&EPA Ground Water Issue
United States
Environmental Protection
Agency
Movement and Longevity of
Viruses in the Subsurface
Ann Azadpour-Keeley1, Barton R. Faulkner1, and Jin-Song Chen2
Background
In order to assist federal and state decision makers, the Applied
Research and Technical Support Branch (ARTSB) of the Ground
Water and Ecosystems Restoration Division (GWERD) has, since
1989, developed a series of over 30 Ground Water Issue Papers
intended to be brief, state-of-science documents focused on a
technical issue of expressed interest and prepared in a concise
and readable format. The purpose of this Issue Paper is to discuss
some of the conditions under which viral contaminants may
survive and be transported in the subsurface, identify sources as
well as indicators of viral contamination, outline the effects of
hydrogeologic settings on viral movement, and introduce the
reader to the current state of virus transport modeling along with
an example of modeling applications.
The 1986 Safe Drinking Water Act (SDWA) amendments directed
EPA to develop national requirements for drinking water
disinfection. The legislation required every public water supply
system to disinfect unless it fulfills criteria assuring equivalent
protection (Macler, 1996). To provide direction for the regulations
associated with "acceptable" health risks to the public (Macler,
1996), EPA established maximum contaminant level goals
(MCLGs) for pathogenic microorganisms in drinking water, setting
a level of zero for viruses (U.S. EPA, 1989a,b). Due to the various
technical and economic considerations involved in monitoring
water for these MCLs, a "treatment technique" was proposed to
reduce or eliminate viruses (Yatesetal., 1990). On June29,1989,
a Surface WaterTreatment Rule (SWTR) was published addressing
microbial contamination of drinking waterfrom surface sources, or
from ground-water sources directly influenced by surface water,
with strict provisions for filtration and disinfection (U.S. EPA,
1989a). On January 14, 2002, a SWTR was promulgated with
special emphasis on the protozoan Cryptosporidium (U.S. EPA,
2002).
The development of a corresponding rule for ground water, the
Ground Water Disinfection Rule (GWDR, later designated as the
Ground Water Rule), to meet SDWA requirements began in 1987
and led to a published discussion piece (draft GWDR, U.S. EPA,
1992). The deadline for the GWDR proposal was dependent upon
completion of studies of the status of public health with respect to
the microbial contamination of ground water, based on studies
(Abbaszadegan et al., 1999a,b; Lieberman et al., 1994, 1999) to
' National Risk Management Research Laboratory, ORD,
U.S. EPA, Ada, Oklahoma.
2 Dynamac Corporation, Ada, Oklahoma.
generate a more careful nationwide picture of the problem. As
there are significant differences between ground water and surface
water in terms of the type and degree of treatment, the GWDR
regulatory workgroup realized that the assessment of vulnerability
as a function of site specific conditions (i.e., hydrogeology, land
use pattern) was a key element to be addressed (Macler, 1996).
Subsequently on May 10, 2000, U.S. EPA proposed "...to require
a targeted risk-based regulatory strategy for all ground-water
systems addressing risks through a multiple barrier approach that
relies on five major components: periodic sanitary surveys of
ground water systems requiring the evaluation of eight elements
and the identification of significant deficiencies; hydrogeological
assessments to identify wells sensitive to fecal contamination;
source water monitoring for systems drawing from sensitive wells
without treatment or with other indications of risk; a requirement
for correction of significant deficiencies and fecal contamination
(by eliminating the source of contamination, correcting the
significant deficiency, providing an alternative source water, or
providing a treatment which achieves at least 99.99 percent
(4-log) inactivation or removal of viruses), and compliance
monitoring to insure disinfection treatment is reliably operated
where it is used." (U.S. EPA 2000)
It should be emphasized that this document is not intended for use
in establishing the finalized GWDR or for the interpretation of the
results of those investigations. To that end, the reader is referred
to the Federal Register (U.S. EPA, 2000).
For further information contact Dr. Ann Azadpour-Keeley (580-
436-8890) at the Ground Water and Ecosystems Restoration
Division of the National Risk Management Research Laboratory,
Ada, Oklahoma.
Introduction
Over 97 percent of all fresh water on earth is ground water and for
over 100 million Americans who rely on ground water as their
principal source of potable water (Bitton and Gerba, 1984), over
88 million are served by community water systems and 20 million
by non-community water systems (U.S. EPA, 2000). Historically,
ground water has been considered a safe source of drinking water
which required no treatment. It has long been believed that this
valuable resource was protected from surface contamination
because the upper soil mantle removed pollutants during
percolation (Amundson et al., 1988). It was also believed that,
even if contaminated, ground water would be purified through
adsorption processes and metabolism of indigenous aquifer
microflora (Dizer et al., 1984).
As water demands increase, the possibility of artificially recharging
ground water with wastewater or surface water will also increase,
-------
particularly in states like California, where ground water supplies
half of the state's fresh water, and Arizona, where ground water
supplies all of the fresh water demand. These activities may result
in increasing the concern for waterborne diseases; a concern not
unwarranted in lieu of the recent worldwide rise in waterborne
diseases and a report by the American Academy of Microbiology
(Colwell, 1996) indicating that drinking water is not safe
microbiologically.
In the United States alone, the annual number of reported illnesses
resulting from contact with waterborne pathogens was estimated
to be as low as one million and as high as seven million; and
between 1971 and 1982, 51 percent of all waterborne disease
outbreaks were due to the consumption of contaminated ground
water (Craun, 1985). Macler (1995) estimated that approximately
20-25 percent of the United States' ground-water sources are
contaminated with microbial pathogens, including more than 100
types of viruses. A literature review by Craun (1989) indicated that
approximately one-half of the surface water and ground-water
sources tested contained enteric viruses. Even nine percent of
the conventionally treated drinking water (coagulation,
sedimentation, filtration, post-filtration disinfection using
chlorine/ozone) tested positive for enteric viruses (Gerba and
Rose, 1993).
Ground water serves as a water source for 93 percent of the
communities in Minnesota, with the most extensive use being from
karst topography in the southern half of the state. In this type of
geology, cracks, sinkholes, and macropores allow rapid percolation
of surface water into ground-water reservoirs. The biological
contamination of 18 private rural wells during 16 months of
sampling showed that 17 out of 18 wells contained detectable
levels of indicator bacteria and coliphages (Amundson et al.,
1988).
Although water-transmitted human pathogens include various
bacteria, protozoa, helminths, and viruses (Bull et al., 1990),
agents of major threat to human health are pathogenic protozoa
(Cryptosporidium and Giardia) and enteroviruses (Schijven and
Hassanizadeh, 2000). Despite ample information regarding the
fate of viruses in the subsurface, research on the persistency of
pathogenic protozoa through passage in soil and ground water is
just now emerging (Brush et al., 1999; Harteret al., 2000). In the
past it was generally believed that the presence of pathogenic
protozoa was confined to surface water. Contrary to that
expectation, recent monitoring results from 463 ground-water
samples collected at 199 sites in 23 of the 48 contiguous states
suggested that up to 50 percent of the ground-water sites were
positive for Cryptosporidium, Giardia, or both, depending on the
parasite and the type of ground-water source (vertical wells,
springs, infiltration galleries, and horizontal wells) (Hancocket al.,
1998).
Viruses are small, obligate, intracellular parasites that infect and
sometimes cause a variety of diseases in animals, plants, bacteria,
fungi, andalgae. Viruses are colloidal particles, negativelycharged
at high pH (pH 7), ranging in size from 20 nm to 350 nm. The
smallest unit of a mature virus is composed of a core of nucleic
acid (RNA or DMA) surrounded by a protein coat. With this unique
feature of viral structure and colloidal physicochemical properties,
the transport of viruses in soil and ground water can act with a
combination of characteristics ranging from solutes, colloids, and
microorganisms.
Enteroviruses (see Table 1) are a particularly endemic class of
waterborne microorganisms which cause a number of ubiquitous
illnesses including diarrhea, gastroenteritis, and meningitis, only
to name a few. Included in this group are poliovirus, hepatitis type
A (HAV), coxsackievirus A and B, and rotavirus. Although
gastroenteritis is the most common disease resulting from these
microorganisms (Lukasiket al., 1996), other associated illnesses
include hepatitis, typhoidfever, mycobacteriosis, pneumonia, and
dermatitis (Bull et al., 1990; Sherris et al., 1990; Levine et al., 1991;
Payment et al., 1991). Therefore, in addition to the protection of
ground-water resources by adequate set-back distances between
the sources of contamination and wells for drinking water, the
major concern in water treatment facilities is the removal of
pathogens prior to consumption.
Since adsorption to soil particles seems to be a significant cause
of virus removal (Schijven and Rietveld, 1996; Schijven et al.,
1998) and the same processes are applicable to other water-
transmitted pathogens to various degrees (Schijven and
Hassanizadeh, 2000), viruses are often selected as conservative
models for the transport of major biological contaminants in the
subsurface. This selection is based on the knowledge that viruses
generally travel greater distances than bacteria (Scheuerman
et al., 1987) and protozoa due to their relatively small size
(see Figure 1), with variations depending on their degree of
inactivation and adsorption characteristics (Keswick and Gerba,
1980; Herbold-Paschke, 1991). It should be pointed out that
although the disease which is caused by polioviruses has
essentially been eradicated in this country, thereby limiting their
presence in the environment, much of the historical data is
available for this virus since it was often used in transport models
as a marker.
Although it goes without question that the United States has one
of the safest public drinking water supplies in the world, current
and future challenges - like the emergence of new waterborne
diseases, varying water source quality, and increased
contamination of ground water - must be met with the best
available scientific knowledge.
Sources of Viruses
As shown in Figure 2, there are a number of avenues available for
the introduction of viruses to the subsurface (i.e., land disposal of
untreated and treated wastewater, land spreading of sludge,
septic tanks and sewer lines, and landfill leachates), as well as a
number of parameters which affect their migration and survival.
Among these, septic systems may pose a significant chemical as
well as biological threat to surface and ground waters. According
to Canter and Knox (1984), one trillion gallons of septic-tank waste
is released into the subsurface annually. Although phosphate and
bacteria are ordinarily removed by soil, nitrate and polioviruses
(used as the viral marker) may escape these processes and move
through the soil into the ground water (Alhajjaret al., 1988; 1990).
The presence of viral particles is even more significant in light of
studies that indicate they are not necessarily inactivated in septic
tanks (Stramer, 1984) and may move into the ground water where
they may survive for long periods of time (Dizer and Hagendorf,
1991; Yates et al., 1985). Gerba and Bitton (1984) isolated
viruses from ground-water samples as deep as 30 meters and as
far as 100 meters from sewage treatment infiltrate basins. Vaughn
et al. (1983) isolated septic tank viruses which had traveled 3.6
meters through the unsaturated zone and 67 meters from the
source through the saturated zone. At several other sites enteric
viruses have migrated laterally in ground water a few hundred
meters (Noell, 1992), and Bales et al. (1993) reportedthat poliovirus
used as the viral indicator was detected from a deep well located
more than 1000 meters from the apparent source area.
Substantial amounts of excess sludge, which may contain viruses
and other pathogenic microorganisms, are generated from
wastewater treatment facilities which use activated sludge
-------
Table 1. Water-transmitted Enteroviruses (modified from Bull et al., 1990)
Group
Pathogen
Disease Contracted
Enteroviruses
Poliovirus
Echovirus
Coxsackievirus A
Coxsackievirus B
New enteroviruses (types 68-71)
Hepatitis type A
Enterovirus 72
Norwalk virus
Calcivirus
Astrovirus
Reovirus
Rotavirus
Adenovirus
Snow-Mountain Agent
Epidemic, non-A, non-B
hepatitis
Meningitis, paralysis, fever
Meningitis, diarrhea, rash.
fever, respiratory disease
Meningitis, herpangina.
fever, respiratory disease
Myocarditis, congenital heart
anomalies, pleurodynia.
respiratory disease, fever.
rash, meningitis
Meningitis, encephalitis, acute
hemorrhagic conjunctivitis.
fever, respiratory disease
Infectious hepatitis
Diarrhea, vomiting, fever
Gastroenteritis
Gastroenteritis
Not clearly established
Diarrhea, vomiting
Respiratory disease, eye
infections, gastroenteritis
Gastroenteritis
Hepatitis
Land
Application
Drinking
Water
\ Well
41
Channelization
Defective
Well
Casing
Soil Factors
Texture
Organics
(humic acids) O •
Ionic
strength
Adsorption
Structure
pH
Permeabiliti
Applied Sludge V\ V \
pH O Microbial antagonism Q
(aerobic vs. anaerobic)
Temp. O Flow rate •
Figure 1. Migration and survival of viruses in the subsurface (modified from Keswick and Gerba, 1980).
-------
Rhinovirus
(24 nm)
Epstein-Barr
Virus
(130nm)
Vaccinia
Virus
(300 nm)
Gravel Sand
> 400 nm 400 nm - 12 nm Silt
^m^^^^^^^^^R 12 ^m - 0.4 nm
^^m
Protozoa
Fungi
100 nm- 10 nm
5 nm - 0.2 nm Bacteria
Sand
Loam
Typical
Bacteria
(2,000 nm)
Small Animal Cell
(12,000 nm)
LARGE PORES MEDIUM PORES FINE PORES
70%
33%
15%
33%
500 - 200 nm Rickettsiae Chlamydiae
30(^0 nm Viruses
10-1 nm Macromolecules
1 nm Molecules
^^H
Atoms
15%
33%
Figure 2. Relative comparison of sizes of microorganisms and molecules with hydraulic equivalent diameters of pore
canals (modified from Matthess and Pekdeger, 1981). Note: Accordingto the Soil Science Society of America,
definitions of the various grain sizes include: gravel, >2 mm; sand, 2 mm - 50 fj,m; silt, 50 fj,m - 2 fj,m; and
clay, <2 nm.
processes. Since anaerobic sludge digestion is not sufficient for
complete viral inactivation, the potential spread of viruses during
sludge disposal needs to be considered. Therefore, waste
management practices should take into consideration hydraulic
loading and contaminant transport characteristics. In this respect,
taking advantage of the unsaturated zone as the means for the
retention of viruses and source control may become valuable, as
was demonstrated by Farrah et al. (1981). It was shown that
enteroviruses introduced as tracers were efficiently retained by a
sludge soil mixture and were not detected in deep wells located on
the sludge disposal site or nearby lagoon. Interestingly, a significant
diversity among the enteroviruses toward the sludge soil mixture
was seen since, duringthe initial part of the examination, poliovirus
accounted for greater than 90 percent of the viruses in sludge,
whereas later, it was determined that echoviruses and
coxsackieviruses were the most common enteroviruses identified
(Farrah et al., 1981).
Due to the above considerations, the various drinking water
standards promulgated since 1975 could be violated by the initial
release of treated and untreated wastewater into the environment.
Clearly, the microbial concentration of wastewater applied to the
land depends on the extent of treatment it receives. For example,
in the United States atypical raw sewage contains 7x106 plaque-
forming units (PFU)/1,000 liters (Gerbaetal., 1975). Primary and
secondary wastewater treatment, followed by disinfection, reduces
virus concentrations to about 600 PFU/1,000 liters. The application
of tertiary treatment followed by disinfection which leads to almost
viral free effluent (6PFU/1000 liters) is not a common practice
(Vilker et al., 1978).
Indicators of Viruses in Water
Prior to recently obtained data, which indicated a significant risk
associated with a low number of enteroviruses in drinking water
supplies (Haas, 1983; Haas and Heller, 1990), it was generally
believed that coliform bacteria were appropriate and reliable
indicators of the sanitary and biological states of aquatic
environments. Viral indicators were not used in the past because
it was believed that:
• viruses were not normal flora of the intestinal tract, and were
excreted only by infected individuals (with the exception of
children), usually several orders of magnitude lower than
those for coliforms;
• there was a lack of viral detection methods for each of the viral
groups of public concern;
• enteric viruses only multiplied within living susceptible cells,
and their numbers would be drastically decreased in sewage
because of the presence of bacteria, and even further
decreased by sewage treatment, dilution, and natural
inactivation; and
• although experimentally it had been shown that infection may
result from the ingestion of only a very few virus particles,
community risk of infection from low level virus contamination
has not been determined.
Marzouk et al. (1980) have questioned the validity of bacterial
indicators in monitoring the virological quality of water, especially
for those countries with high incidence of waterborne illnesses
with viral etiology. It has now been established that the bacterial
indicator system does not accurately reflect the occurrence of
viruses in aquatic environments. Bacterial indicators have a much
higher inactivation rate as compared to enteroviruses. Thus the
reduction of a bacteria to a safe level by treatment or natural die-
off during self purification in natural waters could leave a large
number of pathogenic enteric viruses.
Oliver (1971) has proposed the use of human enteroviruses as
virological indicators of water and wastewater pollution since they
retain their infectious properties for a long period of time. During
-------
the earlier studies, the use of specific enteroviruses, such as
polioviruses and/or HAV, has also been proposed due to the
frequent isolation of these viruses in sewage contaminated surface
waters (Goyal, 1983). It was noted by Payment et al. (1985) that
polioviruses can be used as an indicator of enteroviruses on the
basis of their persistency.
In practice, the use of HAV as a surrogate for poliovirus was
criticized by Metcalf et al. (1978) since hepatitis A is more sensitive
to chlorination and would be readily inactivated by water and
wastewater treatment. Currently, since the disease which is
caused by polioviruses has essentially been eradicated in this
country, thereby limiting their presence in sewage, they no longer
serve as a natural indicator of sewage contamination. Poliovirus
also may not be a suitable index of sewage pollution in those
countries where live attenuated poliovirus is used for vaccination
(Katzenelson, 1978). Additionally, if usedasasingle"marker,"the
transport of poliovirus may be significantly retarded compared to
other viruses (Powelson and Gerba, 1993; 1994).
Recognition of the limitations of enteroviruses as the model of viral
pollution has led to proposals for using bacteriophages (Stetler,
1984; Havelaar, 1987; Morinigo, 1992.). The phage index offers
several advantages because: (1) phage are constant inhabitants
of the human intestinal tract; (2) phage are non-invasive to
humans; (3) quantitative phage assays are cheap, easy and rapid
(Bales et al, 1989; Gerba, 1985); and (4) phage have similar
physical properties to enteric viruses (Snowdon and Oliver, 1989).
For example, it has been shown that MS-2 is similar to poliovirus
in shape and size, 28 nm, and PDR-1 resembles rotavirus in
shape and size, 62 nm (Powelson et al., 1990). Both phages
survive for long periods of time in ground water and have a low
tendency for adsorption to soil surfaces (Yates et al., 1985;
Powelson et al., 1990). The use of coliphage as an indicator of
water hygiene has been suggested by many investigators (Niemi,
1976; Borrego et al., 1987).
Detection systems have become more specific due to the concern
for proliferation of some coliphages in sewage water (Borrego and
Cornax, 1990, Snowdon, 1989: Armon and Kott, 1995), and the
presence of enteric viruses in the absence of coliphages (Deetz
et al., 1984). The use of F-specific phages (Kamiko and Ohgaki,
1992; Nasser and Oman, 1999), and RNA phages of the E
morphological groups (Havelaar et al., 1993) has been suggested.
These viruses are similar to enteroviruses in morphological
characteristics and are only invasive to F-pili carrier bacteria.
Adapting the F-specific phages, using Salmonella typhimurium
WG49 strain (Havelaar et al., 1993) or the combination of fecal
streptococci and E. co//viruses, has also been proposed as the
most promising indicator of remote pollution (Cornaxand Morinigo,
1991). Furthermore, in determining the efficiency of a drinking
water treatment system, the use of Clostridium perfringens and
somatic coliphages as indicators of viruses and protozoa cysts
has been suggested (Payment and Franco, 1993; Hirata et al.,
1991; Geldenhuys and Pretorius, 1989).
Viral Transport and Survival
The ability to determine travel distances and survival times of
viruses in the subsurface is crucial for regulatory agencies which
are attempting to maintain sources of contamination at sufficient
distances from sources of drinking water to protect public health
(Keswick, 1982a; Yates et al., 1987). It is a general consensus
that the transport of pathogens in the subsurface depends on the
extent of their retention on soil particles and their survival. A
myriad of studies have been conducted to determine viral transport
rates under various experimental conditions. Table 2 summarizes
selected studies performed under both laboratory and field
conditions. Results shown in Table 2 indicate that solid materials
could generally adsorb/retain as much as 95 %, or even more, of
the viruses injected into a column. In a column study with
breakthrough (Dowd and Pillai, 1997), 79% -100% of viruses were
removedfromsolution. As in any environmentalfield investigation,
there remains a multiplicity of options with respect to the selection
of an appropriate tracer (see Table 2). For example, despite the
claim of Yeager and O'Brien (1979) that phages are unsuitable
indicators of enterovirus, many others have suggested that phages
are easier to work with, and maybe more accurately evaluated in
quantitative measurements. A thorough review of the earlier
literature suggested that polioviruses were used extensively as
tracers during transport studies; whereas, the more recent works
are focused on bacteriophages.
The major factors which affect viral transport characteristics in the
subsurface are provided in Table 3. Among all the factors,
temperature appears to be the only well defined parameter
causing a predictable effect on viral survival (Yates and Gerba,
1984). A direct relationship between a rise in temperature and
viral inactivation rates (K= log inactivated/hr) among various
viruses has been suggested (personal communications, C.P.
Gerba, 2003). Badawy et al. (1990) stated that during the winter
(4-10°C), viral inactivation rates for coliphage, poliovirus, and
rotavirus were 0.17,0.06, and 0.10 per hour, respectively. Whereas,
during the summer (36-41 °C), the inactivation rates for MS-2,
poliovirus, and rotavirus were 0.45, 0.37, and 0.20 per hour,
respectively. This study also indicated that viruses may remain
viable for 3 to 5 weeks on crops irrigated with sewage effluent;
polio and coxsackievirus up to four months on vegetables during
commercial and household storage; and up to 30 days on
vegetables stored at 4°C. Rhodes etal. (1950), reported a survival
of 188 days for poliovirus in river water at 4°C. Interestingly, Blanc
and Nasser (1996) reported that HAV survives longer than other
enteric viruses at higher temperature. It should be pointed out that
this information is based on ambient air. A more direct comparison
would be the correlation with temperatures in the subsurface. In
this regard the inactivation rates for enteroviruses are 0.06 (10 -
15°C), 0.08 (15 - 20°C), and 0.19 (20 - 25°C).
Microbial ecology may also play an important role in the inactivation
of waterborne viruses (Oliver and Herrmann, 1972; Herrmann and
Oliver, 1973) especially in surface waters. For example, microbial
activity could affect viral survival by the action of proteolytic
enzymes of some bacteria (Oliver and Herrmann, 1972) and
protozoa (Moseetal., 1970) in destroying the viral capsid protein.
In fact, Deng and Oliver (1995) demonstrated rapid inactivation of
HAV in the presence of bacteria.
A report by Wellings et al. (1975) claimed that viruses may survive
for periods of at least 28 days in ground water. Persistence of
enteric viruses in ground water beneath land treatment sites and
septic tank discharges has been well documented in a review by
Keswick and Gerba (1980) where viral particles were recovered at
distances of over 1 kilometer from their source. In an important
study performed to monitor viral movement through the soil,
Stramer (1984) introduced stool containing poliovirus into septic
tanks and detected 220 viral particles per milliliter in a well
53.3 meters away only 12 days after the initial viral introduction.
The same authorfound that the viral particles traveled 4.45 meters
per day and persisted for 100 days in ground water after leaving
the septic tanks.
Investigations on the persistence of viruses and indicator bacteria
in ground water indicate that enteric viruses survive for longer
periods of time (Keswick etal., 1982b; Yeager and O'Brien, 1979;
and Niemi, 1976) because they are more resistant to environmental
conditions (Shuval et al., 1971). To that effect, in an attempt to
-------
Table 2. Virus Transport and Attenuation in the Subsurface
Adsorbent
(Depth)
Influent
Loading
Effluent
Numbers
Experimental
Conditions
Flow
Property
Virus Removal
Capacity
Reference
Virus Attenuation by Laboratory Batch Test
Activated
Carbon
Sediments,
Kaolin,
Cellulose, and
Carbon Black
T4 phage
(108 PFU/ml)
QB, fr, MS2,
andT4
(104-109
PFU/ml)
Virus Transport/Attenuation
5 Soils
(30 - 40 cm)
Sandy Forest
Soil
(20 cm)
Coarse Sand
(13 cm)
Clay Loam
(13 cm)
Alluvial aquifer
sediments
(20 cm)
Ottawa sand
(10-20 cm)
T2 phage
(2xl07
PFU/ml)
T, phage
(4.8 x 107
PFU/ml)
Polio 1
(2xl07
PFU/ml)
Polio 1
(10s PFU/ml)
Polio 1
(10s PFU/ml)
PRD-1,MS2
(109 PFU/ml)
(|>X-174
bacterio phage
3.9x10'
PFU/ml
102-108
PFU/ml
pH = 6.9,
Ionic Strength
0.08 s/l= 1:100
(mg/mL)
T = 23 °C
pH = 7.2
T = 25 °C
Through Percolating Laboratory
<106
PFU/ml
< 106
PFU/ml
4.8 x 10s
PFU/ml
5.0 x 103
PFU/ml
2.5 xlO4
PFU/ml
<0.1 xlO3
PFU/ml
(Not
detected)
108-109
PFU/ml
5x1 04
PFU/ml
Distilled water
and traces of
salts
pH = 6.3,
T = 20 °C
Secondary
effluent (pH
7.2) followed
by distilled
water
Ground water,
sewage effluent
pH8.3,T = 5°C
and 25 °C
Ground water,
sewage effluent
pH4.3,
T = 5 and 25 °C
Ground water
and traces of
salts
pH = 7.3
T = 21 °C
pH = 7.5
T = 6-9 °C
Flask reaction
for 24 hours
Flask
reaction for
one hour
Columns
Continuous
(0.078-0.313
cm/min)
Continuous
and
intermittent
Continuous
(0.001cm/
min)
Continuous
(Avg= 0.001
cm/min)
Intermittent
(a 2 mi-pulse
injection
flushed with
6 pore
volumes)
flow
(1.6-3.4
cm/h)
96% viral removal,
removal rate: 0.04 hr ' -
0.8 hr1 in the 1st 12 hrs.
and 0.002 hr1 in the 2nd
12 hrs.
Viral adsorption was
dependent on surface
acidity of the adsorbents
No virus breakthrough,
over 95% viral removal,
the highest numbers
remained in the top few
centimeters of the
column
97% viral removal,
Polio 1 retention was
greater under
intermittent flow,
breakthrough was only
observed with distilled
water
No virus breakthrough
No virus breakthrough
79- 100% removal,
breakthrough occurred
after 1 -2 pore volumes
No breakthrough
Cookson
and North
(1967)
Sakoda et
al. (1997)
Drewry
and
Eliasson
(1968)
Duboise et
al. (1976)
Sobsey et
al. (1995)
Sobsey et
al. (1995)
Dowd and
Pillai
(1997)
Jin et al.
(1997)
Field Case Studies of Virus Transport/Attenuation
Sewage
infiltration site
soils
(silty sand and
gravel, 18.3
meters)
Flat lands
cypress dome
soils (sandy with
varied clays, 7
meters)
f2 phage
(10s PFU/ml)
Enteric
viruses:
Polio (71*),
Coxsackie
(75*),
Echo (30*)
47% of
initial
loading
dropped
after 7
hrs.
Polio
(52*),
Coxsackie
(6*),
Echo (0)
Settled sewage
effluent
adjusted to 10s
PFU/ml
Secondary
effluent spray
irrigation
Flow
(Avg = 0.6
cm/min)
Ground water
53% removal, 48 hrs.
breakthrough in 1 8
meter well
Removal ratio of 27%
for Polio, 69% for
Coxsackie, andlOO%
for Echo viruses found
in 7 meter deep well
after rainfall
Schaub and
Sorber (1977)
Wellings et
al. (1975)
* Number of PFU counted in 500 mL sample water.
-------
Table 3. Factors Influencing Virus Fate in Soils
Factor
Influence on
Survival
Influence on
Migration
Temperature(
Microbial activity(
Moisture content(
PH(
Salt species and(
concentration(
Virus association(
with soil and other(
particulate matter(
Virus aggregation(
Soil properties(
Virus type(
Organic matter(
Hydraulic conditions(
Viruses survive longer at(
lower temperatures.(
Some viruses are inactivated(
more readily in the presence(
of certain microorganisms;(
however, adsorption to the(
surface of bacteria can be(
protective.(
Some viruses persist longer(
in moist soils than dry soils.(
Most enteric viruses are(
stable over a pH range of 3(
to 9; survival may be pro-(
longed at near-neutral pH(
values. (
Some viruses are protected(
from inactivation by certain(
cations; the reverse is also(
true.(
In many cases, survival is(
prolonged by adsorption to(
soil; however, the opposite(
has also been observed.(
Enhances survival.(
Effects on survival are(
probably related to the(
degree of virus adsorption.(
Different virus types vary(
in their susceptibility to(
inactivation by physical,(
chemical and biological(
factors. (
Presence of organic matter(
may protect viruses from(
inactivation; others have(
found that it may reversibly(
retard virus infectivity.(
Unknown.(
Unknown.(
Unknown.(
Generally, virus migration(
increases under saturated(
flow conditions.(
Generally, low pH favors(
virus adsorption and high(
pH results in virus(
desorption from soil(
particles.(
Generally, increasing the(
concentration of ionic(
salts and increasing(
cation valencies enhances(
virus adsorption.(
Virus movement through(
the soil is slowed or(
prevented by association(
with particulates.(
Retards movement.(
Greater virus migration(
in coarse-textured soils;(
there is a high degree of(
virus retention by the(
clay fraction of soil.(
Virus adsorption to soils(
is probably related to(
physico-chemical(
differences in virus capsid(
surfaces. (
Soluble organic matter(
competes with viruses for(
adsorption sites on soil(
particles.(
Generally, virus migration(
increases with increasing(
hydraulic loads and flow(
rates.(
Modified from Sobsey, 1983.(
-------
monitor the survival of pathogenic microorganisms with ground
water collected from a 145-meter deep well in Florida, it was
shown that poliovirus type 1 (K=-0.0019) was more stable than E
co//or S. faecalis (K=0.0012) while coliphage f2 had the highest
decay rates. This characteristic is further substantiated by data
indicating that both rotaviruses and enteroviruses may be more
resistant to chlorination than indicator bacteria (Melnick et al.,
1978). In terms of their relative susceptibility, some enteroviruses
such as HAV are more stable under adverse environmental
conditionsthan poliovirus 1. The inherent diversityforthe longevity
of this class of viruses toward factors that affect their survival (i.e.,
soil type, pH, temperature) is apparent in Table 4. During this
assessment, the die-off rate constants were calculated from
selected literature which were primarily acquired from ground-
water investigations.
The die-off rates in Table 4 represent the time rate of change of the
concentration of a microorganism in ground water/soil by assuming
the virus die-off follows first-order kinetics. It is noted that die-off
rates are also referred to as inactivation, or decay, or survival rates
in the literature. Inactivation is a process by which viruses lose
their ability to produce progeny (Bitton, 1980; Bitton et al., 1983).
Removal rates in solution in batch studies may represent die-off
rates of viruses, while removal rates in column or chamber studies
may represent attachment/adsorption rates and/or die-off rates
(Powelson and Gerba, 1994).
From the case studies examined (i.e., batch, chamber, column
and field tests), the following findings were observed.
• Viruses adsorbed on solid surf aces can possess a significantly
longer time of activity than viruses suspended in solution.
Different inactivation rates in water and on solids were
reported. For example, the inactivation at pH 7.2 is 0.055 Ir1
for E. co//phage adsorbed on solids, and is 0.28 Ir1 for the
virus in suspension (Sakoda et al.,1997). However, in many
publications the inactivation rates on solids and in solution
were not distinguished. The inactivation rates used in studies
of virus survival and transport are difficult to interpret.
• Transport of a virus in the subsurface can be controlled by
multi-processes, such as advection, dispersion, adsorption,
inactivation/decay, etc. Many case studies usually focus on
only one or a few processes and ignore others which can be
of significance in controlling the transport of viruses.
• Parameters used in transport studies are rarely obtained from
independent experiments, and few experiments have been
designed to obtain these independent parameters. Examples
of the studies developing these independent parameters are
Bales et al. (1991) and Dowd et al. (1998).
• Many column studies have been conducted to examine
adsorption/inactivation of viruses, but few have been
conducted to examine their elution/desorption in columns.
Examples of the studies considering these latter processes
are Jin et al. (1997), Dowd et al. (1998), and Powelson et al.
(1993).
• In many cases, equilibrium adsorption is of little significance,
and kinetic sorption with prevailing attachment/sorption
appears to control virus removal in the field (e.g., Schijven
and Hassanizadeh, 2000).
• Many experimental studies in relation to virus transport have
been published; however, relatively few efforts have been
made to simulate experimental results. Jin et al. (1997) and
Dowd et al. (1998) are two examples of such simulation.
As discussed earlier, viral transport through porous media is
controlled by sorption and by inactivation (Bales et al., 1993; 1995;
Bitton, 1975; Murray and Laband, 1979). However, adsorption of
viruses to soil should not be confused with their inactivation since
adsorption is not permanent and can be reversed by the ionic
characteristics of the percolating water (Vilker et al., 1978; Bales
etal.,1993). Reversible sorption of poliovirustype 1 andcoliphage
T2 from clay resulted in fully infectious particles (Carlson et al.,
1968). Viruses can remain infective after a travel distance of
67 meters vertically and 408 meters horizontally (Keswick and
Gerba, 1980). According to Murray and Parks (1980), various
forces involved in the attachment of viruses to soil particles may
include hydrogen bonding, electrostatic attraction and repulsion,
van der Walls forces, and covalent ionic interaction. Bales et al.
(1991) demonstrated the importance of solution pH and soil-
surface hydrophobicity in attachment and detachment of
bacteriophage from solid surfaces. Bales et al. (1993) have
shown that low levels of organic matter in porous media can retard
viral transport.
Adsorption or release of viruses from soil particles is due to the
amphoteric nature of the external viral proteins. Thus, both ionic
strength and pH strongly affect the adsorption process
(Duboise et al., 1976). Many viruses sorb more strongly in acidic
water. Any sharp increase in the pH may enhance the detachment
and, therefore, the mobility of the viruses that are attached to the
soil matrix. Hydrophobic interactions are also involved in the
adsorptionofvirusestosands(Dizeretal., 1984). Virus adsorption
is significantly influenced by a number of parameters such as the
type of virus, soil type, virus load, pH, and salt concentration
(Gerba and Bitton, 1984). Although viruses including polio, HAV,
reovirus, and coxsackievirus sorb more strongly to clay rather
than silt and sand particulate, the extent of sorption of
coxsackievirus seems to be limited and without any relationship to
the texture of geologic materials. Batch studies with 28 viruses
and 9 soil types indicated a wide range of virus adsorption from
0.01 to 99.9 percent (Goyal and Gerba, 1979). The diversity of
data reported in the literature makes viral transport modeling
difficult (Powelson etal., 1990). According to Yatesetal., (1987),
modeling capabilities far exceed our current understanding of the
behavior of viruses in soil and ground water.
Hydrophobic interactions are apparently also responsible for
sorption of viruses at the air-water interface in unsaturated soils
(Thompson etal., 1998). Some experimental evidence suggests
viruses sorbed at these sites may undergo accelerated inactivation
rates (Thompson and Yates, 1999). When viruses are adsorbed
to the air-water interface they may be considered to be effectively
removed from the transport process (Chu et al., 2001). This is
because environmental models have not yet been developed for
advection at this surface. Just as virus inactivation may be
accelerated at the air-water interface, some have suggested
sorption at the solid-water interface may enhance virus longevity
(Sim and Chrysiopoulos, 2000). These notions have yet to be
rigorously tested experimentally, and as yet, a physical basis for
them has not been established.
It should also be noted that most soils have enormous buffering
capacity to maintain apH balance, thereby averting the release of
viruses. The soil's organic content canfurtherserve as a retardation
factor for some viruses. In general, reoviruses sorb strongly to
organic materials as compared to poiioviruses and HAV. Vilker et
al. (1978) also questioned the results of transport studies based
on artificially high initial concentrations of viruses and high water
flow rates as compared to those observed in thefield (approximately
0.01 cm/min). As expected, the behavior of viruses, as with any
other biotic system in the environment is diverse. For example,
while Drewry and Eliassen (1968) have shown that percolation
through a few meters was sufficient for the removal of viral
-------
Table 4. Die-off Rate Constants (day1) of Pathogens in the Subsurface
Microorganisms
Poliovirus 1
Poliovirus 3
Coxsackievirus A- 13
Coxsackievirus B-l
Coxsackievirus B-3
Coxsackievirus A-9
Coxsackievirus B-3
Fecal streptococcus
Fecal Coliforms
E. coli
E. coli
RotavirusSA-11
Coliphage f2
F+ phage
Die-off Rate
(day1)*
"0.96
"0.52
0.77
0.21
"0.01
b0.02
b0.03
0.013
0.07
0.016
0.024
C0.51
C0.66
c>1.42
c>1.42
1.26
1.0
"3.4
0.41
0.19
b 2.2
"0.12
b0.27
0.23
"0.45
0.32
b 0.001
b 0.018
b0.03
0.36
b0.20
0.39
bo.oi
b0.02
b0.03
Environmental Conditions
SW;pH, 8.3; T, 23-27 °C
SW;pH, 8.3 ;T, 4-8 °C
SW; pH, 7.8; T, 12-20°C
GW;pH, 7.8; T, 3-15 °C
GW; pH, 7.4; T, 10 °C
GW; pH, 7.4; T, 20 °C
GW; pH, 7.4; T, 30 °C
GW saturated loamy soil; T, 10 °C
GW saturated loamy soil; T, 23 °C
GW saturated sandy soil; T, 10 °C
GW saturated sandy soil; T, 23 °C
GW, sandy soils; pH 8.3; T, 5 °C
GW, sandy soils; pH 4.3; T, 25 °C
GW, clay loam; pH 8.3; T, 5 °C
GW, clay loam; pH 8.3; T, 25 °C
SW;pH, 8.3 ; T, 23-27 °C
SW;pH, 7.5; T, 9-12 °C
SW;pH, 8.3; 1,23-27 °C
SW;pH, 8.3 ;T, 4-8 °C
GW;pH, 7.8; 1,3-15 °C
Sand-silty soil; pH 7.8, T, 23 °C
Sand-silty soil; pH 7.8, T, 23 °C
GW;pH, 7.5; T, 9-12 °C
GW;pH, 7.8; T, 3-15 °C
GW;pH, 7.5; T, 9-12 °C
GW;pH, 7.8; T, 3-15 °C
GW; pH, 7.4; T, 10 °C
GW; pH, 7.4; T, 20 °C
GW; pH, 7.4; T, 30 °C
GW;pH, 7.8; T, 3-15 °C
GW; pH, 7.8; T, 23 °C
GW;pH, 7.8; 1,3-15 °C
GW; pH, 7.4; T, 10 °C
GW; pH, 7.4; T, 20 °C
GW; pH, 7.4; T, 30 °C
Experimental
Methods
Chamber*
Chamber
Batch test
Batch test
Column test
Chamber
Chamber
Chamber
Chamber
Batch test
Chamber
Chamber
Chamber
Chamber
Batch test
Chamber
Batch test
Chamber
Batch test
Reference
O'Brien & Newman
(1977)
Keswick et al. (1982b)
Nasser & Oman (1999)
Blanc & Nasser (1996)
Sobseyetal. (1995)
O'Brien & Newman
(1977)
Keswick etal. (1982b)
O'Brien & Newman
(1977)
Keswick et al. (1982b)
Hurst etal. (1980)
McFeters et al. (1974)
Keswick etal. (1982b)
McFeters etal. (1974)
Keswick et al. (1982b)
Nasser & Oman (1999)
Keswick etal. (1982b)
Hurst etal. (1980)
Keswick etal. (1982b)
Nasser & Oman (1999)
* as -logltl Ct/Co; GW, Ground Water; SW, Surface Water; BGS,
Below ground surface
a One log reduction required time (LRT) was used in the reference
paper for the inactivation rate.
b The values were estimated by curve fitting graphically.
°Soil columns (13.3 cm long by 2.5 cm diameter) were each dosed
with 13.5 ml of virus-seeded ground water. In 53 days, a total of
16 doses were given to each column. Each dose (13.5 ml) of
virus-seeded ground water was kept in a column for about 3.5
days, and then drained. Mean value of the 16 doses was
presented in the reference. The values in this table are logltl
reduction per day by dividing the mean value by 3.5 (day).
-------
Table 4. continued
Hepatitis A virus
MS2 bacteriophage
PRD-1 bacteriophage
(j>X-174
bacteriophage
MS-2 bacteriophage
M-l
PRD-1
"0.06
"0.016
"0.03
0.001
0.01
0.015
0.023
°0.42
C0.45
c>0.94
c>0.94
0.05
0.16
0.12
0.19
0.028
0.053
0.032
c>1.45
°>1.45
2.24
0.15
0.28
5.82
0.32
0.57
0.028
0.026
0.055
0.034
d=5
14.2-17.3
0.5
1.8
0
0
GW;pH, 7.4; T, 10 °C
GW; pH, 7.4; T, 20 °C
GW; pH, 7.4; T, 30 °C
GW saturated loamy soil; T, 10 °C
GW saturated loamy soil; T, 23 °C
GW saturated sandy soil; T, 10 °C
GW saturated sandy soil; T, 23 °C
GW sandy soils; pH, 8.3; T, 5 °C
GW sandy soils; pH, 8.3; T, 25 °C
GW clay loam; pH, 8.3; T, 5 °C
GW clay loam; pH, 8.3; T, 25 °C
GW saturated loamy soil; T, 1 0 °C
GW saturated loamy soil; T, 23 °C
GW saturated sandy soil; T, 10 °C
GW saturated sandy soil; T, 23 °C
N. Carolina GW; pH, 7.9; T,12 °C
Arizona GW; pH, 8.2; T, 12 °C
New York GW; pH, 7.3; T, 12°C
Clay loam; pH, 4.3; T, 5 °C
Clay loam; pH, 4.3; T, 25 °C
Wetland, 0-3 BGS (m); summer
Wetland, 3-70 BGS (m); summer
Wetland, 0-70 BGS (m); summer
Wetland, 0-3 BGS (m); winter
Wetland, 3-70 BGS (m); winter
Wetland, 0-70 BGS (m); winter
GW saturated loamy soil; T,10 °C
GW saturated loamy soil; T,23 °C
GW saturated sandy soil; T, 10 °C
GW saturated sandy soil; T, 23 °C
Sandy aquifer; pH 5.7; T, 11.5 °C
Ottawa sand saturated with
phosphate saline solution (pH =
7.5); T, 6 - 9 °C
GW with fresh soil; T, 25 °C
GW leached soil; T, 25 °C
Sand (fine-medium grained)
Sand (fine-medium grained)
Batch test
Batch test
Batch test
Column test
Batch test
Batch test
Batch test
Column test
Field test
Field test
Batch test
Batch test
Field study
Column
study
Column
study
Field study
Nasser & Oman (1999)
Blanc & Nasser (1996)
Blanc & Nasser (1996)
Sobseyetal. (1995)
Blanc & Nasser (1996)
Blanc & Nasser (1996)
Yates&Gerba(1984)
Sobseyetal. (1995)
Chendorain et al. (1998)
Chendorain et al. (1998)
Blanc & Nasser (1996)
Blanc & Nasser (1996)
Bales et al. (1995)
Jin etal. (1997)
Powelson et al. (1991)
Bales et al. (1997)
> = virus reduced to limit of detection
de The initial concentration was 1.4 x 107/ml, the breakthrough
peak was detected on the 3rd day and the concentration dropped
to 50-99 PFU/ml. This is approximately a 5 log,0 reduction.
Very low concentrations (0.6-8 PFU/ml) were detected
between the 3ri day to the 24«> day.
# In the chamber test, nucleopore polycarbonate membranes
(0.015 mm) were sandwiched between natural rubber gaskets of
the plexiglass chamber. Then, the chambers were filled with virus
or bacteria suspended in sterile water. The loaded chambers were
placed in the bottom of a 10-gallon covered container that had been
modified to provide a continuous flow of ground water or in a
natural environment. In the chamber test, the loaded chambers
were placed in a flowing condition (in a natural stream, in a
container with flow, or within a well) while the batch test was
conducted in a static condition.
10
-------
contamination, poliovirus type II used as a "marker" was isolated
from a 30 meter deep well located 100 meters from a wastewater
drain field in Michigan (Macketal., 1972). Therefore, current rule-
making considerations forthe upcoming Ground Water Rule entail
a sampling program requirement. Some of the discrepancies in
the reported results of these investigations also may be attributed
to physical heterogeneity (Harvey et al., 1993) and the earlier
methods used for the detection and concentration of enteric
viruses which were usually less than 50 percent efficient (Gerba,
1985). The use of reliable current methodologies (i.e., molecular
techniques) can, however, minimize the variance between reported
and actual numbers. Practices designed to ensure compliance
with drinking water standards might more properly rely instead on
a cadre of multidisciplinary approaches including predictive models,
geological settings that result in viral retention, as well as sampling
and analysis. To this end, EPA is aiming, by its proposed Ground
Water Rule, to reduce the public health risk related to the ingestion
of waterborne pathogens from fecal contamination for a large
number of people served by ground water.
In an attempt to demonstrate how to obtain parameters from
laboratory experiments which were designed for investigating
inactivation and adsorption of viruses, the following case study is
offered.
A Case Study
To investigate the influence of inactivation and adsorption
mechanisms in water, Rossi and Aragno (1999) presented a batch
agitation technique to examine inactivation-adsorption kinetics
simultaneously. An initial amount of bacteriophage T7 of about
3x 105 plaque-forming units (PFU) with and without colloid clay
particles was used in the batch study, and the evolution of the
amount of bacteriophage was recorded as shown in Figure 3. The
inactivation and adsorption mechanisms of viruses in a
montmorillonite suspension are mathematically described as:
O Q
P~5t =
(D
(2)
where:
C is the number of free viruses per unit volume in the aqueous
phase,
S is the number of viruses per unit mass of solid in the solid
phase,
t is time,
6 is the volume fraction of the aqueous phase,
p is solid density in the suspension,
H1 and |is are the inactivation rate coefficients for free viruses in
the aqueous phase and in the attached solid, respectively,
and
^attachanc' ^deta* are^ne attachment (adsorption) and detachment
(desorption) rate coefficients.
100
z>
LL
Q_
CD
O)
CO
Observed
Simulated
50 100 150
Time (min)
200
Figure3. Adsorption and inactivation kinetics of phage T7 in 2.5% montmorilllonite suspension (/fattach = 0.10 min"1,
/cdetach= 0.073 min"1, u^ = 0.036 min"1, u,s = 0 min"1). Experimental data are obtained from Rossi and Aragno
(1999).
11
-------
The left-hand side of equation (1) is the time rate of change of
viruses in the aqueous phase and in the solid phase, and the right-
hand side is the loss of viruses due to inactivation in the aqueous
phase and in the solid phase, respectively. Equation (2) states
that the time rate of change of the viruses on a solid phase equals
the difference between the attachment of viruses from solution to
solid and the detachment of the viruses from solid phase to
aqueous phase. The system of equations (equations 1 and 2) is
solved using a second-order Runge-Kutta algorithm with proper
initial conditions when the inactivation rate coefficients and
attachment/detachment rate coefficients are known. When
experimental data are available, a least-square curve fitting
technique is applied to estimate the parameters. Results of
Rossi/Aragno parameter estimation indicate that the inactivation
rateofvirusesonsolidphaseisnotofsignificance(i.e., (o.s= 0 min~1).
The same analyses showed that the other parameters are
/fattach= 0.10 min'1, frdeta(,h= 0.073min'1, and n1= 0.036min-1. Inthis
case,6 is 0.975 and p is 0.025 mg/ml. These parameters indicate
that virus attachment processes (the term 6kattachC ) are much
faster than the detachment processes (the term pkdetachS). This is
depicted in Figure 3 where the phageT7concentration dramatically
decreases in the early time period.
Effect of Hydrogeologic Settings on Viral Movement
The concentration and loading of viruses and the hydrogeologic
setting through which they move will control the potential for viral
migration to wells to a much greater extent than biological
survivability. A hydrogeologic setting often consists of a soil
underlain by unconsolidated deposits of sand, silt, and clay
mixtures over rock. The setting further incorporates unsaturated
and saturated zones. For purposes of this discussion, the amount
of precipitation available to transport the virus through the
subsurface will not be considered, although it is recognized that
infiltration acts as a transport mechanism as well as a dilution
factor.
All other factors being equal, the persistence of viruses at a well,
or other source of water, is most likely where saturated flow
transports large concentrations of the particles along short flow
paths through media which contribute little to attenuation. Although
the interrelated processes that control viral movement and
persistence in the subsurface are not completely understood
(Cadmus Group, et. al., 2000), some of the major hydrogeological
factors that can be used to evaluate the potential for viral presence
in ground-water wells include:
• transport mechanisms (unsaturated versus saturated flow
conditions);
• type of media through which the virus will travel (clays versus
sands versus fractured media);
• length of flow path to the extraction point (well); and
• time of travel.
Hydrogeologic settings with shallow water tables are more
susceptibleto viral transport. Viruses are attenuated or immobilized
by processes such as dessication, microbial activity, and
stagnation. Further, viruses commonly bind to soil particles, fine-
grained materials, and organic matter. The lower transport
velocities associated with unsaturated conditions (e.g., move,
stop, move cycle) allow these processes more time to occur. If
viruses are introduced directly into the water table (such as from
leaching tile fields associated with onsite sewage disposal) or if
the volume of contaminants can maintain saturated flowconditions
(such as in some artificial recharge situations), the potential for
contamination is increased (Aller et. al., 1987). Where the viral
concentration is high, the probability of contaminant migration is
increased regardless of the hydrogeologic setting. Therefore, in
hydrogeologic settings with deeper water tables and where
contaminants are not introduced intothe aquiferthrough saturated
flow conditions, viruses are much less likely to survive being
transported to a well.
Hydrogeologic settings with interconnected fractures or large
interconnected void spaces that lack fine-grained materials have
a greater potential for viral transport and well contamination. Karst
aquifers, fractured bedrockand gravel aquifers have been identified
in the proposed Ground-Water Rule as sensitive hydrogeologic
settings (U.S. EPA, 2000). In these settings, fractures and large
void spaces allow rapid transport through the aquifer, thereby
reducing the amount of time and particulate contact available for
attenuation. Potential interaction with rock walls along fractures
is reduced, and contact with fine-grained materials for potential
sorption sites is minimal.
Similar to fractured rock aquifers, gravel aquifers with only a small,
fine-grainedfraction have little potential for viral sorption. However,
as the amount of fine-grained material increases, effective grain
size decreases, the potential for sorption increases, and travel
times decrease. Finer-grained aquifers and aquifers where void
spaces are less interconnected or smaller are, therefore, less
likely to transport viruses significant distances.
The potential for physical viral removal by filtration also appears
to increase as grain size becomes smaller, although the filtration
processes are not well understood due to their size. However,
filtration of bacteria, which are larger than viruses, has been
shown to be an effective removal mechanism.
Hydrogeologic settings where fractures are not as interconnected
or where more tortuous flow paths must be followed to reach a well
also allow for greater viral removal. For example, in many rock
aquifers, ground-water flow follows bedding planes that may
result in an elongated, indirect pathway to a well. In other rock
aquifers, flow must travel around and through cemented portions
of the matrix thereby increasing the flow path. Similarly, sand and
gravel aquifers with fine-grained materials in the matrix will have
less direct flow paths as the water flows around the finer-grained
materials. Generally, it can be stated that tortuosity increases the
length of the flow path and decreases the hydraulic conductivity,
thus decreasing viral survival. Where finer-grained materials are
present or fractures are less interconnected, flow paths are also
longer, thereby offering some protection to wells in more permeable
units.
Hydrogeologic settings where time of travel is short have a greater
potential for viral contamination. Where less permeable units
(called aquitards) restrict or reduce vertical flow to underlying
aquifers, time of travel is increased. Although inactivation rates
have been shown to be extremely variable, time is a major factor
affecting virus viability.
Due to the importance of hydrogeologic settings, the proposed
Ground Water Rule thoroughly addresses this issue to identify
wells that are sensitive to fecal contamination. A component of
the proposed Ground Water Rule requires states to perform
hydrogeologic assessments for the systems that distribute ground
water that is not disinfected (source waters that are not treated to
provide 99.99% removal or inactivation of viruses). The states are
required to identify sensitive hydrogeologic settings and to perform
monitoring for indicators of fecal contamination from sensitive
hydrogeologic settings (see U.S. EPA, 2000, for the complete
proposed strategy).
12
-------
Virus Transport Modeling
One method of addressing regulations associated with virus
exposure, such as ground-water disinfection, the application of
liquid and solid waste to the land, and wellhead protection zones,
is the application of predictive virus transport models.
The states may choose to employ fate-and-transport models as
screening tools to identify hydrogeologic barriers for a particular
water supply aquifer. (U.S. EPA defines a hydrogeologic barrier
as the physical, biological, and chemical factors, singularly or in
combination, that prevent the movement of viable pathogens from
a contaminated source to a public supply well.) To this end, the
subject of modeling will become pertinent and will be discussed
herein. Like most predictive modeling efforts, the results depend
on the conceptual basis of the model as well as the quality and
availability of input data (Corapcioglu and Haridas, 1984). Clearly,
a thorough understanding of the processes and parameters
associated with virus transport are essential elements in their
application.
As shown in considerable detail in Table 3, some of the more
important subsurface virus transport factors include soil water
content and temperature, sorption and desorption, pH, salt content,
organic content of the soil and ground-water matrix, virus type and
activity, and hydraulic stresses. Berger (1994) indicated that the
inactivation rate of viruses is probably the single most important
parameter governing virus fate and transport in ground water.
Some of the existing models require only a few of these parameters
which limit their use to screening level activities, while others
require input information which is rarely available at field scale and
is usually applied in a research setting. One limitation of most
models is that they have been developed for use in the saturated
zone. It has been shown, however, that the potential for virus
removal is greater in the unsaturated zone than in ground water
(Gelhar, 1992).
Despite the number of models developed at present, tests of the
models against field data are not abundant. Simulation results of
the developed models were either compared to the analytical
solutions or fitted to data obtained for laboratory experiments.
Even though some models were developed to handle the complex
processes involved in virus transport, only simplified simulation
results were compared against ideally controlled experimental
conditions (Vilker and Surge, 1980; Matthess and Pekdeger,
1981; Tim and Mostaghimi, 1991; Teutsch et al., 1991).
The existing codes for virus transport can be placed into two
categories. As shown in Table 5, the first group contains computer
codes which are readily available to the public and which have
user's manuals. The second group, shown in Table 6, contain
computer codes which were developed for research purposes.
Better understanding of virus transport mechanisms was the main
motivation in developing these codes, rather than public
dissemination. As a result, further discussions herein will be
limited to the models in Table 5.
VIRALT, developed for EPA's Office of Drinking Water, is a
modular, semi-analytical and numerical code that simulates the
transport and fate of viruses in ground water. The code computes
viral concentrations in extracted water describing both steady-
state and transient transport including advection and dispersion in
the vertical direction in the unsaturated zone. Along ground-water
flow lines in the saturated zone it handles adsorption and
inactivation.
CANVAS was developed in order to improve on its predecessor,
VIRALT. The major enhancements implemented in CANVAS are:
• CANVAS can simulate multiple contaminant sources in the
unsaturated or saturated zones whereas VIRALT is limited to
a single source;
• transverse, as well as longitudinal and horizontal dispersion
in the saturated zone is simulated by CANVAS whereas
VIRALT is limited to longitudinal dispersion;
• a colloidal filtration term is designed to simulate the facilitated
transport of viral particles through the unsaturated and
saturated zones; and
Table 5. Publicly Available Virus Transport Codes: Group I
Program Name
VIRULO
v. 1.0
VIRALT
v. 3.0
CANVAS
v. 2.0
VIRTUS
v. 1.0
Year
2002
1994
1994
1991
Authors
Faulkner et al.
@
U.S. EPA-ORD
Park et al.
@
Hydro-Geologic
Park et al.
@
Hydro-Geologic
Yates et al.
@
U.S. Salinity Laboratory
Description
A Monte Carlo-based screening model for predicting total
virus mass attenuation in the unsaturated zone.
Processes Considered: advection, dispersion, sorption,
inactivation, and uncertainty.
A modular semi-analytic and numerical code for transport
and fate of viruses in the unsaturated zones.
Processes Considered: advection, dispersion, sorption.
and inactivation.
A modular semi-analytical and numerical code for
transport and fate of viruses in the unsaturated and
saturated zones.
Processes Considered: advection, dispersion, sorption.
inactivation, and colloidal filtration.
A numerical code for transport and fate of viruses in the
unsaturated zone. The vims transport is coupled with the
flow of water and heat through soil.
Processes Considered: advection, dispersion, sorption,
and inactivation.
Remarks
Developed
by EPA-
ORD
Developed
for EPA
Descendant
of VIRALT
Research-
oriented
code
13
-------
Table 6. Other Virus Transport Codes (Developed for Research Purposes): Group I
Authors
Chuetal.,
2001
Sim&
Chrysikopoulos,
2000.
Lindqvist et aL,
1994
Tan et al.,
1994
Hornberger et al.,
1992
Tanet al.,
1992
Harvey &
Garabedian,
1991
Lindqvist &
Bengtsson,
1991
Tim&
Mostaghimi,
1991
Taylor &
Jaffe,
1990
Matthess et al.,
1988
Corapcioglu &
Haridas,
1985
Matthess &
Pekdeger,
1981
Vilker & Burge
1980
Vilker etal.,
1978
Title of Research Paper
Mechanisms of virus removal during
transport in unsaturated porous media
Virus transport in unsaturated porous
media
A kinetic model for cell density
dependent bacterial transport in porous
media.
Transport of bacteria in an aquifer
sand: Experiments and model
simulations.
Bacterial transport in porous media:
Evaluation of a model using laboratory
observations.
Transport of bacteria during
unsaturated soil water flow.
Use of colloid filtration theory in
modeling the movement of bacteria
through a contaminated sandy aquifer.
Dispersal dynamics of ground-water
bacteria.
Model for predicting virus movement
through soils.
Saturated and biomass transport in a
porous medium.
Persistence and transport of bacteria
and virus in ground water - A
conceptual evaluation.
Microbial transport in soils and ground
water: A numerical model.
Concepts of a survival and transport
model of pathogenic bacteria and
viruses in ground water.
Adsorption mass transfer model for
virus transport in soils.
Application of ion
exchange/adsorption models to virus
transport in percolating beds.
Journal
WRR
37(2)
WRR
36(1)
WRR
30(12)
WRR
30(2)
WWR
28(3)
SSSAJ
56(5)
ES&T
25(1)
ME
21(1)
Ground
Water
29(2)
WRR
26(9)
JCH
2(2)
AWR
8(188)
STE
21(149)
WR
14(783)
AIChE
178(84)
Solution
Method
FDM
FDM
FDM&
ANAL
FDM
ANAL
Quasi-
ANAL
ANAL
ANAL
FEM
FEM
ANAL
ANAL,
FEM
Not Clear
ANAL
ANAL
Processes Considered
Advection, dispersion, mass-
transfer, adsorption, and
blocking
Advection, dispersion,
adsorption, and mass-transfer
Advection, dispersion, and
non-equilibrium sorption
Advection, dispersion, and
sorption (max retention
capacity included)
Advection, dispersion, and
clogging/declogging
Dispersion and sorption
Advection, dispersion,
sorption, and filtration
Advection, dispersion, non-
equilibrium sorption, and
decay
Advection, dispersion, linear
equilibrium, sorption, and first
order decay.
Program Name: VIROTRANS
Advection, dispersion,
sorption, growth/decay, and
shear/filtration. The change in
parameter values due to
biofilm clogging was
included.
Advection, dispersion,
sorption, and filtration.
Advection, dispersion,
sorption, decay/growth, and
clogging/declogging.
Transport equation is coupled
with nulrient concentration.
Discussion on controlling
factors for bacteria/virus
transport.
Adsorption mass transfer
model.
Ion exchange/adsorption
Medium
Un-
saturated
1-D
Un-
saturated
1-D
Saturated
1-D
Saturated
1-D
Saturated
1-D
Un-
saturated
1-D
Saturated
1-D
Saturated
Sand
Column
Un-
saturated
Soil
Saturated
Column
Saturated
1-D
Saturated
1-D&
2-D
Saturated
medium
Batch &
Column
Saturated
Column
WRR: Water Resources Research SSSJ:
ME: Microbial Ecology WR:
JCH: Jour, of Contaminant Hydrol. AWR:
ES&T: Environ. Sci. & Tech. STE:
Soil Sciences Society of America Jour
Water Research
Advances in Water Resources
Science of the Total Environment
ANAL: Analytical
FEM: Finite Element Method
FDM: Finite Difference Method
AIChE: Am. Inst. for Chem. Eng. Symp. Ser.
14
-------
• allows the virus inactivation coefficient to be either
temperature-dependent or given as a user-specific value.
VIRTUS is a finite difference model for virus fate and transport in
unsaturated soil. The model allows the virus inactivation rate to
vary based on soil temperature. It supports unsteady flow,
transport in layered soils, different inactivation rates for adsorbed
versus freely suspended viral particles, and the flow of heat
through soil. It assumes that viruses are introduced at the soil
surface. VIRTUS is based on mass conservation of a contaminant
in porous media and couples the flow of water, viruses, and heat
through the soil. The model can be used to estimate the number
of viruses that reach ground water after traveling through soil from
a contamination source.
VIRULOwas developed to fill the need for a predictive screening
model. It uses the assumption of gravity flow infiltration and time
averaging to solve governing equations for advection, dispersion,
adsorption, and mass-transfer developed by Sim and
Chrysikopoulos (2000). This model was produced with the idea
that in many cases very little information may be known about a
particular site. It supplies a small database of default parameters
for water flow and virus transport. At a minimum, the user needs
only to select one of the twelve USDA soil categories, a virus
whose attenuation will be predicted, and a thickness of a soil bed
of interest. The Monte Carlo method is employed with known or
assumed distribution functions for the input parameters. Random
number generators are used internally, and a graphical display of
the histogram of predicted attenuations is produced, along with
the number of times a user-specified level of attenuation was not
achieved in a given number of simulations (1,000,000 by default).
Virus transport modeling is inherently fraught with uncertainty. It
has been suggested that models have a tendency to under-predict
virus transport, and hence their use as a sole criterion for purposes
of determining regulatory compliance is questionable (Yates and
Jury, 1995). Currentrule-makingconsiderationsfortheforthcoming
Ground Water Rule consider modeling as a potential tool which
can be useful, but a sampling program will always be a requirement.
Example Application of the VIRULO Screening Model
The use of municipal sewage effluent for irrigation is a growing
trend in urban and suburban areas. It represents an attractive
means by which water that has undergone treatment, but not to a
level making it suitable for open distribution, can fulfill a need at
greatly reduced costs. This is because the soil above the ground-
water table through which irrigation water percolates can be
viewed as a natural means of filtration. In a completely engineered
system, the final stages of treatment to a level suitable for human
consumption are very costly. Depending on the degree of
disinfection applied to the effluent, viruses may have undergone
little or no attenuation prior to irrigation. Therefore, there is a
potential for viral contamination to underlying aquifers if natural
filtration above the ground-water table is not sufficient to remove
viable viruses. U.S. EPA Region VI recently conducted pilot
Comprehensive Performance Evaluations for ground water for
selected water supply systems in Texas and New Mexico (e.g.,
U.S. EPA, 2000). In these evaluations, the ground-water system
itself is considered as a component of the overall water supply
system performance. The evaluations frequently cite a goal of
achieving "99.99% virus inactivation," in order for the ground-
water system to be considered acceptable.
These notions have implications for planning. Parks and golf
courses are the most common sites of irrigation with municipal
sewage effluent. In a gross sense, information from soil surveys,
along with a screening model, can provide an indication of the
level of risk of viral contamination (to the ground-water table) a
particular site may have. Figure 4 shows a map of a portion of
Wake County, North Carolina, which contains the city of Raleigh
and its suburbs. The areas shown outlined in black represent
locations of park lands and open space which might be suitable for
irrigation with municipal sewage effluent.
The VIRULO screening model treats the total cumulative mass
attenuation of viruses probabilistically. It contains a small database
of input parameters describing soil properties that control rate of
water percolation (Figure 5) and virus properties that control
sorption, equilibrium partitioning between suspension and
adsorption to soil particles, and inactivation rates (Figure 6). As
shown in Figures 5 and 6, the parameters are grouped by default
according to USDA soil type and virus of interest. The database
was built from information in the USDA's UNSODA database,
managed by the U.S. Agricultural Research Service, and from an
extensive literature search of experiments for virus behavior in
soils. All parameters were assumed to be either normally or log-
normally distributed, as determined by examination of histograms
of experimental outcomes. VIRULO uses the Monte Carlo method
with computer generated random numbers conditioned on the
parameters to produce outputs of total time-integrated mass
attenuation, defined as the average total amount of viable viruses
leaving the bottom of a soil bed divided by the total amount arriving
at the top of the soil bed (Figure 7). VIRULO presents the
outcomes in a histogram of values of minus the base-10 logarithm
of attenuation (Figure 8).
The soil survey for Wake County includes listings of the seasonal
high water table, which depends on soil type as well as geographic
location (proximity to streams and topography). The soil survey
data can be used as input to the VIRULO model with the default
parameters to get a spatially explicit representation of the possible
level of risk associated with irrigating in a particular park or open-
space area, as shown in Figure 9. The information produced is far
from being definitive because of seasonal variability and soil in-
homogeneity, but it can serve as a guide to highlight areas of
concern. The assumptions used in VIRULO and the conditions
under which large error may be incurred from employing them are
listed in Table 7.
One reason predictive modeling of viral fate and transport is
especially difficult is the fact that only one or two virus particles can
infect any human who ingests them. Thus the margin for error is
very small, and even very low probabilities of virus persistence
may still represent cause for concern.
Setback Distances
Traditionally, state and county regulators have established fixed
setback distances for all geologic settings in their jurisdictions.
For example, the distance between a septic tank and a private well
would, in many instances, be as little as 50 feet and would apply
for tight clays as well as fractured rock. It would apply to areas
where the water table was near the surface as well as at
considerable depth. As discussed in this document, the travel
time or transport distance of viral particles depends on a number
of factors including moisture content, geological setting, type and
depth of the soil overburden, and source loading, only to name a
few.
Frequently, guidelines established as minimum distances became
so standard that a well was often positioned precisely 50 feet from
the septic tank. In the survey conducted as part of the proposed
Ground-Water Rule, setback distances were found to be quite
variable (U.S. EPA, 2000). Some of the distances were presumably
based on scientific principles, while others were holdovers from
past practices.
15
-------
6
NCSUAG Lands
fates Mill/
Open
Water
Figure 4. Map of portion of Wake County, North Carolina.
SWlrulo
jJSJJU
File Edit Run About )k> Start Simulation [ •stop Threshold Attenuation (c): | 4 1 (-login)
sEA Flow Parameters
Parameter
8r
tog,0a
P
:
L
loamysand »
^'ijV| Virus Parameters ijj|j| Histogram -— _ Probability
Mean Strf, Deviation Units
0.05
0
0 39
•12
057
028
1500000.0
4.2E-4
0.00559
117
0.5
o.ot
0
0.04
0.22
0.06
0.04
1B7000.0
2.2E-5
t.06-4
7.38
0.1
IE Uniformly Random
m'm-1
Iofl10(m-')
logUH.)
om-1
m
m
Celsius
m
Figure 5. Flow parameters input panel in VIRULO.
16
-------
File Edit Run About
Threshold Anenuaion (if | 4 | (-logio)
$ Flow Parameters < '':.' virus Parameters Jjj]] Histogram r^ Probability
Parameter
Mean
•3.941
•3.446
0.00134
0.00927
3.5E-6
0.001203
Figure 6. Virus parameters input panel in VIRULO.
Cw(in)
max
time
t
I
Std. Deviation
Units
0.782
0.782
(Ofl10(h-')
00018
00818
nih
5.0E-9
0.003180
ml, '
nfa-
soil
water table v
air
Cw(OUt)
time
Figure 7. Conceptual depiction of soil bed in VIRULO.
17
-------
File E
-------
Table?. Assumptions Made in VIRULOand Possible Consequences
Assumption
Soil is homogeneous
Soil does not induce preferential flow
Soil and soil water are free of dramatic
hydrophobic effects
Water percolation is due to gravity only
Soil is geochemically homogeneous
Microbial predation not considered
Temperature not considered
Irrigation water contains no surfactants
Potential Sources of Large Error in Assumption
Macropores, aggregates, not considered, though they may greatly affect hydraulic
conductivity if present
Roots, dessication cracks, worm holes and burrows may be present, providing a ready
conduit for preferential flow to the water table
Organic matter, recent fires can render predicted sorption, mass transfer, completely
erroneous
Abrupt rainfalls, floods, or periods of extended dryness can produce hydraulic pressure
gradients in soils not considered in VIRULO's hydraulic conductivity model
Microbial activity, decomposition, and mineral weathering can produce conditions that
affect virus longevity
Protozoans present in near-surface can prey on viruses
Temperature can influence viral survivability and longevity
Municipal effluent that has undergone little treatment may contain surfactants, such as
detergent residues, that can affect both viral sorption and hydraulic conductivity
One approach in determining setback distances for septic tanks
in wellhead protection areas and bankfiltration sites is to determine
travel times using ground-water flow characteristics (Yates and
Yates, 1987). This approach has been implemented in the
Federal Republic of Germany, for example, where three concentric
zones protect each drinking-water well. The zone immediately
surrounding the well is faced with the most restrictive regulations
which are founded on the belief that a 50-day residence time is
adequate for inactivation of any pathogen present in contaminated
water (Dizer et al., 1984). However, a comprehensive study by
Matthess et al. (1988) involving the evaluation of "50 days zone"
concluded that the reduction of viruses by 7 log units (current
regulations) requires a much longer residence time. Matthess et
al., indicated that a reduction of 7 log units occurred in "about
270 days (Haltern and Segeberger Forest) in one study, and
about 160-170 days (Dornach)" would be required according to
another study.
Another approach to this important issue is to consider the
vulnerability to virus transport in the subsurface for portions of a
state or county or for individual aquifers. Although there are a
number of approaches to rank vulnerability, DRASTIC is one
assessment methodology that utilizes hydrogeologic setting
descriptions and a numerical ranking system to evaluate the
ground-water pollution potential (Aller et. al., 1987). DRASTIC
assumes that a potential contaminant will be introduced at the
ground surface, have the mobility of water and be flushed toward
the aquifer by infiltration. Utilizing existing information at variable
scales, the methodology was designed to evaluate areas of
100 acres or larger.
DRASTIC is an acronym representing seven reasonably-available
factors that are used to develop a numerical score. They are:
Depth to water, net Recharge, Aquifer media, Soil, Topography
(slope), Impact of the vadose zone media, and hydraulic
Conductivity of the aquifer. DRASTIC uses a weighting system
to create a relative pollution potential index that varies between
65 and 223 with the higher numbers expressing greater
vulnerability.
Although DRASTIC was not designed specifically to evaluate the
movement of viruses in the subsurface, the major transport
mechanisms and flow paths for viral transport are considered and
the flexibility of the systems' rating scheme allows many of these
factors to be taken into account. For example, Depth to Water
addresses saturated versus unsaturated flow conditions and their
importance. Aquifer Media, Soil, and Impact of the Vadose Zone
Media all are based on descriptive soil and rock terms that allow
for variation due to fracturing, grain size, attenuation mechanisms
and overall characteristics that affect flow. Topography addresses
the tendency of viruses to be introduced into the subsurface or to
be carried away by runoff. Hydraulic Conductivity addresses the
relative ease of a contaminant to move with the velocity of water
through the aquifer.
Clearly, meaningful setback distances can only be developed by
using scientific principles that allow for the use of available
knowledge. The establishment of setback distances from sources
of viral contamination to points of extraction (wells) can be
established using DRASTIC if both the hydrogeologic setting and
sensitivity rankings are considered. For example, high pollution
potential indices signal the need for greater setback distances.
However, the hydrogeologic factors that control viral movement
must be evaluated within this context in order to establish
reasonable numbers for setback distances. A matrix that
incorporates the important DRASTIC factors can be utilized to
establish setback distances that include the vulnerability concept.
Setback distances must incorporate the knowledge of saturated
flow, transport pathway length, transport velocities, media
interaction and potential attenuation mechanisms. These setback
distances can be used on a regional scale, but can be modified if
site-specific information is available. The beauty of DRASTIC is
that its rationale and sensitivity factors are easily displayed, so
that modification can be readily made.
Summary
Existing legislation addresses the protection of ground-water
sources of drinking water with respect to pathogenic
19
-------
microorganisms. It is a particularly salient issue since about half
of the drinking water supplies in this country are obtained from
aquifers, and between 1989 and 1990 in the United States 13 of
26 drinking water outbreaks were attributed to contaminated
ground water with viruses being the main etiologic agents (CDC,
1991). Therefore, the transmission and survival of human
pathogens, particularly human enteric viruses, through the soil to
underground sources of drinking water are a serious riskto public
health. Among the diverse sources of ground-water contamination,
septic tank effluents, sludge disposal, and the application of waste
water to the land are most pervasive.
The transport of pathogens in the subsurface depends on their
retention to soil and aquifer materials and their survival. Some of
the more important factors affecting virus transport include soil
water content, temperature, sorption and desorption, pH, salt
content, type of virus, and hydraulic stresses. There are indications
that the inactivation rate of viruses is the single most important
factor governing virus transport and fate in the subsurface.
There continues to be considerable controversy over the use of
appropriate indicators for sanitary and biological states in
environmental investigations. Since adsorption and inactivation
are strongly virus dependent, it is important to realize that there is
no single virus for which its transport characteristics can be used
as a model to adequately describe the transport of all enteroviruses.
One solution may be to use a cocktail of viruses with a range of soil
passage characteristics. The selection of indicators is often
influenced by the cost and time required for analyses as well as the
efficiency of the assay method selected.
The concentration and loading of viruses and the hydrogeologic
setting through which they move are major factors influencing
theirtransport. Included among the most important hydrogeological
factors that can be used to evaluate viral transport are the flux of
moisture in the unsaturated and saturated zones, the media
through which the particles travel, length of flow path, and time of
travel. One tool which can be used to evaluate virus exposure is
the application of predictive virus transport models (Hurst, 1997).
Like most predictive modeling, the results depend on the conceptual
basis of the model as well as the quality and availability of input
data. Clearly, the success of predictive modeling depends on a
thorough understanding of the processes and parameters involved
in viral transport.
Notice
The U.S. Environmental Protection Agency through its Office of
Research and Development partially funded and collaborated in
the research described here under Contract No. 68-C4-0031 to
Dynamac Corporation. It has been subjected to the Agency's peer
and administrative review and has been approved for publication
as an EPA document. Mention of trade names or commercial
products does not constitute endorsement or recommendation for
use.
Quality Assurance Statement
All research projects making conclusions or recommendations
based on environmental data andfunded bythe U.S. Environmental
Protection Agency are required to participate in the Agency
Quality Assurance Program. This project did not involve the
collection or use of environmental data and, as such, did not
require a Quality Assurance Project Plan.
References
Abbaszadegan, M., P.W. Stewart, M.W. LeChevallier, C. Rosen,
S. Jeffery and C.P. Gerba. 1999a. Occurrence of viruses in
ground water in the United States. AWWARF. Denver, CO,
189 p.
Abbaszadegan, M., P.W. Stewart and M.W. LeChevallier. 1999b.
A strategy for detection of viruses in groundwater by PCR.
Appl, Environ, Microbiol. 65(2):444-449.
Alhajjar, B.J., S.L. Stamer, D.O. Cliver and J.M. Harkin. 1988.
Transport modeling of biological tracers from septic systems.
Water Res. 22(7):907-915.
Alhajjar, B.J., G. Chesters and J.M. Harkin. 1990. Indicators of
chemical pollution from septic systems. Ground Water
28(4):559-568.
Aller, L, T. Bennett, J.H. Lehr, R.J. Petty and G. Hackett. 1987.
DRASTIC: A Standardized System for Evaluating Ground-
Water Pollution Potential Using Hydrogeologic Settings.
EPA/600/2-87/035.
Amundson, D., C. Lindholm, S.M. Goyal and R.A. Robinson.
1988. Microbial pollution of well water in southeastern Minnesota.
J, Environ, Sci, Health A23(5): 453-468.
Armon, R. and Y. Kott. 1995. Distribution comparison between
coliphages and phages of anaerobic bacteria (Bacteriodes
fragilis) in water sources, and their reliability as fecal pollution
indicators in drinking water. Water Sci, Technol.
31 (5-6):215-222.
Badawy, A.S., J.B. Rose and C.P. Gerba. 1990. Comparative
survival of enteric viruses and coliphage on sewage irrigated
grass. J. Environ. Sci. Health A25(8): 937-952.
Bales, R.C., S.R. Hinkle, T.W. Kroeger, K. Stocking and C.P.
Gerba. 1991. Bacteriophage adsorption during transportthough
porous media: Chemical perturbations and reversibility. Environ.
Sci. Technol. 25(12):2088-2095.
Bales, R.C., S. Li, K.M. Maguire, M.T. Yahya and C.P. Gerba.
1993. MS-2 and poliovirus transport in porous media:
Hydrophobic effects and chemical perturbations. WaterResour.
Res. 29(4): 957-963.
Bales, R.C., S. Li, K.M. Maguire, M.T. Yahya, C.P. Gerba and
R.W. Harvey. 1995. Virus and bacteria transport in a sandy
aquifer, Cape Cod, MA. Ground Water33(4):653-661.
Bales, R.C., C.P. Gerba, G.H. Grondin and S.L. Jensen. 1989.
Bacteriophage transport in sandy soil and fractured tuff. Appl.
Environ. Microbiol. 55(8):2061-2067.
Bales, R.C., S. Li, T.-C. Yeh, M.E. Lenczewski and C.P. Gerba.
1997. Bacteriophage and microsphere transport in saturated
porous media: Forced-gradient experiment at Borden, Ontario.
WaterResour. Res. 33(4):639-648.
Berger, P. 1994. Regulation relatedtogroundwatercontamination:
The Draft Groundwater Disinfection Rule. In: Uri Zoller (ed.),
Groundwater Contamination and Control, Marcel Dekker Inc.,
NY.
Bitton, G. 1975. Absorption of viruses onto surfaces in soil and
water. Water Res. 9:473-484.
Britton, G. 1980. Introduction to Environmental Virology. John
Wiley & Sons, NY.
Bitton, G., S.R. Farrah, J. Butner, R.H. Ruskin and Y.J. Chou.
1983. Survival of pathogenic and indicator organisms in ground
water. Ground Water2~\ (4): 405-410.
20
-------
Bitton, G. and C.P. Gerba. 1984. Microbial Pollutants: Their
survival and transport in groundwater. In: G. Bitton and C.P.
Gerba (eds.), Groundwater Pollution Microbiology, John Wiley
&Sons, Inc., NY.
Blanc, R., and A. Nasser. 1996. Effect of effluent quality and
temperature on the persistence of viruses in soil. Water Sci.
Technol. 33(10-11 ):237-242.
Borrego, J.J., M.A. Morinigo, A. de Vicente, R. Cornax and P.
Romero. 1987. Coliphages as an indicator of faecal pollution
in water: Its relationship with indicator and pathogenic
microorganisms. Water Res. 21 (12): 1473-1480.
Borrego, J.J. and R. Cornax. 1990. Coliphages as an indicator of
faecal pollution in water. Their survival and productive infectivity
in natural aquatic environments. Water Res. 24(1): 111-116.
Brush, C.F., W.C. Ghiorse, L.J. Anguish, J.Y. Parlange and H.G.
Grimes. 1999. Transport of Cryptosporidium parvum oocysts
through saturated columns. J. Environ, dual. 28:809-815.
Bull, R.J., C.P. Gerba and R.R. Trussell. 1990. Evaluation of the
health risks associated with disinfection. CRC Grit. Rev. Environ.
Contr. 20:77-113.
Cadmus Group, Inc., Science Applications International
Corporation, and AST Associates, Inc., 2000. Regulatory
Impact Analysis for the Proposed Ground Water Rule, U. S.
EPA, Office of Ground Water and Drinking Water, Washington,
DC. pp. 2-6 through 2-7.
Canter, L. and R.C. Knox. 1984. Evaluation of septic tank system
effects on ground water quality. EPA-600/2-84-107.
Carlson, G.F., Jr., F.E. Woodward, D.F. Wentworth and O.J.
Sproul. 1968. Virus inactivation on clay particles in natural
waters. J. Water Pollut. Control Fed. 40: R89-R106.
CDC. Waterborne-disease outbreaks, 1989-1990. MMWR 1991;
40(SS-3):1-21.
Chendorain, M., M. Yates, and F. Villegas. 1998. The fate and
transport of virus through surface water constructed wetlands.
J. Environ, dual. 27:1451-1458.
Chu, Y., Y. Jin, M. Flury, and M.V. Yates. 2001. Mechanisms of
virus removal during transport in unsaturated porous media.
Wat. Resour. Res. 37(2): 253-263.
Cliver, D.O. 1971. Virus and water quality: Occurrence and
control, p. 149. In: V. Snoeyinkand V. Griffin (eds.), Proceedings
of the Water Quality Conference, University of Illinois, Urbana-
Champaign, IL.
Cliver, D.O. and J.E. Herrmann. 1972. Proteolytic and microbial
inactivation of enteroviruses. Water Res. 6:797-806.
Colwell, R.R. 1996. A Global Decline in Microbiological Safety of
Water: A Call for Action. Internet URL:
Cookson, J.T. and W.J. North. 1967. Adsorption of virus on
activated carbon, equilibria and kinetics of the attachment of
Esc/ier/c/i/aco//bacteriophageT4on activated carbon. Environ.
Sci. Technol. 1:46-56.
Corapcioglu, M.Y. and A. Haridas. 1984. Transport and fate of
microorganisms in porous media: Atheoretical investigation. J.
Hydro/. 72:149-169.
Cornax, R. and M.A. Morinigo. 1991. Significance of several
bacteriophage groups as indicator of sewage pollution in marine
waters. Water Res. 25(6):673-678.
Craun, G.F. 1985. A summary of waterborne illness transmitted
through contaminated groundwater. J. Environ. Health
48:122-127.
Craun, G.F. 1989. Causes of waterborne outbreaks in the United
States. Water Sci. Technol. 24:17-20.
Deetz, T.R., E.M. Smith, S.M. Goyal, C.P. Gerba, J.J. Vollet, L.
Tsai, H.L. Dupont and B.H. Keswick. 1984. Occurrence of rota-
and enteroviruses in drinking and environmental water in a
developing nation. Water Res. 18:567-571.
Deng, M.Y. and D.O. Cliver. 1995. Persistence of inoculated
hepatitis A virus in mixed human and animal wastes. Appl.
Environ. Microbiol. 61(1): 87-91.
Dizer, H. and U. Hagendorf. 1991. Microbial contamination as an
indicator of sewer leakage. Water Res. 25(7): 791.
Dizer, H., J.M.Lopez and A. Nasser. 1984. Penetration of different
human pathogenic viruses into sand columns percolated with
distilled water, groundwater, or wastewater. Appl. Environ.
Microbiol. 47(2):409-415.
Dowd, S.E. and S.D. Pillai. 1997. Survival and transport of
selected bacterial pathogens and indicator viruses under sandy
aquifer conditions. J. Environ. Sci. Health 32(8):2245-2258.
Dowd, S.E., S.D. Pillai, S. Wang, and M.Y. Corapcioglu. 1998.
Delineating the specific influence of virus isoelectric point and
size on virus adsorption and transport through sandy soils.
Applied Environ. Microbiol. 64(2):405-410.
Drewry, W.A. and R. Eliassen. 1968. Virus movement in
groundwater. J. Water Pollut. Control Fed. 40, R257-271.
Duboise, S.M., B.E. Moore and B.P. Sagik. 1976. Poliovirus
survival and movement in a sandy forest soil. Appl. Environ.
Microbiol. 31(4):536-543.
Farrah, S.R., G. Britton, E.M. Hoffmann, O. Lanni, O.C. Pancorbo,
M.C. Lutrick, and J.E. Bertrand. 1981. Survival of enteroviruses
andcoliform bacteria in a sludge lagoon. Appl. Environ. Microbiol.
41:459-465.
Farrah, S.R. and D.R. Preston. 1985. Concentration of viruses
from water by using cellulose filters modified by in situ
precipitation of ferric and aluminum hydroxides. Appl. Environ.
Microbiol. 50(6): 1502-1504.
Faulkner, B.R., W.G. Lyon, F.A. Khan, and S. Chattopadhyay.
2002. Predicting attenuation of viruses during percolation in
soils. 1. Probabilistic model. EPA/600/R-02/051a. In Press.
Geldenhuys, J.C. and P.O. Pretorius. 1989. The occurrence of
enteric viruses in polluted water, correlation to indicator
organisms and factors influencing their numbers. Water Sci.
Technol. 21(3): 105.
Gelhar, L.W., C. Welty and K.R. Rehfeldt. 1992. A critical review
of data on field-scale dispersion in aquifers. Water Resour.
Res. 28:1955-1974.
Gerba, C.P. 1985. Microbial contamination of the subsurface
(Chapters). In: C. H. Ward, W. Giger and P. L. McCarty (eds.),
Ground Water Quality. John Wiley & Sons, NY.
Gerba, C.P. and G. Bitton. 1984. Microbial pollutants: Their
survival and transport pattern to groundwater. pp. 65-88. In: G.
Bitton and C.P. Gerba (eds.), Groundwater Pollution
Microbiology, John Wiley & Sons, NY.
Gerba, C.P., 1999. Virus survival and transport in groundwater. J.
Indust. Microbiol. Biotechnol. 22(4/5):535-539.
Gerba,C.P.,C.WallisandJ.L. Melnick. 1975. Fate of wastewater
bacteria and viruses in soil. J. Irrig. Drain. Div. ASCE,
101(IR3):157-174.
Gerba, C.P. and G.E.Schaiberger. 1975. Effect of particulates on
virus survival in seawater. J. Water Pollut. Control Fed.
47(1):93-103.
21
-------
Gerba, C.P. and J.B. Rose. 1993. Estimating viral disease risk
from drinking water, pp. 117-134. In: C.P. Gerba (ed.)
Comparative Environmental Risk Assessment. Lewis
Publishers, Boca Raton, FL.
Goyal, S.M. 1983. Indicators of viruses, pp. 211 -230. In: G. Berg
(ed.) Viral Pollution of the Environment, CRC Press, Inc., Boca
Raton, FL.
Goyal, S.M., and C.P. Gerba. 1979. Comparative adsorption of
human enteroviruses, simian rotavirus, and selected
bacteriophagestosoils. Appl. Environ, Microbiol. 32(2):241 -247.
Haas, C.N. 1983. Estimation of risk due to low doses of
microorganisms: A comparison of alternative methodologies.
Am. J. Epidemiol. 118(4):573-582.
Haas, C.N. and B. Heller. 1990. Statistical approaches to
monitoring, pp. 412-427. In: G.A. McFeters (ed.), Drinking
Water Microbiology. Springer Verlag, NY.
Hancock, C.M., J.B. Rose, and M. Callahan. 1998. Crypto and
Giardia in US groundwater. J. Am. Water Works Assoc.
90(3):58-61.
Harter, T., S. Wagner, and E.R. Atwill. 2000. Colloid transport and
filteration of Cryptosporidium parvum in sandy soils and aquifer
sediments. Environ. Sci. Technol. 34(1):62-70.
Harvey, R.W., N.E. Kinner, D. MacDonald, D.W. Metge and A.
Bunn. 1993. Role of physical heterogeneity in the interpretation
of small-scale laboratory and field observations of bacteria,
microbial-sized microsphere, and bromide transport through
aquifer sediments. Water Resour. Res. 29(8):2713-2721.
Havelaar, A.H. 1987. Bacteriophages as model organisms in
water treatment. Microbiol. Sci. 4(12):362-364.
Havelaar, A.H., M. van Olphen and Y.C. Drost. 1993. F-specific
RNAbacteriophages are adequate model organisms for enteric
viruses in fresh water. Appl. Environ. Microbiol.
59(9):2956-2962.
Herbold-Paschke, K., U. Straub, T. Hahn, G. Teutsch and K.
Botzenhart. 1991. Behavior of pathogenic bacteria, phages
and viruses in groundwater during transport and adsorption.
Water Sci.Technol. 24(2):301 -304.
Herrmann, J.E. and D.O.CIiver. 1973. Degradation of
coxsackievirus type A9 by proteolytic enzymes. Infect. Immun.
7:513-517.
Hirata, T., K. Kawamura, S. Sonoki, K. Hirata, M. Kaneko and K.
Taguchi. 1991. Clostridium perfringens as an indicator
microorganism for the evaluation of the effect of wastewater
and sludge treatment systems. Water Sci. Technol.
24(2):367-372.
Hurst, C.J., C.P. Gerba, and I. Cech. 1980. Effect of environ-
mental variables and soil characteristics on virus survival in
soil. Appl. Environ. Microbiol. 40(6):1067-1079.
Hurst, C.J. 1997. Modeling the fate of microorganisms in water,
wastewater, and soil. pp. 213-221. In: C.J. Hurst (Ed.), Manual
of Environmental Microbiology. ASM Press. Washington, D.C.
Jin,Y.,M.V.Yates,S.S.Thompson,andW.A. Jury. 1997. Sorption
of virus during flow through saturated sand columns. Environ.
Sci. Technol. 31(2):548-555.
Kamiko, N. and S. Ohgaki. 1992. Multiplication characteristics of
FRNA phage and its utility as an indicator for pathogenic
viruses. Water Sci. Technol. 27(3-4):133-136.
Katzenelson, E. 1978. Survival of viruses. In: G. Berg (ed.)
Indicators of Viruses in Water and Food. Ann Arbor Science,
Ann Arbor, Ml.
Keswick, B.H. and C.P. Gerba. 1980. Viruses in groundwater.
Environ. Sci. Technol. 14(11): 1290-1297.
Keswick, B.H., D.S. Wang and C.P. Gerba. 1982a. The use of
microorganisms as ground-water tracers: A review. Ground
Water 20:142-149.
Keswick, B.H., C.P. Gerba, S.L. Seco, R. and I. Cech. 1982b.
Survival of enteric viruses and indicator bacteria in ground
water. J. Environ. Sci. Health 17(6):903-912.
Lukasik, J.S. Truesdail, D.O. Shah and S.R. Farrah. 1996.
Adsorption of microorganisms to sand and diatomaceous earth
particles coated with metallic hydroxides. Kona 14:87-91.
Levine,W.C.,W.T.Stephenson,andG.F.Craun. 1991 .Waterborne
disease outbreaks. 1987-1988. J. Food Prot. 54:71-78.
Lieberman, R.J., L.C. Shadix, B.S. Newport, S.R. Grout, S.E.
Buescher, R.S. Safferman, R.E. Stetler, D. Lye, G.S. Fout and
D. Dahling. 1994. Source water microbial quality of some
vulnerable public ground water supplies. In: Proceedings of the
Water Quality Technology Conference, AWWA, San Francisco,
CA.
Lieberman, R.J., L.C. Shadix, B.S. Newport, M.W.N. Frebis, S.E.
Moyer, R.S. Safferman, D. Lye, G.S. Fout and D. Dahling. 1999.
Unpublished report in preparation.
Mack, G., A. Lu, and M.J. Coohon. 1972. Transport of viruses in
groundwater. Sci. Total Environ. 17: 56-63.
Macler, B.A. 1995. Developing a national drinking water regulation
for disinfection of groundwater. Ground Water Monit. Remed.
15(4):77-84.
Macler, B.A. 1996. Developing the Ground Water Disinfection
Rule. J. Am. Water Works Assoc. 88(3):47-55.
Marzouk, Y., S.M. Goyal and C.P. Gerba. 1980. Relationship of
viruses and indicator bacteria in water and wastewater of Israel.
Water Res. 14:1585-1590.
Matthess, G., and A. Pekdeger. 1981. Concepts of survival and
transport model of pathogenic bacteria and viruses in
groundwater. Sci. Total Environ. 21:149-159.
Matthess, G., A. Pekdeger and J. Schroeter. 1988. Persistence
and transport of bacteria and viruses in groundwater—a
conceptual evaluation. J. Contam. Hydrol. 2:171-188.
McDaniels, A.E., K.W. Cochran, J.J. Gannon and G. W. Williams.
1983. Rotavirus and reovirus stability in microorganism-free
distilled and wastewater. Water Res. 17(10):1349-1353.
McFeters, G.A., G.K. Bissonnette, J.J. Jezeski, C.A. Thomson,
and D.G. Stuart. 1974. Comparative survival of indicator
bacteria and enteric pathogens in well water. Appl. Microbiol.
27(5):823-829.
Melnick, J.L., C.P. Gerba and C. Wallis. 1978. Viruses in water.
Bull. World Health Organization 56:499-508.
Metcalf.T.G. 1978. Indicators for viruses in natural waters. In: D.J.
Mitchell (eds.) Water Pollution Microbiology, vol. 2, Wiley-
Interscience, Inc., NY.
Morinigo, M.A. 1992. Evaluation of different bacteriophage groups
as faecal indicators in contaminated natural waters in Southern
England. Water Res. 26(3):267.
22
-------
Mose, J.R., V. Dostal and H. Wege. 1970. Inactivation of viruses
by protozoans. Arch, Hyg. 154:319-322.
Murray, J.P., and S. Laband. 1979. Degradation of poliovirus by
adsorption on inorganic surfaces. Appl, Environ, Microbiol.
37:480-486.
Murray, J.P., and G.A. Parks. 1980. Particulates in Water.
pp. 97-133. In: M.C. Leckie, M. Kavanaugh and J.O. Leckie
(eds.), Advances in Chemistry Series 189, American Chemical
Society: Washington, DC.
Nasser, A.M., and S.D. Oman. 1999. Quantitative assessment of
the inactivation of pathogenic and indicator viruses in natural
water sources. Water Res. 33:1748-1772.
Niemi, M. 1976. Survival of Escherichia coliphage T7 in different
water types. Water Res. 10(9):751-755.
Noell, A.L. 1992. A Survey of the Fate and Migration of Enteric
Viruses in Subsurface Environments. Master of Engineering
Report. Department of Civil Engineering, Univ. of Wisconsin.
O'Brien, R.T., and J.S. Newman. 1977. Inactivation of Polioviruses
and Coxsackieviruses'msurface water. Appl. Environ. Microbiol.
33(2) :334-340.
Payment, P., M. Trudel and R. Plante. 1985. Elimination of viruses
and indicator bacteria at each step of treatment during
preparation of drinking water at seven water treatment plants.
Appl. Environ. Microbiol. 49:1418-1428.
Payment, P., L. Richardson, J. Siemaiatycki, R. Dewar, M.
Edwardes and E. Franco. 1991. A randomized trial to evaluate
the risk of gastrointestinal disease due to consumption of
drinking water meeting current microbiological standards. Am.
J. Pub. Health 81(6):703-708.
Payment, P., and E. Franco. 1993. Clostridium perfringens and
somatic coliphages as indicators of the efficiency of drinking
water treatment for vi ruses and protozoan cysts. Appl. Environ.
Microbiol. 59(8):2418-2424.
Powelson, O.K., C.P. Gerba, and M.T. Yahya. 1993. Virustransport
and removal in wastewater during aquifer recharge. Water Res.
27(4):583-590.
Powelson, O.K., J.R. Simpson, and C.P. Gerba. 1990. Virus
transport and survival in saturated and unsaturatedflowthrough
soil columns. J. Environ, dual. 19:396-401.
Powelson, D.K, J.R. Simpson, and C.P. Gerba. 1991. Effects of
organic matter on virus transport in unsaturated flow. Appl.
Environ. Microbiol. 57(8) :2192-2196.
Powelson, O.K., and C.P. Gerba. 1993. Comparative removal of
viruses by sandy alluvium during infiltration of wastewater,
USDA Water Conservation Lab, 6th Biennial Symposium on
Artificial Recharge of Groundwater Scottsdale, AZ, May 19-21.
pp. 87.
Powelson, O.K., and C.P. Gerba. 1994. Virus removal from
sewage effluents during saturated and unsaturatedflowthrough
soil columns. Water Res. 28(10):2175-2181.
Rhodes, A.J., E.M. Clark, D.S. Knowles, A.M. Goodfellowand W.
L. Donohue. 1950. Prolonged survival of human poliomyelitis
virus in experimentally infected river water. Can. J. Publ. Hlth.
41:248-254.
Rossi, P., and M. Aragno. 1999. Analysis of bacteriophage
inactivation and its attenuation by adsorption onto colloidal
particles by batch agitation techniques. Can. J. Microbiol.
45:9-17.
Sakoda, A., Y. Sakai, K. Hayakawaand M. Suzuki. 1997. Adsorption
of viruses in water environment onto solid surfaces. Water Sci.
Tech. 35(7): 107-114.
Schaub, S. A. and C. A. Sorber. 1977. Virus and bacterial removal
from wastewater by rapid infiltration through soil. Appl. Environ.
Microbiol. 33(3):609-619.
Scheuerman, P.R., S.R. Farrah and G. Bitton. 1987. Reduction
of microbial indicators and viruses in a cypress strand. Water
Sci. Technol. 19:539-546.
Schijven, J.F., andL.C. Rietveld. 1996. How do field observations
compare with models of microbial removal? pp. 105-114. In:
The Proceedings of the Groundwater Foundation's 12th Annual
Fall Symposium, Boston, MA.
Schijven, J.F., W. Hoogenboezem, P.J. Nobel, G.J. Medema and
A. Stakelbeek. 1998. Reduction of FRNA-bacteriophages and
fecal indicator bacteria by dune infiltration and estimation of
sticking efficiencies. Water Sci. Technol. 38: 127-131.
Schijven, J.F. and S.M. Hassanizadeh. 2000. Removal of viruses
by soil passage: Overview of modeling, processes, and
parameters. CRCCrit. Rev. Environ. Sci. Technol.30(1 ):49-127.
Sherris, J.C. J.J. Champoux, L.C. Fredrick, C. Neidhardt, J.J.
Plorde, C.G. Ray and K.J. Ryan. 1990. Medical Microbiology:
An Introduction to Infectious Diseases. Elsevier, NY.
Shuval, H.I., A. Thompson, B. Fattal.S. Cymbalista and Y.Wiener.
1971. Natural virus inactivation processes in seawater. J. San.
Eng. Div. Proc. Am. Soc. Civ. Eng. 97:587-600.
Sim, Y., and C.V. Chrysikopoulos. 2000. Virus transport in
unsaturated porous media. WaterResour. Res.36(1): 173-179.
Snowdon, J.A., and D.O. Cliver. 1989. Coliphage as indicators of
human enteric viruses in ground water. CRCCrit. Rev. Environ.
Control 19:231-249.
Sobsey, M.D. 1983. Transport and fate of viruses in soils. In:
Microbial Health Considerations of Soil Disposal and Domestic
Wastewaters. EPA-600/9-83-017.
Sobsey, M.D., R.M. Hall and R.L. Hazard. 1995. Comparative
reduction of Hepatitis A Virus, Enterovirus and Coliphage MS2
in miniature soil columns. Water Sci. Technol. 31(5-6):203-
209.
Stetler, R.E. 1984. Coliphages as indicators of enteroviruses.
Appl. Environ. Microbiol. 48(3): 668.
Stramer, S.L. 1984. Fates of poliovirus and enteric indicator
bacteria during treatment in a septic tank system including
septage disinfection. Thesis. Univ. of Wisconsin-Madison.
Teutsch, G., K. Herbold-Paschke, D. Tougianidou, T. Hahn and K.
Botzenhart. 1991. Transport of microorganisms in the
underground—processes, experiments, and simulation models.
Water Sci. Technol. 24(2):309-314.
Thompson, S.S., M. Flury, M.V. Yates, and W.A. Jury. 1998. Role
of the air-water-solid interface in bacteriophage sorption
experiments. Appl. Environ. Microbiol. 61(1):304-309.
Thompson, S.S., and M.V. Yates. 1999. Bacteriophage inactivation
at the air-water-solid interface in dynamic batch systems. Appl.
Environ. Microbiol. 65(3):1186-1190.
Tim, U.S., andS. Mostaghimi. 1991. Models for predicting viruses
movement through soils: VIROTRANS. Ground Water
29(2):251-259.
23
-------
U.S. EPA. 1989a. Drinking Water; National Primary Drinking
Water Regulations; Filteration, Disinfection; Turbidity; Giardia
lamblia, Viruses, Legionella, and Heterotrophic Bacteria: Final
Rule. Fed. Reg., 54:27486 (June 29, 1989).
U.S. EPA. 1989b. Drinking Water; National Primary Drinking
Water Regulations; Total Coliforms (Including Fecal Coliforms
and E. coli): Final Rule. Fed. Reg., 54:27544 (June 29, 1989).
U.S. EPA. 1992. Draft Ground-Water Disinfection Rule. U.S. EPA
Office of Ground Water and Drinking Water, Washington, D.C.
EPA811/P-92-001.
U.S. EPA. 2000. National Primary Drinking Water Regulations:
Ground Water Rule; Proposed Rules. Fed. Reg., 65(91 ):30202
(May 10,2000).
U.S. EPA. 2002. National Primary Drinking Water Regulations:
Long Term 1 Enhanced Surface Water Treatment Rule; Final
Rule. Fed. Reg., 67 (9): 1844 (January 14, 2002).
Vaughn, J.M., E.F. Landry and M.Z. Thomas. 1983. Entrainment
of viruses from septic tank leach fields through ashallow, sandy
soil aquifer. Appl. Environ. Microbiol. 45:1474-1480.
Vilker, V.L. and W.D. Surge. 1980. Adsorption mass transfer
model for virus transport in soils. Water Res. 14:783-790.
Vilker, V.L., L.H. Frommhagen, R. Kamdar and S. Sundaram.
1978. Application of ion exchange/adsorption models to virus
transport in percolating beds. The American Institute for
Chemical Engineers Symposium Series. 74(178):84-92.
Wellings, F.M., A.L. Lewis, C.W. Mountain and L.V. Pierce. 1975.
Demonstration of virus in groundwater after effluent discharge
onto soil. Appl. Microbiol. 29(6):751-757.
Yates, M. and S. Yates. 1987. A comparison of geostatistical
methods for estimating virus inactivation rates in ground water.
Water Res. 21(9):1119-1125.
Yates, M.V.,C.P.GerbaandL.M. Kelley. 1985. Virus persistence
in groundwater. Appl. Environ. Microbiol. 49(4):778-781.
Yates, M.V. andC.P. Gerba. 1984. Factors controlling the survival
of viruses in groundwater. Water Sci. Technol. 17:681-687.
Yates, M.V., L.D. Stetzenbach, C.P. Gerba and N.A. Sinclair.
1990. The effect of indigenous bacteria on virus survival in
ground water. J. Environ. Sci. Health. A25: 81-100.
Yates, M.V., S.R. Yates, J.Wagner and C.P. Gerba. 1987.
Modeling virus survival and transport in the subsurface.
J. Contain. Hydrol. 1:329-345.
Yates, M.V., and W.A. Jury. 1995. On the use of virus transport
modeling for determining regulatory compliance. J. Environ.
Qua/. 25:1051-1055.
Yeager, J.G. and R.T. O'Brien. 1979. Enterovirus inactivation in
soil. Appl. Environ. Microbiol. 38:694-701.
24
-------
United States
Environmental Protection
Agency
Please make all necessary changes on the below label,
detach or copy, and return to the address in the upper
left-hand corner.
If you do not wish to receive these reports CHECK HERED;
detach, or copy this cover, and return to the address in the
upper ieft-hand corner.
PRESORTED STANDARD
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
National Risk Management
Research Laboratory
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
EPA/540/S-03/500
April 2003
------- |