1

1.1 RBF Process Description

In principle, RBF occurs when a well is placed sufficiently close to a river and part of the

surface water is induced to flow underground towards the cone of depressions caused by the

pumping well (see Figure 1-1). During ground passage, the water quality parameters change

due to microbial and physical- chemical processes (Partinoudi, 2004). After river water

infiltration is intercepted by collection wells, the riverbank filtrate requires additional

treatment steps before it can be pumped to the distribution system.

Figure 1-1 Generalized schematic of an RBF system. Source: Ray et al., 2002.

According to Heij (1989) most contaminants are degraded within the first few centimeters of

their path through the subsoil, but others are persistent and mobile and may move over longer

distances within the aquifer. Generally, two major areas during subsurface passage can be

designated:

a biologically high-active infiltration and clogging zone, where intensive degrading

and sorption processes take place

the successive subsurface passage, with lower degrading and sorption rates and an

increasing impact of dilution processes

The first part of the flow-course within the subsoil passage is the so called clogging zone - a

thin layer at the interface between river water and riverbed characterized by intensive physical,

2

chemical, and biochemical processes. Analyses have shown that an immense part of the

cleaning capacity taks place here (Grischek, 2003).

Clogging leads to the reduction of the permeability, and thus a decrease in the infiltration rate

(Grabs, 1981).

Permeability can be increased again by the self-cleaning power of the river itself. The self-

cleaning capacity of a river depends chiefly on the runoff regime, characterized by amount,

frequency, length, time and rate of change of runoff conditions (Schubert, 2007).

After passing the biologically high-active infiltration zone, surface water mixes with adjacent

groundwater. Dilution with groundwater improves the infiltrated surface water quality

because groundwater is usually a source of higher quality. In addition, dilution compensates

for temperature peaks and provides protection against shock loads (Kuehn and Mueller, 2000).

In most cases there is a flow of oxygen-rich surface water into the subsurface environment,

but it is common for dissolved oxygen to be completely used up by aerobic microorganisms at

some distance from the infiltration zone (Partinoudi, 2004).

Without oxygen, a change from oxidizing to reducing conditions can favor the effect of

heavy-metal remobilization of metals such as iron and manganese (Grischek, 2003). On the

other hand, anoxic conditions (no dissolved oxygen) help in the removal of river water nitrate

through anaerobic microorganisms.

After subsoil passage, the mixture of both groundwater and infiltrated surface water is

intercepted by collection wells. The collection wells can employ horizontal laterals or be

vertical wells. The laterals may or may not extend under the riverbed, depending on pumping

needs, the available budget of the utility and local geohydrological conditions (Partinoudi,

2004). [See section 3.3 for more on wells.]

After extraction, bank filtrate is usually treated depending on the bank filtrate quality,

whereby the quality determines the additional treatment steps required in order to produce

good-quality drinking water (Kühn, 1999).

At a minimum, RBF acts as a pre-treatment step in drinking water production and, in some

cases, can serve as the final treatment just before disinfection (Bourg et al., 2002).

3

1.2 Applicable Regulations

In order to understand the rising interest in design and construction of RBF, it is necessary to

get an insight into the log removal credit system and recent development of regulations in the

United States as the level of treatment and monitoring efforts are highly correlated with

legislative requirements.

This section provides an introduction into the log removal credit system of the United States

and an brief review of Environmental Protection Agency (EPA) regulations with particular

emphasis to the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR).

Furthermore, the Microbial Toolbox, as a means to comply with governmental requirements,

is presented.

Introduction to the Log Removal Credit System

“Log removal” is a shorthand term for log10 removal, which refers to the physical and

chemical treatment of water to remove, inactivate, or kill pathogenic organisms such as

Giardia lamblia, Cryptosporidium parvum, and viruses (Ray et al., 2002). The equation of log

removals plays out as follows:

1- log removal equals a 90-percent

2- log removal equals a 99-percent

3- log removal equals a 99.9 percent

4- log removal equals a 99.99 percent target level of reduction, and so on.

Log removal credit is a regulatory term that expresses the amount of pathogens that a water

utility has removed from its water using technologies such as slow sand filtration, RBF and

other conventional types of treatment. Water utilities that employ RBF may receive 1-log

removal credit. This means that the RBF process has removed 90 percent of the initial

concentration of pathogens. However, if the target removal is 99.9 percent (3-logs), the utility

must remove an additional 2 logs using conventional filtration or other alternative techniques.

According to United States law, the granting of log removal credit is, in general, negotiated

between the water utility and primacy agency responsible for enforcing regulations (Ray et al.,

2002).

4

EPA Regulations

The United States Environmental Protection Agency (EPA) Office of Ground Water and

Drinking Water (OGWDW) develops potable water regulations to control microbial

pathogens and disinfectants/disinfection byproducts in drinking water (USEPA, 2005).

A short summary of current drinking water rules is given in table 1-6 (sorted by year of issue).

Basic information and compliance tips for each regulation are located at:

http://www.epa.gov/safewater/regs.html

Table 1-6 Current drinking water rules (by date issued). Source: US EPA Website -

http://www.epa.gov/safewater/regs.html.

Chemical Phase (Chemical Contaminant)

Rules (2006)

Ground Water Rule (2006)

Stage 2 Disinfectants and Disinfection

Byproducts Rule (2006)

Long Term 2 Enhanced Surface Water

Treatment Rule- LT2ESWTR (2006)

Long Term 1 Enhanced Surface Water

Treatment Rule- LT1ESWTR (2002)

Filter Backwash Recycling Rule (2001)

Arsenic Rule (2001)

Unregulated Contaminant Monitoring

List 2 Rule (2001)

Radionuclides Rule (2000)

Drinking Water State Revolving Fund

Rule (2000)

Removal of the MCLG for Chloroform

(2000)

Public Notification Rule (2000)

Revisions to the Unregulated

Contaminant Monitoring Rule (1999)

Interim Enhanced Surface Water

Treatment Rule- IESWTR (1998)

Stage 1 Disinfectants and Disinfection

Byproducts Rule (1998)

Consumer Confidence Report Rule

(1998)

Variances and Exemptions Rule (1998)

Drinking Water Contaminant Candidate

List (1998)

Small System Compliance Technology

List for the Surface Water Treatment

Rule (1997)

Information Collection Rule (1996)

Surface Water Treatment Rule – SWTR

(1989)

Surface Water Treatment Rule (SWTR)

The SWTR became law in 1989 and established a maximum contaminant level goals (MCL)

of zero for Giardia lamblia, viruses, and Legionella, as well as set filtration and disinfection

requirements for all public water systems using either surface water sources or groundwater

sources under the direct influence of surface water. Both, surface water or GWUDISW, are

considered to be vulnerable to microbial contamination.

According to Ray et al. (2002) the SWTR makes the following distinctions amongst drinking

water sources in the United States:

- 5 -

Groundwater: Subsurface water contained in porous rock strata and/or soil that is not

affected by recently infiltrated surface water.

Groundwater Under the Direct Influence of Surface Water (GWUDISW): Water

beneath the surface of the ground that has a significant occurrence of insects or other

microorganisms, algae, organic debris, large-diameter pathogens like Giardia lambia,

or significant and relatively rapid shifts in water characteristics – such as turbidity,

temperature, conductivity, or pH – that closely correlate with meteorological or

surface water conditions (USEPA, 2004).

Surface Water: Water from sources open to the atmosphere, such as lakes, reservoirs,

rivers, and streams.

There are several methods to determine whether a well is categorized as groundwater or

GWUDISW (Partinoudi, 2009):

Hydrogeologic investigation

Water quality monitoring (WQM)

Microscopic Particulate Analysis (MPA)

If either the WQM method or a hydrogeologic investigation indicate a hydraulic connection to

nearby surface water, the water source is designated as a groundwater in hydraulic connection

with surface water, but not all wells that are hydraulically connected are automatically

categorized as GWUDISW (Ray et al, 2002a). Typically, further investigations like MPA are

required (Partinoudi, 2009).

MPA is often used as a method to provide evidence of a hydraulic connection between the

surface and groundwater (Ray et al, 2002a). Water facilities need to collect 3 E. coli samples

in a period of 3 months. If the well produces E. coli–free water within this timeframe and the

well production depth is over 50 feet deep, then the water is not classified as GWUDISW.

If E. coli bacteria are found, the water is characterized as GWUDISW (Partinoudi, 2009).

The SWTR covers surface water systems and those that are classified as GWUDISW, while

the Ground Water Rule applies to wells determined to contain groundwater only.

The Interim Enhanced Surface Water Treatment Rule (IESWTR)

- 6 -

The IESWTR builds on the SWTR and requires tighter turbidity standards for systems that

serve more than 10,000 people. In addition, the IESWTR requires unfiltered systems to

include source water monitoring of Cryptosporidium in their watershed control plans (USEPA,

2007).

The Long Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR)

The LT1ESWTR addresses the concerns covered by the IESWTR as they apply to small

systems (i.e. systems serving fewer than 10,000 people) using surface water or GWUDISW

(USEPA, 2002).

Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR)

The LT2ESWTR builds upon the requirements established by the SWTR, IESWTR, and the

LT1ESWTR. The EPA finalized the LT2ESWTR in the Federal Register on January 5, 2006.

At present, it poses the most important drinking water regulation in the United States.

The EPA believes that implementation of the LT2ESWTR will significantly reduce levels of

Cryptosporidium and improve protection from exposure to other microbial pathogens such as

Giardia lamblia (USEPA, 2007). The LT2ESWTR is being promulgated simultaneously with

the Stage 2 Disinfection Byproduct Rule to address concerns about risk tradeoffs between

pathogens and DBPs.

The following requirements apply to all public water systems that use surface water or

GWUDISW (USEPA, 2005a):

Monitoring:

Under the LT2ESWTR, systems must monitor their water sources to determine treatment

requirements. This monitoring includes an initial two years of monthly sampling for

Cryptosporidium. To reduce monitoring costs, small filtered water systems can first monitor

for E. coli, and be required to monitor for Cryptosporidium only if their E. coli results exceed

specified concentration levels. Systems must conduct a second round of monitoring six years

after completing the initial round to determine if source water conditions have changed

significantly. Systems may use previously collected data in lieu of conducting new monitoring,

and systems are not required to monitor if they provide the maximum level of treatment

required under the rule.

Cryptosporidium parvum treatment:

- 7 -

Filtered water systems will be classified in one of four treatment categories (bins) based on

their monitoring results – see Table 1-7. Systems classified in the lowest treatment bin carry

no additional treatment requirements. Systems classified in higher treatment bins must

provide 90 to 99.7 percent (1.0 to 2.5-log) additional treatment for Cryptosporidium. All

unfiltered water systems must provide at least 99 or 99.9 percent (2 or 3-log) inactivation of

Cryptosporidium, depending on the results of their monitoring.

Table 1-7 Treatment levels in RBF classification. Source: Partinoudi, 2003, 4.

Other requirements:

Systems that store treated water in open reservoirs must either cover the reservoir or treat the

reservoir discharge to provide 4-log virus, 3-log Giardia lamblia, and 2-log Cryptosporidium

parvum inactivation. Furthermore, systems must review their current level of microbial

treatment before making a significant change in their disinfection practice.

- 8 -

The following sources of information and guidance documents are available to help you meet

the LT2ESWTR requirements (USEPA, 2009a):

Table 1-8 Information and Guidance to meet LT2ESWTR requirements. Source: US EPA, 2009a, 30 ff.

EPA guidance manuals located at:

http://www.epa.gov/safewater/regs.

html

EPA Safe Drinking Water Hotline

at (800) 426-4791 (e-mail: hotline-

sdwa@epa.gov)

State drinking water agencies

National Rural Water Association

American Water Works

Association

Source Water Monitoring Guidance

Microbial Laboratory Guidance

Small Entity Compliance Guidance

Microbial Toolbox Guidance

Manual

Ultraviolet Disinfection Guidance

Manual

Membrane Filtration Guidance

Manual

Simultaneous Compliance

Guidance Manual

Low-pressure Membrane Filtration

for Pathogen Removal: Application,

Implementation, and Regulatory

Issues

- 9 -

The LT2ESWTR is the first regulation in the USA that specifically recognizes RBF as a

compliance technology option and includes provisions by which RBF could be used as one of

the compliance options for providing Cryptosporidium removal credits. It provides a natural

technology that will help many water treatment utilities to meet the stringent requirements of

the Stage 2 DBP and LT2ESWTR, and explains the recent, heightened interest in the design

and construction of RBF facilities (Partinoudi, 2004).

Microbial Toolbox

All surface water utilities in the United States are required to comply with specific

Cryptosporidium removal targets in the LT2ESWTR. The “microbial toolbox” is intended to

provide utilities with a wide range of treatment options for meeting LT2ESWTR compliance

requirements (Brown, 2003). The toolbox offers log-removal credits for Cryptosporidium for

various technologies, including riverbank filtration.

Most of the toolbox components require compliance with design and/or required

implementation criteria to receive credit (USEPA, 2007).

The following requirements must be met in order to receive log-removal credit for RBF

(Regli, 2003):

Design Criteria:

25 foot distance between river and well receives 0.5 log credit

50 foot distance between river and well receives 1 log credit

Only vertical and horizontal wells are eligible for removal credit

Only wells in granular aquifers - comprised of sand, clay, silt, rock fragments,

pebbles, or larger particles and minor cement, are eligible for removal credit

- 10 -

Demonstration of aquifer characterization:

Sieve analysis of relatively undisturbed core samples from surface to depth > to

bottom of well screen

each recovered cored interval must be < 2 feet

at least 90% of the cored intervals must contain > 10 % fine grain material (grains

< 1.0 mm diameter)

Turbidity Criteria:

Turbidity monitoring for each well at least every 4 hours during operation

Average annual turbidity values (based on daily maximum values) should be less

than 1 NTU

In other European countries, for example Germany, no guidelines or handbooks are available

on where and how to install RBF systems; however, RBF, as an engineering technique, is

widespread throughout Europe and the design and construction are based upon personal

experience (Grischek et al., 2003).

Table 1-9 is a compilation of selected hydrogeologic information for RBF sites in the

United States and in Germany. As can be seen, the conditions vary mainly for capacity,

travel time, and distance between the river and the wells. At most sites in Europe, the distance

between the riverbank and production wells is >50 m and travel times are >50 days. In the

United States, travel times are <50 days and the distance between river and production well is

generally lower.

Table 1-9 Selected Site Data for RBF Systems in the United Sates and Germany. Source: Grischek et al., 2003,

293.

- 11 -

Systems can implement a variety of source, pre-filtration, treatment, additional filtration, and

inactivation toolbox components to receive Cryptosporidium credit, as summarized in Table

1-9 (USEPA, 2007).

Table 1-9 Microbial Toolbox Summary Table: Options, Treatment Credits and Criteria. Source: US EPA, 2007,

77.

- 12 -

Since 2007, an updated Web tool is available to the public and can be found at:

http://www.waterresearchfoundation.org/research/TopicsAndProjects/Resources/webTools/L

T2ESWTR_Index/index.aspx.

This web based microbial toolbox can help utilities determine which treatment is most

suitable for their water treatment plant. Based on the information entered, the program selects

the treatment options suitable to the treatment facility from a broad range of both new and

established technologies and programs. The Toolbox, which was developed by Environmental

Engineering and Technology Inc. as part of a Water Research Foundation project, features

help screens, cost estimates, and other information to evaluate whether selected items are

applicable for a particular site.

1.3 Source Water Quality Concerns

One of the main aims of a RBF system is to improve source water quality by removing a

variety of physical, chemical and microbiological pollutants. Understanding contaminants

present in the source water is essential for regulation, design and operation issues. This

section provides information pertaining to these applicable contaminants and substances that

cause the greatest water quality concerns to the water industry.

- 13 -

Physical Contaminants

Temperature and turbidity are the physical contaminants of the greatest concern (Ray et al.,

2002) as high temperatures favor regrowth of bacteria in distribution systems, while high

turbidity can negatively impact source water quality.

Temperature

Temperature influences chemical reactions during disinfection (e.g. ozonation).

RBF extraction wells, water is typically at a low and constant temperature.

In addition, the solubility of oxygen also depends on temperature. Water with a high

temperature allows for less oxygen to be dissolved and can cause problems for aquatic species

in surface waters.

According to a 2-year monitoring effort (Wang, 2002) of the temperature of the Ohio River in

Louisville, Kentucky, temperature ranged from a low of 2°C to as high as 32°C, while the

temperature of the collector well, which is located 30.5 m away from the river, remained

relatively unchanged between 15 and 25°C due to the flow through the aquifer and dilution

with groundwater whose temperature ranges around 10°C.

Turbidity

Turbidity is a measure of the cloudiness of water- the cloudier the water, the greater the

turbidity. It is used to indicate water quality and filtration effectiveness (USEPA, 2009b).

Source-water can contain suspended solid matter consisting of particles of many different

sizes. While some suspended material will be large, and heavy enough to settle rapidly (the

settable solids), very small particles will settle only very slowly or not at all (the colloidal

particles). These small solid particles cause the liquid to appear turbid.

Turbidity can fluctuate significantly and is a concern for rivers that traverse through clay-rich

formations (Ray et al., 2002) where the river water becomes loaded with colloidal and

suspended particles such as clay, metal- hydroxo- compounds from e.g. Fn2+

/ Mn2+

.

Another type of particles and source of turbidity are algae and detritus (dead organic material).

The algae grow in the water and the detritus comes from dead algae, higher plants,

zooplankton, bacteria, fungi, etc. produced within the water, and from watershed vegetation

washed in to the water (WOW, 2008).

- 14 -

A variety of negative effects can be listed (Uhl, 2007):

sorption of harmful substances (e.g. hydrocarbons and microorganisms)

corrosion in the distribution system as a result of depositions

favouring transport of microorganisms

aesthetic concerns

may favour formation of disinfection by-products (DBPs) during water treatment

Chemical Contaminants

According to Ray et al. (2002) chemical contaminants can be divided into four major groups:

pH

Inorganics

Synthetic organic compounds (SOCs)

Natural organic matter (NOM)

Pharmaceuticals and personal care products (PPCPs)

Dissolved oxygen

pH

The pH of river water is the measure of how acidic or basic the water is on a scale of 0-14. A

pH of 7 is neutral, below 7 is acidic, and above 7 is basic or alkaline. Acid rain, from auto

exhaust or coal-fired power plants, causes a drop in the pH of water. Pollution from accidental

spills, agricultural runoff and sewer overflows can also change the pH. Buffering capacity is

water's ability to resist changes in pH.

The optimum pH for river water is around 7.4. Extremes in pH can make a river inhospitable

to life. Acidic water speeds the leaching of heavy metals.

Inorganics

Water Hardness originates from the dissolution of minerals containing chemical compounds

such as calcium (Ca2+

) and magnesium (Mg2+

), which are found in regions where sandstone

and limestone are dominant. The level of (Ca2+

) and (Mg2+

) determine the level hardness of

river water and groundwater. Hardness removal is a significant treatment process as hard

- 15 -

water can cause operation calcinations on both the distribution system and domestic

appliances such as showerheads, faucets, etc. Hardness can be reduced during peak flow

periods when the contribution from groundwater is low (Ray et al., 2002).

Bromide in high concentrations in bank filtrate can lead to the formation of bromate during

disinfection with ozone. Bromate is carcinogenic so the addition of ozone is limited by the

concentration of bromide in the source water (Ray et al., 2002).

Nitrogen and other forms of fertilizers do not occur naturally. Substances as ammonium

(NH4+), nitrate (NO3-) or nitrite (NO2-) run in rivers because of the sewage addition or by

traversing agricultural watersheds during flood periods. Rivers can receive large amounts of

these substances seasonaly (Ray et al., 2002).

Iron and Manganese Iron are two of the most abundant elements in earth`s crust and are the

two heavy metals of most significance for the water industry.

Although iron (Fe) and manganese (Mn) are not directly health threatening, they may cause

negative aesthetic effects (such as taste, odor, or color) in drinking water.

According to Schmidt et al. (2003), heavy metals can be removed by subsoil filtration for a

long time and they cannot be easily remobilized with one exception: if conditions in the

aquifer become anaerobic (no oxygen), iron and manganese undergo chemical

reduction and appear in the water, necessitating their elimination by additional treatment.

Synthetic Organic Compounds

Synthetic organic compounds, including pesticides and herbicides, are of great concern in

surface water treatment and often coincide with flow peaks. Rivers that run through

agricultural areas receive large loads of pesticides, especially during spring runoff (Ray et al.,

2002).

Ray et al. (1998) reported concentrations of atrazine, the most heavily used herbicide in the

United States used for control of broadleaf and grassy weeds in corn and soybeans (USEPA,

- 16 -

2009), as high as 12 μg/l in the Illinois River. This concentration is much higher than the

maximum contaminant level (MCL) of atrazine of 3 μg/l required by the EPA.

A wide range of synthetic contaminants, including pesticides, and herbicides, are listed in

table 1-1. Consumer and technical fact sheets of each of these substances are posted by the

USEPA at http://www.epa.gov/ogwdw000/hfacts.html.

Table 1-1 Synthetic organic Contaminants, including pesticides & herbicides. Source: US EPA Website -

http://www.epa.gov/ogwdw000/hfacts.html.

2,4,5 - TP (Silvex)

Adipate

Alachlor

Aldicarb/Aldicarb Metabolites

Atrazine

Benzo(a)pyrene

Carbofuran

Dalapon

Dibromochloropropane

Dinoseb

Dioxin(2,3,7,8-TCDD)

Diquat Simazine

Endothall

Endrin

Ethylene Dibromide

Glyphosate

Heptachlor/Heptachlor Epoxide

Hexachlorobenzene

Hexachlorocyclopentadiene

LindaneChlordane

Methoxychlor2,4 – D

Oxamyl (Vydate)

Pentachlorophenol

Phthalate, di(2-ethylhexyl)

Picloram

Polychlorinated Biphenyls

Toxaphene

Natural Organic Matter

NOM is a collective term assigned to all broken down organic matter that comes from plants

and animals in the environment. The concentration of NOM in source waters is directly

related to the concentration of disinfection by-products (DBPs) in treated waters, such as

trihalomethanes (THMs) and haloacetic acids (HAAs), all of which are potentially

carcinogenic (Vogt et al., 2003). DBPs form when organic and mineral materials in water

- 17 -

react with chemical treatment agents during disinfection. Therefore, NOM in surface water is

a major concern for utilities that use chlorine as the disinfectant and it can be challenging to

reduce NOM prior to disinfection.

The following parameters are typically used as indicators of NOM in surface water (Ray et al.

2002):

Total organic carbon (TOC)

Dissolved organic carbon (DOC)

Biodegradable organic carbons (BDOC)/ Assimilable organic carbon (AOC)

Specific ultraviolet absorption (SUVA)

Ultraviolet absorbance of water at 254 nanometer (UV254)

DOC is responsible for the majority of reactions of interest in drinking water treatment, e.g.

disinfectant demand, DBP formation, biogrowth and coagulant demand (Drewes and

Summers, 2002). Monitoring efforts in Germany report a mean DOC level of 3mg/l at the

Rhine River, 5.5 mg/l at the Elbe River and 6-8 mg/l at Lake Tegel. These higher levels of

DOC at Lake Tegel are partly due to the discharge of sewage from wastewater treatment

plants (Ray et al., 2002).

Pharmaceuticals and Personal Care Products (PPCPs)

PPCPs is an umbrella term for thousands of chemical substances, including prescription and

over-the-counter therapeutic drugs, veterinary drugs, fragrances, and cosmetics. These

compounds are considered micropollutants because they are detected at very low levels, e.g.

nanogram-per-liter (Ray et al., 2002). Many of these products are found in domestic sewage

and ultimately end up in rivers. Some pharmaceuticals and personal care products are

suspected of causing direct endocrine disruption. They have potentially adverse effects in

natural ecosystems, such as causing abnormal physiological processes and reproductive

impairments of aquatic species (Kolpin et al., 2002).

Analytical determination of pharmaceuticals and personal care products in rivers, lakes and

other water sources is difficult due to the fact that many of these compounds are found in

extremely low concentrations and complex instrumentation is required. As a result, there is

very little data on the concentration of these compounds in surface waters within the United

States (Ray et al., 2002).

- 18 -

Representative classes and members of pharmaceuticals and personal care products can be

found in a presentation by Christin G. Daughton located at: http://www.epa.gov/ppcp/. A

summary of these chemical substances is presented in Table 1-2.

Table 1-2 Selected classes and members of Pharmaceuticals and Personal Care Products found in

environmental samples. Source: Ray et al., 20002, 9.

Dissolved Oxygen

Dissolved oxygen (DO) is found in microscopic bubbles of oxygen that are mixed in the water.

DO is an important indicator of a water body's ability to support aquatic life.

Oxygen enters the water by absorption directly from the atmosphere or by aquatic plant and

algae photosynthesis. Oxygen is removed from the water by respiration and decomposition of

organic matter.

In fast-moving streams streams, if unpolluted, are usually saturated with oxygen due rushing

water is aerated by bubbles as it churns over rocks and falls down. In slow, stagnant waters,

oxygen only enters the top layer of water, and deeper water is often low in DO concentration

due to decomposition of organic matter by bacteria that live on or near the bottom of the

riverbed (BASIN, 2007).

The colder the water, the more oxygen can be dissolved in the water. As a result, DO

concentrations at one location are usually higher in the winter than in the summer.

- 19 -

A lack of oxygen during underground passage due to biological activity in or on the riverbed

can lead to anaerobic conditions over a portion of the flow path, which may result the release

of heavy-metals such as iron and manganese from the bank sediment into the flowing water.

Microbiological Contaminants

According to the AWWA Manual of Water Supply Practices M 48 (2006), biological

contaminants in surface water include protozoa, bacteria, and viruses. These waterborne

pathogens can cause life-threatening disease in the immuno-suppressed populations of the

world and illness in the general population. This section includes information about biological

contaminants and highlights the applicable pathogenic species which can cause major

problems for the water industry.

Protozoa

Waterborne parasites, including various kinds of worms and protozoa, are indicators of fecal

contamination as well as the leading sources of those disease acquired through fecal

contaminants in food and/or drinking water. The protozoa comprise a large group of

extremely diverse unicellular organisms and are described in table 1-3 (AWWA, 2006).

Table 1-3 Parasitic pathogenic agents. Source: AWWA, 2006, 162.

- 20 -

Of particular concern are Cryptosporidium parvum and Giardia lamblia which are known to

be extremely resistant to conventional means of disinfection. Under the Long Term 2

Enhanced Surface Water Treatment Rule (LT2ESWTR), utilities are allowed to choose from a

“toolbox” of technologies in addition to existing treatment to comply with log treatment

requirements for Cryptosporidium. At present, bank filtration, is given the potential log credit

of 0.5 for a well setback distance of 25 ft and 1.0 for a well setback distance of 50 ft.

Further information on the LT2ESWTR, the log removal credit system and the microbial

toolbox, see section 1.3.

Cryptosporidium parvum and its potential for causing disease has become a major concern to

water treatment personnel since 1984 when the first waterborne outbreak associated with

Cryptosporidium was reported in Milwaukee, Wisconsin. Cryptosporidium oocysts are

ubiquitous parasites that are widely distributed in the water source and remain quite

environmentally stable. Occysts can survive for months in cold, moist environments, such as

- 21 -

lakes and streams. Once a human is infected, they can cause watery diarrhea, abdominal pain,

nausea, fever, and fatigue. In patients with compromised immune systems, the illness may be

life threatening (AWWA, 2006).

Utilities should consider that Cryptosporidium is resistant to chlorine- based disinfectants.

Research literature shows that turbidity is the key parameter to prevent Cryptosporidium

contamination in drinking water. For instance, when filter-effluent turbidity ranged between

0.1 and 0.3 NTU, Cryptosporidium presence was as much as 90 percent (1 log) greater than

when effluent filter turbidity was 0.1 ntu or less. Watersheds should also be managed in a way

that limits the introduction of Cryptosporidium into the drinking water supplies (AWWA,

2006).

Giardia lamblia is a global parasite that infects numerous mammals including humans, dogs,

cats, beavers, muskrats and other warm-blooded animals. It is the most commonly identified

pathogen in waterborne outbreaks in the United States. Giardia cysts have dimensions

ranging from 5 to 18 μm. It remains viable in river water for up to 28 days (Regnier et al.,

1989). Giardia cysts are not as resistant to disinfection as Cryptosporidium oocysts thus,

treatment designed to inactivate oocysts can effectively inactivate Giardia cysts, too (EPA,

2009).

Bacteria

Bacteria are microorganisms that are simpler and smaller than parasitic pathogens but larger

and more complex than viruses. Bacteria size ranges from approximately 0.2 to 10 μm in

length (Partinoudi, 2004). Natural waters are often contaminated by pathogenic bacteria

excreted by humans and various domestic and wild animals. The main source of bacteria for

entering water sources is sewage (Schijven, 2002). A compilation of bacterial agents that are

known to contaminate public water systems is listed below in table 1-4:

Table 1-4 Bacterial Pathogenic Agents. Source: AWWA, 2006, 73.

Acinetobacter

Aeromonas

Campylobacter

Cyanobacteria

Enterohemorrhagic Escherichia coli

Escherichia coli

Flavobacterium

Heliobacter pylori

Klebsiella

Legionella

Mycobacterium avium complex

Pseudosomonas

Salmonella

Serratia

22

Shigella

Staphylococcus

Vibrio cholerae

Yersinia

Due to improved hygiene standards the threat of these compounds is considered to be

moderate, although these bacteria are capable of multiplying in water supply storage and

distribution systems (AWWA, 2006). Escherichia coli and Legionella are the two waterborne

bacteria with the most significance to the water industry.

Escherichia coli belong to the group of total coliform bacteria that are used as indicators of

sewage contamination. The presence of fecal coliform bacteria is an indication that a water

source has been contaminated by human or animal waste (Partinoudi, 2004). Compared to

other fecal coliform bacteria, e.g. Enterobacter, Escherichia coli is particularly suitable for an

indicator because it is easily detected and enumerated. In addition, it has the ability to remain

viable outside the bowel of warm-blooded organisms for a long time (AWWA, 2006).

Legionella bacteria are ubiquitous in the aquatic environment and can survive in water system

biofilms. These bacteria are able to colonize artificial environments such as cooling towers,

evaporative condensers, hot-water tanks, whirlpool spas, decorative fountains, and the

drinking water distribution system. The mode of transmission is by inhalation of moist

aerosols contaminated with Legionella bacteria. In immuno-suppressed individuals, the

bacteria can cause Legionnaire’s Disease and Pontiac fever (AWWA, 2006).

Viruses

Viruses are the smallest and most basic of known life forms, ranging from approximately 18

to 120 nanometers. Viruses have no reproductive system and replicate by taking over a living

cell and usurping cellular machinery (Yates and Yates, 1988).

More than 120 different enteric viruses are known to infect humans. Enteric viruses are

excreted in the feces of infected individuals. Once in the environment, they can survive for

long periods of time, up to several months under cool and moist conditions (AWWA, 2006).

Their extremely small size and resistance to chemical and environmental degradation present

great challenges to the drinking water industry.

23

The following table 1-5 includes groups of viruses identified as sources of waterborne disease

outbreaks or having the potential to cause outbreaks:

Table 1-5 Viral Pathogenic Agents. Source: AWWA, 2006, 251.

Adenovirus

Astrovirus

Emerging viruses (Parvo, Corona, …)

Enterovirus and Parechovirus

Hepatitis A virus

Hepatitis B virus

Human Calicivirus

Reovirus

Rotavirus

1.4 Generic River & Aquifer

Interactions

Generic river and aquifer interactions

include all those phenomena which occur

naturally in all river-aquifer systems.

Furthermore, pumping-enforced

interactions, such as clogging or dilution,

gain importance once a RBF plant starts to

operate and are discussed in section 2.

Both natural and generated processes are

important for understanding the

environment a RBF system is settled in.

This section identifies some applicable

hydrogeological controls which dominate

the flow of the infiltrating water, such as

the exchange of river water and

groundwater (Gaining & Losing Rivers),

the impact to the aquifer due to fluctuating

river water characteristics e.g. during flood

conditions, and points out the correlation

between river morphology and suitability

for a RBF site (Erosion & Deposition).

Gaining & Losing Rivers

The hydraulic connectivity between the

river and the adjacent aquifer is a basic

requirement for the subsurface flow to an

RBF extraction well and must be assessed

in the initial site investigations. This can be

realized by several measurement methods

and instruments such as flow meter

measurement, drilling, ground penetrating

radar or tracers (Hoehn, 2002).

Surface water is commonly hydraulically

connected to groundwater in three possible

categories (Hoehn, 2002):

Gaining Rivers

Losing Rivers

Flow Trough Rivers

24

Gaining Rivers gain water from inflow of

groundwater through the riverbed (Figure

1-2).

This may occur when the altitude of the

groundwater table in the vicinity of the

stream is higher than the altitude of the

river water stage (Partinoudi, 2004).

Figure 1-2 Gaining River. Source: Hoehn, 2002, 21.

Losing Rivers lose surface water to

groundwater through the riverbed (Figure

1-3).

This may occur when the altitude of the

groundwater table in the vicinity of the

stream is lower than the altitude of the

river-water stage (Partinoudi, 2004). The

geological material below the channel can

either be fully saturated or unsaturated if

the channel is perched above the

underlying water table. The hydraulic

conductivity of an unsaturated leakage is

much lower than under saturated

conditions. Hydraulic conductivity has

great impact to the infiltration capacity

from surface water into groundwater and

must be assessed from pumping tests,

flow-meter measurements or grain-size

distributions (Hoehn, 2002).

Figure 1-3 Losing River. Source: Hoehn, 2002, 21.

Flow Trough Rivers receive groundwater

through the upgradient bank, and lose

water through the downgradient bank

(Figure 1-4). This may occur when the

river turns at a steep angle to the floodplain,

and if the river’s surface remains higher

then the adjacent down-valley water table

(Hoehn, 2002).

Figure 1-4 Flow Trough River. Source: Hoehn,

2002, 21.

25

All these conditions may exist in the same

river at different locations or times of the

year, but in principle, rivers lose water in

peri-alpine floodplain valleys filled with

coarse and very permeable alluvial

sediments. River channels gain water in

flat regions when the river stage is lower

than the adjacent water table (Hoehn,

2002). In both cases, there must be

permeable material that will allow this

hydraulic head to move water.

Knowing whether a stream is originally

gaining or losing is important (Partinoudi,

2004).

Depending on site characteristics it might

be advantageous to be in the vicinity of a

gaining river or a losing river. On the one

hand, wells in gaining areas can be

managed to gain higher quality, as the ratio

of high quality groundwater can be

increased by increased pumping. On the

other hand, wells in losing areas can

increase their yield with a minimum of

energy input, as the natural gradient is

already in the direction from the river to

the well (Partinoudi, 2009).

Fluctuating River Water

Characteristics and their Impact

to the Aquifer

River-aquifer interactions are controlled by

the fluctuating water level of the river.

The resulting gradients between the

changing river level and the gradual

adaptation of the groundwater table in the

adjacent aquifer, control flow and transport

in riverbank filtration (Schubert, 2001).

Figure 1-5 shows an example of surface

water fluctuations of the river Rhine.

26

Figure 1-5 Surface water level of the river Rhine

(1988-1990). Source: Schubert, 2001, 147.

According to Heij (1989), there exits a

linear relationship between surface water

level and the infiltration rate. There is also

an inverse relationship between this level

and the average time water particles

require to flow from the surface water to

the bank.

I.E. higher river water levels, especially

during flood periods, may cause higher

infiltration and increased ground water

flow rates as a result of increased head

gradient. Also, lower log removals are

expected to occur during and shortly after

floods because protective layers may be

removed by flood scour (USEPA, 2003).

Sources of information about high flow

and flood data are listed below:

The National Flood Frequency

Program:

http://pubs.usgs.gov/wri/wri024168

/pdf/entirereport.pdf

WaterWatch:

http://waterwatch.usgs.gov/?state=u

s&map%20type=flood&web%20ty

pe&map

Army Corps of Engineers

http://usace.army.mil/Pages/default.

aspx

It is well known that fluctuating

temperatures and concentration of

components in the river water are balanced

out during subsoil passage. According to

Schubert (2001), the effects of balancing

are caused by an age-stratification of

infiltrated river water. Age stratification

represents the difference in the residence

time of water in the aquifer. Figures 1-6

and 1-7 provide examples of the balancing

effects of subsoil passage. Temperature

and other abiotic parameters of

groundwater do not fluctuate as suddenly

or as extremely as those of surface water

systems.

27

Figure 1-6 Water temperature in Ohio River and in

the production well. Source: Schubert, 2005b, 3.

Figure 1-7 Chloride concentration in the river

Rhine water compared that in the adjacent well

water. Source: Schubert, 200, 157

Erosion & Deposition

According to Schubert (2002) three

different simplified model-regions can be

distinguished along a river:

Upper part (with erosion)

Middle part (with bed load

transport)

Lower part (with deposition)

Although this model assumption does not

truly reflect the natural design of a river, it

can help in selecting RBF sites.

Erosion in upper parts along the river is

characterized by a high river-flow velocity,

a high hydraulic gradient and high shear

force on the riverbed. The grain-size

distribution in these areas is usually limited

to coarse material, as particles of smaller

size and finer material are washed away

downstream. High infiltration capacity and

high hydraulic conductivity of the

streambed lead to the lack of necessary

time for balancing out variations in

temperature and concentration of

pollutants. As a result, no sufficient

protection against sudden contamination

(shock loads), can be secured.

Bed load transport is the movement

(rolling, skipping or sliding) of sediment,

such as soil, rocks, particles, or other

debris along or very near the riverbed by

flowing water. It is instrumental in the self-

28

cleaning process of the riverbed. Table 1-

10 shows the characteristics of the lower

Rhine valley where 80 percent of the RBF

sites are located. On principle, middle or

lower parts with bed load transport along

the river are suitable for a future RBF site

(Schubert, 2002).

Table 1-10 Characteristics of the Rhine river in the

lower Rhine valley region. Source: Schubert, 2002,

36.

Deposition regions occur usually upstream

of dams and near the mouth of the river

and should be avoided when selecting an

RBF site. The deposition of very fine

particles, like silt and fine sand, as well as

slow river flow velocity, can result in a

limited infiltration capacity (Schubert,

2002).

2 Applicable Processes

The treatment effectiveness of RBF results

from a combination of several applicable

processes such as clogging of the riverbed,

the dilution with groundwater after

infiltration, subsurface filtration (filtration,

adsorption, biodegradation, ion exchange,

oxidation/reduction) and additional

treatment steps.

Riverbank filtration is a highly dynamic

process on account of the changes in the

quality of river water due to river water

level and the variations in the physical

(temperature, suspended solids), chemical

(type and concentration of compounds) and

biological (type and concentration of

viruses, bacteria and protozoa) properties

(Schubert, 2005a).

An examination of the basic hydraulic,

physicochemical and biological processes

in bank filtration will help to define several

criteria for the appropriate site for RBF.

This section describes applicable RBF

processes according to the path of the

29

water from the river until the transfer to the

distribution system. An overview of RBF

processes is given in Figure 2-1.

Figure 2-1 Riverbank Filtration Processes. Source:

Amy et. al., 2006, 104.

2.1 Clogging & Cleaning Processes

Clogging

Clogging is the formation of a clogging

layer on top or in the riverbed and can be

defined as an impediment of flow,

typically as a result of physical, chemical,

and biological processes (Grabs, 1981).

According to Riesen (1975), mechanical

clogging of parts of the riverbed during

constant pumping of RBF wells is

unavoidable; however, its effects are not

always harmful. The disadvantage of

clogging is that it can reduce hydraulic

conductivity of the local riverbed and the

aquifer. As a result well-yields are

temporarily or permanently reduced.

On the other hand, some benefits such as

particle- and pathogen removal and

degradation of organic compounds are

positive effects of clogging (Grischek,

2006).

Figure 2-2 shows a picture of a paved and

clogged riverbed.

Figure 2-2 Paved and clogged riverbed near the

outer section of a bend (at Flehe waterworks,

Düsseldorf, well site). Source: Schubert, 2005,3.

Physical clogging results from the

deposition of fine-grained, suspended

sediment at the surface water – ground

30

water interface, and the deposition and

growth of microorganisms. During periods

of low surface water discharge, or in areas

with low flow velocities e.g. the edge of a

river, physical clogging may be

exacerbated (USEPA, 2003).

Chemical clogging results from

precipitation of dissolved surface water

constituents and occurs near the interface

or anywhere along the flow path. This is

due to the change in geochemical

conditions as infiltrating water enters the

riverbed (USEPA, 2003).

Biological clogging results from the

accumulation of bacterial cells in pore

spaces, the production of extra-cellular

polymers, the release of gaseous by-

products from denitrifying bacteria, and

accumulation of insoluble precipitates.

Insoluble sulphite salts can cause clogging

due to the activity of sulphate reducing

bacteria, whereas iron hydroxide and

manganese oxide deposition can be

brought on by bacterial iron-metabolism.

Biological clogging may occur near the

surface water – ground water interface

where nutrients are most available (Baveye

et al., 1998).

Cleaning Processes

Both the positive and negative effects of

riverbed clogging can be diminished by the

regenerative process of streambed scouring.

Scouring is a result of shear forces

imparted on a riverbed by the motion of

the water passing over the riverbed, and

the resistance to this motion imparted by

the riverbed itself (Hubbs, 2004).

The self-cleaning potential of a river

depends chiefly on the runoff regime,

characterized by amount, frequency, length,

time and rate of change of runoff

conditions. During flooding, the river

channel may be scoured and fine sediments

at the surface water – ground water

interface mobilized.

Research efforts by Schubert (2005b) at

the Ohio River in Louisville have shown

that even minor variations in the river level

are able to cause temporary improvements

of the infiltration capacity and flood waves

can even cause significant jumps in the

infiltration rate.

Much of the removal of the contaminants

and microbes discussed above occurs

during the first few centimeters of the flow

path, due to the significant filtering and

sorptive capabilities of sediments in the

riverbed. If this active layer is washed

away or scoured, the effectiveness of bank

filtration may be temporally threatened

(USEPA, 2003).

31

Riverbed scouring plays an essential role

in determining the sustainable yield in

RBF systems.

Therefore, the US EPA (2003) suggests

evaluating the potential for stream channel

scour as part of the initial RBF site

investigations (see section 3.1).

The extent of riverbed scouring can be

estimated as a function of riverbed shear

stress exerted during high-flow events.

Unfortunately, there is no practical

technique for directly measuring shear

force on the riverbed. However, it can be

estimated by the surface slope of the

stream, vertical velocity profiles in the

stream, and the sediment transport on the

riverbed (Hubbs, 2004). Typically, streams

exert higher shear stresses near the upper

part of a river, with decreasing stresses

exerted near the lower part of a river. This

implies that riverbed scouring will

decrease near the terminus of a stream.

Because of this tendency to deposit fine

materials near the mouth of streams, these

locations are usually not well suited for

RBF systems (Hubbs, 2003).

1.4 Subsurface Filtration

Processes

Filtration

Physical filtration is the classical process

for removal of particulate matter and

microbes in water treatment and occurs

primarily by straining and pore

sedimentation (Partinoudi, 2004).

Straining is a purely physical removal

process governed by the size of pore

throats and the size of microbial particles.

Straining occurs when the particles in

suspension in the porous matrix cannot

pass through a smaller pore, and thus their

transport is stopped.

According to Berger (2002), straining of

bacteria and viruses is less effective than

for protozoa because of their smaller size.

However, if the viruses or bacteria are

absorbed onto a solid particle of greater

size than itself, filtration can be an

important removal process (Partinoudi,

2004).

In riverbank filtration the filter medium is

the natural aquifer underneath and adjacent

to the river (Schubert, 2005a). The grain

size distribution has to comply with the

requirements of riverbank filtration. An

important requirement is a sufficient

amount of fine-grained sediments to

achieve adequate pathogen removal. The

determination of the grain size distribution

is part of the initial aquifer characterization

explained in section 3.2.

32

Pore Sedimentation occurs when the

density of a microbial particle is higher

than that of water (Partinoudi, 2004). Pore

settling is likely where groundwater

velocities are low, such as in finer-grained

riverbed material. These materials are

removed during flood periods, and thus

pore sedimentation is significant during

low flow periods of the river (Berger,

2002).

Adsorption

According to Brandt et al. (1993),

adsorption is the adhesion of molecules of

gas, liquid, or dissolved solids to a surface,

while desorption is the reverse of

adsorption.

The fine-grained sediments on many river

bottoms are generally rich in clay and

organic matter and have the potential to

adsorb a variety of contaminants in river

water (Ray et al, 2002a).

Sorption on solids, e.g. grains in the

aquifer, is an equilibrium reaction. which

may setback peaks of organic substances,

such as humic acids, by adsorption and on

the other hand may cause peaks of

previously adsorbed substances by

desorption due to a rapid change in river

water quality parameters. Due to the

permanent infiltration of river water into

the aquifer during bank filtration, the

subsoil tends toward saturation of the

adsorbents (mainly humic acids) and thus

limits the effectiveness of sorption

processes for organic substances in the

bank filtered water (Schubert, 2005a).

Adsorption and desorption are more

important for the removal of

microorganisms. The adsorption of

microorganisms onto the surface of soil

particles is caused by a combination of

electrostatic and Van der Waals forces and

hydrophobic interactions between the

microorganisms and soil particles.

Desorption occurs due to changes in the

ionic strength, the temperature, and pH of

the soil water (Partinoudi, 2004).

Sorption processes will hold back the

transport of microorganisms in the aquifer

significantly. To profit by this process,

sufficient flow path length and flow time is

necessary (Schubert, 2005a).

33

Biodegradation

Biodegradation is the chemical breakdown

of materials by a physiological

environment usually catalyzed by the

activities of microorganisms. It is a

significant process which starts directly

below the river-aquifer interface (Ray et al,

2002a).

Organic material can be degraded

aerobically with oxygen or anaerobically

without oxygen. There is a flow of oxygen-

rich surface water into the subsurface

environment and this input of oxygen to

the streambed stimulates a high level of

activity by aerobic miccroorganisms. It is

common for dissolved oxygen to be

completely used up at some distance to the

streambed. From there, anaerobic

microorganisms dominate microbial

activity. Anaerobic bacteria can use nitrate,

sulfate, or other solutes in place of oxygen

for metabolism (Partinoudi, 2004).

Ion exchange

Ion exchange is an exchange of ions

between two electrolytes or between an

electrolyte solution and a complex.

Clay minerals, organic substances, and

humic acids have a high exchange capacity

for cations, particularly heavy metals. To

profit from ion exchange, the removal of

fine particles during bank filtration is of

significant importance (Schubert, 2005a).

Oxidation/reduction

Aerobic conditions in the aquifer support

high degradation rates of organic

compounds (Schubert, 2005a). As a result,

oxygen depletion by biological activity can

lead to anaerobic conditions over a portion

of the flow path, which may result the

release of heavy-metals such as iron and

manganese from the bank sediment into

the flowing water. This process occurs due

to a redox reaction which reduces iron and

manganese in their water soluble forms

(USEPA, 2003).

At varying distances to the riverbed, the

level of oxygen determines the occurrence

and magnitude of oxidation and reduction

sub-processes as shown in Figure 2-4. The

degree to which substances are reduced

may vary between different rivers and at

different sampling points on a river (Kuehn

and Mueller, 2000).

Figure 2-3 Riverbank Filtration Processes. Source:

Grischek, 2003, 8.

34

On the other hand, if the flow path between

the riverbank and the well is long enough,

iron and manganese can precipitate onto

the sediments in the subsurface before

reaching the extraction well (Tufenkji et al.,

2002). The aquifer becomes reaerated with

increasing distance from the riverbed. This

is one reason for locating RBF wells

greater than 25 or 50 feet from the river, as

discussed in section 1.3 (USEPA, 2003).

Sonheimer (1980) considers aerobic

conditions in the ground, advantageous, as

iron and manganese will not go into

solution and biological oxidation of

organics occurs under anoxic conditions in

the presence of nitrate.

1.5 Dilution Process

Riverbank filtrate includes both

groundwater and river water that has

percolated through the banks or bed of a

river to an RBF extraction well (Partinoudi,

2004).

The dilution of surface water with

groundwater is considered one of the

advantages of RBF because groundwater is

usually a source of higher quality.

Significant differences exist between the

two water sources. River characteristics,

such as temperature, turbidity and level of

contaminants can change significantly

during the year, depending on weather

conditions, river flow or emissions by

municipal and industrial sewage runoff. In

contrast, groundwater remains nearly

constant (Wang, 2002).

To asses how effectively the RBF process

improves water quality, one must

determine the extent of groundwater

mixture to distinguish between true

contaminant removal due to RBF process

and reduction due to dilution (Partinoudi,

2004).

The determination is normally based on

water quality parameters:

natural tracers (bromide, chloride)

inorganic parameters (hardness,

temperature, conductivity)

35

organic parameters (true color,

TOC/DOC)

No tracer is a perfect tracer i.e. there are

advantages and disadvantages to the use of

each of these parameters (Partinoudi,

2004).

It is important that the tracer’s

concentration is significantly different

between the river water and groundwater

to accurately gauge the dilution ratio

between the two sources. According to

Wang (2002), the best way to determine

the amount of dilution is to find a tracer

that exists at a constant concentration at

one of the sources while remaining absent

from the other source, and that is

considered conservative during subsurface

transport. As a result the most consistent

and reliable parameter has to be selected at

each site.

Once a convenient parameter has been

found, results can be calculated with the

following mass balance formula:

X= ((c(RBF)-c(AQUIFER))/(c(RIVER)-

c(AQUIFER))]*100

X: fraction of river water in the RBF

well

c(RBF): concentration of a tracer in

the riverbank filtrate

c(AQUIFER): concentration of a

tracer in the aquifer

c(RIVER): concentration of a tracer

in the river

Example: If the temperature in the river is

21.5°C, 10.1°C in the aquifer and 13.2°C

in the riverbank filtrate, the fraction of the

river water in the RBF well will be

calculated as follows:

X = [(13.2-10.1)/(21.5-10.1)]*100

X = 27.2 %

1.6 Additional Treatment Steps

Bank filtrate is usually treated after

extraction. The level of additional

treatment steps depends on surface water

quality as well as on the cleaning capacity

of the bank passage (Kühn, 1999).

One disadvantage of RBF is that an

additional aeration step may be required

during water treatment due to the depletion

of oxygen by microorganisms during

subsoil passage. This oxygen depletion

may lead to the anaerobic conditions which

can result in the release of iron and

36

manganese from the bank sediment into

the flowing water. This condition may

necessitate the removal of these metals

during additional treatment steps (USEPA,

2003).

The bank filtration has no effect on

recalcitrant substances, such as several

micropollutants. Therefore, the treatment

of bankfiltrate often includes granular

activated carbon filters

(Kühn, 1999).

By taking into consideration that the bank

filtrate quality highly depends on the local

environment (e.g. aerobic/anaerobic

conditions or river water quality), the

additional treatment of riverbank filtrate

may include ozonation, nitrification,

rapid/slow sand filtration, granular

activated carbon filters, oxygenation,

removal of iron and manganese, and

disinfection.

At a minimum, RBF acts as a pre-

treatment step in drinking water production

(mostly in large urban areas) and, in some

cases, can serve as the final treatment just

before disinfection (usually in small

communities) (Ray et al., 2002).

37

References

Bourg, A.C.M., Keziorek, M.A.M., Darmendrail, D. (2002). ”Organic Matter as the Driving Force in the

Solubilization of Fe and Mn during Riverbank Filtration” in Ray, C (ed.) Riverbank Filtration:

Understanding Contaminant Biochemistry and Pathogen Removal, Kluwer Academic Publishers,

Netherlands, 43-54.

Grabs, W. (1981). „Beitrag zur Beschreibung von Kolmationserscheinungen in einem organisch belasteten Kleingewässer“ Beiträge zur Hydrologie 2, 293-311.

Grischek, T. (2003). “Zur Bewirtschaftung von Uferfiltratfassungen an der Elbe” Institut für

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Heij, G.J. (1989). “River-Groundwater Relationships in the Lower Parts of the Netherlands, J. Hydrol.,

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Association, 92, 60-69.

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Univ. of New Hampshire, Durham, NH.

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International Riverbank Filtration Conference Louisville, Kentucky.

Figures/ Tables

Figure 1-1

“Generalized schematic of an RBF system” Source: Ray et al., 2002, page 2.

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Biofiltration in Engineered versus Natural Systems“ in Abstracts of International Workshop on

Riverbank/Riverbed Filtration, Korea.

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Reviews in Environmental Science and Technology, 28(2):926-934.

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Publishers, Netherlands, 85-121.

Brandt, R.K., Hughes, M.R., Bourget, L.P., Truszkowska, K., Greenler, R.G. (1993). “The Interpretation

of CO Adsorbed on Pt/SiO2 of two Different Particle-Size Distributions”, Surface Science, Vol. 286, 15-

25.

Grabs, W. (1981). „Beitrag zur Beschreibung von Kolmationserscheinungen in einem

Organisch Belasteten Kleingewässer“ Beiträge zur Hydrologie 2, 293-311.

38

Grischek, T. (2003). “Zur Bewirtschaftung von Uferfiltratfassungen an der Elbe” Institut für

Grundwasserwirtschaft Technische Universität Dresden, Heft 4.

Grischek, T. (2006). “Investigations into River Bed Clogging at RBF Sites along the Elbe River,

Germany“ International Workshop on Riverbank/ Riverbed Filtration.

Hubbs, S.A. (2003). “Plugging in Riverbank-Filtration Systems: Evaluating Yield-Limiting

Factors“ Program and Abstracts, The Second International Riverbank Filtration Conference, National

Water Research Institute, Cincinnati, Ohio.

Hubbs, S. A. (ed.) (2004). “Evaluation Streambed Sources Impacting the Capacity of Riverbank Filtration

Systems” Riverbank filtration hydrology: Impacts on System Capacity and Water Quality, NATO Science

Series, IV-Earth and Environmental Science, Vol. 60.

Kuehn, W. (1999). “Overview of Riverbank Filtration Issues“ Abstracts Riverbank Filtration Conference,

Nov 4-6, Louisville Kentucky.

Kuehn, W., Mueller, U. (2000). ”Riverbank Filtration: an Overview” Journal American Water Works

Association, 92, 60-69.

Partinoudi, V. (2004). “Riverbank Filtration as a Viable Pretretment and Treatment Method” M.S.Thesis,

Univ. of New Hampshire, Durham, NH.

Ray, C., Schubert, J., Linsky, R.B., Melin, G. (2002). ”Introduction” in Riverbank Filtration: Improving

Source Water- Quality” Kluwer Academic Publishers, Dordrecht, The Netherlands.

Ray, C., Grischeck, T., Schubert, J., Wang, J., Speth, T. (2002a). “A Perspective of Riverbank Filtration”

Journal of American Water Works Association, 94(4): 149-160.

van Riesen, S. (1975). “Uferfiltratverminderung durch Selbstdichtung an Gewässersohlen“ (Shrinkage of

bank filtrate by clogging of the riverbed). Dissertation, Fakultät für Bauingenieur- und Vermessungswesen, Universität Karlsruhe.

Schubert, J. (2005). ”River hydrology and morphology” RBF Workshop….

Schubert, J. (2005a). ”Processes in bank filtration” RBF Workshop….

Schubert, J. (2005b). ”River-aquifer interactions - the clogging process” RBF Workshop….

Sontheimer, H. (1980). “Experiences with Riverbank Filtration along the Rhine River”, Journal AWWA

72, 386-390.

Tufenkji, N., Ryan, N.J., Elimelch, M. (2002). “The Promise of Bank Filtration: A Simple Technology

may Inexpensive Clean up Poor-Quality Raw Surface Water” Environmental Science and Technology, 36:

422A-428A.

US EPA (2003). “LT2ESWTR Toolbox Guidance Manual” Office of Water.

Wang, J. (2002). “Riverbank Filtration Case Study at Louisville, Kentucky” in Riverbank Filtration:

Improving Source -Water Quality, C. Ray, G. Melin, and R.B. Linsky, eds., Kluwer, Academic Publishers, Dordrecht, The Netherlands.

Figures/ Tables

Figure 2-1

Riverbank Filtration Processes. Source: Amy et. al., 2006, page 104.

39

Figure 2-2

Paved and clogged riverbed near the outer section of a bend (at Flehe waterworks, Düsseldorf, well site).

Source: Schubert, 2005, page 3.

Figure 2-3

Riverbank Filtration Processes. Source: Grischek, 2003, page 8.

Brown, R.A. (2003). “Application of the Long Term 2 Enhanced Surface Water Treatment Rule Microbial

Toolbox at Existing Water Plants” Program and Abstracts, The Second International Riverbank Filtration Conference, National Water Research Institute, Cincinnati, Ohio.

Grischek, T., Schoenheinz, D., Ray, C. (2003) “Siting and Design Issues for Riverbank Filtration

Schemes“ in Riverbank Filtration: Improving Source -Water Quality, C. Ray, G. Melin, and R.B. Linsky,

eds., Kluwer Academic Publishers, Dordrecht, The Netherlands.

Partinoudi, V. (2004). “Riverbank Filtration as a Viable Pretreatment and Treatment Method” M.S.Thesis,

Univ. of New Hampshire, Durham, NH.

Partinoudi, V. (2009). Personal communication.

Ray, C., Schubert, J., Linsky, R.B., Melin, G. (2002). ”Introduction” in Riverbank Filtration: Improving

Source Water- Quality” Kluwer Academic Publishers, Dordrecht, The Netherlands.

Ray, C., Grischeck, T., Schubert, J., Wang, J., Speth, T. (2002a). “A Perspective of Riverbank Filtration”

Journal of American Water Works Association, 94(4): 149-160.

Regli, S., (2003). “Potential Uses of Bank Filtration for Regulatory Compliance Regulatory” Program and

Abstracts, The second International Riverbank Filtration Conference, National Water Research Institute,

Cincinnati, Ohio.

US EPA (2009a). “Complying with the Long Term 2 Enhanced Surface Water Treatment Rule: Small Entity Compliance Guide” Office of Water.

US EPA (2007). “The Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR)

Implementation Guidance” Office of Water.

US EPA, (2005). “Occurrence and Exposure Assessment for the Final Long Term 2 Enhanced Surface

Water Treatment Rule” Office of Water.

US EPA (2005a). Rule Fact Sheet - Long Term 2 Enhanced Surface Water Treatment Rule [online].

Available from : http://www.epa.gov/safewater/disinfection/lt2/regs_factsheet.html [Accessed: 1

November 2009]

US EPA (2004). Chapter I-Environmental Protection Agency

Part 141-National Primary Drinking Water Regulations, 40 CFR Ch. I (7–1–04 Edition).

US EPA (2002). Chapter II-Environmental Protection Agency Regulations: Long Term 1 Enhanced

Surface Water Treatment Rule; Final Rule 40 CFR Parts 9, 141, and 142

National Primary Drinking Water.

Figures/ Tables

Table 1-1

Current drinking water rules (by date issued). Source: US EPA Website -

http://www.epa.gov/safewater/regs.html.

Table 1-2

Treatment levels in RBF classification. Source: Partinoudi, 2003, page 4.

40

Table 1-3

Information and Guidance to meet LT2ESWTR requirements. Source: US EPA, 2009a, page 30 ff.

Table 1-4

Selected Site Data for RBF Systems in the United Sates and Germany. Source: Grischek et al., 2003, page

293.

Table 1-5

Microbial Toolbox Summary Table: Options, Treatment Credits and Criteria. Source: US EPA, 2007, page 77.

Hoen, E. (2002). “Hydrogeological Issues of Riverbank Filtration-A Review” in Riverbank Filtration:

Understanding Contaminant Biochemistry and Pathogen Removal” Ray, C. ed., Kluwer, Academic

Publishers, Dordrecht.

Heij, G.J. (1989). “River-Groundwater Relationships in the Lower Parts of the Netherlands, J. Hydrol.,

108(1-4), 35-62.

Partinoudi, V. (2009). Personal communication.

Partinoudi, V. (2004). “Riverbank Filtration as a Viable Pretretment and Treatment Method” M.S.Thesis,

Univ. of New Hampshire, Durham, NH.

Schubert, J. (2005b). ”River-aquifer interactions - the clogging process” RBF Workshop….

Schubert, J. (2001). “Hydraulic Aspects of Riverbank Filtration – Field Studies” Journal of Hydrology

266, 145-161.

Schubert, J. (2002). “German Experience with Riverbank Filtration Systems” in Riverbank Filtration:

Improving Source -Water Quality, C. Ray, G. Melin, and R.B. Linsky, eds., Kluwer Academic Publishers,

Dordrecht, The Netherlands.

US EPA (2003). “LT2ESWTR Toolbox Guidance Manual” Office of Water.

Figures/ Tables

Figure 1-2

Gaining River. Source: Hoehn, 2002, page 21.

Figure 1-3

Losing River. Source: Hoehn, 2002, page 21.

Figure 1-4

Flow Trough River. Source: Hoehn, 2002, page 21.

Figure 1-5

Surface water level of the river Rhine (1988-1990). Source: Schubert, 2001, page 147.

Figure 1-6

Water temperature in Ohio River and in the production well. Source: Schubert, 2005b, page 3.

Figure 1-7

Chloride concentration in the river Rhine water compared that in the adjacent well water. Source: Schubert, 2002, page 40.

Table 1-11

Characteristics of the Rhine river in the lower Rhine valley region. Source: Schubert, 2002, page 36.

41