LvEPA
United States
Environmental Protection
Agency
Office of Health and
Environmental Assessment
Washington DC 20460
EPA/600/6-88/006
May 1986
Research and Development
Development of a
Qualitative Pathogen
Risk Assessment
Methodology for
Municipal Sludge
Landfilling
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EPA/600/6-88/006
May 1986
DEVELOPMENT OF A QUALITATIVE PATHOGEN RISK
ASSESSMENT METHODOLOGY FOR MUNICIPAL
SLUDGE LANDFILLING
Environmental Criteria and Assessment Office
Office of Health and Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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DISCLAIMER
This document has been reviewed In accordance with the U.S. Environ-
mental Protection Agency policy and approved for publication. Mention of
trade names or commercial products does not constitute endorsement or recom-
mendation for use.
11
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PREFACE
Municipal wastewater sludges contain a wide variety of bacteria,
viruses, protozoa, helminths and fungi. There is a need to develop a risk
assessment methodology to investigate the potential risks from
microbiological pathogens present in municipal sludge disposed of in
landfills. Survival characteristics of pathogens are critical factors in
assessing the risks associated with potential transport of microorganisms
from the sludge-soil matrix to the groundwater environment of landfills.
Various models are discussed for predicting microbial die-off.
ill
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DOCUMENT DEVELOPMENT
Larry Fradkln, Document Manager
Environmental Criteria and Assessment Office
Office of Health and Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 45268
Dr. Charles Gerba, Author
Department of Microbiology and Immunology
University of Arizona
Tucson, AZ 85721
Dr. Pat V. Scarplno, Co-Document Manager
C1v1l and Environmental Engineering Department
University of Cincinnati
Cincinnati, OH 45268
Scientific Reviewer(s)
Dr. Richard S. Engelbrecht
Department of Civil Engineering
University of Illinois at Urbana-
Champaign
Urbana, IL 61801
Dr. Elmer Akin
Dr. Malt Jakubowski
Dr. Norm Kowal
Health Effects Research Laboratory
Office of Health Research
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 45268
Dr. Carl A. Brunner
Dr. Joe Parrel 1
Dr. Albert D. Venosa
Wastewater Research Division
Water Engineering Research Laboratory
Office of Environmental Engineering
and Technology Demonstration
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH
Dr. Mark D. Sobsey
Department of Environmental Sciences
and Engineering
School of Public Health
University of North Carolina
Chapel Hill, NC 27514
Technical Editor
Judith A. Olsen
Environmental Criteria and Assessment Office
U.S. Environmental Protection Agency
Cincinnati, OH 45268
1v
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TABLE OF CONTENTS
1.
2.
3.
4.
5.
6.
INTRODUCTION
SLUDGE CHARACTERISTICS AND LANDFILLING METHODS
2.1. SLUDGE CHARACTERISTICS . .
2.2. SLUDGE LANDFILLING METHODS
2.2.1. Trench
2.2.2. Area Fill
2.3. REVIEW OF SITE CONDITIONS AT OPERATED LANDFILLS
PATHOGENS .
3.1. BACTERIA ..... ...
3.2. VIRUSES
3.3. PROTOZOA .
3.4. HELMINTHS. ........
3.5. FUNGI
EXPOSURE PATHWAYS
4.1. AEROSOLS AND DIRECT CONTACT.
4.2. SURFACE WATER AND RUNOFF
4.3. PLANT AND ANIMAL .....
4.4. 6ROUNDWATER. ....
EXPECTED CONCENTRATIONS OF PATHOGENS IN SLUDGE
5.1. PATHOGEN CONCENTRATIONS IN RAW SLUDGES
5.2. PATHOGEN CONCENTRATIONS IN SECONDARY SLUDGES
5.3. PATHOGEN CONCENTRATIONS AFTER STABILIZATION,
DEWATERIN6 AND DISINFECTION. .
SURVIVAL CHARACTERISTICS OF PATHOGENS
6.1. SLUDGE AND SOIL. ......
6.1.1. Viruses ......
6.1.2. Bacteria
6.1.3. Protozoa -
6.1.4. Helminths .
6.2. SUMMARY OF FACTORS CONTROLLING HICROBIAL SURVIVAL. ....
6.3. MODELS FOR PREDICTING HICROBIAL DIE-OFF IN THE
ENVIRONMENT
6.3.1. Viruses ..........
6.3.2. Bacteria. .......
6.4. ASSESSMENT OF PATHOGEN SURVIVAL AT SLUDGE LANDFILLS. . . .
V
Page
1-1
2-1
2-1
2-2
2-2
2-5
2-7
3-1
3-1
3-6
3-7
3-8
3-10
4-1
4-1
4-4
4-5
4-6
5-1
5-2
5-2
5-4
6-1
6-1
6-1
6-3
6-10
6-11
6-13
6-16
6-16
6-18
6-20
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TABLE OF CONTENTS (cont.)
7. TRANSPORT OF PATHOGENS IN THE SUBSURFACE 7-1
7.1. VIRUSES 7_i
7.1.1. Land Application 7-7
7.1.2. Transport 7-10
7.2. BACTERIA 7_15
7.3. PROTOZOA AND HELMINTHS 7-21
7.4. SUMMARY OF MICROBIAL TRANSPORT THROUGH THE SUBSURFACE. . . 7-24
8. EVALUATION OF GROUNDWATER POLLUTION POTENTIAL BY
MICROORGANISMS USING MICRO-DRASTIC , 8-1
9. INFECTIOUS DOSE AND RISK OF DISEASE FROM MICROORGANISMS. 9-1
9.1. INFECTIOUS DOSE 9-1
9.2. ESTIMATED MORBIDITY AND MORTALITY FOR ENTERIC PATHOGENS. . 9-4
9.3. RISK ASSESSMENT FOR DRINKING WATER . 9-8
9.4. SUMMARY OF DISEASE RISK FROM ENTERIC PATHOGENS 9-16
10. GROUNDWATER PATHWAY RISK ASSESSMENT METHODOLOGY 10-1
10.1. GENERAL ASSESSMENT 10-1
10.2. CHARACTERISTICS OF BEST- AND WORST-CASE LANDFILLS 10-4
10.3. EVALUATION OF GROUNDWA1ER CONTAMINATION AT LANDFILLS
BY MICRO-DRASTIC 10-6
10.4. ESTIMATING TRANSPORT OF ENTERIC ORGANISMS AT SLUDGE
LANDFILLS TO GROUNDWATER 10-13
10.4.1. Estimated Concentration of Viruses In the
Sludge 10-16
10.4.2. Percent of Viruses Released from Sludge 10-19
10.4.3. Concentration of Viruses In Sludge Leachate . . . 10-19
10.4.4. Removal Rate by Soil 10-20
10.4.5. Inactlvatlon or Decay Rate of Viruses 10-20
10.4.6. Rate of Travel, Dilution and Dispersion 10-21
10.4.7. Risk Assessment at Example Sludge Landfill A. . . 10-22
10.4.8. Risk Assessment at Example Sludge Landfill B. . . 10-22
10.5. SUMMARY OF GROUNDWATER RISK ASSESSMENT AND RESEARCH
NEEDS * . 10-22
11. SUMMARY AND CONCLUSIONS . n_i
12. REFERENCES 12-1
vi
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LIST OF TABLES
No. Title JPaflfi_
2-1 Sludge Landfming Methods 2-3
2-2 Sludge and Site Conditions Recommended for LandfllUng. ... 2-4
2-3 Site Identification and Sludge Description 2-8
2-4 Site Design and Operation - Existing Conditions 2-9
2-5 Site Design and Operation - Site Preparation 2-10
2-6 Site Design and Operation - Site Operation 2-11
3-1 Bacteria and Parasites Pathogenic to Man That May Be
Present 1n Sewage and Sludge 3-2
3-2 Enteric Viruses That May Be Present In Sewage
and Sludge 3-3
5-1 Densities of M1crob1al Pathogens and Indicators 1n
Primary Sludges 5~3
5-2 Densities of Pathogenic and Indicator M1crob1al Species
1n Secondary Sludges 5~5
5-3 Summary of M1crob1al Reduction During Sludge Treatment. ... 5-7
5-4 Concentrations of Pathogens and Indicators 1n Digested
Sludges ........ 5-9
6-1 Comparative Die-Off of Enterovirus in Water and Soil 6-4
6-2 Temperature Correction Coefficients for the Survival
of Pathogens and Indicator Organisms in Soil and
Water Systems 6~7
6-3 tgo Values in Hours for Various Types of V. cholerae
in Various Waters and Wastewaters 6-9
6-4 Factors That Influence the Survival of Enteric
Pathogens in the Environment 6-14
6-5 Average Die-Off Rate Constants (day"1) for Selected
Microorganisms in a Soil-Water-Plant System 6-21
vii
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LIST OF TABLES (cont.)
No.
Title
7-1
7-2
7-3
7-4
7-5
7-6
7-7
7-8
7-9
8-1
9-1
9-2
9-3
9-4
9-5
9-6
10-1
10-2
10-3
10-4
Hydraulic Conductivities of Subsurface Material
Soil Factors Affecting Infiltration and Movement of
Microorganisms in Soil
Sizes of Waterborne Bacteria, Viruses and Parasites
Factors Affecting Virus Transport in Soil
Effect of pH on Poliovirus Adsorption to Sewage Sludge. . . .
Summary of Virus Migration from Sludge Through Soils
Rate of Virus Removal Through Different Soil Types
Observed Enterovirus Removals During Field Studies
Coliform Bacterial Removal by Soil
Factors and Weights Used to Evaluate Potential for
Microbiological Contamination of Groundwater
Contributors to Uncertainty in Determining Minimum
Infectious Dose for Enteric Viruses
Mortality Rates for Enteric Bacteria and Enteroviruses. . . .
Risk of Disease and Mortality from Concentrations
of Shiqella dysenteriae in Drinklna Water ...........
Risk of Infection, Disease and Mortality from Various
Concentrations of Poliovlrus 1 in Drinking Water
Risk of Infection, Disease and Mortality from Various
Concentrations of Poliovirus 3 in Drinking Water
Risk of Infection, Disease and Mortality from Various
Concentrations of Hepatitis A Virus 1n Drinking Water ....
Characteristics of Best, Worst and Average Operated
Sludge Landfills
Characteristics of Selected Municipal Sludge Landfills. . . .
Rating of Microbial Contamination at Sludge Disposal Site A .
Rating of Microbial Contamination at Sludge Disposal Site B .
7-2
7-3
7-4
7-5
7-8
7-9
7-12
7-14
7-17
8-3
9-3
9-9
9-12
9-13
9-14
9-15
10-5
10-7
10-8
10-9
V111
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LIST OF TABLES (cont.)
No. Title Page
10-5 Factors and Weights Used to Evaluate Potential for
Microbiological Contamination of Groundwater 10-10
10-6 Estimation of M1crob1al Contamination at Two Sludge
Disposal Sites 10-11
10-7 Volume of Sludge and Net Recharge per Year at Sludge
Landfills A and B 10-12
10-8 Estimated Levels of Pathogens and Indicator Bacteria at
Sludge Landfills A and 8 Applied/Hectare. 10-15
10-9 Assumptions Used 1n Assessing Virus Contamination of
Groundwater at Sludge Landfills . 10-17
10-10 Basis of Assumptions Used 1n Assessing Contamination of
Groundwater at Sludge Landfills by Viruses 10-18
10-11 Estimated Concentrations of Viruses 1n Groundwater at
Sludge Landfill A 10-23
10-12 Estimated Concentrations of Viruses 1n Groundwater at
Sludge Landfill B 10-24
10-13 Status of Information for Groundwater Risk Assessment
and Research Needs 10-26
1x
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LIST OF FIGURES
No.
4-1
6-1
7-1
7-2
9-1
9-2
9-3
9-4
10-1
Title page
Pathways of H1crob1al Transport from Sludge Landfills .... 4-2
Virus Decay Rate as a Function of Temperature 6-19
Vertical Movement of Microorganisms as a Function of
8011 TyPe 7-20
Removal of Microorganisms as a Function of the Flow
Rate of Effluent Through the Soil . . 7_22
Secondary Attack Rates of Enteric Viruses 9_5
Percent of Individuals with Clinical Features for
Polio and Hepatitis Virus by Age 9_5
Frequency of Symptomatic Infections 9_7
Annual Risk of Infection from 1 PFU/1000 s, g.-n
Methodology for Estimating Risks from Groundwater
Contamination by Sludge Landfills ... 10_i4
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LIST OF ABBREVIATIONS AND SYMBOLS
HAV
MID
HPN
PFU
sp.
spp.
TCI050
Hepatitis a virus
Minimum Infectious dose
Most probable number
Plague-forming units
Species (singular)
Species (plural)
Time for 90% 1nact1vat1on
Dose at which 50% of Inoculated tissue cultures are Infected
x1
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1. INTRODUCTION
1-1
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2. SLUDGE CHARACTERISTICS AND LANDFILLINS METHODS
2.1. SLUDGE CHARACTERISTICS
Municipal sludge is a complex mixture of solids of biological and
mineral origin that are removed from wastewater in sewage treatment plants.
Sludge is a by-product of physical (primary treatment), biological (activat-
ed sludge, trickling filters) and physiochemical (precipitation with lime,
ferric chloride or alum) treatment of wastewater. Many of the pathogenic
microorganisms present in raw wastewaters find their way into municipal
sludges. Treatment of these sludges by anaerobic or aerobic digestion
and/or dewatering reduces the number of pathogens, but significant numbers
remain. The type of treatment determines the concentration of pathogens and
the relative risk of disposal.
Only dewatered sludges with solids contents >15% are considered suitable
for disposal in sludge-only landfills. Sludges having solids contents <15%
usually will not support cover material. In some operations soil may be
added as a bulking agent to a low solids sludge to produce a sludge suitable
for disposal at sludge-only landfills. Sludges may be dewatered by a number
of processes including drying beds, vacuum filtration, pressure filtration,
centrifugation and heat drying. Chemicals such as alum, limes ferric chlo-
ride or synthetic polyelectrolytes are added to improve the dewatering char-
acteristics of the sludge. In general, only stabilized sludges are recom-
mended for landfilling, but this is not required in all states (U.S. EPA,
1978).
Stabilization of sludges may be accomplished by either aerobic or
anaerobic digestion, lime addition, heat, wet oxidation or incineration.
2-1
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2.2. SLUDGE LANDFILLING METHODS
Several different methods of disposal are used at sludge-only land-
fills. These are listed 1n Table 2-1. The type of method utilized Is
dependent on the characteristics of the sludge and the nature of the site.
Recommended site and sludge conditions are shown 1n Table 2-2. The differ-
ent methods of disposal may have different risks associated with them, and a
description of each is Included.
2.2.1. Trench. For trenches, subsurface excavation 1s required so that
the sludge can be placed entirely below the original ground surface. Soil
Is used only for cover and is not used as a sludge bulking agent. The
sludge 1s usually dumped directly into the trench from hauling vehicles, and
cover 1s generally applied over sludge the same day that 1t is received.
The soil excavated during trench construction in most cases is sufficient
for cover applications. Application is either to narrow or wide trenches.
Narrow trenches are defined as having widths <10 ft (3.0 m); wide trenches
are defined as having widths >10 ft (3.0 m) (U.S. EPA, 1978). Trench depth
Is a function of depth to groundwater and bedrock, sidewall stability and
equipment limitations.
For narrow trenches it is recommended that sludge solids content be at
least 15-20% for 2-3 ft (0.6-0.9 m) widths and 20-28% for 3-10 ft (0.9-3.0
m) widths (U.S. EPA, 1978). However, a review of landfills in operation
Indicates that sludges with a solids content of as low as 3% are disposed of
by this method (U.S. EPA, 1978). The main advantage of a narrow trench is
Its ability to handle sludge with a relatively low solids content. Gen-
erally, application rates for narrow trenches are less than for other
methods. It 1s impractical to install liners in narrow trench operations.
2-2
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TABLE 2-1
Sludge Landfllling Methods*
Trench Only
Area Fill
Narrow trench
Wide trench
Area fill mound
Area fill layer
Diked containment
*Source: U.S. EPA, 1978
2-3
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In wide-trench application, sludges with a solids content of >20% are
recommended. Wide-trench methods are less land Intense than narrow-trench
methods and liners can be Installed to contain sludge moisture and protect
groundwater.
Both stabilized and unstabHlzed sludges can be disposed of by trench
application.
2.2.2. Area Fill. For area fills, sludge 1s placed above the original
ground surface. Because excavation 1s not required and sludge 1s not placed
below the surface, area fill applications are often used in areas with
shallow groundwater or bedrock. The solids content of sludge as received is
not necessarily limited. However, because the sldewall containment (avail-
able in a trench) Is lacking and equipment must be supported atop the sludge
1n most area fills, sludge stability and bearing capacity must be relatively
good. To achieve these qualities, soil is mixed with the sludge as a bulk-
Ing agent. Since excavation 1s not performed 1n the landfilllng area, and
since shallow groundwater or bedrock may prevail, the large quantities of
soil required usually must be Imported from off-site or hauled from other
locations on-slte.
Because filling proceeds above the ground surface, liners can be more
readily installed at area fill operations than at trench operations. With
or without liners, surface runoff of moisture from the sludge and contami-
nated rainwater should be expected in greater quantities at area fills.
There are three methods of area fill application (U.S. EPA, 1978).
These are area fill mound, area fill layer and dike containment.
In area fill mound applications, it is recommended that the solids con-
tent of sludge received at the site be no more than 20%. Sludge is mixed
with a soil bulking agent to produce a mixture that is more stable and has
2-5
-------
greater bearing capacity. Appropriate bulking ratios may vary between 0.5
and 2 parts son for each part of sludge. The exact ratio employed depends
on the solids content of the sludge as received and the need for mound
stability and bearing capacity.
The sludge/so11 mixing process 1s usually performed at one location and
the mixture hauled to the filling area. At the filling area, the sludge/
soil mixture 1s stacked Into mounds ~6 ft (1.8 m) high. Cover material 1s
then applied atop these mounds 1n a minimum 3 ft (0.9 m) thick application.
This cover thickness may be increased to 5 ft (1.5 m) 1f additional mounds
are applied atop the first.
In area fill layer applications, sludge received at the site may be as
low as 15% solids. Sludge is mixed with a soil bulking agent to produce a
mixture that is more stable and has greater bearing capacity. Typical
bulking ratios range from 0.25-1 part soil for each part sludge.
The mixing process may occur either at a separate sludge dumping and
mixing area or in the filling area. After mixing the sludge with soil, the
mixture is spread evenly in layers from 0.5-3 ft (0.15-0.9 m) thick. This
layering usually continues for a number of applications. Interim cover
between consecutive layers may be applied in 0.5-1 ft (0.15-0.3 m) thick
applications. Final cover is from 2-4 ft (0.6-1.2 m) thick.
In diked containment applications, sludge is placed entirely above the
original ground surface. Dikes are constructed on level ground around all
four sides of a containment area. Alternatively, the containment area may
be placed at the top of a hill so that the steep slope can be utilized for
containment on one or two sides. Dikes would then be constructed around the
remaining sides.
Access is provided to the top of the dikes so that hauling vehicles can
dump sludge directly into the containment. Interim cover may be applied at
2-6
-------
certain points during the filling, and final cover 1s applied when filling
1s discontinued. It 1s recommended that the solids content of the sludge be
at least 20%.
Usually diked containment operations are conducted without the addition
of soil bulking agents. Diked containments are relatively large with
typical dimensions of 50-100 ft (15-30 m) wide, 100-200 ft (30-60 m) long
and 10-30 ft (3-9 m) deep. In dike containment, the depth of the fill 1n
conjunction with the weight of the sludge and cover fill results In much of
the sludge moisture being squeezed Into the surrounding dikes and Into the
floor of the containment. Thus, significant leachate emissions can be
expected.
2.3. REVIEH OF SITE CONDITIONS AT OPERATED LANDFILLS
The previous discussions In this assessment were abstracted from the
U.S. EPA Process Design Manual on Municipal Sludge Landfills (U.S. EPA,
1978). This document contains recommended guidelines for the operation of
sludge landfills, though they are not always achieved at operating
landfills. Also contained 1n the report are sludge and site descriptions of
22 operating or recently operated sludge landfills. Fifteen of these are
sludge-only landfills. Tables 2-3 through 2-6 show the site and sludge
characteristics of these sites. Depth to groundwater at these sites varies
from 0-140 ft (42 m). The depth to groundwater at 12 sites appears to be
within 20 ft (6 m). After trenching and/or filling, the depth to
groundwater at 12 sites 1s <10 ft (3m). Gravel 1s Included In the
description of soil type at four sites, and sand for seven; most of the
sites are 1n areas of high rainfall [>20 1n (51 cm)/year]; thus leachate
generation can be expected. At some sites the aquifer beneath the landfill
1s used as a source of potable water. At most sites the sludge 1s exposed
for <1 day, but at others 1t 1s as long as 60 days.
2-7
-------
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2-9
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TABLE 2-5
Site Design and Operation - Site Preparation*
Site
No.
1.
2.
3.
4.
5a.
5b.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Soil Type
Sandy silt and
clay
S1Hy clay
Sand, silt and
clay
S1lty loam
S1H and clay
S1H and clay
Clay
SUty loam
Sand, silt and
clay
Clay, silt and
sand
Sand, gravel and
clay
Clay, sand and
gravel
Sand
Gravel and clay
Gravel and sand
Sllty clay
Trench
Width
(meters)
4.6
0.6-0.9
106.7
0.6
21.3
0.6
NA
0.76
12.2
3.7
NA
NA
1.8
3.4-4.6
4.9-6.7
Trench
Depth
(meters)
6.1
3.0
6.1
0.9
2.1
3.0
NA
2.4
1.5-1.8
3.0
NA
NA
1.8-2.4
4.6
6.1
Trench
Length
(meters)
9.1
variable
335.3
variable
213.4
45.7
NA
variable
137.2
30.5
NA
NA
12.2
15.2
21.3
Trench
Spacing
(meters)
3.0
2.1-3.0
15.2
0.6
6.1-7.6
4.6-6.1
NA
1.2-1.8
1.5-3.0
1.2-1.5
NA
NA
1.2-3.0
2.4
1.5-6.1
Sludge to
Groundwater
(meters)
2.4
0.6
0.6
0.9
1.5
0.6-0.9
4.9
0.6
1.2-10.4
0.6
0-0.3
3.0-42.7
11.3-18.9
1.5
12.2
3.4-6.1
*Source: U.S. EPA, 1978
1 meter = 3.281 feet
NA = Not applicable
2-10
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3. PATHOGENS
Raw sewage may contain a wide variety of pathogenic microorganisms. The
pathogens Include bacteria, viruses, protozoa, helminths and fungi, all of
which can be expected to be present 1n raw, primary and secondary sludges.
Pathogens currently of primary concern are listed In Tables 3-1 and 3-2. It
should be recognized that the 11st of pathogens 1s not permanent, because as
advances 1n analytical techniques and changes 1n society occur, new
pathogens are recognized and the significance of well-known ones changes.
Microorganisms are subject to mutation and evolution allowing for adaptation
to changes 1n their environment. Thus, no risk assessment can be con-
sidered complete when dealing with microorganisms. As new organisms are
discovered and a greater understanding of their ecology Is developed,
previous assumptions must be reevaluated.
3.1. BACTERIA
Members of the genus Salmonella are the most widely recognized enteric
pathogens. Often associated with food and waterborne outbreaks of illness,
they are responsible annually for 1-2 million incidents of disease In the
U.S. population (Aserkoff et al., 1970). There are >1700 Identified
serotypes, many of which are able to infect both humans and animals.
Salmonella species have been studied more than any other pathogenic bacteria
found in sewage, and a good deal is known about their removal during sewage
treatment and survival in the environment.
Shigella bacteria are responsible for -3% of the reported diarrhea cases
in the United States (APHA, 1975). The Incidence of shigellosis 1n a
*
community is clearly related to sanitation and water quality (Feachem et
al.9 1983). Four pathogenic species of Shigella are recognized, but little
3-1
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TABLE 3-1
Bacteria and Parasites Pathogenic to Man That May Be Present
1n Sewage and Sludge*
Group
Bacteria
Pathogen
Salmonella (1700 types)
Shlgella (4 spp.)
Enteropathogenlc
Escher1ch1a coll
Yerslnla enterocolHIca
Campylobacter jejunl
Vibrio cholerae
Leptosplra
Disease/Symptom Caused
Typhoid, paratyphoid, salmonellosls
Badllary dysentery
Gastroenteritis
Gastroenteritis
Gastroenteritis
Cholera
Well's disease
Protozoa
Helminths
Fungi
Entamoeba hlstolytlca
61ard1a lamblla
Ba1ant1d1um coll
Cryptosporldlum
Ascarls lumbrlcoldes
(Roundworm)
Ancyclostoma duodenale
(Hookworm)
Necator amerlcanus
(Hookworm)
Taenla saglnata
(Tapeworm)
Tr1chur1s
(Whlpworm)
Toxocara
(Roundworm)
Strongyloldes
(Threadworm)
Asperglllus fumlgatus
Candida alblcans
Cryptococcus neopormans
Epldermophyton spp. and
Trlchophyton spp.
Trlchosporon spp.
Phlalophora spp.
Amoebic dysentery, liver abscess,
colonlc ulceratlon
Diarrhea, malabsorptlon
M1ld diarrhea, colonlc ulceratlon
Diarrhea
Ascarlasls
Anemia
Anemia
Taenlasis
Abdominal pain, diarrhea
Fever, abdominal pain
Abdominal pain, nausea, diarrhea
Respiratory disease, otomycosls
Cand1d1as1s
Subacute chronic meningitis
Ringworm and athlete's foot
Infection of hair follicles
Deep tissue Infections
*Source: Gerba, 1983
3-2
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TABLE 3-2
Enteric Viruses That May Be Present In Sewage and Sludge*
Viruses
Type
Disease/Symptom Caused
Enterovlruses:
Pollovirus
Echovirus
Coxsack1ev1rus A
Coxsacklevirus B
New enterovlruses
(Types 68-71)
Hepatitis Type A
(Enterovirus 72)
Norwalk virus
Calldvlrus
Astrovlrus
Reovlrus
Rotavlrus
Adenovlrus
Pararotavlrus
Snow Mountain Agent
Epidemic non-A non-B
hepatitis
3
31
23
6
1
1
1
1
3
2
41
unknown
unknown
unknown
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
Gastroenteritis
Hepatitis
*Source: Gerba, 1983
3-3
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data are available on their presence 1n domestic wastes and survival 1n the
environment. There are no data available on Shlgella destruction 1n most
sludge treatment processes (Feachem et a!., 1983). However, It Is believed
that Shlgella destruction proceeds more rapidly than that of Salmonella or
fecal Indicator bacteria (Feachem et a!., 1983).
Campylobacter bacteria are now recognized as a significant cause of
enteric Illness 1n animals and man. The species of most concern as an
enteric pathogen In humans Is Campylobacter jejunl. It 1s now thought to be
at least as prevalent as Salmonella and Shlgella pathogens and has been
Isolated from stools of 4-8% of patients with diarrhea (CDC, 1979).
Outbreaks of enteric Illness have been linked to fecally contaminated food
and water. No Information 1s currently available on the concentrations of
this organism 1n sludge or Its removal by sewage treatment processes.
Vibrio cholerae causes cholera, an acute enteritis characterized by
sudden onset and rapid dehydration. The study of V. cholerae. atypical V.
cholerae and non-01 V. cholerae has been attracting Increasing attention In
recent years because of several seafood-associated V. cholerae outbreaks
along the Gulf Coast of the United States (Morris et al., 1981). Indeed, it
has been suggested that 1t may be endemic 1n this region (Blake et al.,
1980) and that the marine environment may be a natural reservoir for V.
cholerae (Colwell, 1984). It appears that V. cholerae may survive for
prolonged periods 1n wastewater, especially at low temperatures (Feachem et
al., 1983). In a review of the literature, Feachem et al. (1983) were
unable to find any reports on the occurrence of V. cholerae 1n sludge or
during sludge treatment.
3-4
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It is only 1n the last few years that Yersinia enterocolUlca has been
.recognized as an etlologlcal agent of acute enteritis. Yersiniosis occurs
only sporadically in the United States and is transmitted from either
infected animals or humans. Food and waterborne outbreaks have been
documented (Feachesn et al., 1983). This organism has been isolated from
raw, digested and dewatered sludges (Metro, 1983).
LegtospUa bacteria are excreted in the urine of domestic and wild
animals. The bacteria enter municipal wastewater primarily from the urine
of infected rats Inhabiting sewers {Kowal, 1985). Leptosplrosis, caused by
Leptospira species, is uncommon 1n the United States {Kowal, 1985). The
bacteria survive 2-4 days in the environment (Feachem et al., 1983).
Leptospira organisms are rapidly destroyed during anaerobic sludge treatment
and survival is probably <2 days (Feachem et al., 1983).
Although Escherlchia eg 11 1s usually considered nonpathogenic, entero-
toxlgenlc and enteropathogenlc variants are responsible for numerous out-
breaks of enteritis. Several studies 1n different parts of the world have
Indicated that £. co]i is a significant cause of bacterial diarrhea, and
food and waterborne outbreaks of £. coil-caused illness have been documented
(Feachem et al., 1983).
Because indicator bacteria are easy to study and occur abundantly in
sewage and sludge, a great deal is known about the removal of coliform,
fecal conform and fecal streptococci by sewage treatment processes and
their survival in the environment. While not normally considered "frank"
pathogens, they may cause disease especially in compromised or
immunosuppressed individuals. In many, if not most situations, it is
believed that members of these indicator groups are as resistant to
treatment removal and survive in the environment similar to that of the
3-5
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enteric bacterial pathogens, although 1t Is clearly not the situation 1n all
cases (Feachem et al., 1983).
3.2. VIRUSES
More than 100 different virus types may be present 1n raw sewage (see
Table 3-2). The 11st of pathogenic human enteric viruses, which could be
present 1n sewage, Increased at the rate of 1.3/year from 1972-1983. There
are obviously many more viruses yet unrecognized that could be present 1n
domestic wastes. Most o'f the knowledge on viruses 1n sewage 1s limited to
those associated with gastroenteritis. Exceptions are certain
enterovlruses, which are associated with a wide variety of diseases, and
adenovlruses, which may cause eye Infections. Enterovlruses are often
associated with more serious Illnesses such as hepatitis, meningitis,
myocarditis and paralysis (see Table 3-2).
The most commonly studied enteric viruses In sewage and sludge are the
enterovlruses, which Include pollovlruses, coxsackle A and B viruses, echo-
viruses, hepatitis A virus and other recently classified enterovlrus types.
Several new, presently unclassified enterovlruses, which have been respon-
sible for foodborne outbreaks of Illness 1n Australia, have been recently
Isolated 1n cell culture (Grohmann, 1985). While many of the enterovlrus
Infections such as those caused by pollovlrus may be asymptomatic,
symptomatic Infections may be as high as 95% during outbreaks of hepatitis
(Lednar et al., 1985). A great deal of Information 1s available on the
removal of enterovlruses by sewage treatment, and many studies have been
conducted on their occurrence 1n sludges (Leong, 1983).
Rotavlruses are now recognized as a major cause of childhood gastro-
enteritis, sometimes resulting 1n dehydration and death In Infants and
adults (Gerba et al., 1985). Several waterborne outbreaks have been docu-
3-6
-------
merited (Gerba et al., 1985; Williams and Akin, 1986) and the virus has been
Isolated from sewage sludges (Gerba, 1986a).
The Norwalk virus has been demonstrated to be the cause of numerous
waterborne outbreaks of epidemic gastroenteritis (Gerba et a!., 1985).
Since methods have not been developed for its isolation in cell culture, Its
occurrence and concentration in sewage and sludges is unknown. Astro-
viruses, caliciviruses, coronaviruses, pararotaviruses and several other
Norwalk-like agents have been associated with human gastroenteritis, but
little is known about them. Laboratory methods are currently not available
to study most of these agents and they await further characterization.
Adenoviruses primarily cause respiratory infections and eye infections,
although several new types have been found associated with gastroenteritis
(Gary et a!., 1979).
An epidemic non-A non-B hepatitis virus, which has caused large-scale
outbreaks of waterborne disease in Asia and Africa, has recently been recog-
nized (Gerba et al., 1985).
3.3. PROTOZOA
In the past, little attention has been given to the presence of para-
sites 1n sewage because of the popular Impression that the prevalence of
parasite infection in the United States 1s low (Larkin et al., 1976). How-
ever, the continuing occurrence of waterborne outbreaks of giardiasis and
the resistance of cysts to disinfection indicate that they deserve serious
consideration (Erlandsen and Meyer, 1984).
Of the common protozoa that may be found in sewage, only four species
are believed to be of major significance for transmission of disease to
humans (see Table 3-1). All four, Entamoeba histolytica. Giardia lamblla.
Balantidium coll and Cryptosporidium sp. cause mild to severe diarrhea.
3-7
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Waterborne outbreaks of disease for all of these agents are known to have
occurred. 6. lamblla Is now the agent most commonly associated with water-
borne disease outbreaks 1n which an agent can be Identified (Craun, 1984).
Cryptospor1d1um sp. has only recently been recognized as a pathogen 1n man.
It Infects both animals and man and Is apparently a cause of traveler's
diarrhea (Sterling, 1986) and gastroenteritis worldwide. A waterborne
outbreak of cryptospor1d1as1s was recently reported 1n Texas (D'Antonlo et
al., 1985), and the pathogen was also recently Isolated from domestic sewage
effluents (Huslal, 1985) and sludge (Gerba, 1986a).
Limited Information 1s available on the occurrence of protozoa In
sewage, but even less is known about their occurrence 1n sludges.
3.4. HELMINTHS
A wide variety of helminths and their eggs may occur In domestic
sludges. Helminths are worms that Include nematodes (roundworms) and
cestodes (tapeworms). Those of primary concern are listed In Table 3-1.
Many common helminths are pathogenic to domestic animals, such as cats and
dogs. Helminths have been Identified 1n domestic wastewater and sludge, and
Relmers et al. (1981) have found Ascarls. Tr1churls and Toxocara helminth
eggs 1n municipal wastewater sludge 1n both the southeastern and northern
United States.
Ascar1as1s 1s a helminthic Infection of the small Intestine 1n humans by
the roundworm, Ascarls lumbrlcoldes. About 85% of the Infections are
asymptomatic, although the presence of even a few worms 1s potentially
dangerous (Feachem et al., 1983). Large numbers of worms may cause
digestive and nutritional disturbances, abdominal pain and damage to
Internal organs. The prevalence of ascarlasls 1n the United States was
estimated to be ~4 million 1n 1972 (Warren, 1974).
3-8
-------
AscaMs eggs tend to become concentrated In the sludge during sewage
treatment and their removal by sludge treatment has been studied (Feachem et
al., 1983).
Tr1chur1as1s 1s an Infection 1n humans caused by the whlpworm, Tr1churls
trlchlura. Trlchurlasls 1s a helminthic Infection of the large Intestine
and cecum. Most Infections 1n adults are asymptomatic, but there may be
slight abdominal pain and diarrhea. TMchuMs eggs, like AscaMs eggs, tend
to settle 1n primary and secondary sedimentation tanks and are, therefore,
concentrated 1n the sludge from sewage treatment plants. The fate of
TMchuMs eggs during sludge storage, digestion or composting 1s believed to
be similar to that for Ascarls eggs, but Tr-1churls eggs are probably elimi-
nated somewhat earlier during these processes (Feachem et al., 1983).
Ancyclostom1as1s 1s an Infection of the small Intestine with one of the
two species of hookworms, Necator amerlcanus or Ancyclostoma duodenale.
Ancyclostom1as1s 1s frequently symptomless. When 1t does produce Illness
and constitutes a public health problem, the most Important features are
anemia and debility. Because of the low Incidence of hookworm In the United
States, only low numbers have been found 1n sludge. Hookworm eggs and
larvae are less resistant to sludge treatment processes than Ascarls eggs
(Feachem et al., 1983). Problems could arise If raw or Inadequately treated
sludges are applied to pastureland, since once 1n the soil the eggs will
hatch and produce infective larvae.
Taenla saglnata and T. sollum, the beef and pork tapeworms, live 1n the
Intestinal tract where they may cause abdominal pain, weight loss and diges-
tive disturbances. The Infection arises from eating Incompletely cooked
meat containing the larval stage of the tapeworm, rather than from a waste-
water-contaminated material. Humans serve as the definitive host, harboring
3-9
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the adult. The eggs are passed 1n the feces, Ingested by cattle and pigs
(Intermediate hosts), hatch, and the larvae migrate Into the tissues, where
they develop to the cystlcercus stage. The hazard 1s then principally to
livestock grazing on sludge application sites. Taenla eggs are concentrated
1n sewage sludge and may survive for prolonged periods after land disposal
(Feachem et al., 1983). Taenla eggs may not be completely destroyed by all
sludge treatment processes (Feachem et al., 1983). An Investigation of an
outbreak of T. saginata near Tucson, AZ, revealed that cattle became
Infected while grazing on a farm pasture Irrigated with primary sewage
effluent (Slonka et al., 1975). Pastureland fertilized with municipal
sludge was Implicated In a T. saglnata outbreak In Virginia (Hammerberg et
al., 1978).
3.5. FUNGI
Fungi are usually considered to be of minimal health risk 1n the appli-
cation of municipal sludge. The pathogenic fungi listed 1n Table 3-1 can
all be recovered from municipal sludge (WHO, 1981).
These fungi can be divided Into two groups, the yeasts and the fila-
mentous molds. The yeasts Include Candida alblcans and other Candida spp.,
Cryptococcus neoformans and TMchosporon spp., whereas the filamentous mold
fungi Include the various species of Asperglllus. especially A. fumlgatus.
Epidermophyton spp., Phlalophora spp. and TMchophyton spp. These fungi
have been reported to be present 1n sewage and 1n all stages of sludge
treatment (WHO, 1981); because of their environmentally ubiquitous
existence, It Is difficult to evaluate their significance to public health.
The World Health Organization's Working Group on Sewage Sludge Applied to
Land: Health Implications of the M1crob1al Content (WHO, 1981) emphasized
that because of their prevalence in nature, even 1f the sludge were treated
by pasteurization, fungi will recontaminate the sludge.
3-10
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Asperglllus fumigatus Is one of the most prevalent fungi In municipal
compost. This opportunistic pathogen may cause upper respiratory tract
Infections in man (WHO, 1981). Since composted sludge 1s not burled in
landfills, this fungus is not considered in this document.
un
-------
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4. EXPOSURE PATHWAYS
The possible exposure pathways by which Infectious microorganisms may
reach humans from the operation of sludge landfills are shown 1n Figure
4-1. Exposure to one or more routes of transmission 1s dependent on
significant numbers of microorganisms being present to result 1n Infection.
It Is not Inconceivable that some microorganisms during sludge disposal
follow all of the routes Illustrated 1n Figure 4-1. However, 1t Is unlikely
that significant numbers are transmitted by all of the pathways.
Personnel may be exposed through direct contact with the sludge or
through exposure to aerosols generated during burial. Aerosols could be
transported downwind to areas distant from the disposal site. Aerosols
containing viable microorganisms may also contaminate clothing and equipment
directly. Microorganisms may leach from the burled sludge with Infiltrating
water to contaminate the groundwater. Exposure of the sludge to the surface
would result 1n the generation of runoff, which would transport sludge
particles to nearby surface waters. It 1s also possible that 1f the site
becomes saturated with water, surface leachate contamination will occur.
Burrowing animals could come Into contact with the burled sludge and birds
would be exposed to the sludge before burial. These animals could serve to
transport sludge material off-site or expose 1t to the surface.
Translocatlon of viruses from the subsurface plant roots to the aerial parts
of the plant 1s another potential pathway,
4.1. AEROSOLS AND DIRECT CONTACT
Many enteric microorganisms can effectively be transmitted by aerosols.
In fact, the Infectious dose by the aerosol route may be less than by the
4-1
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Surface
Runoff
Surface
Exposure
Sludge
i
Burial
Subsurface
I
Subsurface Soil
I
Groundwater
Direct Contact
Aerosol
Animals
Plants
FIGURE 4-1
Pathways of Mlcrobial Transport from Sludge Landfills
4-2
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Ingested route for some organisms. Aerosols of enteric organisms are gen-
erated during sewage treatment and during the spraying of sewage effluents
and sludges onto land (Pahren and Jakubowskl, 1980). The organisms In such
aerosols can be transmitted by Inhalation or the settling of the organisms
onto surfaces with which humans come Into contact.
The number of microorganisms generating aerosols depends on the type of
sludge disposed, method of application and burial, and number of micro-
organisms present in the sludge. The greatest amount of aerosol generation
occurs during application of sludges with a low solids content applied as
slurries. Dumping of sludges from trucks Into trenches and area fills also
generates aerosols as the sludge Impacts the ground. Aerosols may be more
contained during disposal Into trenches because of protection from wind
scour. The greatest chance for transport of aerosols off-site occurs with
area fill operation. Some aerosol generation occurs during burial of the
sludge. Greater numbers of pathogenic organisms form aerosols during
disposal of primary sludges than treated sludges.
If wind velocities at a site are great enough, suspension of the sludge
particles could occur. Most sludges would not be easily resuspended because
of their moisture content and tendency to mat as they dry. Dried sludges,
however, may be very light and fine 1n texture and, therefore, easily
resuspended. Wind speeds great enough to resuspend sludge would be unlikely
most of the time even at sites with a wind-power potential (U.S. EPA,
1986). Thus, wind data coupled with the operating times of <50% without
cover suggest that for windy sites, the winds will attain speeds capable of
suspending the sludge from the working face for brief periods of time. Such
resuspenslons could be controlled by requiring placement of dally soil cover
over landfllled sludges (U.S. EPA, 1986).
4-3
-------
The possibility of health risks from public and occupational exposures
to these aerosols has been discussed extensively (Pahren and Jakubowskl,
1980), Several studies have dealt with the measurement of aerosols from
activated sludge treatment plants and spray application of wastewater to
land. These studies Included aerosol monitoring and attempted to examine
health effects 1n populations either working at the site or living nearby.
However, epldemiological studies have not produced conclusive results as to
the Impact of such aerosols on human health (Pahren and Jakubowskl, 1980).
The use of tank trucks and high-volume spray guns for application of
liquid sludges 1s much more likely to generate significant mlcroblal
aerosols than landfllUng. In a study of aerosols generated during the land
application of liquid sludge, Sorber et al. (1984) reported that mlcroblal
aerosol concentrations are less than those at wastewater spray application
sites, and no significant health effects should occur 1n Individuals located
>100 m downwind of the sludge application site.
In summary, some aerosollzatlon of pathogenic organisms will occur dur-
ing landfUUng of sludges. Occupational exposure to workers will occur
with a possible risk of disease transmission. Through proper management and
the use of a buffer zone, significant mlcroblal aerosols should not occur
off-site.
4.2. SURFACE WATER AND RUNOFF
During sludge landfill operations, it Is normal practice to bury the
sludge under several feet of earth at the end of each day. Even In those
operations where the sludge may be exposed for several days, the sludge Is
contained in trenches or pits that limit exposure of the sludge to surface
runoff. Thus, exposure by this route 1s Insignificant unless the sludge
becomes exposed by removal of the soil covering. However, if the
4-4
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site becomes saturated with water through rising water tables or flooding,
leachate from the burled sludge could reach the surface and be transported
from the site with surface runoff.
If suspended sludge particles or leachate leave the site, the material
could contaminate surface recreational areas, Irrigated food crops and
drinking waters and pose a threat to human health.
Operating procedures at sludge landfills require control of runon and
runoff from the working face with drainage ditches. In addition, since the
working face is below grade for the surrounding areas, all trench or pit
fills contain runoff by design. However, this is not the case for area or
canyon fills; provisions must be made to contain drainage in the down-
gradient direction in these fills. Based on the assumption of good
operating practices, runoff becomes a part of the groundwater pathway or is
eliminated. The precipitation that runs off of the working face will
collect at the foot or in a drainage control ditch where it will either
percolate Into the soil, be used for dust control or be routed to
treatment. Therefore, the methodology in this assessment does not Include
an Independent surface runoff pathway.
4.3. PLANT AND ANIHAL
Potentially, plant roots and burrowing animals could come into contact
with the buried sludge. In addition, birds (seagulls) could become exposed
to the sludge before burial. Translocation of viruses from the subsurface
plant roots to the aerial parts of the plants has been observed (Murphy and
Syverton, 1958; Ward and Mahler, 1982), but only when grown In hydroponic
culture or when the roots were cut. Ward and Mahler (1982) concluded that
1t was unlikely that viruses penetrate the intact surfaces of roots. Birds
whose feet or other body parts become contaminated could then carry the
4-5
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contamination to drinking water reservoirs. However, transport of signifi-
cant amounts of pathogenic microorganisms by this route appears unlikely.
4.4. 6ROUNDWATER
Contamination of groundwater and use of that groundwater for domestic
purposes appears the most likely route of significant human exposure from
sludge burial. Many of the sludge landfills In the United States are
operated over aquifers that are used as potable sources. "A review of
operating landfill sites (see Section 2.3.) Indicates that many are
constructed within a few meters of the groundwater table. Therefore, this
pathway 1s considered 1n the greatest detail 1n this assessment.
4-6
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5. EXPECTED CONCENTRATIONS OF PATHOGENS IN SLUDGE
The concentrations and types of pathogens 1n sludges depend on two
principal factors: the Incidence of Infection within a community and the
type of treatment the sludge receives. Season, climate and sanitation are
ma3or factors that will determine the pathogenic load a wastewater treatment
plant receives. Various sludge treatment processes, such as anaerobic
digestion and dewaterlng, act to reduce the numbers of some of the pathogens
Initially present.
There are two main types of wastewater sludge: primary and secondary.
Primary sludge 1s obtained after gravity sedimentation of solids In raw
wastewater. This process removes -60% of the total suspended solids from
sewage and results 1n a semlsolld product that typically contains -5% solids
by weight and has a pH of ~6. Both the percentage of solids and pH are
dependent on the characteristics of the specific treatment plant and the
source of sewage.
Secondary sludges are obtained from wastewater treated by any of a
number of secondary processes. Most treatments are biological, such as the
activated-sludge process, trickling filters and rotating biological con-
tactors. Secondary sludges obtained following biological treatment of
wastewater typically have low percentages of solids and may be thickened by
flotation, centrlfugatlon or other means. Secondary sludges are often com-
bined with primary sludges for further treatment, but they may also be pro-
cessed separately.
Prior to disposal, both primary and secondary sludges must be treated to
reduce volatile solids (stabilization) and dewatered.
5-1
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Sludges are stabilized to eliminate odor problems, reduce pathogen
numbers and prevent decomposition under unwanted conditions. Sludges may
also receive further treatment to reduce pathogens by methods such as
composting, heat drying, heat treatment (pasteurization) and y-1rrad1at1on.
5.1 PATHOGEN CONCENTRATIONS IN RAW SLUDGES
Host mlcroblal species contained 1n raw sewage are concentrated 1n
sludge during primary sedimentation. Enteric viruses have too little mass
to settle alone but, because of their strong binding affinity to partlcu-
lates, they are also concentrated in sludge.
The numbers shown 1n Table 5-1 represent typical, average values that
have been detected by a number of Investigators. Different sludges may con-
tain significantly more or less of any organism as determined primarily by
the sewage from which the sludge was derived. The quantities of pathogenic
species will be especially variable, depending on which are circulating 1n a
community at any particular time. Indicator organisms are normally present
In fairly constant amounts. Because the concentrations determined 1n any
study are dependent on particular assays to detect each mlcroblal species,
these concentrations are only as accurate as the assays themselves. This
point 1s especially relevant 1n regard to viruses for which only a small
percentage 1s normally detected by even the best procedures.
5.2. PATHOGEN CONCENTRATIONS IN SECONDARY SLUDGES
The secondary sludges of concern 1n this report are produced following
biological treatments of wastewater. Mlcroblal populations 1n sludges fol-
lowing these treatments will depend on the Initial concentrations In the
wastewater, the die-off or growth during treatments and the association of
these organisms with sludge (Ward et al., 1984). Some treatments, such as
the activated-sludge process, have a deleterious effect on enteric mlcroblal
5-2
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TABLE 5-1
Densities of M1crob1al Pathogens and
Indicators 1n Primary Sludges*
Type
Virus
Bacteria
Parasite
Organism
Various enteric viruses
Bacterlophages
Total conforms
Fecal conforms
Fecal streptococci
Salmonella sp.
C1ostr1d1um sp.
Mycobacterlum tuberculosis
Ascarls sp.
TM churls vulpls
Toxocara sp.
Density
(number/g dry weight)
102-10«
105
108-109
107-10e
106-107
102-103
106
106
102-103
TO2
IQi-lO2
*Source: Ward et al., 1984
5-3
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species. Concentrations of viral and bacterial pathogens have been shown to
be reduced by activated-sludge treatment. Even so, the ranges of concen-
trations 1n secondary sludges obtained following this and most other second-
ary treatments are usually not significantly different from those of primary
sludges. Examples are shown 1n Table 5-2.
STABILIZATION» DEWATERIN6 AND OIS-
Anaeroblc digestion 1s probably the most common method of sludge stabil-
ization practiced 1n the United States (Ward et a!., 1984). It consists of
the degradation of complex organic substances by microorganisms 1n an
environment devoid of free oxygen. Primary and secondary sludges are fed
either continuously or on an intermittent basis into an airtight container.
Heat 1s normally supplied from an exogenous source to energize indigenous
anaerobic microorganisms. Retention times are variable. The process is
usually conducted in the absence of air at residence times ranging from
30-60 days at 20°C to 15 days at 35-55'C, with a volatile solids reduction
of at least 38% (U.S. EPA, 1974).
Certain conditions within an operating digester are normally quite con-
stant. The pH is between 6.5 and 7.5 and the water content is generally'
-95%. However, the temperatures at which the digesters are maintained can
be quite variable. This is probably the most Important operational
parameter affecting pathogen survival (Ward et al., 1984).
In contrast to other pathogens indigenous to sludge, bacteria are free
living and can multiply outside of their hosts. Thus, it is possible for
bacterial numbers to increase. However, the environment does not appear to
be conduci.* to the growth of enteric bacterial pathogens (Ward et al.,
1984).
5-4
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r
Type
Virus
Bacteria
Parasite
TABLE 5-2
Densities of Pathogenic and Indicator Microbial
Species in Secondary Sludges*
Organism
Various enteric viruses
Total coliforms
Fecal coliforms
Fecal streptococci
Salmonella sp.
As car is sp.
Trichuris vulpis
Toxocara sp.
*Source: Ward et a!., 1984
Density
{number/g dry weight)
3xl02
7xl08
8xl06
2xl02
9xl02
IxlO3
3xl02
5-5
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MesophlUc digestion of sludge can result in 1 to 2 orders magnitude of
loss of pathogenic bacteria and viruses (Ward et al., 1984) (Table 5-3).
Little 1nact1vat1on of parasites such as Ascarls .lumbr Icoldes can be
expected under these conditions. However, temperature 1s a major factor in
the survival of these organisms during this process. Thus, sludge
undergoing thermoph1!1c digestion may largely be free of pathogens.
Aerobic digestion 1s conducted by agitating sludge with air or oxygen to
maintain aerobic conditions at residence times ranging from 10-60 days (U.S.
EPA, 1974).
Aerobic digesters are fed with the same types of sludges as anaerobic
digesters. Therefore, they receive the same pathogen load. They are nor-
mally operated at ambient temperatures. However, the possibility of patho-
gen die-off from high temperatures Is reduced relative to anaerobic diges-
tion where temperatures are normally held at ~35°C.
There 1s a paucity of data regarding pathogen 1nact1vat1on during
aerobic digestion of sludge. Ward et al. (1984) estimated that reductions
1n pathogens would be 1n the same order of magnitude observed for anaerobic
digesters (see Table 5-3).
Another type of process used for stabilization of sludges disposed of In
landfills Is chemical treatment with Hme. This process differs from bio-
logical forms of stabilization In that it does not affect the availability
of food for m1crob1al growth. L1me treatment 1s also used to aid 1n the
dewateMng of sludge. The high pH during this process affects mlcroblal
survival. The pH must be sufficiently high for a long enough period 1f the
treatment 1s to be effective for Inactivating viral and bacterial patho-
gens. It 1s well established that the Initial pH of sludge Is dependent on
the amount of Hme added but that the pH decreases significantly over a
period of hours.
5-6
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TABLE 5-3
Summary of Mlcrobial Reduction During Sludge Treatment3
Treatment
Anaerobic d1gest1onc
Aeroblc digestion
Composting
A1r dry1ngd
Lime stabilization
Bacteria
1-2
2-2
2-3
2-3
2-3
Reduct1onb
Viruses
1
1
2-3
1-3
3
Parasites
0
0
2-3
1-3
0
aSource: Ward et al., 1984
bScale: 0 -- <0.5 orders of magnitude
1 -- 0.5-2 orders of magnitude
2 2-4 orders of magnitude
3 >4 orders of magnitude
cMesoph1Hc temperatures are assumed.
^Effects depend on moisture levels attained.
5-7
-------
Substantial 1nact1vat1on of viruses may occur during lime treatment.
Parasite ova are resistant to high pH, and most probably will survive Time
treatment. Bacteria are rapidly Inactivated at pH 12 but, because the pH
decreases to levels suitable for bacterial growth, their numbers Increase
with time. Bacterial pathogens have not been found 1n sufficiently limed
sludge, but their regrowth can be anticipated under proper conditions (Ward
et a!., 1984).
Air drying and dewaierlng may also result 1n pathogen reduction 1n
*-,
sludges (see table' 5-3).' The concentration of pathogens observed In
stabilized sludges is shown In Table 5-4i
Other nonconventlonal treatment ,or disinfection processes such as heat
drying, pasteurization, heat treatment and y-1rrad1at1on also act to
reduce the numbers of pathogens present 1n sludge before disposal. Their
effectiveness on pathogen removal .Is discussed by Ward et al. (1984).
5-8
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tABLE S«4
Concentrations of Pathogens and Indicators In Digested Sludges*
. , Average of
Type of Stabilization Alt types of
OlgeSted-Dewatered Percent
Organism Anaerobic Aerobic Sludge Viable
{g dry weight) (90 samples positive)
Enterovlruses 0.2-210 0-260
Rotavl ruses 14-485 NO
Salmonella spp. 3-103 3
Total conforms 102-106 10M0>
Fecal conforms 102-10« 10MO«
Shlqella so. 20 NO
Yers1n1a
enterocolHIca 10s ND '
Ascarls sp. - - 9.6
TMchuMs sp. - * 2.6
Toxocara sp. - - 0.7
r. , . , , ~,i , i. «-. , ,i ,,,,...
45
48
52
*Source: Data compiled from Saglk et al., 1980; Relmers et al., 1981;
Metro, 1983; Kowal, 1985; Badawy, 1985; Gerba, 1986a
ND = No data
5-9
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-------
6. SURVIVAL CHARACTERISTICS OF PATHOGENS
Host pathogenic microorganisms have a finite lifetime In the environment
once they have left the host organism. However, under the proper conditions
they may actually grow and Increase in numbers. For a risk assessment of
pathogens 1n landfills 1t 1s necessary to predict the persistence of these
organisms 1n the sludge-soil and groundwater environments.
Information on pathogen survival 1n sludge landfills and leachate 1s
essentially nonexistent. However, studies with a laboratory lyslmeter
suggest that total conforms may persist for at least 100 weeks in burled
sewage sludge (Donnelly and Scarplno, 1984). The literature on pathogen
survival 1n water, sludge and soil was reviewed to determine significant
factors controlling survival and the use of models for predicting pathogen
die-off or inactivatlon.
6.1, SLUDGE AND SOIL
6.1.1. Viruses. Solids-associated viruses in sludge have been shown to
be infectious, well protected and able to survive longer in the environment
than free-living viruses in water and wastewater (Gerba, 1984a). Most
available information describes viral survival in soil alone, rather than
survival in a sludge-soil matrix. Only a few studies have been conducted
investigating virus survival In digested sludge applied to soil. These
studies generally Indicate that viral 1nact1vation In sludge can be a slow
process. In Boulder, CO, enteroviruses were Isolated from sludge-soil
samples taken 30 days after subsurface sludge Injection (Metro, 1983). In
sludge-soil samples from a subsurface injection site In Butte, MT, viruses
were recovered 6 months after application (Moore et a!., 1977). At a site
where sludge was applied to a forest plantation, enteroviruses were detected
6-1
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1n the son for as long as 21 weeks after application (Jorgensen and Lund,
1985). In soil flooded with Inoculated sewage sludge, pollovlrus 1 was
found to survive for at least 96 days during the winter and 36 days during
the summer (Larkln et al., 1976). Unfortunately, none of these studies
provide quantitative data, which could be used to aid in predicting rates of
virus 1nact1vat1on.
Soil moisture and temperature are the main factors determining virus
survival In soils, although the nature of the soil may also play a role
(Hurst et al., 1980a). In a study using seeded effluent applied to soil
columns, a 99% die-off of pollovlrus 1 occurred 1n clay soil after 10 days
at 30°C. At 4°C, a comparable die-off did not occur even after 134 days.
At 15% moisture, pollovlrus survival seemed to be optimal (Dubolse et al.,
1979). A similarly designed study demonstrated prolonged survival of polio-
virus 1 at low temperature and soil moisture of 15-25% (Moore et al., 1977).
Only a 90% decrease in virus was seen 1n 3 months at 4°C, and in 1 month at
20°C. Under warm (30°C) dry conditions, Inactlvation occurred in 1 week.
Naturally occurring enteroviruses have been isolated from soils beneath a
sludge disposal site in Denmark {Jorgensen and Lund, 1985) and at several
sites where land application of domestic sewage was practiced (Hurst et al.,
1980b; Goyal et al., 1984). There are several recent extensive review
articles concerning virus survival in soil and groundwater systems (Sobsey,
1983; Vaughn and Landry, 1983; Gerba and BHton, 1984).
Of all the enteric viruses, hepatitis A virus (HAV) (enterovirus type
72) may be the most resistant to thermal inactivation and Inactlvation in
general in the environment (Peterson et al., 1978; Siege!, 1982). HAV has
recently been shown to survive for prolonged periods of time 1n sewage
effluents and soils (Hazard and Sobsey, 1985; Sobsey, 1985). The decay
6-2
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rates observed by Sobsey (1985) for HAV, poliovirus and echovlrus in water
and soil are shown In Table 6-1. These preliminary results suggest that HAV
may be substantially more resistant to inactivation in soil and water than
are the other enteroviruses.
Hurst et al. (1980b) determined the inactivation rates of poliovirus 1
and echovirus 1 buried in basins of sandy soil flooded with sewage to be
0,04 and 0.15 log day"1 when the basins were flooded (that is,
saturated flow). When the basins were dry, decay rates ranged from
0.11-0.52 log.n day"1. Since decay rates are dependent on soil moisture
loss, virus inactivation could be expected to be greater in unsaturated
conditions where soil moisture loss is significant. A number of other
investigators have studied the decay rates of viruses in soils, but since
the information was derived from soils subject to drying, its usefulness in
predicting virus decay in the deep subsurface is subject to question (Reddy
et al., 1981).
Viruses adsorbed to soil and/or sludge can be expected to survive longer
than when freely suspended in the groundwater. Apparently, adsorbed viruses
are protected against inactivation (Liew and Gerba, 1980; Gerba, 1984b).
Information on virus survival in groundwater has only become available in
the last few years. Enteroviruses have been isolated from groundwater at
numerous sites where land application of wastewater is practiced (Keswick
and Gerba, 1980). Stramer (1984) observed that poliovirus 1 survived in
groundwater over 100 days after leaving a septic tank.
6.1.2. Bacteria. Bacterial die-off is influenced by many of the same
factors as virus inactivation with the addition of the availability of
nutrients playing a role. Temperature, pH, moisture and nutrient supply
have the greatest impact on enteric bacterial survival (Gerba et al., 1975).
6-3
-------
TABLE 6-1
Comparative Die-Off of Enterovlrus 1n Water and Soil3
Decay Rates
Type of Water
or Soil
Groundwater
Primary sewage
effluent
Groundwater 1n
Kaollnlte
Groundwater 1n
Corolla
Groundwater 1n
FH
Primary sewage
1n Corolla
Primary sewage
1n FH
Hepatitis A
5°C 25°C
0.006 0.21
Ob 0.024
Oc 0.0045
0.0045 0.036
0.009 0.143
0.0012 0.0178
Ob 0.02
Pollovl
5°C
ND
0.0089
ND
ND
ND
0.006
0.006
(k day"1)
rus 1
25°C
ND
0.143
ND
ND
ND
0.089
0.066
Echovlrus 1
5°C
ND
0.012
ND
ND
ND
0.006
0.006
25°C
ND
0.214
ND
ND
ND
0.071
0.071
aSource: Sobsey, 1985
bNo measurable 1nact1vat1on after 84 days
cNo measurable 1nact1vat1on after 56 days
ND - No data
FH » Loamy soil
Corolla » Coarse sand
6-4
-------
Antagonism by competing mlcroflora may play a significant role, but 1t Is
difficult to quantify. Like most enteric microorganisms, lower tempera-
tures Increase survival time in soil (Crane and Moore, 1984), although
freezing and thawing conditions are detrimental (Kibbey et al., 1978).
Extremes in pH are also detrimental to bacterial survival (Kibbey et al.,
1978; Hudson and Fennel, 1980). Generally, a near neutral pH environment
favors extended bacterial survival (McFeters and Stuart, 1972). Beard
(1940) found that Salmonella .typhpsa survived best between pH 6.5-8 in soils.
Moisture effects in soil systems are of major Importance 1n bacterial
decline. Kibbey et al. (1978) found that bacterial survival rates for
Streptococcus faecalls and Salmonella typhimurlutn increased with increasing
moisture content of the soil at several different temperatures. When
sludges are buried, soil moisture loss 1s probably minimized (Crane and
Moore, 1984). Bacterial survival apparently would be greatest under
saturated conditions (Boyd et al.', 1969; Kibbey et al., 1978). Of all these
factors, temperature is the most easily quantified. A review of the litera-
ture by Reddy et al. (1981) indicates that die-off rate approximately
doubles with each 10°C rise in temperature between 5 and 30°C. Die-off rate
coefficients could be adjusted for temperature by using the following
equation:
where
FT
kl~2
kT]
e
T
die-off rate adjusted for temperature 1~
die-off rate measured at temperature T]
temperature correction coefficient
temperature (°C).
6-5
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In the studies reviewed ;%!Red(ly et al. (1981) the temperature
correction coefficient (e) ranged from 1.02-1.17, with an average value of
1.07+0.05 (Table 6-2), . . i
The nutrient supply andI organicmatter contained 1n the son and perco-
lating water also affect the; r^te of bacterial die-off. A major reason for
enteric bacterial die-off ^tslW^f the host Intestinal tract 1s probably
the Inability of these organisms to lower their metabolic requirements to a
situation of lower nutrteoi aval Will ty (Klein and Caslda, 1967). Mailman
and Lltsky (1951) felt that organiccpntent present 1n sludge enhanced
bacterial survival. Thesurvival of fecal conforms 1s greatly extended 1n
organic soils over that Observed, In miner^ 5°1ls (Tate, 1978), and regrowth
of S. typh1mur1um and E. coll has been observed In burled feces (Temple et
al., 1980). / '.
Of all the pathogenic bacteria. Salmonella survival has been studied
most extensively (Feacheni et al,, 1983). Salmonella bacteria can survive In
animal slurries, sludges and?Q1Is for periods of many months when
conditions are Ideal (that; Is, high moisture and low temperatures).
Salmonellae 1n sludge applied tpaf1() land 1n summer persisted for 6-7 weeks
(Watson, 1980). Hess, and 8ree>.;;(lf.7$| reported that salmonellae on grass
treated with sludge could survive for <16 months 1n the climate of
Switzerland, but most reported times are shorter than this. Salmonella
organisms can multiply vigorously In sterilized sludge or slurry, but under
natural conditions growth 1s limited or strongly Inhibited by the activity
of other mlcroflora (Rndlayl 1973},
Although the shlgellae are among the most Important pathogenic enteric
bacteria, their presence arid persistence 1n the environment have been
studied far less than |ftfie ease; for E, coll and the Salmonella. In clean
waters, survival times are typically... <14 days at warm temperatures (>20°C),
-------
TABLE 6-2
Temperature Correction Coefficients for the Survival
of Pathogens and Indicator Organisms In :So11 an'd Water:iSystems'
Type of Organism
Temperature Range
*Source: Reddy et al., 1981
Temperature
Correction Coefficient
(e)
Fecal conforms
Escher1ch1a coll
Aerobacter aerogenes
Salmonella tvDh1mur1um
Enterobacter aerogenes
Streptococcus faecal Is
Average
15-21
5-10
10-15
15-20
20-25
'.'.':'.--' * '
10-20
10-20
10-20
4-10
10-35
25-37
4-37
,*., ,,.»- , - .-. 1.08 ': .
.-,-.. :. 1.09i
T.17
1.15
1.07
_;.-.: --'»:..,.,;. ;'; t
1.02
* /. ; "" '''"; * ~~. ' 4 f" ;-- ,- '/'*.. - '.
K05
1.03
1.02
,, .,,-;-:. 4l?,.M,03. .
1.06
1.07+0.05
6-7-
-------
whereas the bacteria may survive for a few weeks below 10°C (Feachem et al.,
1983). Interestingly, HcFeters et al. (1974) found that shlgellae died more
slowly In wellwater at 9-12°C than the fecal bacterial Indicators, salmo-
nellae or Vibrio cholerae. No studies could be located on the survival of
Shlgella organisms 1n soils or sludge. A review of the literature on
Shlgella survival 1n the environment by Feachem et al. (1983) suggests that
at temperatures >30°C, Shlgella survival Is less than Salmonella.
V. cholerae appears capable of surviving for 4-10 days In soils
moistened with sewage at 20-28°C (GeMchter et al., 1975). Data are not
available on the survival of V.. cholerae 1n sewage sludges. Although the
traditional view has been that V. cholerae does not survive for prolonged
periods In the environment, more recent studies have suggested that pro-
longed survival and regrowth are possible under certain conditions (Feachem
et al., 1983). Based on a review of the literature, Feachem et al. (1983)
calculated t values 1n hours for V. cholerae In various types of waters
(Table 6-3). This review suggests that V. cholerae exhibits longer survival
1n wellwater and seawater than 1n fresh surface waters and sewage. In
general, though, 1t would appear that above 30°C V. cholerae survival would
be less than that of Salmonella.
Little 1s known about the occurrence and survival of Yerslnla enteroco-
lltlca 1n the environment. The organism 1s capable of growth 1n foods and
water at low temperatures (0-10°C) (Bottone, 1981; Hlghsmith et al., 1977).
Domlnowska and Halottke (1971) found that Y. enterocolUIca survived 38 days
1n the spring and 7 days 1n summer when kept outdoors 1n surface waters.
Current evidence suggests that Y^. enterocolltlca may survive for long
periods of time 1n cool, clean waters with a minimum of bacterial
competition (Feachem et al., 1983).
6-8
-------
TABLE 6-3
Values in Hours for Various Types of V, cholerae
In
Various Waters and Wastewaters*
Classical 01
Type of Water
Environment
Dechlorinated
tap water
Wellwater
Surface water
Seawater
Sewage
Sterilized well-
water, sur-
face water or
sewage
No.
8
1
8
3
1
7
Arithmetic
Mean
22
36
18
95
12
34
Range
3-48
NA
0.16-36
0.36-161
NA
3-65
No.
8
13
10
7
9
9
El Tor 01
Arithmetic
Mean
49
116
53
56
,66 ,,
59
Range
2-163
5-264
1-230
3-235
8-240
32-168
*Source: Feachem et al., 1983
No. = Number of results
NA = Not applicable
6-9
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Little Information Is available on the survival of Campylobacter jejunV
and no Information Is available on Us survival In domestic sludges or
soil. Blaser et al. (1980) found a 7-log reduction In autoclavecl
streamwater took 5-33 days at 4°C and 2-4 days at 25°C.
Information on Leptosplra survival 1n sludges appears to be non-
existent. Leptosplra organisms are rapidly Inactivated under anaerobic
conditions and are very sensitive to inactlvatlon at temperatures >40°C
(Feachem et al., 1983). They survive best In soil under high moisture
conditions at near neutral pH. In marshy areas where the moisture content
was 40-60% and the pH 6.9-7.4, Karaseva et al. (1973) found survival was
from 4-15 days. Splnu et al. (1963) reported that leptosplres survived for
2-5 days 1n streamwater at 22-26°C. Dlesch (1971) recorded a 3-day survival
period 1n streamwater and wellwater. Animal slurries and sludges are more
likely to contain Leptosplra. Dlesch (1971) found leptosplres able to
survive 61 days 1n an oxidation ditch receiving cattle manure. In contrast,
survival was only 4 days 1n sludge from a cattle manure-settling chamber.
Lower survival In the sludge was believed due to the absence of oxygen.
6.1.3. Protozoa. Many of the same factors affecting enteric virus and
bacteria survival also affect protozoa survival (for example, pH, moisture,
temperature and organic content).
Cysts are more susceptible to adverse environmental effects, such as
drying and elevated temperatures, than are the eggs of helminths (Kowal,
1985). Several researchers observed the survival times of Entamoeba hlsto-
lytlca cysts 1n water solutions to be as follows: 4 days (Beaver and
Deschamps, 1949); 6-7 days at 10°C, 3 days at 30°C and 1 day at 40°C (Chang
and Fair, 1941); and 153 days at 12-22°C (Boeck, 1921). No Information Is
available on survival 1n sludge-soil mixtures, but survival may be expected
6-10
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to be similar to survival in water. Coccidian oocysts can remain viable in
soil for 15 months (Griffiths, 1978), but E. histolytica cysts died within 5
minutes after drying. Under agricultural field conditions, they survived 42
hours when the soil was wet, and 18 hours when the soil was dry (Rudolfs et
a!., 1951b). Under optimum conditions of temperature (28-34°C) and
moisture, £. histolytica cysts survived at least 8 days in the soil. The
optimum soil for cyst survival was found to be dark loam containing 30-50%
sand. Soil samples with high proportions of either clay or coarse sand
resulted 1n the lowest cyst survival times (Beaver and Oeschamps, 1949).
The cysts will die rapidly if dried or frozen.
Giardia lamblia cysts survive in water for 32 days at 10-22°C (Boeck,
1921). Using excystation to determine viability, Giardia survival in tap
water was found to be 6 days at 37°C, 25 days at 21 °C and 77 days at 8°C
(Bingham et a!., 1979).
Cryptosporidium sp., which is now known to be present in sewage (Musial,
1985), appears equally resistant as Giardia cysts to chlorine disinfection
(Angus, 1983) and may survive prolonged periods at low temperatures
(Anderson, 1985).
6.1.4. Helminths. The general consensus Is that Ascarls eggs are the
most resistant of all the enteric pathogens to adverse environmental condi-
tions (Cram, 1943; Jackson et al., 1977; Meyer et al., 1978). Several
researchers have observed extended survival times of Ascarls eggs in soils:
Griffiths (1978) found a 4-year survival time and Jackson et al. (1977)
observed at least 3 years. Other researchers found that the eggs survived
on a drying bed for 66 days (Wright et al., 1942). Soil moistures of >75%
(Rudolfs et al., 1951a) or <20% (Reimers et al., 1980) were lethal to
Ascarls eggs. The lowest moisture levels at which all Ascarls eggs were
6-11
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Inactivated was seasonal: 5% In fall, 7% 1n winter, 8% 1n spring and 15% In
summer (Relmers et al., 1981). Eggs were observed to survive for 60-80 days
when the moisture content of the soil was <6% and the temperature was >40°C
(Cram, 1943). Refrigerated AscaMs eggs have survived for >20 years
(Jackson et al., 1977).
TrlchuMs eggs may remain viable 1n soil for 6 years (Griffiths, 1978).
Hookworm eggs survived 60-80 days with soil conditions of 6% moisture and
temperature >40°C (Cram, 1943). At 45°C hookworm larvae survive <1 hour; at
0°C <2 weeks; and at -11°C <24 hours. Hookworms survive best 1n shaded
sandy or loam soils covered by vegetation and protected from drying and
excessive wetness. Clay soil, which packs tightly, Is unsuitable for
survival (Metro, 1983).
One Investigation studied the survival of Jjen_il saglnata eggs In
sewage, water, liquid manure and on grass. The survival times were 16, 33,
71 and 159 days, respectively (Metro, 1983).
Toxocara eggs were Inactivated when the moisture content of the soil was
20% (Smith et al., 1980). Another study observed that moisture and tempera-
ture were responsible for 1nact1vat1on of Toxocara eggs. The lowest
moisture levels at which all Toxocara eggs were Inactivated were 5% 1n the
fall, 7% 1n the winter, 8% 1n the spring and 15% 1n the summer (Relmers et
al., 1981).
The U.S. EPA sponsored a study on the presence of parasites 1n
land-applied sludges at 12 sites nationwide (Thels et al., 1978). The soils
were tested only at sites that had received sludge applications for a
minimum of 5 years. In Springfield, MO, 50% of the sludge samples and 13%
of the soil samples contained parasites. Toxocara was the only parasite
found 1n the soil, while Toxocara. and to a lesser extent Ascarl'S. were
found In the sludge. In Hopk1nsv1lle, KY, the soil samples were negative,
6-12
-------
while 50% of the sludge samples contained Toxocara as well as some Ascarls.
In Frankfort, IN, the soil samples were negative, while 87.5% of the sludge
samples were positive with Ascarls, Toxocara, Trichuris and hookworm. In
Macon, 6A, 7.6% of the 13 soil samples tested were positive for As car is
only. In sludge and soil samples from Kendalville, IN, Columbus, IN,
Wilmington, OH, and Chippewa Falls, WI, no parasites were recovered (Theis
et al., 1978).
Anaerobically digested sludge from Oakland, CA, was sprayed onto irri-
gated crop test plots and onto dryland pasture. The application rates
ranged from 7.4-72.4 dry metric tons/hectare. Throughout a 2-year period
soil samples from lower application rate areas were positive for parasites
in 12 out of 120 samples, and in 21 out of 124 samples from higher
application rate areas. The control plot, where no sludge was directly
applied, was positive for parasites in 7 out of 75 samples. This Indicates
either a high endemic parasite population, contamination from the test plots
or a combination of both. The parasites found in order of frequency were:
Ascarls. Toxascaris. Toxocara and Strongyloides (Theis et al., 1978).
6.2. SUMMARY OF FACTORS CONTROLLING MICROBIAL SURVIVAL
The major factors that influence microbial survival in the environment
are listed in Table 6-4. In sewage sludge pH, temperature and moisture are
the most important factors in controlling the survival of pathogens.
Moisture content of the sludge or sludge-soil mixtures would be greatest in
moist soil and during periods of high rainfall. The type of soil is also
critical in regard to moisture content; survival is less in sandy soils with
greater water-holding capacity, such as loam and muck. Acidic conditions in
soil or water can greatly increase bacterial die-off rates (Gerba et al.,
1975). While more resistant to inactivatibn under acidic conditions, both'
viruses and parasites are inactivated at extremes in pH. The presence of
6-13
-------
TABLE 6-4
Factors That Influence the Survival of Enteric
Pathogens in the Environment*
Parameters
Survival of Pathogens
Temperature
PH
Desiccation and son moisture
Organic matter
Antagonism from soil microflora
Type and strain of organism
Increased survival at lower tempera-
tures
Shorter survival at extremes
Increased survival 1n moist soils
Increased survival and possible growth
of bacteria
Increased survival time of bacteria 1n
sterile soil; no clear trend for
viruses
Survival dependent on both type and
strain
*Source: Gerba et al., 1975
6-14
-------
antagonistic microbes, such as protozoa, has a detrimental effect on
bacterial survival 1n son. The role of biological antagonism against
viruses and protozoa 1n the soil-sludge environment 1s currently unclear and
Its significance remains to be determined. Survival times of all enteric
pathogens are Increased at lower temperatures. While freezing temperatures
may km bacteria and protozoa, they have little effect on viruses and
actually Increase their survival. Low nutrient availability decreases
bacterial survival. In the case of sludges 1t appears that significant
nutrients are available to greatly prolong the survival of Indicator
bacteria (Donnelly and Scarpino, 1984). The presence of organic matter
Increases the survival of enteric viruses, and the adsorption or association
of viruses with soil or sludge particles also extends their survival time
(Hurst et al., 1980a).
The previous review suggests that the order of persistence 1n the
environment, from the longest to shortest survival time, 1s as follows:
helminth eggs < viruses < bacteria < protozoan cysts. In the case of
Indicator bacteria such as conforms and fecal conforms, regrowth may occur
1n burled sludges (Donnelly and Scarpino, 1984).
To determine risks associated with the Iandf1ll1ng of sludge, It Is
necessary to be able to predict pathogen survival. Of all the factors known
to Influence pathogen survival, temperature 1s the most useful In predicting
survival times. The next section 1s a review of attempts to develop models
for predicting viral and bacterial decay 1n water and soil. Insufficient
Information Is available at present for the development of models for
predicting survival of helminths and protozoan cysts.
6-15
-------
6.3. MODELS FOR PREDICTING HICROBIAL DIE-OFF IN THE ENVIRONMENT
6.3.1. Viruses. Virus Inactlvatlon in water and soil has usually been
described as a first-order reaction (Hurst et al., 1980a; Reddy et al.,
1981; Vllker, 1981; Yates et al., 1985). Nonlinear survival curves may
result 1f viral aggregates are present or a significant variation exists 1n
sensitivities among the viral population to the factors causing
Inactlvatlon. The decay rate or Inactlvatlon described by a first-order
reaction rate expression would be:
Decay rate = d_C_ = -kC
dt
where C 1s Infective virus concentration at time t and k Is the first-order
Inactlvatlon constant (time'1). Here k would be an expression of the sum
total of all factors that influence virus inactivation. Measurement of
virus decay has been conducted on a wide variety of surface waters, but such
Information on soils and groundwater has been limited until recently.
Values on virus inactivation were obtained from anaerobic sludge digestion
and soil column studies by Reddy et al. (1981). Values used by Reddy et al.
(1981) were developed from virus Inactivation studies during anaerobic
digestion of sludge and from soil columns flooded with sewage. In their
model calculations, Hatthess and Pekdeger (1985) used values as presented
for surface waters by Akin et al. (1971). Grosser (1985) reviewed virus
decay observed 1n a number of environments and used a variety of values for
virus decay 1n his model calculations. Vllker (1981) discussed in detail
virus Inactlvatlon observed in various environments, but values for ground-
water had not been determined at the time. In general, most of the previous
work has lacked experimentally determined values for k in groundwater and
son.
6-16
-------
Only a few reports exist on decay rates for viruses In groundwater.
Keswlck et al. (1982a) reported decay rates of 0.19 1og._ day"1 for
coxsacklevlrus B3 and 0.21 log,Q day"1 for pollovlrus 1n water from an
84 m deep well with water temperature ranging from 3-1 5°C In Houston, TX,
In wellwater from Florida, BUton et al. (1983) observed a 0.0456
day"1 decay rate for pollovlrus 1. In the most extensive study to date,
Yates and Gerba (1985) found a mean decay rate of 0.1615 for MS-2 collphage,
pollovlrus and echovlrus 1 log., day"1 In 11 groundwater samples
collected from around the United States. Such Information, while providing
an Idea of decay rates for a particular virus that could be used 1n the
development of a model, does not provide Information that can be applied to
specific locations since environmental conditions may vary widely. To avoid
testing each site 1n question, Information 1s needed on the relative Impor-
tance of factors that can be used to predict virus decay. With this 1n
mind, Yates and Gerba (1985) studied the Influence of various factors likely
to be useful 1n predicting virus decay 1n groundwater. They found that
groundwater temperature was the single most Important predictor of virus
decay. Linear regression analysis gave a correlation coefficient of 0.88,
which was significant at the 0.01 level. The coefficient of determination
was 0.775, meaning that 77.5% of the variation In decay rates among samples
could be explained by temperature. The decay rate for collphage MS-2 as a
function of temperature was expressed by the following equation:
Decay rate = (log,,, day"1) = -0.181 + 0.0214 x temperature (°C)
Viruses persisted for longer periods of time 1n wellwater samples than nave
been found 1n experiments using surface waters Incubated at similar tempera-
tures (Yates et al., 1985).
6-17
-------
It Is also Important to note that examination of the equation developed
by Yates et al. (1985) Indicates that as groundwater temperatures approach
~8°C decay becomes negligible (Figure 6-1). It 1s probable that virus decay
occurs at these temperatures but over much greater periods of time than
could be observed 1n laboratory experiments covering a period of 3-4 months.
In Canada, the Ontario Ministry of the Environment (Metro, 1983)
determined the survival times of parasites from farmland application of
sludge. Large numbers of Ascarls. Toxocara and Taenla eggs were then mixed
with sewage sludge and applied to the surface of grass and bare soil, and
then mixed with the top layer of soil. Conditions were monitored and
samples taken periodically to determine the state and number of remaining
eggs. It was concluded that on well-drained, bare soil exposed to full
sunlight, Ascarls eggs would not survive a full year. When the sludge was
mixed with the soil, Ascaris eggs were not recovered below 2 cm after 15
days, suggesting a shorter survival of parasite eggs when this method Is
used.
Some Ascaris eggs in sludge could be expected to survive for several
years, although the numbers would decrease with time. Toxocara eggs had
similar survival times to Ascaris.
Strongyloides stercoralis exists In sewage as a delicate larva and does
not survive most sewage treatment processes. £. stercoralis larvae
typically live for <3 weeks, even under optimal conditions (Feachem et al.,
1983). The optimal conditions for the infective filariform larvae are
20-25°C and high moisture. Free-living larvae may actually penetrate to
depths of at least 30 cm in soil (Shablovskaya, 1963),
6.3.2. Bacteria. Reddy et al. (1981) attempted to define mlcrobial die-
off in water and soil assuming first-order kinetics. First-order die-off
rate constants (k) were calculated from a review of the literature. The
6-18
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6-19
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average die-off constants (day"1) for Indicator organisms, Salmonella spp.
and Shlgella spp. are summarized 1n Table 6-5. The minimum and maximum
die-off rate values covered a large range because studies were conducted
under a wide variety of environmental conditions.
6.4. ASSESSMENT OF PATHOGEN SURVIVAL AT SLUDGE LANDFILLS
The relationships between pH, temperature and moisture are the most
Important and have been quantified with regard to their Impact on pathogen
die-off. For landfills temperature Is probably the most significant factor
In predicting pathogen die-off. Since sludge at most landfills 1s covered
the same day 1t 1s disposed, moisture losses are likely to be minimal. Even
1n arid regions drying would be greatly retarded after burial. The pH of
raw primary sludge ranges from 5-8 (typical pH 6); anaeroblcally digested
sludges have pH ranges from 6.7-7.5 (typical pH 7.0), and for aeroblcally
digested sludges pH ranges are 5.9-7.7 (typical 7.0) (U.S. EPA, 1974,
1978). Host enteric pathogens are very stable 1n these pH ranges, and pH
would not have a major effect on their survival. Only In Hme-condHloned
sludges where the pH may be >10.0 will pH have a significant Impact on
pathogen survival. At pH levels >10 greater pathogen survival 1s
substantially decreased.
When significant amounts of organic matter are present, the survival of
Indicator bacteria, such as total conforms, 1s prolonged by years.
(Donnelly and Scarplno, 1984). Insufficient Information 1s available to
predict survival of Salmonella or other enteric bacterial pathogens 1n
burled sludge, although 1t 1s probably less than that of the Indicator
bacteria. Helminth eggs will probably survive for several years. Viruses
could also survive for prolonged periods 1n burled sludge. Since
temperature 1s a dominant factor 1n virus survival, 1t should be possible to
6-20
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estimate virus survival with a predictive model. Sufficient data appear to
be available to estimate viral and bacterial decay 1n groundwater and
perhaps soil. However, Insufficient data are available on viral and
bacterial decay 1n sludges at different temperatures to be used In a
predictive model. Protozoan cysts probably survive for a shorter period of
time than the other pathogens, but survival data 1n sludges are lacking.
In summary, It appears that If sufficient Information were available,
predictive models for pathogen decay 1n sludge landfills, soil and ground-
water could be developed. Survival times could be predicted on the basis of
sludge-soil type, pH, temperature and moisture.
6-22
-------
7. TRANSPORT OF PATHOGENS IN THE SUBSURFACE
In conjunction with the survival rates, knowledge of pathogen movement
through the sludge-soil matrix 1s critical. Factors affecting bacterial
movement 1n soil Include physical characteristics of the soil, such as
texture and pore size, as well as environmental and chemical factors, such
as temperature and dissolved salts. For example, retention by soil
particles Is great for soils with a high clay content, and movement of the
pathogens through the soil profile 1s substantially reduced. Therefore,
groundwater contamination would not be a major route of exposure with clay
soil conditions unless cracks or fissures are present. By contrast, sand
and gravel permit greater and more rapid movement (Table 7-1). Major
factors which determine the extent of mlcroblal movement are shown In Table
7-2. Of these, size of the microorganisms 1s probably the most Important.
In most soils viruses could be expected to travel the greatest distance
because of their small size, while the movement of protozoa and helminths
would be more limited (Table 7-3) because of their large size.
7.1. VIRUSES
Virus movement 1n groundwater has been demonstrated under both labora-
tory and field conditions. Keswlck and Gerba (1980) reviewed instances of
virus isolation from groundwater. The published data Indicate that viruses
can travel at least 67 m vertically and 408 m laterally in soil. In gravel
and karst substrata, viruses have been observed to travel as far as 1600 m
at rates as high as 100 m/hour (Keswick et al., 1982b).
The major factors that affect virus migration in the subsurface are
listed 1n Tables 7-2 and 7-4. The major mechanism of virus removal in soil
is by adsorption to soil particles (Gerba and Bitton, 1984). This is in
7-1
-------
TABLE 7-1
Hydraulic Conductivities of Subsurface Material*
Saturated Granular Material
Hydraulic Conductivity
(cm/day)
Clay soils (surface)
Deep clay beds
Loan soils (surface)
Fine sand
Medium sand
Coarse sand
Gravel
Sand and gravel mixes
Clay, sand and gravel mixes (till)
0.01-0.2
10~8-10~2
0.1-1
1-5
5-20
20-100
100-1000
5-100
0.001-0.1
*Source: Adapted from Bouwer, 1984
7-2
-------
TABLE 7-2
Son Factors Affecting Infiltration and Movement
of Microorganisms In Soil*
I. Physical characteristics of soil
a. Texture
b. Particle size distribution
c. Clay type and content
d. Organic matter type and content
e. pH
f. Cation exchange capacity (CEC)
g. Pore size distribution
II. Environmental and chemical factors of soil
a. Temperature
b. Moisture content
c. Soil water flux (saturated vs. unsaturated flow)
d. Chemical make-up of Ions 1n the soil solution and their concen-
trations
e. M1crob1al density and dimensions
f. Nature of organic matter 1n waste effluent solution concentration
and size
*Source: Modified from Crane and Moore, 1984
7-3
-------
TABLE 7-3
Sizes of Waterborne Bacteria, Viruses and Parasites*
Size
Microorganism
Bacteria
Salmonella typhl
Shlgella dysenterlae
EscheMchla coll
Vibrio cholerae
Viruses
Enterovlruses (polio, echo, coxsackie)
Rotavlrus
Norwalk-I1ke virus
Hepatitis A
Adenovlrus
1-10
0.02-0.08
Protozoa (cysts)
Glardla lamblla
Entamoeba hlstolytlca
Helminths (eggs)
Ascarls spp.
Taenla spp.
Fungi (spores)
Asperglllus spp.
5-20
25-38
35-40
*Source: Bltton and Gerba, 1984
7-4
-------
TABLE 7-4
Factors Affecting Virus Transport 1n Soil*
Factor
Comments
Soil type
PH
Cations
Soluble organics
Virus "type
Flow rate
Saturated vs.
unsaturated flow
Fine-textured soils retain viruses more effectively
than light-textured soils. Iron oxides Increase the
adsorptlve capacity of soils. Muck soils are
generally poor adsorbents.
Generally, adsorption Increases when pH decreases.
However, the reported trends are not clear-cut due
to complicating factors.
Adsorption "Increases 1n the presence of cations
(cations help reduce repulsive forces on both virus
and soil particles). Rainwater may desorb viruses
from soil due to Its low conductivity.
Organisms can compete with viruses for adsorption
sites. Humlc and fulvlc add reduce adsorption to
soils.
Adsorption to soils varies
strain. Viruses may have
points.
with virus type and
different Isoelectrlc
The higher the flow rate, the lower virus adsorption
to soils.
Virus movement 1s less under unsaturated flow condi-
tions.
*Source: Bitton and Gerba, 1984
7-5
-------
contrast to bacteria, protozoa and helminths, which are primarily removed by
filtration and straining. Mlcroblal adsorption to soil particles 1s
believed to be mediated by a combination of electrostatic and hydrophoblc
Interactions (Gerba, 1984b). These Interactions are Influenced by the
factors listed 1n Table 7-2. For example, viruses adsorb more readily to
clayey soils than to sandy soils, and adsorption Is enhanced 1n the presence
of divalent cations (Gerba, 1984b). In gravel substrata, no virus
adsorption may occur {Grondln and Gerba, 1986).
Once a virus Is adsorbed to a soil or sludge particle, H Is not neces-
sarily permanently Immobilized. A reduction 1n the Ionic strength of the
water content 1n the soil, which can be Induced by rainfall, can cause
viruses to desorb and migrate further 1n the subsurface (Lance et al., 1976;
Sobsey, 1983). This phenomenon was observed In a field study by Well Ings et
al. (1974), when wells at a wastewater land application site 1n Florida,
which had previously been virus free, were found to contain viruses after a
period of heavy rainfall. Eluted viruses occurred as a burst.
Adsorption of the virus to the soil and sludge also appears to be highly
dependent upon Us 1soelectr1c point {Gerba et al., 1979, 1982). Thus, some
viruses such as pollovlrus adsorb more readily to soils and are less likely
to be eluted than others (Goya! and Gerba, 1979; Zerda et al., 1985; Landry
et al., 1980) (see Table 7-4). In recent studies, Sobsey (1985) showed that
hepatitis virus adsorbs significantly less to sandy soils than pollovlrus
type 1. Its adsorptlve behavior appears to more closely resemble that of
echovlrus type 1. In some sandy soils bacteria may actually be removed less
effectively than pollovlrus because of virus adsorption to the soil (Wang et
al., 1985).
7-6
-------
7.1.1. Land Application. Virus binding to the sludge Is also signifi-
cantly Influenced by pH. AH et al. (1984) found that viruses bind well to
sludges at pH 5-7, but above pH 7.0 binding decreases rapidly. Little virus
adsorption occurred between pH 8-9 (Table 7-5). Thus, viruses may be more
mobile when high pH sludges are disposed.
Results of previous research indicate that viruses are tightly bound to
sewage sludges and not easily released (Bitton et al., 1978; Farrah et al.,
1981; Oamgaard-Larson et al., 1977; MSDGC, 1979) (Table 7-6).
Damgaard-Larson et al. (1977) and Farrah et al. (1981) could not detect any
virus movement from surface-applied sludge. Bitton et al. (1978) only
observed movement when freshly applied liquid (nonair-drled) sludges were
applied. Only 0.2% of the poliovirus type 1 was observed 1n a percolate of
a 54-cm column. Moore et al. (197/) observed poliovirus type 1 movement
through 7 cm of soil when air-dried anaerobically digested sludge was
applied. Between 0.2-2% of the virus that was applied was found 1n the soil
percolate.
In contrast to previous studies, Jorgensen and Lund (1985) were able to
isolate naturally occurring enteroviruses from a 3 m deep well at a site
where anaerobically digested sludge was applied to diluvial sand in a forest
plantation. The 30 8. sample contained both poliovirus type 2 and
coxsackievirus 83. It was collected the llth week after sludge applica-
tion. In laboratory studies, Jorgensen (1985) observed elutlon and rapid
movement of coxsackievirus 83 through 100 cm of sandy loam soil after appli-
cation of anaerobically digested sludge under saturated flow conditions. In
contrast, no viruses were detected in percolates from columns of sandy
soil. At the end of the experiment, viruses were detected in soil eluates
at depths <30 cm in the sandy loam soil, but viruses could be detected
7-7
-------
TABLE 7-5
Effect of pH on Pol1ov1rus Adsorption to Sewage Sludge*
PH
5.0
6.0
7.0
7.5
8.0
9.0
Percent of Bound Poliovlrus
42
42
42
35
28
10
*Source: Adapted from Ait et a!., 1984
7-8
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only to a depth of 14 cm in the column containing sand. In contrast virus
movement was <3.5 cm when the same columns were run under aerobic, unsatu-
rated flow conditions.
A review of the studies on virus movement from, land-applied sludges
suggests two major reasons for the elutlon and penetration of viruses
through soil observed by Jorgensen (1985). As shown 1n Table 7-6, the
studies prior to Jorgensen used add soils, which would be expected to
tightly bind any adsorbed virus. Secondly, these studies were conducted
with unsaturated soil. It should be pointed out that, both poliovirus type 1
and coxsacklevlrus B3 adsorb to a much greater degree to sludge and soils
than many of the other enterovlruses (Gerba et al,, 1979) and, thus, greater
movement of other viruses would be expected to occur. Also, 1n the previous
studies sludge was applied to the soil surface and not burled as occurs In
landfills. Virus Inactlvatlon would be expected to be greater in sludge
applied on the soil surface.
7.1.2. Transport. Recently, Yates et al. (1985) reviewed various
proposed models for virus transport in the subsurface. Two basic approaches
have been used to model virus transport: one relies on the assumption of
Instantaneous equilibrium between the suspended and adsorbed virus concen-
trations (Grosser, 1985) and the other uses a mass-transfer or
"rate-controlled" model to account for the distribution of viruses between
the fluid and solid phases (Vllker and Surge, 1980). In both cases, after
several assumptions have been made, the model formulation results in linear
partial differential equations, which can be solved by a variety of methods
(either analytically or numerically) depending upon the problem domain,
heterogeneities 1n aquifer properties and boundary conditions. All of the
models are based on solute transport; however, viruses are colloids and may
7-10
-------
behave differently than solutes during transport through an aquifer. For
example, Grondin and Gerba (1986) recently found that MS-2 collphage moves
at a velocity 1.5-1.9 times faster than the average groundwater flow through
coarse media. At this time, neither approach Is more correct than the
other, as the models are only approximations of observed laboratory
phenomena. In both cases, the mathematical capabilities far exceed what Is
currently known about the behavior of viruses 1n soils and groundwater.
Laboratory experimentation and field verification with different substrata
are needed to validate the usefulness of these models. However, they could
be used as a first approximation based on existing data.
Using actual field data on virus decay, Yates et al. (1985) employed
krlglng, a geostatistlcal technique, to estimate separation distances
between drinking-water wells and sources of contamination. No virus
adsorption was assumed in the model. A safe distance was defined as the
time of travel (regional groundwater flow) that would result 1n 7 logs of
virus inactivation. A 7-log reduction was chosen since this would reduce
the assumed average enteric virus concentration below detection In the
groundwater (that is, <1 virus/1000 ft). An even more simplified approach
1s that of Wang et al. (1981) who found that virus removal through sandy
soils could be predicted by the flow rate. Thus, at a flow rate of 33
cm/day the rate of poliovirus removal was 0.04 log/cm, while at 1352 cm/day
it was 0.007 log/cm. It 1s important to note that most of the observed virus
removal occurred near the soil surface and was significantly less in the
lower depths of the column (Table 7-7).
Almost no studies on virus movement in the subsurface have been made
under conditions of unsaturated flow. This is because of the difficulty In
obtaining water samples under unsaturated flow conditions. In studying
poliovirus type 1 movement through loamy sand, Lance and Gerba (1984) found
4
*
V
I
7-11
-------
TABLE 7-7
Rate of Virus Removal Through Different Soil Types*
Son Type
Rubicon sand
Anthony
sandy loam
FH loamy sand
Gravel
Virus
Polio 1
Echo 1
Polio 1
Polio 1
Echo 1
f2
f2
MS-2
Flow Rate
cm/day
314
282
33
75
76
75
75
75
Rate of
0-17 cm
0.028
0.032
0.144
0.088
0.046
0
0
0
Removal (log-]Q/cm)
Column Depth
17-87 cm
0.005
0.003
0.02
0.015
0.025
0
0
0
*Source: Wang et al., 1981
7-12
-------
that pollovlrus movement was substantially less under unsaturated flow
conditions. Viruses did not move below the 40-cm level when sewage water
was applied at less than saturation. However, field studies at sites where
wastewater Irrigation of food crops 1s practiced (Goyal et al., 1984)
suggest that enterovlruses can travel at least several meters through the
unsaturated zone.
While laboratory studies are essential to an understanding of the basic
mechanisms of mlcroblal fate and transport 1n soils and groundwater,
ultimate validation of actual behavior rests with field observations. With-
out such validation critical errors could be made In assessing mlcroblal
behavior. Apparently no studies have been conducted to determine If viruses
gain entrance Into the groundwater from sludge landfills. Gerba (1986b)
recently reviewed field studies on the transport and fate of viruses from
septic tanks and sites where land application of wastewater Is practiced.
The results suggest that naturally occurring enterovlruses can travel sub-
stantial distances. Table 7-8 shows the removal of enterovlruses observed
at several field sites where land application of wastewater Is practiced.
The observed virus removal ranged from 0.023-0.49 log/m. All were sandy to
gravel soils. Stramer (1984) dosed several septic tank systems with single
doses of poliovlrus type 1 vaccine derived from cell culture or from stools
of recently vaccinated Infants. The viruses were demonstrated to persist
for several months in each of the septic tank systems, and groundwater
contamination was demonstrated at all sites studied. At one site viruses
passed from the septic tank and traveled 50 m through silt loam soil and
were detected in water from a nearby lake 43-109 days after dosing. Little
virus removal occurred during transport through the unsaturated zone.
7-13
-------
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7-14
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A comparison of field and laboratory studies suggests that laboratory
studies overestimate virus removal. For example, at the Phoenix, AZ, land
application site, laboratory studies suggested that at least 2 logs of
pollovlrus 1 removal could be expected during movement of the effluent
through 1 m of soil (Lance et al., 1976). However, field observations sug-
gested removals of only 0.08-0.11 log removal/m. Reasons for lower virus 1n
the field may be due to numerous factors Including: (1) naturally occurring
viruses are not as easily retained by soils as laboratory strains, possibly
because the procedures used to purify the laboratory strains may affect the
ability of the virus to be retained by the soil; (2) soils are not
homogenous 1n the field and viruses may be expected to move at different
rates throughout a field site; and (3) rainfall and other events In the
field have major Impacts on virus movement under field conditions.
7.2. BACTERIA
In contrast to viruses, bacterial removal by soil 1s believed to largely
Involve filtration, although adsorption also plays a role. Bacterial move-
ment through the soil surface appears to be more restricted than that of
viruses, although under the proper conditions bacteria may actually travel
greater distances (Wang et al., 1985). Although bacterial movement appears
to be limited to depths of 10-50 cm 1n most soils, travel distances of
3-122 m have been observed 1n sandy soils, and distances of travel as great
as 920 m have been observed through gravel (Crane and Moore, 1984; Lewis et
al., 1980). , :
A review of the data obtained from septic tank studies suggests that in
permeable soils (but not in coarse sands or gravels) 1-2 m is adequate for
essentially complete bacterial removal (Lewis et al., 1980; Hagedorn, 1980),
provided the soil has both a layer permeable to effluent flow and another
7-15
-------
region adequately restrictive to form a clogged zone. Also, hydraulic
loadings of <50 mm/day appear necessary for efficient removal (Lewis et al.,
1980). A summary of conform removal under unsaturated conditions 1n sandy
soils 1s shown 1n Table 7-9. It appears that 4-8 logs of conform bacteria
would be removed for each meter of unsaturated zone provided hydraulic
loading 1s <50 mm/day. A review of conform bacteria removal at sites where
land application of wastewater 1s practiced Indicates that significantly
less bacteria would be removed (see Table 7-9).
Rainfall can have a major effect on bacterial migration through the
unsaturated zone by lowering 1on1c concentration and Increasing Infiltration
rates (Gerba and BHton, 1984).
Several surveys have Indicated that rainfall and well depth are related
to mlcroblal groundwater quality. Studies 1n the State of Washington
Indicate that shallow drinking-water wells contain average median conform
values of 8 HPN/100 ma. with an average depth of 9.4 m (31 ft), while deep
wells with an average depth of 153.3 m (503 ft) average 4 MPN/100 ma.
(Hendrlcks et al., 1979). It was also observed that virtually all bacterial
contamination coincided with the periods following heaviest rainfall.
Increased levels of bacterial contamination of drinklng-wellwater after
periods of rain have been noted 1n several studies (Gerba and Bltton,
1984). It was also noted that while an Increase 1n conform bacteria
appears almost Immediately after periods of heavy rainfall 1n shallow wells,
the Increase did not occur until 2 weeks later 1n deeper wells (Loehnert,
1981). Thus, any satisfactory study of wellwater quality should Include
sampling during periods of highest rainfall. Sandhu et al. (1979) found
that basic well design and construction had little effect on the extent
7-16
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of microblal pollution In their study area. Unfortunately, few studies have
attempted to coordinate bacterial sampling with rainfall Infiltration.
If bacteria are able to penetrate to the saturated zone, they appear
capable of being transmitted significant distances 1n sandy and gravel
soils, although significant reductions may occur with travel distance (Crane
and Moore, 1984). Subsurface conditions may markedly affect bacterial
transport. For example, both Rahe et al. (1978) and McCoy and Hagedorn
(1980) observed that when confining layers are present or other water-
restrictive layers are present, the bulk of bacterial transport occurs
directly above the water-restrictive layer. Under such conditions Rahe et
al. (1978) observed £. coll movement rates of 1500 cm/hour. They observed
that once the organisms move Into zones of high permeability, they
experience little mixing or dilution, but rather are transported through
macropores relatively unaffected by the medium through which they are being
moved.
Hagedorn (1980) found fecal conforms from sludge-amended land in
groundwater sampling wells 1 m deep. By the fifth week after application,
these numbers fell below the detection limit of 20 cells/100 mn and
remained so for the duration of the sampling program. Donnelly and Scarpino
(1984) found that bacterial Indicators (conforms) were capable of leaching
from lyslmeters containing sewage sludge for at least 13 weeks. Examination
of the sludge in the lyslmeters after 2 years demonstrated that the con-
forms had not died as was indicated in the leachate.
Sedlta et al. (1977) monitored three wells in an area where land appli-
cation of sludge (30 dry tons/acre or 67.2 metric tons/hectare) is applied
by spraying or soil incorporation. No bacteria or viruses were observed 1n
7-18
-------
three monitoring wells at the site. The depth to water was not given In the
report, Liu (1982) studied the effect of long-term farmland disposal of
anaeroblcally digested sludge on microbiological quality of groundwater
using a lyslmeter system. It was observed that after 4 years of heavy
surface application of sludge, no conform or fecal conform bacteria
penetrated 1.8m of loamy sand or s1H loam soil exposed to outdoor
conditions and natural rainfall.
More recently, Yates (1985) evaluated the literature on viral and
bacterial movement through soil. Yates (1985) compared movement observed by
soil type and by percolation rate (application rate) In order to develop a
rating system for predicting groundwater potential by microorganisms origi-
nating from septic tanks.
In order to develop ratings based on soil type, data on the extent of
vertical movement of microorganisms 1n soil were accumulated from a review
of the literature. Some of the data were obtained from column studies
conducted 1n the laboratory, others from field studies. These data were
plotted to determine the Influence of soil type on the distance that a
microorganism was observed to travel In that soil (Figure 7-1). Soil type
was plotted as a function of decreasing particle size from fracture rock to
fine sand, and as a function of Increasing clay content from fine sand to
clay (Yates, 1985).
The data were analyzed using linear regression, and a correlation (r =
-0.83) was found to exist between soil type and the log,- (distance) of
movement. The relationship can be expressed by Equation 7-1:
y = -0.28928X + 1.7967 (7-1)
where y equals log.., distance of movement and x equals soil type.
7-19
-------
Fractured Rock
Coarse Gravel
Coarse Sand
Fine Sand
I
f:
"o
CO
Sandy Loam
Loam
Sandy Clay
Loam
Clay Loam
Clay L.
Log (distance) (m)
-1 0
FIGURE 7-1
Vertical Movement of Microorganisms as a Function of Soil Type
Source: Yates, 1985
7-20
-------
Once the Importance of soil type In limiting microblal movement was
verified, ratings had to be developed to reflect this. Yates (1985) felt
that soil type 1n Itself was not as Important as soil type 1n relation to
the depth to water. In other words, if the site has a shallow water table,
and the soil has a clayey texture, the potential for groundwater contamina-
tion is much less than if the soil is a coarse gravel. Also, the Impor-
tance of the depth to water in a clay soil Is less than the Importance of
depth to water in a sandy soil.
Yates (1985) also evaluated the Influence of the flow rate of water
movement through the soil on removal of bacteria and viruses. Data on the
effect of Infiltration rate of microbially laden wastewater on the degree of
removal of microorganisms 1n the percolating effluent were obtained by
surveying the published literature. The flow rate was found to be corre-
lated (r = 0.88) with the degree of removal of microorganisms. This
relationship, shown In Figure 7-2, can be expressed by using Equation 7-2:
y = -0.53763X - 0.59602 (7-2)
where y equals -Io9-i0 removal per cm and x equals application rate
(log1Q)/cm.
7.3. PROTOZOA AND HELMINTHS
Because of their large size the movement of protozoan cysts and helminth
eggs would be expected to be even more limited than bacteria. Cram (1943)
found no movement of Ascar is eggs, hookworm eggs and Entamoeba histolytica
cysts through a 60-cm layer of sand after application of raw settled sludge.
In another study, Taenia saglnata eggs were completely removed in a
glass cylinder containing a 12-inch (30-cm) column of sand 1n 3 out of 4
experiments; 99.6% of the eggs were removed in the fourth experiment (Newton
et al.s 1949).
7-21
-------
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Digested sludge from Sacramento, CA, was surface spread onto a land
disposal site. Testing was conducted over a 2-year period In areas both
upstream and downstream of the disposal site. None of the soil or stream
samples was positive for parasites (Storm et al., 1979).
In a Canadian soil core experiment using AsjcaM_s_-seeded sludge under
natural conditions, 1t was concluded that there was no appreciable downward
movement of the parasite eggs, even 1n well-drained soil. After 15 days, no
eggs were recovered below 2 cm. The number of eggs found on grass alone was
much lower than when surface soil was Included In the sample, Indicating
that most eggs 1n the sludge would remain at or near the soil surface
(Metro, 1983).
Still, 1t should be recognized that several outbreaks of waterborne
disease attributed to groundwater contaminated by G.l.ardla cysts have
occurred 1n the United States (Jakubowskl and Hoff, 1979).
A recent ep1dem1olog1cal study evaluating risk factors associated with
endemic g1ard1as1s 1n the New England area found the use of shallow house-,
hold wells for drinking water to be a significant risk factor (Chute et al.,
1985). Numerous outbreaks of glardlasls have also occurred from surface
water that was passed through sand filters. G1ard1a can penetrate a meter
of fine sand (0.28 mm average diameter) (Logsdon et al., 1984). When
G1ard1a cysts were applied to a sand column, 0.1-64% of the cysts were able
to penetrate to a depth of 96 cm at operational flow rates of 0.04-0.4
m/hour. No studies could be found on the expected removal of parasites by
soils. Ghlrose (1986) has reported the Isolation of protozoan cysts at
several meters below the soil surface. Finally, studies In Russia have
shown that some free-living forms of adult Strongyloldes stercoralls
penetrated to a depth of 0.3 m 1n soil (Shablovskaya, 1963).
7-23
-------
7.4. SUMMARY OF MICROBIAL TRANSPORT THROUGH THE SUBSURFACE
As Indicated in this review, many factors Influence mlcroblal transport
through the subsurface. No Information Is currently available on the
transport of microorganisms In leachate generated from sludge-only land-
fills. The chemical composition of this leachate would greatly Influence
transport of microorganisms from the burial site. With all factors consid-
ered, viruses have the greatest likelihood of being transported from the
site because of their small size. The movement of bacteria, protozoan cysts
and helminth eggs would be substantially less. No significant movement of
protozoan cysts or helminth eggs would occur unless gravel or fractured
substrata was present. Bacterial movement may be limited to a few cm In
most soils. However, in sandy soils subject to high rainfall significant
movement could occur.
The depth of the unsaturated zone is probably the greatest barrier 1n
preventing mlcroblal movement into the groundwater. However, field studies
suggest that viruses may penetrate several meters of unsaturated soil to
reach the groundwater (see Table 7-8). Quantitative Information on
mlcroblal movement through the unsaturated zone 1s almost nonexistent.
Several models have been developed for predicting mlcroblal transport
through the saturated zone (Grosser, 1985; Vilker and Burge, 1980); however,
these models have yet to be verified by laboratory and field studies. They
are based on solute transport models, which may not be totally useful In
predicting mlcroblal transport since microorganisms are colloids (Grondln
and Gerba, 1986). These models could be useful as an attempt to approximate
mlcroblal movement from sludge landfills.
7-24
-------
Through a review of the literature, Yates (1985) has developed a quali-
tative rating system, which could be used to estimate the probability of
mlcroblal transport from a waste site. Again, actual field verification 1s
lacking.
A comparison of field and laboratory studies on virus and bacterial
movement 1n this section suggests that travel of these organisms In the
subsurface 1s greater 1n the field than laboratory studies would Imply.
Only through field studies at actual sludge landfills will the real poten-
tial for transport be fully understood.
7-25
-------
-------
8. EVALUATION Of 6RQUNDHATER POLLUTION POTENTIAL BY
MICROORGANISMS USING MICRO-DRASTIC
A methodology has been described to evaluate the groundwater pollution
potential of any site based on Its hydrogeologlc setting (Aller et al.,
1985). A relative rating 1s given to various factors used to describe the
site. These factors Include Depth to water table, net Recharge, Aquifer
media, Soil media, Topography, Impact of the vadose zone and hydraulic Con-
ductivity of the aquifer. These factors, which form the acronym DRASTIC,
are used to Infer the potential for contaminants to enter groundwater. The
relative ranking scheme uses a combination of weights and ratings to produce
a numerical value, called the DRASTIC INDEX, which helps rank areas with
respect to groundwater contamination vulnerability. These weights and
ratings were determined empirically by a group of experts (Aller et al.,
1985).
Using a similar methodology, Yates (1985) developed a rating system to
evaluate the potential for groundwater contamination by microorganisms
(bacteria and viruses) from septic tanks. Eight factors are used 1n the
rating system: depth to water, net recharge, hydraulic conductivity,
temperature, soil type, aquifer medium, application rate and distance to a
point of water use. These factors are then ranked In terms of their Impor-
tance relative to the other factors 1n Influencing the survival and movement
of microorganisms through the subsurface. Weights are assigned to each
factor, with a weight of 1 signifying the least Importance and a weight of 5
signifying the greatest Importance. In addition to the weights, which are
constant, each factor 1s assigned a rating based on the conditions found at
the particular site being considered. The ratings are determined from
8-1
-------
graphs, which have been provided for each factor. The graphs were
determined from a review of the literature on mlcroblal survival and
transport 1n groundwater. An Index, which gives an Indication of the
relative potential for groundwater contamination by microorganisms present
1n septic tank effluent, can then be computed by multiplying each factor
rating by Its associated weight and summing all the factors.
The factors and weights used 1n the micro-DRASTIC system developed by
Yates (1985) are shown in Table 8-1. The index used to evaluate a site Is
computed by using Equation 8-1:
Index = 5 DTW + 2R + 3K + 2T + 5S + 3A + 4AR + 50. (8-1)
The higher the Index, the higher the potential for microorganisms to survive
and be transported to the underlying groundwater. The Index may range from
0-290 and provides a relative indication of the potential for groundwater
contamination by microorganisms. A site with a higher Index 1s more likely
to have contamination problems than one with a lower rating. For a more
definitive interpretation of the Index, Yates (1985) suggested the following
scale as a guide:
0-75 not very probable
75-150 possible
150-225 probable
>225 very probable.
Although the system was developed to evaluate the groundwater pollution
from septic tanks, it could also potentially be used to evaluate sites that
practice land application of wastewater and sludge landfills. To evaluate
landfills the factor for application rate would not be used since effluent
is not being applied. Potentially, the amount of sludge applied and the
type of sludge (primary vs. secondary; percent solids) could affect the
8-2
-------
TABLE 8-1
Factors and Weights Used to Evaluate
Potential for Microbiological Contamination of Groundwatera
Factor
Weights
Depth to Water (OTW)
Net Recharge (R)
Hydraulic Conductivity (K)
Temperature (T)
Soil Type (S)
Aquifer Medium (A)
Application Rate (AR)
Distance to Well (D)
5
2
3
2
5
3
aSource: Developed by Yates, 1985
bNot used In the evaluation of landfills since expression was developed
for application of sewage effluent.
8-3
-------
quantity of virus or bacteria leached. However, Insufficient Information
was available to develop a quantitative expression for these factors or
their relative significance to the other factors. All other factors would
essentially remain the same.
8-4
-------
9. INFECTIOUS DOSE AND RISK OF DISEASE FROM MICROORGANISMS
9.1. INFECTIOUS DOSE
Important In any risk assessment 1s the level of concentration of
contaminate that 1s necessary to cause an adverse effect on health.
Ideally, maximum contaminant levels for potentially harmful substances
should be established on firm ep1dem1olog1cal evidence where cause and
effect can be clearly quantified to determine a minimum- or no-risk level.
However, while epidemiology 1s a valuable tool for detecting patterns of
microbiological risk and establishing statistically significant associations
with risk agents, 1t cannot quantitatively demonstrate cause and effect for
pathogens (CST, 1983). Exact data on MID for humans are generally not
possible because of the extreme cost, unethical nature of human
experimentation and uncertainty 1n extrapolating dose-response curves to low
exposure levels.
Risk assessment can be divided Into four major steps: hazard Identifi-
cation, dose-response assessment, exposure assessment and risk characteriza-
tion (NRC, 1983). The continuing occurrence of outbreaks of viral hepatitis
and gastroenteritis 1n the United States clearly demonstrates that a hazard
exists from viral contamination of drinking water.
The estimation of Infective dose 1s difficult. To obtain data, which
could be used for the purpose of predicting the probability of infection
with low numbers of viruses, large numbers of individuals would be required
who would have to be exposed to a highly virulent microorganism. Even if
such experiments could be done, there would still be a great deal of uncer-
tainty when extrapolating dose-response curves to low exposure levels. In
addition, there are a number of factors that contribute to uncertainty in
9-1
-------
determining HID. A number of these factors are listed In Table 9-1 along
with an estimate of their contribution to uncertainty.
Ward and Akin (1984) recently reviewed the literature on MID of human
viruses 1n a limited number of healthy Individuals. The results Indicated
that relatively low numbers of viruses, perhaps 1 or 2 tissue culture PFU,
were capable of causing Infection.
A number of studies have been published in which small numbers of
viruses, primarily vaccine strains, produced Infection 1n human subjects.
Koprowskl et al. (1956) fed pollovirus 1 1n gelatin capsules to adult
volunteers and Infected 2/3 subjects with 2 PFU of the virus. Katz and
Plotkln (1967) administered attenuated pollovlrus 3 (Fox) by nasogastMc
tube to Infants and Infected 2/3 with 10 TCIDcn and 3/10 with 1 TCIDC_
bu bu
of the virus. Minor et al. (1981) administered attenuated pollovirus 1
vaccine orally and Infected 3/6 Infants who were 2 months old with 50
TCID-. of the virus.
bu
The most extensive studies to date on MID for enteric viruses have been
conducted by Schlff et al. (1984). Over 100 healthy adult volunteers were
fed various doses of echovlrus 12, a very mild pathogen, In drinking water.
Using problt analysis, an estimated average MID of 17 PFU was obtained.
The Infective dose of protozoan cysts also appears to be fairly low.
The Infective dose of G1ard1a lamblla and Entamoeba hlstolytlca by the oral
route appears to be between 1 and 10 cysts (Akin, 1983). Essentially one
helminth egg can be considered to be Infectious, although symptoms may be
dose related (Kowal, 1985).
The MIDs for bacteria are generally higher than those for viruses and
parasites. The number of Ingested bacteria necessary to cause Illness
9-2
-------
TABLE 9-1
Contributors to Uncertainty In Determining
Minimum Infectious Dose for Enteric Viruses*
Category
Contribution to Uncertainty
1. Determination of Immune status
2. Assay technique
3. Sensitivity of host
4. Virulence of virus
5. Use of upper 95% confidence limit
6. Route of exposure
7. Choice of dose-response model
8. Synerg1sm/antagon1sm
9. Dietary considerations
10. Distribution of subjects among
doses and number used
One order of magnitude
One order of magnitude
Several orders of magnitude
Several orders of magnitude
Up to one order of magnitude
One order of magnitude
Several orders of magnitude
Many orders of magnitude
Uncertain
1-2 orders of magnitude
*Source: Gerba, 1984a
9-3
-------
appears to range from 102-108 (Akin, 1983). However, more recent
studies suggest that the Infective dose for Salmonella bacteria may be <10
organisms (D'Aoust, 1985). Virulence of the particular type and strain of
organism as well as host factors may play a role in the actual number of
organisms required to cause Infection.
Unlike risks associated with toxic chemicals In water, Individuals who
do not actually consume or come Into contact with contaminated water or
sludge are also at risk. This 1s because microorganisms may also be spread
by person-to-person contact or subsequent contamination of other materials
with which nonlnfected Individuals may come Into contact. This secondary
and tertiary spread of microorganisms has been well documented during water-
borne outbreaks of Infection caused by the Norwalk virus (Gerba et al.,
1985). In the case of Norwalk outbreaks the secondary attack rate 1s ~3054
(Figure 9-1).
9.2. ESTIMATED MORBIDITY AND MORTALITY FOR ENTERIC PATHOGENS
Not everyone who may become Infected with enteric viruses or parasites
will become clinically 111. Asymptomatic Infections are particularly common
among some of the enterovlruses. The development of clinical Illness
depends on numerous factors Including the Immune status of the host, age of
the host, virulence of the microorganisms and type, strain of microorganism
and route of Infection. For hepatitis A virus (HAV) the percentage of
Individuals with clinically observed Illness 1s low for children (usually
<5%) but Increases greatly with age (Evans, 1982) (Figure 9-2). In
contrast, the frequency of clinical symptoms for rotavlrus 1s greatest In
childhood (Gerba et al., 1985) and lowest 1n adulthood. The observed
frequencies of symptomatic infections for various enterovlruses are shown 1n
Figure 9-3 (Cherry, 1981). The frequency of clinical HAV in adults is
9-4
-------
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estimated at 75%. However, during waterborne outbreaks of HAV H has been
observed to be as high as 97% (Lednar et al., 1985).
Mortality rates are also affected by many of the same factors that
determine the likelihood of the development of clinical Illness. The mor-
tality rate for salmonellosis 1n the United States 1s 0.2%, and shlgellosls
Is 0,13% (Berger, 1986). The risk of mortality from HAV 1s 0.6% (CDC,
1985). Mortality from other enterovlrus Infections has been reported to
range from <0.1%-1.8% (Assaad and Borecka, 1977). Mortality rates for
enteric bacteria and enteroviruses are summarized in Table 9-2. The values
for enteroviruses probably represent only hospitalized cases.
9.3. RISK ASSESSMENT FOR DRINKING WATER
The choice of extrapolation model is critical 1n any estimation of risk.
Haas (1983a) compared the simple exponential model, a modified exponential
model (beta) and the log-normal (or Iog-prob1t) model with experimental
dose-response data. He concluded that the following model for viral
Infection (not necessarily disease) developed from the assumptions of random
(Poisson) viral distribution and postlngestion probability of viral infec-
tion that has a B-distribution (Furomoto and Mickey, 1967) was superior at
describing the data set:
P = 1-(1 + N/B)~a
where
P = Probability of Infection
N « Number of organisms ingested
and a and 13 are parameters of distribution (Haas, 1983a).
Once the probability or risk of infection 1s determined, the annual and
lifetime risks can be determined assuming a Poisson distribution of micro-
organisms within the water consumed (Haas, 1983b):
9-8
-------
TABLE 9-2
Mortality Rates for Enteric Bacteria and Enterovlruses*
Organism
Mortality Rate
Salmonella
Shlgella
Hepatitis A
Coxsackle A2
A4
A9
A16
Coxsackle B
Echo 6
9
Polio 1
0.2
0.13
0.6
0.5
0.5
0.26
0.12
0.59-0.94
0.29
0.27
0.9
*Source: Assaad and Borecka, 1977; CDC, 1985; Berger, 1986. Data for
polio, coxsackle and echo probably represent only hospitalized cases.
9-9
-------
Annual Risk = 1(1-P)
365
Lifetime Risk = l(l-P)25550
The estimated annual risk of Infection from one enterovlrus In 1000 a,
of drinking water (assuming 1ngest1on of 2 8,/day), using 1nfect1v1ty data
from different studies, 1s shown 1n Figure 9-4. Even 1f the highest
Infectious dose observed from human studies Is used (Lepow et al., 1962), a
significant risk of Infection may result from low numbers of viruses In
drinking water. Since the Infectious dose of protozoan cysts appears to be
similar to that of viruses (Akin, 1983), the risks could be presumed to be
similar. Annual risks from bacteria appear to be substantially less;
however, for Shlgella and perhaps Salmonella bacteria (D'Aoust, 1985) there
may be significant risk even when present 1n low numbers (Table 9-3).
Risks of mortality for some enteric pathogens also appear to be
significant. Risks of mortality for Shlgella dysenteMae, pollovlrus 1,
pollovlrus 3 and HAV when present at different concentrations In tap water
are shown 1n Tables 9-3 to 9-6. Risk of morbidity from one Shlgella
dysenteriae In 10 8, of drinking water could have a dally risk as high as
1.3x10-6.
Risks for the enteroviruses, even considering that all Infections do not
result in clinical illness, also appear to be significant (see Tables 9-4
and 9-5).
The actual risk will always be underestimated since secondary and
tertiary spread, which has been documented during waterborne disease out-
breaks of Norwalk agent (Gerba et al., 1985), has not been included. Exist-
ing Immunity tends to lower the risk, but recent studies with Norwalk agent
(Blacklow et al., 1979) and echovirus 12 (Schiff et al., 1984) indicate that
existing antibodies for these agents are not protective and multiple
9-10
-------
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9-11
-------
TABLE 9-3
Risk of Disease and Mortality from Concentrations
of Shlgella dysenterlae 1n Drinking Water*
Assuming Risk of Disease
One
Virus 1n Dally Annual Lifetime
Risk of Mortality
Dally Annual Lifetime
10 I 1.0xlO-«
1000 & l.OxlO"5 3.6xlO"3 2.2xlO"1
10,000 8, 9.5x10-7 3.5x10"* 2.4x10"=
1.3xlO~s 4.8x10-" 3.3xlO~a
1.3x10-8 4.7x10-6 3.3x10-*
1.2x10-9 4.4x10-7 3.0x10-=
*Source: Determined from data by DuPont and Hornlck, 1973; Haas, 1983a;
Berger, 1986
9-12
-------
TABLE 9-4
Risk of Infection, Disease and Mortality from Various
Concentrations of Pol1ov1rus 1 1n Drinking Water*
Assuming One
Virus 1n
Dally
Annual
Lifetime
10 a
1000 a
10,000 a
10 a
1000 a
10,000 a
10 a
1000 a
10,000 a
Infection
S.OxlO"3 6.6xlO"1
2.9xlO"s l.OxlO-2
3.6xlO-s 1.3x10-3
Disease
3.1
2.9x10-7
3.6x10-8
1.1x10-2
l.lxlO"4
1.3x10-5
Mortality
2.7x10-7 1.1x10-*
2.6x10-9 9.5x10-7
3.2x10-1° 1
1
5.2X10"1
8.7x10-2
7.6x10-3
9.1x10-"
6.6X10'6
7.7x10-6
*Source: Haas, 1983a; Minor et a!., 1981
9-13
-------
TABLE 9-5
Risk of Infection, Disease and Mortality from Various
Concentrations of Pollovlrus 3 In Drinking Water*
Assuming One
Virus 1n
Dally
Annual
Lifetime
10 ft
1000 ft
10,000 ft
10 ft
1000 ft
10,000 ft
10 ft
1000 ft
10,000 ft
Infection
8xlO"2 1 i
8.8xlO"4 2.7xlO~i l
4.4xlO~5 3.1x10"* 8.9X10"1
Disease
S.OxlO"4 2.6xlO~2 1
8.7xlO"6 3.2xlO"3 2.0X10"1
8.8xlO~7 3.3xlO"4 3xlO~2
Mortality
9.0xlO~6 3.3xl(T3 2.1X10"1
9.6xlO~B 4.4xlO~5 S.OxlO"3
9.6xlO~9 3.5xlO~6 2.5x10""
*Source: Haas, 1983a; Katz and Plotkln, 1967
9-14
-------
TABLE 9-6
Risk of Infection, Disease and Mortality from Various
Concentrations of Hepatitis A Virus In Drinking Water*
Assuming One
Virus 1n
Dally
Annual
Lifetime
10
1000
10,000
10
1000
10,000
10
1000
10,000
ft
ft
ft
ft
ft
ft
ft
ft
ft
2
2
3
2
2
2
1
1
1
Infection
,9x10-3
.9xlO"s
.5X10-.
Disease
.2x10-3
.lxlO~s
.7xlO"6
Mortality
.3xlO"5
.2xlO~7
.6x10-8
6
1
1
5
7
9
4
4
5
.6xlO~!
.OxlO"2
,3xlO"3
.6x10"!
.8x10-3
.8xlO~4
.9x10-3
.3xlO"s
.8xlO"6
1
5.1x10
8.7x10
1
4.2x10
6.6x10
2.9x10
3.0x10
4.1X10
~i
~2
~1
~ 2
~1
-3
"4
*Source: CDC, 1985; Minor et a!., 1981; Haas, 1983a
9-15
-------
Infection and disease can occur. In contrast, existing antibodies for
pollovlrus and hepatitis clearly offer lifelong protection (Evans, 1982).
The actual distribution of pathogens 1n water 1s not known. The assump-
tions made 1n this risk assessment assume a random distribution (Haas,
1983b), which may or may not be the case. Additional research 1s necessary
to determine the type of distribution 1n water for pathogens. This approach
may also be utilized for pathogens 1n sludge.
9.4. SUMMARY OF DISEASE RISK FROM ENTERIC PATHOGENS
Many of the pathogens present 1n sludge are continuing causes of food
and waterborne disease 1n the United States (Craun, 1986). While the
Information on Infectious dose for most pathogens 1s limited, 1t appears
that low numbers (<50 organisms) of viruses and protozoan cysts are capable
of causing Infection (Akin, 1983; Haas, 1983a) 1n a susceptible host. The
number of Individuals who develop clinical Illness will depend upon the
strain and type of organism as well as host factors such as age. The
percent of Individuals who develop clinical disease may be as low as 1% for
pollovlrus to as high as 97% for hepatitis. Significant mortality Is
associated with many of the viral pathogens, such as coxsackle and HAV, In
some age groups.
If the distribution of pathogens 1n the environment (that Is, water
medium) 1s known, the risks of Infection, morbidity and mortality can be
estimated from existing data.
9-16
-------
10. GROUNDWATER PATHWAY RISK ASSESSMENT METHODOLOGY
10.1. GENERAL ASSESSMENT
A major difficulty 1n assessing the risks of groundwater contamination
by sludge-only landfills 1s the absence of any field or laboratory studies
concerning the survival and transport of pathogens Into groundwater by this
method of municipal sludge disposal. Previous studies on land application
of sludge have only been concerned with Its application to the soil surface
or within a few centimeters of the soil surface. Application rates at such
sites are in the order of 22.4 metric tons/hectare vs. >22,417. metric
tons/hectare at sludge landfills (U.S. EPA, 1978; Saglk et a!., 1980).
Thus, the concentration of pathogens/hectare 1s much greater at landfill
sites.
A review of the literature suggests that, in terms of risk, signif-
icant concentrations of pathogens can be expected 1n the sludges that
landfills receive. Most of the methods used 1n pathogen detection are not
100% efficient. In addition, methods do not exist for the detection of all
of the pathogens that may occur 1n sewage sludges. As an example, recent
studies on the occurrence of rotavlruses 1n anaeroblcally digested sludges
suggest they occur 1n concentrations at least equal to that observed for the
enterovlruses (Badawy, 1985) (see Table 5-4). It would be reasonable to
suggest that the actual concentrations of enteric viruses are 10-100 times
that observed experimentally.
It also appears that many of the pathogens are capable of prolonged
survival 1n sludges, especially at low temperatures and high moisture.
Indicator bacteria (conforms and fecal conforms) have been observed to
survive for years in sludge and co-disposal landfills (Donnelly and
10-1
-------
Scarplno, 1984). The high level of organic matter contributes to the
survival and growth of Indicator bacteria. Bacterial pathogens such as
Salmonella are also capable of growth 1n sterilized sludges (Ward et al.,
1984), although this appears unlikely 1n digested sludges because of the
large number of antagonistic bacteria. Under Ideal conditions viruses and
parasites may survive for months to years, especially 1f subsurface
temperatures approach 10°C.
Transport of pathogens from the sludge to the groundwater 1s more diffi-
cult to assess. The nature of the underlying soil 1s probably the most
significant factor In controlling pathogen movement. In clayey soils or
clay-lined landfills there 1s probably no movement of pathogens from the
site. However, 1n larger grained soils at least some movement of pathogens
could probably be assumed. No data base appears to exist to estimate the
numbers of pathogens that could be leached from sludge landfills. The
concentration of fecal conform bacteria In sludge-only landfills has been
reported to range from 2.4xl03-2.4xl04/100 ma and that of fecal
streptococci from 2.1xl03-2.4xlOV100 ma, (U.S. EPA, 1978). This
suggests that significant leaching of pathogenic bacteria and viruses can
occur. The chemical constituents of the leachate and Its pH would be
expected to have an Influence on pathogen survival and transport (Chapters 6
and 7). The high organic content of the leachate (total organic carbon
reported to be 102-1.5xl04 mg/a.) could reduce viral and bacterial
retention by soil particles as well as enhancing survival (U.S. EPA, 1978).
Bacteria and viruses probably have the greatest chance of being leached from
landfills. The amount of rainfall would probably be a major factor In
microblal release from the sludge. In addition, the water content and
weight of the sludge 1n landfills can be expected to Increase water
Infiltration. Infiltration 1s also Increased since the sludge provides
10-2
-------
greater pore space and decreases the potential of surface sealing (Epstein,
1973). Sludges with a pH >7.0 would be expected to bind viruses less, so
greater mobilization of viruses may occur. Studies with surface-applied
sludges suggest that at least 0.1-1% of the viruses applied are released
from the sludge (Alt et al., 1984). Numbers released may actually be
greater since viral 1nact1vat1on would be expected to be greater In
surface-applied sludges because of drying and higher temperatures.
Any organisms released from the sludge would usually have to travel
through an unsaturated zone before reaching the groundwater table. Removal
of microorganisms 1n this zone 1s greater than the saturated zone (Chapter
7). Rainfall may play a significant role 1n the penetration of this barrier
by microorganisms. Most of the landfills described 1n the U.S. EPA's
Process Design Manual for Municipal Sludge Landfills (U.S. EPA, 1978) are
constructed such that they are within 3 m of groundwater. While laboratory
studies suggest substantial removal of microorganisms through the
unsaturated zone, field studies Indicate that penetration of enteric
bacteria and viruses Is possible. The degree of mlcroblal removal will
depend greatly upon the soil type. However, quantitative Information on
pathogen removal through the unsaturated zone Is almost nonexistent
(Chapter 7).
Less removal of microorganisms can be expected once they have entered
the groundwater. Under saturated flow, viruses can travel long distances In
sandy soils. The degree of removal Is determined by the composition of the
substrata. High removals can be expected 1n clay soils, while little
removal probably occurs 1n fractured substrata or karst terrain. The rate
of virus removal through soil observed 1n the laboratory differs from that
observed 1n the field (see Tables 7-1 and 7-8). Laboratory studies with
10-3
-------
pollovlrus and echovlrus suggest that 1-3 logs of virus removal would occur
per meter of travel through sandy saturated loam soils. However, In field
studies observed removals are usually <0.1 log/m. In one recent study,
Strainer (1984) observed <0.05 log/m removal of pollovlrus through sllty loam
soil under saturated flow conditions. The virus traveled over 46 m to
contaminate a nearby lake. These results suggest that laboratory-grown
viruses or laboratory experimental designs do not actually reflect virus
transport through the subsurface 1n the field.
Bacteria and protozoa also appear capable of being transported several
meters through sandy soils (Chapter 7). G1ard1a organisms can penetrate at
least a meter of fine sand. Helminth eggs, because of their larger size,
are unlikely to travel more than a few centimeters unless fractures 1n the
substrata exist. Bacteria and protozoan cysts would not be expected to
travel as great a distance 1n the subsurface as viruses.
10.2. CHARACTERISTICS OF BEST- AND WORST-CASE LANDFILLS
Based on a review of the literature, the best and worst landfill sites
as far as potential risks for contamination of groundwater are shown In
Table 10-1. The Ideal site would utilize digested secondary sludge with a
solids content of >20%. The substrata would be a clayey soil with a deep
groundwater table and 1n an area of low rainfall. With a claylsh soil and a
clay lining, no enteric pathogens would be expected to contaminate ground-
water. A worst-case landfill would dispose of raw or primary sludge with a
solids content of <15%, He within 1 m of the groundwater table, be unllned
with a sand to gravel substrata and 1n an area of high rainfall.
Also presented 1n Table 10-1 are representative conditions present at 15
sludge landfill sites reviewed 1n the U.S. EPA's Process Design Manual on
Municipal Sludge Landfills (U.S. EPA, 1978). A review of the characteMs-
10-4
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tics of these sites suggests that both raw and stabilized sludges are dis-
posed, that the depth to groundwater Is often within 1 m, the substrata Is
clay to gravel and rainfall 1s >76.2 cm/yr. Some sites are clay lined.
10.3. EVALUATION OF GROUNDWATER CONTAMINATION AT LANDFILLS BY MICRO-DRASTIC
Two example sludge landfill sites were evaluated using the mlcro-DRASTIC
rating system developed by Yates (1985) to assess the likelihood of ground-
water contamination. The site characteristics used 1n the micro-DRASTIC
system for each of the two sites 1s shown 1n Table 10-2. The application
rate factor was not used since liquid wastes were not applied to these
sites. The ratings developed by Yates (1985) were used to determine each
factor (Tables 10-3 and 10-4). Scores were determined by multiplying the
ratings by the weights 1n Table 10-5. The total scores and ratings for
directly beneath the site and distances of 100 m and 200 m are shown in
Table 10-6. Using the suggested rating scale of Yates (1985) (Table 10-7),
it was determined that microbial contamination was probable directly beneath
Site A and possible beneath Site B. At both sites it was judged to be
possible at distances of 100 and 200 m.
It should be pointed out that the rating system 1s attributary and has
not been verified in the field. Still, it provides a mechanism for evaluat-
ing the many interacting factors controlling mlcrobial survival and
transport in the subsurface. While the rating system suggests that micro-
bial contamination is possible at all sites, it does not necessarily mean
that microbial contamination will occur. It does suggest that, based on the
current body of information on microbial behavior in the subsurface, 1t
cannot be excluded at the present time. Micro-DRASTIC could potentially be
used like DRASTIC as a first step in evaluating the potential for microbial
10-6
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10-7
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TABLE 10-3
Rating of M1crqb1al Contamination at Sludge Disposal Site A
Directly
Beneath Site
Factor
Depth to ground-
water
Net recharge
Hydraulic
conductivity
Temperature
Soil type
Aquifer medium
Distance
Total Score
Rating3
10
1
1
9
7
10
10
Scoreb
50
2
3
18
35
30
50
188
100
Rating
10
1
1
8
7
5
3
m
Score
50
2
3
18
35
15
15
138
200
Rating
10
1
1
9
7
4
2
m
Score
50
2
3
18
35
12
10
130
aSource: Yates, 1985
''Score 1s obtained by multiplying the weights shown In Table 10-5 by the
rating.
10-8
-------
TABLE 10-4
Rating of Microbial Contamination at Sludge Disposal Site B
Directly
Beneath Site
Factor
Depth to ground-
water
Net recharge
Hydraulic
conductivity
Temperature
Soil type
Aquifer medium
01 stance
Total Score
Rating3
9
7
1
9
2
4
10
Scoreb
45
14
3
18
10
12
50
152
100
Rating
9
7
1
9
2
2
3
m
Score
45
14
3
18
10
6
15
in
200
Rating
9
7
1
9
2
2
2
m
Score
45
14
3
18
10
6
10
106
aSource: Yates, 1985
bScore is obtained by multiplying the weights shown in Table 10-5 by the
rating.
10-9
-------
TABLE 10-5
Factors and Weights Used to Evaluate
Potential for Microbiological Contamination of Groundwater*
Factor
Weights
Depth to Water (DTW)
Net Recharge (R)
Hydraulic Conductivity (K)
Temperature (T)
Soil Type (S)
Aquifer Medium (A)
Distance to Well (D)
5
2
3
2
5
3
5
*Source: Yates, 1985
10-10
-------
TABLE 10-6
Estimation of Microblal Contamination at Two Sludge Disposal Sites*
Total Score at
Distance Indicated
Site
A
B
Directly
Beneath
188
152
100 m
138
111
200 m
130
106
Estimation of Microblal
Contamination
Directly
Beneath
probable
possible
100 m
possible
possible
200 m
possible
possible
*Values developed for site examples from rating system of Yates (1985).
10-11
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contamination for a particular site based upon hydrogeologlc settings. To
be more useful, ratings for sludge type (or any additional treatments, for
example, composting) and application rate could be Included.
10.4. ESTIMATINS TRANSPORT OF ENTERIC ORGANISMS AT SLUDGE LANDFILLS TO
GROUNDWATER
Another approach to determine the likelihood of groundwater contamina-
tion 1s to estimate the leaching of pathogens from landfills and their
concentrations at various distances from the sites. From this Information,
risk of Illness by using the water for drinking could be estimated by the
methods shown 1n Chapter 9. To determine the number of pathogens reaching
any location beneath or distant from the site, the number of pathogens Is
first estimated. This will be dependent on the type of sludge and the
treatments) 1t has received. The number of pathogens leached from the
landfill 1s then determined and their expected rate of removal as they
travel through the unsaturated zone. Once the pathogens have reached the
groundwater (saturated zone) their removal will be less than 1n the
unsaturated zone. This method Is diagrammed 1n Figure 10-1.
To Illustrate how this methodology might be used, two example sites were
chosen, one disposing of primary sludge and the other secondary sludge. The
volume of sludge disposed at each site and net recharge are shown In Table
10-7. From the net recharge the volume of leachate, which could be
generated per hectare, can be determined (that is, the volume of recharge
rainwater that passes through the saturated zone per hectare). From the
literature review (Chapter 5) the number of pathogens expected per hectare
at each landfill site was estimated and 1s shown 1n Table 10-8.
Whether or not a pathogen reaches groundwater and 1s transported to
drinking-water wells depends on a number of factors Including Initial con-
10-13
-------
Concentration of Pathogen in Sludge
Concentration of Pathogen in Sludge Leachate
Removal of Pathogen During Travel Through the Unsaturated Zone
Removal of Pathogen During Travel Through the Saturated Zone
Concentration of Pathogen at any Distance from Site
Estimated Risk of Infection, Morbidity and Mortality
FIGURE 10-1
Methodology for Estimating Risks from Groundwater Contamination
by Sludge Landfills
10-14
-------
TABLE 10-8
Estimated Levels of Pathogens and Indicator Bacteria at
Sludge Landfills A and B Applied/Hectare*
Pathogen
Site A
Fecal Conforms
AscaMs
103-6
SHe B
Enterovlruses
Rotavlrus
Salmonella
103-104
103-6-10«
103-104-4
104-4-10s
unknown
104.4_104-8
106-4-106-8
* Based on literature review contained 1n this document.
10-15
-------
centratlon of the pathogens, survival of the pathogens, number of pathogens
that reach the sludge-soil Interface, the degree of removal through the
unsaturated and saturated soil zones and the hydraulic gradient. The degree
to which each of these factors will Influence the probability of pathogens
entering groundwater cannot be determined precisely. Viruses, because of
their small size, probably have the greatest potential of all the pathogens
of actually reaching the groundwater and being transported from the site.
To determine the numbers of viruses that may be transported from a site,
assumptions were made for each of the principal factors (Table 10-9).
Values were estimated for most favorable, most probable and worst possible
conditions. Host favorable conditions are those conditions most likely to
result In limited virus survival and transport (Table 10-10).
10.4.1. Estimated Concentration of Viruses 1n the Sludge. The observed
ranges of enteroviruses and rotaviruses detected in sewage sludges are
discussed in Chapter 5. The concentration of other enteric viruses such as
Norwalk, hepatitis A and adenovirus is not known, but obviously, they will
also be present. Limited studies on the presence of rotaviruses suggest
that they will also be present in numbers at least equal to that observed
for enteroviruses in anaerobically digested sludge. However, detection
methods for even the enteroviruses in sludge are only 30-50% efficient
(Farrah and Schaub, 1983). Thus, the actual number of pathogenic enteric
viruses 1s undoubtedly many times that detected by conventional methods.
Modification of tissue culture techniques can result in a 10-fold or greater
increase in the numbers of enteroviruses detected in sewage (Morris and
Waite, 1980). For most favorable conditions the number of enteric viruses
was placed at 14/g of sludge, which is the combined total observed for
10-16
-------
TABLE 10-9
Assumptions Used 1n Assessing Virus
Contamination of Groundwater at Sludge Landfills
Item Most Most
(unit of measurement) Favorable Probable
Worst
Possible
Concentration of
viruses 1n sludge;
Secondary (g)
Primary (g)
14
100
3500
10*
7xlO«
106
Percent of viruses
leached from sludge
0.1
10
Concentration of
viruses 1n leachate
(it)
Viruses are suspended
1n total volume of net
recharge.
Viruses are only eluted
slowly or only after sig-
nificant rainfall through
a limited number of
pores. Viruses are
resuspended In only 1%
of the total volume of
leachate.
Removal rate
of viruses
through unsatu-
rated zone (m)
2 logs
0.1 log
0.006 log
Removal rate of viruses 2 logs
1n saturated zone (m)
0.1 log
0.006 log
Inact1vat1on or decay
constant (k)
Rate of travel (m/day)
Since no inactlvatlon (decay) 1s assumed, this
factor 1s not Important 1n the risk assessment,
Dispersion and dilution
10-17
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enterovlruses and rotavlruses and 1s based on the lowest concentration of
enterovlruses that has been observed. Most probable represents the combined
median-range concentrations observed Increased by a factor of 10 to take
Into consideration limits of detection methods. Worst possible 1s the
highest concentration observed for enterovlruses times a factor of 100.
This Is considered to be the highest concentration likely to be present.
10.4.2. Percent of Viruses Released from Sludge. Quantitative studies
have never been conducted on the degree to which viruses can be leached from
sludges during water Infiltration. Laboratory studies have been conducted
for surface application of sludges, but inactivatlon from dessication would
likely reduce the numbers of enterovlruses rapidly under these conditions
(see Chapter 7). In addition, these experiments were done with acid soils,
which would act to reduce virus migration through adsorption. However,
field studies Indicate that transport to groundwater occurs under field
conditions where sandy soils exist. The laboratory studies suggest that at
least 0.1-1% of the viruses present may be leached from the sludge.
However, greater numbers could be leached from burled sludges since
dessication will be less than would occur in surface-applied sludges. Under
most favorable conditions, it is estimated that no more than 0.1% of the
viruses are released from the sludge. For most probable, 1% is estimated,
and under worst possible a 10% release 1s estimated.
10.4.3. Concentration of Viruses 1n Sludge Leachate. It is difficult to
estimate the volume of water at which the viruses will be suspended after
they are leached from the buried sludge. The field studies of WelUngs et
al. (1974) suggest that viruses may only be eluted from soils and penetrate
to groundwater after significant rainfall. If true, then viruses may only
10-19
-------
be released from the sludge 1n "bursts" after a major rainfall rather than
slowly as rainfall migrates through the sludge. Under most favorable and
most probable conditions 1t 1s estimated that viruses are released slowly
Into the net recharge volume at a sludge landfill. For worst possible
conditions viruses are only released 1n 1% of the net recharge volume.
10.4.4. Removal Rate by Soil. Laboratory studies suggest that most
viruses are rapidly removed from water by soil during percolation. Greater
removal would be expected during movement through the unsaturated zone than
the saturated zone (Chapter 7). Little Information 1s available on virus
movement through the unsaturated zone. Removal through sandy soils appears
to be 1n the order of 1-3 logs/m. However, field studies suggest that under
"real-life" conditions virus removal Is 1-2 orders of magnitude less.
Little 1s known on factors governing virus survival and transport under
field conditions. The most favorable situation relies on laboratory data
for sandy soils that suggest 2-log removal of vlrus/m of soil. For favor-
able and probable conditions removal 1s estimated at 0.1 log/m based on
average field conditions (see Table 7-8). Worst possible 1s the lowest
removal under field conditions observed for sllty soil conditions. Since
field studies have not yet shown any differences between virus removal In
unsaturated vs. saturated zones, the rate of removal 1s assumed to be the
same for both zones 1n the subsurface (Chapter 7).
10.4.5. Inact1vat1on or Decay Rate of Viruses. Previous studies have
shown that 1nact1vat1on (decay) rates of viruses can be estimated from the
median temperature of the groundwater (Yates, 1985). Recent research
suggests that hepatitis A virus Is substantially more resistant to thermal
1nact1vat1on than all other enteric viruses 1n groundwater (Sobsey, 1985).
10-20
-------
Research currently in progress will provide this information so that more
accurate estimations can be made. Unfortunately, no data are available on
viral survival in landfill sludge leachates. The leachate composition could
have a major impact on viral inactivation rates. The high organic content
could act to retard virus inactivation (see Table 6-4). Because of the lack
of Information on what virus inactivation would be in sludge leachate, it is
assumed that it would be zero for all conditions. This would be the case
anyway if groundwater temperatures were at or near 10°C {Yates, 1985). This
is not an unrealistic assumption since many sludge landfills are located in
areas where the groundwater temperature would be in this range (U.S. EPA9
1978; Yates and Gerba, 1985).
10.4.6. Rate of Travel, Dilution and Dispersion. In determining the
concentration of viruses at a given point from a landfill, it Is necessary
to determine the time required so that the inactivation (decay) rate of the
viruses can be taken into consideration. The application of proposed models
for virus transport {Yates et a!., 1986) would be useful in predicting rate
of travel, dispersion and dilution. However, current models have not been
>».
verified by laboratory and field studies. A recent laboratory study
suggests that viruses may travel at 1.5-1.9 times faster than the average
flow of groundwater (Grondln and Gerba, 1986), which implies that current
solute models may not be totally applicable to modeling the movement of
microorganisms.
For this risk assessment information on rate of travel is not needed
since no virus Inactivation is assumed to occur. Since no information is
available to verify proposed models, no dilution or dispersion is assumed to
occur.
10-21
-------
10.4.7. Risk Assessment at Example Sludge Landfill A. Using the previ-
ously discussed assumptions, the concentrations of viruses 1n the sludge
leachate and at 10 m and 100 m from the site were estimated (Table 10-11).
10.4.8. Risk Assessment at Example Sludge Landfill B. Primary sludge Is
disposed at Site B so the estimated number of pathogens 1s much greater.
Again, under most favorable conditions, only the sludge leachate would
contain significant numbers of viruses (Table 10-12). Highly significant
risk of Infection (Chapter 9) would exist from groundwater use <10 m from
the site under most probable and worst possible conditions. Risks would
also be significant at 100 m from the site with both assumptions. The
higher net recharge at Site B results 1n a greater dilution of the viruses
than at Site A. Risks would be greater at Site B 1f rainfall were similar
to Site A.
10.5. SUMMARY OF GROUNDWATER RISK ASSESSMENT AND RESEARCH NEEDS
Two approaches were used to determine if sludge landfills pose a risk to
groundwater. In one approach two example landfill sites were evaluated
using Yates' rating system, and in the other approach an attempt was made to
estimate the numbers of pathogens that would leach from the sludge at two
example sites and find their way into the groundwater. The results suggest
that contamination of the groundwater is possible directly beneath sludge
landfill sites as well as at a distance. In terms of potential disease and
mortality from consumption of the water near these sites, the risks appear
significant based on annual and lifetime water use (see Tables 9-4 through
9-6). The example sites are underlaid with silty loam soils but some sites
In the United States are built upon sandy soils. If these sites are not
clay lined, greater risks could be expected from microbial contamination
than the example sites examined in this assessment. Little risk exists from
clay-lined sludge landfills.
10-22
-------
TABLE 10-11
Estimated Concentrations of Viruses 1n Groundwater at Sludge Landfill Aa
Item Most
Favorable
Virus/hectare 2.7xl04
Viruses 1n leachate/hectare 1.7xl02
Virus concentration 1n l.TxlO*
leachate/8.
Virus concentration13 10 m 1.7xlO~25
from site/a.
Virus concentration 100 m
from site/2.
Most
Probable
4.2x10*
4.2x10*
4.1x105
2.0x10"
2.0x10~5
Worst
Possible
IxlO5
IxlO5
9.8xlOe
8. IxlO8
2.0x108
aSecondary sludge
bAfter travel through 3 m of unsaturated soil (total distance 13 m)
10-23
-------
TABLE 10-12
Estimated Concentrations of Viruses 1n Groundwater at Sludge Landfill Ba
Item
Virus/hectare
Viruses 1n leachate/hectare
Virus concentration 1n
leachate/a.
Virus concentration11 10 m
from site/2,
Virus concentration at 100/m
from site/a
Most
Favorable
l.OxlO5
l.OxlO4
1.2xl03
1.2xlO"23
Most
Probable
l.OxlO6
1.0x10*
1.2xl06
6.0x10-*
6.0x10=
Worst
Possible
l.OxlO6
l.OxlO6
1.2xl010
1.0x10"
1.2x10*
aPr1mary sludge
bAfter transport through 3 m of unsaturated soil (total distance 13 m)
10-24
-------
If actual drinking-water wells had existed near these sites, the
potential risks would have been greater than that determined. Since pumping
wells can greatly influence the movement of water, they would be expected to
enhance water movement under a site and reduce microbial removal efficiency.
It is clear from this review that information on the fate of pathogens
at existing landfills is essentially nonexistent. Both laboratory and field
studies are needed to determine the degree of pathogen leaching, survival
and transport in groundwater. Approaches are available to estimate poten-
tial risks from pathogens at sludge landfills, but without adequate informa-
tion the reliability of the conclusions is weakened. The availability of
necessary information to make a risk assessment and research needs are shown
in Table 10-13.
10-25
-------
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10-26
-------
11. SUMMARY AND CONCLUSIONS
The purpose of this document was to Identify human pathogens associated
with sewage sludge and the risks posed by such pathogens following the
disposal of sludge 1n municipal landfills. Background Information on
pathogens of concern and their persistence 1n various landfill environments
has been presented. Attempts have also been made to Identify different
routes by which pathogens disposed of In municipal sludge landfills can
reach humans and to estimate risks associated with each of the potential
routes.
Survival characteristics of pathogens are critical factors 1n assessing
risks associated with potential transport of microorganisms from soil-sludge
to the groundwater environments of landfills, and this document presented
and discussed various modes for predicting mlcroblal die-off. Temperature
Is probably even more Important than pH and moisture content 1n predicting
pathogen survival. The order of persistence 1n the environment from longest
to shortest survival time appears to be helminth eggs > viruses > bacteria >
protozoan cysts.
Factors affecting pathogen movement In the sludge-soil matrix Include
physical characteristics of the soil as well as environmental and chemical
factors. In most soils, viruses could be expected to travel farthest
because of their small size, while the movement of protozoa and helminths
would be more limited. However, many other factors, including rainfall and
soil Inhomogeneitles, have major impacts on pathogen movement under field
conditions. The depth of the unsaturated zone is probably the greatest
barrier preventing mlcroblal movement Into the groundwater.
HIOs for bacteria are generally higher than those for viruses and
parasites. Mathematical modeling Indicates that <50 viruses or protozoan
cysts are capable of causing infection In a susceptible host.
A methodology known as micro-DRASTIC, developed to evaluate the
potential for groundwater contamination of septic tanks by microorganisms
based on eight key rating factors, was applied to assess the likelihood of
11-1
-------
groundwater contamination at two example sludge landfill sites. It was
determined that mlcroblal contamination was probable directly beneath the
first site (secondary sludge; clay, sand, and gravel; silt loam aquifer) and
possible beneath the second site (primary sludge, sllty clay, sllty aquifer
medium). At both sites, pathogenic contamination was judged to be possible
at distances of 100 m and 200 m. Although this rating system has not been
verified In the field, It provides a mechanism for evaluating the many
Interacting factors that control mlcroblal survival and transport in the
subsurface.
Whether or not a pathogen reaches groundwater and is transported to
drinking-water wells depends upon a number of factors, including initial
concentration of the pathogen, survival of the pathogen, number of pathogens
that reach the sludge-soil Interface, degree of removal through the
unsaturated and saturated soil zones, and the hydraulic gradient. The
degree to which each of these factors will Influence the probability of
pathogens entering groundwater cannot be determined precisely. Viruses,
because of their small size, probably have the greatest potential of all the
pathogens of actually reaching the groundwater and being transported from
the site.
Information on the fate of pathogens at existing landfills is sorely
lacking. Additional laboratory and field studies are needed to determine
the degree of pathogen leaching, survival and transport in groundwater in
order to estimate potential risks from pathogens at sludge landfills with
reasonable validity.
11-2
-------
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