EPA 560/5-85-005
August 1985
METHODS FOR ASSESSING EXPOSURE
TO CHEMICAL SUBSTANCES
Volume 5
Methods for Assessing Exposure to Chemical
Substances 1n Drinking Water
by
Douglas A. D1xon, Stephen H. Nacht, G1na H. D1xon,
Patricia Jennings, Thomas A. Faha
EPA Contract No. 68-01-6271
Project Officer
Michael A. Callahan
Exposure Evaluation Division
Office of Toxic Substances
Washington, D.C. 20460
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF PESTICIDES AND TOXIC SUBSTANCES
WASHINGTON, D.C. 20460
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DISCLAIMER
This document has been reviewed and approved for publication by the
Office of Toxic Substances, Office of Pesticides and Toxic Substances,
U.S. Environmental Protection Agency. The use of trade names or
commercial products does not constitute Agency endorsement or
recommendation for use.
m
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FOREWORD
This document 1s one of a series of volumes, developed for the U.S.
Environmental Protection Agency (EPA), Office of Toxic Substances (OTS),
that provides methods and Information useful for assessing exposure to
chemical substances. The methods described 1n these volumes have been
Identified by EPA-OTS as having utility 1n exposure assessments on
existing and new chemicals 1n the OTS program. These methods are not
necessarily the only methods used by OTS, because the state-of-the-art 1n
exposure assessment 1s changing rapidly, as 1s the availability of
methods and tools. There 1s no single correct approach to performing an
exposure assessment, and the methods 1n these volumes are accordingly
discussed only as options to be considered, rather than as rigid
procedures.
Perhaps more Important than the optional methods presented 1n these
volumes 1s the general Information catalogued. These documents contain a
great deal of non-chem1cal-spec1f1c data which can be used for many types
of exposure assessments. This Information 1s presented along with the
methods 1n Individual volumes and appendices. As a set, these volumes
should be thought of as a catalog of Information useful 1n exposure
assessment, and not as a "how-to" cookbook on the subject.
The definition, background, and discussion on planning of exposure
assessments are discussed 1n the Introductory volume of the series
(Volume 1). Each subsequent volume addresses only one general exposure
setting. Consult Volume 1 for guidance on the proper use and
Interrelations of the various volumes and on the planning and Integration
of an entire assessment.
The titles of the nine basic volumes are as follows:
Volume 1: Methods for Assessing Exposure to Chemical Substances
(EPA 560/5-85-001)
Volume 2: Methods for Assessing Exposure to Chemical Substances 1n the
Ambient Environment (EPA 560/5-85-002)
Volume 3: Methods for Assessing Exposure from Disposal of Chemical
Substances (EPA 560/5-85-003)
Volume 4: Methods for Enumerating and Characterizing Populations Exposed to
Chemical Substances (EPA 560/5-85-004)
Volume 5: Methods for Assessing Exposure to Chemical Substances 1n
Drinking Water (EPA 560/5-85-005)
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Volume 6: Methods for Assessing Occupational Exposure to Chemical
Substances (EPA 560/5-85-006)
Volume 7: Methods for Assessing Consumer Exposure to Chemical
Substances (EPA 560/5-85-007)
Volume 8: Methods for Assessing Environmental Pathways of Food
Contamination (EPA 560/5-85-008)
Volume 9: Methods for Assessing Exposure to Chemical Substances
Resulting from Transportation-Related Spills
(EPA 560/5-85-009)
Because exposure assessment 1s a rapidly developing field, Its
methods and analytical tools are quite dynamic. EPA-OTS Intends to Issue
periodic supplements for Volumes 2 through 9 to describe significant
Improvements and updates for the existing Information, as well as adding
short monographs to the series on specific areas of Interest. The first
four of these monographs are as follows:
Volume 10: Methods for Estimating Uncertainties 1n Exposure Assessments
(EPA 560/5-85-014)
Volume 11: Methods for Estimating the Migration of Chemical Substances
from Solid Matrices (EPA 560/5-85-015)
Volume 12: Methods for Estimating the Concentration of Chemical
Substances 1n Indoor A1r (EPA 560/5-85-016)
Volume 13: Methods for Estimating Retention of Liquids on Hands
(EPA 560/5-85-017)
Michael A. Callahan, Chief
Exposure Assessment Branch
Exposure Evaluation Division (TS-798)
Office of Toxic Substances
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ACKNOWLEDGEMENTS
This report was prepared by Versar Inc. of Springfield, Virginia, for
the EPA Office of Toxic Substances, Exposure Evaluation Division,
Exposure Assessment Branch (EAB) under EPA Contract No. 68-01-6271
(Task 12). The EPA-EAB Task Manager for this task was Stephen H. Nacht,
the EPA Program Manager was Michael Callahan; their support and guidance
1s gratefully acknowledged. Acknowledgement 1s also given to Patrick
Kennedy of EPA-EED who assisted 1n the final publication of the report.
A number of Versar personnel have contributed to this task over the
three year period of performance, as shown below:
Program Management - Gayaneh Contos
Task Management - Douglas D1xon
Technical Support - Glna Hendrlckson D1xon
Patricia Jennings
Thomas Faha
Steve Mitchell
Michael Neely
Sharon Burke
Chip Prokop
Editing - Juliet CrumMne
Secretarial/Clerical - Shirley Harrison
Lucy Gentry
Donna Barnard
v~n
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TABLE OF CONTENTS
Page No.
FOREWORD v
ACKNOWLEDGEMENT vi 1
TABLE OF CONTENTS 1x
LIST OF FIGURES xi
LIST OF TABLES X11
1. INTRODUCTION 1
1.1 Purpose and Scope 1
1.2 Methodological Framework 1
2. DRINKING WATER SYSTEMS AND EXPOSURE PATHWAYS 5
2.1 Sources of Contamination 5
2.2 Drinking Water Supplies 5
2.3 Water Treatment Processes 7
2.4 Distribution Systems 12
2.5 Uses of Finished Water 12
2.6 Water Quality Requirements 14
3. IDENTIFICATION OF CONTAMINATED WATER SUPPLIES 19
3.1 Identification of Surface Water Supplies 19
3.1.1 Hydrologlcally Linked Data File (HLDF)
System 19
3.1.2 Federal Reporting Data System (FRDS) 39
3.2 Identification of Ground Water Supplies 40
3.2.1 Identifying Site-Specific Ground Water
Supplies 41
3.2.2 Identifying Nonsite-Specific Ground Water
Supplies 43
4. QUANTIFICATION OF RAW WATER CONCENTRATIONS OF
CHEMICAL SUBSTANCES 47
4.1 Monitoring Data 47
4.2 Estimation of Concentration 1n Surface Water 50
4.2.1 Conservative Estimates 50
4.2.2 Chemical Fate Models 62
ix
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TABLE OF CONTENTS
Page No.
4.3 Estimation of Concentration 1n Ground Water 72
4.3.1 Release Rate Models 73
4.3.2 Solute Transport Models 73
4.3.3 Practical Model Application 82
5. CONCENTRATION OF CHEMICAL SUBSTANCES IN FINISHED WATER 87
5.1 Public Water Systems 87
5.1.1 Unit Processes 1n Water Treatment 87
5.1.2 Addition of Contamination during Water
Treatment and Distribution 110
5.1.3 Determination of Finished Water Quality 115
5.2 Private Systems 116
5.2.1 Guidelines for Selection of Suitable Private 117
Drinking Water Sources
5.2.2 Home Drinking Water Treatment Systems 117
6. EXPOSED POPULATIONS 131
6.1 Identification of Exposed Populations 131
6.2 Enumeration of Exposed Populations 132
6.3 Characterization of Exposed Populations 134
7. CALCULATION OF EXPOSURE 135
7.1 Ingestion Exposure 135
7.2 Dermal Exposure 136
7.3 Inhalation Exposure 136
8. REFERENCES 139
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LIST OF FIGURES
Page No.
Figure 1 .
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11 .
Figure 12.
Figure 13.
Figurel4.
Framework For Assessing Exposure Via
Drinking Water
Pathways Illustrating Human Exposure to
Chemical Substances In Drinking Water
Illustration of an Underground Hydrologlc
System
Schematic Representation of an Infiltration
Gallery System
Schematic Diagrams of Basic Water Treatment
Plant Designs
IFD Retrieval System Procedure for SIC Code
Report
Example of a Portion of an SIC Code IFD Retrieval
Report Sorted by NPDES Number
Example of WQAB RCHDAT Retrieval for Flow and
Facility Information
WQAB SITEHELP Example of River Mile Locations
for REACH 02040201004
WQAB SITEHELP Display of Company A Discharge
Pipes
WQAB SITEHELP Display of Drinking Water Intake
for Water Supply Company B
Example of PATHSCAN Report
Ease of Stripping as a Function of Henry's Law
Constants for Selected Organics
Chemistry of the Lime-Soda Ash Process
2
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30
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33
35
36
37
97
103
XI
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LIST OF TABLES
Page No.
Table 1. Summary of Estimated Water Use 1n the United
States, In Billions Gallons Per Day, at 5-Year
Intervals, 1950-1980 13
Table 2. Water Quality Criteria for Public Water Supplies ... 15
Table 3. National Interim Primary Drinking Water Standards .. 17
Table 4. National Profile of Community Water Supply
Systems 18
Table 5. Interactive Programs for Accessing Data 1n the
Hydrologlcally Linked Data Files of EPA
Monitoring and Data Support Division 25
Table 6. Percentage of Ground Water Use of Total
Use for Each State 1n 1980 45
Table 7. Receiving Water Flow Rates for Industrial
Discharge (Direct and Indirect) 55
Table 8. Chemical Fate Models for Estimating Pollutant
Concentrations 1n Surface Waters 64
Table 9. EXAMS Input Requirements 70
Table 10. Primary Factors Affecting the Three Components of
Leachate Release Rate Models 74
Table 11. Leachate Release Rate Models 75
Table 12. Comparison of Analytical and Numerical Models 77
Table 13. Physical Parameter Characteristics Addressed by
Ground Water Models 78
Table 14. Parameter Values Used in SESOIL to Estimate
NTA Concentrations in the Unsaturated Zone 83
Table 15. Parameter Values Used in ATD123 to Estimate
NTA Concentrations 1n the Saturated Zone 85
Table 16. Simulated Average NTA Concentrations in Ground
Water at 20 m Depth 1n an Aquifer of 50 m
Average Depth 86
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LIST OF TABLES
Page No.
Table 17. Frequency of Use in U.S. of Water Treatment
Methods 88
Table 18. Removal of Contaminants During Drinking Water
Treatment 90
Table 19. Summary of Water Treatment Chemicals CODEX Ill
Table 20. Contaminants that May Be Introduced 1n the
Distribution System 114
Table 21. Essential Factors That Should be Considered 1n a
Sanitary Survey of Ground Water Supplies 118
Table 22. Essential Factors That Should be Considered 1n a
Sanitary Survey of Surface Water Supplies 119
Table 23. List of Conditions Unfavorable to the Control of
Contamination That May Require Specifying Distances
Greater than 50 Feet for Siting of Wells 120
Table 24. Efficiency of Home Drinking Water Treatment Units
Containing Activated Carbon in Removing
Trihalomethanes (THMs) and Nonpurgeable Total
Organic Carbon (NPTOCs) 122
Table 25. Range of Percent Specific Halogenated Organic (HO)
Reduction for Line Bypass, Faucet Mount,
Stationary, and Pour-Through Units 1n the Ground
Water Study 126
Table 26. Range of Percent Specific Halogenated Organic (HO)
Reduction for Line Bypass, Faucet Mount, Sanitary
and Pour-Through Units in the Surface Water Study .. 127
Table 27. Drinking Water Intake Rates and Volumes
Consumed by Age and Sex 137
XTM
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1. INTRODUCTION
1.1 Purpose and Scope
The Toxic Substances Control Act (TSCA) of 1976 (PL94-469) authorizes
the U.S. Environmental Protection Agency (EPA) to assess human and
environmental exposure to chemical substances. An exposure assessment
for a chemical substance attempts to determine the amounts of that
chemical substance to which populations are exposed as well as to
Identify and estimate the size of exposed populations. The EPA Office of
Toxic Substances, Exposure Evaluation Division (OTS-EED), 1s responsible
for conducting exposure assessments for chemical substances 1n support of
Sections 4, 5, and 6 of TSCA.
Exposure assessments for each of the categories, Including exposure
via drinking water, have historically been limited by a lack of complete
and reliable data. Accurate calculation of exposure to a chemical
substance through drinking water relies heavily on actual monitoring data
on the concentration of the chemical substance 1n finished or processed
drinking water, preferably at the final point prior to consumption or
other use which leads to exposure - the tap. For most chemical
substances, however, these data are Insufficient, difficult to obtain, or
nonexistent. The goal of this report, therefore, is to catalog pertinent
Information, data bases, and tools, and to provide a systematic approach
or methods whereby the exposure to a given chemical substance 1n drinking
water may be estimated at any desired level of detail. The methods are
also applicable when options for reducing exposure are being analyzed.
The methods ensure that all pertinent components are evaluated,
appropriate values assigned, and reasonable exposure scenarios
constructed.
1.2 Methodological Framework
The methodological framework for calculating exposure to chemical
substances 1n drinking water Is presented 1n Figure 1. The framework
provides the foundation of this methods report pointing out the major
Information requirements and showing the steps to be taken in the proper
sequence, to calculate exposure.
This volume 1s organized to reflect the framework or flow of
required Information. Section 2 provides an overview of drinking water
systems and the pathways of exposure to chemical substances 1n drinking
water, from the source of the substance through the treatment and
distribution systems to the consuming population. Section 3 catalogues
and discusses the various data bases and Information sources that aid 1n
the Identification of contaminated drinking water supplies. Section 4
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presents and discusses methods and simulation models that can be used to
estimate the concentration of chemical substances 1n both surface and
ground water. Section 5 discusses drinking water treatment systems and
processes, the effect the systems and processes have on different types
of chemical substances, and how the Information can be used to predict
the concentration of a chemical substance 1n finished drinking water.
Section 6 briefly discusses the enumeration and characterization of
exposed populations; detailed Information on this subject 1s provided 1n
Volume 4 of this series. Finally, Section 7 discusses the procedures for
calculating exposure as a result of contact with contaminated drinking
water.
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2. DRINKING WATER SYSTEMS AND EXPOSURE PATHWAYS
A comprehensive assessment of exposure to chemical substances 1n
drinking water requires an understanding of the principles of water
supply and distribution. This includes sources of contamination, sources
of water for treatment and use, treatment techniques, distribution
systems, and the ultimate uses of water.
2.1 Sources of Contamination
Chemical substances of concern may enter water destined for human use
by:
• Discharge of Industrial or municipal wastewater to surface water
• Leachate from landfills and septic tanks into ground water
• Overflow and seepage from surface impoundments into surface and
ground water
• Nonpoint sources of pollution - urban runoff, agricultural and
silvicultural runoff, construction runoff, mine drainage,
combined (sanitary and stormwater) sewer overflow, spills,
washout of atmospheric contaminants
• Formation or addition of chemical substances during water
treatment and distribution.
The list is not all-inclusive; 1t does represent the most common sources
of contamination that must be considered in an exposure assessment.
Figure 2 summarizes some of the major pathways of exposure to chemical
substances 1n drinking water.
2.2 Drinking Water Supplies
Drinking water supplies are generally classified into two broad
categories: surface water and ground water. Surface water supplies
include rivers, streams, natural lakes, and impoundments. Sea water and
inland saline water are theoretical surface water supplies. However,
since desalination to render those waters usable is not yet
cost-effective on a large scale (Clarke et al. 1977), they are not widely
used as drinking water supplies.
Ground water sources are less easily defined; the term usually
refers to wells, springs, and Infiltration galleries. Wells are taps
into aquifers, which are underground permeable geological units that can
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transmit economically significant quantities of water under normal
hydraulic conditions (Freeze and Cherry 1979). There are two types of
aquifers: unconHned aquifers, those that have the water table as their
upper boundary; and confined aquifers, those that are bound above and
below by relatively Impermeable strata. Confined aquifers are the
sources of artesian wells. Springs are natural surface releases of
ground water that may be due to gravity or artesian flow. Figure 3
Illustrates an underground hydraulic system Including wells, springs, and
confined and unconflned aquifers.
Infiltration galleries, also known as filter galleries, are systems
constructed 1n river and lake beds that are designed to collect
Interstitial water. Usually they are horizontal conduits or pipes with
perforations so that ground water can enter by gravity flow (Steel and
McGhee 1979). The sand and sediment of the river or lake bed act as a
natural filter In these systems, eliminating the need for 1n-plant
filtration. The collected water 1s then pumped to the treatment plant
for further processing and distribution. Infiltration galleries are used
1n a number of U.S. cities. Figure 4 Illustrates a typical Infiltration
gallery system.
Surface and ground waters to be used as public, private, or
Industrial supplies are termed raw water prior to treatment; after
treatment for Improved quality, they are called finished or potable
waters. Although there 1s some distinction between finished and potable
water (I.e., finished water 1s water that has been processed or treated
and not necessarily used for drinking purposes; potable water 1s water
that, treated or untreated, 1s suitable for drinking purposes), the two
terms are often used Interchangeably. This report will refer to
"finished" water throughout.
2.3 Water Treatment Processes
Figure 5 presents simplified flow diagrams for the two most common
water treatment schemes. The unit processes comprising these treatment
trains are discussed 1n Section 5 of this report.
Type I (filtration) plants are generally used by municipalities with
surface water sources. Chlorine may be added at numerous points to
control mlcroblal growth; activated carbon Is applied to remove organic
compounds causing unpleasant tastes and odors. Coagulants (such as alum)
are added to remove suspended solids, and oxldants (e.g., ozone and
potassium permanganate) may be added to begin decomposition of chemical
compounds. The chemicals are blended with the raw water; the mixture Is
then sent to a flocculatlon basin.
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Flocculatlon 1s a process whereby slow mixing of the water and
chemicals causes formation of large particles ("floe"); this 1s both a
physical and chemical process. The mixing brings particles together, and
electrostatic charges 1n the coagulants bind them. The floe-laden water
1s sent to another basin for the solids to settle out (clarification),
then the water 1s filtered through sand or sand plus a mixture of media,
such as garnet, gravel, or anthracite 1n layers (ASCE 1967, Clarke et al.
1977).
Softening plants (Type II) are designed to render water usable by
removing hardness, strictly defined as divalent cations but largely
calcium and magnesium. Hardness Is termed carbonate when the calcium and
magnesium are present as carbonate or bicarbonate compounds; noncarbonate
hardness 1s magnesium and calcium present as sulfates, nitrates, or
chlorides. If not removed, magnesium and calcium compounds often
precipitate out of water, causing scale In hot water heaters and 1n the
distribution system and shortening their useful lives. These cations are
also nuisances. They combine with soaps used for personal bathing and
laundering, rendering them Ineffective and causing excessive amounts to
be used. It 1s for these reasons that water Is softened (ASCE 1967,
Clarke et al. 1977).
Classification of water hardness 1s not exact; the following 1s an
example of hardness classification (ASCE 1967). Regardless of the
chemical form of the hardness, 1t 1s expressed as equivalent amounts of
calcium carbonate.
• Soft: 0-60 ppm as CaC03
• Moderately hard: 61-120 ppm as CaC03
• Hard: 121-180 ppm as CaC03
• Very hard: >180 ppm as CaC03
The hardness of a water depends on the geochemistry of the source.
Generally, ground waters are harder than surface waters. Waters with
hardness of 120ppm CaC03 are usually softened (ASCE 1967).
The physical treatment process 1n a softening plant 1s similar to
that of a filtration plant. The chemicals used and their dosages are,
however, different. The basic chemical concept of softening 1s the
substitution of sodium Ions for magnesium and calcium. The pH of the
water 1s raised (> 11) to precipitate the hardness compounds; this pH
adjustment provides a large measure of disinfection as well. The
recarbonatlon step lowers the pH by bubbling COp Into the water (Clarke
et al. 1977, ASCE 1967).
11
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In the Type II plant schematic, flocculatlon and clarification are
accomplished 1n one step. The flocculator-clar1f1er may be used In
filtration plants (Type I) as well. Additional unit processes may be
used 1n either type of plant and are discussed 1n Section 5. Treatment
within homes (softeners, carbon filters) 1s also discussed 1n that
section.
2.4 Distribution Systems
Finished water 1s generally pumped from the treatment plant
throughout the service area. Most modern pressure pipe used 1n
distribution systems 1s concrete, steel, asbestos-cement, or cast iron;
many distribution systems use a combination of these. Pressure Is
maintained throughout the system by Intermittent pumping stations and
natural head caused by topography (Clarke et al. 1977). Piping within
the home need not withstand very high pressures and 1s often constructed
with polyvinyl chloride (PVC). Copper pipe, too expensive for large
diameter uses, may also be placed in homes. Contamination may occur in
the distribution system by:
• Leaching of metals, chemicals, or fibers from pipe material and
joint adhesive
• Infiltration of contaminated water into broken or cracked low
pressure water pipe
• Bacterial growth within the distribution system.
2.5 Uses of Finished Water
Table 1 Illustrates the trends in water use over the last three
decades. It 1s apparent that withdrawal from public supply grows with the
population; per capita use, currently 183 gallons per day, has also grown
but at a much lower rate (Solley et al. 1983). Total per capita use
includes industrial, commercial, domestic, and public uses. Domestic and
public use of water, which includes such activities as drinking, food
preparation, bathing, washing clothes and dishes, flushing toilets,
watering lawns and gardens, firefighting, street washing, and use at
municipal parks and 1n swimming pools, averages 120 gallons per Individual
per day. Finished water ingested by individuals is a small proportion of
total domestic and public use, estimated as approximately 0.5 gallons per
day (2 liters) (USEPA 1982a). Human ingestion of drinking water is further
discussed 1n Section 7.
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2.6 Water Quality Requirements
Different uses of water require various degrees of quality. Table 2
lists recommended criteria for raw water to be used for public water
supplies. Most of these criteria apply to surface waters that have been
polluted by Industrial, agricultural, and domestic discharges (Clarke et
al. 1977); 1t 1s Implied that treatment will remove most, If not all, the
contamination.
Exposure to chemical substances via the Ingestlon of drinking water
was officially recognized as a hazard by the passage 1n 1974 of the Safe
Drinking Water Act (PL 93-523) and Its amendment in 1977. The Act set
Interim drinking water standards for Inorganic and organic substances based
mostly on health effects that may occur from a lifetime of drinking 2
liters of water per day (CEQ 1979, Clarke et al. 1977). Table 3 lists
these standards, known as Maximum Contamination Levels (MCLs). An MCL of
100 ppb for total trlhalomethanes (chloroform and related compounds) was
added later; It currently applies only to systems serving more than 10,000
persons (AWWA 1979).
All the drinking water standards apply to public water systems.
Public systems serve approximately 84 percent of the U.S. population (see
Table 4); the remainder are served by private systems, mostly wells (CEQ
1979).
Ongoing scientific investigation is revealing that exposure to
pollutants in drinking water is not limited to exposure via ingestion.
Brown et al. (1984) and Scow et al. (1979), for example, report that the
body's absorption of water pollutants through the skin - by washing,
showering, and bathing - has been seriously underestimated. According to
Brown et al. (1984), in fact, for specific organic chemicals such as
toluene, ethylbenzene, and styrene, the primary route of exposure for these
chemicals may be via dermal absorption. Brown et al. (1984) and Scow et
al. (1979) also discuss the potential for volatilization of volatile
organic carbons (VOCs) from drinking water and subsequent inhalation while
showering and bathing. Exposure to contaminants in drinking water via
dermal absorption and inhalation is a relatively new area of concern with
limited technical documentation. No doubt, future investigations will shed
considerable new information on this subject.
14
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Table 2. Water Quality Criteria for Public Water Supplies3
Substance
Col i forms (MPN)
Fecal col i forms (MPN)
Inorganic chemicals (mg/1)
Ammonia-N
b
Arsenic
b
Barium
b
Boron
b
Cadmium
b
Chloride
b
Chromium (hexavalent)
b
Copper
Dissolved oxygen
Iron
b
Lead
b
Manganese
b
Nitrate - N
b
Selenium
b
Silver
b
Sulfate
b
Total dissolved solids
b
Urany ion
b
Zinc
Organic chemicals (mg/1)
Alkyl benzyl sulfonates
b
Carbon chloroform extract
b
Cyanide
Permissive criterion
10,000
2,000
0.5
0.05
1.0
1.0
0.01
250
0.05
1.0
4
0.3
0.05
0.05
10
0.01
0.05
250
500
5
5
—
0.15
0.20
Desirable criterion
100
20
0.01
Absent
Absent
Absent
Absent
250
Absent
Virtually absent
Near saturation
Virtually absent
Absent
Absent
Virtually absent
Absent
Absent
50
200
Absent
Virtually Absent
—
0.04
Absent
Herbicides
2,4-D
2,4,5-T -t- 2,4-TP
0.1
Absent
15
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Table 2. (continued)
Substance
Permissive criterion Desirable criterion
b
Oil and grease
b
Pesticides
Aldrin
Chlordane
DDT
Dieldrin
Endrin
Heptachlor
Lindane
Methoxychlor
Toxaphene
b
Phenols
Virtually Absent
0.017
0.003
0.042
0.017
0.001
0.018
0.056
0.035
0.005
0.001
Absent
Absent
Absent
Absent
Absent
Absent
Absent
Absent
Absent
Absent
Absent
aCriteria for raw or untreated surface or groundwater.
bSubstances that are not significantly affected by the following treatment process:
coagulation (less than about 50 mg/liter of alum, ferric sulfate, or copperas, with
alkali addition as necessary but without coagulant aids or activated carbon),
sedimentation (6 hours or less), rapid sand filtration (3 gpm/ft2 or less), and
disinfection with chlorine (without consideration to concentration or form of chlorine
residual).
Source: Clarke et al. (1977).
16
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Table 3. National Interim Primary Drinking Water Standards
Constituent
Maximum concentration
(in mg/1 unless specified)
Inorganic chemicals
Arsenic
Barium
Cadmium
Chromium
Lead
Mercury
Nitrate (as N)
Selenium
Silver
Fluoride
Turbidity
Coliform bacteria
Organic chemicals
Endrin
Lindane
Methoxychlor
Toxaphene
2,4-D
2,4,5 TP Silvex
**
Total trihalomethanes
Radionuclides
Radium 226 and 228 (combined)
Gross alpha particle activity
Gross beta particle activity
0.05
1
0.010
0.05
0.05
0.002
10
0.01
0.05
1.4-2.4*
1 TU up to 5 TU
1/100 ml (mean)
0.0002
0.004
0.1
0.005
0.1
0.01
0.1
5pCi/l
15pCi/l
4 mrem/year
Source: Environment Reporter (1983).
*Depending on annual average maximum daily air temperature; lowest MCL
associated with temperatures of 79.3 to 90.5°F (26.3 to 32.5°C).
**
The sum of chloroform, bromoform, bromodichloromethane, and
chlorodibromomethane.
.17
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Table 4. National Profile of Community Water Supply Systems
Percent of Percent of
systems population
Size of population served
25-2.499 80 8
2,500-9,999 12 9
10,000 - 1,000,000 8 83
Type of ownership
Public 56 84
Private 44 16
Primary source of water
Ground 74 39
Surface 13 49
Purchased 13 12
^Purchased water refers to drinking water bought from another community
system. No data exists on the amount of purchased water that is surface
or ground water; however, it is believed that the majority is surface
supplied (e.g., the largest wholesalers of drinking water are the State
of California, the cities of New York and Chicago, and the Metropolitan
District Commission of Boston, all of which obtain drinking water from
surface supplies).
Source: CEQ (1979)
18
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3. IDENTIFICATION OF CONTAMINATED WATER SUPPLIES
The first step towards calculation of human exposure to a chemical
substance 1n drinking water 1s the Identification of contaminated water
supplies. This step follows the determination that the chemical
substance, based on the sources of the substance and Its
chemical/physical properties, will be present 1n water. The
Identification of the sources of a chemical substance and the
environmental releases are part of the materials balance process. The
methodology for performing a materials balance 1s described 1n JRB
(1980). Source analysis 1s also discussed 1n Section 2 of Volume 2 of
this methods series (I.e., Methods for Assessing Exposure to Chemical
Substances 1n the Ambient Environment). The analysis of fate and
transport of a substance to determine the media to which 1t will
partition 1s discussed 1n Section 3 of Volume 2.
The purpose of this section Is to Identify raw drinking water
supplies that may be contaminated with the chemical due to Its release
Into the environment. Because raw drinking water supplies can
essentially be divided Into the categories of surface and ground water,
and because there are data bases and Information resources related to
each, the procedures for Identifying contaminated surface and ground
water supplies are presented separately 1n the subsequent sections.
3.1 Identification of Surface Water Supplies
This section describes data bases, Information resources, and
procedures that may be used for Identifying surface water supplies which
are used as sources of raw drinking water and which are possibly
contaminated with the chemical substance of Interest. The primary
Information resources or tools for Identifying surface water supplies are
the data bases of the Hydrologlcally Linked Data File (HLDF) system
maintained by the EPA Monitoring and Data Support Division, Water Quality
Analysis Branch, and the Federal Reporting Data System (FRDS) maintained
by the EPA Office of Drinking Water. Each of these systems 1s described
1n the following subsections.
3.1.1 Hydrologlcally Linked Data File (HLDF) System
The HLDF system 1s a group of data bases that Include locatlonal and
supporting Information relating to Industrial wastewater dischargers,
receiving water flow rates, water supply Intakes, water quality
monitoring stations, and fish kills. The data records 1n the data bases,
each «f which will be subsequently described, Include the name of the
water body or reach on which the subject of the data record 1s located
and a unique Identifying numeric code called a REACH number. The REACH
19
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number, Including Its derivation and format, will also be subsequently
described. The HLDF data bases, therefore, all have a common data record
element (I.e., the REACH name and number) to which Integrated data base
retrievals may be keyed. The data bases are thus "hydrologlcally linked."
The HLDF system consists of the following minor file, four major
files, and one auxiliary file:
I. Minor File
• REACH File
II. Major Files
• Industrial Facilities Discharge (IFD) File
• Water Supply Data Base (WSDB) File
• Stream Gaging Inventory Data (GAGE) File
• Pollution-Caused F1shk1ll (FISHKILL) File
III. Auxiliary File
• S10RET Water Quality Data File
Following 1s a description of each of these data files except the
FISHKILL File, which Is not pertinent to this methods report.
REACH File - This file contains a listing of all REACH numbers in the
conterminous U.S. By definition, a reach is an arbitrary boundary
that defines a certain hydrologic system (e.g., river, stream,
lake). In case of a river, the boundary may be defined as the
continuous portion of the river where no tributaries intervene (i.e.,
that portion of the river between the confluence with two
tributaries). The REACH number is the mechanism or common data
element that hydrologlcally links the four major and one auxiliary
data bases. A REACH number is a combination of the 8-digit U.S.
Geological Survey hydrologic unit number (2-digit USGS region number
+ 2-digit subreglon number + 2-d1g1t accounting unit number + 2-d1git
cataloging unit number.) and an EPA 3-digit segment number. All
river basins or portions of river basins in the U.S. have a unique
20
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hydrologlc unit number. Major water bodies or portions of water
bodies within basins, as Identified by the hydrologlc unit number,
have a segment number. Each major stream, river, or lake or segment
thereof 1s uniquely Identified, therefore, by the Il-d1g1t REACH
number. Detailed Information on the USGS hydrologlc unit numbering
system 1s available 1n State Hydrologlc Unit Haps - Brochure (USGS
undated). The hydrologlc unit numbering system 1s also, along with
the EPA segment numbering system, described 1n General Information on
IFD. Drinking Water Supplies. Stream Gages. Reach, and F1shk111 Files
and Retrieval Procedures for Hydrologlcally Linked Data Files (USEPA
1981a).
The REACH file consists of approximately 68,000 segments which
represent some 700,000 miles of streams or shorelines. An estimated
61,000 of the segments or reaches are stream segments and about 7,000
are shoreline segments. All segments 1n the REACH file have been
Uneallzed (the x, y coordinates (latitude/longitude) have been
assigned to all points that define the segment and the sequence of
the coordinates that makes up the segment has also been Identified),
which allows for data retrieval and analysis downstream or upstream
of a point or between points. The Uneallzed segment data are used
for mapping and location plotting for STORET, IFO, GAGE, FISHKILL,
and WSDB data.
Industrial Facilities Discharge (IFD) File - IFD 1s a comprehensive
data base of point source dischargers. Currently, there are more
than 40,000 direct discharge facilities In the IFD file, of which
nearly half are Publicly Owned Treatment Works (POTWs). Included as
contributors to POTWs are 11,500 Indirect discharge facilities (SCS
1983).
There are 113 data elements within the IFD data file for which data
have been collected from various sources; the following are the most
Important:
(1) Permit Compliance System (PCS) - PCS was used to Identify
National Pollutant Discharge Elimination System (NPDES)
permitted facilities to be Included 1n the IFD file. General
Information about each facility was extracted from the PCS file
to form a building block upon which more specific Information
could be added.
(2) NPDES Permit Files - The NPDES permits were accessed at the
regional EPA offices. Discharge and location Information was
obtained for both direct and Indirect point source dischargers.
In addition, various state and local agencies provided
additional and more recent Information not found 1n the regional
NPDES files.
21
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(3) EPA's 1978 NEEOs Survey File - The NEEDs Survey was used to add
Information on existing POTWs Identified by a NPDES number.
Planned POTWs that are required to achieve certain effluent
limitations were also Included.
The facilities that are Included 1n the IFD file represent an
on-going effort that was begun 1n 1978. An effort of this magnitude
requires constant attention 1n order to reflect current conditions.
Every attempt 1s made by EPA-MOSD to keep the file as up-to-date as
possible with the resources that are available.
The Industrial facilities 1n the IFD data file are linked to the
REACH data file by a common USGS hydrologlc unit number and EPA's
segment number. The linkage of IFD with REACH allows the hydrologlc
p1n-po1nt1ng of facilities along waterways. This linkage facilitates
hydrologlcal analysis of point source discharger Information during
assessment of potential pollution problems downstream or upstream of
a point and between two stream locations.
The IFD data file 1s organized as a hierarchical Information system
of three levels: facility level, discharge pipe level, and
contributing Indirect facility level. This organizational structure
allows facilities to be viewed 1n their entirety or as separate
discharge pipes within a facility. The facility level contains
Identification codes and summarized discharge Information (e.g.,
name, address, NPDES number, city, county, total facility flow, SIC
codes, receiving water name). The discharge pipe level Includes the
components of each Individual discharge, such as location, flow, and
SIC code activity. The Indirect facility level Includes data on
Industrial flow from Industries that discharge to another facility,
such as a POTW, rather than directly to surface water.
Water Supply Data Base (WSDB) - This 1s the key data file for
Identifying drinking water systems that use potentially contaminated
surface water supplies. The WSDB contains Information on the
location of surface water utilities; the locations of the utilities'
treatment plants, Intakes, and sources of raw water; the populations
served; and the average and maximum dally production. The locatlonal
data for utilities that serve populations greater than 25,000 are
very accurate, within +. 5 seconds of latitude-longitude. Locatlonal
data for utilities that serve populations fewer than 25,000 are
considerably less accurate, within +. 10 minutes of
latitude-longitude. All locatlonal data 1n WSDB have been assigned a
REACH number to facilitate the hydrologlc Unking with other EPA-MDSD
data files. A complete description of WSDB 1s available 1n Versar
(1981).
22
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Stream Gaging Inventory (GAGE) File - The GAGE data file contains
Information on approximately 37,000 stream gaging locations
throughout the U.S. Information stored Includes location of gaging
stations, types of data collected, frequency of data collection,
media 1n which data are stored, Identification of the collecting
agency, and, where available, mean annual flow and 7-day-10-year
(7-Q-10) low flow. The latter are mainly estimated flows of the
61,000 stream segments.
Like the previously discussed data files, all locatlonal data 1n the
GAGE file have been assigned the appropriate REACH number. GAGE
data, therefore, may be hydrologlcally linked to the locatlonal data
1n IFD and WSDB.
STORET Water Quality Data File - STORET 1s the major data base for
water quality data for EPA. STORET basically Includes the locatlonal
Information for water quality monitoring stations and the Inclusive
parameter Information. Detailed Information on STORET, Including
retrieval options, 1s described 1n USEPA (1981b). The STORET User
Assistance Group (382-7220) will also provide Information and
assistance 1n the retrieval of needed data. STORET 1s considered an
auxiliary file 1n the HLDF system because the locatlonal data have
not been assigned REACH numbers. The water quality monitoring
stations, however, may be accessed via the mapping capabilities of
the HLDF system.
Identification of contaminated surface water supplies relies
principally on Information contained 1n IFD and WSDB. As previously
mentioned, the HLDF system facilitates an Integrated approach to data
gathering for other steps 1n the drinking water exposure assessment
process. The entire procedure for locating sources of contamination,
affected drinking water supplies, water quality monitoring stations, and
gaging stations that contain flow data necessary for estimating the
concentration of a chemical substance 1n raw drinking water supplies will
be described later 1n this report.
There are many retrieval procedures and Interactive programs
available 1n the HLDF system. Programs are available for batch
processing of data when the number of data entries or the expected amount
of data 1n the retrieval 1s anticipated to be large. Programs are also
available for direct on-Hne work Including the use of a Cathode Ray Tube
(CRT) terminal for Immediate mapping and display of retrieved
Information. Retrievals may be performed by the Investigator or they may
be requested from:
U.S. Environmental Protection Agency
Monitoring and Data Support Division
Water Quality Analysis Branch
Environmental Analysis Section
401 M Street, S.W.
Washington, DC 20460 (202-382-7046)
23
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Retrievals by the Investigator will secure the required data much more
rapidly, as well as allow the Investigator flexibility 1n the sample
retrieval design. However, the following requirements must be considered:
1. The user must have a valid EPA, National Computer Center-IBM
(NCC-IBM) computer USERID and account number.
2. The user must be familiar with the text editors of TSO and
OBS-WYLBUR (currently supported by NCC-IBM). User guides for TSO
and OBS-WYLBUR are available from EPA User's Support Group
(202-488-5960).
The major programs for assessing the data 1n the HOLF system are
listed 1n Table 5. The programs were developed by EPA-MDSD, Water
Quality Analysis Branch, and are not part of the STORET user's package.
The choice of program or the approach to Identifying potentially
contaminated drinking water supplies depends on the Information Initially
1n hand. Identification may begin with a SIC code(s), NPDES permit
number(s), REACH number(s), a political or geographic boundary (e.g.,
state, county), or a boundary or polygon defined by latitude-longitude
coordinates. The possible approaches will be described through
examples. The program examples will Include:
• Retrieval of Industrial dischargers for a specific SIC category,
and Identification of the REACH number and water body receiving
the Industrial discharge.
• Retrieval of flow data for a receiving water body.
• Assignment and retrieval of river mile locations for Industrial
dischargers, drinking water Intakes, water quality monitoring
stations, and gage locations.
• Retrieval of Industrial dischargers, drinking water Intakes,
water quality monitoring stations, and flow gages 1n hydrologlcal
(upstream) order.
• Identification of a REACH number(s) and subsequent Identification
of a raw surface drinking water supply(s) contaminated by a waste
disposal site, spill, or a nonpolnt source of pollution.
Following are example programs:
EXAMPLE #1 - IFD Retrieval Using SIC Code: The materials balance and
fate and transport analysis for a chemical substance determines that
the chemical 1s discharged to and 1s persistent 1n surface water.
24
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Table 5. Interactive Programs for Accessing Data in the
Hydrologically Linked Data Files of EPA Monitoring
and Data Support Division
Program name
Text editor
Description
IFDARS
OBS-WYLBUR
WQAB RCHDAT
TSO
The "user friendly" IFD automatic
retrieval system allows any user to
retrieve NPDES facility, pipe level,
or indirect discharge data for
assorted criteria. A menu is
provided to select standard report
formats and several retrieval and
selection options. The IFD SIC code
retrieval is one of the basic
programs that will list, for a
specific SIC code, the facility
location, the facility flow, and the
REACH number of the receiving water
body.
Procedure to allow the user
interactive access to IFD and GAGE
files for stream flow and NPDES pipe
discharge data, or discharge flow
summary for a user-specified REACH
or NPDES number.
HYDRO
TSO
The HYDRO option facilitates the
retrieval of data from STORET, IFD,
FISHKILL, GAGE, WSDB, and REACH data
files in hydrological order.
Hydrologic ordering may be in the
form of a tree diagram, or a digital
plotted location map. The results
of a STORET analysis of water
quality data at individual stations
appear in hydrological sequence
together with data from the other
files.
PATHSCAN
TSO
Interactive version of HYDRO.
Procedure to allow the user
interactive use of IFD, water
supply, gage and stream reach files
to retrieve NPDES and drinking water
facilities upstream or downstream
from a specified location.
-------
Table 5. (continued)
Program name
Text editor
Description
SITEHELP*
TSO
IHSBRWSE
TSO
Interactive procedure to facilitate
assigning and retrieving of river
mileage locations to IFD pipes,
stream flow gaging stations,
drinking water supplies, and STORET
water quality monitoring stations.
This procedure graphically displays
data locations and stream segment
using a CRT terminal. This
procedure can be used to browse IFD,
GAGE, WSDB, and STORET files, for
example, to assist environmental
analysis and modeling.
Procedure to allow the user
interactive access to data in the
HLDF system, (i.e., IFD, GAGE, WSDB,
REACH).
Source: USEPA, Monitoring and Data Support Division, Water Quality
Analysis Branch.
*Program requires the use of a Tektronix CRT terminal to assign river
mile locations. However, any standard terminal can be used to browse
the HLDF system.
26
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Environmental release occurs from manufacture of the substance. The
manufacturing facilities are Included 1n a known SIC category. Human
exposure may occur via drinking water If the substance contaminates
raw surface water supplies.
The IFD File will be used to access the facility and discharge
Information for the specific SIC category. The EPA-MDSD Water
Quality Analysis Branch has provided automatic retrieval procedures
which are "user friendly" to facilitate this process. The retrieval
procedure (known as TXPI004 Automatic Retrieval System) allows the
user to retrieve facility and pipe level data for assorted criteria.
In addition, the data can be sorted In a variety of different ways.
The retrieval procedure 1s as follows (user responses are shown 1n
lower case, between quotes.):
1. Log on to OBS-WYLBUR.
2. Type "exec from $wcha045 gollb(txpretS) clr".
3. Follow the Instructions and the prompts given. If problems
are encountered during the process, press the ATTN or BREAK
key and start over with step two.
Figure 6 1s a sample of a terminal session. Figure 7 1s a portion of
the resulting sample retrieval (SIC 2865 - Organic chemicals Industry,
which was selected for Illustrative purposes only). From this
retrieval the various NPDES numbers of the facilities have been
determined, as well as the REACH number of the water bodies to which
each of these facilities discharge waste water.
EXAMPLE #2 - Retrieval of Flow Data (WQAB RCHDAT): Receiving water
flow data are required for estimating the 1n-stream concentration (or
raw drinking water concentration) of a chemical substance discharged
1n Industrial waste water (see Section 4.2 for procedures to estimate
the concentration of a chemical substance 1n raw surface water).
Retrieval of flow data requires the use of the REACH number or NPDES
number and the Interactive program under TSO, of the EPA-IBM computer
system, referred to as WQAB RCHDAT (Note: for a user to become STORET
validated 1n this procedure, the EPA-MDSD Water Quality Analysis
Branch will place the Interactive program Into the user's command
library). Figure 8 1s an example of a retrieval session for REACH
number 02040201004. The output from this retrieval Includes the reach
name (Delaware River) and mean annual and 7-Q-10 low stream flows for
each gaging station on the reach. This procedure can also be used to
determine all other Industrial dischargers on the reach (by responding
27
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EXEC FROM *WCHA045.GOLIB
-------
TYPE 'C' TO CONTINUE
TYPE 'R' TO REENTER THE SIC CODE
ENTER? C
ENTER THE STATE ABBREVIATION FOR WHICH YOU WANT THE RETRIEVAL*
USE ONLY OFFICIAL ALPHABETIC STATE ABBREVIATIONS*
IF YOU WANT THE ENTIRE COUNTRY* JUST PRESS 'RETURN'.
ENTER THE STATE ABBREVIATION:
THE ENTIRE COUNTRY HAS BEEN SELECTED FOR RETRIEVAL.
TYPE 'C' TO CONTINUE OR 'R' TO REENTER THE STATE ABBREVIATION.
ENTER? C
5ELECT HOW YOU WANT THE DATA SORTED USING THE APPROPRIATE NUMBER
FROM THE FOLLOWING LIST.
1, NPDES NUMBER
2, STATE AND FACILITY NAME
ENTER? i
ENTER A TITLE FOR THIS REPORT -
- LIMIT THE LENGTH TO 60 CHARACTERS
- DO NOT USE PARENTHESES OR SINGLE QUOTES IN THE TITLE
ENTER? **5IC-2865 SORTED BY riFI-Eo NUriSER FOR Tht WHOLE COU.N frJlr'-f*
i.-!':-r$'JQ959289.TErtP SAVED AND CATLG'D ON USER27
CHANGE FRTY=3rTIME=2 ?? (Y OR ri)I N
JOB 1978 SVM03 SUBMITTED
NOTE THIS JOB NUMBER FOR FUTURE REFERENCE
THE RETRIEVAL OUTPUT WILL BE ROUTED TO REMOTE 020
ENTER C TO START ANOTHER RETRIEVAL OR E TO EXIT: £
£HD OF TXPRET3 RETRIEVAL SrSTEM, GOODBYE AND GOOD LUCK!
EXEC END
7
Figure 6. IFD Retrieval System Procedure for SIC Code Report
(continued)
29
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with anything but "nop" or '"/.sum" to the "PIPE DISCHARGE UNITS?"
prompt by the computer), their discharge pipe flow rate, and the
percentage that their flow represents 1n relation to other Industries
on the reach.
EPA was recently engaged 1n two programs entailing the assigning of
river miles to Industrial dischargers, drinking water Intakes, gaging
stations, and water quality monitoring stations. EPA-MDSD concentrated on
400 reaches that they determined to be most Impacted by Best Available
Technology (BAT) regulations; EPA-OTS made more than 10,000 assignments to
reaches where Industries with frequent occurrences 1n the Canonical
Environments Data Base are located. The WQAB RCHDAT retrieval Identifies
the river miles assigned. If river miles have not been assigned, a "-1.00"
will appear 1n place of a value. River miles may be assigned by the
Investigator, however, by the use of the Interactive program WQAB
SITEHELP. This program will be particularly helpful 1n determining the
relative hydrologlc position (upstream/downstream) of a discharge pipe to a
drinking water Intake point. Following 1s a description of the program and
an example problem:
Example #3 - Assigning River Miles to Waste Water Pipes and Drinking
Water Intakes (WQAB SITEHELP): This example problem Involves the
determination of a drinking water Intake's relative position to a
waste water pipe discharging a chemical substance of Interest. If the
Intake 1s located upstream of the waste water discharge pipe, the raw
water supply will not be affected by the chemical's discharge. The
TSO Interactive program to accomplish this goal and to assign "river
mile locations" 1s referred to as WQAB SITEHELP. The program 1s
accessed via the same procedure as WQAB RCHDAT. Because of Its
graphic nature, however, the program requires the use of a Tektronix
CRT terminal to assign river mile locations. Complete details on the
procedures used to retrieve and assign river mile locations, through
the use of the SITEHELP procedure, may be obtained from EPA-MDSD.
The IFD retrieval (see Example #1) Identified Company A 1n New Jersey
(NPDES number NJ0005142) as discharging to REACH 02040201004. Typing
1n this REACH number results 1n a graphic display of the reach and the
relative location of this facility to one drinking water Intake, as
Illustrated 1n Figure 9. Located on this example Reach are: 19
Industrial facilities (as designated by the 19 unique NPDES numbers);
three drinking water Intakes (as depicted by the 9-d1g1t
Identification code with Dl, D2, and 03; and nine sets of monitoring
stations (as Identified by the 9-d1g1t Identification codes ending
with H1-M9. (Note: a set of monitoring stations can contain as many
as 12 separate stations.) The river flow 1s always 1n the
32
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direction of "x", as shown 1n the example. Company A's second
discharge pipe 1s located at river mile 1.81 and the drinking water
Intake 1s located downstream at river mile 1.63 (see, also,
Figure 10). A subsequent retrieval, Figure 11, lists the drinking
water utility as Water Supply Company B, which withdraws water from
REACH 02040201004 (Delaware River). The raw water Intakes of Water
Supply Company B are just 0.18 miles downstream from the wastewater
pipe of Company A. Therefore, the raw water quality 1s possibly
affected by chemical substances 1n Company A's wastestream.
The previously described Interactive program (SITEHELP) enables the
user to Identify the relative locations of Industrial discharge pipes and
drinking water Intakes on a single water body. The program will not
Identify pipes or Intakes that occur 1n water body segments that are
downstream of the segment under study. To accomplish this goal, a "HYDRO"
or PATHSCAN" program 1s required. Although both provide the user with
Information on consecutive hydrologlcally linked segments, they differ 1n
that "HYDRO" 1s used in a "batch mode", while PATHSCAN 1s an Interactive
procedure. A complete description of both procedures Is found 1n General
Information on IFD; Drinking Water Supplies. Stream Gages. Reach, and
F1shk111 Files and Retrieval Procedures for Hydrologlcally Linked Data
Files (USEPA 1981a). Discussion herein will be limited to Pathscan because
of Its Interactive nature.
Figure 12 Is an example PATHSCAN session for Company A, NPDES Number
NJ0005142, REACH 02040201004, investigated 1n example #1. The NPDES number
was designated as the starting point of the Investigation (It it is
possible, however, to use other designators such as REACH #, Dunn &
Bradstreet #, Needs #, US6S Gage # or FRDS #). The report presents
information on REACH 02040201004 and two reaches downstream and lists the
stream flow gages on each reach, showing the mean annual and 7-Q-10 flow
rate (in CFS). It also includes other industrial facilities in various SIC
categories with information on wastewater pipes) flow rate and type of
wastewater (cooling, process, or both). Drinking water intake points are
also listed, including the name, the daily withdrawal, and the population
served. Also listed for each drinking water facility is the EPA Office of
Drinking Water FRDS identification number. This FRDS number may be used
for cross referencing of information contained in the Office of Drinking
Water's computer data base, the significance of which will be discussed in
the subsequent section1.
^Occasionally, an FRDS number for a particular utility differs between
the two data bases because the state may change FRDS numbers.
34
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The final type of retrieval option or Interactive program Involves the
Identification of surface drinking water supplies that may be contaminated
by leachate or runoff from a waste disposal site, a spill, or from a
nonpolnt source (e.g., combined sewer overflow, urban and agricultural
storm water runoff). In the HLDF system, there are no data files that
provide the location of these contamination sources. The location of waste
disposal sites can be found 1n data bases discussed 1n Volume 3 of this
methods series (I.e., Methods for Assessing Exposure from Disposal of
Chemical Substances). Information on transportation-related hazardous
materials spills 1s discussed 1n Volume 9 of this series (I.e., Methods for
Assessing Exposure to Transportation Related Spills). Nonpolnt sources of
contamination must be located geographically according to political
boundaries (e.g., state, county, city) or according to U.S. Geological
Survey hydrologlc unit basins. In all cases, the location of the
contamination source must be used to Identify the receiving water body(s)
contaminated and the respective REACH number(s). The REACH number(s) of
the contaminated receiving water body(s) 1s required to Identify raw
drinking water Intake points.
The first eight digits of the REACH number are obtained from U.S.
Geological Survey Hydrologlc Unit Maps. Hydrologlc Unit Maps delineate
river basins 1n the U.S. A hydrologic unit map has been prepared for each
of the 50 states at a cost of $2.25 each. They can be purchased at the
USGS Sales Office 1n Reston, Virginia, for all 50 states. The USGS Branch
of Distribution in Arlington, Virginia, sells maps for states east of the
Mississippi River.
To obtain the first eight digits of the REACH number, the Investigator
must locate the site or area under study on the pertinent state hydrologlc
unit map and record the hydrologlc unit number of the basin in which the
site or area is located. The EPA segment number, or last three digits of
the REACH number, may be obtained from a catalog (unpublished) of REACH
maps (organized by hydrologlc units) available 1n the Water Quality
Analysis Branch Office of EPA-MDSD. Information on segment numbers and
REACH maps may also be obtained by contacting Mr. Robert C. Horn,
Environmental Engineer, Monitoring Branch of EPA-MDSD. REACH numbers
should be obtained for the water body segment of interest and for all
downstream segments also possibly contaminated by the chemical substance of
interest.
Once the REACH numbers have been identified, water supplies on or
downstream of the receiving water body may be identified by several of the
previously discussed HLDF system's interactive programs. In particular, a
Pathscan or HYDRO retrieval will identify drinking water intakes and thus
drinking water supplies on or downstream of the point where contamination
occurs.1 HYDRO retrievals, as detailed in USEPA (1981a), may be
In most cases, the locational data is dependable but exceptions do exist,
and this possibility should be taken into account when making an Identifi-
cation, especially when a facility serving less than 25,000 people is
Involved.
38
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restricted to Include only drinking water Intakes, or any combination of
Industrial and POTW discharge pipes, gages Including flow data, and water
quality monitoring stations. If the reach under study 1s one of the 400
BAT Impacted receiving streams or 1s the site of an Industry with frequent
occurences 1n the Canonical Environments Data Base, as previously
discussed, the HYDRO or PATHSCAN retrieval will Illustrate the river mile
locations of all data points. This will permit the determination of
distances between the point of chemical discharge and drinking water
Intakes.
The Interactive program SITEHELP may also be used for a detailed
examination of single reaches. As previously described, SITEHELP allows
the user to display the reach under study on a CRT terminal. SITEHELP also
allows the user to assign river mile locations to all data points on the
reach. SITEHELP procedures that are "user friendly" have recently been
developed for non-graphic (standard hard copy) as well as graphic (CRT)
terminal users, by the Water Quality Analysis Branch of EPA-MDSD.
The previous discussions on Interactive programs of the HLDF system
are presented to aid the Investigator or exposure assessment team 1n
determining the type of retrievals that will assist 1n Identifying
contaminated drinking water supplies. Retrievals may be performed by the
Investigator, or retrievals may be requested from the Water Quality
Analysis Branch of EPA-MDSD. Self-performed retrievals are preferred
because they allow the user much more flexibility and control 1n acquiring
needed Information. Before retrievals are performed, however, the
procedures described 1n USEPA (1981a) should be reviewed.
The Water Qualtiy Analysis Branch of EPA-MDSD continues to enhance the
"user friendly" procedures to meet the needs of the user environment. In
addition, "special" retrievals using newly developed software packages are
also possible to assist 1n retrieving data from the HLDF system.
3.1.2 Federal Reporting Data System (FRDS)
FRDS 1s an Information management system maintained by the EPA Office
of Drinking Water. FRDS contains Inventory data as well as the compliance
status of each public water supply 1n the U.S. and territories. The data
base 1s updated yearly with data collected by the Individual states; as
such, the data represent the most up-to-date public water supply
Information available.
Four types of data are collected by FRDS, based on regulatory
reporting requirements (Mark 1980):
1. Inventory. This Includes facility name and address, public water
supply capacity, source Information (surface and ground)
39
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Including name and location, the number of wells 1f applicable,
monitoring requirements, population served, number of service
connections, and the treatment techniques used.
2. Violation. This Includes data pertaining to non compliance with
EPA or state standards by a specific water supply.
3. Variance and exemption. This Includes data pertaining to
authorized exceptions to the standards which are granted to a
specific water supply.
4. Enforcement action. This Includes Information pertaining to
action taken against a public water supply.
In addition, summary statistics for each state are generated and maintained
within the PROS data base.
Unlike the WSDB, FRDS does not Include REACH numbers and 1s,
therefore, not exactly hydrologlcally linked to any other EPA surface water
data bases. Retrievals are possible, however, by hydrologlc unit code and
according to geographic or political boundaries but not by river, lake,
stream, or water supply name. When Identifying surface water supplies
potentially contaminated with a chemical substance, PROS 1s a supplementary
data source. PROS retrievals may be used to confirm or add Information to
that obtained from WSDB. The major application of FRDS 1s to aid 1n
Identifying potentially contaminated ground water supplies and 1n supplying
treatment techniques for specifically Identified drinking water utilities
Identified 1n HLDF system retrievals. The use of FRDS for Identifying
potentially contaminated ground water supplies 1s discussed 1n the
following subsection. Section 5 discusses the use of FRDS for obtaining
Information on treatment procedures.
For additional Information on FRDS Including retrieval requests,
Inquiries should be directed to:
Mr. Avrum W. Marks
Manager-Computer Systems Staff
U.S. Environmental Protection Agency
Office of Drinking Water
401 M Street, S.W.
Washington, D.C. 20460
(202) 382-5513
3.2 Identification of Ground Water Supplies
Because the problem of ground water contamination has only recently
received much attention, no computerized data bases yet exist such as those
for surface waters (e.g., WSDB). Nearly all of the available Information
40
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1s in text form. There is much information on a regional, state, and
county basis; unfortunately, the sources and origins of the data are not
uniform or interrelated. The US6S has, however, recently begun a large
coordinated series of ground water investigations - Regional Aquifer
Systems Analyses (RASA). This program is a systematic effort to
characterize 28 to 29 hydrogeological regions which make up most of the
contiguous U.S. (Bennett 1979). The overall objective of RASA is to
assemble specific information on aquifers within the regions, especially
those used as drinking water sources, such that predictive capabilities can
be developed in case of contamination or overuse. Because RASA was only
conceived in 1978 and is not expected to be fully completed until 1989, it
is of minimal use for present exposure assessments.
This section will discuss data sources that will provide locational
information on aquifers. Exposure assessments can essentially take on two
forms — site-specific and nonsite specific; therefore, the discussion has
been divided into two parts. The first identifies data sources that would
best suit a site-specific study (Section 3.2.1), and the second identifies
sources for nonsite-specif1c studies (Section 3.2.2). The investigator
might also find use for the information sources described in Section 3.2.1
for nonsite-specific studies.
3.2.1 Identifying Site-Specific Ground Water Supplies
Characterization of a chemical substance's production, use, and
disposal or "materials balance" will determine the sources and pathways of
entry of the substance to the environment. The nature of a chemical
substance's use in industry as well as its production history are required
to determine the modes of its disposal and subsequent discharge to drinking
water supplies. Guidelines for performing a source analysis or materials
balance can be obtained in JRB (1980) and in Volume 2 of this methods
report series (i.e., Ambient Volume).
The major sources of ground water contamination in site-specific
studies will be landfills, surface impoundments (e.g., ponds, lagoons), and
deep-well injections. Volume 3 of this series (i.e., Disposal Volume)
discusses the characteristics of each and the methods for assessing the
effects on aquifers. This effort requires information on the locations of
the chemical's disposal sites.
This section will describe information sources that will aid in
determining whether one of the above disposal practices, in a site-specific
area, poses a threat to ground water, and whether the aquifer is used as a
drinking water source.
-------
Determination of a disposal site's proximity to an aquifer may be
accomplished by the use of state ground water assessments. These ground
water assessments are usually published on a county basis by agencies such
as state water control boards and departments of natural resources (e.g.,
Virginia 1978, Illinois 1968). The reports characterize the physical
conditions (e.g., hydrology, climate, soils), hydrogeology (e.g., rock
formations, ground water location and movement), quality of the water
(e.g., pH, total dissolved solids, bacteria), uses (e.g., large
withdrawals, domestic wells), problems (e.g., depletion, deterioration),
and recommendations for future usage. This information may then be used to
assess the potential hazard of disposed chemicals to ground water supplies
based on the locales of the disposal site and aquifer. The disposal site
need not be located directly above an aquifer to pose a threat. Subsurface
lateral movement of water can extend the infiltration zone beyond the
surface area directly above the aquifer. The information in these reports
is also needed for models which simulate contaminant transport in
subsurface waters (see Subsection 4.3).
The USGS's water resources investigations include studies of ground
water resources for each state on a county basis (e.g., USGS 1976a). They
are similar to the state reports previously mentioned. The USGS reports
define the geologic and hydrologic characteristics of the region. Maps
depicting the size, shape, and depth of aquifers as well as graphs and
diagrams illustrating the hydrogeology are included.
Site-specific ground water information can also be acquired using the
National Water Data Exchange (NAWDEX). NAWDEX is an interagency program
managed and coordinated by the USGS that aids in identifying, locating, and
acquiring water related data. It serves as a means of exchanging water
data among nearly 150 organizations including federal, state, and local
governments and interstate, academic, and private sectors. Information is
accessible at the Program Office, located within the Water Resources
Division of the USGS in Reston, Virginia, and at 60 assistance centers
located throughout the country. Most of the information centers have
hydrologlsts or other specialists who can aid 1n identifying data sources
(Edwards 1980).
tn addition to Information Indices, NAWDEX centers also have access to
the USGS's Water Data Storage and Retrieval System (WATSTORE) (Edwards
1980). WATSTORE is the data bank for all the information collected by the
USGS at its sampling sites throughout the country (Showen 1978). WATSTORE
contains a Water Quality File which offers chemical, physical, biological,
and radiochemlcal data on approximately 5,800 ground water quality wells.
Data entered in the Water Quality File are also entered in the EPA's STORE!
System. A ground water Site Inventory File is also contained within
WATSTORE. This file comprises data on wells, springs, and other sources of
42
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ground water. The data Include site location and Identification,
geohydrologlc characteristics, well construction history, and one-time
field measurements such as water temperature, pH, and hardness. The data
currently cover approximately 600,000 wells (Edwards 1980).
The Federal Reporting Data System (FRDS) should be used to determine
whether an aquifer 1s being used as a drinking water supply. It 1s the
principal data source for Identifying either public or private drinking
water utilities or companies that use ground water as a raw water supply.
The retrievals from FRDS are available on a county or state basis. The
locations of the pumping wells are reported; however, when the total number
of wells 1s greater than three, only the geographical center of all the
wells 1s reported. In such cases where 1t 1s uncertain as to which aquifer
a well may be pumping from, the county reports previously mentioned usually
contain Information on the usage levels from the aquifers; this Information
can then be used to determine whether an aquifer 1s being used for drinking
water.
3.2.2 Identifying Non-Site-Specific Ground Water Supplies
Exposure assessments that deal with chemicals of a ubiquitous nature
will require generalized Information on aquifers. Before obtaining that
Information, however, the source assessment should have characterized the
chemical as to where (e.g., state, region) 1t 1s of most concern and by
what mode 1t may contaminate ground water. Examples of chemicals that
would require a non-site-specific Investigation are household products that
might be discarded as solid waste and destined to a landfill, or those that
might be discarded via a septic tank. In both Instances, there 1s
potential for the chemical to leach Into ground waters.
This section describes Information sources that will aid 1n
Identifying regional aquifer systems and ground water usage levels that
would be appropriate for non-site-specific assessments.
USGS characterizes the nation's ground waters 1n a series of summary
appraisals of 22 hydrogeologlcal regions of the U.S. Each region 1s
characterized 1n a separate document, and the entire series 1s listed under
Geological Survey Professional Papers - 813. The documents describe the
major aquifers 1n the region and their respective geological types (I.e.,
consolidated or unconsolldated). In addition, the documents discuss:
• Populations within the region
• Major economic Industries
• Ground water quantity
43
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• Ground water usage (private and Industrial)
• Ground water problems
• Conjunctive uses of ground water and surface water
• Ground water studies taking place and the need for continued
Investigations.
Each document also describes the aquifers on a state basis for those
states within the region. Maps depicting the location, size, and type of
aquifers 1n the states are also Included 1n the reports. The series Is
currently being updated from the 1978 reports.
The U.S. Water Resources Council, 1n a four-volume report (USWRC
1978), assessed the nation's water supplies on a regional and subreglonal
basis. The first three volumes summarize the data, and the fourth volume
comprises the series of regional reports. The reports contain much the
same Information as the USGS appraisal reports. The ground water
Information deals mostly with the volume and dally withdrawal from the
aquifers. The report discusses the problems of overdraft and contamination
of aquifers, along with the problems associated with recharging of the
ground water. The report also estimates the use of ground waters for the
year 2000 for each region.
There were no data sources found that report the percentage of ground
water used for drinking water. Solley et al. (1983) report the percentage
of total water used that 1s ground water for each state (Table 6) and the
amounts withdrawn. In addition, they characterize the geographical use of
surface and ground waters throughout the country.
44
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Table 6. Percentage of Ground Water Use of Total
Water Use For Each State in 1980
State
Alabama
Alaska
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
Florida
Georgia
Hawai i
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
Montana
Nebraska
Nevada
New Hampshire
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
Rhode Island
South Carolina
South Dakota
Tennessee
Texas
Utah
Vermont
Virginia
Washington
West Virginia
Wisconsin
Wyoming
Percent
3
22
53
25
39
18
4
7
18
17
32
35
5
9
18
84
5
14
5
2
5
6
22
43
7
2
60
20
7
7
46
5
10
9
7
61
16
1
7
4
48
5
38
22
85
4
9
4
11
35
Source: Solleyetal. (1983).
45
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4. QUANTIFICATION OF RAW WATER CONCENTRATIONS OF CHEMICAL SUBSTANCES
The next step 1n the drinking water exposure assessment method 1s the
quantification of the chemical substance 1n raw water supplies, or the
concentration of the substance 1n water Immediately prior to withdrawal
for treatment. Quantification may be accomplished 1n two ways:
• Acquisition of waterborne monitoring data for the chemical
substance.
• Estimation of the concentration based on the chemical-physical
properties and environmental fate of the substance and the
hydrologlcal factors that determine a substance's concentration 1n
water supplies.
Monitoring data are often limited or nonexistent. Estimation,
therefore, becomes the only practical way to quantify the concentration
where monitoring data are not available. The purpose of this section Is
to catalog and describe: (1) sources of Information and data bases from
which the Investigator or exposure assessment team can obtain monitoring
data (Subsection 4.1), and (2) the methods or tools (e.g., models) that
can be used to estimate the concentration of chemical substances 1n
surface water (Subsection 4.2) and ground water (Subsection 4.3).
4.1 Monitoring Data
Monitoring data, when available, will generally provide the most
accurate quantification of the concentration of a chemical substance 1n
raw water supplies. It 1s therefore the preferred Information resource
1n this step of the drinking water exposure assessment process. However,
monitoring data must be carefully evaluated for accuracy, precision, and
representativeness, for it can often be misleading. Common problems
Include: outdated results, data that reflect discontinued practices or
emissions, varying analytical methods and reported detection limits, and
questionable sampling and analysis QA/QC. The quality of available
monitoring data, therefore, must be determined and its limitations
reported in the exposure assessment. Section 4 of Volume 2 of this
methods series (I.e., Ambient Volume) and the Appendices to Volume 2
provide details on the sources of monitoring data. This section will
briefly review the sources of monitoring data that are applicable for a
drinking water exposure assessment.
Monitoring data for a chemical substance in ambient water or,
preferably, raw drinking water supplies may be obtained from the
following three major information resource categories:
1. Federally-funded data management systems or computerized water
quality data bases.
-------
2. Published scientific literature.
3. Unpublished Information, Including government task and project
reports.
A comprehensive drinking water exposure assessment should access the
available monitoring data 1n each of these categories. Each of these
categories 1s described below.
There are two major federally funded water quality data bases. These
are the EPA-supported STORET data base and the USGS supported National
Water Data Storage and Retrieval System (WATSTORE). STORET 1s updated
with the data contained 1n WATSTORE on a yearly basis, and 1s, therefore,
the most comprehensive monitoring data base available. The data 1n
STORET are also available via a greater number of retrieval options. In
particular, STORET monitoring stations and data may be plotted on maps 1n
relation to water bodies, a retrieval capability that 1s not available
via WATSTORE. Both STORET and WATSTORE are discussed In detail 1n
Appendix A of Volume 2 of this series.
The quality of STORE! and WATSTORE data, particularly data summaries,
should be carefully evaluated before use in any exposure assessment.
Problems frequently encountered with STORET and WATSTORE summary data
Include:
• Data source unknown. Summary retrievals for pollutants do not
include station location information. This problem may be
overcome by requesting a station Inventory along with all summary
retrievals.
• Quality of data unknown. Sampling and analytical procedures are
not reported 1n data retrievals. The QA/QC procedures to provide
defensible data are, therefore, unknown. Station Inventories
will provide leads to obtain information on data QA/QC.
• Unknown and/or varying detection limits. Because of varying
analytical detection limits, problems frequently arise In
interpreting non-detections 1n relation to detected values.
Typical STORET summaries set all non-detections equal to the
detection limit when computing statistics. Other operational
approaches (e.g., eliminating all non-detections) are possible.
Remark codes, which describe the data detection limitations,
should be carefully reviewed before inclusion of data in the
exposure assessment process.
48
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Data may be outdated, often reflecting results of discontinued
practices. Unless time (I.e., specific years of data Interest)
limitations are specified, STORE! and WATSTORE retrievals will
provide all reported results for the pollutants of Interest.
Changes 1n analytical and sampling procedures, pollutant discharge
control measures, and other related historical factors that affect
reported results should be reviewed when STORE! data are
evaluated. Retrievals should be restricted to the time period
that best represents current environmental conditions.
Users of on-Hne monitoring data, such as S!ORE! and WA!S!ORE, should be
aware of these problems and deal with them accordingly before data
Inclusion Into an exposure assessment for a chemical substance.
The published scientific literature Includes professional and trade
journals, government reports, books, and symposium proceedings.
Information on specific chemicals may be Identified by a number of
bibliographic on-line search systems. The DIALOG and ORBIT search
systems, 1n particular, are very useful for Identifying literature that
may possibly contain monitoring data. These and other search systems are
discussed 1n the Information Resource Matrix, Appendix A of Volume 2 of
this series.
Unpublished Information including government task and project
summaries, as well as ongoing research projects that may contain
monitoring data for a chemical substance of interest, may be obtained
from a number of sources. The National Water Data Exchange (NAWDEX), a
computerized data base maintained by the U.S. Geological Service, is the
most comprehensive information resource for identifying or locating
possible sources of unpublished data. NAWDEX's primary objective 1s to
assist users of water data in the identification, location, and
acquisition of needed data. For example, NAWDEX can be used to identify
water data available 1n a geographic area and to locate the names and
addresses of organizations from which the identified data can be
obtained. NAWDEX is not a repository of water data; however, it does
have direct access to some large water data bases such as STORE! and
WATSTORE. Further information on NAWDEX is available in the Information
Resource Matrix or by contacting:
National Water Data Exchange (NAWDEX)
U.S. Geological Survey
421 National Center
Reston, VA 22092
Telephone: (703) 860-6031
49
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Other sources of unpublished data which may prove useful are
universities; often those with special geographic ties to a chemical's
production or use conduct ongoing research efforts 1n related special
areas. Unpublished task or project reports prepared by or for government
agencies or divisions of government agencies may contain pertinent
monitoring data. A 11st of government agencies that may have performed
monitoring surveys to support the development of policies or regulations
for a chemical substance or group of substances should be prepared; those
agencies should then be contacted 1n the course of preparing the exposure
assessment. In particular, the EPA Office of Drinking Water should be
consulted for available unpublished monitoring data. State agencies with
regulatory control of drinking water supplies 1n specific geographic
areas of interest for a chemical substance may also have unpublished
monitoring data. Finally, drinking water utilities or treatment plants
where contamination 1s known or suspected may monitor the quality of
their raw water supplies. The Information Resource Matrix, Appendix A of
Volume 2, also discusses additional sources of unpublished monitoring
data.
4.2 Estimation of Concentration in Surface Water
The concentration of a chemical substance 1n surface water can be
estimated by either of two procedures:
1. Conservative estimate - simple dilution of the substance
discharged by surface flow, assuming no other mechanism of
attenuation (fate or transport).
2. Modeling - concentration calculated using an appropriate fate and
transport model.
The procedure chosen for use depends on the level of detail desired
and the amount of time and financial resources available. Conservative
estimates will obviously provide a less accurate concentration. The
procedure may, however, be used as a screening evaluation of possible
surface water concentrations. It may also be used when either the time
or data necessary to make an accurate estimate is limited. Modeling
requires a good understanding of models and their input data
requirements. Modeling is also much more labor-, data-, and
time-Intensive. The following subsections provide details on the two
estimation procedures.
4.2.1 Conservative Estimates
Conservative estimation assumes a constant wastewater discharge and
simple dilution of the discharged substance in the receiving stream. The
ambient background concentration of the substance 1s assumed to be equal
50
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to zero. Attenuation of the substance due to Its fate and transport 1s
not considered 1n the calculation and complete mixing of the chemical 1n
the receiving water Is assumed. As such, the procedure provides a
conservative estimate of the concentration of the substance 1n the
receiving stream or drinking water supply.
There are two approaches for making conservative calculations of the
concentration of a chemical substance 1n receiving water. The first
approach 1s for assessments performed on specific plants and receiving
streams and requires actual flow rates for the receiving water body. The
second or statistical approach 1s used 1n situations where the sources of
contamination are too numerous to deal with Individually. This approach
relies on the use of mean and low (I.e., 7-Q-10) stream flow rates for an
Industrial discharge category of Interest. The low stream flow rate
represents the minimum average dilution that may be expected to occur
over a consecutive 7 day period with a recurrence Interval of 10 years.
Although there 1s no strict water quality or technical basis for doing
so, the 7-Q-10 1s the most commonly used design stream low flow for waste
load allocation analyses (surface water concentrations calculated under
low flow conditions are compared to acute ambient water quality criteria
or other toxldty data to determine potential for environmental
Impacts). Use of the site-specific and generic approaches are described
1n the following paragraphs.
Calculation of potential surface water concentrations in
site-specific assessments relies on three pieces of information: the
flow rate of the discharge stream, the concentration of the chemical
substance in the discharge stream, and the receiving water flow rate
(both mean and low flow). Alternatively, when the wastewater flow rate
and concentration of the chemical substance of interest are not
available, the total dally discharge of the substance (e.g., mass/day)
may be used to conservatively estimate receiving water concentrations.
The concentration of the substance in the discharge stream and the flow
rate of the discharge stream or, alternatively, the daily mass loading,
will have been determined or estimated as a result of the materials
balance performed for the substance and are not within the scope of work
of this volume (See JRB 1980 and Volume 2, Section 2 (i.e., Ambient
Volume) and Volume 3, Sections 2 through 7, of this series (i.e.,
Disposal Volume)).
The mean and low flow rate for a specific water body can be obtained
from a number of information sources. As discussed in Subsection 3.1,
the integrated approach (HYDRO, SITEHELP, IHSBRWSE, AND RCHDAT) to
locating Industrial sources of discharge, receiving waters, and drinking
water supplies will also identify the flow gages and the mean annual and
7-day-10-year (7-Q-10) low flow rates for the period of record. Flow
data may also be accessed by using EPA-MDSD's GAGE File. The REACH
51
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number (USGS 8-d1g1t hydrologlc unit number plus the 3-d1g1t EPA segment
number) may be used to Identify gages and obtain the mean annual and
7-Q-10 flow for a specific water body. The flow rates obtained from
these types of retrievals are all reported on an annual basis for the
period of record.
Flow rates may also be calculated for shorter periods of record as
well as for time periods within a year (e.g., month, season). These
hydrologlc statistics can be computed by using the EPA STOrage and
RETMeval (STORET) Flow Data File (FDF). Information on STORET-FDF,
Including the various programs available to STORET users for analysis of
flow samples, 1s available 1n the Handbook of the Water Quality Control
Information System STORET-Part FL (Flow Data File) (USEPA 1981b).
Inquiries and specific retrievals should be directed to EPA-STORET User
Assistance, 1n Washington, D.C.
Finally, stream flow data can be accessed manually by referring to
the USGS reports published annually on a state-by-state basis (e.g.,
"Water Resources Data for Virginia, Water Year 1980"). Locations of
gaging stations are provided 1n a map 1n the front of each report, and
average, high, and low flows are summarized for each station on an annual
basis and over the period of record. Dally flows are also provided,
allowing calculation of seasonal averages.
Following acquisition of the receiving water flow rate, the
concentration of the chemical substance 1n the receiving water body may
be calculated using a Stream Dilution Factor (SDF) or by simply diluting
the dally load by the receiving stream flow rate. The SDF 1s the ratio
of receiving water flow rate to discharge stream flow rate, and should be
calculated for the mean receiving water flow rate and the 7-Q-10 flow
rate. The concentration of the chemical substance 1n the receiving water
body, using both SDFs, 1s calculated as follows:
Receiving Stream Concentration = Effluent Concentration
SDF
The following examples describe the site-specific approach for
calculating the receiving water concentration of a chemical using either
a SDF or simply diluting a dally mass loading:
Calculation of In-Stream Pollutant Concentration using an SDF:
Evaluation of the process chemistry for producing chemical A at an
organic chemical manufacturing plant located 1n Beaumont, Texas, results
1n a wastewater concentration estimate of 1560 ug of A/1. Using the
procedures discussed 1n Section 3.1, the following Information was
obtained:
-------
Facility name and location:
Receiving stream name:
REACH #:
Facility flow (MGD):
Receiving stream mean flow (MGD):
Receiving stream low flow (MDG):
Plant D; Beaumont, Texas
Neches River
12020003/001
5.40
5,280
186
The stream dilution factors (SDFs) can be calculated from the above
Information as follows:
Mean SDF = Mean stream flow
Facility flow
Low SDF = Low stream flow
Facility flow
5.280 = 978
5.40
186
5.40
= 34.4
Finally, the chemical A 1n-stream concentration can be calculated using
the following equations:
Chemical A In-Stream Concentration (Mean Flow) = Chemical A effluent cone.
Mean SDF
= 1.560 = 1.60 ug/1
978
Chemical A In-Stream Concentration (Low Flow) = Chemical A effluent cone,
Low SDF
= 1.560 = 45.3 ug/1
34.4
Calculation of In-Stream Pollutant Concentration Using a Dally Mass
Loading: The reported or estimated* dally wastewater loading during the
production or Industrial use of chemical B at an organic chemical
manufacturing plant located In York, New York 1s 10 kg/day. Using the
procedures discussed 1n Section 3.1, the following Information was
obtained:
*When plant specific data are not available, annual waterborne emissions
can be estimated using generic emission rates. Waterborne emissions
during organic chemical manufacturing average 0.4 percent of
production/use (see Volume 2 of this Method series for more detailed
Information).
53
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Facility name and location:
Receiving stream name:
REACH #:
Receiving stream mean flow (MGD):
Receiving stream low flow (MGD):
Plant X, York, New York
Genessee River
04130003/013
1125
55
Chemical B 1n-stream concentration can be calculated as follows:
Mean receiving water concentration = Dally load (mass/day)
Mean stream flow (volume/day)
= 10 kg/day
1125 MGD x 3.79 1/gal
= 2.3 x 10-9 kg/1 or 2.3 ug/1
Low receiving water concentration = Dally load (mass/day)
Low stream flow (volume/day)
= 10 kg/day
55 MGD x 3.79 1/gal
= 4.8 x TO"8 kg/1 or 48 ug/1
The second approach to calculate the concentration of a chemical
substance 1n receiving water bodies that are too numerous to work with
Individually relies on the basic principles previously discussed and on
statistical mean and low flows for an Industrial category. Table 7
summarizes the mean pipe flow and the mean and 7-Q-10 receiving stream
flow rates for the major Industrial categories. Data are presented both
for direct Industrial discharge and Indirect discharge (I.e., Industrial
discharge via a Publicly Owned Treatment Works (POTW)). These data were
calculated by comparing the hydrologlc location of all Industrial
dischargers for each specific SIC code, the reported discharge pipe flow
rate as recorded 1n IFD, and the flow data of receiving streams as
recorded 1n the GAGE File. Since the flow data calculated do not fit a
normal statistical distribution, they are presented for two percentlle
ranks, the 10th and 50th. The 50th percentlle Is the median receiving
stream flow for the Industrial category. The 10th percentlle Indicates
that 10 percent of the receiving stream flows for the Industrial category
of Interest are less than the listed value; the 10th percentlle
represents the lower range of expected dilution. The flow data presented
1n Table 7 may be used to estimate a range 1n the concentration of a
chemical substance discharged by one of the major Industrial categories
1n a receiving water body for both mean and low flow conditions. For
54
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example, the range of 1n-stream concentrations of chemical A calculated
using the dally plant loading (e.g., 10 kg/day) and generic data on the
receiving stream flows for the organic chemicals Industry (I.e., SIC 286)
1s presented below:
Industry/
discharge type
Stream flow
percentHe
Receiving stream
flow (MLD)
Mean Low
Surface water cone.
(ug/1)*
Mean Low
Organic chemicals (SIC 286)
Direct discharge
10
50
Indirect discharge 10
50
180
3000
140
2200
2.9
220
3.7
170
56
3.3
71
4.5
3400
45
2700
59
Calculated by dividing chemical release (I.e., 10 kg/day) by receiving
stream flow (I.e., MLD).
Additional data presented 1n Table
the pipe flow and number of plants
flow data can be used to calculate
The data on number of plants can be
loads per plant when waterborne em1
entire Industrial category (NOTE:
either produce or use the chemical
equally divided among all plants).
7 that can be of occasslonal use are
1n each Industrial category. Pipe
Industrial wastewater concentrations.
useful 1n determining annual or dally
sslons data are only available for an
this calculation assumes all plants
of Interest and that discharge 1s
The concentration of a chemical substance 1n a receiving water body
calculated by these procedures 1s a crude estimate. The estimated
concentration essentially represents a worst-case situation. As can be
seen from the two approaches discussed above, the results can vary by as
much as several orders of magnitude. The models discussed 1n the
subsequent section use data on the chemical/physical properties of the
chemical substance of Interest to evaluate the probable aquatic fate of
the substance, along with dilution, to yield a much more accurate
estimate of concentration.
4.2.2
Chemical Fate Models
The Increased concern over toxic pollutant discharges to surface
waters has lead to the recent development of numerous mathematical
models. These models are designed to estimate the fate of a chemical
62
-------
upon discharge and Its effect on the quality of the receiving water. The
complexity of these models can range from relatively simple desk top
calculations to complex computer algorithms. Table 8 lists several
chemical fate models appropriate for freshwater aquatic systems.
Depending on the sophistication of the model, mathematical models can
account for transport processes such as advectlve and dispersive flows,
multiple loading sources, multiple tributaries, and water column/bed
sediment Interactions. In addition, the transformation processes of
volatilization, photolysis, hydrolysis, oxidation, and blodegradatlon can
also be accounted for. The models listed 1n Table 8 are further
discussed, along with technical guidance for modeling, 1n a waste load
allocation document prepared by the EPA Office of Water Regulations and
Standards; release of the document 1s expected during the summer of
1983.
It 1s not within the scope of this document to discuss all the models
1n Table 8; since the models essentially only differ 1n level of
complexity, the selection of one model over another will depend on the
level of detail desired and the resources available to the user. This
section will discuss two of the models listed 1n Table 8, one that 1s
straightforward and easy to use and another which 1s relatively complex.
These two will probably be of most use to EPA-OTS, not solely because of
their capabilities but also because of their accessibility and relative
ease of use.
Generally, the simplest model that will sufficiently address the
problem should be used. The time and cost of running sophisticated
models will often prohibit their use; furthermore, the data requirements
of complex models will often exceed the data that 1s available, thus
making a more simplistic model--a less data Intensive model—more
desirable. The Water Quality Assessment Methodology, WQAM, (Mills et al.
1982) 1s the simplest model available. It 1s essentially a dilution type
calculation described 1n the previous section; except that 1t does have
provisions for degradation processes. The methodology 1s designed as a
screening procedure that makes use of available generic data. WQAM's
major advantage Is that all the mathematical expressions are algebraic
and can be solved using a desk calculator; the analyst needs no
programming experience. The calculations need relatively little external
Input since much of the needed Information 1s provided by tables and
figures within the manual. The user need only provide minimal
hydrologlcal and cl1matolog1cal data peculiar to the system being
modeled. WQAM predicts far field, average steady state pollutant
concentrations 1n lakes, rivers, and estuaries as a function of long-term
average minimum and maximum non-point source loads.
63
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WQAM 1s a two-volume document divided Into six chapters. The first
three chapters provide general Information for the user. This Includes
Introductions Into transport and transformation processes and canonical
data. Included 1n the data are physico-chemical and usage
characteristics for the EPA's 129 Priority Pollutant List. The remaining
three chapters provide a step-by-step approach for assessing the fate and
effects of a pollutant 1n lakes, rivers and streams, and estuaries.
The call numbers for WQAM are EPA-600/6-82-004a and b; copies are
available from the EPA's Environmental Research Lab 1n Athens, Georgia,
or the EPA Office of Publications 1n Cincinnati.
The most useful model to EPA-OTS for estimating surface water
concentrations, because of Its detail and availability, 1s the Exposure
Assessment Modeling System (EXAMS) (Burns et al. 1982). EXAMS 1s
contained within the EPA-OTS Graphical Exposure Modeling System (GEMS)
(GSC 1982a). GEMS 1s a computer system that Integrates environmental
modeling, physico-chemical properties estimation, and environmental data
sets with a data manipulation feature that Includes statistical analysis
and graphic display capabilities. Its purpose 1s to aid environmental
analysts 1n the efficient performance of exposure assessments.
EXAMS was developed by the EPA's Environmental Research Laboratory 1n
Athens, Georgia. The model 1s designed to allow for the rapid screening
and evaluation of organic chemicals 1n streams, rivers, ponds, and lakes
due to continuous long term toxicant loadings. EXAMS Is a steady state,
3-d1mens1onal model which Integrates the physico-chemical properties of
the pollutant with the transport and physico-chemical characteristics of
the aquatic system. Steady state means that the loading and transport
mechanisms are assumed to be constant. As a 3-d1mens1onal model, EXAMS
divides the aquatic system Into water compartments and associated
sediment and blotlc compartments; each compartment 1s assumed to be
homogeneous. Concentrations are estimated for each compartment, and the
compartments are linked via differential equations.
EXAMS, like all mathematical models, requires an extensive amount of
Input data. Table 9 lists the Input requirements for EXAMS; 1t also
exemplifies the complexity of the model. The requirements can be divided
Into three groups: environmental data, chemical data, and loading data.
The environmental data Include climatic, biological, hydrologlcal, and
sediment characteristics. The chemical data Input relates the various
chemical characteristics (e.g., partition coefficients) of the compound
of Interest. Loading data Input concerns the Influx rate of the compound
plus stream flow, rainfall, Interflow, non-point source flow, and drift
(Flksel et al. 1981). EXAMS does contain six canonical environment
set-ups which can be used for nons1te-spec1f1c screening procedures.
69
-------
Table 9. EXAMS Input Requirements
Parameter
Units
River and tributary flow nrVhr
Non-point source water input
(direct surface runoff)
Compartment length m
Compartment width m
Compartment surface area nr
Compartment depth m
Compartment volume rn3
Stream velocity m/s
Chlorophyll concentration mg/L
pH
pOH
Concentration of suspended sediment mg/L
Percent organic carbon content of
benthic and suspended sediment
Extinction coefficient m~^
Non-point source sediment input kg/hr
Length for dispersive mixing m
Eddy dispersivity nr/hr
Cross sectional area of adjoining reaches rrr
Interflow m3/hr
Reaeration rate coefficient cm/hr
Wind speed over river m/s
Rainfall mm/month
Cloud cover tenths
70
-------
Table 9. EXAMS Input Requirements (Continued)
Parameter
Units
Evaporation loss
Water temperature
Sediment load
Latitude
Spectral irradiance
Distribution function (ratio of
optical path length to vertical
depth in water)
Sediment density
Percentage water weight of sediment
Cation exchange capacity of sediment
Anion exchange capacity of sediment
Molar concentration of oxidants
Biomass in water and sediment
Fraction of planktonic biomass
Biotemperature
Bacterial density
Percent of active bacteria
Dissolved organic carbon
mm/month
°C
kg/hr
degrees
protons/cnrVs/nanometers
g/cm3
milli eg/100 g dry wt
milli eg/100 g dry wt
moles/L
mg/L and g dry wt/nr
cells/100 g dry wt
mg/L
Source: Fiksel et al. 1981.
71
-------
Another advantage to using EXAMS 1s that 1t Incorporates
comprehensive second-order kinetics for organic chemical decay. Most
models assume only first-order decay kinetics. EXAMS, however, 1s not
appropriate for Inorganic constituents such as heavy metals. MEXAMS (see
Table 8) 1s very similar to EXAMS and 1s designed specifically for metals
transport.
Copies of EXAMS and user guidance may be obtained from:
The Center for Water Quality Modeling
Environmental Research Laboratory
USEPA
College Station Road
Athens, Georgia 30613
404-546-3123
It 1s suggested that the models 1n Table 8 be reviewed to see which
one can provide the best representation of a particular scenario. Again,
however, the logistics of running those models as compared to WQAM or
EXAMS may discourage their use. Another source of models which may be
useful for surface water quality 1s the Environmental Modeling Catalogue
(USEPA 1980a).
4.3
Estimation of Concentration 1n Ground Water
The major sources of ground water contamination are releases from
waste disposal sites. Volume 3 of this methods series (I.e., Disposal
Volume), discusses 1n detail waste disposal practices and associated
releases. Leachates from disposal sites will percolate through the
unsaturated zone to the saturated zone.
Transport of the contaminants 1s dependant on many meteorological,
chemical, hydrologlcal, and geological parameters, as well as the nature
of the pollutant. Unlike estimating concentrations 1n surface waters,
estimates of releases to ground water should only be made with the aid of
mathematical models. There are too many variables determining quantity
and speed of leachate transport through the unsaturated zone to
reasonably simplify for making conservative estimates. The numerous
assumptions required to make such estimates would only lead to
meaningless Information.
The following parts of this section will discuss the nature and
requirements of ground water models and those models which will be of
prime use to EPA-OTS exposure analyses. Models designed to predict the
72
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dynamics of leachate movement can be divided Into two major groups:
(1) release rate models—those that estimate the quantity and rate of
leaching from a disposal s1te--and (2) solute transport models—those
that predict the migration of the leachate from the source. The use of
these models does require some knowledge 1n hydrogeology, and the user 1s
advised to consult to references such as Mercer and Faust (1981) and
Freeze and Cherry (1979).
4.3.1 Release Rate Models
Release rate models are designed specifically for predicting the
amount of leachate from a waste disposal site that 1s released Into the
subsurface or unsaturated zone. This Information 1s required for
predicting the amount of contaminant that reaches ground water using a
solute transport model.
Release rate models are generally divided Into three components:
leachate generation, constituent concentrations, and leachate release
rates from the site (Versar 1983). The primary factors affecting these
components are listed 1n Table 10. Data requirements for these models
usually Include precipitation characteristics (e.g., amount, duration,
frequency), water table elevation, evapotranspiration, solar radiation,
temperature, humidity, soil profile, hydraulic conductivity, and pressure
head (Versar 1983). Measurements and characteristics of the landfill are
also required.
Table 11 lists several release rate models and their advantages and
disadvantages. Because of time and cost restraints of the more complex
models, the more simplified and less data Intensive versions made be the
most useful. Of the four models listed, the Release Rate Computations
(RRC) (SCS Engineers 1982 as cited in Versar 1983) and the Post-Closure
Liability Trust Fund Model (PCLTF) (USEPA 1982b as cited 1n Versar 1983)
are probably the most useful. The ease of use and low cost of RRC will
make it desirable when time and money are limited. PCLTF is the only one
of the models listed that accounts for all three components and as such
has a higher degree of accuracy.
4.3.2 Solute Transport Models
Whereas release rate models estimate the quantity and quality of
constituents that may leach from a disposal site, solute transport models
predict the dispersion of the constituents from the source. Solute
transport models are mathematical models which, depending on the
complexity of the model, can estimate the migration of a chemical over
time in one, two, or three dimensions (Versar 1983).
Mathematical models employ sets of equations, based on explicit
assumptions, to describe the physical processes affecting ground water
73
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Table 10. Primary Factors Affecting the Three Components of
Leachate Release Rate Models
Leachate generation
Leachate constituent
concentrations
Leachate
release
Precipitation
Liquid content of waste
Ground water intrusion
Soil moisture capacity
Evapotranspiration
Runon/runoff control
Landfill type
Surface/cap conditions
Waste composition
Physico-chemical properties
Contact time
Chemical reactions
Facility age
Landfill design
Liner type
Source: Versar 1983.
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Table 11. Leachate Release Rate Models
Model
Advantage
Disadvantage
Reference
Release Rate Computations
Hydrologic Evaluation of
Landfill Performance
(HELP/HSSWOS)
Post-Closure Liability
Trust Fund (PCLTF)
DRAINMOD/DRAINFIL
• simple, easy to use
calculations
• requires only minimal
amounts of data;
• estimates both vertical
and lateral dispersion
• addresses all
components of leachate
release;
• suitable for many
situations; provides
some generic site types
• can account for passage
of leachate in both
unsaturated and
saturated zones
• limited in scope because
of numerous assumptions
• ignores pertinent
rainfall characteristics
• leachate dispersion
capabilities have not
been field tested
• complex and data
intensive
SCS Engineers 1982
Perrier and Gibson
1980
USEPA 1982b
• complex and data
intensive; high cost of
running model
Skaggs 1982
Source: Versar 1983.
75
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flow, which may 1n turn be used to predict contamination. There are two
sets of mathematical models, stochastic and deterministic. Stochastic
models attempt to define cause and effect relationships using
probabllstlc methods; deterministic models define the relationships based
on the physical processes Involved (USEPA 1982a). Deterministic models
are the more applicable models; there are two types, analytical and
numerical.
Analytical models simplify mathematical equations by making
generalized assumptions, thus allowing solutions to be obtained by
analytical methods. They provide estimates of waste constituent
concentrations and distributions by simulating plume migration from the
source. The generalized assumptions usually Involve steady state
conditions, radial flow from the source, and an Infinite aquifer extent
(Mercer & Faust 1981). Analytical models are not as complex as numerical
models and as such are less time consuming and expensive to run (USEPA
1982a).
Numerical models characterize ground water contamination without
simplifying the physical and chemical parameters. Equations are
approximated numerically resulting 1n a matrix equation that requires a
computer for solution. Numerical models are more sophisticated than
analytical models and will require more data, time, and money to run
(USEPA 1982a).
Both types of models address physico-chemical and hydrogeologlcal
parameters. Table 12 lists advantages and disadvantages of both
analytical and numerical models. Table 13 outlines some of the variables
that are addressed by solute transport models.
The transport and fate of contaminants to ground water are affected
by subsurface factors which can be categorized Into two major groups,
those of the unsaturated zone (soil column) and those of the saturated
zone (ground water aquifer). Because of the dissimilarities between the
two, most ground water models will only consider one or the other.
Many Investigators have designed their own ground water models to
suit the need for their particular study; therefore, there are numerous
models available to an Investigator (USGS 1976b). The remainder of this
section will discuss examples of ground water models which will probably
be of most use to EPA-OTS.
(1) Analytical Models. Again, because they are not as complex as
numerical models, analytical models will probably be most useful. The
two models described here are probably sophisticated enough to provide a
sufficient level of accuracy for most Investigations.
76
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Table 12. Comparison of Analytical and Numerical Models
Model type
Advantages
Disadvantages
Analytical Models
Numerical Models
Provide quantitative-
predictive assessments
Attempt to specify
pollutant concentrations
Allow quick assessments
at moderate cost
Identify physical
processes
Provide quantitative-
predictive assessments
Identify physical
processes
Attempt to specify
pollutant concentrations
Applicable to wide range
of complex situations
Can be applied as a
research tool
Physical processes
incorporated are not
fully understood
Require specialized skills
and equipment
Require field verification
May have limited
applicability based on
model theory
Physical processes are not
fully understood
Require analytical and
field verification
Are data intensive
Potentially high operating
costs
Require specialized skills
May have limited
applicability based on
model theory
Source: USEPA 1982a.
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Table 13. Physical Parameter Characteristics Addressed by
Ground Water Models
Hydrologic Zone
• Saturated - Void spaces in material filled with water; below water
table.
• Unsaturated - Void spaces in material at least partially filled
with air; above water table.
Hydrologic Characteristics (saturated-unsaturated zones)
• Porosity
- Intrinsic: Movement of liquids/gases through porous media.
- Secondary: Movement of liquids/gases through fractures,
joints, or solution cavities in the media.
• Homogeneity
- Homogeneous: Material having identical characteristics at all
locations, uniform.
- Heterogeneous: Material having different characteristics at
different locations, non-uniform.
• Isotrophy
- Isotropic: Hydraulic properties of material are equal in all
directions.
- Anisotropic: One or more of the hydraulic properties of the
material vary according to flow direction.
Transport Mechanisms
• Homogeneity
- Miscible: Uniform mixing of contaminant in system.
- Immiscible: Non-uniform mixing of contaminants.
1 78
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Table 13. Physical Parameter Characteristics Addressed by
Ground Water Models (continued)
• Dilution
- Convection: Transport of contaminants by convective ground
water flow only.
- Multiple: Transport of contaminants by convection, dispersion,
and conduction.
• Phases
- Single: Single phase (e.g., liquid phase).
- Multiple: More than one phase (e.g., liquid-gas phases).
Contaminant Properties
• Constituent Number
- Single: Model transport of single constituent.
- Multiple: Model transport of two or more constituents.
• Contaminant Type
- Organics: Organic chemicals/compounds.
- Inorganics: Inorganic chemicals/compounds (non-metals).
- Metals: Metal species.
- Radioactives: Radioactive materials.
• Degradation
- Conservative: Movement of contaminants without degradation.
- Nonconservative: Movement of contaminants considering
degradation which could include sorption, chemical, or
biological degradation.
Source: USEPA 1982a.
79
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(a) SESOIL. The Seasonal Soil Compartment Model (SESOIL) was
developed by Bonazountas and Wagner (1981) for the Office of Pesticides
and Toxic Substances. SESOIL 1s described as a "user-friendly"
statistical-analytical model designed for long-term environmental
pollutant fate analysis for the unsaturated zone. It can describe water
and sediment transport 1n terms of quality and quantity plus pollutant
transport and transformation. It can be used for a wide variety of
applications Including screening and review of new chemicals.
Model simulations are based on a three cycle rationale: the water
cycle, sediment cycle, and the pollutant cycle. The water cycle takes
Into account rainfall, Infiltration, exflltratlon, surface runoff,
evapotransplratlon, ground water runoff, snow melt, and Interception
(USEPA 1982a). The sediment cycle Includes (1) sediment resuspenslon due
to wind and (2) sediment washload due to rain storms. The pollutant
cycle characterizes convection, diffusion, volatilization, adsorption/
desorptlon, chemical degradation, complexatlon of metals, biological
action, hydrolysis, oxidation, and nutrient cycles (USEPA 1982a). The
user has the option of running the model on one of four different levels
of spatial and time variations.
Aside from predicting chemical distribution 1n the unsaturated zone,
other outputs Include hydrologlc relationships among precipitation,
surface runoff, Infiltration, evapotransplratlon, soil moisture, and
ground water runoff. Concentrations are reported according to the level
of application.
The real advantage 1n using SESOIL for modeling of the unsaturated
zone 1s that 1t has been Integrated Into GEMS (see Section 4.2.2). This
greatly enhances the application of the model. In addition. Input and
output data files have been developed to further support the operation of
SESOIL. SESOIL, therefore, provides a detailed mechanism, with a high
degree of accuracy, to model contaminants 1n the unsaturated zone with
minimal effort. The results may then be used as Input Into a model
designed for the saturated zone.
(b) AT1230. The Analytical Transient One-, Two-, and
Three-Dimensional Simulation Model (AT1230) (Yeh 1981a) was developed at
the Environmental Sciences Division of the Oak Ridge National
Laboratory. AT123D provides generalized analytical transient one-, two-,
or three-dimensional solutions for estimating contaminant transport 1n
both the unsaturated and saturated zones. The model contains 450
options: 288 for the three-dimensional case, 72 for each of the two
dimensional cases (x-z plane and x-y plane), and 18 for the
one-dimensional case 1n the longitudinal direction. The model provides
eight different sets of source configurations, three kinds of source
releases, four variations of aquifer dimensions and modeling of
80
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radioactive wastes, chemicals, and heat. Transport mechanisms
characterized are: advectlon, hydrodynamlc dispersion, adsorption,
degradation, and waste losses to the atmosphere from the unsaturated zone.
AT123D 1s written 1n FORTRAN and model setup time can be extensive.
Although the model has yet to be field validated, 1t has been applied 1n
a number of Investigations. AT123D 1s contained within the EPA-OTS's
computer modeling library; however, 1t has not been Integrated Into the
GEMS system.
(2) Numerical Models. Numerical models provide the best approach to
modeling hydrogeologlc conditions and contaminant characteristics.
However, they are often more difficult to use because they require
complex data and Involve greater costs to run. Their Immediate use In
exposure assessments 1s minimal because of the sophistication needed to
run them, but they will be of greater use 1n the future. The following
are descriptions of two numerical models.
(a) RWSTM. The Random Walk Standard Transport Model (RWSTM)
(Prickett et al. 1981) 1s a generalized computer code that can simulate a
large class of solute transport problems 1n ground water. The model
characterizes both dispersion and attenuation of conservative and
non-conservative contaminants 1n the saturated zone. The model can
simulate one- or two-dimensional nonsteady/steady flow problems,
time-varying pumpage, Injection by wells, recharging, exchange between
surface and ground waters, and flow from springs. Contaminant
concentrations can be Identified in any segment of the model.
Although the user manual provides the necessary Information for model
application, the user is still required to have hydrogeological,
mathematical, and programming knowledge. RWSTM has been field validated
and 1s available for use. Copies of RWSTM are available from the
IlUnios State Water Survey Division, Champaign, Illinois.
(b) FEMWASTE. FEMWASTE (Yeh 1981b, as cited in Versar 1983)
was developed by 6.T. Yeh of the Oak Ridge National Laboratory. It 1s a
two-dimensional mass transport model for both the unsaturated and
saturated zones. FEMWASTE combined with FEMWATER (Yeh and Ward 1981b, as
cited in Versar 1983), a ground water flow model, can provide solute
transport estimates for a variety of boundary and initial moisture
conditions (Versar 1983). The model accounts for the effects of
convection, dispersion, sorption, and first-order decay.
FEMWASTE 1s a complex model, and it too will require the user to have
knowledge of hydrogeology, differential equations, and programming.
FEMWASTE has been field validated and is presently being used by the USGS
1n Carson City.
81
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4.3.3 Practical Model Application
A practical application of two of the ground water models previously
discussed 1s Illustrated 1n a recently completed exposure assessment
Involving the modeling of n1tr1lotr1acet1c add (NTA) 1n ground water.
GSC (1982b), using Information from Versar (1982), predicted the fate of
NTA 1n ground water. They used two models, SESOIL and AT123D. SESOIL
was used to estimate the transport of NTA 1n the unsaturated zone, and
AT123D was used for the saturated zone. The results from SESOIL were
used as the Inputs for the AT123D model. These two models were chosen
because of their versatile capabilities and their relative ease of use.
In order to run the model, GSC had to make several estimates and
assumptions. The Information used for the modeling 1s as follows:
Unsaturated Zone
• Table 14 lists the Information used 1n SESOIL for modeling the
unsaturated zone.
• The source of NTA was residential septic tanks. A representative
housing density of 2,000 houses per 1,000 acres was used to
estimate the total NTA effluent to ground water. However, to
facilitate SESOIL output, only a single house was used, and the
result was extrapolated for the total.
• The average septic drainage area of each house was estimated to be
50 m2.
• The mean concentration of NTA in the effluent was estimated to be
12 mg/1 (6.1 mg/1 - 18 mg/1).
• The unsaturated soil column was estimated to be 5 meters, of which
the top meter was assumed to be aerobic and the lower four meters
less aerated.
• Three different soil types were used, each assigned different
hydraulic conductivities.
• Three different decay rates of NTA were used for the top meter.
• Four different decay rates of NTA were used to the lower four
meters.
• Thus, 36 runs in all were made for NTA transport using SESOIL
(3 soil types x 3 decay rates - upper layer x 4 decay rates -
lower layer).
-------
Table 14. Parameter Values Used in SESOIL to Estimate
NTA Concentrations in the Unsaturated Zone
Time of simulation: Monthly simulation for 10 years*
Effluent quantity per house: 300 gal/day (4 persons per house)
Average precipitation: 8.5 cm/month**
Soil density: 1.32 gm/cm3
Disconnectedness Index: 4.0
Porosity: 0.35
Permeability: 7.15 x 10~9 cm2 (soil type 1)
1.44 x ID"8 cm2 (soil type 2)
5.32 x lO"8 cm2 (soil type 3)
NTA solubility: l,200mg/l
Adsorption coefficient: 6.3 [(ug/gm)/(ug/ml)]
Henry's Law constant: 0.0***
Molecular weight: 191-257 gm/mole
Decay rate: Upper layer 0.11 day"1 (half-life = 6.3 days)
0.16 day"1 (half-life = 4.3 days)
0.22 day"1 (half-life = 4.3 days)
Lower layer 0 day"1 (half-life = » )
0.00019 day"1 (half-life = 10 yr.)
0.00038 day-1 (half-life = 5 yr.)
0.0019 day'1 (half-life = 1 yr.)
Source: GSC 1982b.
* Maximum permissible simulation period in SESOIL.
** Observed at Clinton, Massachusetts, a relatively wet location.
***Assumed 0.0 because of NTA's high solubility and relatively low
vapor pressure.
83
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Saturated Zone
• Table 15 lists the Information used 1n AT123D to model NTA
transport 1n the saturated zone,
• The results from SESOIL were used as the source of NTA (kg/hr) to
the saturated zone.
• The saturated zone was estimated to be a water table aquifer with
a mean depth of 50 m.
• The model calculates the concentrations of NTA at different levels
of the aquifer.
• AT1230 was run 36 times to correspond to the runs of the SESOIL
model.
Table 16 presents the range of NTA concentrations from a 50 m well.
The aquifer 1s located Immediately below the hypothetical 2,000-house
complex, and thus, the concentrations can be considered conservative.
The concentrations of NTA were estimated to range from 0.08 ug/1
(assuming: low end of expected septic system effluent concentration =
6.1 mg/1; the shortest half-life 1n the aerobic zone = 3.1 day; soil with
moderate permeability = soil type 1; and the shortest half-life 1n the
saturated zone = 1 year), to 57 ug/1 (assuming: high end of expected
septic system effluent concentration = 18 mg/1; the longest half-life 1n
the aerobic zone = 6.3 day; soil with higher permeability = soil type 3;
and the longest half-life 1n the saturated zone = 10 years). The NTA
concentrations are those at the 20 m depth; these are the average over
the 50 m depth. Because NTA concentrations will decrease with Increased
depth, wells that only collect water near the upper layers of the aquifer
will contain higher concentrations of NTA; water 1n wells that penetrate
to the bottom of the aquifer will contain lower concentrations (Versar
1982).
84
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Table 15. Parameter Values Used in AT1230 to Estimate
NTA Concentrations in the Saturated Zone
Time of simulation: 136 years*
Hydraulic gradient: 0.05**
Distribution coefficient: 0.0031 nrVkg [3.15 (ug/gm)/(ug/ml)]***
Porosity: 0.35
Bulk density: 1320 kg/m3 (1.32 gm/cm3)
Dispersivity: 30 m (longitudinal)
5 m (lateral)
5 m (vertical)
Decay rate: 0 hr"1 (half-life = »)
7.92 x 10-6 hr-1 (half-life = 10 yr.)
1.58 x 10~5 hr"1 (half-life = 5 yr.)
7.92 x 10~5 hr"1 (half-life = 1 yr.)
Source: GSC 1982b.
* An average detention time calculated on the basis of assumed
drainfield area, hydraulic conductivity, and hydraulic gradient.
** A slightly higher than average value was conservatively assumed.
***Taken as half of the value used in SESOIL.
05
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Table 16. Simulated Average NTA Concentrations in Ground Water at
20 m Depth1 in an Aquifer of 50 m Average Depth
NTA concentration in aquifer^ (uq/1)
Soil type2 NTA half-life in Septic effluent Septic effluent
aquifer (years) 6.1 mg/1 NTA 18 mg/1 NTA
Soil type 1
Soil type 2
Soil type 3
Soil type 1
Soil type 2
Soil type 3
1
1
1
10
10
10
0.08-0.14
0.25-0.44
1.0-1.5
6.5-12
8.5-15
11-19
0.23-0.41
0.74-1.3
3.0 -4.5
20-36
26-45
33-57
Source: GSC 1982b
1 Depth at which average concentration occurs in a well with a
screened, penetrating depth of 50 meters into an aquifer of 50 meters
average depth.
2 Soil type 1 = Moderate percolation; loam and silt soil.
Soil type 2 = Between soil types 1 and 3 (i.e., sandy loam to loamy
sand)
Soil type 3 = Rapid percolation; sandy soil.
3 Concentration ranges for the three biodegration half-lives in the
aerobic zone of the soil column are presented for the low and high
end of the expected septic system effluent concentrations.
86
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5. CONCENTRATION OF CHEMICAL SUBSTANCES IN FINISHED WATER
Section 4 discusses the parameters affecting the concentrations of
chemical substances in surface and ground waters and presents techniques
for estimating chemical concentrations. Treatment applied to those
waters prior to their use by consumers will affect the chemical
concentration and, in turn, determine the consequent exposure via
drinking water. The effects of treatment are discussed In this section.
Drinking water may be drawn from either public or private supplies,
and may be treated or used directly. Public supplies that are treated
are subject to a myriad of unit processes, discussed 1n Section 5.1.1.
Section 5.1.2 guides the reader in methods to (1) determine or predict
the processes used by water supply systems and (2) quantify the effect of
water treatment on the chemical substance of interest. Section 5.2
discusses the methods used by consumers to treat water 1n their homes.
5.1 Public Water Systems
Section 2 of this report briefly discussed the two types of water
treatment systems commonly used by municipalities. Type I (filtration)
plants employ sedimentation, coagulation, flocculation, and filtration;
the finishing step usually involves adding chlorine and fluoride. Type
II (softening) plants use lime and soda ash to precipitate the cations
that cause water hardness (calcium and magnesium), then utilize settling,
filtration, and finishing (see Figure 3). The following subsections
discuss the unit processes that comprise these treatment schemes. A
number of other processes may be used for removal of specific
contaminants; these processes are generally incorporated into the basic
Type I and II schemes and are also discussed below.
5.1.1 Unit Processes in Water Treatment
The typical systems discussed in Section 2 are simply combinations of
unit processes. The following subsections define the unit processes used
in water treatment, discuss the purpose(s) for which they are Intended,
and describe the conditions under which and combinations 1n which they
are used.
Some of the unit processes described below are rarely used; others
are nearly universal. Table 17 presents Information on the frequency of
their use. Each subsection discusses the combinations (or treatment
schemes) in which a unit process is customarily used.
Available data on removal of chemical substances during the most
common processes used 1n water treatment are presented in Table 18.
Removal data available for processes seldom used are not Included. These
37
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uncommon processes, used only at a few plants worldwide, Include: 1on
exchange, reverse osmosis, electrodlalysls, and ultraflltratlon. Data
may be reported for specific compounds or for chemical classes. Table
18 also lists some data on removal of Total Organic Carbon (TOC). The
organic constituents with which EPA 1s generally concerned occur at the
low ppb or ug/1 range, and constitute only a small fraction of the TOC.
Data on TOC removal 1s presented for two reasons:
• The level of TOC 1n water 1s known to affect the degree of
formation of chlorinated compounds and the degree of reaction
between trace chemicals and chlorine (Morris and Baum 1978).
• Removal of TOC by a water treatment process may be used, 1n the
absence of other data, as a qualitative Indicator of whether or
not a chemical of Interest that comprises a small fraction of the
TOC 1s affected by treatment.
Data on TOC removal should not be applied 1nd1scr1m1nantly to determine
removal efficiency for all organic compounds.
The data 1n Table 18 may come from bench-scale studies performed 1n
the laboratory, from pilot-scale studies conducted to aid 1n treatment
plant design, or from tests of the raw and treated water 1n actual
treatment plants. The data from all three types of studies should be
valid for assessing removal efficiency. The removal processes 1n
drinking water treatment plants are physical and chemical processes,
which can be carefully controlled 1n small-scale studies (rather than
biological processes, which are more difficult to control 1n the
laboratory). The key to Interpreting the data 1n Table 18 1s to
determine the basic appropriateness of study design by evaluating
consideration such as:
• Are raw water concentrations treated 1n the study representative
of those encountered 1n water treatment?
• Is the pH at which the study was conducted near the pH of the
water at that point in treatment?
• Are doses of treatment chemicals used in the study reasonable?
The pH of water during drinking water treatment can fluctuate
widely. Many removal processes (notably adsorption, oxidation, and
coagulation) are extremely sensitive to pH, with the optimum pH
determined by the specific coagulant or oxidant added or adsorbant used
(Weber 1972). The pH of water 1s usually adjusted, either by carbonation
to decrease the pH (via carbonic acid formation) or by Hme or soda ash
addition to increase the pH, to bring the water near the optimum pH for
the subsequent process(es). Coagulation is best achieved at pH greater
than 8; oxidation is also greatly favored at high pH (8 to 10 units or
39
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greater) (Weber 1972). These processes, when used, generally occur early
1n the water treatment scheme. The pH of the water may therefore be
maintained at an alkaline pH through much of the treatment, then
carbonated or otherwise neutralized prior to adsorption (1f applied) or
distribution. Adsorption Is greatly favored at neutral or addle pH
(Weber 1972).
(1) Aeration. ASCE (1967) defines aeration 1n water treatment as
"the process by which a gaseous phase, usually air, and water are brought
Into Intimate contact with each other for the purpose of transferring
volatile substances to or from the water." Translated Into practical
terms, aeration has two major applications:
• Removal of dissolved gases, such as hydrogen sulflde, carbon
dioxide, methane, and volatile organic substances.
• Addition of oxygen for oxidation of reduced metals, such as
ferrous Iron.
Aeration 1s generally used for treatment of ground water. The
natural reaction of flowing surface water effectively volatilizes the
contaminants aeration 1s designed to strip (Clarke et al. 1977). Surface
waters similarly do not retain reduced metals; they are naturally
oxidized. An exception to this may be Impoundments with anaerobic
hypol1mn1ons (Clarke et al. 1977). The metals and gases 1n ground water
may, however, be amenable to oxidation or stripping (ASCE 1967).
Three types of aerators are commonly used (ASCE 1967):
1. Waterfall, cascade, or tray types, which work by creating numerous
droplets of water, thus Increasing the water surface-to-air volume
ratio.
2. Diffusion aerators In which air 1s Injected Into the water 1n a
tank.
3. Mechanical aerators, which employ motor-driven Impellers alone or
1n conjunction with dlffusers.
The first type 1s by far the most common 1n water treatment (Clarke et
al. 1977). The third 1s common 1n wastewater treatment.
The use of multiple trays or cascades 1s effective 1n removing gases
and oxidizing Iron. Aeration 1s also called for when reduced manganese
1s present, but aeration must be accomplished 1n conjunction with
chemical oxidation. Chlorine and potassium permanganate are commonly
added (see Section 5.1.1(7)), and coke or stone in the trays also may aid
removal.
95
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Aeration 1s an Initial step 1n water treatment. It 1s generally
followed by (optionally) chemical oxidation, then sedimentation and
filtration. Criteria for use of aeration of ground waters Include (ASCE
1967, Clarke et al. 1977):
• Carbon dioxide > 10 ppm
• Hydrogen sulflde > 1-2 ppm
• Iron > 0.3 ppm
• Manganese > 0.05 ppm
• Tastes and odors attributed to volatile organlcs.
Criteria also exist for avoiding the use of aeration:
• Aeration 1s not to be used 1n conjunction with 1on exchange,
since oxidized metallic compounds may foul the exchange resin
(USGS 1964).
• Increased corrosiveness caused by addition of oxygen may cause
problems 1n the distribution system (ASCE 1967).
• Aeration as a treatment step late 1n the sequence 1s to be
avoided, as airborne contamination may be Introduced with no
means of effective removal prior to Its Introduction Into the
distribution system (ASCE 1967).
The efficiency of contaminant removal by aeration 1s summarized 1n
Table 18. Removal via stripping may be predicted for specific compounds
on the basis of chemical properties like Henry's law constant, as
Illustrated In Figure 13.
(2) Chemical oxidation. This water treatment process Involves the
addition of strong oxidizing agents to break down chemical substances.
Oxidizing agents are generally fed to the water near the beginning of
treatment, prior to coagulation or softening.
Numerous chemicals are used as chemical oxldants (ASCE 1967, Clarke
et al. 1977):
• Chlorine, when added Initially 1n high doses of up to 30 mg/1
(NAS 1982a) (prechlorlnatlon), oxidizes mlcroblal cells, reduced
metals, and organic compounds; breakpoint chlorlnatlon (see
Section 5.1.1(9)), also oxidizes compounds.
96
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,1 _
Concentration in air
Ease of stripping -
0.1 1.0
Concentration in water, fjg/L
10 100 1000
I I Tetrachloroethylene
1,1,1 -Trichloroethane
trichloroethyiene I.
Chlorobenzene „' _. , . ^. .
Benzene 1.1-Dichloroethylene
Cis-1,2-Dichloroethylene
Trans-1,2-Dichioroethyiene
" 1,4-Dichlorobenzene
^ 1,3-Dichlorobenzene
_ Methyiene Chloride
'1,2-Dichloroethane
1,2-Dichlorobenzene
1,2,4-Trichlorobenzene
t
Vinyl Chloride
Source: Love et al . 1983.
FIGURE 13. EASE OF STRIPPING AS A FUNCTION OF HENRY'S
LAW CONSTANTS FOR SELECTED ORGAN ICS
97
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• Potassium permanganate, when added up to concentrations of 10
mg/1 1n raw water (NAS 1982a), oxidizes compounds. The
permanganate reduces the Insoluble manganese dioxide, which 1s
removed by settling and filtration.
• Chlorine dioxide 1s a strong oxldant, added to levels of 0.2 to
2 mg/1. It 1s more expensive than most oxldants, so although 1t
1s an effective disinfectant, 1t 1s usually added only at the
beginning of treatment.
• Ozone, which forms highly efficient nascent oxygen.
Table 18 lists the available data on destruction by chemical
oxidation. The effectiveness of chemical oxidation varies with the
nature of the organic or metallic compounds. It 1s often possible,
however, to predict removal by applying knowledge of chemical
stolchiometry. For example, 1t 1s known that 1 mg/1 of potassium
permanganate will theoretically remove 1.06 mg/1 Iron or 0.52 mg/1
manganese. Equations can be constructed for any combination of chemical
oxldant and contaminant by simply applying the principles of balancing
oxidation-reduction reaction equations.
Ozone (03) has been used for water treatment since 1903 (Nebel
1982); Its use Is widespread 1n Europe, but limited 1n the U.S. (Clarke
et al. 1977). All Its applications are related to its oxidizing ability
(Weber 1972):
• Reduction of color
• Disinfection (bacterial and viral)
• Increased settleablHty
• Oxidation of organic materials (Including phenollcs,
trlhalomethane precursors, and algal blomass)
• Oxidation of reduced metals (Iron and manganese) or cyanide.
Ozone for water treatment 1s produce by a high-voltage electrical
discharge that splits the divalent oxygen molecules, leading to 63
recombinations (Weber 1972). Ozone is generally unstable; once produced,
1t is immediately Introduced Into the water in a highly baffled mixing
chamber (ASCE 1967). The large amount of electricity needed to generate
usable concentrations of ozone (1% w/w) is the major factor in the
currently prohibitive cost of this unit process.
98
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Ozone 1s under Increased scrutiny of late as an alternative to
disinfection by chlorlnatlon. As discussed 1n Section 5.1.1(9),
chlorlnatlon of naturally occurlng organlcs during water treatment leads
to the formation of trlhalomethanes (THMs). These substances are
regulated by EPA as recognized carcinogens, necessitating a review of
standard water treatment procedures. The use of ozone has two major
advantages:
• Disinfection 1s achieved without THM formation, while adding the
benefits of Its other functions.
• Use of ozone 1s relatively cost effective when compared to the use
of chlorlnatlon followed by activated carbon adsorption.
Ozone may be used as a pretreatment step prior to conventional
coagulat1on-flocculat1on-f1ltrat1on or as the final step before the water
enters the treatment system (Nebel 1982). Addition of a low
concentration of chlorine 1s, however, recommended to ensure sterile
water throughout the distribution system (Clarke et al. 1977).
It should be noted that the term "chemical oxidation" encompasses the
action of molecular oxygen 1n the aeration process (Section 5.1.1(1)).
(3) Coagulation and Flocculatlon. Coagulation and flocculatlon
remove turbidity and the contaminants associated with 1t. Coagulation 1s
the process that reduces the net repulsive forces between electrolytes 1n
solution. Flocculatlon 1s defined as aggregation by chemical bridging
between particles (Clarke et al. 1977). The two processes may be
performed consecutively 1n separate basins or concurrently 1n one basin.
Stumm and O'Mella (1968) describe six steps 1n coagulation and
flocculatlon; the steps are not discrete and may overlap.
1. Hydrolysis of multlvalent metal Ions and polymerization to
multlnuclear species.
2. Adsorption of hydrolysis products to accomplish destabH1zat1on of
colloids.
3. Aggregation of destabilized particles by bridging.
4. Aggregation by particle transport and van der Waals1 forces.
5. Aging of floe, Involving bridge alterations and floe hydratlon.
6. Precipitation of metal hydroxide.
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It 1s obvious that this treatment process 1s complex, and 1t 1s not
fully understood. The action and effectiveness varies with the chemicals
used and those to be removed (Clarke et al. 1977).
Coagulation Involves coagulants and auxiliary compounds termed
"coagulant aids." The most widely used coagulants are aluminum and Iron
salts: aluminum sulfate (alum), ferrous sulfate (copperas), ferric
chloride, and ferric sulfate. Alum 1s added 1n the range of 5 to
150 mg/1, depending on the raw water chemistry; each mg/1 of alum removes
0.5 mg/1 of alkalinity (as CaC03). Copperas 1s used 1n conjunction
with excess lime or chlorine. One mg/1 removes 0.5 mg/1 calcium
carbonate 1n the lime-copperas treatment. The chlorine-copperas
combination results 1n the formation of ferric sulfate and ferric
chloride, which form Insoluble hydroxide complexes with calcium (Clarke
et al. 1977). Ferric chloride and ferric sulfate may be added directly
at maximum levels of 60 and 100 mg/1, respectively.
Coagulant aids have many purposes (Clarke et al. 1977):
• Adds and alkalis are added as needed to adjust the pH for
optimum coagulant action.
• Activated silica added to between 1 and 5 mg/1, has a strong
negative charge. It reacts with positive metal hydroxides to
stabilize the floe.
• Clays add weight and stability to floe. The amount used varies
widely among water treatment plants, but usually does not exceed
15 mg/1 (NAS 1982a).
• Polyelectrolytes Increase the rate and degree of flocculation by
adsorption, charge neutralization, and interparticle bridging.
Dosages can range from less than 1 to 5 mg/1, though expense of
the chemicals usually keeps the amounts small.
Synthetic polyelectrolytes are high-molecular-weight, water-soluble
polymers (such as cross-linked styrenes, acrylamides, acrylates, phenols,
and pyridlnes) that disassociate and produce highly charged ionic
chains. The polymers may be cationlc (positive), anlonic (negative), or
polyampholytlc (both charges). Polyelectrolyte coagulation aids should
be selected for use only after careful characterization of the water to
be treated so that contaminants can be selectively removed (ASCE 1967).
Coagulants and auxiliary chemicals are added to the water 1n a
flash-mixing basin (if coagulation and flocculation are separate) or 1n
the coagulation-flocculatlon unit. After the chemicals have been added,
the mixture is agitated slowly enough so that particles are formed, yet
100
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not destroyed by the mixing action. Flocculatlon can be achieved by use
of paddles or the mixture can be forced to flow through baffled chambers
(ASCE 1967).
Flocculatlon 1s followed by settling (see Section 5.1.1(4)) to remove
the suspended floe. Table 18 presents data on the removal of some
chemical constituents by coagulation and flocculatlon. These processes
are Inherent 1n the Type I filtration plant process scheme used for most
surface waters, and with sedimentation, they characteristically effect
nearly 100 percent removal of solids (measured as turbidity) (Clarke et
al. 1977).
(4) Sedimentation. Sedimentation, the use of tanks to reduce the
amount of settleable solids, 1s second only to chlorlnatlon and
filtration 1n frequency of use 1n water treatment (ASCE 1967).
Sedimentation basins are known variously as settling tanks, settling
basins, or clarlflers. There are two basic applications of sedimentation
1n water treatment (ASCE 1967):
• Plain sedimentation, used to remove partlculate that occurs
naturally 1n surface water.
• Sedimentation following coagulation, designed to remove the floe
created by flocculatlon of coagulants and water.
The effectiveness of a sedimentation tank depends on how well the
tank was designed with respect to the characteristics of the solids to be
removed. The geometry of the tank and the flow rate through the tank are
the critical design considerations (ASCE 1967). Tanks may be round or
rectangular; Influent water 1s fed Into the center of round tanks and
flows outward, while 1n rectangular tanks, the water flows the length of
the basin and out the end over weirs. Plain sedimentation tanks are
generally rectangular. Clarlflers used after coagulation may be either
shape.
The theory behind sedimentation following coagulation 1s complicated,
Involving the laws of physics and chemistry (Clarke et al. 1977, ASCE
1967). Gravity affects the rate at which particles move downward through
water, as described by numerous equations Including Stoke1s Law.
Electronic charges on the surface of floe particles, measured by the
zeta potential (Stumm and O'Mella 1968), cause two particles that contact
each other to adhere and form one larger particle; the larger the
particles are, the faster the rate of subsidence (Clarke et al. 1977).
The efficiency of sedimentation 1s directly related to the detention
time 1n the basin. Engineers therefore design the sedimentation basin to
101
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hold water for a length of time sufficient to achieve the desired removal
of solids. The nature of the particles to be removed determines the
upper limit of efficiency; e.g., colloids are rarely removed by
sedimentation, while dirt and sand are removed at up to 100 percent
efficiency.
No data on the effect of sedimentation alone on contaminant removal
have been Identified.
(5) Lime-soda ash softening. The purpose of softening 1s to reduce
a water's magnesium and calcium content. These cations, as discussed 1n
Section 2, consume soap and cause scaling 1n piping and water heaters.
Consumers generally object to water with hardness greater than 150 mg/1,
expressed as calcium carbonate (Clarke et al. 1977). Such waters are
usually softened.
Figure 14 displays the chemical reactions that achieve softening by
the addition of Hme (Ca(OH)2) and soda ash (Na2C03). Lime-soda
ash softening also removes Iron, manganese, strontium, and aluminum 1f
sufficient quantities of the reactants are added (Clarke et al. 1977).
The optimum concentrations of calcium and magnesium 1n the finished water
are 75 to 85 mg/1 and 20 to 40 mg/1, respectively (ASCE 1967).
Apart from removal of divalent cations, lime-soda softening has
numerous benefits. The addition of Hme generally aids 1n coagulation,
and the elevated pH that results from Its use also provides a measure of
disinfection (Clarke et al. 1977).
Variations of this process are 1n use throughout the United States:
• Excess Hme treatment, 1n which Hme above the sto1ch1ometr1c
level 1s added, reduces hardness to 30 mg/1 of CaCO.3 and 10
mg/1 of magnesium hardness. It 1s accomplished 1n two stages of
Hme addition, between which the water 1s recarbonated by
bubbling 1n C02 (ASCE 1967, Clarke et al. 1977). The total
lime dosage can range from 100 to 650 mg/1 (NAS 1982a).
• Split treatment, 1n which a portion of the raw water 1s bypassed
to reduce Hme requirements and produce a moderately soft water,
may Involve softening of 50 to 90 percent of the Influent water
(ASCE 1967).
Lime-soda ash softening 1s used for most waters from which hardness
must be removed; the alternative 1s 1on exchange, which 1s more expensive
and difficult to operate. Many ground waters and some surface waters are
treated by lime-soda ash softening. Table 17 presents the frequency of
use.
102
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(1) C02 + CA(OH)2 - CAC03| + H20
(2) CA(HC03)2 + CA(OH)2 - 2 CAC03| + H20
(3) MG(HC03)2 + CA(OH)2 - CAC03j + M6C03 + 2 H20
(M) M6CC3 + CA(OH)? - M6(OH)2{ +
(5) MGSOq * CA(OH)2 - MG(OH)2J +
(6) CASOM + NA2C03 -
FIGURE 14. CHEMISTRY OF THE LIME-SODA PROCESS
(CLARKE ET AL. 1977)
103
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Lime-soda ash softening may result 1n the alkaline destruction of
organlcs and precipitation of metal hydroxides as well as removal of
hardness. The few data relevant to this are presented 1n Table 18.
(6) Direct filtration. Direct filtration refers to a system of
treatment for water rather than a single unit process. In direct
filtration, coagulants are flash-mixed with the raw water, then sent
directly to sand filters. The sedimentation step, usually an Important
component In a filtration plant, 1s left out entirely because the floe
are so small that they are effectively removed by filtration alone;
sedimentation has little effect. Direct filtration therefore requires
less capital Investment and 1s under scrutiny for widespread application.
Some research on the efficiency of contaminant removal has been
performed (see Table 18). Direct filtration 1s somewhat less effective
than the complete complement of processes 1n a filtration plant. Most
data are based on pilot plants; very few full-scale direct filtration
plants are currently 1n use.
(7) Filtration. Water filtration through Inorganic media 1s a
physical and chemical process (ASCE 1967). It 1s simply defined as a
process for clearing liquid of suspended material (USGS 1964). Sand 1s
the usual filtration medium, and the gravity-flow rapid sand filter 1s
the standard of the water Industry (ASCE 1967). Filtration can be
achieved by any of these media:
• Rapid sand filtration operates at high flow rates and comprises
a simple medium (sand), with size gradation (fine to coarse) of
the sand. It 1s generally used after coagulation and settling
to remove nonsettleable floe (Clarke et al. 1977).
• Slow sand filtration 1s limited to waters of low turbidity, low
color, and low microblal content. There 1s some biological
action 1n the filter which may aid 1n the removal of organic
compounds (USGS 1964).
• D1atom1te filters are constructed with a layer of dlatomaceous
earth on top of a sand substrate. These filters are unstable
and difficult to maintain; thus, their applicability 1s limited
(ASCE 1967).
• Mixed media filters may Incorporate strata of other materials,
such as anthracite or garnet. Efficiency of contaminant removal
exceeds that of regular sand filters (ASCE 1967).
Most filtration units operate 1n the same manner. Water 1s fed to
the top of the filter (at varying rates) and flows downward through the
104
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sand grains. The pores between grains and attraction of van der Waals1
forces trap contaminants 1n the filter (Clarke et al. 1977). When the
filter becomes laden with floe particles, Its efficiency decreases
drastically and the filter bed Is hydraullcally expanded (back-washed);
the water then washes out Impurities and 1s drawn off. The filter bed
again settles Into Its natural arrangement, with larger (heavier) grains
at the bottom (ASCE 1967, Clarke et al. 1977).
Table 18 lists the data on removal of chemicals during filtration.
Unless anthracite 1s Incorporated Into the filter, removal 1s limited to
suspended constituents; dissolved Ions are unaffected.
(8) Carbon adsorption. Adsorption 1s defined by Stone et al. (1975)
as a surface phenomenon Involving the accumulation of substances at a
surface or Interface between one phase and another. Adsorption from
solution onto a solid results from two driving forces: a d1saff1n1ty of
the solute for the solvent, and an attraction between the solute and the
adsorbent. In the case of adsorption on activated carbon, these forces
are Joined by an additional factor. Activated carbon 1s a porous
substance, and large molecules (such as high molecular weight organlcs)
are physically trapped 1n the carbon matrix. One pound of activated
carbon has a surface area of over 100 acres (Clarke et al. 1977).
Activated carbon may be applied by either of two methods at a dosage
usually not exceeding 200 mg/1 (NAS 1982a): (Clarke et al. 1977, Stone
et al. 1975):
• Batch contact, 1n which carbon 1s added (powdered, granular, or
pelletlzed) to the water (usually as a slurry). The adsorbent
and the water are mixed, and the reaction 1s allowed to occur
for a predetermined length of time (usually longer than 15
minutes and often up to 48 hours (Stone et al. 1975)). The
water 1s then allowed to settle. Activated carbon may be added
at any point prior to filtration.
• Column operation, in which water 1s filtered through fixed beds
operated In series or parallel. Columns utilize granular
activated carbon and operate at rates of 1 to 2
I1ters/second/m2 with a two-hour contact time.
Activated carbon adsorption 1s probably the most effective means of
controlling organic compounds 1n water (Stone et al. 1975, Clarke et al.
1977). The cost of operating activated carbon columns 1s, however, very
high. Carbon 1s exhausted after a few weeks of adsorption and must be
replaced or regenerated. Heating the carbon to approximately 900°C will
accomplish regeneration; however, large amounts of energy are required
(Stone et al. 1975). Activated carbon 1s used mainly by water utilities
105
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as a last resort 1n treating organlcs; 1t 1s generally less expensive to
use chemical oxidation or preventatlve methods. For example, utilities
that prechlorlnate water may experience problems with high concentrations
of chlorinated organlcs. These could be removed by carbon adsorption,
but they could be prevented by chlorinating only the finished water after
oxidation, coagulation, and filtration to reduce the precursor pool of
organic reactants (NAS 1980).
The effectiveness of activated carbon 1s Illustrated by the data 1n
Table 18. The effectiveness of carbon adsorption 1s, however, best
expressed 1n terms of Isotherms, which take Into account the solute
concentration and the surface concentration at various points 1n time. A
removal efficiency represents only one point on a compound's Isotherm
(NAS 1980). Adsorption 1s believed to be a step-wise process, whereby
the least water-soluble solutes are removed from solution first (Weber
1972). There may therefore be relatively large differences 1n organic
solute removal by carbon adsorption, as seen 1n the data 1n Table 18.
All compounds studied to date are removed to some degree. Though there
are no data on removal of heavy metals by carbon adsorption, Stone et al.
(1975) believe that addition of a chelatlng agent (such as EDTA) to the
water would produce an organometalUc complex that would be absorbed by
the carbon, ensuring nearly 100 percent removal.
One problem with activated carbon column adsorption 1s the tendency
for organlcs to desorb from the column when the capacity has been
exhausted. Compounds that have accumulated over the useful life of the
column may appear 1n column effluent 1n a slug; this phenomenon, known as
the chromatographlc effect or breakthrough, can be prevented by
monitoring and careful treatment planning and operation. A related
difficulty 1n carbon bed operation 1s the tendency for organlcs to
preferentially sorb and desorb on the carbon surface. This occurance Is
related to the differences 1n solubility discussed above (and other less
well-understood factors). For example, substituted phenols will replace
unsubstltuted phenol and cause Its rapid desorptlon (NAS 1980). Water to
be treated must be fully characterized with regard to combinations of
organlcs that may display this phenomenon.
The growth of microorganisms, particularly bacteria, on granular
activated carbon beds has also been recognized as a problem as bacteria
are washed out of the filter and because of the appearance of bacterial
metabolites 1n filter effluent (NAS 1980). Since that first recognition
that bacteria can live 1n GAC filters, other Investigators (most recently
Neukrug et al. 1982) have studied the effect of bacterial decomposition
of organlcs by the combined bacterial-carbon action (termed biological
activated carbon, or BAC). The control of the microorganisms 1n the
carbon bed 1s apparently not worth the effort required to achieve
biologically-mediated, effective organlcs removal.
106
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Other adsorbents have been shown to be as effective as activated
carbon; some are more efficient 1n removing selected contaminants (see
Table 18). Synthetic organic polymers (e.g., XAD, AmberUte,
polyurethane) show great promise but are not yet economically feasible.
(9) Chlorlnatlon. Chlorine 1s added to public drinking water
supplies primarily to prevent the spread of waterborne disease;
additional benefits Include oxidation of organic and metallic
contaminants and control of nuisance mlcroblal growth In the water
treatment plant and distribution system (Sawyer and McCarty 1978, Clarke
et al. 1977). Chlorlnatlon has been practiced as an emergency measure
since 1850, and regularly in the U.S. since the early 1900s (Sawyer and
McCarty 1978). The vast majority of waters that are treated before
consumption are chlorinated (see Table 17).
Chlorine may be added to water In a number of forms; chlorine gas,
hypochlorltes, chloramlnes, and chlorine dioxide are the major compounds
used (Clarke et al. 1977). All the chlorine compounds used 1n water
treatment function by the formation of hypochlorous add, the primary
disinfecting agent (Sawyer and McCarty 1978).
The significant aspect of Chlorlnatlon with regard to exposure to
toxic substances 1s the reactivity of chlorine with a wide variety of
chemicals. Chlorine reacts with ammonia to form chloramlnes, non-toxic
compounds with significant disinfecting power (Sawyer and McCarty 1978).
Chlorine also reacts with hydrogen sulflde, Iron, manganese, and nitrogen
oxides. In order to ensure sufficient chlorine dosage to retain a
residual level through the distribution system, a practice known as
breakpoint Chlorlnatlon 1s common. In this process, the combined
chlorine content 1s measured, then additional chlorine to fully oxidize
the compounds 1s added. This often requires heavy chlorine dosages (over
10 mg/1) (Clarke et al. 1977, Sawyer and McCarty 1978).
The formation of chlorinated organlcs during water treatment has been
well studied. Among the factors affecting the extent of chlorinated
organlcs formation are:
• Point of chlorine application. Chlorlnatlon at the beginning of
treatment to control algal growth 1n the system
(prechlorlnatlon) allows chlorine to react with organic
compounds 1n the raw water. If Chlorlnatlon 1s used only as a
final step, many organic molecules that would have reacted will
have been removed by coagulation, filtration, etc.
• The amount and type of organlcs 1n the water. Phenols are
readily chlorinated, as are simple sugars and adds. Simpler
organic compounds, when chlorinated, form trlhalomethanes
(THMs). Chloroform 1s the most common THM formed during water
107
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treatment, and because of chloroform's cardnogenlclty to
animals, THMs are now regulated by EPA (see Section 2). If
bromine 1s present 1n the water that 1s to be chlorinated,
bromlnated organlcs are also formed (Sawyer and McCarty 1978).
The pH and temperature at which the reaction occurs.
Chlor1nat1on at high pH, such as 1s present 1n lime-soda
softening plants, Increases the reaction rate (Stevens et al.
1976). THM concentrations are generally higher 1n the summer
(Brett and Caverly 1979, Smith et al. 1980).
A large number of organic compounds have been examined for their
ability to serve as THM precursors. The most commonly recognized
precursors are humlc and fulvlc adds, the naturally-occurring compounds
1n peat and vegetation that give surface waters their characteristic
brown-yellow coloring. Rook (1972) and Bellar et al. (1974) were the
first to demonstrate THM formation from chlorlnatlon of surface waters.
Since that time, polyelectrolyte coagulants (LHtlefleld 1979), algal
byproducts (Morris and Baum 1978, Hoehn et al. 1980), and algal and
bacterial blomass (Hoehn et al. 1980) have been shown to produce THMs
when chlorinated. Some reduction 1n formation of THMs has been noted
when chlorine dioxide or chloramines are substituted for gaseous chlorine
and hypochlorites in disinfection (Hoehn and Randall 1977, Symons et al.
1975).
Ingestion of chlorinated organlcs as a result of drinking water
treatment affects primarily persons consuming treated surface waters.
The organic precursor molecules usually occur naturally in lakes,
reservoirs, and rivers and are not often found in ground water.
Though chlorlnatlon of drinking water 1s known to cause formation of
chlorinated organlcs, it is not likely that the practice will be
abandoned. Chlorine is the only disinfectant that persists through the
treatment and distribution system, minimizing the risk of contamination
before the water reaches the consumer. Water utilities experiencing
problems with chlorinated organlcs generally try to remove the organlcs
from the water prior to chlorlnatlon; if THMs or other compounds are
still a problem, carbon filtration or resin adsorption may be used as a
final treatment step.
(10) Fluorldation. Most public water supply systems add fluoride
ion as a final step in the treatment process. Over 37 thousand tons of
fluoride compounds were consumed by water utilities in 1981 (Nebel
1982). At an optimum level of 1.0 mg/1, fluoride has been shown to
significantly reduce the incidence of dental caries; an additional
benefit of increased fluoride intake may be the prevention of
osteoporosis and arterioscelerosis in the elderly (Clarke et al. 1977).
108
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Fluoride 1s commonly applied 1n the following forms (Clarke et al.
1977):
• Sodium fluoride, a crystalline salt that can be handled manually.
• Sodium s1licofluor1de, applied by dry feeder and the most
commonly used compound.
• FluoslHdc acid, a strong add requiring great care 1n
handling; used mainly by very large water works.
Less commonly-used fluoridating chemicals Include ammonium
s1!1cofluor1de and fluorspar (CaF2) (ASCE 1967). The chemicals may be
fed Into a channel or main leading from the water filters or added
directly to the water 1n Its storage tank or clearwell.
Some water supplies are derived from sources naturally rich 1n
fluoride due to geological formations. Consumption of water with a
fluoride concentration greater than 2 mg/1 may result 1n discoloration
(mottling) or pitting of tooth enamel, occasionally leading to loss of
teeth (Clarke et al. 1977, USGS 1964). Many utilities have replaced
their high-fluoride supplies; the alternative 1s an additional treatment
process. Reduction 1n fluoride concentration may be achieved by
filtration through bone char or activated alumina (Clarke et al. 1977,
ASCE 1967). These filtering media cannot be combined with sand, gravel,
or carbon 1n mixed media filters, because the regeneration of bone char
and activated alumina require backwashlng with caustic solution, which
may damage the more conventional media.
It has been shown that the presence or addition of other halogens
(I.e., chlorine and bromine) leads to the formation of halogenated
organics. The reactions between fluorine and organlcs have not been
studied.
Many of the fluoride compounds used 1n water treatment are byproducts
of other mineral mining. For example, fluorspar 1s manufactured from the
waste of phosphate mining (NAS 1971). Concern for the purity of these
chemicals has led to the Inclusion of sodium fluoride and sodium
s1!1cofluor1de 1n the National Academy of Science's Water Treatment
Chemicals Codex (Rehwoldt 1982). The Codex recommends limits of
Impurities based on existing Maximum Contaminant Levels (MCLs),
recommended use patterns, and safety factors; the guides have been
formulated only for direct additives, but future expansion 1s planned.
109
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5.1.2 Addition of Contamination During Water Treatment and Distribution
(1) Water treatment. The National Academy of Science (NAS) formed
the Committee on Water Treatment Chemicals to Investigate the addition to
finished water of harmful chemicals that are Impurities 1n water
treatment aids. Table 19 summarizes the results of their Initial efforts
to control exposure to these Impurities.
The committee calculated the Recommended Maximum Impurity Content
(RMIC) for each Impurity expected 1n each water treatment chemical. The
following formula was used:
RMIC = MCL or SNARL
Maximum dosage x safety factor
Where maximum dosage was based on the committee's knowledge of use
patterns, the safety factor was 10, and the MCL or SNARL (Suggested
No-Adverse Reponse Level) was obtained from EPA or NAS data (Rehwoldt
1982). The safety factor 1s Intended to take Into account the use of
more than one water treatment chemical containing an impurity as well as
other exposure routes.* The NAS proposes to expand the codex to address
some direct additives, such as polyelectrolytes, 1n a methodology-
oriented fashion and others 1n the current monograph style.*
(2) Distribution system's effects on chemical quality. Within the
distribution system, changes in water's chemical quality can result from
corrosion, deposition, leaching, and reactions involving water treatment
chemicals and their residuals (NAS 1982b).
Components of pipes or linings that may enter the water as it passes
through are a common source of chemical contamination. Table 20 lists
the contaminants related to water distribution systems and records some
of the levels measured in tap water.
Chlorinatlon of finished water, discussed in the previous section,
can result in the formation of chlorinated organics. Trlhalomethanes
(THMs) are formed both instantaneously and during the time the water
travels between the water treatment plant and the consumer's tap.
Samples at the tap may have twice the THM content of the water leaving
the plant (NAS 1982b). Other chlorinated organics have been detected in
tap water and attributed to the chlorine-organic reaction: chlorinated
phenols, simple acids, polynuclear aromatic hydrocarbons, and benzenes
(NAS 1982b). An exposure assessment for any chlorinated chemical species
should take Into account the possibility that formation 1n water
treatment may be a source of exposure.
*Personal communication between Robert Rehwoldt, NAS, and Gina
Hendrickson, Versar, June 17, 1984.
110
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Table 19. Summary of Water Treatment Chemicals CODEX
Chemical
Aluminum
sulfate (alum)
Ammonium
sulfate
Calcium
hydroxide (lime)
Calcium
hypochlorite
Calcium oxide
(quicklime)
Powdered/granular
activated carbon
Chlorine
Function
Coagulant
Combined chlorine
disinfection
Softening, pH
adjustment
Disinfection,
oxidation
Softening
pH adjustment
adsorbent
Disinfection,
oxidation
Maximum
dosage, mg/1
150
25
650
20
500
200
30
Impuri ty
Arsenic
Cadmium
Chromi urn
Lead
Mercury
Selenium
Silver
Arsenic
Pyridine
Selenium
Lead
eem**
Arsenic
Cadmium
Chromium
Lead
Selenium
Silver
Mercury
Arsenic
Cadmium
Chromium
Lead
Selenium
Silver
Arsenic
Chromium
Lead
Mercury
Silver
Carbon tetrachloride
Trihalomethanes
Mercury
RMIC*. mq/kg
30
7
30
30
1
7
30
200
50
40
200
30
10
2
10
10
2
10
10
10
2
10
10
2
10
30
30
30
1
30
100
300
7
111
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Table 19. Summary of Water Treatment Chemicals CODEX (continued)
Chemical Function
Ferric chloride Coagulant
Ferric sulfate Coagulant
Ferrous sulfate Coagulant
Potassium Oxidant
permanganate
Sodium Coagulant
aluminate
Maximum
dosage, mg/1 Impurity
60 Arsenic
Cadmium
Chromi urn
Lead
Mercury
Selenium
Silver
100 Arsenic
Cadmium
Chromi urn
Lead
Mercury
Selenium
Silver
80 Arsenic
Cadmium
Chromium
Lead
Mercury
Selenium
Silver
1 0 Cadmi urn
Chromi urn
Mercury
40 Arsenic
Cadmium
Chromium
Lead
Mercury
Selenium
Silver
RMIC*. mg/kg
80
20
80
80
3
20
80
50
10
50
50
2
10
50
60
10
60
60
3
10
60
100
500
20
100
30
100
100
5
30
100
112
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Table 19. Summary of Water Treatment Chemicals CODEX (continued)
Chemical
Sodium
carbonate
(soda ash)
Sodium
chlorite
Sodium hydroxide
Sodium metabi-
sulfite, sodium
pyrosulfate
Sulfur dioxide
Sulfuric acid
Function
pH adjustment
C102 production
pH adjustment
Cl removal
Cl removal
pH adjustment
Maximum
dosage, mg/1
100
10
100
15
10
50
Impuri ty
Chromium
Lead
Mercury
Selenium
Mercury
Arsenic
Selenium
Arsenic
Selenium
Selenium
RMIC*. ing/kg
50
50
20
100
2
300
70
500
100
20
*RMIC =• recommended maximum impurity content.
**eem = ether extractable material.
Source: HAS 1982a.
113
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Table 20. Contaminants That Hay Be Introduced in the Distribution System
Component
Steel mains
Lead piping
"Metal" pipe
Copper pipe
Asbestos-cement pipe
Contaminant
Iron
Lead
Cadmium
Chromium
Manganese
Zinc
Nickel
Cobalt
Silver
Copper
Asbestos
Measured levels
0.18 - 10.2 mg/1
0.03 - 1.5 mg/1
a
a
a
a
a
a
a
0.18 - 2.3 mg/1
not detected -
>500 x 106 f/1
Plastic pipe (PVC)
and 1inings
Vinyl chloride
Metallic pigments
and lubricants
O.03 - 1.3 ug/1
Plastic pipe
solvents
Coal tar and asphalt
lining
Methyl ethyl ketone, 0.11 - 375 mg/1
cyclohexanone, tetrahydrofuran (total solvent)
N,N-dimethy1 formamide
PAHs including:
phenanthrene, anthracene,
fluoranthene, pyrene,
methyl pyrene, benzo(a)pyrene,
benzo(ghi)perylene,
i ndeno(1,2.3-cd) pyrene,
di benzo(a,h)-anthracene
<10 ng/1
to 290 ug/1
Representative quantitative data not available, but increase in concentration
within distribution system noted.
Source: NAS 1982b.
114
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5.1.3 Determination of Finished Water Quality
There are two basic components to the use of the data 1n this section
to determine whether water treatment affects the presence of a chemical,
and 1f so, what the effect 1s:
• Defining the Individual and combined processes used 1n treating
drinking water.
• Determining whether data are sufficient to support a prediction of
the occurrence or extent of chemical removal by water treatment.
The Federal Reporting Data System (FRDS) contains Information on the
types of treatment used by each water supply system 1n the U.S. For any
water supply system, therefore, the assessor may retrieve data from FRDS
on the unit processes used. From Information presented 1n Sections 2 and
5.1.1 on the probable sequence of processes, treatment schemes may be
reconstructed. Table 17 lists the treatment processes covered 1n the
FRDS; some processes Important 1n terms of contaminant removal, such as
carbon adsorption, are conspicuously missing.
In the absence of specific data on processes used, a more general
approach may apply. That approach entails the assumption that:
• Ground waters are treated by aeration, Hme-soda softening,
filtration, and chloMnatlon - 1f they are treated at all.
• Surface waters are treated by presedlmentatlon, coagulation,
flocculatlon, sedimentation for floe removal, filtration, and
chlorlnatlon.
The data 1n Table 18 may be used to Indicate, qualitatively, whether
removal may be expected for some types of chemicals and, 1n the case of
the specific substances listed, the efficiency of removal. If removal
efficiency data are not available for a substance being assessed,
quantitative results of treatment can be predicted only 1f removal 1s
closely associated with chemical properties (e.g., removal via aeration
1s related to a substance's volatility, as described by Henry's Law
constant). Otherwise, further study of the effects of treatment are
Indicated. If, however, data on process-by-process removal (such as
those 1n Table 18) are available, the calculation of finished water
concentrations 1s straightforward:
n
C =C -1C xR
F R 11
1=1
115
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where
Cp = finished water concentration
CR = raw water concentration
GI = concentration prior to entering treatment 1
R^ = removal effected by treatment 1
Calculation of finished water concentrations may not, however,
accurately represent the concentrations at the user's tap. Chlorinated
organlcs formed as a result of drinking water disinfection have been
shown to Increase through the distribution system (Smith et al. 1980).
This 1s due to the fact that the haloform reaction (and similar
reactions) may take hours, and chlorlnatlon just prior to discharge does
not allow the reaction to become complete in the treatment system.
Two additional types of toxic contamination may occur 1n the
distribution system; both are related to structural components. Metals
may be dissolved from Iron, steel, or copper pipe, especially if the
water is corrosive. Piping constructed of polyvlnyl chloride (PVC) is
used 1n homes and 1n rural community systems. Pipe joints are glued
together, and water may leach adhesives and solvents over time. There
1s, however, no means of quantifying distribution system effects at this
time. Examination of monitoring data for finished water at the treatment
plant and water in the distribution system may provide, 1f only
qualitatively, the necessary information for a particular substance.
5.2 Private Systems
Private drinking water systems are often used by individuals residing
in areas of low population density or 1n other areas where no public
drinking water supply is available. The potential for exposure to
chemical substances in private drinking water supplies may be greater
than for Individuals supplied by public drinking water. In a public
water system, the finished water 1s routinely monitored to determine
whether suspected chemicals are present. In a private water system,
monitoring of water for potential contaminants is the responsibility of
the individual using the supply.
It 1s possible for an individual to install a private water supply
without ever conducting a sanitary survey of the potential water source.
It is not uncommon for individuals to contact a health or environmental
agency to complain about illnesses in the family or strange odors or
tastes in the water only to find that their drinking water source is
116
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located too close to a source of contamination. Although state health
departments and the Environmental Protection Agency (EPA) have
established guidelines for selection of suitable private drinking water
sources, 1t 1s the responsibility of the Installers of the private
drinking water supply to follow these guidelines. The most Important
guidelines for selection of suitable private drinking water sources are
presented 1n Section 5.2.1.
The concentration of a chemical substance 1n finished drinking water
from a private supply is determined not only by the proximity of the
water to a source of contamination, but also by the efficiency of any
treatment system 1n removing chemical substances. Several alternatives
for home drinking water treatment are available. In Section 5.2.2,
Information on home drinking water treatment systems 1s presented. The
selection of a home drinking water treatment system 1s determined
primarily by chemical substances present 1n the water supply and by the
cost an Individual 1s willing to bear.
5.2.1 Guidelines for Selection of Suitable Private Drinking Water Sources
Guidelines for the selection of a suitable private drinking water
supply have been outlined for ground water supplies and surface water
supplies by the EPA's Office of Drinking Water. Table 21 lists the
essential factors that should be considered 1n a sanitary survey of
ground water supplies; Table 22 lists factors for surface water supplies
(USEPA 1974).
When a properly constructed well penetrates an unconsolldated
formation with good filtering properties, and when the aquifer Itself 1s
separated from sources of contamination by Impervious materials, research
and experience have demonstrated that 50 feet 1s an adequate distance
separating a contamination source and a well (USEPA 1974). In cases
where sources are severely limited, however, a ground water aquifer that
might become contaminated may be considered for a water supply 1f
treatment 1s provided (USEPA 1974). Lesser distances should be accepted
only after a comprehensive sanitary survey, conducted by qualified state
or local health agency officials, has satisfied the officials that such
lesser distances are both necessary and safe. Conditions that are
unfavorable to the control of contamination and that may require
specifying greater distances between a well and sources of contamination
are presented 1n Table 23.
5.2.2 Home Drinking Water Treatment Systems
The systems most frequently available for use 1n treating drinking
water 1n the home Include (1) filtration units containing activated
carbon; (2) distillation units; and (3) water softening units. Other
117
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Table 21. Essential Factors That Should Be Considered in a Sanitary Survey
of Ground Water Supplies
• Character of local geology; slope of ground surface.
• Nature of soil and underlying porous strata; whether clay, sand, gravel, rock
(especially porous limestone); coarseness of sand or gravel; thickness of
water-bearing stratum; depth to water table; location, log, and construction
details of local wells in use and abandoned.
• Slope of water table, preferably as determined from observational wells or as
indicated, presumedly but not certainly, by slope of ground surface.
• Extent of drainage area likely to contribute water to the supply.
• Nature, distance, and direction of local sources of pollution.
• Possibility of surface-drainage water entering the supply and of wells
becoming flooded; methods of protection.
• Methods used for protecting the supply against pollution by means of sewage
treatment, waste disposal, and the like.
• Well construction:
1. Total depth of wel1.
2. Casing: diameter, wall thickness, material, and length from surface.
3. Screen or perforations: diameter, material, construction, locations, and
lengths.
4. Formation seal: material (cement, sand, bentonite, etc.), depth intervals,
annular thickness, and method of placement.
• Protection of well at top: presence of sanitary well seal, casing height above
ground, floor, or flood level, protection of well vent, protection of well from
erosion and animals.
• Pumphouse construction (floors, drains, etc.), capacity of pumps, drawdown when
pumps are in operation.
• Availability of an unsafe supply, usable in place of normal supply, hence
involving clanger to the public health.
Source: USEPA 1974.
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Table 22. Essential Factors That Should Be Considered in a Sanitary Survey
of Surface Water Supplies
• Nature of surface geology: character of soils and rocks.
• Character of vegetation, forests, cultivated and irrigated land, including
salinity, effect on irrigation water, etc.
• Population and sewered population per square mile of catchment area.
• Methods of sewage disposal, whether by diversion from watershed or by treatment.
• Character and efficiency of sewage-treatment works on watershed.
• Proximity of sources of fecal pollution to intake of water supply.
• Proximity, sources, and character of industrial wastes, oil field brines, acid
mine waters, etc.
• Adequacy of supply as to quantity.
• For lake or reservoir supplies: wind direction and velocity data, drift of
pollution, light intensity data (algae).
• Character and quality of raw water: coliform organisms (HPN), algae, turbidity,
color, objectionable mineral constituents.
• Nominal period of retention in reservoir or storage basin.
• Probable minimum time required for water to flow from sources of pollution to
reservoir and through reservoir intake.
• Shape of reservoir, with reference to possible currents of water, induced by
wind or reservoir discharge, from inlet to water-supply intake.
• Protective measures in connection with the use of watershed to control fishing,
boating, landing of airplanes, swimming, wading, ice cutting, permitting animals
on marginal shore areas and in or upon the water, etc.
• Efficiency and constancy of policing.
• Treatment of water: kind and adequacy of equipment; duplication of parts;
effectiveness of treatment; adequacy of supervision and testing; contact period
after disinfection; free chlorine residuals carried.
• Pumping facilities: pumphouse, pump capacity and standby units, storage
facilities.
Source: USEPA 1974.
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Table 23. List of Conditions Unfavorable to the Control of Contamination
and That Hay Require Specifying Distances Greater than 50 Feet
for Siting of Wells
Nature of the contaminant. Human and animal excreta and toxic chemical wastes
are serious health hazards. Salts, detergents, and other substances that
dissolve in water can mix with ground water and travel with it. They are not
ordinarily removed by natural filtration.
Deeper disposal. Cesspools, dry wells, disposal and waste injection wells, and
deep leaching pits that reach aquifers or reduce the amount of filtering earth
materials between the wastes and the aquifer increase the danger of
contamination.
Limited filtration. When earth materials surrounding the well and overlying the
aquifer are too coarse to provide effective filtration - as in limestone, coarse
gravel, etc. - or when they form a layer too thin, the risk of contamination is
increased.
The aquifer. When the materials of the aquifer itself are too coarse to provide
good filtration - as in limestone, fractured rock, etc. - contaminants entering
the aquifer through outcrops or excavations may travel great distances. It is
especially important in such cases to know the direction of ground water flow
and whether there are outcrops of the formation (or excavations reaching it)
"upstream" and close enough to be a threat.
Volume of waste discharged. Since greater volumes of wastes discharged and
reaching an aquifer can significantly change the slope of the water table and
the direction of ground water flow, it is obvious that heavier discharges can
increase the threat of contamination.
Contact surface. When pits and channels are designed and constructed to
increase the rate of absorption - as in septic tank leaching systems, cesspools,
and leaching pits - more separation from the water source will be needed than
when tight sewer lines or waste pipes are used.
Concentration of contamination sources. The existence of more than one source
of contamination contributing to the general area increases the total pollution
load and, consequently, the danger of contamination.
Source: USEPA 1974.
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less frequently used systems available for treating drinking water 1n the
home Include reverse osmosis units, magnetic units, ozonator carbon
units, and units that combine ultraviolet light with activated carbon.
All of these systems can be Installed by users of private or public water
supplies. Information on filtration units containing activated carbon 1s
presented 1n Subsection 5.2.2(1). Information on distillation units 1s
presented 1n Subsection 5.2.2(2), and Information on water softeners 1s
discussed 1n Subsection 5.2.2(3). Lesser-known systems available for
home water treatment are discussed 1n Subsection 5.2.2(4).
(1) Home drinking water treatment units containing activated carbon
for organlcs reduction. Filtration units containing activated carbon are
of several types. These types Include: (1) pour-through, (2) faucet
bypass, (3) faucet no-bypass, (4) stationary, and (5) line bypass
(Changing Times 1981). Pour-through units are portable and require no
Installation. The user holds the filter over a receptacle and pours tap
water Into the top. Faucet filters are of two designs and fit onto the
mouth of the tap. The faucet bypass design has a bypass valve which
allows water used only for cooking and drinking to be filtered, thereby
prolonging the life of the filter. The faucet no-bypass design filters
all water that flows through the tap. Stationary types are tapped Into
the cold water pipe under the sink so that all the water flowing through
the pipe 1s filtered. Line bypass types are also Installed by cutting
Into the water line beneath the sink, but they use a separate faucet
attached to the sink to deliver filtered water for drinking and cooking.
Unflltered water can still be drawn from the regular faucet.
According to Russo (1978), filtration units containing activated
carbon remove algae, carbon tetrachloride, chlorine, chloroform, dirt
particles, hydrogen sulflde, Iron 1n suspension (rust), and sulfur. The
effectiveness and longevity of a carbon filter depend partly on Its
design, the quality and amount of filtering material, the volume of water
passing through 1t, and the length of time the water 1s 1n contact with
the filter. The efficiency of 31 carbon filtration units 1n removing
trlhalomethanes (THMs) and non purgeable total organic carbons (NPTOCs)
was tested for the EPA, Office of Drinking Water (ODW), by Gulf South
Research Institute. Trlhalomethanes are formed by the reaction of
chlorine with organic materials in water. NPTOCs include harmless
organic matter as well as residues of DDT and other pesticides. Most of
the units tested are designed to do nothing more than improve the water
aesthetically by removing taste and odor, but they were tested for THM
and NPTOC removal anyway. The water used in the study was New Orleans
city tap water from the Mississippi River, chosen partly because of the
challenge its array of pollutants and organic materials presented to the
filters (Changing Times 1981; USEPA 1980b). Table 24 presents the
results of these tests regarding the efficiency of home filters in
removing THMs and NPTOCs according to type of activated carbon treatment
unit. In general, the line bypass types of activated carbon units were
the most efficient in removing THMs and NPTOCs.
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Table 24. Efficiency of Home Drinking Water Treatment Units Containing
Activated Carbon in Removing Tribalomethanes (THMs) and
Nonpurgeable Total Organic Carbon (NPTOCs)
Type
Pour-through
Test life Average reduction, %
Product (gallons) THM NPTOC
Filbrook Pour-Thru 1,000 40*
Activated Carbon
H2OK Portable Drinking 2,000 19
Water Treatment Unit
Puriton Bacteriostatic 1,000 21
14
10
6
Drinking Water Treatment
Unit
Faucet bypass Aquaguard, Model AGT-31 500
Cartridge T-3XL
Concept Bacteriostatic 40
Home Water Filter
Filter Fresh Model FF-1
Hurley Town and Country
Instapure Model Fl-C
Water Washer, Countertop
Model 1000
Faucet no-bypass Mini Aqua Filter
Stationary AMF-Cuno Housing 1M
Cartridge AP-117
Filterite, Model 1 PC
Cartridge 1C-9
Fulfo Water Filter Model
WC-10
Keystone Model 3121
Housing with Model 310
Cartridge
Sears Taste and Odor Filter 3,420
43
16
12
18
1,200
4,000
200
1,000
200
3,000
3,000
3,000
3,000
6
69
24
41
6
34
18
15
21
6
31
11
11
2
7
8
11
9
46
12
122
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Table 24. (continued)
Test life
Type Product (gallons)
Line bypass Aquacell Bacteriostatic
Water Treatment Unit
Aqualux Water Processor,
Model CB-2
Aqualux Water Processor,
Model HB
Argenion Bacteriostatic
Water Treatment Unit,
Model 1
Continental Water Filter,
Model 350**
Culligan Super Guard,
Model SG-2
Everpure, Model QC4-THJM
Mariner Renaturalizer
Water Units
Polarisdynamic Water Unit
Purogen Water Detoxifier
Seagull IV
System 1 Water Processor,
Model SY1-34
Ultrapure Bacteriostatic
Waterco, Model AS-5
2,000
2,000
2,000
2,000
720
4,000
1,000
3,000
2,500
2,500
1,600
2,500
3,000
3,000
Average reduction, %
THM NPTOC
86
98
45
23
99
89
99
47
61
38
70
43
40
25
23
23
28
—
87
28
55
21
18
6
30
20
20
123
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Table 24. (continued)
Type
Product
Test life Average reduction, %
(gallons) THM NPTOC
Others
Rohm and Haas Ambersorb 3,500
XE-340***
93
Wunderbar Portable Water
Cleaner-Filter
200
* According to EPA the Filbrook was tested for 1,000 gallons, based on comparable life
to other pour-through units. However, EPA says that sales literature can be
interpreted to indicate a lifetime of 300 gallons, for which the average reduction
would be 741.
** Not widely available.
*** Experimental
- Information not available
Source: USEPA 1980b.
124
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In another phase of the study, four tests were conducted to determine
the effectiveness of home drinking water treatment units containing
activated carbon 1n removing organlcs {USEPA 1982c). The first test was
conducted using ground water samples spiked with four organic compounds.
The second test was conducted to evaluate the effects of differing water
quality on the performance of typical carbon units. Four home water
treatment models were tested using the drinking water 1n four cities:
Miami, Florida; P1co Rivera, California; Atlanta, Georgia; and Detroit,
Michigan. The third test was conducted to evaluate the performance of
units under nonaccelerated home use conditions. Three filter types of
activated carbon units were tested with New Orleans tap water 1n three
different homes. The fourth test was conducted using surface water
samples spiked with the four organlcs used 1n the ground water test and
three pesticides.
The results of the tests to determine the effectiveness of home units
1n reducing levels of four organic compounds 1n spiked ground water
samples are presented 1n Table 25. Carbon tetrachlorlde reduction ranged
from 55 percent for a faucet-mount unit to 99 percent for four-line
bypass units. Trlchloroethylene reduction ranged from 70 percent for a
faucet-mount unit to 99 percent for four Une-bypass units.
Tetrachloroethylene reduction ranged from 62 percent for a faucet-mount
unit to 99 percent for four Une-bypass units. 1,1,l-Tr1chloroethane
reduction ranged from 40 percent for a faucet-mount unit to 99 percent
for three Une-bypass units.
The results of the tests to evaluate the effects of differing water
quality on the performance of typical carbon units yielded filter
efficiencies for reducing THMs and NPTOCs comparable to laboratory tests
with New Orleans drinking water. The USEPA (1982c) reported that the
field test tends to confirm the validity of the central laboratory
testing as being generally representative of a unit's performance on
various waters.
The results of the tests to evaluate the performance of typical
activated carbon units for removal of THMs and NPTOCs under
nonaccelerated home use conditions were similar to the GSRI laboratory
results obtained with New Orleans drinking water, with the exception of
one unit which gave lower results in the home test for THM reduction.
USEPA (1982c) reported that the home tests generally confirmed the
validity of laboratory testing as representing efficiencies and
conditions obtained under actual use conditions in a home.
The results of the test to determine the effectiveness of home units
in reducing the levels of four organlcs and three pesticides 1n spiked
surface water samples are questionable. These data are presented in
Table 26. USEPA (1982c) reports that data for reductions of three
pesticide chemicals were probably indicative of the value of activated
carbon units for reducing these chemicals.
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Table 25. Range of Percent Specific Halogenated Organic (HO) Reduction for Line Bypass,
Faucet-Mount, Stationary, and Pour-Through Units in the Ground Water Study
Unit
Rated capacity
(gal Ions/liters)
Range of average percent HO reduction*
Line Bypass
Aqualux CB-2
Continental Model 350
Culligan Model SG-2
Everpure QC4-THM
Seagull IV
Aquacell
Faucet-Mount
2000/7571
720/2725
4000/15142
1000/3785
1000/3785
2000/7571
99-99
99-99
99-98
99-99
98-95
99-93
98-86
99-99
99-98
95-99
98-97
99-95
99-99
99-99
99-99
99-99
98-97
99-98
99-99
99-99
99-99
99-99
98-97
99-97
Hurley Town and Country
Water Washer Model 1000
4000/15142
1000/3785
99-93
96-40
97-94
95-55
99-98
95-70
99-99
99-62
Pour-Through
Filbrook**
300/1136
99-72
98-82
95-94
99-98
Stationary
Sears Taste and Odor
3000/11356
98-70
98-80
99-96
99-98
1
2
3
4
*
1,1,1-Trichloroethane
Carbon tetrachloride
Trichloroethylene
Tetrach1oroethy1ene
Range in reduction indicates gradual decline in effectiveness with time; best removals were
obtained when filter was first installed.
Filbrook was tested for 500 gallons, but results are adjusted to 300 gallons as being more
representative of claimed lifetime.
Source: U.S. EPA 1982c.
126
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Table 26. Range of Percent Specific Halogenated Organic (HO) Reduction for Line Bypass
Faucet-Mount, Stationary, and Pour-Through Units in the Surface Water Study
Unit
Rated capacity
(gallons/liters)
Range of average percent HO reduction*
Line Bypass
Aqualux CB-2
Continental Model 350
Culligan Model SG-2
Everpure QC4-THM
Seagull IV**
Aquacel1
Faucet-Mount
Hurley Town and Country
Water Washer Model 1000
Pour-Through
Filbrook***
Stationary
Sears Taste and Odor
2000/7571
720/2725
4000/15142
1000/3785
1000/3785
2000/7571
4000/15142
1000/3785
300/1136
3000/11356
99-90
95-95
77-89
99-99
99-99
99-96
99-92
99-60
99-75
79-88
99-54
85-95
99-45
99-99
99-99
99-80
99-50
50-20
99-40
51-30
99-98
99-99
95-83
99-99
99-98
99-89
99-79
96-60
99-45
78-35
p-Dichlorobenzene
Hexachlorobenzene (Cgd5)
Chlordane (Technical grade, 601)
Range in reduction indicates gradual decline in effectiveness with time; best removals were
obtained when filter was first installed.
** Units plugged prematurely
*** Filbrook was tested for 500 gallons, but results are adjusted to 300 gallons as being more
representative of claimed lifetime.
;ource: USEPA 1982c.
127
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A factor not considered 1n the 6SRI studies performed by EPA 1s the
desorptlon of organlcs by activated carbon filters. This "chromato-
graphlc effect," or breakthrough, commonly occurs soon after the capacity
of the adsorbant has been exhausted (Taylor et al. 1979). The
chromatographlc effect has been well documented 1n full-sized columns,
but has not been studied extensively 1n home filters. It 1s believed by
Taylor et al. (1979) and others that homeowners not replacing filter
cartridges as often as recommended may receive exposure to organic
chemicals at levels higher than those 1n the water prior to treatment.
(2) Home Distillation Units. Distillation 1s another method that
can be used 1n home water treatment to remove undesirable substances.
During the process of distillation, one liquid 1s separated from another
liquid or solid by way of vaporization and condensation. The boiling
water vaporizes leaving behind most of the solids previously contained 1n
the liquid. The mere separation of liquids from solids does not require
a very complex distillation apparatus. The removal of volatlles by
distillation, however, 1s a more difficult feat. If the distillation
apparatus 1s not properly adjusted, volatile organlcs may vaporize with
the water and condense 1n the distillate 1n a highly concentrated form.
For example, 1t 1s possible that THMs present 1n water running through a
poorly operating still can be present 1n the finished product at ten
times their concentration 1n the undlstllled solution (Mother Earth
News 1980a). Some distillers have no distillation column and, therefore,
are not capable of extracting more than one volatile at one operating
temperature (Mother Earth News 1980a). Other distillers are capable of
fractional distillation but require precise adjustment of the
temperatures to do the job they are capable of (Mother Earth
News 1980a). Still other distillers are so automated that the operator
has little control over the distillation temperature (Mother Earth
News 1980a). According to the chemistry reports available from the firm
that manufactures this highly-automated model, this distiller has been
designed to efficiently remove chloroform.
Tests to determine the efficiency of removal of carbon tetrachlorlde,
trichloroethylene, tetrachloroethylene, 1,1,1-trichloroethane,
p-dichlorobenzene, hexachlorobenzene, and chlordane by two distillers
were recently conducted for the EPA, ODW, by Gulf South Research
Institute during the third phase of the study (USEPA 1982c). These data
were, however, discarded because an organic solvent was used, thereby
invalidating the results. Consequently, no quantitative information is
available on the efficiency of select distillers for removing organlcs
from water. As a final note, distillers may also remove beneficial
substances (such as essential minerals) from drinking water.
(3) Home Water Softeners. Although water can be softened in a
number of ways, for the home water supply, the ion-exchange process is
the most commonly used method (Clarke et al. 1977). The Ion-exchange
128
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process Involves the exchange of calcium and magnesium Ions, which harden
water, for sodium Ions, which soften water (see Sections 2 and
5.1.1(2)). The exchange 1s accomplished by a device called a water
conditioner or water softener, and the device consists of a tank filled
with a natural or synthetic mineral or a synthetic resin.
There has recently been concern about the potential adverse health
effects associated with soft water. Part of this concern 1s due to the
effects the additional sodium may have on Individuals on
sodium-restricted diets. Another part of this concern 1s the Indication
1n several studies of an Inverse correlation between Incidence of
cardiovascular disease 1n humans and routine consumption of hard water.
The USEPA (no date) recommends that when water must be softened, because
of laundry or scaling problems, only the water being supplied to the
water heater should be softened, hard water should be used for drinking
and cooling. Persons concerned with sodium Intake often practice split
softening; others may do so as well. The advantages to consumers of
softening only heated water are twofold: (1) a smaller, less-costly
softener 1s needed, and (2) problems associated with too-soft water
(e.g., soap removal) are mitigated by mixing hard (cold) and softened
(hot) water to produce a moderately hard mixture.
(4) Less frequently used systems for treatment of home drinking
water. Among the less frequently used systems available for treating
drinking water 1n the home are (1) reverse osmosis units; (2) magnetic
units; (3) ozonator carbon units; and (4) units that combine ultraviolet
light with activated carbon.
Reverse-osmosis or membrane filters require a cartridge filter to
pre-clean the water and prevent clogging. The reverse-osmosis type of
filter uses a semi permeable cellulose acetate membrane which, under
normal water pressure, allows the passage of water molecules but rejects
impurities (Coffee 1977, Mother Earth News 1980b). According to Russo
(1978), reverse-osmosis filters are capable of removing arsenic,
asbestos, barium, cadmium, chromium, coliform bacteria, cyanide, Iodine,
iron 1n solution, lead, mercury, selenium, silver, other heavy metals,
and radioactive elements.
Magnetic units are particularly effective in removing substances by
promoting clumping of particulate matter 1n the liquid, thereby causing
it to fall out of suspension; these units are not very effective 1n
reducing volatile chemicals present in water (Mother Earth News 1980b).
Ultraviolet light units have no effect on suspended particles or
dissolved volatile compounds. Consequently, they are also equipped with
activated carbon filters which are useful for removing these substances.
129
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The research by Gulf South Research Institute (USEPA 1982c) that was
discarded because an organic solvent was used, thereby Invalidating the
results, Included tests of reverse osmosis and ozonator carbon units.
Consequently, no quantitative Information 1s available on the efficiency
of select reverse-osmosis units and ozonator units for removing organlcs
from water. No attempts to test the efficiency of reverse-osmosis units
for removing heavy metals and other substances have been conducted.
130
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6. EXPOSED POPULATIONS
Studies of populations exposed to chemical substances via drinking
water comprise three basic elements:
• Identification of exposed populations
• Enumeration of exposed populations
• Characterization of exposed populations according to age and sex.
Identification relies on Information produced earlier 1n the methods
report: examination of the sources of the chemical substance. Source
examination allows the Identification of the affected raw or finished
drinking water supplies. The population that consumes this water 1s the
exposed population. Once Identified, the exposed population can be
enumerated and characterized by the population enumeration techniques
presented 1n Volume 4 (Section 6) (I.e., Methods for the Enumeration and
Characterization of Populations Exposed to Chemical Substances) of this
series. This section will summarize the population methods report and
Indicate how 1t fits Into the overall assessment.
6.1 Identification of Exposed Populations
Exposed populations can be Identified either through knowledge of the
sources of chemical contamination or by examination of monitoring data.
The former can be divided Into three types of sources:
1. Sources that can be geographically defined (e.g., Industrial
effluents, waste disposal site leachate, and non-point sources of
water pollutlon).
2. Sources related to the treatment processes used 1n production of
finished drinking water (e.g., use of chemicals as coagulant aids
and for disinfection).
3. Sources arising from the distribution system (e.g., dissolution of
solvents from glued pipe joints).
Monitoring data, as discussed 1n Subsection 4.1, may Identify water
supplies with contamination of unknown origin.
Comprehensive Identification must consider all three source types as
well as available monitoring data. Volume 2 of this series (I.e.,
Ambient Volume) catalogs data bases and discusses and presents methods
for Identifying geographically defined sources of chemical
contamination. Sources of contamination related to drinking water
treatment processes and distribution systems are discussed 1n Section 5
of this volume.
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Sources of contamination, having been Identified, must then be keyed
to water supplies, whether raw or finished, and to the consumers of those
supplies. Consumers may be Identified according to specific utilities
when the contamination 1s geographically limited, or according to supply
type (I.e., surface vs ground) and treatment processes when the source
contamination 1s widespread. The following subsection briefly discusses
enumeration of the exposed population.
6.2 Enumeration of Exposed Populations
There are three basic approaches for enumeration; the procedure of
choice depends on how the exposed population has been Identified and the
financial and manpower resources available:
1. Direct contact with the ut1!1ty(s) that use the contaminated water
supply
2. Use of the computerized water supply Inventories of either the EPA
Office of Drinking Water (FRDS) or EPA Monitoring and Data Support
Division (WSDB)
3. Use of generic data on population served and water supply (ground
or surface), treatment, and distribution system type.
Each of these approaches 1s described 1n detail in Volume 4
(Section 6) of this series. Basically, however, direct utility contact
will supply the most accurate and up-to-date Information. The utilities
to be contacted should be clearly defined and relatively limited so that
the effort remains within the scope of available resources. It may be
necessary to use one of the computerized inventories (WSDB and/or FRDS)
to assemble a 11st of the utilities to be contacted.
The two drinking water supply inventories, discussed in detail in
Section 3 of this volume, Include as one of the data elements the
population served by the utility. Both data bases can be used to
enumerate populations that consume surface supplied water; however, only
FRQS has data on populations who derive drinking water from ground water
supplies.
The population data 1n FRDS is much more accurate than the same data
in WSDB. FRDS is updated yearly and thus reflects the population data
collected by individual states the previous year. FRDS population data
can be retrieved according to the following:
132
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• EPA Region
• State
• County
• City or utility.
An PROS retrieval may be further restricted according to ground water
or surface water and according to treatment process(es). Retrievals for
specific geographic categories should exclude utilities that purchase
their water supply from other utilities. These utilities are designated
with a P code 1n the PROS Inventory.
The utilities that sell drinking water, either raw or finished, to
other utilities Include the population of the purchasing utility 1n their
total population figures. This retrieval restriction, therefore, will
prevent counting populations twice.
Finally, populations that obtain their drinking water from household
wells may be approximated by retrieving all populations served by public
or private systems for the geographic category of Interest, as listed
above, and subtracting this total from the total population of the
geographic category as recorded 1n the 1980 Census of Population.
Retrievals from the PROS Inventory should be directed to:
Mr. Avrum Marks
Manager-Computer Systems Staff
EPA-Off1ce of Drinking Water
401 M Street, S.W.
Washington, DC 20460
(202) 382-5513
The population data Included 1n the WSDB Inventory contain two levels
of accuracy. The data for surface water utilities that serve populations
greater than 25,000 are very accurate, reflecting Information obtained
via direct phone contact with these utilities 1n 1981 (Versar 1981). The
data for surface water facilities serving fewer than 25,000 were
collected from a nationwide Inventory conducted 1n the late 1960s and
early 1970s (Versar 1981).
The major advantage 1n using the WSDB Inventory for retrieving
population data 1s the Integrated assessment approach to Identifying
Industrial and POTW sources of contamination, affected surface water
supplies, US6S gages which contain flow data, and the municipal or
private systems that use the affected surface water as raw water supply.
This approach, the retrieval categories and applicable programs, and the
EPA office to which retrievals should be directed are discussed 1n detail
133
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1n Subsection 3.1. To obtain the most accurate accounting of exposed
populations, a comprehensive exposure assessment should access the
population data contained 1n both EPA drinking water supply Inventories.
Exposed populations may also have to be enumerated by the use of
generic data on population served and water supply, treatment, and
distribution system type. This approach 1s applicable when the sources
of contamination are widespread and no specific water supplies are
Identified. The population methods report (Volume 4, Section 6) has
generic data on population served by water supply type, treatment
process, and distribution system materials.
Finally, a rather crude system of enumerating exposed populations
based on the use of sample monitoring data can be used. The method
extrapolates data on the frequency of detection of the substance. It 1s
described 1n detail 1n Volume 4. The method, however, should only be
used 1n the absence of more refined data.
6.3 Characterization of Exposed Populations
Drinking water Intake rates are a function of the Individual's age
and sex as described 1n the following section. In order to obtain a
precise exposure distribution, therefore, the exposed population must be
characterized according to age and sex. If the chemical substance of
Interest has special effects on particular age classes such as the
elderly or children, further characterization of the enumerated
population 1s Indicated. It 1s also possible, for example, that a
chemical substance 1s determined to be teratogenlc; enumeration of women
of chlldbearlng age may be then required.
The simplest and most rapid method of characterizing a large
population 1s to assume that the age and sex distributions approach those
of the total U.S. population. Volume 4, Section 2, of this series has
data depicting the age and sex distribution by percent for the total U.S.
population. Characterization within specific geographic areas, such as
states, counties, cities and townships, involves the use of Bureau of
Census publications also described 1n Volume 4, Section 2.
134
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7.
CALCULATION OF EXPOSURE
Human exposure via contact with drinking water may occur through
three exposure routes: 1ngest1on, dermal contact, and Inhalation. Of
these, the first 1s usually considered the most significant, through the
latter two (dermal contact and Inhalation) may be Important 1f the
chemical being assessed has certain physical/chemical properties.
Calculating exposure for each of the three possible routes 1s discussed
below.
7.1
Ingestlon Exposure
To calculate the annual rate of exposure to an Individual as a result
of Ingesting chemical substances 1n drinking water, three Items of
Information are necessary: (1) the concentration of the chemical
substance 1n drinking water expressed 1n mg/1 or ug/1, (2) the dally rate
of Intake of drinking water 1n I/day or 1/kg/day, and (3) the number of
days per year the Individual consumes water from the source containing
the chemical substance. The annual exposure rate, as calculated below,
1s expressed 1n mg/year, ug/year, mg/kg/year, or ug/kg/year:
E = I x C
where
E = exposure 1n mass/time or mass/unit body weight/time
I = Intake rate, 1n volume/time or volume/unit body weight/time
C = concentration of chemical substance 1n mass/volume.
The accepted standard drinking water Intake rate 1s 2 liters per day (NAS
1977, USEPA 1980). It must be noted that the Intake rate for drinking
water and the corresponding volume consumed vary with age and sex; these
Intake rates and corresponding volumes consumed are presented 1n Table 28.
The example that follows Illustrates how the annual rate of exposure
to an Individual as a result of Ingesting chemical substances 1n drinking
water 1s obtained.
A drinking water supply contains chloroform at a concentration of 50
ug/1. A 1-year old male of median weight for his age group drinks all
of his water from this supply 365 days per year. What Is the extent
of this Individual's annual chloroform exposure?
135
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To calculate exposure, consult the data provided 1n Table 27.
According to this table, a 1-year old male consumes .25 1/kg/day of
drinking water. For a 1-year old male of median weight, this
corresponds to 2.03 I/day. The annual drinking water Intake rate 1s
obtained by multiplying the concentration of chloroform by the
drinking water Intake rate by the number of days the drinking water 1s
consumed per year as follows;
(50 ug/l)(.25 l/kg/day)(365 days/year) = 4,563 ug/kg/year
A 1-year old male of median weight weighs 10.1 kg. Multiplying
10.1 kg by 4,563 ug/kg/year yields a resultant exposure to this
Individual of 56,086 ug/year or 56 mg/year.
In deriving exposure values, one may wish to take Into account the
possibility that an Individual may use drinking water from more than one
source. For example, at home the Individual may use a private source of
drinking water, but at work a public source may be used. Another
possibility 1s that at home an Individual may use a public source of
drinking water, but at work another public source may be used. Taking
these factors Into consideration would require that separate assessments be
performed for each source of drinking water for an Individual.
7.2 Dermal Exposure
Dermal absorption of pollutants may occur as a result of contact with
potable water during showering, bathing, housecleanlng, dishwashing, etc.
The relative significance of this exposure route varies by chemical. It 1s
often disregarded, but Brown et al. (1984) recently estimated that dermal
exposure can comprise from 29 to 91 percent of the dally dose of I1poph1l1c
(I.e., high log Kow) compounds, with an average of 64 percent.
The method used by Brown et al. (1984) was similar to that discussed 1n
detail by Scow et al. (1979). Data requirements Include concentration of
contaminant 1n water, a permeability constant (chemical-specific), duration
of exposure, and body surface area exposed. Pick's law 1s the basis of the
method. Scow et al. (1979) presents permeability constants and some data
on duration and frequency of water-contact activities. Volume 7 of this
series presents detailed Information on body surface areas.
7.3 Inhalation Exposure
Inhalation exposure can occur when a chemical volatilizes from drinking
water or when the water becomes a mist or aerosol with droplets of
resplrable size. The volatility of a compound determines, in large part,
the significance of this exposure route. No sophisticated exposure
assessment methods have been created, though screening-level calculation
may proceed as described below.
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Table 27. Drinking Water Intake Rates and Volumes Consumed by Age and Sex
I/kg/day3
Age
Birth
6 mos.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18-74
18-24
25-34
35-44
45-54
55-64
65-74
Male
.26
.26
.25
.22
.20
.18
.16
.13
.11
.08
.06
.04
.04
.04
.04
.04
.04
.04
.04
.03
.03
.03
.03
.03
.03
.03
Female
.21
.21
.20
.18
.16
.14
.13
.11
.09
.07
.05
.04
.04
.04
.04
.03
.04
.04
.04
.02
.02
.02
.02
.02
.02
.02
50th Percentile weight
in kilograms'*
Male
3.40
7.82
10.10
12.57
14.61
16.55
18.70
20.84
23.54
26.30
29.31
32.96
36.90
40.37
46.74
52.93
59.87
64.93
68.30
69.0
69.7
69.5
69.2
68.8
68.2
67.3
Female
3.25
7.20
9.57
11.97
13.95
15.99
17.90
20.12
22.49
25.16
27.95
31.42
35.71
41.91
46.45
50.74
52.85
53.85
55.05
63.7
64.3
64.0
64.1
63.7
62.8
62.3
I/day
Male
0.88
2.03
2.53
2.77
2.92
2.98
2.99
2.71
2.59
2.10
1.76
1.32
1.48
1.61
1.87
2.12
2.39
2.60
2.73
2.07
2.09
2.09
2.08
2.06
2.05
2.02
Female
0.68
1.51
1.91
2.15
2.23
2.24
2.33
2.21
2.02
.76
.40
.26
.43
.68
.86
.52
2.11
2.15
2.20
1.27
1.29
1.28
1.28
1.27
1.26
1.25
a USEPA 1982d.
b USDHEW 1977; 1979.
137
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This exposure route 1s most likely to become Important when the water
1s heated and dispersed as a mist; such may be the case during a shower.
An example screening calculation for dally exposure to a volatile compound
(e.g., a chemical substance with a vapor pressure >10~3 mm of Hg @ 20°C
(Lyman et al. 1982)) 1s as follows:
Amount of water used = 5 gal/m1n (Richards 1981)
x 10 minutes/shower (assumed)
= 50 gallons (190 liters)
Concentration
Loading
A1r concentration
(simple dilution)
= 50 ug/1 (assumed)
= 50 ug/1 x 190 1 = 9500 ug
(assuming all volatilizes)
9500 ug
2 x 3 x 2 m bathroom
9500 uq
12 ma
= 790 ug/m3
Exposure
= 790 ug/m3 x 1 m/hr (Inhalation rate)
x 0.33 hr (assumed duration In bathroom)
= 260 ug/day (assuming one shower per day)
The above approach provides a rough approximation of exposure. A
detailed analysis requires use of the chemical's physical-chemical
properties and Hquld-alr mass transfer coefficients to predict
inhalation concentrations. This type of analysis is outside the scope of
this report; Information and estimation techniques, however, may be
obtained from Lyman et al. (1982).
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8. REFERENCES
ASCE. 1967. American Society of C1v1l Engineers. Water treatment plant
design. New York, NY: American Water Works Association.
AWWA. 1979. American Water Works Association. News of the field . . .
update. J. Amer. Water Works Assoc. 71(9).
Bellar TA, Llchtenberg JJ, Kroner RC. 1974. The occurrence of
organohalldes 1n chlorinated drinking waters. J. Amer. Water Works
Assoc. 66:703.
Bennett GO. 1979. Regional ground water systems analysis. Water
Spectrum 811:36-40.
Blanck CA. 1979. Trlhalomethane reduction 1n operating water treatment
plants. J. Amer. Water Works Assoc, 71(9):525-528.
Bonazountas M, Wagner JM. 1981. "SESOIL" - A seasonal soil compartment
model. Washington, DC: U.S. Environmental Protection Agency. Contract
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147
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1272-101
!EPORT DOCUMENTATION IMPORT NO. 2.
PAGE EPA 560/5-85-004
Title and Subtitle
Methods for Assessing Exposure to Chemical Substances -
/olume 5: Methods for Assessing Exposure to Chemical Substances
in Drinking Water
Author(s) Douglas A. Dixon, Stephen H. Nacht, Gina H. Uixon,
Patricia Jennings, Thomas A. Faha
Performing Organization Name and Address
'ersar Inc.
>850 Versar Center
ipringfield, Virginia 22151
, Sponsoring Organization Name and Address
nited States Environmental Protection Agency
'ffice of Toxic Substances
xposure Evaluation Division
ashinaton. D.C. 20460
3. Recipient's Accession No.
5. Report Date
8/85
6.
8. Performing Organization Rept. No.
10. Project/Task/Work Unit No.
Task 12
11. Contract(C) or GrantCG) No.
(C) EPA 68-01-6271
(G)
13. Type of Report & Period Covered
Final Report
14.
Supplementary Notes
PA Project Officer was Michael A. Callahan
PA Task Manager was Stephen H. Nacht
Abstract (Limit: 200 words)
This report, one of a series of reports concerning exposure assessment, describes
ethods for estimating exposure to chemical substances via drinking water. The report is
rganized to reflect the framework or flow of required information. Section 2 provides_an
verview of drinking water systems and the pathways of exposure to chemical substances in
rinking water, from the source of the substance through the treatment and distribution
/stems to the consuming population. Section 3 catalogues and discusses the various data
ises and information sources that aid in the identification of contaminated drinking
iter supplies. Section 4 presents and discusses methods and simulation models that can
2 used, to estimate the concentration of chemical substances in both surface and ground
iter. Section 5 discusses drinking water treatment systems and processes, the effect the
/stems and processes have on different types of chemical substances, and how the infor-
ition can be used to predict the concentration of a chemical substance in finished
-inking water. Section 6 briefly discusses the enumeration and characterization of ex-
)sed populations; detailed information on this subject is provided in Volume 4 of this
;ries. Finally, Section 7 discusses the procedures for calculating exposure as a result
: contact with contaminated drinking water.
locument Analysis a. Descriptors
Identifiers/Open-Ended Terms
Exposure Assessment/Drinking Water
Toxic Substances/Drinking Water Treatment
COSATI Field/Group
• liability Statement
Distribution unlimited
19. Security Class (This Report)
Unclassified
20. Security Class (This Page)
Unclassified
21. No. of Pages
147
22. Price
SI-Z39.18)
See Instructions on Reverse
OPTIONAL FORM 272 (4-77)
(Formerly NTIS-35)
Department of Commerce
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