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When wells are placed close to a surface water source (such as a lake or a river) and pumped, a portion of the surface water is induced to flow to the well. As the water travels from the river to the well through the riverbed sediments and underlying aquifer material, suspended and dissolved contaminants of surface water are “naturally” filtered out using a combination of physical, chemical, and biological processes. If the surface water is a river, the system is called riverbank filtration (RBF). If a lake serves as source water, the system is a lakebank filtration. These natural filtration systems have been operating for more than 100 years in Europe and for over half a century in the United States, providing safe drinking water to communities. For the RBF systems to work effectively, there must be a hydraulic connection between the river and the alluvial aquifer where the wells are located. Unclogged river bottoms are ideal for RBF operations. RBF systems are known to remove turbidity, microbes, and chemicals present in surface water and the removal efficiency is a function of well location, pumping rate, source water quality, etc. A fraction of dissolved organic carbon (DOC) is also removed which helps in reducing the formation potential of disinfection byproducts during chlorination of the filtrate from RBF systems. RBF systems can be adapted to a given site using engineering judgment. Use of inflatable dams to raise water levels in rivers in low-flow periods can augment well yields. Similarly, diverting a part of the water from the river to an infiltration basin and strategically placing wells between the river and the infiltration basin can enhance yield. Over the years, several improvements to the design and construction of the RBF systems have taken place. Use of these methods at future sites can improve the efficiency of RBF. Besides siting issues, periodic maintenance and early-warning systems to monitor river water quality are needed for sustainable operation of RBF systems. RBF has one of the best potentials to be used as a natural filtration system in populated riparian communities in developing countries. This chapter presents some of the advantages and limitations of using RBF for water treatment. Design, cost, maintenance, and future research needs are presented.

Water treatment technologies have evolved over the past few centuries to protect public health from pathogens and chemicals. As more than a billion people on this earth have no access to potable water that is free of pathogens, technologies that are cost effective and suitable for developing countries must be considered. Sustainable operation of these treatment processes taking into consideration locally available materials and ease of maintenance need to be considered. In this chapter, we consider natural filtration for communities of various sizes. In natural filtration, slow-sand filtration and riverbank filtration are considered. Slow-sand filtration is suitable for small to medium size communities, whereas riverbank filtration can be suitable for small to very large communities depending on site and river conditions. Membrane filtration is another technology that can have application to individual households to moderately large communities. Both pressurized and gravity-fed systems are considered. For the developing regions of the world, small membrane systems have most applications. Solar distillation is a low-cost technology for sunny regions of the world. Particularly, it has the most application in tropical and semitropical desert regions. It can use low quality brackish water or groundwater for producing potable water. These systems can solely operate with solar energy. The scale of application is for individual households to very small communities. Solar pasteurization, like solar distillation depends on solar energy for purifying small quantities of water for individual or family use. It is most suitable for remote, sunny, high mountain regions such as the Andean mountains, central Africa or the Upper Himalayas where electricity is not available. Also, reliance on firewood is not feasible due to barren landscape in many of these regions. Also, case studies of natural (riverbank and lakebank) filtration, membrane filtration, solar distillation, and solar pasteurization are presented.

Riverbank filtration (RBF) is a low-cost and efficient water treatment technology for the removal of many surface water pollutants. It is widely used by water utilities in developed as well as developing countries to produce drinking water from surface water which is often polluted. In this research, the presence of explosive chemicals in riverbed sediments or in flowing water is considered as a potential threat to the quality of filtrate produced from RBF systems. For this, degradation experiments were conducted to examine the persistence of these compounds in river sediments. In addition, a model RBF system was setup to examine the breakthrough of the major explosive chemicals and their metabolites. Results show that HMX was the most mobile and compound followed by RDX. TNT and DNT degraded quickly. Thus, the presence of RDX and HMX could produce breakthroughs in high capacity collector wells located along riverbanks.

A novel combination of riverbank filtration (RBF) and aquifer storage recovery (ASR) in the Albany region of Georgia (USA) was investigated in order to study possible changes in water quality. In areas where there are seasonal changes in water availability, seasonal excesses can be stored underground to meet shortterm demands. Using RBF as a source water, rather than obtaining water directly from the surface water, would reduce treatment costs. The RBF site taps the Flint River through the Upper Floridan Aquifer producing water that can be injected into the deeper Clayton Aquifer for storage and subsequent recovery. This study tests the conceptual framework of having such RBF and ASR schemes coupled together and, more importantly, looks at the hydrogeochemical changes that are likely to occur. It was seen, in the scenarios considered, through numerical modeling, that acceptable water can be obtained from such coupled systems. Injection of the RBF water in an aquifer with arseniferous pyrite did not mobilize any significant arsenics.

Riverbank filtration (RBF) is considered a “natural” filtration technique in which the bed and bank areas of a river serve as “treatment” zones for the river water. When wells are placed adjacent to a river and pumped, the treatment zones remove most surface water pollutants. This technology has been in operation for more than a century in Europe and for more than half a century in the United States. In many areas of the world, particularly in the populated regions of India and China, RBF has significant potential. Riverbank filtration can be used along perennial as well as ephemeral rivers in desert countries. However, studies are needed to evaluate the connectivity of the surface water and ground water, dynamic variation of the redox zone(s), flash flood impacts, and climate changes for the sustainable operation of RBF systems in desert environments.

Riverbank filtration is a low cost treatment technology which is effective in removing various chemical, and biological contaminants from the surface water. In the United States, utilities that employ horizontal collector wells, have reported clogging of the riverbed in vicinity of the wells, particularly around the laterals that go toward the river. In this paper, we show the impact of clogging and associated reduction in leakage on flow and transport simulations.

In Europe, riverbank filtration (RBF) has been the primary mode of drinking water production for many cities located along major rivers such as the Danube in Central Europe (from Austria to Black Sea), Rhine and Elbe in Germany, Lot and Seine in France, and Rhine in the Netherlands, as well as along rivers in Austria, Switzerland, Slovenia, and Spain. Many of these systems have been operating for well over a century. Lake bank filtration is also common in many European countries, including Finland, where wells are placed close to natural lakes or artificial reservoirs for drinking water production. In the United States, RBF systems are also used for drinking water production. They have been operating in many cities located along the Columbia, Missouri (including the sub-basins of Platte and North Platte), Mississippi (including the sub-basins of Des Moine, Minnesota, Cedar, and Illinois), Ohio (including the Wabash River basin), Colorado, Rio Grande, Russian, and Connecticut River basins for nearly half a century.

The NATO Advanced Research Workshop primarily focused on three issues: (a) hydrogeology and contaminant biogeochemistry issues for riverbank filtration, (b) removal of pathogens by riverbank filtration, and (c) national experiences in riverbank filtration. The following conclusions were drawn.

The variably-saturated flow equation (VSFE) is a special form of the well known Richards’ equation for unsaturated flow in which the elastic storage arguments are used to define the specific storativity (which is useful for saturated flow simulation). The Richards’ equation, under transient conditions, is highly nonlinear. Traditionally, numerical techniques have been used in solving this equation. The moisture-content form of Richards’ equation requires less computer time and is subject to low mass balance errors while simulating transient infiltration into very dry soils. However, this form of Richards’ equation is limited to complete unsaturated conditions and cannot handle positive pressure upper boundary or layered soil profiles. For this reason, while simulating water movement in variably saturated soils, the pressure-based form of Richards’ equation is used. The pressure-based form is prone to mass balance errors and requires large amounts of computer time due to the iterative nature of solution. A recently reported mixed form of Richards’ equation is used in this investigation for its mass conservative property. The computer time requirement for the mixed form Richards’ equation is similar to the pressure-based form. A series of numerical experiments were conducted using the VSFE which contained the mass-conservative form of the Richards’ equation. The Galerkin finite element technique was used to solve the equation numerically. The effects of the type of mass lumping (matrix diagonalization), initial and boundary conditions on the accuracy, stability, and the rate of convergence of this equation are presented. The influences of time varying top boundary conditions and layered heterogeneity on water movement are also presented. In addition,“tricks” for efficient time step control and steady-state simulation using this mass conservative formulation are shown. Finally, simulation results indicate that this mixed-form equation is superior to the pressure-based form.