. In addition, many streams are being modified by dams for navigation and power production, significantly altering the flow characteristics of the stream and the composition of the streambed, impacting the natural renewal process of bank filtration. As bank filtration systems are being designed and operated under more demanding conditions, clogging of the streambed can occur. This results in decreased aquifer yield and changes in water quality as the flowpaths to the well are altered. Understanding the causes of clogging in the riverbed is essential if RBF systems are to be effectively designed and managed as reliable water supplies.
This workshop will focus on the elements of streambed clogging, scouring, and the impact of these phenomena on long-term sustainable yield from bank filtration systems. The characteristics of both the stream and the adjacent aquifer will be considered in determining how to best design and operate bank filtration systems. Case studies from the United States and Europe will be presented.
This topic is timely as many cities are looking for low-cost solutions to source water contamination problems. The need for a better understanding of clogging in bank filtration systems was identified as one of the most complex issues of bank filtration at a previous NATO ARW at Tihany, Hungary in September 2001. Much work has been done on bank and riverbed clogging since that conference, and the benefit of this work will be brought to the participants of this workshop. In addition, this will serve as an avenue to exchange information between the European and American experts and the participants on the causes of clogging and the mechanisms to control/minimise clogging.
General Approach of the Conference
Much is known about the process of Riverbank Filtration as an effective mechanism for improving water quality. Likewise, the science of sediment transport in streams and riverbed scouring is well documented. However, the interaction between these riverbed dynamics and the impact on yield and water quality in RBF systems has yet to be adequately addressed. This conference will bring together experts in these two fields to advance the overall understanding of how Riverbank Filtration systems work, and how to better design and manage RBF systems.
It is generally understood that the clogging of riverbed material in the vicinity of a well reduces infiltration rates and decreases the production yield from the wellfield. When this occurs, streambed infiltration areas extend significantly away from the production center of the well. This causes the water to travel for a longer distance, thus allowing the water to undergo geochemical and biological reactions. Longer flow paths can lead to the depletion of oxygen and the development of anoxic conditions where the redox reactions favor denitrification. However, excessively longer flow paths and the associated redox reactions could result in increased manganese and iron concentrations, causing high costs in water treatment. The system can be driven into a sulphate reducing condition, thus producing unfavourable taste and odour.
Excessive riverbed scouring can result in the opposite of riverbed clogging, removing the biologically active surface layer responsible for much of the effectiveness of Riverbank Filtration systems. The biological active layer (“Schmutzdecke”) is a key element in the attenuation of contaminants at RBF sites. If this surface layer is removed during floods due to the higher shear stress, the risk of contaminants penetrating the aquifer is increased. To evaluate the risk of such events and to propose effective monitoring measures, it is necessary to understand how this protective layer is re-established following high flow events in streams.
The approach to this workshop will be to introduce the key aquifer and stream characteristics impacting yield and water quality of bank filtration systems, and to provide the framework for analysing these. Specific characteristics will include:
• shear stress imparted on the streambed during normal and high-flow events,
• analysis of streambed materials to evaluate streambed movement,
• specific capacity of the wellfield as a function of pumping rate, driving head, and stream/aquifer temperature,
• mechanical, chemical, and biological factors that impact riverbed clogging.
After these mechanisms are introduced and discussed, experience from field applications of RBF will be discussed in light of these mechanisms in an attempt to better understand how RBF systems can be better designed and managed for optimum production and water quality benefits.
These mechanisms will be further considered during a field trip to the RBF system in the Cunovo and Rusovce area south-east to Bratislava, Slovak Republic, where a newly built dam affected the flow regime of the River Danube and the production capacity of the RBF system in this area. The effectiveness of measures taken to manage clogging and infiltration to the RBF system following dam construction will be the focus of this field trip. Also, the changes in water quality with time will be discussed at this RBF site since the dam was built. This will provide valuable educational experience to scientists from the United States and many partner countries regarding the impact of changing river hydraulics on yields from RBF systems.
Some of the key questions to be addressed at the conclusion of this conference are:
• what are the magnitudes of the shear stress observed in free flowing and navigable rivers?
• what magnitude of the shear stress would be adequate to sustain capacity in a RBF system?
• What magnitude of shear stress is excessive, resulting in deteriorated water quality in RBF systems?
• what is the relationship between the shear stress and the bed material size when the bed materials begin to move?
• how would riverbed clogging affect the specific capacity of the wells?
• how would the driving heads and river water temperature affect the production rate of water?
• what are the dominant processes in riverbed clogging – physical, chemical or biological, and how are they measured?
• what are some of the mechanisms associated with clogging that affect the quality of the filtrate?
In addition, an objective of this workshop is to establish a framework for modelling for flow reduction and water quality variation from plugging in RBF systems.
The final product of this workshop - a book capturing the current state of knowledge on the above stream and aquifer characteristics and answers to the above questions - will provide a valuable source of information to hydrologists designing and managing RBF systems world-wide. This technology is applicable to major river systems such as the Danube, Rhine, Dnipro, Nile, Ohio, Mississippi, and Missouri, as well as many smaller river systems.
Signficance of Hydrologic Aspects on RBF Performance by JÜRGEN SCHUBERT
Evaluating Streambed Forces Impacting the Capacity of Riverbed Filtration Systems by STEPHEN A. HUBBS
Impact of Riverbed Clogging on Ground Water by IGOR MUCHA, ĽUBOMÍR BANSKÝ, ZOLTÁN HLAVATÝ, DALIBOR RODÁK
New Approaches for Estimating Streambed Infiltration Rates by W. MACHELEIDT, T. GRISCHEK, W. NESTLER
Bioclogging in Porous Media: Tracer Studies by PETER ENGESGAARD, DORTE SEIFERT, AND PAULO HERRERA
Riverbank Filtration in the Netherlands: Well Fields, Clogging and Geochemical Reactions by PIETER. J STUYFZAND , MARIA H.A. JUHÀSZ-HOLTERMAN & WILLEM J. DE LANGE
Clogging-Induced Flow and Chemical Transport Simulation in Riverbank Filtration Systems by CHITTARANJAN RAY AND HENNING PROMMER
Use of Aquifer Testing and Groundwater Modeling to Evaluate Aquifer/River Hydraulics at Louisville Water Company, Louisville, Kentucky, USA by DAVE C. SCHAFER
Changes in Riverbed Conductivity and Specific Capacity at Louisville by STEPHEN A. HUBBS
Experience with Riverbed Clogging Along the Rhine River by JÜRGEN SCHUBERT
Heat as a Groundwater Tracer at the Russian River RBF Facility, Sonoma California by J CONSTANTZ, GRACE SU, AND CHRISTINE HATCH
Monitoring clogging after start-up of a RBF-system at the River Enns, Austria by B. WETT
Managing Resources in a European Semi-Arid Environment: Combined use of Surfance and Groundwater for Drinking Water Production in the Barcelona Metropolitan Area by JORDI MARTÍN-ALONSO
Presentation of Data for Factors Signficant to the Yield from Several Riverbank Filtration systems in the U.S. and Europe by TIFFANY G. CALDWELL
