vvEPA
United States
Environmental Protection
Agency
Office of Health and
Environmental Assessment
Washington DC 20460
EPA-600/8-83-030
November 1983
Research and Development
Rapid Assessment of
Potential Ground-Water
Contamination Under
Emergency Response
Conditions
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EPA-600/8-83-030
November 1983
RAPID ASSESSMENT OF POTENTIAL GROUND-WATER CONTAMINATION
UNDER EMERGENCY RESPONSE CONDITIONS
by
Anthony S. Donigian, Jr., T. Y. Richard Yo,
and Edward W. Shanahan
Anderson-Nichols & Co., Inc.
Palo Alto, CA 94303
EPA Contract 68-03-3116
Work Assignment No. 3
EPA Project Officer
Lee A. Mulkey
Environmental Research Laboratory
Athens, GA 30613
Technical Project Monitor
John Schaum
Office of Health and Environmental Assessment
Washington, DC 20460
OFFICE OF HEALTH AND ENVIRONMENTAL ASSESSMENT
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, DC 20460
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NOTICE
This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
11
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FOREWORD
The Exposure Assessment Group of EPA's Office of Research and
Development has three main functions: 1) to conduct exposure assessments;
2) to review assessments and related documents; and 3) to develop guidelines
for Agency exposure assessments. The activities under each of these
functions are supported by and respond to the needs of the various EPA
program offices. In relation to the third function, the Exposure Assessment
Group sponsors projects for the purpose of developing or refining techniques
used in exposure assessments. This study is one of these projects and was
done for the Office of Emergency and Remedial Response.
The Comprehensive Environmental Response, Compensation, and Liability
Act of 1980 established a national fund for the purpose of cleaning up
spills and abandoned sites containing hazardous substances. When these
sites are discovered, EPA must decide quickly if an urgent threat exists
requiring immediate action. This project is intended to aid the Agency in
making these decisions by providing a method for rapidly evaluating the
human health and environmental threat caused by discharges to ground water.
The Agency's final decision must also consider the threat caused by releases
to the air and surface waters. The Exposure Assessment Group hopes to
eventually provide similar methods which can be used to assess the threats
associated with the other media as well.
James W. Falco, Director
Exposure Assessment Group
111
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CONTENTS
Section
Abstract v
Figures vi
Tables vii
Acknowledgments ix
1. Introduction 1
1.1 Scope and Limitations of This Manual 1
1.2 Required User Background, Training and Preparation 2
1. 3 Format of the Manual 4
1.4 Caveat 4
2. Overview of Rapid Assessment Methodology 5
2.1 Application Scenarios 5
2.2 Methodology Flowchart 6
2.3 Critical Compound and Site Characteristics 9
2.4 Auxiliary Sources of Information 16
3. Rapid Assessment Nomograph and Its Use 25
3.1 Development of the Assessment Nomograph 26
3.2 The Nomograph and How to Use It 33
3.3 Linkage of Unsaturated and Saturated Zone Assessments 41
3.4 Assumptions, Limitations, and Parameter Sensitivity 43
4 . Parameter Estimation Guidelines 48
4.1 General Parameter Estimation 49
4.2 Unsaturated Zone Parameter Estimation 58
4.3 Saturated Zone Parameter Estimation 90
5. Example Applications and Result Interpretation 100
5.1 Example 1: Assessment of a Continuous Contaminant Source 100
5.2 Example 2: Assessment of a Pulse Contaminant Source 108
6. References 121
Appendices
A. U.S. Soil Conservation Service Runoff Estimation Method 127
B. Glossary of Terms 134
C. Worksheets and Enlarged Nomographs 141
±v
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ABSTRACT
EMERGENCY RESPONSE actions at chemical spills and abandoned hazardous
waste sites often require rapid assessment of the potential for ground-water
contamination by the chemical or waste compound. This manual provides a
rapid assessment methodology for performing such an evaluation within the
24-hour emergency response time frame so that emergency actions can be
taken. The methodology consists of a decision flowchart, graphical
(quantitative) procedures for estimating contaminant concentrations and
travel times through soils and ground water, and guidelines for estimating
required parameters representing critical contaminant and site
characteristics.
The quantitative procedures for estimating contaminant transport are
based on a variety of simplifying assumptions related to contaminant
characteristics and the subsurface environment to conform to the data, time,
and resource limitations expected during an emergency response.
Consequently, the assessment methodology provides order-of-magnitude
estimates of contaminant concentrations with time and distance below the
land surface; the procedures are not intended to provide an indepth analysis
of the complex fate and transport processes in the subsurface environment.
In addition to the components of the methodology, this manual discusses
critical compound and site characteristics, describes assumptions and
limitations of the procedures, provides auxiliary sources of information (to
supplement this manual) and presents example applications. To effectively
use this manual, potential users will need an understanding of the
fundamental concepts of soil science, hydrogeology, and chemistry, in
addition to an appreciation of the assumptions and limitations of the
methodology. Familiarity and prior training in the use of this manual is
highly recommended for efficient use during an emergency response situation.
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FIGURES
Page
2.1 Flow Chart for Rapid Assessment of a Potential Ground-Water
Contaminant Under Emergency Response Condition 7
3.1 Continuous vs. Pulse Contaminant Inputs and Associated Responses 31
3.2 Contaminant Movement Expressed by Profile and Time Response to
Continuous and Pulse Inputs 32
3.3 The Rapid Assessment Nomograph and Procedures for its Use 34
3.4 Rapid Assessment Nomograph - Enlarged Scale, C/Co <0.4 36
3.5 Time Response From The Unsaturated Zone and Approximations
For Input To The Saturated Zone 42
3.6 Schematic Linkage of Unsaturated and Saturated Zone Assessments 44
4.1 Mean Annual Percolation Below a 4-Foot Root Zone (a. Hydrologic
Soil Group A; b. Hydrologic Soil Group B) 62
4.2 Meal Annual Percolation Below a 4-Foot Root Zone (a. Hydrologic
Soil Group C; b. Hydrologic Soil Group D) 63
4.3 Generalized Hydrologic Soil Groups for the U.S 65
4.4 Average Annual Precipitation, Potential Evapotranspiration, and
Surface Water Runoff for the U.S 66
4.5 Percentage Nitrogen (N) in Surface Foot of Soil 81
4.6 Distribution of Organic Matter in Four Soil Profiles 82
5.1 Soil Profile Response for Example #1: Demonstrating Fate and
Movement of Pollutant 104
5.2 Example #1: Time Response at Ground-Water Table 107
5.3 Example #1: Time Response at the Stream (X=100 m) Ill
5.4 Example #2: Time Response at Ground-Water Table for Pulse Input 116
5.5 Example ft2: Time Response at the Stream (X=100 m) 120
VJ
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TABLES
Page
2.1 Critical Compound and Site Characteristics 10
2.2 Summary of Chemical/Physical Data Available from Handbooks and
Data Bases 21
3.1 Required Parameters for Unsaturated Zone Assessment.., 30
3.2 Worksheet for Rapid Assessment 37
3.3 Supplementary Worksheet for Assessment of a Pulse Input Situation.... 40
4.1 Unsaturated Zone Parameters and Associated Information
Needed/Useful for Evaluation 59
4.2 Hydrologic Soil Classifications 64
4.3 Runoff Coefficients for Hydrologic Soil Groups 68
4.4 Representative Values of Porosity 71
4.5 Specific Yields, in Percent, of Various Materials 71
4.6 Relative Importance of Processes Influencing Aquatic Fate of
Priority Pollutants 73
4.7 Regression Equations for the Estimation of Koc 79
4.8 Average Organic Matter Contents and Ranges of Mineral Surface
Soils in Several Areas of the United States 80
4.9 pKa Values for Selected Organic Acids 86
4.10 pKb Values for Selected Organic Bases 88
4.11 Saturated Zone Parameters and Associated Information Needed/Useful
for Evaluation 91
4.12 Range of Values of Hydraulic Conductivity and Permeability 95
4.13 Representative Horizontal Field Hydraulic Conductivity Ranges for
Selected Rocks 96
4.14 Regional Dispersivities 98
t
vii
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TABLES (Cent.)
Paqe
5.1 Example 11: Profile Response for Continuous Input To
Unsaturated Zone [[[ 102
5.2 Example #1: Time Response for Continuous Input To
Unsaturated Zone [[[ 1°5
5.3 Example #1: Time Response for Continuous Input To
Saturated Zone [[[ 109
5.4 Example #2: Time Response for Pulse Input To Unsaturated Zone -
Standard Worksheet .................................................
5.5 Example |2: Time Response for Pulse Input To Unsaturated Zone -
Supplementary Worksheet
5.6 Example #2: Time Response for Pulse Input To Saturated Zone -
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ACKNOWLEDGMENTS
This manual is the result of support and guidance from a number of
groups and individuals. Financial support was provided by the EPA Office of
Emergency and Remedial Response through the Exposure Assessment Group and
the Environmental Research Laboratory (Athens, GA) of EPA's Office of
Research and Development. Mr. Lee Mulkey (Athens ERL) was the Project
Officer and Mr. John Schaum (Exposure Assessment Group) was the technical
Project Monitor; the technical assistance and guidance provided by these
individuals was instrumental to the successful completion of this manual.
Anderson-Nichols was assisted in this effort by Battelle, Pacific
Northwest Laboratories, Richland, WA, and Dr. P.S.C. Rao of the University
of Florida, Gainesville, FL. Battelle PNL provided technical review of
reports and assistance in the compound and site characterization efforts;
Dr. Rao assisted in the review of methods and development of procedures for
estimating contaminant fate and transport in the unsaturated zone.
In addition, technical review comments were provided by Dr. Wayne
Pettyjohn of Oklahoma State University and the EPA RSK Environmental
Research Laboratory in Ada, OK. Peer review comments and suggestions on the
draft manual were provided by Dr. Carl Enfield (EPA-RSKERL), Dr. Charles
Faust of GeoTrans, Inc., and Mr. Robert Carsel (EPA-Athens ERL) in addition
to the project team members noted above. These reviews and suggestions were
especially helpful in preparing this final manual.
Among the authors, Mr. Anthony Donigian was project manager responsible
for the overall technical content of the manual, development of the
methodology and parameter estimation guidelines, and preparation of the
manual. Mr. T. Y. Richard Lo developed the assessment nomograph and
application procedures, and prepared example applications. Mr. Edward W.
Shanahan assisted in the methodology development, and the methods review and
parameter estimation for the saturated zone procedures.
Mr. John Imhoff was involved in the methodology review and development,
and assisted in the preparation of the interim report. Guidance in chemical
parameter estimation was provided by Mr. J. David Dean and Mr. Brian R.
Bicknell; Mr. Bicknell also assisted in preparing the draft manual.
Technical support was provided by Mary Maffei, word processing was
provided by Ms. Lyn Hiatt and Ms. Sandy Guimares, and the drafting and
graphics were prepared by Ms. Virginia Rombach. The dedicated assistance of
all these individuals allowed the successful completion of this project, and
is sincerely appreciated.
ix
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SECTION 1
INTRODUCTION
The purpose of this manual is to provide a methodology for estimating
potential ground-water contamination, under emergency response conditions,
at an abandoned hazardous waste or toxic chemical spill site. Specifically,
this manual is designed for use by field personnel to quickly estimate how
contaminant concentrations might change with time and distance from an
emergency response site. The procedures include evaluation of critical
contaminant and site charcteristics as input to an assessment methodology
for analyzing the fate and movement of chemicals through both the
unsaturated and saturated (i.e. ground water) soil zones. A graphical
technique (i.e. nomograph) has been developed for contaminant movement
through both the unsaturated and saturated (ground water) zones to provide a
complete, integrated assessment methodology. Guidelines for evaluating
critical waste and site characteristics are provided to allow estimation of
needed nomograph parameters.
1.1 SCOPE AND LIMITATIONS OF THIS MANUAL
The phrase EMERGENCY RESPONSE is emphasized throughout this manual because
it has been the over-riding criterion (and constraint) for selection,
evaluation, and development of pollutant transport assessment methods and
parameter evaluation techniques included herein. Emergency response
situations require assessments of potential ground-water contamination to be
completed in less than 24 hours. Consequently, extensive field sampling,
laboratory analyses, data search and collection, and sophisticated computer
analyses are generally impractical during this limited time frame. Although
these extensive sampling and analysis activities may be initiated during the
emergency response period, the results are not expected to be available for
use in an emergency assessment.
The assessment procedures in this manual are designed to allow emergency
response personnel to make a first-cut, order-of-magnitude estimate of the
potential extent of contamination from a waste site or chemical spill within
the 24-hour emergency response time frame. These procedures are not
intended to provide a definitive, indepth analysis of the complex fate and
transport processes of contaminants in the subsurface environment.
The primary goal of this manual is to provide the basis for determining the
need for emergency actions, such as emergency sampling, containment/removal,
drinking water restrictions, etc. in order to preclude or minimize human
exposure from ground-water contamination at an emergency response site. Two
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specific emergency response situations are envisioned where the assessment
procedures in this manual would be applied.
1. Discovery of an abandoned hazardous waste site where an assessment
of the potential extent of the waste plume is needed within the
emergency response time frame.
2. Spill (or leakage) of a toxic waste or chemical where the potential
for ground-water contamination and/or the extent of contamination
must be assessed within the emergency response time frame.
Time and resource limitations expected during an emergency response have
required a number of simplifying assumptions in our assessment procedures;
additional simplifications may be needed by the user due to limited data and
information available at a particular emergency response site. The major
assumptions incorporated into the assessment procedures in this manual are
as follows:
1. Homogeneous and isotropic properties are assumed . for both the
unsaturated and saturated zones (or media).
2. Steady and uniform flow is assumed in both the unsaturated and
saturated zones.
3. Flow and contaminant movement are considered only in the vertical
direction in the unsaturated zone and the horizontal direction in
the saturated zone.
4. All contaminants are assumed to be water-soluble and exist in
concentrations that do not significantly affect water movement.
A variety of other assumptions and limitations in the procedures are further
discussed in Section 3.5. The user should carefully review all the
assumptions and limitations, and must make specific judgements as to their
validity for the specific site, contaminant(s), and emergency situation
being analyzed. Perhaps the most critical aspect of an emergency response
situation will be the ability of the user to adequately characterize, within
the 24-hour time frame, the subsurface media (e.g. heterogeneities, depth to
ground water, soil/aquifer properties, aquifer thickness) through which the
contaminants may move. Consequently, access and/or availability of data,
expertise, and familiarity with local, site-specific soils and hydrogeologic
conditions is critical to the successful application of the assessment
procedures in this manual.
1.2 REQUIRED USER BACKGROUND, TRAINING, and PREPARATION
Effective use of this manual requires an understanding of a mix of
disciplines, such as hydrology, hydrogeology, soil science, chemistry, on
the part of the intended user, and sufficient familiarity or training with
the techniques, procedures, and auxiliary sources of information described
herein. Moreover, this manual is not intended to be a primer on pollutant
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fate and movement through soils and ground water; a variety of excellent
introductory textbooks and reports in these areas are available to the
potential user to provide the needed background (e.g., Freeze and Cherry,
1979; EPA, 1981; Thibodeaux, 1979).
Ideally, academic training in any one of the above disciplines supplemented
with experience, job training, and/or exposure (e.g. short course
attendance) in the other disciplines provides a profile of the recommended
background for a user. Alternatively, an engineering or science
undergraduate degree with appropriate training is acceptable as long as a
basic understanding in the following areas is included:
a. the hydrologic cycle and its components
b. hydrogeologic concepts, processes, and terminology related to
ground-water movement
c. soil science concepts related to soil processes and water movement
d. chemical processes, parameters, and terminology
e. mathematical capabilities and skills in the use of scientific hand
calculators.
In many emergency response situations, the user will have access to experts
in the above disciplines to provide guidance in parameter evaluation. Thus,
the user must have sufficient comprehension of the appropriate terminology
in order to communicate effectively with the experts and "ask the right
questionsl"
User training and preparation is needed to develop familiarity with the
assessment procedures described in this manual and the wide range of
auxiliary sources of information that supplement and complement the
parameter evaluation guidelines in Section 4. In essence, the user should
be able to ask and answer the question - "What information do I need and
where can I get it?"
Training and/or familiarity with the specific procedures described herein is
absolutely essential to effectively use this manual. Without prior study
users cannot expect to use this manual for assessing potential ground-water
contamination within a 24-hour period. Although every effort has been made
to simplify the procedures and parameter evaluation guidelines, prior study
is needed to become familiar with the assumptions/limitations, the
step-by-step calculations, the application of the nomographs, the parameter
evaluation guidelines, and the auxiliary sources of information. Also,
knowledge of the most sensitive, critical parameters will allow the user to
allocate data search efforts most effectively.
Familiarity with supplementary sources of information cannot be
over-emphasized. Section 2.4 describes a variety of handbooks and data
bases from which contaminant characteristics (and input parameters) can be
evaluated or estimated. Precious time can be saved if the user is knowledge-
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able about which sources are most likely to contain the information he is
seeking.
Since site characterization may require the greatest effort during an
emergency assessment, preparation of a regional or local data base on
meteorology, hydrologic characteristics, soils/aquifer properties,
ground-water characteristics, prior hydrology/hydrogeologic studies, and
local experts (i.e. contacts and phone numbers) could considerably shorten
the time needed to obtain data and improve the resulting parameter
estimates. A similar, regional data base for the characteristics of wastes
and chemicals produced in, or transported through, the region would be
extremely valuable. Recommendations for the contents and format of such a
regional data base have been developed for EPA (Battelle PNL, 1982a).
1.3 FORMAT OF THE MANUAL
Section 2 describes the types of hazardous waste and spill situations for
which the assessment procedures are designed, and provides a methodology
flow chart to guide an application. An overview of critical compound and
site characteristics is provided along with a discussion of recommended
sources of information. Section 3 describes both the unsaturated and
saturated zone methodologies and the assessment nomograph. A detailed
description of the assessment methodology. Section 3 also discusses linkage
of unsaturated and saturated zone assessments and the assumptions and
limitations of the assessment procedures - these should be carefully
reviewed and understood by the user.
Section 4 provides guidelines for estimating the input parameters for both
the unsaturated and saturated zone assessments. Emphasis is placed on
obtaining local site and compound specific data in order to obtain realistic
parameter estimates. However, quantitative guidelines are provided for most
parameters as a last resort if no other information is available.
Section 5 presents example applications for the assessment nomograph for
both zones and demonstrates linkage procedures. Section 6 includes cited
references, Appendix A provides a description of the SCS Curve Number
procedure for estimating surface runoff; Appendix B is a glossary of terms;
and Appendix C provides blank worksheets and copies of enlarged nomographs
for ease of use during an application.
1.4 CAVEAT
Although all efforts have been made to insure the accuracy and reliability
of the methods and data included in this manual, the ultimate responsibility
for accuracy of the final predictions must rest with the user. Since
parameter estimates can range within wide limits, especially under the
resource and time constraints of an emergency response, the user should
assess the effect of methodology assumptions and parameter variability on
predicted concentrations for the specific site. The methodology predictions
must be evaluated with common sense, engineering judgement and fundamental
principles of soil science, hydrogeology, and chemistry. Accordingly,
neither the authors nor Anderson-Nichols assume liability from use of the
methods and/or data described in this manual.
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4
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SECTION 2
OVERVIEW OF RAPID ASSESSMENT METHODOLOGY
An emergency response to releases of hazardous substances is generally
comprised of three steps - characterization, assessment, mitigation -
defined as follows (Battelle PNL, 1982a):
o Characterization - the acquisition, compilation, and processing of
data to describe the scene so that a valid assessment of
alternative actions can be made.
o Assessment - an analysis of the severity of an incident; the
evaluation of possible response actions for effectiveness and
environmental impact.
o Mitigation - the implementation of the best response action and
followup activities.
The assessment procedures for potential ground-water contamination in this
manual draw upon data and information developed in the characterization
phase in order to provide a tool for performing parts of the assessment
phase when ground-water contamination is suspect. The EPA Field Guide for
Scientific Support Activities Associated with Superfund Emergency Response
(Battelle PNL, 1982a) provides an excellent framework within which to view
these procedures as part of the arsenal of the emergency response team for
assessments of hazardous substance releases. This field guide identifies
the calculation of transport rates of hazardous materials as an important
element in the assessment phase. When subsurface fate and movement of
hazardous substances is important at an emergency response site, these
calculations can be made with the procedures described herein based on the
methodology assumptions and data expected to be available within the
emergency response time frame.
2.1 APPLICATION SCENARIOS
Ground-water contamination by hazardous materials may result from surface
spills; seepage from waste injection operations, waste storage/burial sites;
and leaks from underground containers (i.e., waste or storage) or
pipelines. The rapid assessment procedures are designed for application in
two typical scenarios, or cases, based on the temporal nature of the release:
Case 1 Analysis - Typically a hazardous waste site or chemical/waste
storage facility where the release is relatively continuous and
constant over an extended period of time (e.g. years).
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Case 2 Analysis - Typically a spill incident (or a short-term release
from a storage facility) where the release can be assumed constant
over a relatively short span of time (e.g. weeks, months) producing
a pulse-type release.
The assumption of a constant release either on a continuous or pulse basis
is necessary for the analytical solutions from which the nomographs have
been developed. Consequently, although actual releases will be
time-varying, the user will need to approximate the actual release by either
the Case 1 or Case 2 assumptions above in order to perform an assessment
within the emergency response time frame. (See Section 3 for further
discussion.)
Superimposed on the temporal nature of the release is the time period of
concern for the assessments and the associated quantities of the forces
driving the movement of the contaminant. In most cases, the driving force
will be water movement through the soil to ground water; for large volume
spills the mass of the material may be sufficient to move through the soil.
The time period can vary from an assessment of the historical movement and
current extent of the contaminant plume, to a projection of the plume at
some time in the future. For the discovery of an abandoned hazardous waste
site, the user may need to evaluate the current extent of contamination
based on the age of the site, the period of release, and ground-water
recharge estimates during the past; whereas, for a spill situation the user
may need to project the future movement of the plume based on precipitation
forecasts and resulting expected recharge. Thus, the time period of concern
and the temporal nature of the release jointly determine the appropriate
type of analysis (i.e., Case 1 vs. Case 2) and parameter estimates for the
driving force behind contaminant movement.
2.2 METHODOLOGY FLOWCHART
The overall flowchart for the rapid assessment methodology is shown in
Figure 2.1. Prior to initiating application of these procedures, the
On-Scene Coordinator (OSC) at the emergency response site must determine
that (1) the potential for ground-water contamination exists, or (2)
contaminants have reached ground water, and (3) an assessment of the
potential or current extent of contamination must be made within the 24-hour
emergency response time frame. These decisions will be based on the results
of the characterization phase of the emergency response effort and will
depend on current conditions (e.g., current contamination of wells or
streams, weather forecasts), compound characteristics (e.g., toxicity,
solubility, sorption, volatility), and site characteristics (e.g., depth to
ground-water, soil/aquifer characteristics, distance to drinking water wells
and streams). If no emergency assessment is deemed necessary, the
procedures in this manual should not be used, except as preliminary guidance
for subsequent detailed sampling, analysis, and investigations possibly
including numerical modeling techniques.
If an emergency assessment is deemed necessary, the steps in Figure 2.1
should be followed as discussed below:
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STEP 1
STEP 2
r
STEP 3
STEP 4
STEP 5
1 —
VARY VALUE:
PAR/
TO TEST <
1
1
k---
r~
1
1
ADJUST
IF N
1
1
1 ^
HAZARDOUS MATERIAL
RELEASE OCCURS
1
C
\
A
ETERMINE
ZON
FFECTED B
SURFACE SPILL OR
RELEASE IN UNSATURATED ZONE
t
ASSESS FATE AND TRANSPORT IN
UNSATURATED ZONE
EVALUATE ASSUMPTIONS AND
DETERMINE INPUT PARAMETERS
USING ESTIMATION GUIDELINES
(SECTION 4)
OF CRITICAL
METERS
ENSITIVITY
- —
ESTIMATE CHANGE IN CONCENTRATION
~ WITH TIME AND DEPTH IN
•^ UNSATURATED ZONE USING NOMOGRAPH
(SECTIONS 3 S 5)
ARAMETERS,
ICESSARY
EVALUATE METHODOLOGY ASSUMPTIONS
" ~~ AND VALIDITY OF RESULTS
ASSESS THREAT OF POTENTIAL
GROUND-WATER CONTAMINATION
/ STOP \
^
PERFORM
SATURATED
ZONE
ANALYSIS
1
SUBSURFACE
Y RELEASE
1 1
RELEASE IN OR NEAR
SATURATED ZONE
1
1 — »H ASSESS FATE AND TRANSPORT
SATURATED ZONE
EVALUATE ASSUMPTIONS AND
DETERMINE INPUT PARAMETERS
USING ESTIMATION GUIDELINES
(SECTION 4)
VARY V
TO 1
ESTIMATE CHANGE IN CONCENTRAT1C
UITH TIME AND DISTANCE IN
SATURATED ZONE USING NOMOGRAPH
(SECTIONS 3 AND 5)
ML
'
EVALUATE METHODOLOGY ASSUMPTIOt
AND VALIDITY OF RESULTS
*
COMPARE CONCENTRATION PLUME WI1
LOCATION OF POTENTIAL SITES TC
ASSESS HAZARD
/ STOP \
IN
ALLIES OF CRITICAL
PARAMETERS
EST SENSITIVITY
1
II 1
|
^
1
1
UST PARAMETERS,
IF NECESSARY
1
5 1
H
i mz
Figure 2.1 Flow Chart for Rapid Assessment of Potential Ground-Water
Contaminant Under Emergency Response Conditions.
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STEP 1 involves the determination of which zone, unsaturated or
saturated, will be affected by the contaminant release and
which associated branch to follow in the flowchart. Most
surface and near-surface releases will need to move through the
unsaturated zone before reaching ground water; thus an
unsaturated zone analysis (left branch in Figure 2.1) will be
needed. For shallow ground-water depths, highly permeable
soils, and/or highly fractured surface materials, the user may
choose to ignore the unsaturated zone and assume direct release
to the saturated, ground-water zone. This assumption ignores
any attenuation or retardation in the unsaturated zone and, in
many cases, will over-estimate actual concentrations reaching
ground water.
STEP 2 involves an initial evaluation of the methodology assumptions
(both unsaturated and saturated zones) for the specific site,
and estimation of the nomograph input parameters based on the
guidelines in Section 4. These two aspects are closely linked
since parameter values can be adjusted to partially compensate
for certain assumptions and limitations. However, significant
parameter uncertainties should be identified early in the
application so that associated impacts can be assessed.
STEP 3 includes calculation of concentrations with time and distance
using the nomograph described in Section 3. For the
unsaturated zone the depth to ground water will usually be the
distance measurement of interest; for the saturated zone
horizontal distances to nearby wells or streams may be needed.
Sensitivity analyses should be performed on critical parameters
(e.g., decay rate and retardation in the unsaturated zone,
ground-water velocity in the saturated zone) in order to assess
the effects of possible inaccuracies in parameter estimation.
STEP 4 requires the user to re-evaluate the methodology assumptions
based on the predicted concentrations and results of
sensitivity analyses. Further parameter adjustments and
re-calculation of concentrations may be necessary. This is a
critical step since the predictions will be used next to assess
the potential or current extent of ground-water contamination.
STEP 5 provides the assessment results upon which to make decisions on
needed emergency response actions. The need for an emergency
response, and the possible alternative actions, are decisions
to be made by the On-Scene Coordinator and other emergency
personnel which are not addressed in this manual. For
unsaturated zone analysis, concentration estimates for various
depths will indicate if the contaminant will reach ground water
at levels and within the time frame where emergency response
actions may be needed. If ground-water contamination is
predicted the user may need to perform a saturated zone
analysis, using the results of the unsaturated zone analysis as
input to estimate the contaminant plume migration in ground
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water. The results of the saturated zone analysis can provide the
concentrations and associated travel times at potential impact sites (e.g.,
wells, streams) where human exposure or ecological impacts may occur.
Complete application of the assessment procedures may require a number of
iterations of the steps discussed above, as new data becomes available or as
additional questions arise from the emergency situation. Following the
step-by-step procedures outlined above and shown in Figure 2.1 will allow
the user to perform consistent assessments of potential ground-water
contamination in a variety of circumstances.
2.3 CRITICAL COMPOUND AND SITE CHARACTERISTICS
The extent of contaminant fate and transport following releases to the land
surface and subsurface depends upon a variety of critical compound and site
characteristics. Table 2.1 lists the major characteristics of concern for
determining potential ground-water contamination at a specific site. This
section briefly describes the compound and site characteristics listed in
Table 2.1 to provide the user with an understanding of the types of
information needed to perform a valid assessment. Guidelines for
translating these characteristics into specific parameter values required by
the assessment procedures are provided in Section 4.
2.3.1 Critical Compound Characteristics
To assess the potential for ground-water contamination in an emergency
response situation, several properties of the compound or waste must first
be determined. Much of this information may be difficult to accurately
quantify within a 24-hour time frame, but it is likely that an applicable
range of values can be estimated. Some properties are used directly in the
assessment or to estimate parameters, while others are needed to interpret
the results. Those characteristics deemed crucial to an informed assessment
and listed in Table 2.1 are discussed below:
1. Contaminant Identity
The identities of the contaminants must be known to determine those
physical/chemical properties necessary for assessing pollutant fate
and migration. The physical state of the contaminant (gas, liquid,
or solid) should be assessed as part of the identification
process. Within the emergency response time frame, it may be
possible to identify only general classes of chemicals rather than
specific compounds. In such instances, parameter estimation will
be especially difficult.
2. Extent of the Contamination
The extent of the contamination must be defined to determine the
source term used in estimating transport into the soil and
ground water. This assessment should provide an estimate of the
mass of the pollutant entering, or potentially entering, the
subsurface environment by adjusting for volatilization into the
air, runoff, and containment or removal measures on the land surface,
-------
TABLE 2.1 CRITICAL COMPOUND AND SITE CHARACTERISTICS
Critical Compound Characteristics
1. Contaminant Identity and Physical State
2. Extent of the Contamination
3. Solubility
4. Adsorption
5. Degradation
6. Toxicity
7. Concentration and Loading
8. Density, Viscosity, and Temperature
Critical Site Characteristics (Applicable to Both the Unsaturated and
Saturated Zones Unless Otherwise Indicated)
1. Identity of Subsurface Medium
2. Aqe of Site
3. Distances to Wells, Streams, Property Boundaries
4. Porosity
5. Infiltration, Net Recharge, and Volumetric Water Content
(Unsaturated Zone Only)
6. Bulk Density
7. Hydraulic Conductivity (Saturated Zone Only)
8. Chemical Characteristics of Medium
9. Dispersion
10. Depth to Ground Water (Unsaturated Zone Only)
11. Hydraulic Gradient (Saturated Zone Only)
12. Effective Aquifer Thickness (Saturated Zone Only)
13. Structural and Geologic Features
10
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if necessary. Information on the volatility and reactivity of
the waste may be required in making this assessment. In
addition, the cross-sectional area of the spill or the disposal
site should be ascertained.
3. Solubility
The solubility of a compound affects its mobility in the soil and
ground water. The release of the contaminant from a landfill or
surface spill is usually controlled by its tendency to dissolve
in the water moving through the soil. A material's solubility
may also affect the ease with which it can adsorb on soil
particles, with less soluble wastes being more easily adsorbed.
Solubility generally provides an upper limit on dissolved
concentrations that can be found in the soil environment. The
existence of solvents other than water should also be determined
since it can affect the compound's miscibility with soil water
and ground water.
4. Adsorption
Adsorption can be a significant means of retarding contaminant
movement through the soil or ground water. It is a property
dependent upon both the nature of the compound and the soil.
Adsorption capabilities for organic, nonionic compounds are often
described in terms of adsorption (or partition) coefficients for
a particular compound/soil combination. These coefficients are
often estimated from the organic carbon (or organic matter)
content of the soil and the organic carbon partition coefficient
(which in turn can be estimated from compound characteristics
such as the octanol/water partition coefficient). Adsorption of
ionic compounds is also a function of ion exchange capacities and
clay type and content. This is especially important for soils or
media with low organic matter.
5. Degradation
Degradation by both chemical and biological mechanisms is
important because it can prevent contaminants from reaching
ground water and can reduce levels of contaminants already
present. Common degradation mechanisms in the environment are
hydrolysis, photolysis, biodegradation, chemical oxidation, and
radioactive decay. Hydrolysis and chemical oxidation are
important primarily for contaminants in soils and saturated
media. Photolysis can occur only in surface waters or on the
surface of the soil. Biodegradation is most important in surface
waters and in the top few feet of soil where bacterial
concentrations are high; however, anaerobic decomposition in deep
soils and ground water is possible. Radioactive decay occurs in
all environments under all conditions.
11
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6. Toxicity
To assess the hazard of any predicted or observed ground-water
contamination, the toxicity of the pollutants must be determined.
Since nearly all chemicals are toxic at very high concentrations,
the concern in this assessment is for materials that are moderately
to severely toxic or are carcinogenic, mutagenic, or teratogenic to
humans or aquatic organisms.
7. Concentration and Release/Loading Rate
Compound concentrations and volume or release/loading rates from a
spill or waste site are especially important because of the effects
on other characteristics and the extent of contamination.
Concentration will affect solubility, adsorption, degradation, and
toxicity. Since many of these characteristics are usually measured
at low concentrations and/or in aqueous solutions, changes at high
concentrations can be significant, such as exceeding solubility
limits or adsorption capacities, or reducing effective microbial
populations. Low volume releases from spills may only contaminate
a few feet of soil which could be removed by excavation; whereas
large volume and/or continuous releases can result in much larger
scale contamination.
8. Density, Viscosity, and Temperature
These compound parameters are important in evaluating the mixing
characteristics of the contaminant in soil water and ground water.
Differences in these properties between the water and the
contaminant can lead to density stratification, floating, or
sinking of materials which will significantly impact transport
behavior. Major differences in these characteristics may require
an evaluation of the validity of the assessments which assume
contaminant transport with the water movement.
2.3.2 Critical Site Characteristics
To assess potential ground-water contamination at a hazardous waste or spill
site, a number of site characteristics listed in Table 2.1 are important in
addition to the waste characteristics discussed above. Critical site
properties for both the unsaturated and saturated zones are identified and
briefly discussed below. Many of the parameters which define important site
characteristics are shared by both subsurface zones, although the values for
the parameters may be different for each zone. The discussions are intended
to provide an overview of the information needed to characterize an
emergency response site in appropriate detail to estimate contaminant
transport and fate in the subsurface environment; specific guidelines on
parameter estimation are presented in Section 4.
1. Identity of Subsurface Medium (Unsatuirated and Saturated Zones)
Perhaps the most critical site characteristics which must be
determined is the dominant material types of the subsurface zones.
-------
While the subsurface materials for either zone will rarely be
homogeneous, it is necessary to identify the major soil or rock
types in order to assign reasonable values to such parameters as
porosity, bulk density, hydraulic conductivity, dispersion
coefficients, and chemical characteristics.
2. Age of the Site (Unsaturated and Saturated Zones)
The age of the site will be most important in analyzing
newly-discovered landfills, uncontrolled waste disposal sites, or
leaking chemical storage facilities. The extent of pollutant
migration at the emergency response site cannot be adequately
assessed without knowledge of the length of time that contamination
has been occurring, unless other data are available. Many surface
chemical spills are investigated immediately after their occurrence
and thus the age of the incident is known.
3. Distances (Unsaturated and Saturated Zones)
Distances to water wells, streams, and property boundaries from the
hazardous waste or spill site are fundamental concerns in an
emergency response. This information represents horizontal
distances that the waste material must travel on the land surface
or in the ground, before reaching potential receptor sites of
concern.
4. Porosity
The total porosity, usually stated as a fraction or percent, is
that portion of the total volume of the material that is made up of
voids (air) and water. In determining the retardation coefficient,
a measure of adsorptive capabilities, the total porosity of the
aquifer is needed. Due to dead-end or unconnected pores, effective
porosity is somewhat less than total porosity. Effective porosity
is often estimated as the specific yield in unconfined aquifers
which is the quantity of water that will drain from a unit volume
of aquifer under the influence of gravity. Effective porosity is
required for the calculation of the interstitial pore-water
velocity in ground water based on Darcy's Equation.
5. Infiltration, Net Recharge, and Volumetric Water Content
(Unsaturated Zone Only)
Infiltration and net recharge refer to water movement below the
land surface to the unsaturated soil zone and ground water.
Infiltration is generally greater than net recharge since it
includes evaporation and transpiration quantities which are usually
deducted to estimate net recharge to ground water. Both of these
components are a function of climatic, topographic and soil
properties, and are important in estimating contaminant movement
into and through the unsaturated zone to ground water. Their
13
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relative importance depends on the time frame of the analysis (See
Section 4).
The volumetric water content is the volume of water in a given
volume of media, usually expressed as a fraction or percent. It
depends on properties of the media and the water flux estimated by
infiltration or net recharge. The volumetric water content is used
in calculating the water movement through the unsaturated zone
(pore water velocity) and the retardation coefficient. In satura-
ted media, the volumetric water content equals total porosity.
6. Bulk Density (Unsaturated and Saturated Zones)
The bulk density of the medium is required in calculating the
retardation factor, a measure of adsorption processes. The bulk
density is the dry mass per unit volume of the medium (soil or
aquifer), i.e., neglecting the mass of the water.
7. Hydraulic Conductivity (Saturated Zone)
The velocity of ground-water flow is essential to assessing the
spread of contamination; it is an especially sensitive parameter
for plume migration in the saturated zone. The hydraulic
conductivity (or permeability) of the aquifer is needed to estimate
flow velocity based on Darcy's Equation. It is a measure of the
volume of liquid that can flow through a unit area of media with
time; values can range over nine orders of magnitude depending on
the nature of the media. Heterogeneous conditions produce large
spatial variations in hydraulic conductivity, making estimation of
a single, effective value extremely difficult.
In the unsaturated zone, conductivity is an extreme function of
soil moisture, increasing by orders of magnitude as moisture
content increases. This indicates the difficulty in assessing
dynamic pollutant transport through the unsaturated zone as a
function of dynamic soil moisture conditions.
8. Chemical Characteristics of Medium (Unsaturated and Saturated Zones)
The primary chemical characteristics of the medium include organic
carbon content, ion exchange capacity, clay type and clay content.
These properties are used in conjunction with the adsorption
characteristics of the compound (as discussed in Section 2.3.1) to
allow formulation of an appropriate partition coefficient for the
specific compound/medium combination. The partition coefficient is
used with bulk density, and either total porosity (saturated zone)
or volumetric water content (unsaturated zone) to calculate a
retardation factor, to represent the impact of adsorption on
retarding contaminant movement through the medium.
14
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9. Dispersion (Unsaturated and Saturated Zones)
Hydrodynamic dispersion in subsurface media is a phenomenon that
causes the spreading of a contaminant. The complicated system of
interconnected passages comprising a porous media system causes a
continuous division of the contaminant mass into finer offshoots.
Variations in the local velocity (both magnitude and direction)
along and between these tortuous flow paths gives rise to this ever
increasing spreading on the microscopic scale. On a larger or
macroscopic scale, inhomogeneity due to variations in permeability
and porosity also gives rise to further spreading. On a megascopic
scale, the effects of layering and the associated differences in
permeabilities and porosities can give rise to further spreading
(Pickens, et al, 1977).
Dispersion is often considered together with molecular diffusion in
determining a dispersion coefficient. Because the actual spread of
a contaminant depends on inhomogeneity at various scales in
addition to the tortuosity and local velocity variation on a
microscopic scale, the selection and measurement of the dispersion
parameter (i.e., dispersivity) should be related to the scale and
detail of the modeling effort. This dependence on scale is
demonstrated by the fact that dispersivity values measured in the
laboratory can range from 10~2 to 1 cm, while field values can
range from 10"s to 100's of meters.
10. Depth to Ground Water (Unsaturated Zone)
The depth to ground water must be estimated in order to evaluate
the likelihood that contaminants moving through the unsaturated
soil will reach the ground water. Seasonal fluctuations, if
significant, should be identified, as well as the impacts of
pumping and recharge sources, natural or man-made.
11. Hydraulic Gradient (Saturated Zone)
To determine the magnitude and direction of ground-water flow, the
hydraulic gradient must be known. It is the slope of the water
table in an unconfined aquifer, or the piezometric surface for a
confined aquifer. As for the ground-water depth, the effects of
pumping and recharge should be considered in estimating the
hydraulic gradient since these actions can reverse expected
ground-water flow directions.
12. Effective Aquifer Thickness (Saturated Zone)
The available zone of mixing in the aquifer is described using an
effective aquifer thickness. For good mixing between the ground
water and the contaminant, this effective thickness may equal the
actual total thickness of the aquifer, but in many cases it will be
considerably less. In cases where the pollutant is of a
significantly different density than water, the extent of mixing
15
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may be reduced and the contaminant plume will be concentrated
over only a portion of the aquifer's thickness.
13. Structural & Geologic Features (Unsaturated & Saturated Zones)
A general assessment of the soils, topographic and geologic
environment of the study site is necessary to effectively
evaluate the potential for ground-water contamination. Rapid
assessments made within an emergency response time frame must
assume homogeneous conditions due to time constraints, but
heterogeneous properties will retard or increase contaminant
migration and should be at least qualitatively assessed. Folds,
faults, fractures, sinkholes, clay lenses, and soil variations
are examples of features that should be considered when
estimating appropriate ranges of parameters used in the rapid
assessment methodology.
2.4 AUXILIARY SOURCES OF INFORMATION
To obtain the data necessary to evaluate critical compound and site
characteristics during an emergency response, a variety of information
sources should be consulted prior to and during the emergency. As noted in
Section 1.2, the need to be familiar with the various sources of information
that might be needed during an emergency response cannot be
over-emphasized. The EPA Field Guide (Battelle PNL, 1982a) mentioned
previously includes a useful check-list of activities for chemical
characterization that should be performed before and between emergency
responses, during the response, and following the response; an analogous
checklist is provided for hydrologic assessments. In support of our
recommendations, the EPA Field Guide also emphasizes the importance of
pre-emergency planning and preparation especially in the collection and
aggregation of data sources for compound and site characterization. This
guide should be an important part of the library of an emergency response
team.
This manual is not intended to be a stand-alone document since the
supporting data that might be needed in an emergency response would fill
multiple volumes many times the size of this report. The sections below
describe various information sources for both compound and site
characteristics; these sources will be further referenced in the specific
parameter estimation guidelines in Section 4.
2.4.1 Sources of Compound Characterization Information
During an emergency response, data on waste characteristics are available
from five major sources:
1. Records
2. Onsite Observations
3. Analyses
16
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4. Handbooks and Data Bases
5. Experts
These information sources must be applied jointly to determine the
necessary input data for a ground-water contamination assessment. For
example, transportation records may first be used to determine the chemical
identity of a spilled cargo of waste before consulting a data base for a
list of the physical/chemical properties of the waste. Much of the
information in this section is published in the chemical characterization
section of the EPA Field Guide, to which the user is referred for
additional sources.
1. Records
Records can provide the most rapid, positive identification of the
materials involved at an emergency, and, if available, should be
the preferred means of identification. A variety of useful records
(e.g., shipping papers and transportation labels) are now required
when transporting hazardous materials. Transportation records
contain information on the quantities of hazardous materials
transported and may be used to estimate quantities involved in
emergencies. A complete description of available records and how
to use them in identifying spilled material is provided by
Huibregtse, et al, (1977). Also, the Association of American
Railroads is developing a computerized tracking system for rapidly
identifying railcars containing hazardous materials (Guinan 1980).
The use of records to identify chemicals present at uncontrolled
waste sites is much more difficult. Waste manifests, which
describe each shipment of waste received at a facility, are a
possible source. In many cases, however, these have only recently
been required.
2. Onsite Observations
Observable characteristics such as odor, color, density, and
reaction may be useful in rapidly identifying an unknown material.
An excellent method of quick identification of spilled materials
based on easily observable characteristics is presented in the
Field Detection and Damage Assessment Manual for Oil and Hazardous
Materials Spills (EPA 1972). Over 300 hazardous materials are
identified by odor, color, reaction, etc.
The U.S. Coast Guard Chemical Hazard Response Information System
(CHRIS) Manual CG-446-1 and CG-446-2 (U.S.C.G. 1974a, 1974b)
describes observable characteristics of approximately 900 hazardous
chemicals. The OHM-TADS data system maintained by EPA can be used
to identify chemical substances based on observable characteris-
tics. Physical properties of the unknown material (physical state,
odor, color turbidity, miscibility, reactions) are input to the
17
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computer system, which then performs a search to obtain possible
identities.
It should be noted that the use of observable characteristics may be
limited to identifying general classes of chemicals rather than
specific compounds.
Onsite observations may also be important in establishing the extent
of the contamination. Aerial photography and remote sensing may be
needed to supplement ground observations in detecting the boundaries
of a large spill or dump site, but such information may not be
available within the 24-hour emergency response time frame.
3. Analyses
Analytical methods may be employed if other methods fail to identify
the contaminants present. In emergency conditions where rapid
response is required, the available techniques may be limited to
qualitative field methods. Laboratory methods, while providing more
definitive results, require considerably more time. Mobile
laboratories have now made many complex instrumental methods
available for use in the field, helping to reduce the time
requirements of laboratory analysis.
The Field Detection and Damage Assessment Manual for Hazardous
Materials Spills (EPA 1972) describes analytic tests that may be
used in the field to identify chemicals. A variety of commercial
products are currently available for infield detection and
identification of hazardous materials. These products include
portable spectrophotometers/ ion-specific electrodes, gas
chromatographs, and organic vapor analyzers. Information on such
systems can be obtained from manufacturers and scientific supply
houses.
Once the identity of the contaminant is known, analytical methods
can be used in conjunction with a sampling program to determine the
extent of the contamination. Under emergency response conditions,
maximum use must be made of existing sampling sites such as wells,
ponds, drainage ditches, runoff collection devices, and so on. Hand
or gasoline powered augers provide a rapid means of quickly
obtaining subsurface samples over a large area. Sampling techniques
are described in EPA (1980).
4. Handbooks and Data Bases
Handbooks and data bases are an excellent source of
physical/chemical data on hazardous wastes including toxicities,
solubilities, densities, degradation rates, reactivities,
volatilities, and adsorption data. As were previously discussed,
data bases and handbooks also aid in identifying wastes based on
observable characteristics. The data source descriptions provided
below were taken largely from the EPA Field Guide:
18
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Handbooks -
CHRIS, the Coast Guard Hazardous Chemical Data Manuals CG 446-1 and
CG 446-2, are excellent sources of data on approximately 900
hazardous materials. The data contained in these and other CHRIS
manuals are designed for use with the Coast Guard's Hazard
Assessment Computer System (HACS), a computerized simulation system
that models the physical behavior of chemical spills and provides
information describing the extent of the hazard associated with
these spills (Parnarouskis et al 1980).
Manual CG-446-1, A Condensed Guide to Chemical Hazards, contains a
summary listing of physical/chemical properties of several hazardous
materials. It is designed to be carried to the scene of an
accident. Manual CG-446-2, Hazardous Chemical Data, contains
detailed information on the properties of hazardous chemicals.
The EPA Field Detection and Damage Assessment Manual for Oil and
Hazardous Materials Spills (EPA 1972) is useful for supplying data
needed for identifying any of 329 hazardous materials in the field.
The Handbook of Environmental Data on Organic Chemicals (Verschueren
1977) is an excellent source of data describing the behavior of over
1,000 organic chemicals in the environment. This is perhaps the
most complete collection of environmental chemical data that can be
easily taken into the field.
Dangerous Properties of Industrial Materials (Sax 1979) is a
collection of physical, chemical, and toxicological data on almost
13,000 common industrial and laboratory materials. The data deal
primarily with the hazards posed by the materials and include acute
and chronic toxic hazard ratings, toxicity figures, a description of
toxicology, treatment of poisoning, and storage, handling, and
shipping guidelines.
Physical Chemical Properties of Hazardous Waste Constituents
(Dawson, English and Petty 1980) is a collection of data on 250
chemicals commonly found in hazardous waste streams. This
collection is an excellent reference for predicting the behavior of
chemicals following spills. For each chemical, quantitative
estimates are included of the relative human health hazard posed by
its release to the environment.
The Merck Index (1976) contains general chemical data on almost
10,000 chemical substances. This work contains descriptions of the
preparation and chemistry of the various substances, with citations
to the original published sources of the data.
Aquatic Fate Process Data for Organic Priority Pollutants (Mabey et
al, 1982) this report includes physical transport, and
transformation data for 114 organic priority pollutants in aqueous
solutions, and provides methods of calculating partition coeffi-
cients and volatilization rates.
19
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Handbook of Chemical Property Estimation Methods (Lyman et al, 1982)
is a collection of estimation methods for several physical and
chemical properties of organic chemicals with emphasis on
environmental processes; it does not actually contain the data. The
handbook includes definitions and principles of the properties,
overviews of the available methods, and specific instructions for
the use of each one including detailed examples. An appendix of the
handbook also contains a listing of selected reference books which
contain compilations of many physical/chemical properties of organic
chemicals.
Data Bases -
OHM-TADS - The Oil and Hazardous Materials-Technical Assistance Data
System contains chemical, physical, and biological data on over 850
hazardous chemicals and industrial materials. OHM-TADS contains
data describing physical/chemical properties, toxicity,
environmental fate and persistence, and emergency response methods.
These data are maintained on computer by EPA and are accessible by
remote terminal or by microfiche.
Octanol/Water Partition Coefficient Data Base, a data base
containing octanol/water partition coefficients for several thousand
chemicals, is maintained by Dr. Corlan Hansch at Pomona College,
Pomona, California (714—621-8000 ext. 2225). This is perhaps the
most complete source of Kow values currently available. The
material in this data base can be purchased in hard copy form, on
microfiche, or on magnetic tape.
The Chemical Substances Information Network (CSIN) is a computerized
data collection system currently being developed by EPA. Sources
for this system will initially include the National Library of
Medicine, the Chemical Information System, EPA's Chemicals in
Commerce Information System, Bibliographical Retrieval Services,
System Development Corporation, and Lockheed's Dialog System.
Table 2.2 summarizes the data available from the major handbooks and data
bases notes above.
5. Experts
An additional source of information on compound characteristics lies
with experts within the chemical industry, scientific community, and
hazardous waste response teams.
The Chemical Manufacturers Association (CMA) Chemical Transportation
Emergency Center (CHEMTREC) telephone hotline [(800) 424-9300 or
483-7616 in Washington, DC] maintains a directory of industry
experts who can be contacted for information related to emergency
response. CHEMTREC can rapidly provide information on approximately
18,000 chemicals and trade-name products.
20
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TABLE 2.2 SUMMARY OF CHEMICAL/PHYSICAL DATA AVAILABLE FROM HANDBOOKS AND DATA BASES
Handbook or Data Base
Chemical Synonyms
Molecular Weight
Solubility in Water
Vapor Pressure
Boiling Point
Melting Point
Liquid Specific Gravity
Vapor Specific Gravity
Saturated Vapor
Concentration
Observable Characteris-
tics
to Odor Threshold
i—i
Sampling and Analysis
Methods
Chemical Reactivity
Reactions in Water
Reactions in Air
Biodegradation Rate
Constant
BOD
Hydrolysis Rate
Constant
Photolysis Rate
Constant
Bioconcentration Factor
Row
Kd
Koc
Number of Chemicals
Chris Manual
CG446-1,2
(U.S.C.G.
1974b)
X
X
X
X
X
X
:y X
X
i™
X
X
X
X
X
>r
900
EPA Field
Detection Versch-
Manual ueren
(1972) 1979
X X
X
X
X
X
X
X
X
X X
X
X X
X X
X
X
X
X
329 1,000
Sax
1979
X
X
X
X
X
X
X
X
X
X
13,000
Dawson
English
and
Petty,
1980
X
X
X
X
X
X
X
X
X
* X
X
X
X
X
250
Merck
Index
Wind-
holz OHM-
(1976) TADS
X X
X
X X
X
X X
X X
X X
X X
X
X
X
X
10,000 850
Ma bey
et al
SRI
(1982)
X
X
X
X
X
X
X
X
X
X
X
X
X
114
Source: after Battelle PNL, 1982a
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Other contacts can be found within local universities, technical
assistance teams (TAT) and regional response teams (RRT).
Directories of possible contacts are also available through trade
organizations and professional societies.
2.4.2 Sources of Site Characterization Information
Site characterization data by its very nature will be much more site and
region specific than compound characteristics. Consequently, pre-emergency
collection of relevant meteorologic, soils, geologic, and topographic data
is especially important. Also, prior hydrologic and hydrogeologic studies
of the region may provide a wealth of information. However, regional data
must be examined to insure it is representative of site-specific conditions
at the emergency response site.
In an emergency response situation, data on site characteristics should be
sought from six major sources:
1) Prior Studies
2) Textbooks
3) Well Owners
4) Records
5) Experts
6) Onsite Observations
Textbooks•, regional studies, and lists of consultants should be in the hands
of the emergency response team before they reach the spill site. It will
probably be necessary to refer to many of these data sources at each site,
since the required information is seldom found in a single source.
1. Prior Studies
Federal, state, and local government agencies may have performed
detailed soils, geologic, water supply, or water quality studies in
the area of the site. These prior studies are valuable sources of
data on site characteristics. An emergency response team should
contact the U.S. Geological Survey, the state geological survey, the
local health department and water district, and the local
engineering department as a start in the search for prior technical
reports. It is expected that many of the site properties might be
available in detailed prior investigations. Appendix A of the EPA
manual for ground-water/subsurface investigations at hazardous waste
sites (EPA, 1981) summarizes an extensive list of contacts and
information sources.
2. Textbooks
For some of the geologic and soils properties required in a rapid
assessment, tables in geology or ground-water textbooks provide a
readily available data source. Ranges of hydraulic conductivity,
22
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bulk density, and porosity should be correlated with types of
materials in most texts.
3. Well Owners
Owners of nearby wells may be able to provide information on the
aquifer thickness (based on perforated interval of well log), the
depth to ground water, the hydraulic gradient in the area, and the
nature of the water-bearing strata. Well locations and property
boundaries should be sought in assessing the hazards of the spill,
thus, conversations with well owners are recommended to search for
possible data and sources, such as the drilling company or drillers
familiar with the area.
4. Records
To determine the age of the site, records of waste disposal
operations or property ownership should be consulted. Waste
manifests, describing shipments to the site, may prove useful, but
have only recently been required.
5. Experts
In describing the ground water and unsaturated zone of the site,
local geologists, water resources engineers, county officials, and
university professors will be of assistance. Without detailed prior
studies, the estimation of many of the required parameters should be
guided by as much expert advice as can be gathered. Local agencies
can also aid in locating wells and property boundaries in the site
area.
6. Onsite Observations
Wells, topography, property lines, and stream locations should be
verified by field reconnaissance at the site.
The major factor which will determine the success and accuracy of the site
characterization is the availability of soils/geologic data from previous
investigations. Without existing knowledge of subsurface characteristics
such as predominant composition and thickness of unsaturated and saturated
layers, evaluation of many site parameters will be largely conjecture. It
is not likely that field testing will be able to provide adequate geologic
data within the time frame of an emergency response assessment. When
subsurface material composition is known, many site characteristics
including porosity, bulk density, hydraulic conductivity, dispersion, and
chemical characteristics can be estimated with reasonable accuracy in some
cases (see Section 4) . Values for these media-related parameters can be
combined with macrogeologic data from reports or regional experts to
estimate contaminant transport rates. If available, additional localized
23
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structural and geologic data which identify nonhomogeneity of the subsurface
materials can be used to adjust and/or interpret quantitative estimates of
contaminant transport, which assume media homogeneity. Thus, the ultimate
accuracy of any estimate of contaminant transport will be largely dependent
on the amount of specific localized information available for the emergency
response site.
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SECTION 3
RAPID ASSESSMENT NOMOGRAPH AND ITS USE
The quantitative, graphical procedures for contaminant fate and movement in
both the unsaturated and saturated zones are presented in this section. A
single nomograph was developed for predicting contaminant movement in both
soil zones to provide a comprehensive, integrated methodology for use under
emergency response conditions. Graphical procedures were selected so as not
to require prior experience with computers or programmable calculators by
emergency personnel. However, analogous techniques for both the unsaturated
and saturated soil zones have been programmed on hand-held calculators
providing greater flexibility for assessments (see Pettyjohn et al, (1982)
for ground-water programs). With the rapid advances in personal computers
and programmable calculators, as emergency response teams acquire the
necessary capabilities the techniques described herein can be easily
computerized for their use.
Section 3.1 describes in detail the development of the assessment nomograph
and Section 3.2 describes its general use, while Section 3.3 describes
procedures for linked unsaturated-saturated zone assessments. Finally,
Section 3.4 discusses the assumptions and limitations of the technique so
that the user can effectively assess the accuracy of predicted
concentrations for the specific emergency response situation.
3.1 DEVELOPMENT OF THE ASSESSMENT NOMOGRAPH
This section describes the nomograph developed for assessment of potential
ground-water contamination to predict contaminant movement based on input
parameters for contaminant and site characteristics.
The background and basis for the methodology is presented, including a
discussion of the convective-dispersive transport equation for porous media,
the types of pollutant source inputs usually encountered in an emergency
response situation (i.e. continuous and pulse inputs) and the corresponding
analytical solutions for each input condition. The parameters required to
perform an assessment are listed and discussed, followed by the description
of the assessment nomograph and its usage. This nomograph is actually a
graphical solution of the transport equation and is the heart of the rapid
assessment methodology. The same nomograph is used for both zones assuming
only vertical transport in the unsaturated zone and only horizontal (or
longitudinal) transport in the aquifer (saturated zone). However, the input
parameters are evaluated differently for each zone, as will be discussed in
Section 4.
25
-------
3.1.1 Contaminant Fate and Transport in Soils
Movement of contaminants in the soil (saturated or unsaturated) can be
described by the following equation (Van Genuchten and Alves, 1982)
dt
= D* dc
2 -
V*
- k*C
(3.1)
where C = solution concentration (mg/1)
D* = D/R
V* = V/R
k* = k/R
R = 1 + 13 Kd = retardation factor (dimensionless)
N
D = dispersion coefficient (cm /day)
V = average interstitial pore-water velocity (cm/day)
k = degradation rate coefficient (day" )
B = bulk density (g/cm )
N = 0, volumetric water content (dimensionless), for
unsaturated zone
ne, effective porosity (dimensionless), for saturated
zone
partition coefficient (ml/g)
Equation 3.1 states that the change in contaminant concentration with time
at any distance, (X) is equal to the algebraic sum of the dispersive
transport (1st term to right of equal sign), the convective transport (2nd
term) and the degradation or decay of the compound (3rd term) . Van
Genuchten and Alves (1982) note that various modified forms of this same
basic equation have been used for a wide range of contaminant transport
problems in soil science, chemical and environmental engineering, and water
resources.
Equation 3.1 considers only one-dimensional transport
applicable under steady, uniform flow conditions,
constant with space and time. This equation
advection, equilibrium adsorption (linear isotherm),
(first-order kinetics). Analytical solutions to the
been developed for both continuous (step function)
contaminants as boundary conditions. A step function
of contaminants and is
i.e. velocity, V, is
considers dispersion,
and degradation/decay
transport equation have
and pulsed inputs of
implies the input of a
26
-------
constant concentration contaminant for an infinite amount of time, while a
pulse load is a constant concentration input for a finite amount of time.
Clearly, the terms infinite and finite are relative to the time frame of the
analysis.
When the pollutant source is applied as a step function (continuously) with
the following boundary conditions:
C (x,o) = 0 (3.2)
C (o,t) = C0
,.. t, - 0
the analytical solution, as given by Cho (1971), Misra (1974), van Genuchten
(1982) and Rao (1982), can be expressed as:
C(x,t)
!—•"»'»-» erfc(A2) + exp(Bi) efrc(B2)]= P(x,t) (3.3)
where
_x (,v*- Vv*2+4D*k* ) Bi = _?_ (V*+ \/V*2+4D*k*
2D* 2D*
(3.4)
it-t Vy*2+4D*k* ) x+t Vv*2+4D*k*
v4o*t B2 = \/4D*t
(NOTE: Exp(Ai) denotes the exponential of Alr i.e., eAl' while erfc
(A2) represents the "complementary error function" of A2, a function
commonly used in applied mathematics. Erfc(A2) produces values between
0.0 and 2.0 (Abramowitz and Stegun, 1972)).
The boundary conditions shown in Equation 3.2 indicate that (1) no
contaminant is present in the soil prior to input from the source, (2) the
input concentration at the surface is constant at C0, and (3) a
semi-infinite column is assumed with a zero concentration gradient at the
bottom. This last boundary condition is often assumed to allow development
of the analytical solution; van Genuchten and Alves (1982) indicate that
this assumption has a relatively small influence on the accuracy of the
solution in most circumstances when applied to well-defined finite systems.
27
-------
Note that for large values of x and/or t, the second term within the
brackets in Equation 3.3 can be neglected (i.e., erfc(B2) approaches zero)
and produces the following:
>t = [exp(A ) erfc(A,)] (3.5)
C0 2 1 2
The validity of Equation 3.5 depends on the values of the parameters and
variables that define A^ and A2. Moreover, Equation 3.5 is comprised of
two terms: exp(A^) is time- independent and represents the eventual
steady-state concentration at x, while erfc(A2) is time-dependent and
corrects for the moving pollutant front (Rao, 1982) . Thus, the steady-state
condition, where C/CO is constant and erfc(A2> = 2, simplifies Equation
3.5 to
= exp(Ax) (3.6)
C
o
Under the appropriate conditions stated above, these equations can greatly
simplify calculations of contaminant concentrations.
When the pollutant source is applied as a pulse with a pulse duration, to,
and boundary conditions as shown below:
C (x,o) = 0
C (o,t) =|Co, o<_t <_to
|0 t>to (3.7)
C (oo,t)= 0
the analytical solution, as given by van Genuchten and Alves (1982) , and
Rao, (1982) , can be expressed as:
= P(x,t) 0 t
where P(x,t) is as defined in Equation 3.3.
Comparing Equations 3.8 and 3.3 shows that the analytical solution to the
pulse boundary condition is the result of subtracting the solutions to two
continuous inputs lagged by the pulse duration, to. This is further
explained below.
3.1.2 Continuous and Pulse Contaminant Inputs and Associated Responses
The rapid assessment procedures discussed in this section are directed to
two types of contaminant releases found in most emergency situations:
continuous and pulse. As noted above, continuous release (or continuous
input to the zone) implies the input of a constant source concentration of
contaminant to the soil profile for an extended amount of time. This
28
-------
pollutant source could be an uncontrolled hazardous waste site, an abandoned
dump site, a waste lagoon, a leaking chemical/waste container, etc. A pulse
input is the application of a constant source concentration for a short time
period relative to the time frame of the analysis. In this case, the
pollutant source could be a surface spill or a short-term leak from a
storage tank. The assessment methodology can be used to predict movement of
contaminants in the subsurface resulting from either one of these release
situations under emergency response conditions.
Movement of contaminants in the subsurface zones can be expressed by either
profile responses or time responses resulting from continuous or pulse
inputs. Profile responses are plots of pollutant concentration with
distance, x, at various defined times, t. Time responses are plots of
concentration changes with time, t, at certain specific locations x. For
the unsaturated zone, the distance measure will be the vertical soil depth
or depth to ground water; for the saturated zone, the down-gradient
horizontal distance to a specific point (e.g., well, stream) will be of
interest.
Figure 3.1 graphically illustrates time responses (i.e. C/Co vs t) at a
chosen soil depth or distance (x=L) resulting from both continuous and pulse
contaminant inputs from the source (x=0). Note that the figure is designed
to show that the superposition of two continuous input functions and their
associated responses (Figure 3.la and 3.1b), produces a pulse input and its
response (Figure 3.1c). In effect, the continuous input starting at time
t2 is subtracted from the continuous input starting at time tj_; the
result is an input pulse of duration to (i.e. t2 -t]_) . Similarly, at
the point x=L, superposition of the two continuous response functions
results in the response function produced by the pulse input. This concept
is the basis for the analytical solution for the pulse boundary condition
given in Equation 3.8.
Figure 3.2 shows profile and time responses for both the continuous and
pulse type releases expected in emergency situations. Specific assessments
may involve evaluation of concentrations at many different x and t values.
When profiles are desirable, concentrations must be evaluated at specific
times for different values of x; when time responses are needed,
concentrations will be estimated for different values of t, for defined soil
depths or down-gradient locations. As noted above, for most unsaturated
zone assessments, users will be concerned with the concentration and time of
arrival of contaminants at the ground-water table. Thus, time responses for
an x value equal to the depth to ground water will be commonly calculated.
For ground-water (saturated zone) assessments, the horizontal distance in
the direction of ground-water flow to a potential impact point is often used.
3.1.3 Required Parameters
In order to predict contaminant movement in soils and ground water,
parameters regarding transport and pollutant fate, and boundary or source
conditions of an emergency situation must be evaluated. These parameters
are listed in Table 3.1, along with their symbols and recommended units.
29
-------
TABLE 3.1 REQUIRED PARAMETERS FOR RAPID ASSESSMENT PROCEDURES
Parameter/Boundary Condition
Source Concentration
Interstitial Pore Water
Velocity
Dispersion Coefficient
Degradation/Decay Rate
Parameter
Retardation Factor (function
of following characteristics)
Partition (Adsorption)
Coefficient
Soil Bulk Density
Volumetric Water Content*
Symbol
C0
V
D
k
R- 1 + B KH
e
Recommended Unit
mg/1
cm/day
B
e
day-1
dimensionless
ml/g
g/cm^
dimensionless
Pulse Duration (Pulse input only)
day
* - For saturated zone assessments, the volumetric water content is equal to
the effective porosity, ne.
30
-------
SOURCE INPUT, X=0
TIME RESPONSE, X=L
C/
Co
C/
Co
C/
(a) Continuous Input, beginning at tj, and Associated Time Response
Co
C/
Co
C/
(b) Continuous Input, beginning at t^, and Associated Time Response
Co
C/
Co
to
(c) Pulse Input of Duration t0, and Associated Time Response
Figure 3.1 Continuous vs. Pulse Contaminant Inputs
and Associated Responses
-------
*- C/CO C/.Co
Profile Response
Time Response
[a) For Continuous Input
Co
Profile Response
Time Response
(b) hor Pulse Input
Figure 3.2 Contaminant Movement Expressed by Profile and
Time Response to Continuous and Pulse Inputs
32
-------
Transport parameters include the interstitial pore water velocity (V) and
dispersion coefficient, (D) . Pollutant fate parameters include the
degradation/decay coefficient (k) and retardation factor, (R) . Retardation
is primarily a function of the adsorption process which is characterized by
a linear, equilibrium partition coefficient (K^) representing the ratio of
adsorbed and solution contaminant concentrations. This partition
coefficient, along with soil bulk density (B) and volumetric water content
(€), are used to calculate the retardation factor. Retardation is important
in contaminant transport in the unsaturated zone because it affects
pollutant movement by modifying the convective, dispersive and degradation
terms in the transport equation (Equation 3.1) as follows:
V* = V/R (3.9)
D* = D/R
k* = k/R
Boundary conditions of a waste or spill situation are characterized by the
contaminant concentration, Co, of the pollutant source. For a release
situation characterized as a pulse input, the pulse duration, (to) must
also be specified.
Section 4.2 includes further discussion of the parameters listed in Table
3.1 and provides guidelines for estimating their values.
3.2 THE NOMOGRAPH AND HOW TO USE IT
The assessment nomograph was developed to facilitate computation of the
analytical solution to the transport equation for emergency situations which
can be characterized as continuous (step function) input. However, through
superposition (as discussed above) the same nomograph can be used for
waste/spill conditions characterized as pulse input. The nomograph (Figure
3.3) predicts contaminant concentration as functions of both time and
location in either the unsaturated or saturated zone. Separate
computations, parameter estimates, and use of the nomograph is required for
each zone. The prediction requires evaluation of four dimensionless input
values - A^, A2, B]_, and 82 - and subsequent evaluation of the
result, C/Co, according to Equation 3.1 through use of the nomograph.
Direct computation of C/Co is quite cumbersome; in addition to parameter
calculations, it involves evaluation of both the exponential and
complementary error functions, and subsequent arithmetic operations. The
nomograph facilitates these computations.
As shown in Figure 3.3; the nomograph consists of two groups of curves
joined in the center by three vertical axes. Both curve groups have two
axes, vertical and horizontal. The horizontal axis to the left is for entry
of AI and to the right entry of Bj_. Both axes are scaled to provide
evaluation of their corresponding exponential functional values (exp [A^]
and exp [BjJ , respectively) . The vertical axis to the left is for entry
of A2 and to the right, entry of B2. Both axes are scaled to provide
33
-------
0.2 0.4 0.6 0.8 10 1.2 1.4 1.6 1.8
limilllllll I lilllM'11 I1 I1 I I I ' I ' I I "
-2)00 TfoULo!? UU -ob -oil
-3.'00 -I.'SO -l|!o-o'.8 -
-------
evaluation of their corresponding complementary error functional values
(erfc [A2] and erfc [82], respectively): the intersection of A^ and
A2, and BI and B2 (points A and B in Figure 3.3) represents the
product of the axes, i.e. expfA^) times erfc(A2) . The two groups of
curves represent points of equal multiplicands. The solution, C/Co, is
located in the middle as represented by the center axis. The remaining two
axes on both sides of the solution are multiplicands of the exponential and
the erfc values. The curves represent points of equal multiplicands.
Step-by-step procedures are outlined below to demonstrate use of the
nomograph.
Step 1: A^, A2, BI, and B2, must first be calculated. This can be
done by inputting selected parameter values into Equation 3.4.
Step 2: Once Alf A2, Blf and B2 are calculated, C/Co can be
obtained from the nomograph (Figure 3.3). Start by entering
values of A^ and A2 to the left group curves and B^ and B2
to the right. As represented by the dotted lines labeled "step
2," the entering lines join at points "A" and "B" respectively.
Step 3: Then draw curves "AM^" and "BM2" by following the patterns in
each respective curve group. As shown in Figure 3.3 these curves
intersect the center axes at points "M]_" and "M2".
Step 4: The solution, C/Co, can finally be obtained by drawing a straight
line connecting points "MI" and "M2". The solution is found
at the point where line "M1M2" intersects the solution line,
C/Co. In this example, the solution is located at point "S".
The precision of a nomograph is determined both by its size and the
divisions of the axes. Large nomographs with fine divisions, in general,
will allow greater precision. The full scale nomograph provided in this
section (Figure 3.3) is precise enough for use with a continuous input or a
long pulse input situation. However, higher precision is needed for
conditions with a short contaminant pulse, especially for low C/Co values.
For this reason, a nomograph with an enlarged scale (Figure 3.4) is provided
to magnify the lower portion of the full nomograph, for C/Co values less
than 0.4. For ease of use, enlarged foldout versions of both the full-scale
and expanded-scale nomographs are provided in Appendix C.
To organize application procedures and provide a record of calculations and
predicted concentrations, worksheets are provided to complement the
nomograph for predicting contaminant concentrations for different values of
x and t. Step-by-step procedures in applying these worksheets in emergency
assessments are discussed below separately for the two contaminant input
situations.
Worksheet Procedures for Continuous Input Assessment
Step 1: Evaluate "required parameters" and enter values in Table 3.2.
-------
U)
C\
0.01 0.05 0.10
0.60
0.60
0.65
+ 00
-3.00 -1.50 -1 0-0.8 -06-04 -02
0.0
0.0 0.2 0.4 0.6 0.8
1.0
1.2
1.3
Figure 3-4 Rapid Assessment Nomograph - - - Enlarged Scale, C/C < 0.4.
-------
Table 3.2
Sheet of
Calculated by
Checked by
Date
Date
WORKSHEET FOR RAPID ASSESSMENT NOMOGRAPH
ZONE: UNSATURATED _
SATURATED
Site: Date of Incident:
Location:
On Site Coordinator:
Scientific Support
Coordinator:
Compound Name:
Compound Characteristics:
REQUIRED PARAMETERS:
Co =
V =
D =
k =
Kd =
B =
6 =
PRELIMINARY CALCULATIONS:
* V
1 V - / -
1. V - /R -
* n
2- D = D/D =
Agency:
Agency:
DATA SOURCES / COMMENTS
k. _
- V
4.
4D*k* =
5
X
6
t
7
x/
72D*
8
\/4D*t
9
See Footnote H 2
A1
A?
B1
B?
10
11
From Nomograph3
M1
M?
c/ro
12
C
37
-------
Table 3.2
Sheet of
Calculated by
Checked by
Date
Date
NOMOGRAPH WORKSHEET (con't.)
ZONE: UNSATURATED
SATURATED
5
X
6
t
7
x/
X2D*
8
\/4D*t
9
See Footnote # 2
A1
Ap
B1
B2
10
11
From Nomograph
M1
Mp
C/CO
12
C
Footnotes:
1.
2,
Refer to Table 3.1 for definitions and units, and to
Chapter 4 for estimation guidelines.
2
= Col. 7 X (Item 1 - Item 4) = - (V* -\ V* + 4D*k* )
A, = [Col.5 - Col. 6 X Item 4] / Col.8 = X " S/m!! +
C- \i L\\j \,
BT = Col. 7 X (Item 1 + Item 4) = —^ (V* + yV*2 + 4D*k*)
[i v -»- 1 vv*2 + dn*k*
Col .5+ (Col .6 X Item 4)] / Col .8 = /;,L+
J /*
Figure 3.3 or Figure 3.4 (See Figure 3.3 for use of
nomograph) .
-------
Step 2: Perform preliminary calculations.
Step 3: Enter values of x and t.
o To obtain a profile response, enter different values of x
for a selected time, t.
o To obtain a time response, enter different values of t for a
selected location, x.
Step 4: Perform calculation and apply nomographs, to evaluate C/Co and
C as instructed in the worksheet.
Step 5: Go back to Step 3 for further evaluation, if necessary.
Worksheet Procedures for Pulse Input Assessment
As mentioned earlier in Section 3.1.2, the analytical solution for a pulse
contaminant input results from the superposition of solutions for two separate
continuous input functions lagged by the pulse duration. Since the assessment
requires substracting two continuous input response (i.e. C/Co) values, a
supplementary worksheet (Table 3.3) is provided.
Step-by-step procedures for the pulse input situation are provided below:
Step 1: Evaluate "required parameters," enter pulse duration (to) and
source concentration (Co) in Table 3.3 and other parameter
values in Table 3.2.
Step 2: Perform preliminary calculations in Table 3.2.
Step 3: Enter values of x and t in Table 3.3, and in Table 3.2 for
continuous input assessment.
o To obtain a profile response, enter different values of x
for a selected time, t, in both Tables
o To obtain a time response, enter different values of t for a
selected location, x, in both Tables
Step 4: Perform continuous input assessment using work sheet Table 3.2
and enter result C/Co, in column 11 of Table 3.2 and column 4
of Table 3.3.
Step 5: Evaluate (t-to) in Table 3.3. If t> to, go to Step 6.
Otherwise, pulse concentration (Column 6) equals the continuous
input concentration (Column 4). Go to step 8.
Step 6: Evaluate C/Co at (t - to) using worksheet Table 3.2 and enter
result in column 5 of Table 3.3.
S*-pn 7: Subtract column 5 from column 4 and enter result in column 6.
-------
Table 3.3
Sheet
of
SUPPLEMENTARY WORKSHEET FOR PULSE INPUT ASSESSMENT
ZONE: UNSATURATED
SATURATED
to =
Co =
1
X
2
t
3
t- to
CONTINUOUS INPUT
ASSESSMENT
(From Worksheet )
4
C/Co^)
5
C/Co(t-to)
PULSE ASSESSMENT
Col. 4, ti to
Col. 4-5, t >to
6
C/Co^
~ v Col .
Co X c
0
7
C
40
-------
Step 8: Multiply column 6 by Co and enter result in column 7 of Table
3.3.
Step 9: Go back to Step 3 for further evaluation if necessary.
Detailed examples demonstrating the use of the nomograph and the worksheets
for both continuous and pulse inputs are provided in Section 5. The user is
encouraged to work through these examples and procedures to become familiar
with them prior to an emergency response situation.
3.3 LINKAGE OF UNSATURATED AND SATURATED ZONE ASSESSMENTS
Since the assessment nomograph can be applied to both the unsaturated and
saturated zones individually, linkage procedures are required for situations
where an assessment of contaminant movement through both saturated and
unsaturated media is needed. The linkage procedures require the following two
steps:
1. Approximation of the time-varying concentrations leaving the
unsaturated zone by either a continuous step function or pulse input.
2. Estimation of Co (i.e., source concentration) for the saturated
zone assessment based on Step 1 (above) , recharge from the waste
site, and ground-water flow.
Figure 3.5 shows typical time responses for concentrations reaching ground
water as estimated by an unsaturated zone assessment for both continuous and
step function inputs; the dashed lines show the approximations needed to
convert the time responses into continuous or pulse inputs for applying the
nomograph to the saturated zone. The approximations in Figure 3.5 are
designed so that the area under the dashed line is approximately equal to the
area under the associated time response curve. This ensures that the
contaminant mass entering ground water is the same for both the time response
and its approximation.
Since the arrival time of a contaminant at a particular point in the aquifer
is often the primary reason for a saturated zone assessment, users should
evaluate the sensitivity of these arrival times to the starting time of the
input approximation. For example, in Figure 3.5 the starting dates for the
step function and pulse input approximation are day 15 and day 10,
respectively; varying these starting dates by 2 to 3 days would help to
evaluate the impact of the approximation on the contaminant arrival time at
the point of concern.
The second step in the linkage procedure is to determine the value of Co,
the source concentration, to use in the saturated zone assessment. Unless the
waste/spill site is adjacent to a well and/or the ground-water table itself is
the impact point of concern, dilution and mixing in the aquifer must be
considered in estimating C0 for the saturated zone assessment. The
following equation should be used to estimate C0 for the saturated zone:
41
-------
O)
E
z
rr
i-
z
LU
O
z
O
O
Step function approximation
for input to saturated zone
Time response from
continuous step function
input to the unsaturated zone
l
10
I '
20
DAYS
I '
30
I
40
o>
E
•.
Z
O
z
UJ
o
z
O
O
Pulse approximation for
input to saturated zone
Time response from
pulse input to the
unsaturated zone
10
40
DAYS
Figure 3-5 Time Responses From The Unsaturated Zone and Approximations
For Input To The Saturated Zone
-------
c = CuqL (3.10)
0 ~~~
where C = source concentration for saturated zone, mg/1
C = maximum step function or pulse concentration
from the unsaturated zone, mg/1
q = recharge rate from the site, cm/yr
L = width of leachate plume at the water table, m
V = ground-water (Darcy) velocity, cm/yr
m = effective aquifer thickness or zone of mixing, m
Figure 3.6 schematically illustrates the linkage and underlying assumptions
in Equation 3.10, which considers dilution of the contaminant load by
recharge from the site and ground-water flow. The dilution terms (i.e., qL
and V^m) in the equation are written as a velocity times a distance since
the representation is a vertical plane with a unit width, which drops out of
the calculation.
Users should note that the q and Vd terms in the equation are bulk or
volumetric velocities, i.e., these are not pore-water velocities.
Guidelines for estimating q, V^ and m are included in Section 4, L is
determined from the dimensions of the waste/spill site, and Cu results
from the approximation shown in Figure 3.5. With this information and
nomograph parameter estimates for the saturated zone, the user can apply the
nomograph to estimate contaminant concentrations in the aquifer.
3.4 ASSUMPTIONS, LIMITATIONS, AND PARAMETER SENSITIVITY
To effectively and intelligently use the rapid assessment procedures
described in this manual, the user must understand and appreciate the impact
of assumptions and limitations on which the procedures are based, and the
relative sensitivity of the required parameters. These two aspects are
interrelated; performing sensitivity analyses on certain parameters will
allow the user to assess the impact of specific assumptions. Sensitivity
analyses were noted in Section 2.2 as a key element in applying the
assessment methodology.
3.3.1 Methodology Assumptions
The assumptions on which the assessment nomograph is based are as follows:
1. All soil and aquifer properties are homogeneous and isotropic
throughout each zone.
2. Steady, uniform flow occurs only in the vertical direction
throughout the unsaturated zone, and only in the horizontal
-------
Figure 3.6 Schematic Linkage of Unsaturated and Saturated
Zone Assessments
44
-------
(longitudinal) plane in the saturated zone in the direction of
ground-water velocity.
3. Contaminant movement is considered only in the vertical direction
for the unsaturated zone and horizontal (longitudinal) direction
for the saturated zone.
4. All contaminants are water soluble and exist in concentrations
that do not significantly affect water movement.
5. No contaminant exists in the soil profile or aquifer prior to
release from the source.
6. The contaminant source is applied at a constant concentration
continuously; a pulse input can be handled by superposition
(Section 3.1).
7. There is no dilution of the plume by recharge outside the source
area.
8. The leachate is evenly distributed over the vertical dimension of
the saturated zone.
The assumption of homogeneous and isotropic conditions is equally critical
in both zones. In many cases, extensive heterogeneities will exist for both
soil and aquifer properties, but the emergency response time frame precludes
adequate consideration of variations even if they are known to exist.
Adjustment of certain parameters may be possible to estimate an "effective"
parameter value that partially accounts for property variations. However,
conditions involving soil cracks, fractured media, impermeable layers, clay
lenses, etc. will require the user to make a qualitative assessment on their
potential impact on predicted concentrations.
The assumption of steady, uniform flow is much more critical in the
unsaturated zone than in the saturated zone. Pore water velocities are
significantly more dynamic and variable in the unsaturated zone since they
depend on the percolation flux from rainfall and variable soil moisture
conditions, which in turn affect other soil properties. Under-estimation of
travel times in the unsaturated zone can occur if mean annual percolation
rates are used to estimate movement of the contaminant front during shorter
time periods (e.g., months). Ground-water flow velocities are also
difficult to estimate, but they are less dynamic than in the unsaturated
zone. Consequently, great care is needed in estimating velocities in both
zones.
The assumption that contaminants are water-soluble and exist in
concentrations that do not impact water movement is relevant to both zones
but may be more critical for the unsaturated zone. Surface and unsaturated
soils will likely experience higher concentrations than ground water due to
accidental spills or releases. Also, the majority of contaminants that
reach ground water after traveling through a reasonable depth of unsaturated
soil will likely be water soluble. Although water solubility is assumed
45
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since the contaminant is moving with the water, the same basic form of the
transport equation has also been used to assess movement of the soluble
portion of oil spills in ground water (Duffy et al, 1980) .
The accommodation of contaminant pulse inputs was discussed in Section 3.1
using the principle of superposition. The same principle and procedures are
used for both zones to assess plume migration from a pulse input. However,
for short pulses and low concentrations the precision of numbers read from
the nomograph may be the primary limitation (see discussion below).
3.3.2 Limitations and Parameter Sensitivity
In addition to the assumptions noted above the major limitations of the
procedures described herein include the precision with which numbers can be
read from the nomograph (an inherent limitation of graphical procedures) and
the reliability and accuracy of parameter estimates. As shown on the
nomograph, the C/Co values can be read from Figure 3.3 (full-scale) to two
decimal digits (i.e. 0.01) and from Figure 3.4 (expanded scales, C/Co <0.4)
to three decimal digits (i.e. 0.001). If greater precision is required,
direct calculation of the solution by Equation 3.3 may be needed.
The greatest limitation on predictions will be the accuracy and reliability
of the data for estimating parameters. In most emergency situations,
specific compound and site data will be difficult to obtain; however, all
efforts should be made to acquire the most reliable and site-specific data
as possible through the sources and guidelines provided in Section 4. Even
with relevant data for parameter estimation, users should perform
sensitivity analyses as recommended in Section 2.2 in order to assess the
impact of possible parameter variations and methodology assumptions on
predicted concentrations.
Pettyjohn et al (1982) have performed sensitivity analyses on the major
parameters for an analogous nomograph for the saturated zone only; the user
is referred to that source for complete details. Depending on the specific
data available for individual parameters, the user should consider assessing
the sensitivity of the following parameters which are generally the most
sensitive:
Degradation/decay rate
Retardation factor
Pore Water Velocity
Source Contaminant Concentration
Effective aquifer thickness (saturated zone only)
Dispersion coefficient
Degradation/decay and retardation are interrelated since retarding the
movement of the contaminant will allow greater time for degradation to
occur. Velocity is a sensitive parameter for both zones. Since it is
highly variable and can range over orders of magnitude, assessments of its
sensitivity in site-soec if ic situations is highly r
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For the saturated zone, the effective aquifer thickness or zone of mixing
represents the degree to which the contaminant is uniformly mixed in the
vertical direction. For very shallow aquifers, using the entire thickness
may be appropriate. For deep aquifers, mixing zones considerably less than
the total may be required. Consequently, the effect of varying mixing
depths should be assessed by the user.
Dispersion in ground water can be significant especially at low ground-water
velocities. Since the coefficient can vary over a wide range, accurate
estimates of expected subsurface conditions can be extremely difficult.
Sensitivity should be analyzed.
Source contaminant concentrations may be the most difficult of all data to
obtain and/or characterize, especially for landfill, lagoon, or other waste
site situations. If a range of possible or probable values can be
estimated, the user should definitely evaluate the concentration predictions
that would result from the full potential range of source values.
47
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SECTION 4
PARAMETER ESTIMATION GUIDELINES
The most important part of the rapid assessment methodology is estimation of
reasonable and valid parameter values for a specific emergency response
situation. Section 2.3 described and discussed the critical compound and
site characteristics that determine the potential for ground-water contamina-
tion at a particular hazardous waste or spill site. This section provides
specific guidelines for estimation of the parameter values needed for use of
the rapid assessment nomograph described in Section 3. The format of this
section is as follows:
Section 4.1 General Parameter Estimation
Section 4.2 Unsaturated Zone Parameter Estimation
Section 4.3 Saturated Zone Parameter Estimation
For each parameter, guidelines are provided, to the extent possible, for
calculating the parameter value and estimating the relevant compound and
site characteristics on which it depends. Thus, discussions of
characteristics are grouped according to the affected parameters. For
example, since the retardation factor for organic compounds depends upon
organic carbon content, organic carbon partition coefficient, bulk density,
and porosity (saturated zone), these characteristics are discussed under the
section on estimating the retardation factor. For parameters needed in both
the unsaturated and saturated zone assessments, the primary discussion is
Section 4.2 (unsaturated) with any adjustments required for the saturated
zone in Section 4.3.
Some repetition of information in Section 2.3 (characteristics) and 2.4
(data sources) is included in this section to preclude the need to
continuously turn back to the earlier sections and to clarify the
presentation. Once the user is familiar with the content of this manual,
this section will likely receive the most usage on a continuing basis
especially during an emergency response.
The user will note that the following statement is repeated numerous times
in this section:
Local site-specific information should be used whenever
possible; significant errors can result from using general or
regional data.
48
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This emphasizes the need to search for and use local site-specific
information for the parameter being discussed. The statement is repeated to
insure that the user is aware of possible errors that can result from the
use of general or regional data whenever the parameter must be estimated.
4.1 GENERAL PARAMETER ESTIMATION
This section discusses general characteristics important to assessment
procedures in both zones, including identity and concentration of
contaminants, nature of the soils and geologic strata, age of the
waste/spill site, and depth to ground water. The contaminant concentration
is the only characteristic discussed that results in a specific parameter
value used in the nomographs. However, the other characteristics are
important in applying the assessment procedures, evaluating assumptions, and
determining compound/site characteristics.
4.1.1 Identity of Contaminants
Obviously the identity of the contaminants present at the waste/spill site
is necessary to evaluate the relevant physical/chemical properties needed
for predicting fate and migration. In many cases the identity will have
been established by emergency personnel (e.g. at a spill site) or prior
analyses (e.g. drinking water problems) in order to determine the need for
an emergency ground-water assessment. Identification can be established
quickly, on the order of several hours, through the use of records and
observable characteristics. Chemical analyses can be used, if necessary,
but they require considerably more time, and may need to be limited to
qualitative field methods in order to give results within the emergency
response 24-hour time frame.
Records provide the most rapid, positive identification of contaminants
involved in a hazardous waste accident and should therefore be the focus of
the initial efforts at contaminant identification. Shipping papers and
transportation labels are now required when transporting hazardous
materials. In addition, the Association of American Railroads is developing
a computerized tracking system for rapid identification of railcars
containing hazardous materials (Guinan, 1980).
The use of records to identify chemicals present at uncontrolled waste sites
is much more difficult. Waste manifests, listing each waste shipment
received at the facility, are a possible source of data, but these manifests
have only recently been required in many cases. Waste site owners and/or
companies who have disposed materials at the site may be able to provide
some information on the types of contaminants present.
If records are unavailable or incomplete, observable characteristics such as
odor, color, density, and reaction should be investigated as clues to the
identity of the waste. The following handbooks and data bases (described in
section 2.4) provide information to aid in waste identification based on
observable characteristics:
49
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1) Field Detection and Damage Assessment Manual for Oil and
Hazardous Materials Spills, U.S. EPA, Washington, DC, 1972.
2) U.S. Coast Guard Chemical Hazard Response Information System,
Manual CG-446-1, A Condensed Guide to Chemical Hazards, and
Manual CG-446-2, Hazardous Chemical Data, Washington, DC, 1974.
3) OHM-TADS Data System, U.S. EPA.
In addition to printed and computerized information on observable
characteristics, experts within the chemical industry (Chemical Transpor-
tation Emergency Center (CHEMTREC) at (800) 424-9300 or 483-7616), at local
universities, and at regional response teams (RRT) can be contacted for
assistance.
Field analytical methods will be difficult to apply within an emergency
response time frame and should therefore be called upon for compound
identification only after first considering records and observable
characteristics. The Field Detection and Damage Assessment Manual for
Hazardous Spills (EPA 1972), the EPA Field Guide for Scientific Support
(Battelle PNL 1982a) and the EPA's OHM-TADS system describe the use of
several analytical methods for identifying hazardous chemicals. A variety
of chemical products are available for in-field analysis. The application
of these analytical methods will require the presence of a skilled
technican, experienced in the operation of these instruments.
4.1.2 Contaminant Concentration
The source concentration of the specific contaminant(s) to be analyzed is a
required input parameter for both the unsaturated and saturated zone
assessments. For the unsaturated zone, the user must specify the
concentration of the contaminant available to the soil after deducting
potential losses due to volatilization, decay processes, clean-up/removal
operations, retention by liners and/or non-leaking drums, etc. In many
emergency response situations, the initial contaminant concentration may be
the most difficult of all parameters to estimate. A variety of sources of
information should be consulted to uncover data specific to the waste site
or spill under investigation.
Records and industry experts should be the primary sources contacted
initially to uncover concentration data. Although waste disposal site
records (if available) and transport manifests do not often contain
concentration data, they may identify the general category of the
waste/contaminant, the industry or companies that generated the compound,
and possible contacts for further information. Also, the procedures and
sources used to identify the contaminant (e.g. CHEMTREC, AAR) may also be
useful in estimating concentrations. Industry contacts and experts may be
able to provide estimates of concentrations at which the chemical is
normally transported (i.e. for spills) or resulting from a particular
industry or industrial process (i.e. for waste sites).
50
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Chemical analyses by mobile laboratories or other emergency or field
procedures can provide the needed information, and will usually be ordered
by the on-scene coordinator once it is determined that a toxic or hazardous
compound is involved. However, the results of chemical analyses may not be
available within the emergency response time frame, especially if subsurface
sampling is required. The above sources should be contacted concurrently
while samples are being taken and analyzed in order to expedite obtaining
concentration information and performing the assessment procedures.
Lacking any information on the contaminant concentration, we recommend that
the user assume the source concentration equal to the water solubility of
the contaminant. In most situations this is an appropriate assumption for
an initial assessment since movement of the contaminant through the
unsaturated zone will occur primarily by the infiltrating water carrying the
water soluble portion of the compound. Although retardation and decay
processes will subsequently reduce unsaturated zone concentrations, the
water solubility is a reasonable estimate of the source contaminant
concentration. This assumption has been used by Falco et al (1980) in a
screening procedure for assessing potential transport of major solid waste
constituents in releases from landfills and lagoons.
Water solubility data for specific compounds and hazardous waste
constituents is available in the following data sources:
1) CHRIS Manual CG 446-1,2 U.S. Coast Guard, 1974
2) OHM-TADS, U.S. EPA Data Base
3) Physical Chemical Properties of Hazardous Waste Constituents,
U.S. EPA, 1980
4) The Merck Index, Merck and Company, Inc. (Windholz, 1976)
5) Handbook of Environmental Data on Organic Chemicals (Verschueren,
1977)
6) Aquatic Fate Process Data for Organic Priority Pollutants, (Mabey
et al 1982)
In addition, Lyman et al (1982) describe a variety of methods of estimating
solubility in water and other solvents from data on melting point,
structure, octanol-water partition coefficients, activity coefficients, and
other compound characteristics.
Alternatively, for -compounds that are considered to be a small fraction of
the total waste volume at a site, Falco et al (1980) assumed the
concentration in the leachate to be the equilibrium concentration resulting
from partitioning between the solid and ' dissolved phases of the waste
compound. Thus the source solution concentration could be estimated as
follows:
51
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C F (4.1)
S= K
om
where Cs = source solution concentration, mg/1
Kom = partition coefficient between organic matter and
solution, 1/mg
F = fraction of solid waste that is the contaminant of
interest
F must be evaluated from records and other information available for the
specific waste site, and Kom is discussed in Section 4.2.
The user should be aware that for water insoluble or slightly soluble
compounds from waste sites or spills, the assumption of using water
solubility values could lead to significant errors. This will be especially
important for large volume spills of such chemicals where gravity and the
mass of the spill are the driving forces for moving the contaminant through
the unsaturated zone. (See Section 4.2 for further discussion). The above
assumptions and methods of estimating the source concentration should be
used only as a last resort when no other data or information is available.
Chemical Loss Mechanisms
In addition to leaching to ground water and chemical decay processes in the
soil, chemical losses from the spill site may occur via photochemical decay
and volatilization. These processes will help to reduce the contaminant
concentration available to move through the soil, and should be considered
when estimating this concentration value.
Photolysis rates depend on numerous chemical and environmental factors
including the light absorption properties of the chemical, the light
transmission characteristics of the chemical (if pure) or its environment
(water, soil, etc.), and the available solar radiation of appropriate wave
length and intensity. Estimation of the chemical's general photolytic
reactivity and the light transmission properties of its environment or
solvent will usually be very difficult. Also, most existing models and data
(e.g. Smith et al, 1977; Callahan et al, 1979) for predicting photolytic
decay in the environment are applicable to atmospheric and aquatic systems.
Consequently, the quantitative estimation of attenuation of a chemical
concentration by photolysis at a spill site during a 24-hour emergency
response period would be impossible. The best we can do is to assess the
probability of photolysis being an important loss mechanism and then adjust
the assessment results accordingly when photolysis is ignored. The
following steps are recommended:
1) Determine whether the chemical is exposed to direct solar
radiation. If most of the chemical has percolated into the soil,
52
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photolysis can be neglected; if the chemical is directly exposed,
go to step 2.
2) Determine whether the chemical is susceptible to photolysis by
consulting with a) industry officials familiar with the specific
chemical or b) environmental photolysis reference books and
literature (e.g. Callahan et al, 1979; U.V. Atlas of Organic
Compounds 1966-1971). This step may be subject to considerable
error, however, since the photochemical reactivity of a chemical
is determined by its physical state (dissolved, solid, liquid,
adsorbed) and environment (solvent, etc.) as well as its molecular
structure.
3) If both 1 and 2 above are positive, the user may conclude that
photolysis is a possible or significant depletion mechanism for
the chemical. However, further analysis to quantitatively
estimate this depletion would require laboratory studies not
possible within an emergency response time frame.
Volatilization may provide a significant attenuation mechanism for chemical
spills on land. The rate of loss of chemicals from soil or surface pools
due to volatilization is affected by many factors, such as the nature of the
spill, soil properties, chemical properties, and environmental conditions.
The mechanisms for chemical loss from the land are direct evaporation from a
pool or saturated soil surface, vapor and liquid phase diffusion from
chemicals incorporated into dry soil, and advection with vapor and liquid
water due to capillary action (i.e. the wick effect). Thus, a comprehensive
model of the volatilization process would be extremely complex; however, a
number of relatively simple methods exist to estimate these losses, and
three of them are presented here. (Thibodeaux, 1979; Hamaker, 1972; Swann
et at, 1979). The reader is referred to the original literature or the text
Handbook of Chemical Property Estimation Methods (Lyman et al, 1982) where a
number of models are described along with conditions of use and parameter
estimation methods.
Volatilization - Method 1
This method (Thibodeaux, 1979) is primarily applicable for a liquid pool of
pure chemical. However, it can be used for a mixture of chemicals to
estimate the reduction in the source concentration of one specific chemical
due to the volatilization flux, assuming a constant volume mixture. It
requires estimation of the area of the pool, wind speed at the spill site,
pool temperature, and the Schmidt Number (Sc) for the chemical vapor.
The flux of chemical is given by:
N = 0.468 U-78 L--11 Sc--67 Pvp M/T (4.2)
2
where N = flux of chemical from pool, flq/m /hr
U = wind speed at 10m height, m/hr
53
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L = length of pool, m
Sc « Schmidt Number for chemical vapor (see below)
P = chemical vapor pressure, mmHg
T = pool temperature, °K
M = chemical molecular weight, g/mole
The Schmidt number for a gas is defined by:
Sc = v/D (4.3)
2
where v = kinematic viscosity, cm /s
D = gas diffusion coefficient, cm/s
Schmidt numbers for many chemicals are tabulated by Thibodeaux (1979) and
.nay be estimated for similar chemicals by the following equation:
(4.4)
where M = molecular weight
Method 2
This method is applicable to situations in which the chemical has been
applied to or spilled on the soil surface. Researchers at Dow Chemical
Company (Swann et at, 1979) correlated volatilization rate with a number of
chemical properties. The first-order rate constant for volatilization of
chemicals spilled or applied to the soil was found to be approximated by the
following correlation equation:
oc
where k = volatilization rate constant, day
v J
K = soil adsorption coefficient based on organic carbon
oc
content, ml/g
54
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P = vapor pressure of chemical, mmHg
S = water solubility of chemical, fig/ml
Since kv is a first-order rate constant, the concentration loss function
due to volatilization is represented as:
C = C exp(-k t) (4.6)
where Co = initial concentration of the chemical, fig/1
C = concentration of the chemical after time t, fJg/I
t = time, day
Method 3
This method (Hamaker, 1972) allows estimation of volatilization rates from
chemicals distributed in a soil column such as after initial infiltration of
a spill. It assumes a semi-infinite impregnated soil layer and no upward
water flux. The loss of chemical is given by
_
2CO (Dt/7T ) 2
where
Q = total loss of chemical per unit area over time t,
fig/cm
Co = initial concentration of chemical in the soil, fig/cm
D = diffusion coefficient of chemical vapor in the soil-air,
2 ,
cm /sec
t = time, sec
n = 3.14159...
For the situation where chemical is incorporated in moist soil, the upward
flux of water due to evaporation and capillary action will greatly enhance
the movement of chemical to the surface and its subsequent volatilization.
Estimation of this flux requires use of a more complex model (e.g. Hamaker,
1972) which necessitates the determination of water fluxes in the soil. The
user should recognize that Method 3 will significantly under-estimate
volatilization under moist soil conditions.
Generally, the preceding methods require knowledge of vapor pressure,
solubility and diffusion coefficients, all of which are available from
sources previously identified (See Table 2.2). Additional sources of data
for these methods, including the Schmidt number (Method 1) , can be found in
the following:
55
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1. Chemical Engineers Handbook (Perry and Chilton, eds., 1973)
2. Chemodynamics, (Thibodeaux, 1979)
3. Gaseous Diffusion Coefficients (Marrero and Mason, 1972)
4. Handbook of Chemical Property Estimation Methods (Lyman et al,
1982)
4.1.3 Nature of Soils and Geological Strata
A reliable study of contaminant movement through the unsaturated and/or
saturated zones requires a careful assessment of the types of soils and/or
geological formations present. The methodologies incorporated in this
manual accept only homogeneous descriptions of the transport media being
modeled, but users can choose parameter values that can partially account
for any heterogeneities that are known to be present. For this reason, a
thorough knowledge of the soils and geology at the site is important in the
sound application of the relatively simple methods in this manual.
Data on the types of soils, presence of cracks or sinkholes, and occurrences
of lenses of heterogeneous materials in the unsaturated zone can be found in
soil surveys (performed by the U.S. Soil Conservation Service), well
drillers' logs (usually kept by well owners or local departments of health
or water), and construction design reports (on file with local engineering
department or building inspector). If a soils expert is on the spill site,
a quick evaluation of the general character of the surface material may be
possible. The first aim of the soils assessment is the establishment of the
predominant nature of the unsaturated zone so that the bulk density,
porosity, organic content, and volumetric water content can be estimated.
The presence of heterogeneities (cracks, clay lenses, sinkholes, etc.) can
be used as a basis for adjusting the parameter values chosen under the
assumption of homogeneity, or for interpreting the final model results.
An evaluation of the nature of the ground-water formations present at the
site should include searches for prior hydrogeological investigations (by
the U.S. Geological Survey, State Geological Survey and Department of Water
Resources, and local and regional health and water agencies). A second
major source of geological data lies with experts in universities,
consulting firms, and government agencies. Drillers' well logs represent a
third significant record of the composition of the saturated zone. Among
the data being sought are the type of aquifers present (confined or water
table), the predominant composition of the strata, the presence of
fractures, • and the existence of clay lenses. The assessment nomograph
incorporated in this methodology is designed to simulate a single water
table (unconfined) aquifer, but users should be aware of the existence of
other types of aquifers and/or multiple water-bearing formations to assess
the reliability of the predicted results and to perform qualitative
assessments beyond the focus of the nomograph. Fractures can greatly
increase the spread of contamination, while clay lenses retard this
movement. Knowledge of their presence will govern the choice of parameter
values and the interpretation of the predictions.
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4.1.4 Age of the Waste Site or Spill
The age of the waste site or spill is essential in estimating the time
duration of leaching of the contaminant into the unsaturated and saturated
zones. For many surface spills, the investigation will occur immediately
after the accident and the age of the site is therefore known. The analysis
of newly-discovered uncontrolled disposal sites with the methodologies
contained in this manual will require knowledge of the age of the site.
Predictions of contaminant transport can then be related to real time and
the extent of the plume at the time of the analysis can be estimated. To
establish the age of an uncontrolled waste site, records of waste shipments
should first be consulted. Any information found in the site records can be
supplemented by tracing ownership of the property to determine the length of
time the area was used as a landfill.
4.1.5 Depth to Ground Water
In evaluating transport in the unsaturatea zone, the depth to ground water
must be estimated in order to assess the likelihood that contaminants will
reach the ground water. Since ground-water levels are often within 10 to 20
meters of the land surface, and can be 3 meters or less, the potential for
ground-water contamination from waste sites and chemical spills is a
significant problem. Seasonal fluctuations, if significant, should also be
considered since these fluctuations can range from 1 to 5 meters or more in
many parts of the country. Also, the effects of pumping and recharge areas
should be evaluated.
Local site-specific information should be used whenever possible;
significant errors can result from using general or regional data.
Prior hydrogeologic and water supply studies in the general region of the
site are valuable sources of data on site characteristics, including depth
to ground water. Contact should be made with the U.S. Geological Survey,
the State Geological Survey, the State Department of Water Resources, and
the local and county water, health, and engineering departments a^ a start
in the search for existing technical reports and information.
The depth to ground water can be determined by talking to the owners of
nearby wells or by making depth measurements at these wells as long as the
wells are not being actively pumped, and therefore accurately represent the
water-table level. Also, water-surface elevations in nearby perennial
streams, lakes, marshes, and other waterbodies (e.g., mines, gravel pits,
flooded excavations) can be used to estimate the depth to ground water since
these are areas where the ground-water surface intersects the land surface.
If prior studies, observations, or information from nearby wells are not
available or do not provide the required data on depth to ground water, then
local experts in hydrogeology (at universities, consulting firms, and
governments agencies) should be contacted for guidance.
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4.2 UNSATURATED ZONE PARAMETER ESTIMATION
Table 4.1 lists the nomograph parameters for an unsaturated zone assessment
and the various types of information needed and/or useful for their
evaluation. Except for contaminant concentration, which was discussed in
Section 4.2, estimation guidelines for each parameter are provided below in
the order shown in Table 4.1.
4.2.1 Pore Water Velocity
Estimation of pore water velocity is a necessary and important element in
analyzing transport of contaminants through the unsaturated soil zone. In
essence, the water (or other fluid) moving through the pore spaces in the
soil is the driving mechanism for contaminant movement through the soil and
to ground water. Although the term conventionally implies water movement,
pore velocity could also refer to the movement of other solvents or fluids
as might occur in a large volume chemical spill infiltrating through the
soil.
Pore water velocity is a function of the volumetric flux per unit surface
area and the volumetric water content, as follows:
v = -3 <4-8>
e
Where V = pore water velocity, cm/day
q = volumetric flux per unit area, cm/day
6 = volumetric water content, dimensionless
In reality, the velocity of water movement through the unsaturated zone is a
highly dynamic process resulting from the combined effects of stochastic
rainfall inputs and soils, topographic, and vegetation characteristics of
the site. However, under the steady flow assumption of our transport
equation, the pore water velocity is assumed constant for the time period of
interest. The specific time interval of concern also determines the
appropriate method of estimating the volumetric flux, q, for the two types
of problems addressed in this manual:
Case 1 - Waste Sites; To assess the extent of the contaminant plume
emanating from a leaking waste site, long-term or annual values of
water infiltrating or percolating through the unsaturated zone of the
site represents the volumetric flux, q. For the saturated zone, this
value is also called the recharge rate representing the moisture
actually reaching ground water.
Case 2 - Spills; To estimate contaminant movement from a spill site,
the volumetric flux is based on the volume of the spill (for large
spills) and/or expected percolation/recharge volumes derived from
short-term (5-day, 10-day, monthly) precipitation forecasts.
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TABLE 4.1 UNSATURATED ZONE PARAMETERS AND ASSOCIATED INFORMATION
NEEDED/USEFUL FOR EVALUATION
Parameter
Name
Information Needed/Useful
For Evaluation
Co
Initial contaminant
concentration
Contaminant identity, solubility,
waste/site records, organic carbon
partition coefficient, decay rates
and processes
V
Pore water velocity
Meteorologic and soil characteris-
tics, infiltration, percolation,
volumetric water content, spill
volume/waste quantity, soil porosity
Degradation/decay rate
Contaminant identity, relevant
attenuation processes, environ-
mental conditions
Retardation factor
Contaminant identity, adsorption
characteristics, soil organic
carbon, bulk density, ion exchange
capacity, clay content/type,
volumetric water content
Dispersion Coefficient
Subsurface/soil characteristics,
pore water velocity, dispersivity
-------
Guidelines and recommendations for estimating the volumetric flux for each
case and the volumetric water content are presented below:
Percolation/Recharge
To estimate percolation and recharge values for a specific site, the
conventional water balance equation can be written in the following form.
PER = P - ET - DR (4.9)
where PER = Percolation and Recharge, cm/yr
P = Precipitation, cm/yr
ET = Evapotranspiration, cm/yr
DR = Direct Surface Runoff, cm/yr
As s simplification for use within the emergency response time frame, the
equation ignores any man-made water additions (e.g. irrigation, which could
be added to P if known) and any change in soil moisture storage. PER
includes both percolation and recharge to the ground-water systems of
concern. For sites where the ground-water table is close to the land
surface, percolation and recharge will be equal. However, for most sites
where ground water is considerably below the surface, some of the
percolating water will move laterally within the soil or upon reaching the
ground-water surface, and subsequently discharge to a surface stream. Thus,
PER should be used to assess contaminant movement through the unsaturated
zone, but this value may need to be reduced to estimate recharge to deep
aquifers or where impermeable strata exist.
A variety of local meteorologic and hydrologic data sources should be
contacted to estimate percolation and recharge values for the specific site
based on the water balance components of Equation 4.9. As discussed above,
the appropriate time frame for the needed data and associated data sources
will be different for Case 1 and Case 2 analyses.
Case 1 Analyses will require an estimate of the age of the waste site, or
the time when hazardous waste releases may have begun, in order to determine
^the time period for the needed data. In most cases, this time period will
be a number of years. In order of preference, the following methods of
obtaining site-specific estimates of percolation and recharge are
recommended:
1) Obtain annual estimates of PER from local sources and
calculate an average value for the time period
2) Obtain annual estimates of P, ET, and DR from local sources,
calculate annual values of PER from Equation 4.9 and
calculate an average value for the time period.
3) Obtain mean annual values for PER from local sources, or
obtain mean annual values of P, ET, and DR from which a mean
annual value of PER ~an be calculated.
60
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Local site-specific information should be used whenever possible;
significant errors can result from using general or regional data.
Local sources of historical data needed for estimating PER for Case 1
analyses include:
o Local or regional water agencies
o Local or regional offices of State and Federal water agencies
(e.g. U.S. Geological Survey, National Weather Service;
Forest Service, Department of Agriculture, EPA)
o University libraries and departments of engineering,
agriculture, soils, etc.
o First order weather stations - usually found at airports
Lacking any local data, the user can obtain a preliminary estimate of mean
annual percolation for areas in the eastern half of the U.S. from Figures
4.1 and 4.2, based on the U.S. Soil Conservation Service hydrologic soil
classifications defined in Table 4.2. The isopleths of mean annual
percolation in these figures were derived from application of the U.S. Soil
Conservation Service Curve Number procedure (U.S. SCS, 1964) for estimating
potential direct runoff at more than fifty sites in the Eastern U.S.
(Stewart et al, 1976).
The Western U.S. was not included due to irrigation applications and the
highly variable rainfall patterns and steep gradients (due to orographic
effects) which preclude interpolation of percolation estimates between
widely separated meteorologic stations.
To use these figures, the user must determine or estimate the hydrologic
soil group for the soil at the waste site and then choose the appropriate
figure for that class i.e.
A or B: Figure 4.1
C or D: Figure 4.2
Hydrologic soil groups for a variety of soils have been determined by the
U.S. SCS (U.S. SCS, 1971); local offices and/or the state conservationist
should be contacted for this information for the site. Alternately, Figure
4.3 provides an approximate mapping of hydrologic soil groups based on
generalized soils information. Due to the extreme spatial variability of
soil characteristics, Figure 4.3 should be used only as a last resort when
site-specific information is not available.
Figure 4.4 provides an overview of the spatial variability of the three
independent variables of the water balance equation - precipitation,
evapotranspiration, surface runoff - on a national scale. This information
is provided to supply the user with general background with which to assess
possible major errors in locally supplied information. The national maps
should not be used to estimate PER for a number of reasons; significant
61
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Figure 4.la Mean annual percolation below a 4-foot root zone In Inches. Hydrologlc Soil
Group A. Four Inches available water-holding capacity. Straight-row corn.
(Stewart et al.. 1976)
1 inch - 2.54 cm.
Figure 4.1b Mean annual percolation below a 4-foot root zone In Inches. Hydrologlc Soil
Group B. Eight Inches available water-holding capacity. Straight-row corn.
(Stewart et al.. 1976)
62
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•o
Flaure 4.2» He»n «nnu»l percolation below i 4-foot root zone In Inches. Hydrolojlc Soil
Group C. Eight Inches available water-holding capacity. Straight-row corn.
(Stewart et «!.. 1976)
Figure 4.2b Mean annual percolation below a 4-foot root zone In Inches. Hydrologlc Soil
Group D. Six Inches available water-holding capacity. Straight-row corn.
(Stewart et •!.. 1976)
63
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TABLE 4.2 HYDROLOGIC SOIL CLASSIFICATIONS (U.S. SCS, 1964)
Group/Runoff Potential
Group A. Low Runoff Potential
Group B.
Moderately Low Runoff
Potential
Group C.
Moderately High Runoff
Potential
Group D. High Runoff Potential
Description
Soils having high infiltration
rates even when thoroughly wetted
and consisting chiefly of deep/
well-to excessively-drained sands
or gravels. These soils have a
high rate of water transmission.
Soils having moderate infiltration
rates when thoroughly wetted and
consisting chiefly of moderately
deep to deep/ moderately well to
well-drained soils with moderately
fine to moderately coarse
textures. These soils have a
moderate rate of water
transmission.
Soils having slow infiltration
rates when thoroughly wetted and
consisting chiefly of soils with a
layer that impedes downward
movement of water/ or soils with
moderately fine to fine texture.
These soils have a slow rate of
water transmission.
Soils having very slow
infiltration rates when thoroughly
wetted and consisting chiefly of
clay soils with a high swelling
potential/ soils with a permanent
high water table/ soils with a
claypan or clay layer at or near
the surface/ and shallow soils
over nearly impervious material.
These soils have a very slow rate
of water transmission.
64
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in
Figure 4.3 Generalized Hydrologic Soil Groups For The U.S. (Battelle, 1982)
-------
en
en
Figure k.k Average Annual Precipitation,
Potential Evapotranspiration,
and Surface Water Runoff for
the U.S. (Geraghty et. al., 1973)
1 inch =
2.54cm
-------
local and regional variations are masked by the national isopleths; actual
evapotranspiration is usually less than the potential evapotranspiration,
especially in the arid west; surface runoff isopleths are derived from
U.S.G.S. gaging station data which includes significant contributions of
baseflow derived from ground water. In many areas of the country and
especially the Western U.S., ignoring the runoff component in the
calculation of annual PER values will not lead to significant errors, and
may actually result in better percolation values since most runoff data
include significant ground-water contributions.
Case 2 Analyses will require forecasts of expected future conditions,
primarily rainfall and associated runoff, in order to assess the potential
for ground-water contamination from a spill. The same water balance
equation (Equation 4.9) is used to estimate PER but the P, ET, and DR terms
must be evaluated differently from the Case 1 analyses. The primary
differences result from the much shorter time frame of concern; spill
situations will require assessment of the contaminant plume from a few days
to a few months in the future in order to determine the appropriate
emergency response actions. Because of this shorter time frame,
recommendations for evaluating the water balance components are as follows:
1. P should be estimated from the quantitative precipitation forecasts
(QPF) for the local region available from the local or regional
office of the National Weather Service. Generally 5-day to 30-day
forecasts are available; longer forecasts may often be qualitative in
terms of "above-normal" or "below-normal" expected rainfall.
2. ET can be effectively ignored for the short time frames of 5 to 10
days without significant inaccuracy, especially during heavy rainfall
periods. For time periods of one month or longer, ET estimates
should be included in the water balance calculation.
3. Soil moisture storage and resulting effects on direct surface runoff
become significant during the short time frame of a Case 2 analysis.
Also, contaminated runoff although removed from the immediate spill
site can reinfiltrate further downslope.
The same sources of local data noted under the Case 1 analysis are also
important for a Case 2 analysis. One critical addition is the local or
regional National Weather Service office; local precipitation forecasts are
absolutely essential for a Case 2 analysis (except possibly in large-volume
spills, discussed below). Other local information sources include TV/radio
stations, local meteorologists, and other agencies either making or needing
weather forecasts. Experience with local conditions in water agencies,
universities, hydrologists, and other water experts is especially important
in estimating ET and DR values for the short time frame analysis.
Local site-specific information should be used whenever possible;
significant errors can result from using general or regional data.
Lacking any local data, the user should consult the following publications
which contain meteorologic data on a national scale:
67
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1. Climatic Atlas of the U.S. (Environmental Data Service, 1968)
2. Water Atlas of the U.S. (Geraghty et al, 1973)
Both publications include various types of evaporation and
evapotranspiration data. The Climatic Atlas also includes normal monthly
precipitation on a national basis from which forecasts of above or below
normal rainfall might be estimated. In addition, Thomas and Whiting (1977)
have published annual and seasonal precipitation probabilities for 93
weather stations across the U.S. which could be used to further quantify
qualitative forecasts.
Short term estimates of direct runoff from forecasted storm events are
difficult to make, and are highly dependent on local site-specific
conditions and existing soil moisture conditions. Lacking any local
information or guidance from local hydrologists or water agencies, the user
can choose runoff coefficients from Table 4.3 to estimate the portion of the
rainfall that will result in runoff. The values in this table were derived
by applying the SCS curve number procedure (U.S. SCS, 1964) for one-inch and
four-inch storm events for each hydrologic soil group, and under each of the
three antecedent soil conditions. Thus, the user should choose the low
values in Table 4.3 for a one-inch forecast, the high value for a four-inch
forecast, and prorate other forecasted amounts between the extremes. The
values were developed for pasture land in good condition with an average
slope of 2-5 percent; for more accuracy and/or significantly different land
conditions the user should apply the SCS procedures directly as described in
Appendix A.
The methodology in this manual is not directly applicable for large volume
chemical spills where gravitational forces and the hydraulic pressure head
(due to ponding) are the driving forces behind the chemical movement through
the unsaturated zone. The primary reason for this is because the equations
and parameters from which the nomograph was developed are based on water
movement through porous media.
TABLE 4.3 RUNOFF COEFFICIENTS FOR HYDROLOGIC SOIL GROUPS*
5-Day Antecedent Rainfall
(inches)
Dormant
Season
10/1-3/31
<0.5
0.5-1.1
Growing
Season
4/1-9/30
<1.4
1.4-2.1
Hydroloqic Soil Groups
B
0.0 0.0 -0,2 0.0 -0.14 0.0 -2.3
0.0-0.04 0.0 -0.20 0.02-0.40 0.08-0.51
0.0-0.18 0.07-0.49 0.22-0.66 0.36-0.75
'Derived from 1* to 4* rainfall events on pasture land kept in good condition
with average slopes of 2-5 percent.
68
-------
However, if a qualitative or semi-quantitative assessment is required in an
emergency situation, the methodology could be used for a gross or relative
evaluation. The pore water velocity could be estimated by using the volume
of the spill (i.e. area x average depth) and its infiltration rate to
calculate the volumetric flux term in Equation 4.8; the infiltration rate
might be grossly estimated by timing the drop in the surface of the ponded
chemical, or estimating the total time for the ponded chemical to infiltrate
or disappear. This estimated pore velocity could then be used, along with
the other parameters (adjusted accordingly) in the methodology to estimate
the concentration and time to enter the ground water. Clearly, the results
will need to be analyzed and used with extreme caution, and only as a gross
approximation. Chemicals with viscosities greater than water can be
expected to move slower, while chemicals with a lower viscosity would likely
move faster than water. The methodology predictions should be analyzed and
adjusted in this manner.
For longer time frames, such as a few months, where infiltration from
rainfall would be significantly greater than the spill volume, the pore
water velocity should be derived from the water balance equation as
described under the Case 2 analyses above.
Volumetric Water Content
The volumetric water content is the percent of the total soil volume which
is filled with water. Under saturated conditions, the volumetric water
content equals the total porosity of soil and is considerably less than
porosity under unsaturated conditions. Conceptually, under steady flow
conditions water (i.e. volumetric flux or percolation) is flowing through
the pore spaces occupied by the volumetric water content. Thus, the flux
and moisture content are directly related with higher flux values requiring
higher moisture content, and vice versa.
Volumetric water content values will range from 5% to 10% at the low end to
less than the total porosity (discussed below) at the higher end. For most
soils, this results in a range of 5% to 50%. If no other local information
is available, we recommend that the user select a value within this range
(with the upper value modified to reflect total porosity of the
site-specific soils) corresponding to the relative value of the flux as
estimated by the percolation rate. Thus, for high percolation values (see
Figures 4.1 and 4.2) water content values of 30% to 50% should be used, and
for low percolation values 10% to 20% would be recommended. Alternately,
the user may assume that the volumetric water content is equal to the field
capacity for the particular soil type. Field capacity is the moisture
retained by the soil after free drainage. Although this is not a rigorous
definition, it is usually equal to the 1/3 bar soil moisture value by
volume. Representative value ranges of field capacity by soil type are as
follows:
Field Capacity
Sandy soils 0.05 - 0.15
Silt/loam soils 0.13 - 0.30
Clay soils 0.26 - 0.45
69
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Total and Effective Porosity
The total porosity, usually stated as a fraction or percent, is that portion
of the total volume of the material that is made up of voids. Effective
porosity is less than total porosity, being reduced by the amount of space
occupied by dead-end pores. In unconfined aquifers, the term specific
yield, a measure of the quantity of water that will drain from a unit volume
of aquifer under the influence of gravity, can be used as an estimate of
effective porosity. The terms total and effective porosity are applicable
to both the saturated and unsaturated zones.
Total porosity is required in the saturated and unsaturated zone
methodologies in determining the retardation effects of adsorption. The
effective porosity of the aquifer is necessary for calculating the velocity
of flow within the voids using Darcy's Law. Effective porosity is not
needed for the unsaturated zone analysis contained within this manual.
Tables 4.4 and 4.5 provide representative values of total porosity and
specific yield (an estimate of effective porosity) for several different
soils and geologic materials.
4.2.2 Degradation Rate
The unsaturated zone can serve as an effective medium for reducing
contaminant concentration through a variety of chemical and biological decay
mechanisms which transform or attenuate the contaminant. Depending on
chemical and soil characteristics, processes such as volatilization,
biodegradation, hydrolysis, oxidation, and radioactive decay may be
important in reducing concentrations prior to reaching the ground-water
table. Also, both volatilization and photolysis may be important in
reducing the concentrations of surface spills (see Section 4.1.2) and thus
reduce the amount and concentration of contaminants available to move
through the unsaturated zone.
The equations and nomograph for contaminant migration allow the use of a
degradation or decay rate to represent disappearance of the pollutant by the
attenuation mechanisms listed above. A first-order rate process is assumed
with the degradation rate representing the aggregate disappearance rate of
the compound by all significant decay or transformation processes. The input
degradation rate is in units of inverse time (i.e. per day) and is related
to the half-life of a compound as follows:
k =0-693 (4.10)
where k = degradation rate, day"1
= half-life, days
In evaluating an appropriate degradation rate, the following steps are
recommended:
1. Determine if degradation can be significant for the specific time
frame, compound, and situation being analyzed. For most instances
70
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TABLE 4.4 REPRESENTATIVE VALUES OF POROSITY
Material
Porosity,
Percent
Material
Porosity,
Percent
Gravel, coarse 28C
Gravel, medium 32e
Gravel, fine 34C
Sand, coarse 39
Sand, medium 39
Sand, fine 43
Silt 46
Clay 42
Sandstone, fine-grained 33
Sandstone, medium-grained 37
Limestone 30
Dolomite 26
Dune Sand 45
Loess 49
Peat 92
Schist 38
Siltstone 35
Claystone 43
Shale 6
Till, predominantly silt 34
Till, predominantly sand 31
Tuff 41
Basalt 17
Gabbro, weathered 43
Granite, weathered 45
Granite, weathered 45
These values are for repacked samples; all others are undisturbed.
Source: Pettyjohn, W.A., et al, 1982
TABLE 4.5 SPECIFIC YIELDS, IN PERCENT, OF VARIOUS MATERIALS
(Rounded to nearest whole percent)
Specific Yield
Material
Clay
Silt
Sandy clay
Fine sand
Medium sand
Coarse sand
Gravelly sand
Fine gravel
Medium gravel
Coarse gravel
# of Determinations
15
16
12
17
17
17
15
17
14
14
Max.
5
19
12
28
32
35
35
35
26
26
Min.
0
3
3
10
15
20
20
21
13
12
Ave.
2
8
7
21
26
27
25
25
23
22
Source: Pettyjohn, W.A. et al, 1982
71
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involving the fate and movement of non-persistent compounds,
degradation should be considered. However, high concentrations of
toxic chemicals may effectively sterilize the soil and reduce or
eliminate microorganisms that biologically degrade the compound.
Also, if decay of the compound is extremely slow relative to the time
frame of interest, or if daughter products produced by transformation
are also toxic, the user may decide to ignore degradation in order to
estimate maximum potential concentrations.
2. Assess the major decay mechanisms for the specific compound of
concern.
3. Evaluate compound-specific rates for each major decay mechanism.
4. Use the sum of the decay rate or the maximum if one decay mechanism
is predominant, as the value of the decay rate for the assessment
nomograph calculations.
The same information sources used in identifying the compound may be helpful
in determining major decay or loss mechanisms and associated rate values.
Companies associated with the waste/spill incident, or companies within the
same industry, can be an extremely valuable source of this information.
Table 4.6 provides a summary of the relative importance of different
chemical fate processes for a wide variety of compounds in various
classifications. If the specific compound is not included in Table 4.6,
industry sources may be able to provide the classification or names of other
compounds with similar degradation mechanisms. (For example, volatilization
is a major process for most halogenated aliphatic hydrocarbons). Although
Table 4.6 was developed primarily for the aquatic environment, it may be
appropriate for many spill situations and appears to be the best summary of
the relative importance of different chemical processes for a variety of
compounds. The user should confirm the validity of the compound-specific
information in Table 4.6 with any other available data.
Degradation rates for specific mechanisms have been compiled for numerous
chemicals and hazardous compounds in the following publications:
1. Physical/Chemical Properties of Hazardous Waste Constituents, Dawson
et al (1980) .
2. Aquatic Fate Process Data for Organic Priority Pollutants, Mabey et
al (1982) (Note: This publication includes available data for all
compounds listed in Table 4.6, except metals and inorganics).
3. Handbook of Environmental Data on Organic Chemicals, Verschueren, K.
(1977).
Also, degradation rates for pesticides in both field and laboratory
conditions have been collected and published by Rao and Davidson (1980),
Nash (1980) , and Wauchope and Leonard (1980). This information is based on
72
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TABLE 4.6 RELATIVE IMPORTANCE OF PROCESSES INFLUENCING
AQUATIC FATE OF PRIORITY POLLUTANTS (After
Mills et al., 1982; Callahan et al.5 1979)
Compound
Process
PESTICIDES
Acrolein _ + -t t - -
Aldrin * + ?-- +
Chlordane •* + ?-- +
ODD * + _-- +
DDE + + . + - +
DDT + + .- + +
Dieldrin + + _ + _•»-
Endosulfan and Endosulfan Sulfate *++?+-
Endrin and Endrin Aldehyde ???•»•- +
Heptachlor + + - ? ++ +
Heptachlor Epoxide +-??-+
Hexachlorocyclohexane (a,0,6 isomers) + ? + ---
-Hexachlorocyclohexane (Lindane) +_+_--
Isophorone -:-? + --
TCDD +..?- +
Toxaphene +++_-+
PCBs and RELATED COMPOUNDS
Polychlorinated Biphenyls +++?-+
2-Chloronaphthalene -?++--
HALOGENATED ALIPHATIC HYDROCARBONS
Chloromethane (methyl chloride)_+----
Dichlororethane (methylene chloride) -+?---
TriChloromethane (chloroform) -*?---
Tetrachloromethane (carbon tetrachloride) 1 +• . - - ?
Chloroethane (ethyl chloride) -+?-+-
1,1-Dichloroethane (ethylidene chloride) _+?---
1,2-Dichloroethane (ethylene dichloride) _+?___
1,1,1-Trichloroethane (methyl chloroform) _+->__
1,1,2-Jrichloroethane ?+---?
1,1,2,2-Tetrachloroethane ?+---?
Key to Symbols:
•H- Predominant fate determining process - Not likely to be an important process
+ Could be an important fate process ? Importance of process uncertain or not
known
73
-------
TABLE 4.6 continued
Compound
Process
Hexachloroethane ?????+
Chloroethene (vinyl chloride) +_____
1,1-Dichloroethene (vinylidene chloride) ?+?--?
1,2-trans-Dichloroethene -+?___
Trichloroethene _+?_._
Tetrachloroethene (perchloroethylene) _++___
1,2-Dichloropropane ? + -? + ?
1,3-Dichloropropene ?+-?+-
Hexachlorobutadiene + + ?-? +
Hexachlorocyclopentadiene + + _ + + +
Bromomethane (methyl bromide) -+__+_
Bromodichloromethane ????-+
Dibromochloromethane ? + ??- +
Tribromomethane (bromoform) ? + ??-•§•
Dichlorodifluoromethane ? + -?-?
Trichlorofluoromethane ? + ---?
HALOGENATED ETHERS
Bis(choromethyl) ether - - ? ++
Bis(2-chloroethyl) ether _+__.?
Bis(2-chloroisopropyl) ether _+__.?
2-Chloroethyl vinyl ether _+?_+_
4-Chlorophenyl phenyl ether +??+-+
4-BromophenyT' phenyl ether +?? + - +
BisŁ2-chloroethoxy) methane --?-+?
MONOCYCLIC AROMATICS
Benzene ++-___
Chlorobenzene + + - ? - +
1,2-Dichlorobenzene (^-dichlorobenzene) ++_?_+
1,3-Dichlorobenzene (m-dichlorobenzene) ++???+
1,4-Dichlorobenzene (Ł-dichlorobenzene) •*• + -?.+
1,2,4-Trichlorobenzene •»••»--?_•»•
Hexachlorobenzene +_._._
Key to Symbols:
•H- Predominant fate determining process - Not likely to be an important process
+ Could be an important fate process ? Importance of process uncertain or not
known
74
-------
TABLE 4.6 continued
Compound
Process
1
Ethylbenzene
Nitrobenzene
Toluene
2,4-Dinitrotoluene
2,6-Dinitrotoluene
Phenol
2-Chlorophenol
2,4-Dichlorophenol
2,4,6-Trichlorophenol
Pentachlorophenol
2-Nitrophenol
4-Nitrophenol
2,4-Dim'trophenol
2,4-Dimethyl phenol (2,4-xylenol)
2-chloro-m-cresol
4,6-Dinitro-p_-cresol
PHTHALATE ESTERS
Dimethyl phthalate
Diethyl phthalate
Di-n-butyl phthalate
Di-n-octyl phthalate
Bis(2-ethylhexyl) phthalate
Butyl benzyl"phthalate
POLYCYCLIC AROMATIC HYDROCARBONS
4
4
4
4
T
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
Acenaphthene"
Acenaphthylene
Fluorene
Naphthalene
Anthracene
Fluoranthene^
Phenanthrene
Benzo(a)anthracene
Benzo(b)fluoranthene
Benzo (Jc) f 1 uor an thene
Chrysene
Key to Symbols:
+4 Predominant fate determining process - Not likely to be an important process
+ Could be an important fate process ? Importance of process uncertain or not
known
4
4
4
4
4
4
4
4
4
4
4
-
_
_
-
4
4
4
4
_
_
*.
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
75
-------
TABLE 4.6 continued
Compound
Process
+
+
+
Pyrene + - + +
Benzo(ghi)perylene + - + +
Benzo(a)pyrene + + + +
Dibenzo(a,h)anthracene + - + +
Indeno(l,2,3-cd)pyrene + - + +
NITROSAMINES AND MISC. COMPOUNDS
Dimethylnitrosamine ++
Diphenylnitrosamine + - ? +
Di-n-porpyl nitrosamine ++
Benzidine + - ? +
3,3'-Dichlorobenzidine ++ - - +
1,2-Diphenylhydrazine (Hydrazobenzene) + - ? +
Acrflonitrile - -f ? -
METALS AND INORGANICS
Asbestos +
Antimony +
Arsenic + + +
Berylumm + - ?
Cadmium +
Copper +
Chromium +
Cyanides _+++_-
Lead +_ + + .+
Mercury ++++-+
Nickel +__. + -
Selenium + + + - + +
Silver +-__--
Thallium +____+
Zin6 +___ + +
Key to Symbols:
•H- Predominate fate determining process - Not likely to be an important process
+ Could be an important fate process ? Importance of process uncertain or not
known
Notes
aBiodegradation is the only process knoen to transform polychlorinated biphenyls
under environmental conditions, and only the lighter compounds are measurably
biodegraded. There is experimental evidence that the heavier polychlorinated
biphenyls (five chlorine atoms or more per molecule) can be photolyzed by ultra-
violet light, but there are no data to indicate that this process is operative
in the environment.
Based on information for 4-nitrophenol
cBased on information for PAH's as a group. Little or no information for these
compounds exists.
76
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agricultural pesticide applications and should be used with caution for the
waste/spill situation only if other data is lacking.
4.2.3 Retardation Factor
The process of adsorption of contaminants onto soil particles and associated
organic matter retards the movement of the contaminant through both
unsaturated and saturated media. As discussed in Section 3, the adsorption
process is included in the assessment nomograph by the retardation factor
which is defined as follows:
R= 1+i K* (4.11)
where R = Retardation factor (dimensionless)
B = Bulk density, g/cc
N = Effective porosity (saturated conditions), or Q, volumetric
water content (unsaturated conditions), dimensionless
K^ = Partition coefficient, ml/g
Thus, the major determinant of the retardation factor, R, is the partition
coefficient, K^, which represents the ratio of the adsorbed pollutant
concentration to the dissolved (or solution) concentration. Under the
linear, equilibrium isotherm assumption employed in this manual, the form
and units of K^ are as follows:
K, Cs (4.12)
d * Cw"
Where K = Partition coefficient (ml/g)
d
C = Pollutant concentration on soil (ppm)
s
C = Pollutant concentration in water (mg/1)
Since B and N usually vary within a small range of values and Kd can vary
by many orders of magnitude, the resulting value of R is primarily
determined by K^, which in turn is a function of the specific compound and
soil combination.
Guidelines for estimating N, either as total porosity under saturated
conditions or volumetric water content under unsaturated conditions, are
presented in Section 4.2.1. Guidelines for evaluating K^ and B are
discussed below.
Partition Coefficient
Since K^ can have a different value for each compound and soil
combination, values of K^ from previous studies (or other sources) at the
77
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waste/spill site should be used whenever possible. For most spill sites and
many waste sites, this information will not be available and K^ will need
to be estimated by other means.
For neutral organic compounds, a body of knowledge has been developed over
the past decade (see Lyman et al, 1982) whereby K^ values can be estimated
from the soil organic carbon content and the organic carbon partition
coefficient for the compound as follows:
K, K OC (4.13)
d = °C 100
where K = Organic carbon partition coefficient (ml/g)
oc
OC = Percent organic carbon content of soil or sediment
(r 'mensionless)
Equation 4.13 assumes that the organic carbon in the soil or sediment is the
primary means of adsorbing organic compounds onto soils and sediments. This
concept has served to reduce much of the variation in K^ values for
different soil types.
Koc values for a number of chemicals and hazardous compounds have been
tabulated by Rao and Davidson (1980) , Dawson et al (1980) and Mabey et al
(1982). Also, a variety of regression equations relating Koc to solubility,
octanol-water partition coefficients (Kow) • an<^ other compound
characteristics have been developed; Table 4.7 from Lyman et al (1982)
presents the major regression equations available, the chemical classes
represented, the number of compounds investigated, and the associated
correlation coefficient. Users should review the discussion by Lyman et al
(1982) to comprehend the limitations, assumptions, and parameter ranges
underlying the equations in Table 4.7. Koc estimates from more than one
equation should be evaluated in order to assess the variability in the
estimates.
Data on the compound characteristics needed for the regression equations can
be obtained from Dawson et at (1980) , Mabey et al (1982) , and other sources
listed in Table 2.2. Also, a very complete data base of Kow values is
maintained by Dr. Corlan Hansch at Pomona College, Pomona, California
(714-621-8000 ext. 2225) . This data base is available in microfiche form for
easy use in the field. Koc values should be used directly whenever
available; otherwise estimation of Koc from Kow is appropriate.
Organic Carbon/Organic Matter Content
Organic content of soils is described in terms of either the percent organic
carbon, which is required in our estimation of K^, or the percent organic
matter. These two values are conventionally related as %OC = %OM/1.724.
Typical values of percent organic matter range from 0.4% to 10.0% (Brady,
1974). Table 4.8 lists the range and average organic matter content for
mineral surface soils in various parts of the U.S; organic soils, such as
78
-------
Regression Equations for the Estimation of K
oc
Eq. No.
4-6
44
4-7d
4-8
4-9
4-10
4-11
4-12
4.13d
4.14d-'
4 16
4-16
Equation*
log Koc > -0.65 log S -f 3.64 IS in mg/L)
log K0Ł - -0.64 log S + 0.44
(S irwmole friction)
log K0( • -0.667 log S t 4.277
(S in p moles/L)
log KK • 0.544 log KOW + 1.377
log Koc - 0.937 log KQW.- 0.006
logKee- 1.00 log K0>(- 0.21
log Koc - 0.94 log KOĄ< «• 0.02
logKoe- 1.029logKow-0.18
log Koe - 0.624 log KOW + 0.666
log KQC • 0.0067 (P - 45N) + 0.237
log Koc - 0.681 log BCF(f) + 1.963
log Koc - 0.661 log BCF(t) t 1.886
No."
106
10
15
46
19
10
9
13
30
29
13
22
s
0.71
0.94
0.99
0.74
0.96
1.00
e
0.91
0.64
0.69
0.76
0.63
Chemical Qeises Represented
Wide variety, mostly pesticides
Mostly aromatic or polynuclear aromatics; two chlorinated
Chlorinated hydrocarbons
Wide variety, mostly pesticides
Aromatics, polynuclear erometics, triazinei and dinitro-
aniline herbicide!
Mostly eromatic or polynuclear aromatics; two chlorinated
s-Tnazmes and dimtroaniline herbicides
Variety of insecticides, herbicides and fungicides
Substituted phanylureai and alkyl-N-phenylcerbemetes
Aromatic compounds: ureas, 1,3,6-triazines, cerbamafes,
and uracils
Wide variety, mostly pesticides
Wide variety, mostly peitlcldei
Ref.
[26]
[25]
(111
[26]
[9]
[26]
[7]
[38]
[61
[IB]
[26]
[26]
a. KOC - toil (or udimant) adiorption cotfficitnt; S - water tolubility; KOW - octanol-watar partition coafficiant; BCF(f) " bioconcantration factor
from tlowing^atar taiti; BCF(t) - bioconctntration factor from modal acoiyitami; P • parachor; N • numbar of titat in molacul* which can par-
ticipata in tht formation of i hydrogan bond.
b. No. • numbar of chamicali uiad to obtain rigranion aquation.
c. r1 • corralation coafficiant for ragrassion aquation.
d. Equation originally given in tarmi of Kom. Tha ralationihip Kom • Koc/1.724 was used to rawrita tha equation in termi of K^.
a. Not available.
f. Specific chemical! used to obtain regression equation not specified.
TABLE 4.7
REGRESSION EQUATIONS FOR THE ESTIMATION OF KQC. Lyman et al., 1982,
(Reference numbers keyed to Lyman et al., 1982, Chapter 4)
-------
peat or muck soils, can have values in the range of 15% to 20% or greater.
Agricultural soils are commonly in the range of 1% to 5% organic matter.
Figure 4.5 shows a national distribution of % Nitrogen in the surface foot
of soil; % Nitrogen and %OC are generally related as %OC = 11 x % N. This
information can be used to estimate %OM and %OC as a basis for determining
The values in Table 4.8, and those mentioned above are primarily for the top
15cm of the soil profile. Organic content normally decreases sharply with
depth, as shown in Figure 4.6 which compares the relative change in percent
organic matter with depth for a prairie soil and a forest soil. Below 60 cm
in depth, percent organic matter values of less than 2% are common. Users
must evaluate appropriate %OM values for the specific region or regions of
the soil profile through which the contaminant will be moving. Thus for
surface spills, a weighted value of surface and subsurface %OM for the
unsaturated zone should be used; whereas subsurface releases from waste
sites will require the subsurface %OM at the appropriate depth. For many
subsurface or saturated zone releases, a %OM value of less than 1% may be
reasonable.
Local site-specific information should be used whenever possible;
s ign i ficant errors can result from using general or regional data.
TABLE 4.8 AVERAGE ORGANIC MATTER CONTENTS AND RANGES OF
MINERAL SURFACE SOILS IN SEVERAL AREAS OF THE
UNITED STATES
(Lyon et al, 1952)
Organic Matter (%)
Soils
240 West Va. soils
15 Pa. soils
117 Kansas soils
30 Nebraska soils
9 Minn, prairie soils
21 Southern Great Plains soils
21 Utah soils
Range
0.74-15.1
1.70- 9.9
0.11-3.62
2.43-5.29
3.45-7.41
1.16-2.16
1.54-4.93
Av.
2.88
3.60
3.38
3.83
5.15
1.55
2.69
Retardation Factors for Ionic Species
The processes which govern the adsorption of substances which ionize are
very different from those for substances that are nonionic. Most soils have
80
-------
NITROGEN
Percent N
Highly Diverse
insufficient Data
Under 0.05
0.05-0.09
5S! 0.10-0.19
0.20 and Over
Figure 4.5 Percentage nitrogen (N) In Surface Foot Of Soil (Parker, et_al_., 1946)
-------
PRAIRIE SOIL (Minn.)
Well drained
2 4
Poorly drained
FOREST SOILS (Indiana)
A.
Well drained Poorly drained
i i i i
02468 101214
PERCENT ORGANIC MATTER IN SOIL
Figure 4.6 - Distribution of organic matter in four soil
profiles. (Brady, 1974)
82
-------
a net negative charge, and therefore ions that are positively charged are
attracted to them. Some positively charged ions are preferentially adsorbed
to soil materials and will displace other positively charged ions already on
the exchange sites. This process is referred to as cation exchange or base
exchange. Anions (negatively charged particles) can either be attracted or
repelled by soil particles depending upon the net charge of the soil. The
anion exchange capacity of soils is usually less than cation exchange
capacity, unless extremely low pH's are encountered or high amounts of Fe or
Al oxides, or hydroxides are present. A rule of thumb is that anion
repulsion (negative adsorption) is roughly 1 to 5% of the cation exchange
capacity (CEC) in non-alkaline soils, and up to 15% in alkaline soils (pH
8.5) (Bolt, 1976).
Acids and Bases in Solution - By definition acids are substances which
give-up (donate) protons (hydrogen atoms) in solution. Bases, on the other
hand, take-on (accept) protons from solution. A typical reaction for a
monoprotic (one hydrogen) acid dissolved in water is
HA = H+ + A- (4.14)
where the double arrow indicates an equilibrium dissociation reaction. The
ratio between the products and reactants in this reaction is always a
constant known as the dissociation constant, Ka, where
K [H+] [A~] (4.15)
[HA]
K is usually expressed as a logarithm, pK ,
a a
pKa = -log (K ) (4.16)
3
The reaction for a monoprotic base in solution is
HB+ + OH~ (4.17)
and the reaction constant is
= [HB+] [OH"] _ [HB+] Kw (4.18)
[B1 " m [B*i
83
-------
The constants pK , pK. , and pK are related by
a b w
14 = pK + pK = pK (4.19)
3 D W
for any given compound. K is the dissociation constant for water, equal
to 10~14.
Retardation Factor for Acids and Bases - If the constants pKa or
are known for an acid or base and the pH of the solution is known, the
fraction of unionized acid, or base can be determined. For the acid the
fraction unionized acid is
[H+]
For a base, the fraction unionized is
H.21)
If we assume that the ionized portion of the acid is unattracted to soil
materials, then the retardation factor for the acid is
R .„ = 1+O.V3 (4'22)
acid
n
For the base we will assume that the ionized portion is exchanged similarly
to any monovalent ion (Kd * 100) and that the unionized portion is adsorbed
hydrophobically. Thus, the retardation factor for the base is
1 + ft KB + 100 (1 -8) (4.23)
i\. — Q
base
n
The value of Kd in either of these cases is determined exactly as
described above for the neutral (nonionic) species.
The number 100 in Equation 4.23 is an estimate of KJ B/n for a model
monovalent cation. This number can range from less than 1 up to 105 for
84
-------
various species. A substitute for this number for a particular soil can be
estimated by
BV= CEC B <4
n 100 r*+ n
when Kd+ = adsorption partition coefficient for the charged cation, cc/g
CEC = cation exchange capacity of the soil, milliequivalents/lOOg
Łt+ = sum of all positively charged species in the soil location,
milliequivalents/cc
The quantity Ł«+ is about 0.001 for most agricultural soils.
In reality, the exchange of the cation or anion is governed by a selectivity
coefficient which varies for different soils, and competing ion pairs. When
the ionized substance is adsorbed, it reduces the concentration of ionized
substances in solution which causes more of the unionized substance to
accept or donate protons. Thus, for strongly adsorbed ions, the
concentration of the substance in solution could approach very small
values. On the other hand if the selectivity for the ion is low or
repulsion occurs, virtually all the substance could remain in solution.
Thus, the above approach will give an answer between these two extremes; a
conservative assumption would be a retardation factor of 1.
To use this methodology, the user should first decide whether the substance
is an organic acid or base. This may not be easy to determine. If the
substance is not listed in the tables in this section or one does not have
prior knowledge about the compound, a retardation factor of 1 should be
used. Some pKa and pKb values for specific compounds are found in
Tables 4.9 and 4.10. Values of pKa > 14 indicate fully protonated forms,
while values <0 indicate fully deprotonated forms of the acid; for bases,
pKb values less than 0 indicate complete protonation while values greater
than 14 indicate a completely deprotonated form.
Harris and Hayes (1982) give references which contain pKa and pK^ values
for various organic acids and bases. These are listed below:
Dissociation Constants of Organic Acids in Aqueous Solution, (Kortum et
al 1961)
Dissociation Constants for Organic Bases in Aqueous Solution, (Perrin,
1965)
lonization Constants of Organic Acids in Aqueous Solution (Sergeant and
Dempsey, 1979)
85
-------
TABLE 4.9 pKg VALUES FOR SELECTED ORGANIC ACIDS
Compound pKa Ref
Aliphatic Acids 3.8 - 5.0 A
Acetic Acid (Substituted) 0.2-4.3 A
Aliphatic Acids (Diabasic) A
1st Carboxyl 1.3 - 4.3
2nd Carboxyl 4.3 - 6.2
p-Aminobenzoic Acid B
K! (NH3 group) 2.29
K2 (COOH group) 4.89
m-Aminobenzoic Acid B
K! (NH3 group) 3.07
K2 (COOH group) 4.73
m-Aminophenol B
K! (NH3 group) 4.17
K2 (OH group) 9.87
Aminocyanomethane 5.34 B
Aniline 27. B
Benzoic Acid 4.2 A
Benzoic Acid (Halogenated) A
Ortho 2.8 - 3.3
Meta 3.8
Para 3.9 - 4.1
3-B\romo-4-methoxy anilinium ion 4.08 B
Bromoacetic Acid 2.90 B
Butf3-enoic Acid 4.34 B
t-Butane 19. B
Benzoic Acid (Dicamba) 1.93 C
Benzoic Acid (Amiben) 3.40 C
p-Cyanophenol 7.95 B
4-Chloro-3-nitroanilinium ion 4.08 B
Cyanoacetic Acid 2.47 B
Chloromethylphosphonic Acid 1.40 B
Carboxylic Acids 4.5 ± 0.5 B
CH3OH2+ -2 B
C6H5OH2+ -6.7 B
2-Chlorophenol 8.52 D
Dichloroacetic Acid 2.90 B
2, 4 Dichlorophenol 7.85 D
2, 4 Dinitrophenol 4.04 D
2, 4 Dimethylphenol 10.6 D
4, 6-Dinitro-o-cresol 4.35 D
Glycine B
K! 2.35
K2 9.78
Hydroxymethylphosphonic Acid 1.91 B
p-Methoxybenzoic Acid 4.47 B
(Continued)
86
-------
TABLE 4.9 (Cont.)
Compound pKa Ref
m-Methylsulfonybenzoic Acid 3.52 B
Methane 40. B
p-Nitrophenylarsenic Acid 2.90 B
p-Nitrophenol 7.2 B
p-Nitroanilinium 1.0 C
2-Nitrophenol 7.21 D
4-Nitrophenol 7.15 D
Phenol 10. A, B
m-Phenoxybenzoic Acid 4.47 B
Pyridinium Ion 5.2 B
Phenoxy Acid (2, 4D) 2.8 C
Picolinic Acid (Picloram) 1.90 C
Phenol (Dinoseb) 4.4 C
Pentachlorophenol 4.74 D
RNH3+ 10. B
p-Tolyacetic Acid 4.37 B
Tetralol-2 10.48 B
1, 3, 5 - Trlhydroxybenzene (K]_) 8.45 B
Trifluoroacetic Acid 0.23 B
Toluene 35 B
2,4, 6 Trichlorophenol 5.99 D
References:
A. Stevenson, 1982
B. Harris and Hayes, 1982
C. Weed and Weber, 1974
D. Mills et al, 1982
87
-------
TABLE 4.10 pKb VALUES FOR SELECTED ORGANIC BASES
Compound
Aliphatic Araine Homologues
Anilines (substituted)
Acetanilide
Acetamide
Atrazine
Amitrole
Benzidine
CH3:~
C6H5CH2:-
C6H5NH:~
C6H50:-
Carboxylate Anions
Methanol
p-Nitroaniline
Pyridine
Pyrimidine
Phenol
Propazine
Prometryne
Prometone
RHN2
Simazine
pKa
3.10-4.20
6.90-9.40
13.6
14.5
12.32
9.83
9.34, 10.43
-26
-21
-13
4.0
9.5 + 0.5
16
6.8
13.0
8.8
12.7
20.7
12.15
9.95
9.72
4.00
12.35
Ref.
A
A
A
A
C
C
D
B
B
B
B
B
B
B
B
B
A,B
A
B
C
C
C
B
C
References:
A. Stevenson, 1982
B. Harris and Hayes, 1982
C. Weed and Weber, 1974
D. Mills et al, 1982
88
-------
Bulk Density
Bulk density is the mass of a unit volume of dry soil, as measured in the
field, usually expressed in g/cc or Ib/ft-*. The entire volume is taken
into consideration including both solids and pore spaces. Thus, loose
porous soils will have low values of bulk density and more compact soils
will have higher values. Bulk density values normally range from 1.0 to 2.0
g/cc, and soils with high organic matter content will generally have low
bulk density values.
Brady (1974) has presented the following ranges of bulk density for selected
surface soil types commonly found in agricultural areas:
Bulk Density (g/cc)
well-decomposed organic soil 0.2 - 0.3
cultivated surface mineral soils 1.25 - 1.45
clay, clay loam, silt loam 1.00 - 1.60
sands and sandy loams 1.20 - 1.80
Ritter and Paquette (1967) have listed the following bulk density ranges for
material classes encountered in road and airfield construction:
Bulk Density (g/cc)
silts and clays 1.3 - 2.0
sand and sandy soils 1.6 - 2.2
gravel and gravelly soils 1.8 - 2.3
Subsoils will generally be more compact than surface soils and thus have
higher bulk densities. Very compact subsoils regardless of texture can have
bulk densities of 2.0 g/cc or greater; values of 2.3 to 2.5 g/cc should be
considered as upper limits. Because of this relatively small range of
values, users can choose bulk density values for the waste/spill site from
the above information if local site-specific data are not available. Mean
or average values for a soil type can be used, and if no data are available
a value of 1.5 g/cc can be used with reasonable accuracy for many soils.
4.2.4 Dispersion Coefficient
The dispersion process is exceedingly complex and difficult to quantify,
especially for the unsaturated zone. It is sometimes ignored in the
unsaturated zone, with the reasoning that pore water velocities are usually
large enough so that pollutant transport by convection i.e. (water movement)
is paramount. Consequently, unless site specific information or studies are
available to establish that dispersion is or is not significant, and data is
available to estimate the dispersion coefficient, we recommend that the user
perform at least two separate assessments. The first assessment would
ignore dispersion and the second assessment should include a reasonable
value of a dispersion coefficient to evaluate the importance of dispersion
in the unsaturated zone for the specific site. A dispersion coefficient, D,
of 0.01 will effectively ignore dispersion and subsequently simplify
89
-------
calculations. However, dispersion should not be ignored for saturated zone
analyses. Since most available information on dispersion is for ground-
water systems, discussion and parameter guidelines for the dispersion
coefficient are provided in Section 4.3.3. Users should consult that
section to estimate a coefficient for the unsaturated zone.
4.3 SATURATED ZONE PARAMETER ESTIMATION
Table 4.11 lists the parameters required for a saturated zone assessment and
the types of information needed or useful in their estimation. The
following sections provide guidelines for estimating each of these input
parameters in the order shown in Table 4.11.
4.3.1 Effective Aquifer Thickness (or Zone of Mixing)
The extent of the aquifer subject to contamination is described using an
effective aquifer thickness which represents a zone of mixing. For good
mixing between the ground water and the contaminant, this effective
thickness may equal the total thickness of the aquifer. However, in most
cases it will be less than the total thickness, especially for deep
aquifers. In cases where the pollutant has a significantly different
density and/or viscosity than water, the extent of mixing may be reduced and
the contaminant plume will be concentrated over only a portion of the
aquifer's thickness. The saturated zone methodology in this manual assumes
that the chemical pollutant mixes with the ground water to the effective
thickness or mixing zone. The model does not consider immiscible wastes or
portions of wastes that either entirely float on top of the water table or
sink to the bottom of the aquifer and remain there. For example, the major
portion of gasoline is immiscible in water and its total movement in the
subsurface cannot be studied effectively with this manual. However, that
portion of gasoline that is soluble in water can be analyzed using the
assessment methodology.
Local site-specific information should be used whenever possible;
significant errors can result from using general or regional data.
The user should search for prior hydrogeological investigations in the
offices of Federal, State, County, and Municipal agencies as the initial
step in gathering estimates of the total thickness of the aquifer being
studied. Hydrogeologists in neighboring universities, consulting firms, and
government agencies are another possible source of data on the structural
thickness of water-bearing strata and may be able to provide recommendations
for an effective mixing depth. If these reports and contacts are not
helpful, nearby well owners can be consulted. The perforated intervals of
their water supply wells provide a lower limit estimate of the thickness of
underlying aquifers since most wells are not perforated for the entire
thickness. This information, contained on their drilling logs, should be
used carefully and only in the absence of other data.
An estimate of the minimum thickness to use for the mixing zone can be
obtained as follows:
90
-------
Table 4.11 SATURATED ZONE PARAMETERS AND ASSOCIATED INFORMATION
NEEDED/USEFUL FOR EVALUATION
Parameter
Name
Information Needed/Useful
for evaluation
m
Effective aquifer thickness
(or zone of mixing)
Aquifer characteristics, total
aquifer thickness, contaminant
density, ground-water density
V
Ground-water (interstitial
pore water) velocity
Hydraulic conductivity,
hydraulic gradient, effective
porosity, specific yield
Dispersion coefficient
Aquifer characteristics,
dispersivity, molecular
diffusion, ground-water
velocity
Retardation factor
Degradation/decay rate
Partition coefficient, bulk
density, total porosity,
K
oc'
ionic characteristics
Contaminant identity, relevant
attenuation processes,
environmental conditions
Co
Source contaminant concentration
Contaminant identity,
solubility, waste/site
records,organic carbon
partition coefficient,
decay rates and processes,
unsaturated zone assessment.
91
-------
m = q L (4.25)
vd
where
ra = effective (minimum) aquifer thickness, m
q = recharge from the site, cm/day
V, = Darcy flow velocity, cm/day
L = Width of leachate plume at water table, m
Equation 4.25 calculates the minimum aquifer thickness that will accept
recharge from the site based on the aquifer properties; calculation of V^
is discussed in the next section. This calculated minimum value should be
used only as a guide to the lower limit of a reasonable mixing zone depth.
In assessing which portion of the total aquifer thickness is subject to
mixing with the contaminant, knowledge of the density and viscosity of the
ground water and the pollutant is needed. Major differences in these
characteristics indicate a tendency toward reduced mixing and therefore a
smaller effective thickness.
In the temperature range normally expected in ground water, the water
density can be assumed as 1 g/cc or 62.4 lb/ft3. Viscosity is generally
reported in units of centipoise (.01 g/sec-cm) and common values for organic
liquids are in the range of 0.3 to 20 centipoise at ambient temperatures;
water has a viscosity of 1 centerpoise at 20°C (Grain, 1982). To
establish, these characteristics of the contaminant, first measure or
estimate its temperature, and then determine its density from one of the
following sources:
1. OHM-TADS - U.S. EPA Data Base.
2. CHRIS Manuals - U.S. Coast Guard, 1974.
3. Dangerous Properties of Industrial Materials by N.I. Sax, 1979.
4. Handbook of Environmental Data on Organic Chemicals, by Verschueren,
1977.
5. The Merck Index, Merck and Co., (Windholz, 1976)
6. Physical/Chemical Properties of Hazardous Waste Constituents, U.S.
EPA, 1980.
Information on viscosity is less wide-spread. Data can be found in the
Handbook of Chemistry and Physics (Weast 1973) and in Grain (1982) which is
contained in the Handbook of Chemical Property Estimation Methods (Lyman et
al, 1982); Grain (1982) also provides methods of estimating viscosity from
other chemical data.
Information on the compound may also be available from experts in the
chemical industry or at universities.
92
-------
The estimation of effective aquifer thickness will be quite difficult
because of uncertainties concerning the mixing properties of the
contaminant. It is recommended that a range of thickness values be used in
the computation to evaluate the effect of errors in estimating this
parameter on the predicted pollutant concentrations.
4.3.2 Ground-Water (Interstitial Pore Water) Velocity
The velocity of ground-water flow within the voids (i.e., interstitial pore
water velocity) is required as an input to the saturated zone methodology in
this manual. If the value of this parameter has not been established in
previous investigations it can be calculated by using Darcy's Law.
In the Darcy equation, the Darcy flow velocity, V
-------
Local site-specific information should be used whenever possible;
significant errors can result from using general or regional data.
Tables 4.12 and 4.13 contain values of horizontal hydraulic conductivity (K)
and permeability (k) for a variety of geologic media. As can be seen in
these tables, hydraulic conductivity increases with increasing particle size
and with increasing occurrences of fractures. These values should be used
only if site specific information is not available.
Ground-Water Flow Gradient
In order to determine the velocity of ground-water flow using Darcy's Law,
the ground-water flow hydraulic gradient must be estimated. The flow
gradient is influenced by both natural and man-made factors. In most cases,
ground water moves in roughly the same direction as surface water drainage,
and the ground-water flow gradient varies in magnitude in a direct
relationship with surface topography (i.e. the gradient is steepest where
the land slopes most steeply and vice versa). Man-made influences on the
flow gradient include artificial recharge areas (disposal wells) , areas of
enhanced recharge (landfills) and pumping wells. Areas of increased
recharge tend to cause the ground water to flow radially outward from the
recharge point, while pumping wells tend to cause ground water to flow
radially inward towards the well. These artificial influences on the
ground-water flow patterns may be very important in assessing the local
magnitude and direction of the ground-water flow gradient.
Data on the ground-water flow gradient should be sought in existing
hydrogeological reports from the U.S. Geological Survey, state water and
geological agencies, and local health, water, and engineering departments.
Experts in the engineering and geology departments of nearby universities,
in consulting firms, and in government agencies may also be able to provide
guidance. Also, water table elevations at several points in the area can be
used to estimate the gradient and direction (See Section 4.1.5 for
estimating depth to ground water).
Local site-specific information should be used whenever possible;
significant errors can result from using general or regional data.
If these data sources are not helpful, the flow gradient can be roughly
estimated as equivalent in magnitude and direction to the general slope of
the land surface in the area of the waste/spill site. This estimate will
suffer from substantial error if significant pumping or artificial recharge
is occurring in the area. It is most appropriate as a regional estimate of
ground-water flow, and becomes less valid when applied to smaller regions.
4.3.3 Dispersion Coefficient
Hydrodynamic dispersion in subsurface media is a process that causes the
spreading of a contaminant beyond that which results from convection alone.
Variations in local velocity (magnitude and direction) give rise to
dispersive spreading on microscopic, macroscopic, and regional scales. The
magnitude of dispersion varies significantly with the scale of the analysis,
94
-------
RANGE OF VALUES OF HYDRAULIC CONDUCTIVITY AND PERMEABILITY
Rocks Unconsolidoted k k K K K
^ deposits ^ (dorcy) (cm2) (cm/s) (mA) (aol/doy/ll2)
.
a>
o
O
0)
c±:
•22 "°
« n °
i« 1 "
~3 -a 0
w ° c in j>
* § 3 ° 0
» o *>
a. S.y ™
.5*Q-"o —
TJ O 0 *"
0) F Af O9 *"
^^S §c S
*J p « op —
1 "i^c: *O
I Ł75l5
' ^ at
? 01 C
" oo c °
ills
=Il
|0-
rlO5
-IO4
IO3
-IO2
-10
-1
-10"'
-ID'2
ID"3
io-4
to-5
ID'6
ID'7
io-8
r-10"3
-ID'4
-ID'5
-io-6
-io-7
-io-8
-io-9
•io-10
10-"
ID"12
io-13
ID'14
io-15
10'16
rlO2
-10
.,
-io-1
-.to'2
-ID'3
-io-4
-io-5
io-6
JO'7
ID'8
ID'9
io-10
10-"
pi
-io"
-JO"2
-io-3
-io-4
ID'5
-io-6
-io-7
io-8
io-9
io-'°
10-"
JO'12
io-'3
1
plO6
-io5
-IO4
-IO3
•IO2
1 W
tf\
' t\J
1
-10-'
to'2
Iv
ID"3
ID"4
HJ
ID'5
JO'6
10"7
CONVERSION FACTORS FOR PERMEABILITY AND HYDRAULIC CONDUCTIVITY UNITS
Permeability, k*
Hydraulic conductivity. K.
cm*
ft*
darcy
m/s
ft/s
gal/day/ft*
cm*
1
9.29 x 10*
9.87 x 10~»
1.02 x 10-»
3.11 x 10~«
5.42 x 10-'°
ft*
1.08 x 10-»
1
1.06X 10-«»
1.10 x 10-«
3.35 x 10-'
5.83 X 10-»»
darcy
1.01 X 10*
9.42 x 10'<>
1
1.04 x 10'
3.15 x 10*
5.49 x 10~*
m/s
9.80 x 10*
9.11 x 10'
9.66 X 10~«
1
3.05 X 10-«
4.72 x 10-»
ft/s
3.22 x 10»
2.99 x 10«
3.17 x 10'»
3.28
1
1.74 x 10-«
gal/day/ft*
1.85 x 10*
1.71 x I0«*
1.82 X 101
2.12 x 10*
5.74 x 10'
1
•To obtain k in ft*, multiply k in cm* by 1.08 X 10~J.
TABLE 4.12 RANGE OF VALUES OF HYDRAULIC CONDUCTIVITY AND
PERMEABILITY. (After Freeze and Cherry, 1979)
95
-------
TABLE 4.13 REPRESENTATIVE HORIZONTAL FIELD HYDRAULIC
CONDUCTIVITY RANGES FOR SELECTED ROCKS
Rock
Horizontal Field Hydraulic Conductivity
(gpd/sq ft)
Gravel
Basalt
Limestone
Sand and gravel
Sand
Sand, quick
Dune sand
Peat
Sandstone
Loeses
Clay
Till
Shale
IxlO3
-6
1x10
2xlO~2
2
2x10
o
ixitr
50
IxlO2
4
IxlO""1
-3
2x10-
-4
2x10
-4
5x10
5
1x10
- 3x 104
4
- 2x10
- 2xl04
3
- 5x10
3
- 3xlOJ
- 8xl03
- 3xl02
- IxlO2
- 50
- 20
- 2
- 1
1
- 1x10
Source: Pettyjohn et at (1982)
-5
Note: 1 gpd/sq. ft. = 4.72 x 10 cm/sec
96
-------
and choosing appropriate coefficients often requires careful assessment of
earlier studies. Applications of this manual for rapid assessment of
potential ground-water contamination may be directed toward either local or
regional evaluation of contaminant plume migration. Consequently, prior
investigations may not provide data on an appropriate scale for the
application.
For both the unsaturated and saturated zones, the effects of dispersion are
based upon the input of dispersion coefficients with dimensions of L^/T.
These coefficients incorporate two forms of the dispersive process, dynamic
dispersion (or dispersivity) and molecular diffusion. For typical flow
velocities, molecular diffusion is a negligible part of total dispersion
(Pettyjohn et al 1982), and thus it is often ignored.
In a saturated zone assessment, a longitudinal (horizontal) and transverse
dispersion coefficient is required as an input parameter. As discussed
earlier, the dispersion coefficient, D, is made up of a molecular diffusion
component and a dynamic dispersion component as follows:
D = aV + D* (4.28)
2
where D = Total dispersion coefficient, cm /day
a = Dispersivity, cm
V = Ground-water (interstitial) velocity, cm/day
D* = Molecular diffusion coefficient, cm2/day
Dispersivity is far more significant than molecular diffusion except when
ground-water flow velocities are very low (Freeze and Cherry, 1979). Table
4.14 provides regional dispersivities determined in earlier studies in a
variety of aquifer types; dispersivities for local or small scale
applications may be less than these values by an order of magnitude or more.
Evidence indicates that a general rule of thumb for dispersivity would be to
set it equal to 10% of the distance measurement of the analysis (Gelhar and
Axness, 1981). Thus, for a well or stream 100 meters down gradient from the
source, a dispersivity of 10 meters would be appropriate. For the
unsaturated zone, a 5-meter depth to ground water would require a 0.5 m
dispersivity. This approximate rule of thumb, along with Table 4.14 and
discussion above, should help the user to estimate a dispersion coefficient
in the absence of other data. Sensitivity analyses on the dispersion
coefficient are strongly recommended.
4.3.4 Retardation Factor
In using a nomograph for evaluating landfill permits, Pettyjohn et al (1982)
recommend that a retardation factor of 1.0 be used unless the permit
applicant can show that retardation is significant through field data and
testing. In effect, this produces a "worst case" situation since
retardation is ignored and the contaminant is routed straight through the
aquifer. Since ion exchange is the major retardation mechanism for the
saturated zone (since organic matter content is usually low), the clay
97
-------
TABLE 4.14 REGIONAL DISPERSIVITIES (a)
Type of
aquifer
Glacial till
Limestone
Location
Washington
Alberta, Canada
Cutler area, Fla.
Hypothetical
Longitudinal
dispersivity
(ax)
(ft)
Alluvial
sediments
Glacial
deposits
Limestone
Fractured
basalt
Rocky Mountain
Arsenal, Co
Colorado
California
Lyon, France
Barstow, CA
Sutter Basin, CA
Alsace, France
Long Island, N.Y.
Alberta, Canada
Brunswick, GA
Idaho
Hanford site,
100
100
100
40
200
260-6600
49
70
10-20
200
300
100
10-20
22
0.01-100
70
33
1.6-330
Source: Pettyjohn, et al, 1982
Note: 1 ft. = .3048 m
98
-------
content of the aquifer material tends to control retardation. In performing
a saturated zone assessment, if the user feels that retardation is
significant based on contaminant characteristics and aquifer composition,
the guidelines for estimating the retardation factor in Section 4.2.3 may
assist in evaluation; otherwise a value of R = 1 is recommended.
4.3.5 Degradation/Decay Rate
Degradation and decay mechanisms are generally more significant in surface
and unsaturated soils than in ground water. However, hydrolysis and
chemical oxidation can occur in saturated media, and anaerobic decomposition
is possible even in deep aquifers. Considering the long travel times that
occur in most ground-water systems, even decay rates that correspond to
half-lives of 2 years or more can substantially reduce ground-water
concentrations prior to discharge to a well or surface waters.
Consequently, the user should carefully consider the use of a non-zero decay
rate in the saturated zone assessment and analyze the impacts of a
reasonable range of decay rates for the compound of concern. Section 4.2.2
discusses estimation of decay rates and sources of information.
4.3.6 Source Contaminant Concentration
As described previously, the assessment nomograph requires source
contaminant concentration in ground water as a critical input parameter for
a saturated zone assessment. If contaminant movement through the
unsaturated zone is important, the Co value for the saturated zone is based
upon the concentration predicted by the unsaturated zone and the linkage
procedures described in Section 3.3. If the water table is sufficiently
high so that the leachate directly enters ground water, the Co value is the
estimate of the leachate concentration (see Section 4.1.2).
99
-------
SECTION 5
EXAMPLE APPLICATIONS AND RESULT INTERPRETATION
Two examples are given to demonstrate how the assessment nomograph and
accompanying worksheets can be used for assessments of emergency response
situations involving continuous input and pulse input of contaminants to the
unsaturated zone with subsequent linkage to the saturated zone.
The nomographs and worksheets are computational tools for evaluation of
contaminant concentrations at different values of x and t. As mentioned in
Section 3, the user must determine from the potential hazards of the
emergency situation which C(x,t) values need to be evaluated. If a time
response is desirable C(x) should be evaluated at different values of t; or
if a profile response is needed, C(t) should be evaluated at different x
values.
In most emergency response situations especially involving chemical or waste
spills, time responses which provide expected contaminant concentrations and
time of arrival at the ground-water table and/or at a point in the aquifer
are usually needed. This is the type of information an On-Scene Coordinator
may need, to assess the potential for ground-water contamination and
associated emergency actions. Profile responses are not often evaluated in
a rapid assessment situation, but they are helpful in showing the movement
of a contaminant through the unsaturated or saturated zones.
For both examples below, time responses for both the unsaturated and
saturated zones are calculated and plotted as they are commonly needed for
emergency assessments. In the first example, a profile response is also
evaluated in order to familiarize the user with the associated calculation
steps and some fundamental concepts of fate and transport phenomena. Since
time responses are most often needed for subsequent saturated zone
assessments, the unsaturated zone results are further interpreted and
analyzed to demonstrate how time responses are used as input to the
subsequent saturated zone assessment.
5.1 EXAMPLE #1: ASSESSMENT OF A CONTINUOUS CONTAMINANT SOURCE
Consider a recently discovered (continuous) leak of an industrial solvent
from a surface storage tank. The following data are developed from past
investigations conducted by the company and chemical characteristics of the
solvent:
V =0.55 cm/day B =1.5 gm/cm3
D =13.75 cm2/day •© =0.15
100
-------
k =0.004 day ~ Co = 1500 mg/1
K, =0.07 ml/gm
Depth to water table = 250 cm
The worksheet in Table 5.1 describes the development of the above parameter
values under the "Data Sources/Comments' heading.
5.1.1 Evaluation of Profile Responses
Concentration profiles expected to result from this chemical leak are
evaluated at different times to show the potential movement of the compound.
As shown in Table 5.1, three profiles are evaluated at 50, 200, and 1000 days
after the leak began. The calculations are performed according to the
procedures discussed in Section 3.1.4. Results of these profile responses —
concentrations tC/Co) vs depth (x) at specific times (t) — are plotted in
Figure 5.1.
The plot (Figure 5.1) indicates that most of the compound remains in the top
20 cm of the soil for 50 days. In 200 days, the compound has leached below
150 cm, and in 1000 days, steady-state is attained. While moving downward,
the chemical is being adsorbed and degraded. With a retardation factor of
1.7, very little retardation is occurring. Degradation is the major cause for
the decrease in concentration values found at greater depths.
5.1.2 Evaluation of Time Response at the Ground-Water Table
The time response is evaluated at the ground-water table. In this example,
the mean depth to ground water was 250 cm. Concentrations at different times
are estimated as shown in the worksheet, Table 5.2, according to the
procedures presented in Section 3.1.4. Results are plotted in Figure 5.2.
The plot (Figure 5.2) shows a steady state concentration of 300 mg/1 (C/Co =
0.20) at the ground-water table. This concentration is then used to develop
the source concentration (Co) for the saturated zone assessment.
5.1.3 Evaluation of Time Response in Ground Water
The spill site is located 100 m up gradient from a local stream that supplies
a water supply reservoir. The goal of the assessment is to determine when and
in what concentrations the contaminant plume will reach the stream. A recent
hydrogeologic study of the area indicated the following parameter estimates:
Ks = 10~3 cm/sec dh = 0.1% (gradient)
dl
n = 0.33 a = 2.6 m (dispersivity)
ne = 0.26 B = 1.9 g/cc
101
-------
TABLE 5.1 PROFILE RESPONSE FOR CONTINUOUS
INPUT TO UNSATURATED ZONE
Sheet
of
Calculated by
Checked by
Date
Date
WORKSHEET FOR RAPID ASSESSMENT NOMOGRAPH
ZONE: UNSATURATED X_
SATURATED
Date of Incident:
Site: Example No. 1
Location:
On Site Coordinator:
Scientific Support
Coordinator:
Agency:
Agency:
Compound Name:
Compound Characteristics:
REQUIRED PARAMETERS:
Co = 1500 mg/1
DATA SOURCES / COMMENTS
Company records
V
D
k
R
= 0.55 cm/day
13-75 cm2/day
= 0.004 day"1
= 1 + -I-K. = 1.700
K. = 0.07 ml/gtn
B = 1-5 gm/cm
e = 0.15
Based on 30 cm/yr recharge rate
Dispersivity = 25 cm, i.e., 10%
Company data on compound
Company data on compound
Company soils data
Field capacity for sandy loam
depth
PRELIMINARY CALCULATIONS:
* V,
= /R = 0.324 cm/day
*
2. D .
8.088 cm /day
3. k* = k/ = 0.0024 day"1
K ~ ' ' ~"
4.yV*2+4D*k* = 0.427
10
30
10
50
50
50
200
2D*
0.62
1.85
4.64
0.62
/4D*t
40.22
40.22
40.22
80.44
-0.06
-0.19
-0.48
-0.06
See Footnote # 2
-0.28
0.21
1.33
-0.94
0.46
1.39
3.48
0.46
0.78
1.28
2.40
1.19
From Nomograph3
M,
1.23
0.63
0.04
1.70
0.43
0.28
0.0:
0.15
'Co
0.83
0.46
0.03
0.93
1244
686
52
1388
102
-------
TABLE 5.1 continued
Sheet
of
Calculated by
Checked by
Date
Date
NOMOGRAPH WORKSHEET (con't.) ZONE: UNSA™ATED
SATURATED
5
X
40
100
150
50
150
250
6
t
200
200
200
1000
1000
1000
7
x/
/2D*
2.47
6.J8
9.27
3-09
9.27
15.45
8
\A5*t
80.44
80.44
80.44
179.87
179.87
179.87
9
See Footnote # 2
A1
-0.26
-0.64
-0.96
-0.32
-0.96
-1.60
Ap
-0.57
0.18
0.80
-2.10
-1.54
-0.99
B1
1.86
4.64
6.97
2.32
6.97
11.61
B?
1.56
2.31
2.93
2.65
3.21
3.77
10
11
From Nomograph
M1
1.22
0.42
0.10
1.45
0.76
0.37
M?
0.18
0.16
0.0
0.0
0.0
0.0
C/Co
0.70
0.29
0.05
0.73
0.38
0.19
12
C
1049
434
75
1088
567
279
Footnotes:
1,
2.
Refer to Table 3.1 for definitions and units, and to
Chapter 4 for estimation guidelines.
Aj = Col. 7 X (Item 1 - Item 4) = -—^ (V* -\,V2 + 4D*k* )
A2 = [Col. 5 - Col. 6 X Item 4] / Col .8 =
x "
3j = Col.7 X (Item 1 + Item 4) = ~ (V* + y V*2 + 4D*k*)
;ol.5+ (Col .6 X Item 4)] / Col .8 = ^-^
Figure 3.3 or Figure 3.4 (See Figure 3.3 for use of
nomograph).
103
-------
C / Co
0.2 0.4 0.6 0.8 1.0
Steady State Profile
(1000 days and after)
Ground-Water Table
Figure 5.1 Soil Profile Response For Example #1: Demonstrating Fate and
Movement of Pollutant.
104
-------
TABLE 5.2 TIME RESPONSE FOR CONTINUOUS
INPUT TO UNSATURATED ZONE
Sheet 1
of
Calculated by
Checked by
Date
Date
WORKSHEET FOR RAPID ASSESSMENT NOMOGRAPH
ZONE: UNSATURATED L
SATURATED
Date of Incident:
Site: Example No. 1
Location:
On Site Coordinator:
Scientific Support
Coordinator:
Compound Name:
Compound Characteristics:
REQUIRED PARAMETERS:
Co = 1500 mg/1
V = 0.55 cm/day
D = 13.75 cm /day
k = 0.004 day"
= 1.700
0.07 ml/gm
B =
6 =
gm/cm
3
0.15
PRELIMINARY CALCULATIONS:
1. V* = V/R = 0-324 cm/day
2. D* = D/D = 8.088 cm2/day
K •""--
Agency:
Agency:
DATA SOURCES / COMMENTS
Company records
Based on 30 cm/yr recharge rate
Dispersivity = 25 cm, i.e., 10% depth
Company data on compound
Company data on compound
Company soils data
Field capacity for sandy loam
day"
4. y'V*2 + 4D*k* = 0.
427
5
X
250
250
250
250
6
t
25
50
75
100
1
7
*/
/2D*
15.45
15.45
15.45
15-45
r
8
\/4D*t
28.44
40.22
49.26
56.88
9
See Footnote # 2
Ai
-1.60
-1.60
-1.60
-1.60
A2
8.42
5.69
4.43
3.64
B1
11.61
11.61
11.61
11.61
B2
9.17
6.75
5.73
5.15
10
11
From Nomograph3
M1
0.0
0.0
0.0
0.0
M2
0.0
0.0
0.0
0.0
C/CC
0.0
0.0
0.0
0.0
12
c
0.0
0.0
0.0
0.0
105
-------
TABLE 5.2 continued
Sheet
of
Calculated by
Checked by
Date
Date
NOMOGRAPH WORKSHEET (con't.) ZONE: UNSATURATED
SATURATED
5
X
250
250
250
250
250
250
250
250 -
250
250
250
6
t
125
150
175
200
300
400
500
600
800
1000
1500
7
*/
/2D*
15.45
15.45
15.45
15.45
15.45
15.45
15.45
15.45
15.45
15.45
15.45
8
X/4~D*t
63-59
69.66
75.24
80.44
98.52
113.76
127.18
139-32
160.88
179.87
220.29
9
See Footnote # 2
A1
-1.60
-1.60
-1.60
-1.60
-1.60
-1.60
-1.60
-1.60
-1.60
-1.60
-1.60
Ap
3.09
2.67
2.33
2.05
1 .24
0.70
0.29
-0.05
-0.57
-0.99
-1 .78
B1
11.61
11.61
11.61
11.61
11.61
11.61
11.61
11.61
11.61
11.61
11.61
B2
4.77
4.51
4.32
4.17
3.84
3.70
3-65
3.64
3.68
3-77
4.05
10
11
From Nomograph
M1
0.0
0.0
0.0
0.0
0.01Ł
0.065
0.14
0.21
0.32
0.37
0.40
M?
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0^0
0.0
0.0
C/Co
0.0
0.0
0.0
0.0
0.008
0.03
0.07
0.11
n.16
0.19
0.20
12
c
0.0
0.0
0.0
0.0
12.0
45.0
105.0
165.0
240.0
285.0
300.0
Footnotes:
1.
2,
Refer to Table 3.1 for definitions and units, and to
Chapter 4 for estimation guidelines.
Aj = Col. 7 X (Item 1 - Item 4) = -^ (V* -y'V*2 + 4D*k* )
i i x - t
A = [Col. 5 - Col. 6 X Item 4] / Col. 8 = - -
Bl = Col. 7 X (Item 1 + Item 4) = -^r (V* + y/V*2 + 4D*k*)
B2 = [Col .5+ (Col .6 X Item 4)] / Col .8 = x + t* + 4D*k*
Figure 3.3 or Figure 3.4 (See Figure 3.3 for use of
nomograph) .
106
-------
0.2 - -
0.15
O
O
O 0.1 --
0.05 - -
Approximate Input for
Saturated Zone Assessment
(C= 300 mg/l. t ^550 days)
Steady State Concentration
=300 mg/l
At x= 250 cm (Ground-Water Table)
\ I-
0 100 200 300 400 500 600 700 800 900 1000 1100
t, days
Figure 5.2 Example #1: Time Response at Ground-Water Table
-------
Total aquifer thickness = 18 m
Effective aquifer thickness = 6m
Based on the linkage procedures and Equation 3.10 in Section 3.3, the source
concentration was calculated as follows:
Co = (300 mg/l)(.Q822 cm/day) (20 m)
(.864 cm/day)(6ml
Co = 95 mg/1
This calculation assumes a plume width of 20 meters, an effective mixing
depth of 6 meters, a recharge rate of 30 cm/yr (0.0822 cm/day), and a
ground-water velocity of .864 cm/day (i.e., Vd = Ks(dh/dl) = (10~3
cm/sec) (.001)).
Figure 5.2 shows the step function input to the saturated zone used to
approximate the actual contaminant outflow from the unsaturated zone. The
step function was assumed to begin at day 550 (i.e., 550 days after the
beginning of the leak). As discussed in Section 3.3, this beginning time
should be varied to evaluate the influence of the step function
approximation on the arrival time and response at the discharge or impact
point.
Table 5.3 is the worksheet with calculations for the ground-water time
response at the stream and Figure 5.3 plots the calculated C/Co values.
Figure 5.3 shows that the plume begins to reach the stream between 1000 and
2000 days and reaches a steady-state concentration of 27 mg/1 at 6000 days.
Note that the time scale is in days after entering the ground water under
the site. The total travel time of the spill to the stream would be the
above numbers plus 550 days, the beginning day of the step function input to
ground water. Note that changing the beginning day of the step function
approximation in Figure 5.2 by 200 to 300 days would not have a major impact
on the relative arrival time of the plume at the stream. Thus the step
function approximation is reasonable.
5.2 EXAMPLE #2: ASSESSMENT OF A PULSE CONTAMINANT SOURCE
Consider a chemical leak similar to Example No. 1 except that the leak is
discovered and fixed after 200 days. The following data from Example fl
apply:
V =0.55 cm/day
D =13.75 cm2/day
k = 0.004 day"1
K = 0.07 ml/gm
Depth to water table = 250 cm
B =1.5 gm/cm
9 = 0.22
Co = 1500 mg/1
t = 200 days
108
-------
TABLE 5.3 TIME RESPONSE FOR CONTINUOUS
INPUT TO SATURATED ZONE
Sheet i_
of
Calculated by
Checked by
Date
Date
WORKSHEET FOR RAPID ASSESSMENT NOMOGRAPH
ZONE: UNSATURATED _
SATURATED
Site: Example No. 1
Date of Incident:
Location:
On Site Coordinator:
Scientific Support
Coordinator:
Agency:
Agency:
Compound Name:
Compound Characteristics:
REQUIRED PARAMETERS:
Co = 95 (mg/1)
DATA SOURCES / COMMENTS
Assumes L = 20m, m = 6m
V
D
k
R
= 3.32 (cm/day)
= 860 (cm2/day)
- 0.0004 (day"1)
- 1 + 4-K. - 1.06
0 d
Kj = 0.01 (ml/gm)
d o
R = 1.9 (gm/cmj)
B = 0.33
= (10"3cm/sec) (.001) /.26
Dispersivity = 2.6m
Company data, 4.75 yr half-life in G.V
Company data
Recent G.W. Study
Recent G.W. Study
PRELIMINARY CALCULATIONS:
* V
1. V . VR.
2. D* . D/D .
3.132 (cm/day) 3.
= k/n= 3.774 x IP" (day
R —•
81
1.32 (cm2/day) 4 . y'V*2 + 4D*k* = 3-322
5
X
IOOOC
6
t
1000
2000
2500
2800
7
*/
X2D*
6.16
6.16
6.16
6.16
8
V/4~5*t
1801.5
2547.7
2848.4
3014.4
9
See Footnote # 2
N
-1.17
-1.17
-1.17
-1.17
A2
3-71
1.32
0.60
0.23
B1
39-77
39.77
39.77
39.77
B2
7.39
6.53
6.43
6.40
10
11
From Nomograph^
M1
0.0
0.02
0.12
0.23
M2
0.0
0.0
0.0
0.0
C/CO
0.0
0.01
0.06
0.12
12
C
0.0
0.95
5.7
11. 4*
109
-------
TABLE 5-3 continued
Sheet
of
Calculated by
Checked by
Date
Date
NOMOGRAPH WORKSHEET (con't.) ZONE: UNSATURATED
SATURATED
5
X
1000C
6
t
3000
3200
3500
4000
6000
7
x/
'2D*
6.16
6.16
6.16
6.16
6.16
8
\Ao*t
3120.2
3222.6
3370.2
3602.9
4412.7
9
See Footnote # 2
A1
-1.17
-1.17
-1.17
-1.17
-1.17
Ap
0.01
-0.20
-0.48
-0.91
-2.25
B1
39.77
39.77
39.77
39-77
39.77
B2
6.40
6.40
6.42
6.46
6.78
10
11
o
From Nomograph
M1
0.31
0.38
0.47
0.56
0.62
M?
0.0
0.0
0.0
0.0
0.0
C/Co
0.15
0.19
0.23
0.28
0.31
12
C
14.25
18.05
21.85
26.60
29.45
Footnotes:
1,
2,
Refer to Table 3.1 for definitions and units, and to
Chapter 4 for estimation guidelines.
Aj = Col.7 X (Item 1 - Item 4) = -^ (V* -yV2 + 4D*k* )
A? = [Col.5 - Col.6 X Item 4] / Col .8 =•
- t\/V*2 + 4D*k*
Bj = Col. 7 X (Item 1 + Item 4) = -^ (V* + yV*2 + 4D*k*)
B2 = [Col.5+(Col.6 X Item 4)] / Col .8 = jL±-L/* + 4D*k*
Figure 3.3 or Figure 3.4 (See Figure 3.3 for use f
nomograph) .
110
-------
0.04
0.03
O
O
O
0.02
0.01
At x=±100 meters (or 10000 cm)
(Distance Between Stream and Spill Area)
Steady State Concentration = 29 mg/l
1000
2000
3000
4000
5OOO
6000
t, days
Figure 5.3 Example No. 1: Time Response At The Stream (x=100m)
-------
A time response is evaluated to assess the chemical concentration as it
reaches the ground-water table. The calculations are shown in worksheets,
Tables 5.4 and 5.5, according to the procedures stated in Section 3.1.4.
The response is evaluated at 250 cm, the estimated depth to ground water.
The reader should note that concentrations are evaluated at times which
differ by one pulse period (i.e. 200 days). This procedure can help to
minimize the number of calculations required, since values of C/Co in column
5 of Table 5.5 can be directly entered by shifting the values in column 4
down to the appropriate row. The results are plotted in Figure 5.4
indicating a bell-shape time response curve. The plot indicates that the
plume begins to arrive at the ground-water table in approximately 200 days,
with a peak concentration of 120 mg/1 (C/Co = 0.08) occurring in about 600
days. It also indicates that the plume would completely enter the ground
water in about 1300 - 1400 days.
The primary purpose of the unsaturated zone analysis is to obtain a
concentration-time response at the ground-water table, so that the bell-
shape time response curve can be approximated by a pulse input and applied
as a pollutant source for the saturated zone assessment. Following the same
approximation procedures discussed in Section 3.3 and using the same
parameter values from Example #1, the pulse concentration of 105 mg/1 shown
in Figure 5.4 produces a Co = 33.0 mg/1 for the saturated zone assessment.
Tables 5.6 and 5.7 show the worksheet calculations for the time response at
the stream, which is plotted in Figure 5.5. Note that the arrival times for
the pulse and step function inputs are similar, but that the maximum
concentration for the pulse input is only 3.4 mg/1 at 3400 days after the
spill while the step function (Figure 5.3) produced 29 mg/1 at 6550 days.
112
-------
TABLE 5.4 TIME RESPONSE FOR PULSE INPUT
TO UNSATURATED ZONE - STANDARD
WORKSHEET
Sheet
of
Calculated by
Checked by
Date
Date
WORKSHEET FOR RAPID ASSESSMENT NOMOGRAPH
ZONE: UNSATURATED X.
SATURATED
Site: Example No. 2
Location:
On Site Coordinator:
Scientific Support
Coordinator:
Compound Name:
Compound Characteristics:
Date of Incident:
Agency:
Agency:
REQUIRED PARAMETERS:
Co = 1500 mg/1
DATA SOURCES / COMMENTS
Company records
B
0
0.55 cm/day
13-75 cm2/day
0.004 day"1
1 + -jj-Kd= 1.700
= 0.07 ml/gm
= 1.5 gm/cm
0.15
Based on 30 cm/yr recharge rate
Dispersivity = 25 cm, i.e., 10%
Company data on compound
Company data on compound
Company soils data
Field capacity for sandy loam
depth
PRELIMINARY CALCULATIONS:
1. V* = V/D = 0.324 cm/day
p
2. D* = D/D = 8.088 cm~2/day
3. ic* . %*
0.0024 day
~1
4.yV*2 + 4D*k* = 0.427
250
100
2D*
15.45
8
4D*t
56.88
See Footnote # 2
1
1.60
1
3.64
B
11.61
5.15
10
11
From Nomograph^
M
3.0
M2
0.0
°/
CO
0.0
12
0.0
250
^— •—
250
200
300
15.45
15.45
80.44
-1.60
2.05
98.52
-1.60
1.24
11.61
11.61
4.17
0.0
0.0
0.0
3.84
.016
0.0
0.008
0.0
IHWHMI^^H
12.0
250
400
15.45
113.76
-1.60
0.70
11.61
113
-------
TABLE 5.4 continued
Sheet
of
Calculated by
Checked by
Date
Date
NOMOGRAPH WORKSHEET (con't.) ZONE: ""SATURATED _H.
SATURATED
5
X
250
250
250
250
250
6
t
500
600
800
1000
1200
7
*/
'2D*
15.45
15.45
15.45
15.45
15.45
8
V4~D*t
127.18
139.32
160.88
179.87
197.03
9
See Footnote # 2
A1
-1.60
-1.60
-1.60
-1.60
-1.60
Ap
0.29
-0.05
-0.57
-0.99
-1.33
B1
11.61
11.61
11.61
11.61
11.61
B2
3.65
3.64
3.68
3-77
3-87
10
11
0
From Nomograph
M1
0.14
0.21
0.32
0.37
0.39
M2
0.0
0.0
0.0
0.0
0.0
C/Co
0.07
0.11
0.16
0.19
0.20
12
C
105.0
165.01
240.0
285.0
300.0
1
Footnotes:
1.
2.
Refer to Table 3.1 for definitions and units, and to
Chapter 4 for estimation guidelines.
AJ = Col .7 X (Item 1 - Item 4) = -^ (V* -y/V*2 + 4D*k* )
r i x - t
A = [Col.5 - Col. 6 X Item 4] / Col. 8 = - —
j = Col. 7 X (Item 1 + Item 4) = ^ (V* + y/v*2 + 4D*k*)
r i Y + t Vv* +
B = [Col.5+(Col.6 X Item 4)] / Col .8 = J*
Figure 3.3 or Figure 3.4 (See Figure 3.3 for use of
nomograph) .
114
-------
Of _,
TABLE 5.5 TIME RESPONSE FOR PULSE INPUT TO Sheet 1
UNSATURATED ZONE - SUPPLEMENTARY WORKSHEET
SUPPLEMENTARY WORKSHEET FOR PULSE INPUT ASSESSMENT
ZONE: UNSATURATED X_
to = 200 days Co = 1500 mg/1 SATURATED
1
X
250
250
250
250
250
250
250
250
2
t
200
300
400
500
600
800
1000
1200
3
t- to
0
100
200
300
400
600
800
1000
CONTINUOUS INPUT
ASSESSMENT
(From Worksheet )
4
C/CO«>
0.0
0.008
0.03
0.07
0.11
0.16
0.19
0.20
5
C/Co(t-to)
0.0
0.0
0.0
0.008
0.03
0.11
0.16
0.19
PULSE ASSESSMENT
Col. 4, ti to
Col. 4-5, t >to
6
''Co^
0.0
0.008
0.03
0.06
0.08
0.05
0.03
0.01
r~ v Col.
CoX 6
7
C
0.0
12.0
45.0
93.0
120.0
75.0
45.0
15.0
115
-------
O
o
O
Approximate Pulse Input for
Saturated Zone Assessment.
(C = 105 mg/l, 400ŁtŁ1000;
to= 600 days.)
C= 120 mg/l
At x=250 cm (Ground-Water Table)
100
200
1100
1200
Figure 5.4 Example #2; Time Response at Ground-Water Table. (Pulse Input)
-------
TABLE 5.6 TIME RESPONSE FOR PULSE INPUT
TO SATURATED ZONE - STANDARD
WORKSHEET
Sheet
1
of
Calculated by
Checked by
Date
Date
WORKSHEET FOR RAPID ASSESSMENT NOMOGRAPH
ZONE: UNSATURATED_
SATURATED
Date of Incident:
Site: Example No. 2
Location:
On Site Coordinator:
Scientific Support
Coordinator:
Agency:
Agency:
Compound Name:
Compound Characteristics:
REQUIRED PARAMETERS:
Co = 33 (mg/1)
DATA SOURCES / COMMENTS
Results from pulse input linkage
V
D
k
R
=
—
=
= 1
Kd
B
0
3.32 (cm/day)
860 (cm2/day)
0.0004 (day~1)
+ -7TKd = 1.06
= 0.01 (ml/gm
1.9 (gm/cm3)
0.26
= (10"3cm/sec) (.001) /.26
Dispersivity = 2.6m
Company data, 4.75 yr half-life in G.W
Company data
Recent G.W. Study
Recent G.W. Study
PRELIMINARY CALCULATIONS:
1. V* = V/D = 3.132 (cm/day)
3. k* = k/D= 3.774 x 10"\day"1)
K
2. D* = D/D = 811.32 (cm2/day)
K — —
4. \ V*2 +4D*k* = 3.322
5
X
1000C
1000C
1000C
1000C
6
t
1400
2000
2600
3200
7
*/
X2D*
6.16
6.16
6.16
6.16
8
\/4D*t
2131.5
2547.7
2904.8
3222.6
9
See Footnote # 2
Ai
-1.17
-1.17
-1.17
-1.17
A2
2.51
1.32
0.47
-0.20
B1
39.77
39.77
39.77
39.77
B2
6.87
6.53
6.42
6.40
10
11
From Nomograph^
M1
0.0
0.02
0.16
0.38
M2
0.0
0.0
0.0
0.0
C/CO
0.0
0.01
J).08
0.19
12
C
0.0
.33
2.64
6.27
117
-------
TABLE 5.6 continued
Sheet
of
Calculated by
Checked by
Date
Date
NOMOGRAPH WORKSHEET (con'U
ZONE: UNSATURATED
SATURATED
5
X
1000C
1000C
1000C
1000C
IOOOC
6
t
3800
4400
5000
5600
1700
2300
2900
3500
4100
7
*/
/2D*
6.16
6.16
6.16
6.16
6.16
6.16
6.16
6.16
6.16
8
X/4D*t
3511.7
3778.8
4028.2
4263-1
2348.8
2732.1
3067-8
3370.2
3647-7
9
See Footnote # 2
A1
-1.17
-1.17
-1.17
-1.17
-1.17
-1.17
-1.17
-1.17
-1.17
Ap
-0.75
-1.22
-1.64
-2.02
1.85
0.86
0.12
-0.48
-0.99
B1
39.77
39.77
39.77
39.77
39.77
39.77
39.77
39-77
39.77
B2
6.44
6.51
6.61
6.71
6.66
6.46
6.40
6.42
6.48
10
11
o
From Nomograph
M1
0.53
0.59
0.61
0.62
0.0
0.07
0.27
0.47
0.57
Mp
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
C/CO
0.27
0.30
0.31
0.31
0.0
0.03
0.13
0.23
0.29
12
C
8.91
9.90
10.23
10.23
0.0
.99
4.29
7.59
9.57
Footnotes:
1.
2,
Refer to Table 3.1 for definitions and units, and to
Chapter 4 for estimation guidelines.
Aj = Col.7 X (Item 1 - Item 4) = -— (V* -\'V*2 + 4D*k* )
r i x - t Vv*2 + 4D*k*
A2 = [Col.5 - Col.6 X Item 4] / Col .8 =- //4D*t
Bj = Col.7 X (Item 1 + Item 4) = ^5* (V* + y/V*2 + 4D*k*)
r -i v -I- t \/V*2 + dn*k*
B? = [Col. 5+ (Col.6 X Item 4)] / Col .8 = /.Lt
Figure 3.3 or Figure 3.4 (See Figure 3.3 for use of
nomograph).
118
-------
TABLE 5.7 TIME RESPONSE FOR PULSE INPUT TO Sheet 1 of i_
SATURATED ZONE - SUPPLEMENTARY WORKSHEET
SUPPLEMENTARY WORKSHEET FOR PULSE INPUT ASSESSMENT
ZONE: UNSATURATED
to = 600 days Co = 33 mg/l SATURATED X
1
X
10000
10000
2
t
2000
2600
3200
3800
4400
5000
5600
2300
2900
3500
4100
3
t- to
1400
2000
2600
3200
3800
4400
5000
1700
2300
2900
3500
CONTINUOUS INPUT
ASSESSMENT
(From Worksheet )
4
^Co'f
0.01
0.08
0.19
0.27
0.30
0.31
0.31
0.03
0.13
0.23
0.29
5
C'CO^-^
0.0
0.01
0.08
0.19
0.27
0.30
0.31
0.0
0.03
0.13
0.23
PULSE ASSESSMENT
Col.4,tŁto
Col. 4-5, t >to
6
C/Co^
0.01
0.07
0.11
0.08
0.03
0.01
0.0
0.03
0.10
0.10
0.06
r_ v Col .
Co X c
0
7
C
.33
2.31
3.63
2.64
0.99
0.33
0.0
0.99
3.30
3.30
1.98
119
-------
At x = 100 meters (Distance Between Stream and Spill Area)
0.12 -
0.02 -
1OOO
2000
C=3.emg/l
3000 4000
t, days
5000
6000
Figure 5-5 Example #2: Time Response At The Stream (x=100m)
-------
SECTION 6
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U.S.C.G. 1974b. Hazardous Chemical Data, CG-446-2, U.S. Coast Guard,
Washington, D.C.
124
-------
U.S. SCS. 1964. Hydrology, National Engineering Handbook, Section 4, Pt. I,
Watershed Planning, Washington, D.C.
U.S. SCS. 1971. SCS National Engineering Handbook, Section 4, Hydrology.
U.S. Govt. Printing Office, Washington, DC.
U.V. Atlas of Organic Compounds Vols. 1-4. 1966-1971. Collaboration of
Photo-
electric Spectrometry Group, London and Institut fur Spectrochemie and
Angewandte Spectroskopie, Dortmund, Plenum Press, New York.
van Genuchten, M.Th. and W.J. Alves. 1982. Analytical Solutions of the One-
Dimensional Convective-Dispersive Solute Transport Equation. U.S.
Department of Agriculture, Tech. Bulletin No. 1661.
Verschueren, K. 1977. Handbook of Environmental Data on Organic Chemicals,
Van Nostrand Reinhold Co., New York.
Wauchope, R.D. ajid R.A. Leonard. 1980. Pesticide Concentrations in Agricul-
tural Runoff: Available Data and an Approximation Formula. Chapter 16
in: CREAMS, A Field Scale Model for Chemicals, Runoff, and Erosion from
Agricultural Management Systems. Vol. III. U.S. Department of
Agriculture Conservation Research Report No. 26.
Weast, R.C. (ed). 1973. Handbook of Chemistry and Physics. 53rd ed., The
Chemical Rubber Co., Cleveland, OH.
Weed, S.B. and J.B. Weber. 1974. Pesticide-Organic Matter Interactions.
Chapter 3 in: Pesticides in Soil and Water, W.D. Guenzi, ed., Soil
Science Society of America, Inc.
Windholz, M., ed. 1976. The Merck Index, 9th ed., Merck and Co., Inc.
Rahway, NJ.
125
-------
APPENDICES
A. U.S. SOIL CONSERVATION SERVICE RUNOFF ESTIMATION METHOD
B. GLOSSARY OF TERMS
C. BLANK WORKSHEETS AND ENLARGED NOMOGRAPHS FOR RAPID
ASSESSMENT PROCEDURES
126
-------
APPENDIX A
U.S. SOIL CONSERVATION SERVICE
RUNOFF ESTIMATION PERIOD
(taken directly from: Stewart et al., 1976)
127
-------
SIMULATION OF DAILY POTENTIAL DIRECT RUNOFF
INTRODUCTION
The amount and seasonal distribution of direct runoff
was estimated to assess potential transport of pesticides
and nutrients. The effects of some land management
practices on direct runoff were also estimated. Hydrol-
ogists have developed several rainfall-runoff models of
various degrees of complexity for making these esti-
mates. The more physically realistic models are quite
complicated and require a great deal of input informa-
tion and computer time. The national scope of this
report and the severe time constraints involved dictated
the use of a rather simple method of estimating runoff
from rainfall. Any input information required must also
be readily available. After considering several possi-
bilities, we decided to use the Soil Conservation Service
procedure for estimating direct runoff from storm
rainfall (4).
THE SOIL CONSERVATION SERVICE PROCEDURE FOR ESTIMATING DIRECT RUNOFF
FROM STORM RAINFALL
The Soil Conservation Service procedure for estimat-
ing direct runoff from storm rainfall (sometimes called
the SCS curve number method) was designed to use the
most generally available rainfall data: total daily rainfall.
For this reason rainfall intensity is largely ignored. The
basic relationship is the equation:
Q =
(i)
where
Q = runoff in inches
P = rainfall in inches
la = initial abstraction in inches
S = potential maximum retention plus initial
abstraction.
The initial abstraction before runoff begins is con-
sidered to consist mainly of interception, infiltration and
surface storage. Utilizing limited data from small experi-
mental watersheds, the following empirical relationship
was developed:
Ia = (0.2)S. (2)
Substituting this relationship into equation (1) gives
(P-0.2S)'
v~ P+0.8S
,P>(0.2)S
(3)
which is the rainfall-runoff relation used in the SCS
method.
The parameter CN (runoff curve number of hydrol-
ogic soil-cover complex number) is defined in terms of
the parameter S as:
CN =
1000
S+10
(4)
Note that runoff equals rainfall when S = 0 and CN =
100.
The potential maximum retention, S , and therefore
the runoff curve number are related to sofl surface and
profile properties, the vegetative cover, management
practices, and the soil water content on the day of the
storm. Solutions of equation (3) are shown as a family
of curves in Fig. 1.
Soil water content on the day of the storm is
accounted for by an Antecedent Moisture Condition
(AMC) determined by the total rainfall in the 5-day
period preceding the storm.
Three AMC groups have been established with the
boundaries between groups dependent upon the time of
year as shown in Table 1.
The seasonal difference in the AMC groupings is an
attempt to account for the greater evapotranspiration
between storms during the growing season.
The different infiltration characteristics of soils are
accounted for by classifying soils into four groups based
128
-------
HYDROLOGY: SOLUTION OF RUNOFF EQUATION Q-
P« 0 to 12 inches
0*0 to 8 inches
I Curves on this shed are for the ';
4567
RAINFALL (P) IN INCHES
Moekui, Victor; Estimating dlrtet runoff amounts from itorm rainfall:
Central Technical Unit, October 1955
u. i otrutnaort or AOMCUUVW
SOIL CONSERVATION SERVKX
arrmoo - HTDKUOT MANOI
STANOMO WO NO
ES- 1001
inert 1 o _2_
0»Tt l-»-M
Figure 1.-Solutions of Eq. 3. [From SCS National Engineering Handbook (4)|
-------
Table 1. Seasonal rainfall limiU foi antecedent
moisture condition*1
AMC group
Total 5-day antecedent rainfall
Dormant season Growing season
1
I!
Ill
inches inches
1.1 >2.I
From SCS National Engineering Handbook (4).
upon the minimum rate of infiltration obtained for a
bare soil after prolonged wetting. The influences of both
the surface and the profile of a soil are included. The
hydrologic soil groups as defined by SCS soil scientists in
the National Engineering Handbook are:
A. (Low runoff potential). Soils having high infiltration
rates even when thoroughly wetted and consisting
chiefly of deep, well to excessively drained sands or
gravels. These soils have a high rate of water transmis-
sion.
B. Soils having moderate infiltration rates when
thoroughly wetted and consisting chiefly of moderately
deep to deep, moderately well to well drained soils with
moderately fine to moderately coarse textures. These
soils have a moderate rate of water transmission.
C. Soils having slow infiltration rates when thoroughly
wetted and consisting chiefly of soils with a layer that
impedes downward movement of water, or soils with
moderately fine to fine texture. These soils have a slow
rate of water transmission.
D. (High runoff potential). Soils having very slow
infiltration rates when thoroughly wetted and consisting
chiefly of clay soils with a high swelling potential, soils
with a permanent high water table, soils with a claypan
or clay layer at or near the surface, and shallow sofls
over nearly impervious material. These soils have a very
slow rate of water transmission.
The SCS has classified over 9,000 soils in the United
States and Puerto Rico according to the above scheme.
A sample from the extensive table in the SCS National
Engineering Handbook is shown in Table 2. Rainfall-
runoff data from small watersheds or infiltrometer plots
were used to make the classifications where such data
were available, but most are based on the judgement of
soil scientists and correlators who used physical prop-
erties of the soils in making the assignments.
The interaction of hydrologic soil group (soil) and
land use and treatment (cover) is accounted for by
assigning a runoff curve number for average soil moisture
condition (AMC II) to important soil cover complexes
for the fallow period and the growing season. Rainfall-
runoff data for single soil cover complex watersheds and
plots were analyzed to provide a basis for making these
assignments. Average runoff curve numbers for several
soil-cover complexes are shown in Table 3. Average
runoff curve numbers (AMC II) are for the average soil
moisture conditions. AMC I has the lowest runoff
potential. AMC III has the highest runoff potential.
Under this condition the watershed is practically satu-
rated from antecedent rains. Appropriate curve numbers
for AMC I and III based upon the curve number for
AMC II are shown in Table 4.
Curve numbers for a "good hydrologic condition"
were used in the potential direct runoff simulations.
"Hydrologic condition" refers to the runoff potential of
a particular cropping practice. A row crop in good
hydrologic condition will have higher infiltration rates
and, consequently, less direct runoff than the same crop
in poor hydrologic condition. Good hydrologic condi-
tion seemed an appropriate description of corn under
modern management practices.
Seasonal variation not accounted for by the seasonal
dependency of the AMC classes is included by varying
the average moisture condition curve number according
to the stages of growth of a particular crop. For the
simulations reported here, with straight row corn as the
index crop, the average (AMC II) curve number was set
equal to that for fallow for the period from March 1
until the average emergence date for corn. Emergence
dates were assumed to be 2 weeks after the average
planting date reported by the USDA (5). During the
growing season, AMC 41 curve numbers for each day
were calculated by the following equation:
CN-F-
(F-CNave)
(5)
where
CNj = the curve number for the ith day for AMC
II.
F = fallow curve number.
Cj = crop coefficient for the ith day. C < 1 .
Cave = average crop coefficient for the growing
season.
CNave= average growing season curve number for
AMC II.
The crop coefficients Cj are defined as the ratio of
the crop evapotranspiration to potential evapotranspira-
tion for a given day when sofl water is not limiting. Crop
130
-------
Table 2.-Soil names and hydiologtc classifications' (Sample)
AA»tR&
AASTAD
A0AC
AdAJJ
ABUUTT
C
a
o
c
D
A4Bb»TTSTUMN C
«dCAL
AdtGb
AttfcLA
AdcLL
ArttS
Ad IL tNt
AdJOUA
ABU
AttuH
AbAA
ABRAHAM
AdSCQTA
AdSHfcft
AtfSTcO
A^.AC10
ACADEMY
ACAUlA
ACANA
ACASCO
•Uc IT UNAS
ACtL
ACKER
A C * Mt N
AGO
ACUL I TA
ACUHA
ACOVt.
ACHct
ALkfcLANt
AC TUN
T . _
AuT
ADA
AJA Irt
ADAMS
* DAMSON
A JAMST JHN
A JAMSVILLc
ACATUN
AJAVEN
ADi) IELUU
A 001 SUN
A OPT
AU6
AOcL
AOELAIOt
ADELANTU
AOfcL 1NU
ADttLPHIA
ADfcNA
ADGER
AOIL1S
AUlKJNDALK
AJlV
AJJUNTAS
AJK1NS
ADLtR
AD0LPH
ADRIAN
AENEAS
AtTNA
AFTON
A&AR
AGASSI/
AGATc
AWAUAH
A*tNCY
Awtfc
AGNcK
AGNUS
AGJAO ILL A
AGUA DULLC
AGUA FftlA
•GUALT
AullfcDA
AGU1L1TA
AGUIRRE
AGUST1N
p
0
B
tt
p
p
o
C
tf/C
0
e
c
B
D
tt
C
V
AHL C ALMT
A HI SI ROM (
ALOHA
Anntt' B ALUNiU
AHC/LT D AlOVA*
AXTANJM C ALPENA
AHKAHKtt C ALPHA
AIBL'.ITO (. ALPUN
AIRlfc B/C AIPJHA
AIRMAN 0 ALPS
A1LEY B ALSLA
AINAKtA B ALSPAJWI
AlHMWlT C ALSTAU
AIROT1* B ALSTO.N
AIRPC-RT 0 ALTAHONT
AITS B ALTAVISTA
AJL. (
ALTOORF
AKAKA A AITMAR
AKASHA B ALTU
AKtLA C ALTUGA
ALAULIN V ALTON
ALAt A ALTUS
B
C
B
C
B
C
B
B
C
B
C
B
B
0
C
0
B
C
c
B
B
AlAtLUA B ALTVAN B
ALAGA A ALUM
ALAKA1 it ALUSA
ALAMA 1
> ALVIN
;> ALAMANCE B ALVIRA
0
0
b
J
d
B
ALAMC b ALVISO
ALAMLSA C ALVOR
ALAFAHA D AMADUR
ALAPAI 1
ALBAS 1
t AMAGON
) AMALU
ALBANC 0 AMANA
ALbAhT C AMAKGOSA
B ALBATDN 0 AMARILLO
B
C
C
c
c
6
it
B
C
tf
0
A
B
ALBLt C AHASA
ALdEMARLE 1
) AHBERSON
ALbtttvILLE C AMBOY
ALB1A C AMBRAil
ALBICI. B AMEOEE
ALBRIGHTS C AMELIA
ALCALDE C AMENIA
ALCtSTER
S AMERICUS
ALCliA B AMES
ALCChA B AMESHA
ALCGVA B AMHERST
ALDA C AMITY
ALDAX D AMMUN
ALOEK 0 AMOLE
(. ALOES B AMOR
0
0
c
0
c
A
A
0
B
B
C
C
p
A
ALDEKLALE C AMOS
ALDERHOOD C AMSDEN
ALDlHi. C AMSTERDAM
ALDfctLL C AMTOFT
ALtKKAGlK B AMY
ALtKEDA C ANACAPA
ALEX B ANAHUAC
ALEXANDRIA C ANAMITE
ALEXIS B ANAPRA
ALFOkD B ANASAil
ALGAIiSEt B A NAT ONE
B
D
B
C
0
c
0
0
0
B
O
B
8
C
C
A
B
B
A
C
B
C
C
B
C
B
C
B
B
D
0
B
0
0
B
B
0
ALCERITA B ANAVERDE B
ALGIERS C/D ANAHALT
ALGOMA B/D ANCHO
ALHAMBRA B ANCHORAGE
B ALICE A ANCHOR BAY
C
B
C
0
A/0
e
B
o
B
0
0
c
tt
d/C
d
A
C
B
B
B
B
ALICEL
ALICIA
ALlUA
ALIKCHI
ALINE
ALKO
ALLAGASH
ALLARO
ALLEGHENY
ALLEMANOS
ALLEK
ALlt SHALE
ALLthS PARK
ALLENSVILLt:
ALLthllNE
ALLENirOOO
ALLISSIO
ALLEY
ANCHOR POINT
ANCIOTE
ANCO
ANDtRLY
ANDERS
ANDERSON
ANDES
ANDORINIA
A NO OVER
ANDREEN
A NO REE SON
A MORES
ANOREnS
A NED
ANETM
ANGELICA
ANGELINA
ANGELO
ALLIANCE B ANGIE
ALLIGATOR 0 ANGLE
ALL IS O ANGLEN
ALLISON C ANGOLA
ALLOUEI C ANGOSTURA
ALLONAY
ANHALT
U ALMAC 8 ANIAK
B
ALMEKA C ANITA
ALMONI D ANKENY
D
B
A
0
0
0
c
c
c
B
C
C
0
B
C
8
C
D
A
0
ANVAUF
ANNABtLLA
AMNANDALE
ANMSTON
AMOftA
AKUNES
ANSAR1
ANSEL
ANSEL MO
AMSOh
ANTELOPE SPRINGS
ANTERO
ANT FLAT
AK1HO
ANTHONY
ANT I CO
ANTILON
ANTIOCH
ANTLER
ANTOINE
ANT RJ BUS
AHIY
AMVIK
AMHAY
ANŁA
ANIIANO
APACHE
APAHUtt
APISHAPA
APISON
ATOPKA
APPIAN
APPLECATE
APPLE TON
APPL1NG
APR3N
APT
APTAKISIC
ARABY
ARADA
AS AN S AS
ARA? 1 EN
ARAVE
ARAVETON
ARBELA
ARBONE
ARBOR
ARBUCKLE
ARCATA
ARCH
ARCHABAL
ARCHER
ARCH IN
ARCO
A* COL A
ARO
AROEN
ARDENVOIR
ARCILLA
AREDALE
ARENA
ARENALES
ARENOTSVILLE
ARENOSA
ARENZVILLE
ARGONAUT
ARGUELLO
ARCYLE
ARIEL
ARIZO
ARKABUTLA
ARKPORT
A Rl. AND
AR1.E
ARLINC
ARLINGTON
ARLOVAL
ARMAGH
ARMIJO
ARnlNGTON
ARMO
B/0 ARMOUR
C
C
A
B
C
B
0
0
D
A
MJTtX ~ A bLAMC H YD HO LOG 1C SOU GROUP INDICATES THE
TMO SOIL
CROUPS SUCH AS B/C INDICATES THE
ARHSTEH
ARMSTRONG
ARMJCHEE
ARNtCARO
ARNHART
ARNHE IN
ARNO
ARNOLD
ARNOT
ARMY
SOIL CROUP HAS NOT
C
B
C
B
A
C
D
B
A
B
C
C
C
B
B
B
B
0
C
C
B
B
B
B
B
C
0
A
C
B
A
C
C
c
B
8
C
B
C
0
c
3
B
C
B
B
B
B
B
B
C
C
B
C
C
B
B
C
B
C
A
B
A
B
D
B
B
C
A
C
B
B
B
D
C
C
D
D
D
B
B
C
0
0
AR03STOOH
A«3SA C
ARP C
ARtlNSTON B
ARRI T3LA O
A44DLINF C
AtlQN D
AMOK
HRJKSMITH
A*I3TJ SECO
A4IA
ARTOIS
ARVAOA
AtVANt
ARVESON
ARVILLA
A3ZELL
ASA
ASBURY
ASZALON
ASOHOFF
ASHBY
ASHCKOFT
ASHDALE
ASHE
ASHKUM
ASHLAR
ASHLEY
ASH SPRINGS
ASHTON
AS-
AUXVASSE O
AUIQUI B
B AVA C
C
c
0
B
C/D
A
BEE*
AVALANCHE B
AVALON B
AVERY ft
AVON C
AVONBURC 0
AY3NOALE i
3ETERMINEO
ORAINEO/UNDRAINED SITUATION
1 From SCS National Engineering Handbook (4).
131
-------
Table 3.-Runoff curve numbers for hyilrologjc soil-cover complexes
(Antecedent moisture condition II. and Ia = 0.2 S)
Cover
Land use Treatment or practice
Fallow Straight row
Row crops
••
Contoured
••
" and terraced
Small grain Straight row
n
Contoured
»
" and terraced
H ft n
Close-seeded legumes2 Straight row
or rotation meadow
Contoured
••
" and terraced
" n n
Pasture or range
Contoured
H
"
Meadow
Woods
Farmsteads
Roads (dirt)3
(hard surface)
Hydrologic conditic
Poor
Good
Poor
Good
Poor
Good
Poor
Good
Poor
Good
Poor
Good
Poor
Good
Poor
Good
Poor
Good
Poor
Fair
Good
Poor
Fair
Good
Good
Poor
Fair
Good
....
in
A
77
72
67
70
65
66
62
65
63
63
61
61
59
66
58
64
55
63
51
68
49
39
47
25
6
30
45
36
25
59
72
74
Hydrolopic soil group
B
86
8)
78
79
75
74
71
76
75
74
73
72
70
77
72
75
69
73
67
79
69
61
67
59
35
58
66
60
55
74
82
84
C
91
88
85
84
82
80
78
84
83
82
81
79
78
85
81
83
78
80
76
86
79
74
81
75
70
71
77
73
70
82
87
90
D
94
91
89
88
86
82
81
88
87
85
84
82
81
89
85
85
83
83
80
89
84
80
88
83
79
78
83
79
77
86
89
92
1 From SCS National Engineering Handbook (4).
Close-drilled or broadcast.
Including right-of-way.
132
-------
Table 4.-Curve numbers (CN) and constants for I lie case lg = 0.2S
CN for
condi- CN.for
,ion conditions
11 ' "'
100
99
98
97
96
95
94
93
92
91
90
89
88
87
86
85
84
83
82
81
80
79
78
77
76
75
74
73
72
71
70
69
68
67
66
65
64
63
62
61
1
2
100
97
94
91
89
87
85
83
81
80
78
76
75
73
72
70
68
67
66
64
63
62
60
59
58
57
55
54
53
52
51
50
48
47
46
45
44
43
42
41
From SCS
l^r\r f^XT in
100
100
99
99
99
98
98
98
97
97
96
96
95
95
94
94
93
93
92
92
91
91
90
89
89
88
88
87
86
86
85
84
84
83
82
82
81
80
79
78
s ,
values
(inches)
0
.101
.204
.309
.417
.526
.638
.753
.870
.989
.11
.24
.36
.49
.63
.76
.90
2.05
2.20
2.34
2.50
2.66
2.82
2.99
3.16
3.33
3.51
3.70
3.89
4.08
4.28
4.49
4.70
4.92
5.15
5.38
5.62
5.87
6.13
6.39
Curve2
starts
wlicrc
P =
(inclicsf
0
.02
.04
.06
.08
.11
.13
.15
.17
.20
.22
.25
.27
.30
.33
.35
.38
.41
.44
.47
.50
.53
.56
.60
.63
.67
.70
.74
.78
.82
.86
.90
.94
.98
.03
.08
.12
.17
.23
.28
CN for
condi-
tion
II
60
59
58
57
56
55
54
53
52
51
50
49
48
47
46
45
44
43
42
41
40
39
38
37
36
3i
34
33
32
31
30
25
20
15
10
5
0
CNfor
conditions
I HI
40
39
38
37
36
35
34
33
32
31
31
30
29
28
27
26
25
25
24
23
22
2}
21
20
19
18
18
17
16
16
15
12
9
6
4
2
0
78
77
76
75
75
74
73
72
71
70
70
69
68
67
66
65
64
63
62
61
60
59
58
57
56
55
54
53
52
51
50
43
37
30
22
13
0
s .
values
(inches)
6.67
6.95
7.24
7.54
7.86
8.18
8.52
8.87
9.23
9.61
10.0
10.4
10.8
11.3
11.7
12.2
12.7
13.2
13.8
14.4
15.0
15.6
16.3
17.0
17.8
18.6
19.4
20.3
21.2
22.2
23.3
30.0
40.0
56.7
90.0
190.0
infinity
Curve2
starts
where
P =
(inches)
.33
.39
.45
.51
.57
.64
.70
.77
.85
.92
2.00
2.08
2.16
2.26
2.34
2.44
2.54
2.64
2.76
2.88
3.00
3.12
3.26
3.40
3.56
3.72
3.88
4.06
4.24
4.44
4.66
6.00
8.00
11.34
18.00
38.00
infinity
National Engineering Handbook (4).
^J-tllmv* 1
133
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APPENDIX B
GLOSSARY OF TERMS
(Source: The Water Information Center,
Port Washington, N.Y.)
134
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GLOSSARY
Acidization - The process of forcing acid through a well screen or into the
limestone, dolomite, or sandstone making up the wall of a borehole. The.
general objective of acidization is to clean incrustations from the well
screen or to increase permeability of the aquifer materials surrounding a
well by dissolving and removing a part of the rock constituents.
Anion - An atom or radical carrying a negative charge.
Annular Space (Annulus) - The space between casing or well screen and the
wall of the drilled hole or between drill pipe and casing.
Aquiclude - A saturated, but poorly permeable bed, formation, or group of
Formations that impedes ground-water movement and does not yield water
freely to a well or spring. However, an aquiclude may transmit appreciable
water to or from adjacent aquifers, and where sufficiently thick, may con-
stitute an important ground-water storage unit.
Aquifer - A geologic formation, group of formations, or part of a formation
that is capable of yielding a significant amount of water to a well or
spring.
Aquitard - Used synonymously with aquiclude.
Artesian - The occurrence of ground water under greater than atmospheric
pressure.
Artesian (Confined) Aquifer - An aquifer bounded by aquicludes and contain-
ing water under artesian conditions.
Artificial Recharge - The addition of water to the ground-water reservoir
by activities of man.
Backwashing - The surging effect or reversal of water flow in a well.
Backwashing removes fine-grained material from the formation surrounding
the borehole and, thus, can enhance well yield.
Barrier Well - A pumping well used to intercept a plume of contaminated
ground water. Also a recharge well that delivers water to or in the vicin-
ity of a zone of contamination under sufficient head to prevent the further
spreading of the contaminant.
Base Flow - The flow of streams composed solely of ground-water discharge.
Biochemical Oxygen Demand (BOD) - A measure of the dissolved oxygen con-
sumed by nucrobiai life while assimilating and oxidizing the organic matter
present in water.
135
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Borehole - An uncased drilled hole.
Brine - A concentrated solution, especially of chloride salts.
Casing - Steel or plastic pipe or tubing that is welded or screwed together
and lowered into a borehole to prevent entry of loose rock, gas, or liquid
or to prevent loss of drilling fluid into porous, cavernous, or fractured
strata.
Cation - An atom or radical carrying a positive charge.
Chemical Oxygen Demand (COD) - The amount of oxygen, expressed in parts per
million, consumed under specified conditions in the oxidation of organic
and oxidizable inorganic matter in waste water, corrected for the influence
of chlorides.
Coliform Group - Group of several types of bacteria which are found in the
alimentary tract of warm-blooded animals. The bacteria are often used as
an indicator of animal and human fecal contamination of water.
Cone of Depression - The depression, approximately conical in shape, that
is formed in a water-table or potentiometric surface when water is removed
from an aquifer.
Connate Water - Water that was deposited simultaneously with the geologic
formation in which it is contained.
Consumptive Use - That part of the water withdrawn that is no longer avail-
able because it has been either evaporated, transpired, incorporated into
products and crops, or otherwise removed from the immediate water environ-
ment.
Contamination - The degradation of natural water quality as a result of
man's activities, to the extent that its usefulness is.impaired. There is
no implication of any specific limits, since the degree of permissible
contamination depends upon the intended end use, or uses, of the water.
Curie - The quantity of any radioactive material giving 3.7 x 10 disinte-
grations per second. A picocurie is one trilliorith of a curie, or a quan-
tity of radioactive material giving 22.2 disintegrations per minute.
Drainage Well - A well that is installed for the purpose of draining swampy
land or disposing of storm water, sewage, or other waste water at or near
the land surface.
Dry Well - A borehole or well that does not extend into the zone of satura-
tion.
Effluent - A waste liquid discharge from a manufacturing or treatment proc-
ess, in its natural state, or partially or completely treated that dis-
charges into the environment.
136
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Eutrophication. - The reduction of dissolved oxygen in natural and man-made
lakes and estuaries, leading to deterioration of the esthetic and life-
supporting qualities.
Evapotranspiration - The combined processes of evaporation and transpira-
tion.
Exfiltration - The leakage of effluent from sewage pipes into the surround-
ing soils.
Field Capacity - The moisture content of the soil after water has been re-
moved by deep seepage through the force of gravity. It is the moisture re-
tained largely by capillary forces.
Flow Path - The direction of movement of ground water and any contaminants
that may be contained therein, as governed principally by the hydraulic
gradient.
Fracture - A break in a rock formation due to structural stresses. Frac-
tures may occur as faults, shears, joints, and planes of fracture cleavage,
Ground Water - Water beneath the land surface in the saturated zone that is
under atmospheric or artesian pressure. The water that enters wells and
issues from springs.
Ground-Water Reservoir - The earth materials and the intervening open
spaces that contain ground water.
Hazardous Waste - Any waste or combination of wastes which pose a substan-
tial present or potential hazard to human health or living organisms.
Head - The height above a standard datum of the surface of a column of wa-
ter that can be supported by the static pressure at a given point.
Heavy Metals - Metallic elements, including the transition series, which
include many elements required for plant and animal nutrition in trace con-
centrations, but which become toxic at higher concentrations. Examples
are: mercury, chromium, cadmium, and lead.
Hydraulic Conductivity - The quantity of water that will flow through a
unit cross-sectional area of a porous material per unit of time under a hy-
draulic gradient of 1.00 at a specified temperature.
Hydraulic Fracturing - The fracturing of a rock by pumping fluid under high
pressure into a well for the purpose of increasing permeability.
Hydraulic Gradient - The change in static head per unit of distance alonq a
flow path.
Infiltration - The flow of a liquid through pores or small openings.
137
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Injection Well - A well used for injecting fluids into an underground stra-
tum.
Intermittent Stream - A stream which flows only part of the time.
Ion Exchange - Reversible exchange of ions adsorbed on a mineral or synthe-
tic polymer surface with ions in solution in contact with the surface. In
the case of clay minerals, polyvalent ions tend to exchange for nonvalent
ions.
Iron Bacteria - Bacteria which can oxidize or reduce iron as part of their
metabolic process.
Irrigation Return Flow - Irrigation water which is not consumed in evapora-
tion or plant growth, and which returns to a surface stream or ground-water
reservoir.
Leachate - The liquid that has percolated through solid waste or other man-
emplaced medium from which soluble components have been removed.
Loading Rate - The rate of application of a material to the land surface.
Mined Ground Water - Water removed from storage when pumpage exceeds
ground-water recharge.
Mineralization - Increases in concentration of one or more constituents as
the natural result of contact of ground water with geologic formations.
Monitoring (Observation) Well - A well used to measure ground-water levels,
and in some cases, to obtain water samples for water-quality analysis.
Nonpoint Source - The contaminant enters the receiving water in an inter-
mittent and/or diffuse manner.
Organic - Being, containing, or relating to carbon compounds, especially in
which Hydrogen is attached to carbon, whether derived from living organisms
or not; usually distinguished from inorganic or mineral.
Overburden - All material (loose soil, sand, gravel, etc.) that lies above
bedrock.In mining, any material, consolidated or unconsolidated, that
overlies an ore body, especially deposits mined from the surface by open
cuts.
Oxidation - A chemical reaction in which there is an increase in valence
resulting from a loss of electrons; in contrast to reduction.
Percolate - The water moving by gravity or hydrostatic pressure through in-
terstices of unsaturated rock or soil .
Percolation - Movement of percolate under gravity or hydrostatic pressure.
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Perennial Stream - One which flows continuously. Perennial streams are
generally fed TiT part by ground water.
Permeability - A measure of the caoacity of a oorous medium to transmit
fluid.
Piezometric Surface - The surface defined by the levels to which ground wa-
ter will rise in tightly cased wells that tap an artesian aquifer.
Plume - A body of contaminated ground water originating from a specific
source and influenced by such factors as the local ground-water flow pat-
tern, density of contaminant, and character of the aguifer.
Point Source - Any discernible, confined and discrete conveyance, including
but not limited to any pipe, ditch, channel, tunnel, conduit, well, dis-
crete fissure, container, rolling stock, or concentrated animal feeding
operation from which contaminants are or may be discharged.
Potentiometric Surface - Used synonymously with piezometric surface.
Public Water Supply - A system in which there is a purveyor and customers;
the purveyor may be a private company, a municipality, or other governmen-
tal agency.
Recharge - The addition of water to the ground-water system by natural or
artificial processes.
Reduction - A chemical reaction in which there is a decrease in valence as
a result of gaining of electrons.
Runoff - Direct or overland runoff is that portion of rainfall which is not
absorbed by soil, evaporated or transpired by plants, but finds its way
into streams as surface flow. That portion which is absorbed by soil and
later discharged to surface streams is ground-water runoff.
Salaquifer - An aquifer which contains saline water.
Saline - Containing relatively high concentrations of salts.
Salt-Water Intrusion - Movement of salty ground water so that it replaces
fresh ground water.
Saturated Zone - The zone in which interconnected interstices are saturated
with water under pressure egual to or greater than atmospheric.
Self-Supplied Industrial and Commercial Water Supply - A system from which
water is served to consumers free of charge, or from which water is sup-
plied by the operator of the system for his own use.
Sludge - The solid residue resulting from a process or waste-water treat-
ment which also produces a liquid stream (effluent).
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^Specific Conductance - The ability of a cubic centimetre of water to con-
duct electricity: varies directly with the amount of ionized minerals in
the water.
Storage (Aquifer) - The volume of water held in the interstices of the rock.
Strata - Beds, layers, or zones of rock.
Subsidence - Surface caving or distortion brought about by collapse of deep
mine workings or cavernous carbonate formations, or from overpumping of
certain types of aquifers.
Surface Resistivity (Electric Resistivity Surveying) - A geophysical pros-
pecting operation in which the relative values of the earth's electrical
resistivity are interpreted to define subsurface geologic and hydrologic
conditions.
Surface Water - That portion of water that appears on the land surface,
i.e., oceans, lakes, rivers.
Toxicity - The ability of a material to produce injury or disease upon ex-
posure, ingestion, inhalation, or assimilation by a living organism.
Transmissivity - The rate at which water is transmitted through a unit
width of an aquifer under a unit hydraulic gradient.
Unsaturated Zone (Zone of Artesian) - Consists of interstices occupied par-
tially by water and partially by air, and is limited above by the land sur-
face and below by the water table.
Upconing - The upward migration of ground water from underlying strata into
an aquifer caused by reduced hydrostatic pressure in the aquifer as a re-
sult of pumping.
Water Table - That surface in an unconfined ground-water body at which the
pressure is atmospheric. It defines the top of the saturated zone.
Water-1 able Aquifer - An aquifer containing water under atmospheric condi-
tions.
Well - An artificial excavation that derives fluid from the interstices of
the rocks or soils which it penetrates, except that the term is not applied
to ditches or tunnels that lead ground water to the surface by gravity.
With respect to the method of construction, wells may be divided into dug
wells, bored wells, drilled wells, and driven wells.
Well Capacity - The rate at which a well will yield water.
Withdrawal - The volume of water pumped from a well or wells.
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APPENDIX C
WORKSHEETS AND ENLARGED NOMOGRAPHS
FOR RAPID ASSESSMENT PROCEDURES
141
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Sheet of
Calculated by
Checked by
Date
Date
WORKSHEET FOR RAPID ASSESSMENT NOMOGRAPH
ZONE: UNSATURATED _
SATURATED
Site:
Location:
On Site Coordinator:
Scientific Support
Coordinator:
Compound Name:
Compound Characteristics:
REQUIRED PARAMETERS:
Co =
V =
D =
k =
B =
e =
PRELIMINARY CALCULATIONS:
* V ,
1. V = =
2. D* . % .
Date of Incident:
Agency:
Agency:
DATA SOURCES / COMMENTS
3.
4.
V*2 + 4D*k* =
5
X
6
t
7
x/
72D*
8
V/4D*t
9
See Footnote # 2
N
A2
B1
B2
10
11
From Nomograph3
M1
"2
C/CO
12
C
142
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Sheet of
Calculated by
Checked by
Date
Date
NOMOGRAPH WORKSHEET (con't.)
ZONE: UNSATURATED
SATURATED _
5
X
6
t
7
*/
72D*
8
\/4D*t
9
See Footnote # 2
A1
Ap
B1
B2
10
11
From Nomograph
Mi
M2
C/Co
12
C
Footnotes: 1
Refer to Table 3.1 for definitions and units, and to
Chapter 4 for estimation guidelines.
2. Aj = Col.7 X (Item 1 - Item 4) = -^ (V* -y'V*2 + 4D*k* )
r -i x - t VV* +
A2 = [Col.5 - Col. 6 X Item A] / Col. 8 =-* — 7M*t
B1 = Col .7 X (Item 1 + Item 4) = ~ (V* + yv*2 + 4D*k*)
[. i Y + t vV*2 + 4n*k*
Col. 5+ (Col. 6 X Item 4)] / Col .8 = /^n
Figure 3.3 or Figure 3.4 (See Figure 3.3 for use of
nomograph). .
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M
RAPID ASSESSMENT
NOMOORAPH
0.2 0.4 0.6 '0.8 1.0 1.2 i.4 1.6 1
\
—t . WW ™ k/ • J I V* I
.00 -1 50 -1.0-0'.8-0
1 0
1 2
B
-------
-t-
un
0.60
RAPID ASSESSMENT
NOMOGRAPH c/Co
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ADDENDUM TO RAPID ASSESSMENT OF POTENTIAL GROUNDWATER CONTAMINATION
UNDER EMERGENCY RESPONSE CONDITIONS
The purpose of this addendum is to provide additional explanation on how
to apply the procedures described in this manual to situations involving non-aqueous
wastes. In this situation two phase flow may exist and the procedures described
in the manual will not yield valid concentration predictions. Two phase flow
may exist when both:
x < JL and t < JL
RCSA9 CSAVQ
where x = distance
t = time
M = mass of contaminant
Cs = water solubility limit of contaminant
A = area of spill or discharge
V = velocity
R = retardation factor
0 = water fraction of soil
Under these conditions the procedures describee in this manual should not
be used.
Additionally, the user should understand that C0 is the initial water phase
concentration and can never exceed the water solubility limit. As explained in
Section 4.1.2, lacking other information it is recommended that C0 should be
assumed equal to Cs.
Finally, for pulse input problems involving non-aqueous waste, the pulse
duration (t0) should be set equal to M/(CSAVO).
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In summary, the following guidelines should be used for non-aqueous wastes:
o Constant Input Problems
1) set C0 = Cs
.2) apply only where x > M and t > M
KUcMW Uc
o Pulse Input Problems
1) set C0 = Cs
2) set t0 = M/(CSAVO).
3) apply only where x > M and t > M
*USGPO: 1983-759-102-0782
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