&EPA
United States
Environmental Protection
Agency
Off Ice of Solid Waste
and Emergency Response
Washington DC 20460
July 1986.
Solid Wane
Criteria for Identifying
Areas of Vulnerable
Hydrogeology Under the
Resource Conservation
and Recovery Act
Appendix D
Development of Vulnerability
Criteria Based on Risk
Assessments and
Theoretical Modeling
Interim Final
-------
GUIDANCE CRITERIA FOR IDENTIFYING
AREAS OF VULNERABLE HYDROGEOLOGY
APPENDIX D
DEVELOPMENT OF VULNERABILITY CRITERIA
BASED ON RISK ASSESSMENTS AND THEORETICAL MODELING
Office of Solid Waste
Waste Management Division
U.S. Environmental Protection Agency
401 M Street, S.W.
Washington, D.C. 20460
July 1986
-------
TABLE OF CONTENTS
Page
List of Tables iv
List of Figures v
1.0 Introduction .......................................... 1-1
2.0 Theoretical Considerations Affecting Discharge
and Exposure Potential ............................... 2-1
2.0.1 Relationship between TOTioo and the
Potential Size of a Plume ................. 2-2
2.0.2 Analysis of Peak Concentration as a
Function of TOT ........... ; ........... '• 2-4
2.0.3 Application of the Liner Location Model... 2-14
2.1 Potential for Exposure Through a Ground-Water
Resource .................. ' ............... . ....... 2-19
2.1.1 Theoretical Relationship between TOTioo
and Well Yield... ......................... 2-20
2.1.2 Frequency Distribution of TOTioo among
Well-studied Aquifers ..................... 2-22
2.1.3 Contamination of High Capacity Production
Wells .................................... 2-25
2.1.4 Contamination of Individual Drinking Water
Wells ..................................... 2-26
2.2 Potential for Exposure to Contaminated Surface
Water ................. ........................... 2-27
2.2.1 Surface Water Exposure Pathway: Hydro-
geologic Settings ......................... 2-27
2.2.2 Contamination of Potable Surface Water
Supplies .................................. 2-28
2.2.3 Contamination of Surface Water Ecosystems. 2-28
2.2.4 Bedrock Springs Contamination ............. 2-29
2.3 Potential for Exposure Through the Basement
Seepage Pathway ...... . ........................... 2-30
-------
2.3.1 Description of Condition 2-30
2.3.2 Representative Hydrogeologic Settings 2-30
2.4 Considerations for Location and Unit Design 2-31
2.4.1 Controlling Discharge from a Unit 2-32
2.4.2 Considerations for Unit De-sign 2-34
2.4.3 Considerations for Storage and Disposal
Units 2-35
3.0 Case Study Examples and Exposure Estimation Methods... 3-1
3.1 Case Studies: Three Exposure Pathways 3-2
• 3.1.1 Ground-Water Resource Pathway: Chemical
Plant Site 3-3
3.1.2 Ground-Water Resource Pathway: Abandoned
Gravel Pit/Landfill 3-4
3.1.3 Potable Surface Water: Multi-Source Waste
Site 3-5
3.1.4 Surface Water Ecosystems: Mining and Ore
Processing Facility 3-6
3.1.5 Bedrock Seeps and Springs: Municipal and
Industrial Landfill 3-9
3.1.6 Basement Seepage Pathway: Quarry/Landfill
Site 3-10
3.1.7 Basement Seepage Pathway: Chemical Landfill
Site 3-11
3 . 2 Health Risk Assessment Methods 3-12
3.2.1 Assessment Methodology 3-17
3.2.2 Methods for Interpreting Results 3-23
3.2.3 Results of Preliminary Exposure and Health
Risk Assessments 3-24
3.3 Case Studies: Health Risk Assessment 3-25
3.3.1 Case Study D-l 3-27
ii
-------
3.3.2 Case Study D-2 3-43
3.3.3 Case Study D-3 3-62
3.3.4 Case Study D-4 3-71
3.3.5 Case Study D-5 3-79
3.3.6 Case Study D-6 3-87
4.0 Estimating the Number of Facilities located in
Vulnerable Ground-Water Settings 4-1
4.1 Methodology 4-1.
4 . 2 Results 4-6
4.3 Continuing Efforts . ., 4-8
5.0 References 5-1
Attachment 1: Application of Liner Location Model
to the Analysis of Time-of-Travel Criteria
for Siting of New Land Disposal Facilities
iii
-------
LIST OF TABLES
2.0-1 Hydrogeologic Data Colleted from Liner-location
Project Literature Survey 2-5
2.0-2 Critical Times and Peak Concentrations and
100-foot Travel Times for Twelve Scenarios 2-18
3 . 3-1 Estimated Flow Rates and Volumes 3-35
3.3-2 Contaminant Concentration 3-42
3.3-3 Summary of Pumping Test Results 3-51
3.3-4 Contaminant Concentrations at Selected Wells 3-56.
3 . 3-5 Tabulation of Carcinogenic Risks 3-58
3.3-6 Tabulation of Hazard Indices for Systemic
Toxicants 3-60
3.3-7 Results of Benzene Plume Simulation 3-69
3.3-8 Concentration of Metals in Monitoring Wells 3-74
3 . 3-9 Tabulation of Carcinogenic Risks 3-77
3.3-10 Chemical Analyses for Selected Organic
Contaminants in Ground Water at a Depth of
18.3 Meters at Sites 1 and 3 through 7 3-83
3.3-11 Data from Installation of Monitoring Wells 3-94
3.3-12 Laboratory Analytical Results of Groundwater
Quality Monitoring 3-105
3.3-13 Incremental Carcinogenic Risk Associated
with Lifetime Consumption of Trichloroethylene
- and 1,1,1-Trichloroethane 3-106
4.2-1 Distribution of Facilities by Region 4-7
C ~ . '
4.3-1 Geologic Settings 4-9
4. 3-2 Regolith Systems 4-10
4.3-3 Bedrock Systems 4-11
iv
-------
LIST OF FIGURES
2.0-1 Potential Areal Extent of a Plume as a Function
of TOT Per Unit Time 2-10
2.0-2 Ratio of Peak to Steady State Concentrations as a
Function of Time of Travel 2-15
2.1-1 Locations of Literature Survey Study Areas in
Relation to the Lower 48 States and 10 USGS
Ground-water Regions 2-23
2.1-2 Histogram of Ground-water Velocities Generated in
Literature Survey in the Liner-location Project.... 2-24
2.4-1 Schematic Illustrations of Unit Design 2-38
3.1-1 Site Map Showing Location of E-W Transect and
Major Surficial Features at Love Canal 3-13
3.1-2 West-East Cross-Section of Love Canal 3-14
3.2-1. Hypothetical Well Locations Used in Risk
.' Assessments 3-16
3.3-1 Waste Units 3-28
3.3-2 Geologic Cross Section 3-31
3.3-3 Glaciolacustrine Aquifer Potentiometric Contours... 3-34
3 . 3-4 Schematic Flow Diagram 3-37
3.3-5 Well and Piezometer Location Plan and Formation
Intervals 3-39
3 . 3-6 Facility Location 3-45
3.3-7 Hydrogeologic Cross Sections A-A1 and B-B' 3-46
3.3-8 Flow Net Analyses for the Alluvial Aquifer,
August 1984 3-47
3.3-9 Iso-Specific Conductance Map for the Alluvial . •'-
Aquifer, June - July 1984 3-53
3.3-10 Ground-water Dewatering Plan and Location of
Corrective Action and Compliance Point
Monitoring Wells 3-54
3.3-11 Location of Deep Well Borings, and Geologic
Sections 3-63
3. 3-12 Geologic Section A-A1 3-65
-------
3. 3-13 Geologic Section B-B' 3-66
3.3-14 Well Pattern and Plume Outline 3-73
3.3-15 Cross-section of Ground-Water Plume 3-75
3.3-16 Location of Monitoring Sites 3-80
3.3-17 Hydrogeologic Cross-Section 3-81
3.3-18 Site Plan ,. 3-89
3.3-19 Locations of Off-Site Monitoring Wells 3-90
3.3-20 On-Site Sub-Surface Soil Boring Locations and
Locations of Site Soil Sections 3-91
3.3-21 Site Section A-A1 3-92
3 .3-22 Site Section B-B' 3-93
3.3-23 Inferred Surficial Aquifer Plume from Section A-A'. 3-98
3.3-24 Subsurface Cross-Section A-A' from Site to River... 3-99
3.3-25 Inferred Bedrock Potentiometric Surface from 1982
Data with 1984 Data Superimposed 3-100
3.3-26 Inferred Bedrock Aquifer Plume for
1,1,1-Trichloroethane (1984 Data Superimposed) 3-101
3.3-27 Inferred Surficial Aquifer Plume for
1,1,1-Trichloroethane (1984 Data Superimposed) 3-104
VI
-------
1.0 INTRODUCTION
This Appendix presents the results of the analyses that EPA
performed in developing the definition of ground water vulnerability,
In developing the vulnerability definition, EPA's primary goal was
the identification of locations where the potential for exposure
to releases of hazardous waste or waste constituents could be
significant in the event of the failure or absence of engineered
containment barriers or monitoring and response activities.
The Agency examined the effect on ground-water quality from
*
a number of land-based hazardous waste management units located
.in a variety of hydrogeologic settings. This examination
identified three generic potential pathways in the saturated
zone through which the public or the environment could be ad-
versely affected; these pathways are discussd in Section 2.0
of the main text of this guidance. EPA believes that results
from these hydrogeologic assessments show that exposure potential
is not minimized at locations where any of the three pathways
exist. The vulnerability definition therefore must be able to
identify these three pathways so that further steps can be taken
to minimize potential exposure to human health and the environment
in the event of a release.
Location vulnerability is determined for hazardous waste
landfills, surface impoundments, and waste piles by calculating
the time of travel of water along 100 feet of a ground-water flow
line originating at the base of a hazardous waste management
unit (TOT]_oo)- For landfills and surface impoundments used
1-1
-------
for disposal, TOT]_oo values less than on the order of 100 years
are considered to indicate vulnerable settings. For those land
storage or treatment facilities where wastes will be definitely
be removed at closure, the vulnerability of the ground water
will be determined by comparing the TOT^QO to the time that would
be necessary to correct a problem in the event that design and
operating controls in place at the facility failed. Determination
of this time is site specific, and the permit writer should
first ascertain that wastes and contaminated soils will be removed
from the site at closufe before considering a value for TOT^QO
that is less than on the order of 100 years.
The case studies and theoretical modeling analyses described
in this Appendix discuss how the vulnerability definition can be
used to recognize these pathways and thereby minimize potential
exposure to the environment and human health by triggering further
investigation of the location and reevaluation of design or
operation considerations.
Chapter 2 of this Appendix describes the theoretical consid-
rations affecting discharge and exposure potential, and how the
concept of TOT^QO incorporates these considerations. Using examples
and plume modeling, it examines the relationship between TOTj_oo
contaminant discharge and travel through each of the three routes
of exposure. The final section in Chapter 2 discusses overall
site design and location strategy based on the objective of
maximizing TOT^oO and minimizing contaminant access to exposure
pathways.
Chapter 3 of this Appendix presents illustrations of the
1-2
-------
three exposure pathways, and a health-risk and exposure estimation
method for the the ground-water resource pathway. Ground-water
quality data for actual or simulated ground water plumes were
analysed to determine if any health risks might exist at a variety
of hypothetical exposure points. Finally, case studies are
included that illustrate the TOTioo criteria and the health-risk
assessment for the ground-water resource pathway.
Chapter 4 of this Appendix provides estimates on the
number of facilities located in vulnerable settings.
1-3
-------
2.0 THEORETICAL CONSIDERATIONS AFFECTING
DISCHARGE AND EXPOSURE POTENTIAL
This chapter describes a series of exposure conditions that
may result from ground-water contamination. The experience gained
from investigations of CERCLA (Superfund) sites and the case studies
described later in this Appendix has been used to identify and
illustrate these exposure conditions.
Sections 2.0-1 through 2.0-3 examine the theoretical con-
siderations affecting discharge of ground water and potential for
exposure. The relationship between TOT and plume size is discussed,
and an analysis of peak concentration in the plume versus TOT is
described, using the Liner Location Model.
Section 2.1 discusses for the ground-water pathway the
relationship between TOT and well yield and the TOT distribution
among aquifers. The section contains a general discussion of the
hydrogeologic settings where contamination can spread to high
capacity production wells and individual drinking water wells.
Section 2.2 describes exposure potential through the second
pathway, surface water contamination. Included are general
examples illustrating the correlation between short TOT^oO set-
tings and the contamination of potable surface water supplies and
surface water ecosystems, and the occurrence of contaminated
seeps and springs.
Section 2.3 illustrates how exposure can occur through the
basement seepage pathway. Section 2.4 discusses overall siting
design and location strategies to minimize the potential for
exposure through any of the three pathways.
2-1
-------
Although the three pathways have been separately explained
in this chapter, one must remember that they are closely linked
in actuality. -For example, contaminated ground water can
discharge to surface water; leachate migrating along a shallow
basement seepage pathway can discharge to drainage swales. Hence,
the separation of the three pathways is a simplification to
facilitate description and illustration of each route for the
purposes of this appendix.
2.0.1 Relationship between TOT^QO an<^ t^6 Potential Size of a
Plume
The potential size of a plume is a function of the hydro-
geologic characteristics of a location and the properties of the
constituents released from the wastes. The potential rate of
growth of a plume can be described by TOT^QO'
TOT].oo measured for water should describe the rate of growth
of a plume unless constituents that move faster than water are
present, such as when immiscible fluids are placed in the unit.
However, EPA believes that these situations are atypical of most
hazardous waste management units. When immiscible fluids are
known to be present, their TOTiQO can be easily calculated by
converting the hydraulic conductivity (K) to a conductivity for
the fluid of concern. This conversion requires a knowledge of
the dynamic viscosity (/-c, kg/m sec) and density ( /j , kg/m3) of
the fluid. The relationship is given by (Freeze and Cherry, 1.979):
2-2
-------
where g is the acceleration due to gravity (m/sec2) and k is the
specific or intrinsic permeability (m2), which is a function of
the porous medium alone and which includes all the textural
characteristics of the medium (i.e./ mean grain diameter, grain
size distribution, sorting coefficient, sphericity and roundness
of grains, and the nature of their packing configuration).
However, such a recalculation of TOTiQO should not fundamentally
change the interpretation of the plume isolation properties of
the location, or of the.potential for the hydrogeologic setting
to be used as a ground-water resource. TOT^QO calculated for
water provides a simple means for comparing the natural contain-
ment characteristics of any hydrogeologic setting, thus providing
a descriptive baseline for comparing the exposure potential at a
facility. Where appropriate, the TOT^QO f°r immiscible constit-
uents can be calculated for the purpose of comparison.
The maximum potential extent of plume growth in ground water
*
is described by the size of the ground-water flow cell, which is
the distance between recharge and natural discharge zones. Flow
cell characteristics can be related to geologic settings, and the
dimensions can also be related to topographic position within the
setting. In some settings, such as coastal plain deposits, the
flow cell can be quite large, on the order of tens of miles or
more. Other settings, such as low-permeability glacial till
deposits with hummocky topography, have fairly short distances
(on the order of hundreds of feet, depending on the topographic
position). Table 2.0-1 lists the sizes of the flow systems at the
sites studied in the Liner Location Project (which is discussed
2-3
-------
in more detail in Section 2.1.2). Freeze and Cherry (1979,
Chapter 6) presents a more comprehensive discussion on flow
systems.
Figure 2.0-1 shows that potential plume size is directly
related to TOT^QO' However, the maximum extent of a plume in
ground water will be limited by any natural discharge zone.
Except where such boundaries to the flow cell e.xist, the oppor-
tunity for exposure to a plume increases when TOT increases
because the plume will underlie a greater area of land. Of
course, when a plume's growth is limited by a natural discharge
»
zone, the potential impact of the contaminated ground water on
surface water quality must be considered.
2.0.2 Analysis of Peak Concentration as a Function of TOT]_QO
EPA examined whether there is a direct relationship between
TOT^oO an^ risk, to determine if waste disposal in certain hydro-
geologic settings presents inherently less risk than in others.
This analysis used peak concentrations as a proxy for risk because
a common factor in all risk assessments is a comparison of con-
stituent concentration data with toxicity guidelines for those
constituents. The other factor in risk assessments is an evalu-
ation of exposure potential; this factor is considered separately
in the analyses presented in this Appendix.
The theoretical analysis of peak concentration versus TOT
considers four contaminant release scenarios: continuous release
at a constant release rate, continuous release at a rate deter-
mined by the ground-water flow velocity, constant rate contaminant
release for a limited time period, and flow controlled contaminant
2-4
-------
to
01
TABLE 2.0-1
HYDROGEOLOGIC DATA COLLECTED FROM LINER-LOCATION PROJECT LITERATURE SURVEY
Unsaturatcd lone
Stuly
Area
1-1
1-2
2-1
2-2
2-3
2-4
2,3-1
3-1
3-2
3-3
4-i
4-2
5-1
Earth
Hitcrlal
gravel
gravel, sand
alluvium
gravel, sand
gravel, sand
Silt
clay, silt
sand, gravel
-
sand, gravel
sand, gravel
—
sandstone
.
sandstone
Myor
Ihickness
(ft)
_c
_
10-20
50-100
50-100
100-250
-
20-200
200
—
0-300
—
20-80
Earth
Material
gravel
silt, clay
sand, gravel
gravel, sand, silt
basalt
alluvlus
gravel, sand, silt
clay
gravel, sand, silt
gravel, sand, silt
clay, silt
sandstone
clay, silt
sand, gravel
sand, gravel
sand, groveli
clay, silt
basalt
silt, sand
sediment, basalt
sandstone
faulted sandstone
sandy clay
sandstone
sandstone
Saturated Zone
Layer
Thickness
(ft)
25
300
>400
0-3000
400-1000
30-40
150
60
600
300
200
MOO
>200
30-60
200
100
>100
>1200
5000
0-700
>100
0-135
70
>300
flow Velocity
Mln Max
Vh
25
-
0.01
2.8
65
4.5
0.15
-
0.70
1.7
-
0.9
0.63
0.21
67
-
0.08
0.38
5
0.11
5.6.
0.025
0.43
0.09
'
V« V V.
tit/day)" '
110
0.006
0.04
6.3
- - -
_ _ _
- 2.10 -
3.6x10 ' - 6*10 *
2.10
5.0
2-6
1.8 -
1.6
-
-. . 220 -.
4a - id"
0.21
0.64
25 -
0.22
12.0
-
_
0.60
flow Syr.tra
Distance m»
Itech. to Ulccjiy
Boundaries'*
(ft)
21.000
40,000 .
_
-
* -
42,000
-
-
21,000
-
—
27,000
-
32,000
32,000
32.000
53,000
_
21,000
~
-
-
-
•
Pr iKiry
. lUdc ol
Discharge
river
aquifer :
river
river
river
river
river
aquifer
wolls
nquifer
aquifer
well
river
lake
« fuller
aquifer
wells
_
spring
—
wells
wells
wells
Guicr ic
Seating
1
.1
5
l
I 1
1
1
1
1
1
7
1
1
1
6
1
Source
Konizeskl et al.
(1968)
Dion (1969)
Price (1962)
UMkXfilst (19UI)
llardt et. al
(I960)
Anderson (1972)
Bertoldi (1971)
Tanuka et al.
(1974)
Newcunb et al.
(1972)
Barracluuqh,
et al.(1976)
lubcrtson.
et ol. (1974)
Luidy (1978)
Ri^nond 1 ,
et al. (1983)
U«.fy et al.
(1967)
continued
-------
TABLE 2.0-1 (continued)
stilly
Area
5-2
«-l
6-2
6-3
6-4
6-5
6-6
to
1
°* 6-7
6-8
6-9
6-10
6-11
7-1
7-2
7-3
Unsaturatcd Sane
earth layer
Hiterlal Thickness
(ft)
sandstone 50-100
Kscitont 0-500
•and. silt, 10
gravel
sandstone 20-50
•and. silt.
gravel
sandstone 50-200
6-10
fractured 0-200
llsttctone
lUwstone
-
karstlc
lloestone
Ehale
sand, gravel 10
-
sand, gravel
' Saturated Zone
Parch Layer
Hater lal Thickness
(ft)
sands torn
liacstofw
sandstone
coal
sand, silk, gravel
sandstone
1 Ues tone
fractured llaestone
binristane
shale, liaestone
sandstone
karstlc llaestona
karstlc dolomite
karstlc limestone
shale, slltstone
saw Is tone
ahale
sand, gravel
• granite
sand, gravel, silt
sand, gravel
ISO
550
20
70
15
300
50
600
100
SO
100
-
—
)1,000
40
40
>100
150
-
-
90
t
Flow Syst
t»
Flow Velocity Distance frui Primary
Min Max tech. to Dlochg. Node of Generic
V v* V. Va Boundaries*
h fft/day)" * (ft) '
0.27 -
0.04 -
_
0.61
0.10
0.20
0.49
0.13
0.04 - -,
talO'30
0.06
26
1.9
24
0.002d
0.03 - .
o.ooad
0.02
* -.
1
0.64
3.0 - 21,000
0.4 - 53,000
•3,000
3.0
5.3 - 6,000
0.40 - 16,000
_ _ -
0.24
0.16 - „
2x10 ~
0.26
5.000
2.6
180
- 0.003d
0.26 - .
- 0.01d
0.05 - 53.000
— — —
3
1.3 - 10.000
Discharge Settling
stream
aquifer
strca
river
tell
spring
spring
anuiter
aquifer
aquifer
stream
—
spring
aquifer
t^jf in)
Oftilr.f
spring
™
-
river
1
I
1
1
1
1
1
7
1
1
1
3
1
1
1
Source
luison 11965)
Kunlkow |1976)
Davis (1975)
Konikow (1*76)
Ttauqer et al.
(1964)
lurk et al.
(1971)
Klant* Ct al.
(1979)
Hall rt al.
(197S)
Harvey et al.
Skelton et al.
(1979)
Harvey (1980)
Zchner (1983)
Baker et al.
(1967)
Otton (1972)
ftothrock et al.
(1947)
continued
-------
TABLE 2.0-1 (continued)
to
StuJy
Area
™
7-5
7-6
7-7
7-1
7-9
7-10
7-11
7-12
7-13
7-14
8-1
8-2
9-1
Unsaturatcd lone
Earth . Layer
Material ThickiMM
(ft)
till, sand I
_ _
..
•and, gravel
-
•tit
-
•lit, clay
sand, gravel 10
•aid, gravel, 10
silt
till 10-20
•aprollte 3-17
gneiss
(weathered)
•lit, clay 10
Saturated Zone
Earth
Material
till, sand
•hale
ll*c»ton*
•and, gravel
sand
•and, gravel
dolcnite
•and, gravel
clay, silt
Bond, gravel
.sand, gravel
silt, clay
sand, gravel
limestone
•and, gravel
silt, clay
•and, gravel
aandctono
Clay till
till
dolcnite
dolomite
shale
eaprolite
gneiss
(weathered)
silt, clay
dolcnite
Layer
IMckneea
(ft)
>1000
200
25-260
90
75-130
50
200
50
-
40
60
50
100
30
100
20
74
20-217
30
IS
60
>50
0-50
100
100
MOO
Flow Velocity D
Min Kax Rei
V. V V. V*
h tft/dav)h
•
0.025 -
3.4
1.9
. _
0.21 -
0.04 >
0.15
1
»•> - -5
1 txlO *
1.4
~ —
0.01
0.001
o.a
18
-
0.0055 -
0.055
0.03 s -
i«io- -
0.023 -
0.56
0.002 -
0.17
-
0.51
. _
1
_ _
0.43. -
0.27 -
l.B
-
«•• -.4
- 6*10 *
4.8
— ~
0.10
0.002
1.6
51
• •
_ • _
- -
_ -
-
0.043
3.1
0.01
0.69
Flow System
i stance (ton
cf). to Dischg.
Boundaries b
(ft)
-
-
16,000
130,000 .
-
•
-
(00
-
^ •
-
—
"
_
-
-
16,000
•
5,200
5,200
5,200
4,200
-
5,000
10,500
10,500
Primary
Made of Generic
Discharge Settling
aquifer
-
river
river
.
well*
-
stream
-
river
aquifer
-
~
creek
aqui lei
underflow
river
rlvor
river
river
river
stre.au
stream
1
river
I
1
1
1
1
1
1
.1
2
1
3
2
1
1
Source
Kent ct.al.
(1972)
Kj>mlck et al.
(1VUI)
kJthsrhtld
ct al. (19U2)
leixcl ft al.
tt ton (1972)
Glbb (1978)
Otton (1972)
Planert (1980)
Petti John (1977)
tutinotf et al.
(1*02) ,.
Hr.lld ct al.
(19U2)
)
rurylond DLP
(1981)
McCrcevy and
Sloto (1980)
Trainer et al.
(1*62)
sgr,
^fcs'
rf-^ S
Kl' s
3
00
i^
00
^~
• SB
' 1
continued
-------
TABLE 2.0-1 (continued)
Unsaturated tone
Study tarth Layer
Area Material Thickness
(ft)
9-2
9-3
9-4
10-1
10-2
10-3
ro 10-4
00
10-5
10-«
10-7
lo-i
10-,
10-10
sand, gravel
sond, gravel 10
•and, Bllt,
clay
— _
•and ISO
•and
clay, sand 10-30
_ »
_ .
— —
Saturated lone
Earth
Miter lal
sand, gravel
sand, silt, clay
crystalline rock
sand, silt, clay
basalt
sand
•and
•and, gravel
^
clay. Band
•and
•and
•llty clay
luKBtona
llacstone
und, clay
Layer
ttilckneu
(ft)
35
80
>SOO
200
WOO
1000
>400
>1000
20
100
ISO
75
100
>1000
23
•.•mtatone. lutestone 100
•and
•and, gravel 30
sand
clay
Band, gravel
clay
•Ant, gravel
crystalline cock
100
30
200
200
100
MOO
Flow Velocity -
Min Max
Vh
1.9
2.4
-
0.36
—
0.006
0.21
0.05
0.042
0.02
0.02
-
o.sa
9.011
9.0035
1.1
0.53
0.24
0.10
-
Vu Vh
Tft/dayr
6.2
14
—
3.0
— -
0.29
0.47
0.2
B.4
4.3
0.2
-
.
0.011
0.001
3.5
1.1
- . 0.64
U10'5 -
0.26
•• ~
Flow System
Distance Frui Prinary
Rech. to Oischg. Hide of
V" Boundaries b Discharge
v (It)
creek
3.200 river
aquifer
2,000 river
— — —
- -
streon
• - %«!!•
3,000 Cfrlnjs
-• 3,000 sprlnja
3,000 creek
- - -
52.000 creek
» - ocean
.
*MI
MllB
MllS
6xlO~* - aquifer
aquifer
— —
Vcncric
Setttlni
1
1
1
1
1
1
S
1
I
2
1
1
7
Source
Qjr.luic et al.
llarni (l»78)
LaSala (1968)
.
K-wson et al.
(19b7)
Mri.wicr at al,
(1966)
Hx>t rt al.
(196S)
Ohlll { 1902)
Knollin et al.
(1964)
llonr^.w et al.
(196S)
llutchinson
et al. (1978)
M..,t ||V«|
North Carolina
D.N.M. (1978)
Mack (1962)
continued
-------
TABLE 2.0-1
K)
Utsaturatod lone
Sluly
Area
10-11
•
10-12
10-13
10-14
11-1
11-2
11-3
'.1-4
11-5
11-6
11-7
11-a
r.irth Layrr
Material Ihickness
(ft) .
-
sand.
sand.
sand.
clay
sand.
sand.
sand.
sand.
-
•and.
sand.
clay
sand.
-
gravel 10-20
gravel 10-100
silt, 90
gravel
gravel
gravel
gravel
-
gravel
•lit.
gravel
Saturated lone Flow Systra
Earth Layer
Material Hilckness
(ft)
sandstone
Bond, gravel
schist
said, gravel
clay
sand, gravel
sand
•ilty clay
sand, gravel
lumlatona
sand, gravel
sand, gravel
fine sand
sand, gravel
Eliale
sand, gravel
Itarstone
cand, gravel
sand, gravel
ohale
sand, silt, clay
cand, gravel
cltale* schist
•0
200
>100
90
20
200
10
100
150
>200
100
30
100
30
>50
100
-
-
100
>200
75
200
>500
flow Velocity Distance Mru»
Mln MOM Hech. to UlccJig
vh
0.64
0.03
0.16
-
0.04
1.3
-
0.64
-
0.32
0.22
-
1.3
-
0.4S
—
5
0.45
"
21
27
V* V. V. Boundaries0
Yft/day)5 ' (It)
...
0.10 - 42,000
- . 0.72 - SS.OOd
iKlO"* - S»10~*
0.19
2.1
- - - -
- ' 1.3 - 10,000
- - -
0.64
- d 0.45 - . 2,000
0.04° - l.f 100
2.2
-
3.0 - 13,000
...
.
3.0 - 5,000
- - •
- 55 - 15,000
- 80
Primary
. Hide o(
Discharge
well
stream
a^iiter
well
strcon
-
river
-
-
river
aquifer
river
-
river
-
river
well
river
wells
Gittcric
betttlng
1
1
1
1
|
'l
1
1
a
i
i
i
i
i
Source
UvxfcTkrr et al.
(1979)
LMwillc et al.
(19bl|
Luzier (1900)
Getzcn (1972)
SfrinJUe (1978)
Croft (1973)
Dalsln (1978)
Marie (1975)
flonort et al.
(1979)
teutb (1970)
Hilton ct al.
(1960)
Kllnuth (19*4)
Ktnslow et al.
* Vertical groundwater flow U toward unless otherwise Indicated
Mailimn horlnntal distance fccn recharge to discharge groundwater divide*
c A dash indicates that Information MS not reported
Onward groundwater Clow
-------
FIGURE 2.0-1
POTENTIAL AREAL EXTENT OF A PLUME AS A FUNCTION
OF TOT PER UNIT TIME
c
•o *-.
4) 4J
— t+-
« *-*
HJ I/)
u u
*J HJ
0)
V >>
-------
release for a limited time period. The first of these scenarios
shows increasing steady state concentrations with increasing TOT,
the second and_third show peak or steady state concentrations to
be unrelated to TOT and the fourth shows decreasing peak concen-
trations with increasing TOT.
Steady State
If the release of a contaminant into an aquifer for a finite
period of time is assumed to occur at a point, then the following
equation describes the variation of contaminant concentration
with time and distance along the direction of the flow:
-(x-V(t-l
Q(t') exp (
C(x,t)
t-t'))2\
(t-t1) J
Q(t') exp 4Dx(t-t') / dt1 (2)*
8 n0VlT3(t-t')3DxDyDz
where
C(x) = Concentration (grams/meter^)
distance x (meters);
Q(t') = Time dependent contaminant release rate
(grams/second) to the aquifer at point.x = 0;
V = Seepage velocity for the aquifer (meters/year);
Dx = Dispersion in the direction of flow
(meters2/year);
Dy = Dispersion in the horizontal direction
perpendicular to the direction of flow
(meters^/year);
Dz = Dispersion in the vertical direction
(meters^/year); and,
ne = Effective porosity (0 < ne _f.l);
*Equation (2) is modified by GCA Corporation from Freeze and Cherry
(1979) equation 9.6 (on page 395) for the case y = z = 0.
2-11
-------
This equation describes the effects of hydrodynamic dispersion
It does not consider the effects of contaminant degradation or
sorption to soil particles.
For a release rate Qo, which does not vary with time, the
steady state concentration (t—? °° ) is given by:
4-ff x ne y DyDz
(3)
**
In the analysis, the following assumption/definitions are
also made:
Cmax(x) = Maximum concentration at distance x considering
all values of C(x,t)
Time of Travel (TOT) = x
V
Dv = c< Tv
Dz = XTV
The values ° have units of
meters. The contaminant release rate, Qo, used in Equation (3)
can be written as follows:
Qo = JV (4)
where
j = either a constant or a variable (units of g/m)
depending on whether or not the release rate, Qo,
is flow dependent.
** Equation (3) is from Hunt (1978).
2-12
-------
Equation (3) can then be written as:
C(x, oO ) = jv
41T x ne v «T °^L (5)
4TT x
If the release rate is constant with respect to velocity,
then the source term Qo is constant and j is inversely proportional
to V. In this case, as TOT increases, j increases and the peak
concentration increases. With constant contaminant release, the
steady state concentration at distance x is higher for longer TOT.
If the release rate is flow-controlled (proportional to the
flow velocity within the aquifer), then Qo is proportional to V,
and j is constant. In this case, the steady state concentration
at distance x is independent of velocity and, therefore, TOT.
Releases Over a Limited Time Period
Some releases may only last for a period Tr. In this case,
the time dependent release rate Q(t') used in Equation (2) is
given by:
Q(t') - jV for 0Tr
For a constant release rate Qo over a finite period Tr, the term
jV will be constant and the peak concentration Cmax(x) at a
distance x will be independent of the TOT.
For flow-controlled releases having a. finite period, the
peak concentration, Cmax(x), at a distance x will actually
decrease with increasing TOT. The amount of this decrease will
depend upon the period of release and the distance from the
2-13
-------
source. This relationship is illustrated in Figure 2.0-2, which
shows the ratio of maximum to steady state concentration for
different values of TOT and release period. In this example, the
distance x has been chosen as 30 meters and the longitudinal and
traverse dispersivities,
-------
4)
4)
O
o
II
X
L.
o
8
X
X
E
O
Time of Travel to Reach 100 Feet (Years)
Symbols (Period of Release)
• 1 YR.
a 2 YR.
T 3 YR.
O 5 YR.
* 7 YR.
A 10 YR.
FIGURE 2.0-2 Ratio of Peak to Steady State Concentration as a Function of
Time of Travel (TOT) and Period of Release at a Distance of
100 Feet from the Release Point (
«
0.1)
2-15
-------
problem can be isolated for examination by holding other aspects
constant.
Modeling also provides an opportunity to examine the effects
of hazardous waste management in hydrogeologic settings with
long TOTs. The steady-state characteristics of plumes in these
settings cannot be thoroughly examined using case studies, simply
because insufficient time has passed since facility operations
began in those settings for a plume to mature to such dimensions.
Modeling provides a method for estimating when such dimensions
might be reached, and what the characteristics of such a plume
and its relationship to an uppermost aquifer might be.
The model selected for this work is the Liner Location Model
developed by EPA to assess the contaminant concentrations and
health risks associated with a range of TOT^oO conditions (as well
as other characteristics) at hypothetical sites. The model has a
number of subroutines, including ones for ground-water flow and
solute transport. The version of the model used in this analysis
was not designed for site-specific use; EPA is refining the model
and plans to make it adaptable for site-specific use.
Results of Model Use
This effort examined six generic, vertically-oriented ground-
water flow fields covering a range of ground-water flow velocities
from 100 feet in 10 years to 100 feet in 1,000 years. Peak con-
centrations were determined for a point 100 feet along the ground-
water flow line from the source. The hydrologic subroutine is
described in Attachment 1.
Different scenarios were generated for each setting by varying
2-16
-------
key parameters, as follows:
0 Two contaminant mobilities were examined. These were class 1,
retardation factor of 1.3, and class 2, retardation factor of
32.
0 Two source loading mechanisms were examined: equal mass
input and flow field controlled mass input. Equal mass
inputs could be controlled by either the facility design/
failure mode or an underlying unsaturated zone. Flow
field controlled inputs are masses released at a rate
determined by the flow field which continue for a fixed
time period. The total mass released varies with flow
field velocity.
The principal results of the hydrologic model are summar-
ized in Table 2.0-2, which shows peak contaminant concentrations
and 100-foot travel time for the six generic settings. Variations
are shown for the two chemical mobility classes and for the two
source loading assumptions. For the hydrogeologic settings
considered, there is no clear relationship between peak concen-
trations produced by instantaneous equal mass releases at the
source and velocity or TOTioO- This is consistent with the dis-
cussion in Section 2.0.2 which showed these variables to be
independent. Variations in concentration shown in Table 2.0-2
are due to variations in other variables such as porosity and
the influence of multilayer velocities in scenarios M, N, and O.
Where time-limited mass releases are controlled by the flow field
(including diffusion-controlled transport with high velocity
contrasts), peak concentrations decrease with increasing
2-17
-------
TABLE 2.0-2 CRITICAL TIMES AND PEAK CONCENTRATIONS AND 100-FOOT TRAVEL TIMES
FOR TWELVE SCENARIOS
ro
H*
OD
Scenario
identification
J-1-100
J-2-100
K- 1-100
K-2-100
L-1-100
L-2-100
M-1-100
M-2-100
N-1-100
N-2-100
0-1-100
0-2-100
Start
(yr)
300
8,000
35
800
k
80
250
8,000
120
3,000
5
150
Critical
End
(yr)
5,000
110,000
1»50
11,000
53
1,100
120,000
360,000
800
20,000
120
3,500
times
Peak time
(yr)
1,250
32,270
115
3,000
12
320
1,360
33,000
260
6, MO
21.5
550
Peak concentrations
Standard load
(mg/1)
k2.k
1.80
19.5
.92
20.5
.87
1.2
.0
-------
The difference in relationships between peak concentration
and velocity/TOT^QO highlights the importance of the source term
in the model. _This modeling study also shows that the lowest con-
centrations are associated with settings that include very low
velocity surficial layers with diffusion-controlled transport
overlying an aquifer that would otherwise have received
higher inputs of contaminants and would not have met the current
TOTiQO criterion.
Conclusions of Preliminary Use of Liner Location Model
This preliminary analysis supports the use of the TOT^oO
criterion where source removal or corrective action can limit the
duration of the contaminant releases. In this circumstance, the
magnitude or mass loading of the release is controlled by the
low-velocity flow field.
This analysis also shows that zero concentration cannot be
achieved for nondegrading constituents as long as a waste source
exists. Contaminants will move, albeit slowly and in minimal
volume, through low-velocity flow fields. These constituents can
eventually reach aquifers and, hence, points of potential exposure.
However, as shown in Table 2.0-2, these times may be far into the
future, on the order of thousands of years. This result further
supports the view that the TOT]_go criterion describes settings
that minimize the potential for exposure to releases.
2.1 POTENTIAL FOR EXPOSURE THROUGH A GROUND WATER RESOURCE
The potential for exposure to contamination through a ground
water resource can be described by two main factors. The first
factor relates to the plume character, which includes its potential
2-19
-------
size and the peak concentration of contaminants, as discussed
in Section 2.0. The second factor in potential exposure is
related to the"probability that the saturated zone could supply a
sufficient volume of water for residential use or other purposes.
As described in this section, the vulnerability criterion, TOT^oO'
provides a measure for potential exposure because it incorporates
a consideration of these factors.
2.1.1 Theoretical Relationship between TOT^QO and Well Yield
This section discusses the theoretical relationship between
*
TOT^oo of ground water within a saturated zone and the potential
yield (Q) of a discharging well in the same zone.
Time of Travel
The technical analysis examined well-documented mathematical
expressions, commonly used by hydrogeologists to analyze travel
time and well yield.
The general expression for calculating TOT in a homogeneous,
isotropic media through which ground water is flowing under the
influence of a uniform hydraulic gradient is:
TOT = Lne (7)
KT~
where TOT = time of travel, (T)
L = length of flow path, (L)
ne = effective porosity, (dimensionless)
K = hydraulic conductivity, (L/T)
i = hydraulic gradient, (dimensionless).
Equation (7) is used in the definition of ground-water
2-20
-------
ruuu
8472 • 00- 2A
vulnerability when L is set equal to 100 feet. It shows that TOT
is inversely proportional to both hydraulic conductivity and
hydraulic gradient. A long TOT can be associated with very low
permeability materials, very low hydraulic gradient, or both.
Well Yield
The steady radial flow to a discharging well in a confined
aquifer is described by (Thiem, 1906):
Q = ?TTKh h - hw (8)
In (r/rw)
where Q = constant well yield, (L^/T)
K = hydraulic conductivity, (L/T)
b = constant aquifer thickness, (L)
h = hydraulic head at radial distance r, (L)
hw = hydraulic head at the well, (L)
r = radial distance associated with h, (L)
rw = radius of the well, (L)
A more general form of the equation can be obtained by
letting r = rl, rw = r2, while h = 'hi and hw = h2. Equation (8)
•
can then be rearranged to obtain an expression for the hydraulic
conductivity (Todd, 1959, page 83):
K
Q In (r2/rl)
2^Tb (h2-h1)
Consideration of the equations for TOT and well yield can be
taken further by substituting Equation (9) for K in Equation (7).
This yields the following expression:
TOT = 2TT L n b (h2-hj) (IQ)
Q In (r2/ri)i
2-21
-------
Both well yield and TOT are sensitive to hydraulic conductivity.
A very low conductivity regime will tend to have both long TOT
and low well yields. Facilities located in such "non-aquifers"
(i.e., aquitards) should have a minimal potential for exposing
human and environmental resources to contaminants released to
ground water because the chances for aquifer exploitation are
minimal.
However, the relationship between yield and TOT is also
influenced by porosity, well drawdown, aquifer thickness and
hydraulic gradient. A setting with a high hydraulic conductivity
and a very low hydraulic gradient can have both long TOT and high
potential well yields. This occurrence illustrates the importance
of considering changes in hydraulic gradient due to aquifer
exploitation in evaluating TOT, as discussed in Section 3.2.2
of the main text of this guidance.
2.1.2 Frequency Distribution of TOT Among Well-studied Aquifers
This section summarizes information on 67 case studies of
existing hazardous waste land treatment, storage, and disposal
facilities reviewed during Phase I of the Liner Location Project
for the Office of Solid Waste (EPA, 1983). The location of the
67 facilities is shown in Figure 2.1-1.
Figure 2.1-2 is a histogram that presents the frequency of
occurrence of horizontal ground-water velocities collected in the
survey. Table 2.0-1 summarizes the basic data for each case
study. Because the majority of cases represented well-studied
aquifers that were also well developed for water supply, the
velocities may be biased toward the high end of the range of
2-22
-------
NJ
10
OJ
EXPLANATION
• 6-1
Groundwater region
Location and designation of
groundwater study area
10-8
0 WO tOO MO 400 MO Mllll
FIGURE 2.1-1 LOCATIONS OF LITERATURE SURVEY STUDY AREAS IN RELATION TO THE
LOWER 48 STATES AND 10 USGS GROUND-WATER REGIONS
-------
o
ec
ec
o
>•
S*
Oi
U.
50 -
30 -
20 -
10 .
0 -
<
yjiy
c
IX'X'X'X-X
x:::x ::x::-::x:x:::
o
•--^•--1
EXPLANATION
Frequency based on
1 i terature survey
o Frequency of value used
in model scenarios
<
10
-------
possible velocities. In addition, some, but not most, case
studies represent confined aquifers, not the uppermost aquifer.
Consequently, there is some question about how representative this
data-base is of conditions underlying RCRA facilities.
A TOT]_QQ scale is shown at the bottom of Figure 2.1-2 in order
to show the relationship of the criteria to the aquifer-oriented
database. Clearly, TOTiQO values on the order of 100 years occur
infrequently among the 67 case studies (about 4%).
This information suggests important conclusions: TOT^QO
*
values on the order of .100 years or more are uncharacteristic of
•
aquifers, and facilities located in nonvulnerabie settings are
unlikely to discharge to geologic formations that supply a sig-
nificant quantity of water for sustained uses.
2.1.3 Contamination of High Capacity Production Wells
A common condition resulting in risk and exposure occurs
when contaminated ground water is intercepted by high capacity
production wells. The public is at risk when municipal wells are
contaminated, while the potential for worker exposure exists when
industrial wells are threatened by contamination. If irrigation
wells become contaminated, the irrigated crops may also take up
the contaminants, which can result in contamination of the entire
food chain.
The conditions described above are most likely to occur in
areas with high-yield aquifers in which high-production wells are
likely to be located. In general, these aquifers consist of thick
deposits of unconsolidated sands and gravels, or other highly
porous media, such as fractured or poorly cemented sedimentary
2-25
-------
rocks, or fractured limestones. Often, the well fields are situ-
ated near streams and rivers, where induced recharge from surface
waters supplements the available ground-water supply. The TOT^oo
in these types of hydrogeologic settings is always very short
because such productive aquifers are highly permeable.
Because continuous pumping of significant quantities of
water at these well fields can alter the pre-existing flow paths
and even create reversals in the direction of ground-water flow,
sources of contamination may be very difficult to identify.
Pumping may also shorten TOT^QO if it has been calculated under
natural conditions, because the cone of depression around such
wells will increase the hydraulic gradient, which is also directly
proportional to velocity.
2.1.4 Contamination of Individual Drinking Water Wells
Contamination of domestic water supplies is becoming in-
creasingly more common. In 1970, nearly 20 percent of the United
States population relied on individual wells for drinking water
and domestic use. In rural areas, many contaminated domestic
wells have had to be abandoned due to releases from hazardous
waste management facilities.
Individual drinking wells can be located in many kinds of
hydrogeologic settings because even aquifers with very small
yields (as low as half a gallon per minute) can provide sufficient
quantities of water for domestic use. The geologic settings
range from fractured crystalline bedrock to highly permeable sand
and gravel deposits. TOT^oO is highiy variable because of the wide
range of hydrogeologic settings. Well depths range from only a
2-26
-------
few feet to over a thousand feet, although the majority of wells
are between 100 and 300 feet deep. In general, domestic wells
located in unconsolidated materials are shallow, depending on the
depth to the water table. These wells are the most susceptible
to ground-water contamination because most hazardous waste facil-
ities are located at or near the surface; hence, contaminants
will often be most concentrated near the top of the aquifer.
Exceptions would include contamination from underground injection
wells that dispose of wastes to deeper portions of the aquifer,
v
and contamination by constituents that are much denser than water.
2.2 POTENTIAL FOR EXPOSURE TO CONTAMINATED SURFACE WATER
The theoretical discussions of ground water contamination
presented in Sections 2.0 and 2.1 also relate to the second pathway
of exposure, surface water contamination, because contaminated
ground water can discharge to surface water bodies through springs,
seeps, and baseflow.
This section describes conditions and representative hydro-
geologic settings that can lead to contamination of surface water.
2.2.1 Surface Water Exposure Pathway: Hydrogeologic Settings
Surface waters and ground waters are interdependent compo-
nents of the hydrologic cycle; a change in one of these components
may have a significant impact on the other. Contamination may be
transported from ground water to surface water in discharge areas,
which occur in topographic lows. These situations arise when the
net saturated flow of ground water is toward the water table,
which is often at or very near to the ground surface.
2-27
-------
If the discharge rate is low or flow occurs over a large area
diffuse seepage may occur, moistening the ground. However, seepage
along streams or lake banks may produce a volume sufficient to
provide a main source of stream flow during dry periods (baseflow).
Surface water bodies may also receive ground water from
springs. Springs arise when a discharge from an aquifer is
concentrated in a small area, and they commonly occur in areas of
fractured bedrock or karst topography.
Discharge of ground water is related to precipitation and
will vary seasonally with the amount of water that is stored in
the saturated zone and, therefore, with the slope of the potentio-
metric surface. Nested piezometers may be installed to determine
if an area has an upward component of flow characteristic of a
discharge area.
2.2.2 Contamination of Potable Surface Water Supplies
An example of a situation that presents a risk to human health
is the contamination of surface water bodies, such as lakes,
•
reservoirs, ponds, or rivers, that serve as drink'ing water supplies.
A risk can also exist if creeks, streams, rivers, or their tributar-
ies that eventually empty into a drinking supply are contaminated.
Surface water may become contaminated by direct discharge of con-
taminants from a point source to the water body or by contaminated
runoff. Contaminated ground water may also be a source of surface
water contamination if it discharges to the surface water body.
2.2.3 Contamination of Surface Water Ecosystems
When a body of surface water becomes contaminated, it poses
a risk to aquatic organisms or the entire ecosystem that it
2-28
-------
hosts. Humans are also at risk if they have contact with the
contaminated water through recreational activities or if they
ingest aquatic life/ such as fish, that dwell in the water.
Animals may also be exposed if they drink the water or ingest any
aquatic organisms.
2.2.4 Bedrock Springs Contamination
In some cases, the identification of contaminated ground
water is first made in areas where springs are visibly contam-
inated. Indications of contaminated springs or seeps include
noxious odors, dead or dying vegetation or animals near the
»
springs, and the presence of oil. The presence of a contaminated
spring is usually a strong indication of a much larger problem.
In general, springs and seeps occur where the water table
intersects the surface. Several types of springs can occur,
depending on the hydrogeologic setting. A depression spring is
likely to occur in a topographic low spot, thereby creating a
local discharge zone. Contact springs are likely to occur at the
contact between a high permeability layer and an underlying low
permeability layer. Faulting can create a similar condition when
a low permeability layer is juxtaposed with a high permeability
layer. In areas underlain by limestone, springs are very common
because of the creation of solution features, such as caverns and
sinkholes. Springs are also common in areas with fractured, low
permeability rock. Water movement occurs along the joints and
fractures, and spring water discharges where the fractures intersect
the surface.
Given otherwise similar hydrogeologic settings, the
2-29
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will nearly always be shorter where springs and seeps are present
than where they are absent. Springs and seeps often reflect the
presence of pathways of low resistance, such as solution channels
in limestones or joints in crystalline rocks, along which ground
water tends to flow. Abandoned mine shafts create a similar
condition, in which rapid transport of contaminants occurs in
water-filled shafts.
2.3 POTENTIAL FOR EXPOSURE THROUGH THE BASEMENT SEEPAGE PATHWAY
2.3.1 Description of Condition
Exposure can occur when contaminants enter basements of homes
and buildings through ground-water seepage or vapor phase transport
of methane and other toxic gases. To anyone living in the area,
this condition poses a serious threat through exposure 'to toxic
chemicals and fumes and through the potential for fires and
explosions resulting from highly combustible gases.
2.3.2 Representative Hydrogeologic Settings
This condition can occur in a variety of hydrogeologic
•
settings. .However, the risk from contaminants seeping into
basements is most likely to be present in areas where the water
table is permanently or seasonally above the level of the basement
floor or where an upper isolated saturated zone exists. Vapor
phase transport is a more serious problem in settings where there
are interconnected pathways between the contaminated aquifer and
the surface, such as fractured bedrock or porous unconsolidated
sand and gravel deposits. The presence of noxious odors is often
the first indication of a problem.
varies in settings where basement seepage occurs.
2-30
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The pathways themselves may be localized features with short
TOTioo values that provide the path of least resistance for con-
taminant transport in a predominantly long TOT^QO setting. For
instance, such pathways may consist of sand lenses, permeable
topsoil, or man-made conduits such as buried utility lines or
gravel-^f illed drainage swales.
When a facility is underlain predominantly by a low perm-
eability layer (where TOTioo ^s long), increased recharge, both
artificial and natural, could cause ground-water mounding. This
elevation of the water table may create the opportunity for
contaminants to travel through previously inaccessible pathways
(the 'bathtub effeet'),. unless that pathway is already accessible
due to a high water table. One must also examine the potential
impact of artificial containment barriers installed to lengthen
TOT100' or tne failure or stripping off of a cover, in causing a
bathtub effect (see Section 3.1 for examples of contaminant
transport through the basement seepage pathway). The potential
for this pathway to exist may be recognized by examining flow
patterns that would result from the greatest hydraulic head that
could occur at a unit. Section 3.2.2 of the main text discusses
how these heads can be determined. If the pathway could exist,
modifications in unit design might prevent migration, as discussed
in the next section.
2.4 CONSIDERATIONS FOR LOCATION AND UNIT DESIGN
The optimum nonvulnerable setting for a hazardous waste man-
agement unit is one that minimizes the potential for exposure to
2-31
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human health or the environment by limiting waste migration
potential through each of the three pathways: exposure to a
contaminated ground water resource, exposure to surface water
contaminated by discharging ground water, and exposure through
the "basement seepage" (near-surface flow) pathway. The vulner-
ability definition is an important trigger for evaluating overall
site performance under several major design scenarios.
2.4.1 Controlling Discharge from a Unit
The hydrogeologic characteristics of a location can control
*
the amount of fluid released to the saturated zone from a landfill,
surface impoundment, or waste pile, thereby helping to control a
plume at its source. An effective design evaluation includes an
assessment of how natural controls can be used to minimize fluid
discharge, in addition to engineered components such as liners
and caps.
The volume of fluid discharged across an area within the
saturated zone per unit time (Q) can be calculated as:
Q = -KiA, (11)
where Q = flow (L3/T)
K = hydraulic conductivity (L/T)
i = hydraulic gradient
A = cross-sectional area of flow (L2).
Because Q o<_ K and Q oi i, settings with low hydraulic
gradients and low hydraulic conductivities (i.e., long TOT^QO
values) can minimize discharge from the waste management unit
depending upon whether the discharge is controlled by the flow
field. This can best be understood by considering the potential
2-32
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performance differences of a unit in the unsaturated and saturated
zones.
Unsaturated Zone
The potential discharge from the facility located wholly
above the water table equals the amount of infiltration passing
through the cover (or direct precipitation, if no cover is present)
and the bottom liner (if any), plus the volume of any run-on and
fluids present within the unit. If the liner and the cover are
truly impermeable, there should be no discharge. If this condition
is not satisfied, the discharge will be as high as the infiltration
through the cover, or the fluid volume placed within the unit
plus 'incident precipitation and run-on during unit operation.
Consequently, prevention or minimization of discharge requires
both advanced design considerations and long-term, .active unit
maintenance.
When a discharge occurs from a unit in the unsaturated zone,
the hydraulic gradient along' the flow path from the unit to the
ground-water table will be high (close to 1.0). If the discharge
is substantial, a ground-water mound might be created beneath the
unit; mounding can increase the pre-existing hydraulic gradient
within the saturated zone as well, with a consequent increase
in Q and reduction of TOT^QQ•
The relationship between TOTj^oO an^ peak concentration (or
risk) for such cases is discussed in Section 2.0.2 under the
descriptions for the constant release scenario, in which peak
concentration increases with increasing TOT^QO f°r a continuous
release. A release occurring over a limited time period displays
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a peak concentration unrelated to
Saturated Zone
This discussion applies only to below-grade units, in which
the maximum elevation of waste placement is below the top of the
saturated zone. At closure, the final cover would fill the
excavation to the original grade.
At a facility where waste is located entirely within the
saturated zone, the potential discharge through the liner (if
any), can be limited to the natural flux of ground water passing
across the boundary of the unit. The discharge would be greater
only when the hydraulic gradient is increased by either fluid
addition during operation (assuming no impermeable liner) or
infiltration through the cover in excess of pre-existing conditions
In addition, the seepage velocity of ground water would be equal
to pre-site velocity unless the gradient is increased.
This situation corresponds to the flow field controlled
scenarios described in Section 2.0.2, in which peak concentrations
(and hence, risk) are reduced as TOTiQO increases. The success of
a unit located entirely within a low-permeability saturated zone
primarily depends on the ability of the final cover to limit
infiltration to levels that are not significantly greater than
those prior to unit construction; failure of the cover to perform
properly could allow mounding and migration along the third
pathway.
2.4.2 Considerations for Unit Design
Limiting access to the three exposure pathways is critical
for optimal unit design. One design scenario for a unit in a
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low-permeability nonvulnerable setting would be to:
0 review the impact of passive flow barriers that may be
installed,
0 keep wastes well below grade to prevent formation of the
basement seepage pathway or leachate springs (see Figure
2.4-1), and
0 maintain the integrity of the cover so that excess
infiltration does not create a bathtub effect.
This design scenario optimizes the use of passive methods to
minimize the potential for exposure to releases that occur due
to human oversight and the failure or absence of man-made barriers.
It highlights the other major option for minimizing exposure
potential, which is to provide long-term (perpetual) monitoring
and response. For example, if such active controls were ensured
through an institutionalized oversight and response program,
hydrogeologic setting would be less critical in long-term exposure
minimization.
2.4.3 Considerations for Storage and Disposal Units
Unit design and location considerations can be affected by
whether a unit is operated and closed as a storage unit or as a
disposal unit.
Storage Units
Because wastes are removed from storage units at closure, a
release from a storage unit can occur only during a limited
period of time. Because the owner or operator is responsible
for ground-water monitoring and corrective action during this
period (the active period of the storage unit), any release that
occurs should be detected and corrected as necessary, in response
to the permitting standards of 40 CFR 264 Subpart F. As discussed
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OSWER POLICY DIRECTIVE K
9472•00-2A
'*!'.•-*.".'-*.''-•-'>'.
X
I
3}
CLAY
FIGURE 2.4-1 Schematic illustrations of unit design. Figure A
shows waste disposed above grade. The high
hydraulic head causes flow along the near surface
silty layer as well as vertically into the clay.
Figure 3 shows the optimal unit desiqn, with wastes
deposited below grade,, with a thick cap filling the
excavation, thus inhibiting access through the basement
seepage pathway.
2-36
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in Section 2.0.2, such limited time releases can occur under
either a constant release or a flow-controlled release scenario.
A constant release scenario, typical of a unit placed in the
unsaturated zone, yields a peak concentration that is unrelated to
TOTiQO* A storage unit located in an unsaturated zone should not
pose a risk of exposure if the setting provides an adequate time
period for plume detection and implementation of corrective
action.
A storage unit placed in the saturated zone would be
characterized by a flow-controlled release, in which peak con-
centration decreases as TOT^QO increases. While the long TOT^oO"
saturated zone setting may be more protective in the event of a
release, the major location consideration is to provide adequate
time for plume detection and response. In fact, a longer TOT^QO
setting may impede the efficiency of a corrective action, owing to
increased sorption capacity of fine-grained sediments and the
decreased ability of collection wells to capture and remove the
plume rapidly.
Disposal Units
Because wastes are not removed from disposal units at
closure, the potential exists for continuous and long-term release
of contaminants to the environment. A disposal unit could have
either a flow-controlled continuous release, or a constant con-
tinuous release.
As discussed in Section 2.4.2, a leaking disposal facility
located in an unsaturated zone would correspond to a constant
release scenario; the magnitude of the constant rate of flow
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from the unit depends on the degree of failure of the unit
design, is complicated by ground-water mounding, and thus is
generally unpredictable.
Releases occurring from disposal units located in the sat-
urated zone may be controlled by the natural ground-water flow
velocities. Although the peak concentration in flow-controlled
releases is unrelated to TOT^oO' tne size of the plume is limited
in a long TOT100 setting (Section 2.0.1), and discharges from the
unit would be minimal and predictable (Section 2.1.1). Thus, a
long TOT^oO setting is especially important for disposal facilities
*
where the absence of long term care necessitates a setting that
minimizes the potential for exposure to future releases. Isolation
of wastes completely within saturated, low-permeability materials
offers this potential.
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3.0 CASE STUDY EXAMPLES AND EXPOSURE ESTIMATION METHODS
This chapter uses case studies to illustrate exposure and
health risk estimates for each exposure pathway in a variety of
hydrogeologic settings. The case studies show that exposure to
ground-water contamination is most frequently documented at
locations with hydrogeologic settings exhibiting short TOT^Q' Tne
vast majority of ground-water contaminant plumes and their ultimate
threat to human health and the environment have resulted from
hazardous waste disposal in locations where ground-water flow is
rapid and contaminants may be transported to a well, spring, or
surface water body. In hydrogeologic settings with predominantly
long TOTiQO values, observed health threats have resulted from the
failure to recognize and prevent seepage of contaminated ground
water and associated toxic vapors along near-surface, short
TOTiQO pathways into basements and subsurface utilities.
However, evidence of contamination in short TOT^oO
settings is expected because many existing hazardous waste sites
located in settings with long TOT^gO values would not be expected
to have ground water contaminated to the point where a problem
would have been detected. Conversely, sites exhibiting short
TOT100 values would develop ground-water plumes rapidly as a result
of improper or ill-considered waste disposal activities and con-
sequently are much more likely to cause detectable contamination
that subsequently would be investigated.
Because plume detection may be biased towards short TOTioo
settings, and because of the occurrence of basement seepage path-
ways, long TOTiQO settings should not be considered automatically
3-1
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safe for siting. The examples presented in this section suggest
strongly that regional hydrogeologic settings and related land
and water uses surrounding the hazardous waste management facility
site should be evaluated thoroughly during the facility permitting
process.
The brief case descriptions in Section 3.1 illustrate the
relationship between TOTioo and tne three exposure pathways.
Exposure and risk through the potential pathways are discussed
for each case in qualitative terms, because sufficient data
were not readily available for quantitative risk assessments.
An exception is the example in Section 3.1.7 for which more
quantitative information was available for the third pathway
analysis.
As an example of the type of health risk methodology that
can be applied to a specific pathway, Section 3.2 discusses
assessment methods that can evaluate the potential health threat
to humans exposed to contamination through potable ground water.
Finally, case studies illustrating the application of this
health risk assessment for ingestion of contaminated drinking
water are presented in Section 3.3; other pathways are indicated
when present.
3.1 CASE STUDIES: THREE EXPOSURE PATHWAYS
These case studies are general summaries designed to il-
lustrate the relationship between TOT]_oo an^ a^ three exposure
pathways. No rigorous health assessment methodology has been
used for these case studies.
3-2
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3.1.1 Ground-Water Resource Pathway: Chemical Plant Site
Description of Condition
A large chemical plant was operated at the site until 1982.
Nearby residents have filed complaints about odors and irritants
in the air since 1973. The town drilled five highly productive
wells in the area, but odors in the water from these wells indi-
cated the presence of contaminants. Local and state authorities
conducted a more detailed investigation of the company's disposal
practices in 1978 after the company submitted a proposal for
expansion at the site. The investigation resulted in the shutdown
of two town wells as a precautionary measure, which reduced the
town's drinking water supply by 40%. The company has agreed to
clean up the contaminated areas and restore the quality of the
aquifer supplying the town wells.
Hydrogeologic Setting
The site occupies about 500 acres and is underlain by
unconsolidated sands and gravels deposited near the end of the
Wisonsin Glaciation. These deposits have been extensively mined,
especially in the southern portion of the property. The plant
and associated landfill are located on the northern part of the
property.
The stratified glacial deposits range in thickness from a
few tens of feet to about 120 feet. A thin discontinuous layer
of till separates the sands and gravels from the underlying meta-
morphic gneiss bedrock. The ground water in the gneiss occurs
primarily in the joints and fractures in the uppermost portion of
the formation. The hydrogeologic investigation of the site showed
3-3
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that there is a hydraulic connection between the ground water ij
the bedrock and the overlying aquifer.
Based on existing hydraulic conductivity data, an average
hydraulic gradient of .004, and an effective porosity of 20 per-
cent, velocities were determined to range from 3 ft/day (sand and
gravel) to .2 ft/day (silty fine sand). Therefore, the shortest
TOT^QO would be about 33 days and the longest would be 500 days.
In addition to the very short TOT^oO' the original flow
paths have been altered significantly by interference from
multiple pumping wells in the area. Furthermore, the ground
water flow paths are subject to change, depending on the rates of
recharge and pumping. This variation makes a reasonable long
term prediction of contaminant migration very difficult in this
type of setting.
3.1.2 Ground-Water Resource Pathway: Abandoned Gravel Pit/Landfill
Description of Condition
This site in the northeastern U. S. includes two landfills
located in an abandoned gravel pit on a lake shore. Both municipal
and industrial wastes, including chemical wastes, were disposed of
for nearly 50 years. Twenty-one homes adjacent to the landfill were
obtaining drinking water from private wells when the contamination
was discovered in 1979. In 1980, volatile organic compounds
were detected in a residential well south of the site. The lake
and the domestic wells are seriously threatened by the landfills.
Hydrogeologic Setting
The site is located in unconsolidated sand and gravel deposits
where TOTjoO values would be expected to be short, underlain by an
3-4
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irregular bedrock surface. A deep bedrock trough containing as
much as 150 feet of glacial and marine sediments underlies the
northeastern part of the site. The general direction of ground-
water flow is eastward toward the lake; however, local flow
patterns are much more complex and vary temporally with fluctua-
tions in rainfall and the lake level.
3.1.3 Potable Surface Water: Multi-Source Waste Site
Description of Condition
The site area, located within a valley, provides an example
of a long-term, multi-source contamination problem. Seepage from
industrial and municipal waste impoundments is the major source of
ground-water contamination. However, leaking sewers and storage
tanks, use of sewage sludge as fertilizer, and spills of contam-
inated fluids in commercial and industrial areas have added to
the problem. The ground water flows toward the east and discharges
to a shallow narrow stream that drains into a major reservoir on
the river that supplies about half of the total water used in
the valley. Elevated concentrations of total dissolved solids
are present in ground water and surface water sampled in the
stream and its tributaries. The dissolved solids consist of
high concentrations of iron, chromium, lead, lithium, strontium
and zinc. A plume of nitrate-rich ground water extends to the
stream from a large industrial park, 3 to 4 miles downgradient
from the site. The continued movement of contaminated water
poses a potential threat to the water quality of the lake.
Hydrogeologic Setting
The site area lies within a bedrock valley that is partly
3-5
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filled with unconsolidated deposits consisting of beds and l
of sand, silt, gravel, and clay up to several thousand feet
thick. The bedrock valley is comprised of relatively imper-
meable igneous and sedimentary rocks.
The unconsolidated deposits form several major hydrogeologic
units at the site. The uppermost aquifer isjsomposed of sand
and gravel; the water table within this aquifer ranges from land
surface near the stream, to as much as 50 feet below land surface
elsewhere in the valley. Underlying this uppermost aquifer is a
confining unit composed of silt, clay, and fine sand; several
artesian aquifers are interfingered with these confining beds.
Regional ground-water flow is from the recharge areas along the
bordering highlands to the discharge areas in the lowlands, where
water from both the shallow and underlying deep aquifers seeps
into the stream. TOTiQO for this setting is estimated to be short
through the unconsolidated sands and gravels of the uppermost
aquifer.
3.1.4 Surface Water Ecosystems: Mining and Ore Processing Facility
Description of Condition
An abandoned mining and ore processing facility produced
titanium dioxide for paint pigments between 1931 and 1971.
During its period of operation, the facility either disposed of
acidic wastes in sedimentation ponds or discharged these wastes,
untreated, into a nearby river. Between 1977 and 1980, four major
fish kills occurred in the river; the State has attributed these
fish kills to the facility. Although the acidic waste liquids
are no longer present in the evaporation ponds, ground water and
3-6
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soils still exhibit acidic conditions. Residual sludges and
other materials are buried on the site; some unreacted ore and
ferrous sulfate is located within the soil in evaporation ponds
or scattered at the surface.
Surface water runoff from the site exhibits low pH values
(acidity) and high metals concentrations; ground-water sampling
has also revealed low pH values, elevated metals concentrations,
and sulfate contamination. Human exposure from the facility is
considered to be low, given the remote location of the site. The
nearest drinking well is located to the north upgradient of the
site; when tested, the water did not contain metals or other con-
taminants above ambient background levels. The closest drinking
water source downstream of the river is 40 miles away.
The two environments at risk of exposure are terrestrial
flora and fauna around the clay-lined iron sulfate pit and the
aquatic ecosystem of the river. The primary routes of exposure
to these receptors are ground-water discharge and surface water
runoff. The forest areas.located in the path of ground-water
flow and surface runoff, and benthic flora and fauna in the river
downstream of the site, face the highest risk. Water having
certain low pH values has been shown to be acutely toxic to
aquatic species.
Hydrogeologic Setting
The facility lies in the foothills of the Blue Ridge
Mountains along a river; and occupies approximately 510 acres.
The facility is set on a hillside within the river drainage
basin. Soils are composed of clay and silty clay. The soil is
3-7
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a dark reddish clay loam with a low permeability. Soils of this
type commonly exhibit permeabilities of 10~5 to 10~9 cm/sec
(Freeze and Cherry, 1979). Borings taken in November of 1982
indicate that sand and gravel materials exist/ either within the
clay and silt matrix, or in thin lenses interspersed between
clay and silt, and the soil gradually changes with depth into
saprolite, a decomposed clay with a rich igneous horizon. Most
of the horizon contains mica flakes and rock fragments. The
saprolite material becomes coarser with depth and changes into
silt-sized particles.
Bedrock consists of anorthosite, a gray, plutonic rock of
Precambrian age that contains titanium-rich minerals in this
locality. The bedrock strikes northeast and dips steeply to the
southeast, and occurs at a depth of about 40 feet at the site.
Although limited data are available on the site hydrogeologj^
ground-water flow is apparently controlled by the geology of the
valley. The inference is that the potentiometric surface slopes
toward the river; hence, ground-water discharges to the river.
Areas upgradient and north of the site appear to be free of
ground-water contamination. Two wells located north and north-
west of the site revealed no contamination. However, ground-water
samples on and downgradient from the waste burial site showed
contamination. Ground-water contamination is also evidenced by
vegetative stress in the area.
The primary surface water of concern is the eastward-flowing
river, which discharges into another river approximately 3.5 miles
downstream. The surface water runoff from all six areas of
3-8
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concern discharges into this river. Several seeps have developed
from the iron sulfate disposal area and apparently contaminate
surface runoff.flowing off the area and toward the river.
3.1.5 Bedrock Seeps and Springs: Municipal and Industrial Landf;
Description of Condition
The site was used as a municipal landfill and an industrial
waste disposal site from 1966 to 1974. Materials were disposed of
in unlined pits on the site,' resulting in contamination of local<
soil, surface water, and ground water by organic and inorganic
compounds.
Hydrogeologic Setting
The site lies on a plateau and is underlain by a sandstone,
shale, and limestone formation. The bedrock stratigraphy beneath
the site consists of the fractured and weathered sandstone under-
lain by the soft, grey-brown to reddish shale and claystones. A
limestone lies below the shale resting conformably on "red beds."
Soils at the site are 10-14 feet thick and con-sist mainly of
silts and sands, probably derived from the bedrock.
The sandstone and the unconsolidated material overlying it
constitute the uppermost aquifer. The limestone that underlies
the shale is also an a'quifer; although its water-bearing properties
have not been directly investigated at the site, it is thought
to be an unconfined aquifer.
Seeps have been identified at the contact of the sandstone
and shale; the seeps are the result of infiltrating water that
is unable to percolate through the less permeable shale and
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discharges on the slopes at the sandstone/shale contact. Seeps
have also been identified at elevations typical of the limestone
in the site area. Samples collected from one of the offsite seeps
revealed concentrations of benzene, ethylbenzene, 1,3-dichloro-
propane, vinyl chloride, and trichloroethylene. This seep likely
results from ground-water discharged at the sandstone/shale
contact.
A contaminated spring also emerged at a neighboring farm.
The elevation of the spring is typical of the elevation of the
limestone; however, this unit has not been confirmed the source
of discharge.
3.1.6 Basement Seepage Pathway: Quarry/Landfill Site
Description of Condition
A 125-acre site located in the Ohio River floodplain was
an active sand and gravel quarry both before and during the period
when the landfill was in operation from 1948 to 1975. In 1975,
flash fires around water heaters were reported by families .living
in homes adjacent to the landfill. Seven families eventually had
to be evacuated when explosive levels of methane gas were detected
in the area. The presence of other toxic gases as well as methane
were documented by Federal, State, and local authorities. In
February of 1980, over 50 chemicals were identified when approxi-
mately 400 exposed drums were discovered on the river bank adjacent
to the landfill. A venting system was installed in 1980 and the
wastes were removed in 1981.
3-10
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Hydrogeologic Setting
The site is underlain by relatively permeable alluvial
deposits consisting of unconsolidated sands and gravels. Because
of the site's proximity to the river, the water table is rela-
tively close to the surface. The gases, such as methane that
are generated by the decaying wastes tend to accumulate at or
near the top of the aquifer.
3.1.7 Basement Seepage Pathway: Chemical Landfill Site
Description of Condition
A canal, originally designed as part of a system to generate
hydroelectric power, was used from the 1920s until the 1950s as a
landfill for chemical wastes. Over 21,000 tons of various chemi-
cals were dumped in the canal before the landfill was closed and
covered in 1952. An elementary school and numerous homes were
constructed near the site, and odors and residues were first
reported during the 1960s. As the water table rose during the
1970s, these reports increased, and contaminated ground water
began to seep out of the ground. Residents were relocated, the
school was demolished, and millions of dollars have been spent
on efforts to clean up the site.
Hydrogeologic Setting
The hydrogeology of the site includes both shallow and deep
groundwater flow systems. The shallow system, where most of the
contamination occurred, consists of interbedded layers of silts
and fine sands underlain by leaky confining beds of lacustrine
clays and glacial till. The lower aquifer is a fractured dolomite
bedrock, which overlies a relatively impermeable shale. Because
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of the relatively low permeability of the shallow system, a
relatively long TOT^QO to tne deeper flow system is present at
the site. Contaminated ground-water seepage occurred at the
surface because of the "bathtub effect" described in Section 2.3.2
A detailed flow net that included the effects of engineered
barriers, removal of the cover, and changes in infiltration rates
would have revealed this shallow flow path and the potential for
exposure. Refer to Figures 3.1-1 and 3.1-2.
3.2 HEALTH RISK ASSESSMENT METHODS
The health risk assessment methodology presented in this
appendix focuses on the risks associated with the consumption of
contaminated ground water. Although site-specific data were used
to generate the risk estimates, the health assessments should not
be construed to represent potential or actual risks to exposed
populations. The risks associated with exposure to contaminants
either on-site or off-site may be quite different from the risks
projected here. The methodology does not quantitatively con-
sider the exposure pathways of surface water and the basement
seepage route. Also, several health risk routes of exposure
(inhalation, skin absorption, ingestion) and other environmental
media (air, soil) may be important factors in assessing risk for
a particular site. Additional environmental impacts such as
aquatic toxicity or damage to wetlands may be significant for a
particular facility. However, for the purpose of evaluating a
parameter to describe ground water vulnerability such as TOT^oO'
the health risk assessment methodology provides a way to perform
3-12
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LEGEND
HIGH. RELATIVE ELECTROMAGNETIC CONDUCTIVITY
LOW
MODERATELY HIGH CONDUCTIVITY
EXTREMELY HIGH CONDUCTIVITY
SUSPECTED SWALE
SUSPECTED SAND LENS
Figure 3.7-1. Sice map showing location of E-W transect and major surficial
features at Love Canal. (Adapted from EPA 600/4-82-030a).
3-13
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• SEASONAL HI0H WATER TABLE
PERMEABILITY!
Iff7 to 10 §cm/i
H1
•t»
SILT FILL -PERMEABILITY: >10 Bcm/i
SILTY SAND -PERMEABILITY: >W**n/t
•7th ST.
BASEMENT
Wth ST.
LOVE
CANAL
iORIO. DiPTHj
/
OROUi
1.B-2
4.0 -e
8.0ft.
12.0ft.
— 23.0 ft.
LEGEND: BURIED UTILITIES ARE
8 —STORM SEWER
A - SANITARY SEWER
W- WATER MAIN
>- PRESUMED FLOW PATH FOR LEACHATE
— 3a.o h.
ACTUAL FLOW PATH FOR LEACHATE
Lgure 3.7-2. West-East cross section of
-------
preliminary conservative risk calculations for ground-water
contamination.
To facilitate the assessment of health risk, points of
hypothetical exposure were chosen. Point B in Figure 3.2-1
represents background (or upgradient) ground-water quality.
Individuals would be exposed to this water quality if no release
from a hazardous waste management unit occurred. Hydrogeologic
conditions at the site are assessed carefully to ensure that
Point 3 does in fact represent an appropriate background position
since it must be outside the influence of any potential ground-watei
mound associated with the unit. Point C represents ground-water
quality at the RCRA "point of compliance" monitoring points (see
40 CFR 264.95). Point A is located at the end of a 100-foot-long
ground-water flow line that originates beneath the unit. Where
actual monitoring data are not available at a site for this
point, data from the monitoring well located downgradient from
the unit that is closest to Point A are used. Point D is site-
• '
specific, just within the leading edge of the plume.
Wherever possible, actual ground-water monitoring data for
RCRA facilities are used in conjunction with well-characterized
hydrogeologic descriptions. These data are available for a number
of facilities within relatively fast ground-water flow regimes.
Where such data are not available for important geologic settings,
modeling techniques are used to estimate likely concentrations at
steady-state conditions. Conservative assumptions for important
parameters, such as dispersion, are used when modeling is necessary.
3-15
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FIGURE 3.2-1: HYPOTHETICAL WELL LOCATIONS
USED IN RISK ASSESSMENTS
_.., / UASTF \
w ^v s
\
1001
?
PLUME ::..'. ~
Stream
\ <^-
;
f
where:
B - background water quality
C » compliance point water quality ("uppermost aquifer")
A * point 100 feet along flowline
D m point within leading edge of plume (point D may be within a stream)
NOTE: The distance from point C to point A need not be
measured in the horizontal plane.
3-16
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The objectives of these analyses are to determine:
' how large the plume is or may become,
0 what the quality of water is within this plume,
0 what the health risk would be to an individual
withdrawing water from various locations in this
plume for drinking purposes,
0 whether the contamination has reached or will reach the
uppermost aquifer,
0 when the potential for exposure (and hence potential
for adverse risk) could or did occur at these points.
3.2.1 Assessment Methodology
The health risk assessment case studies are based on analyti-
cal data available from ground-water monitoring at well-documented
sites and ground-water quality data from computer simulation at
partially or poorly documented sites. These data are listed in
tables, along with the maximum actual or simulated concentration
of significant contaminant compounds found at various monitoring
points at each site. Ground-water quality data corresponding to
positions A-D shown in Figure 3.2-1 are used to the extent
possible in the health risk assessments.
The health risk assessment in this appendix does not consider
actual or potential site-specific exposure of humans to ground-
water, but instead considers a hypothetical exposure to ground-
water at the positions indicated by points A-D at the sites.
The risk calculation is intended to assess the potential health
risk to individuals using ground water withdrawn at these points,
and not to determine actual or potential risks to any populations
residing near a land storage or disposal facility.
The hypothetical exposure scenario to be used for each risk
3-17
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calculation includes the following parameters:
0 70 kg (150 pound) adult,
8 per capita consumption equals 2 liters of water
per day,
0 lifetime exposure (70 years), and
0 consumption of untreated ground water.
These factors are used to determine the dose of chemicals
that a person drinking water withdrawn from wells at points A-D
would receive. The dose is defined as the amount of chemical
taken into the body and is expressed in milligrams per kilogram
body weight per day (mg/kg/day) or micrograms per kilogram body
weight per day ( g/kg/day). Only intake from drinking water is
considered, although intake may occur from other sources, such
as air and food. Intake is divided by the body weight in order
to permit comparison. Pharmacokinetic factors such as absorption,
body distribution, metabolism, and excretion are not considered
in the calculation of dose. One hundred percent absorption is
conservatively assumed for all contaminants.
The hypothetical exposure is calculated by multiplying the con-
centration of chemical in the ground water at the monitoring
point (analytical data or simulated concentration) by 2 liters
per day, and dividing by 70 kilograms. For example, drinking 2
liters per day of water containing 6 ppm of a contaminant would
result in the following exposure:
6 ppm = 6 rag/liter
6 mg/liter x 2 liter/day » 0.16 mq/kg/day
70 kg
After hypothetical exposures are calculated, conventional
measures of human health risk are applied to the obtained values
3-18
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to assess hypothetical risks that humans would experience if
they drank ground water withdrawn from wells at these positions.
Health risks are calculated for each chemical found or predicted
for which applicable health standards or guidelines exist. In
addition to risk assessments for individual compounds, risks due
to mixtures of noncarcinogenic compounds are calculated.
Noncarcinogenic risks are considered to be independent of each
other and additive. It is not possible to estimate, with any
degree of confidence, the risks associated with exposure to
multiple carcinogens; therefore, carcinogenic risks for single
compounds only will be presented.
The health risk assessment methodology used in this
appendix is considered conservative. However, caution should
be exercised when assuming that determination of the dose of chemica.
to a hypothetical person drinking water withdrawn from points A-D
is a conservative estimate of risk. Points A-D may not reflect
worst case dose estimates at any particular time. In addition,
only risk from ingestion is considered and intake from other
sources may increase overall risk. While .the methodology for
noncarcinogens considers at additivity, synergistic and antagon-
istic effects are not considered and may result in different
levels of risks. Again, assuming the methodology is employed
only to give a measure of the magnitude of a hypothetical risk
rather than to predict actual or potential risk to specific
populations at specific sites, the methodology can be considered
conservative and appropriate.
Two risk assessment methods are used, one for carcinogens and
3-19'
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one for systemic toxicants. Carcinogens are defined as substances
evaluated as human carcinogens or potential human carcinogens by^P
the U.S. EPA Carcinogen Assessment Group (CAG, 1984) for which
carcinogenic potencies have been developed. This list currently
includes approximately 54 chemicals. The carcinogenic potency is
used in a linear multi-stage model procedure for low-dose extrap-
olation (U.S. EPA, 1980). The risk estimates are calculated
using the formula: Risk = Exposure x Potency. The model leads to
a plausible upper limit (upper 95 percent confidence limit) of
carcinogenic risk. It is based on a 70 kilogram person who
drinks 2 liters of water per day over a 70-year lifetime. The
risk value obtained represents increased carcinogenic risk over a
person's lifetime from a single chemical.
For systemic toxicants, the analysis uses Acceptable Daily
Intakes (ADIs) as contained in the Summary of Acceptable Daily
Intakes (ADI) for Oral Exposure. (May, 1985). Some of the ADIs
are considered interim by the EPA and are noted as such here. In
some instances, two ADIs were presented for a single constituent.
•
Where this was encountered for the constituents examined in the
case studies, the more stringent ADI was used. Current EPA
policy is to use ADIs for risk assessments involving systemic
toxicants; in this appendix, ADIs are not calculated for carcinogens
or suspected carcinogens.
ADIs are based upon laboratory animal studies and upon actual
human exposure data where available. The ADI is usually calculated
from a subchronic or chronic No Observable Adverse Effect Level
(NOAEL) or Lowest Observable Adverse Effect Level (LOAEL) in
3-20
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laboratory studies. The NOAEL is the dose at which no toxic
effects are observed in laboratory animals under experimental
conditions. The LOAEL is the lowest dose at which an adverse
response is observed. The NOAEL is a safer endpoint and the
LOAEL is used only if a no effect dose has not been determined.
The ADI is obtained by dividing the NOAEL or LOAEL by a "safety
factor" of usually 10, 100, or 1,000, depending upon the quality
and confidence level of the data. the most sensitive effect seen-
in a test animal is the toxic endpoint chosen for calculating
ADIs.
To assess the effect of exposure to mixtures of systemic
toxicants, the Hazard Index was used (Federal Register (Vol. 50,
No. 6, pp 1170 -1176)). For a single substance, this index is
the ratio of the estimated daily intake to the ADI. For a mixture
of toxic substances, these ratios are summed. A Hazard Index in
excess of 1.0 is considered to be unacceptable. The following
equation represents a Hazard Index for a mixture of systemic
toxicants:
HI » Ei/ALi + E2/AL2 +...+ Ej./ALi
where,
E^ - exposure level to the itn toxicant, and
AL^ = maximum acceptable levels for the itJl toxicant
At some sites, very high concentrations of chemicals (such as
3,4 dimethylphenol) that do not have specifically quantified toxi-
city values are present in ground water. Assessing the toxicity
of these chemicals is done, when appropriate, by assuming toxicities
equal to that of an isomer, if quantified, or to the most toxic
3-21
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member of the chemical family, if quantified.
The risk values calculated for exposure to carcinogens and
systemic toxicants determine whether hypothetical exposure to
ground-water at each site represents a potential threat to human
health.
For carcinogens, data are presented as per person incremental.
risks given as negative powers of 10. A risk of 1 x 10~6 means
that, upon lifetime exposure to two liters of water per day
containing the specified concentration of the carcinogen, a person
incurs an.increased risk of developing cancer of one in 1 million.
A risk of 4.3 x lO'S, fOr example, means an increased risk of
4.3 in one hundred thousand. A 1 in 1 million increased risk
means that each individual who is exposed to the ground water over
his or her lifetime has an additional (i.e., incremental) chance
of getting cancer of 1 in 1 million.
There is no current EPA policy as to the level of risk that
is acceptable. In its Ambient Water Quality Criteria, EPA
•
calculated concentrations of carcinogens in water that would give
increased incremental risks of 1 x 10"5, 1 x 10~6, and 1 x 10"7 to
people exposed to such water over their lifetimes. The selection
of these risk levels did not imply their acceptability. Because
carcinogens are assumed not to have a threshold dose (a level
below which exposure does not elicit a response), any exposure to
a carcinogen carries with it a risk of developing cancer.
Systemic toxicants, on the other hand, have threshold dose-
response curves; a threshold dose exists below which a toxic
response is not seen (the NOAEL). The.chronic or subchronic
3-22
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NOAEL divided by a safety factor is assumed to provide an adequate
margin of safety for lifetime human exposure. Therefore, any
daily exposure lower than the ADI is assumed to carry no risk of
toxic effects in the general population, based upon currently
available data. A daily exposure greater than the ADI (a Hazard
Index equal to or greater than 1.0) carries some risk of toxicity
upon chronic exposure.
3.2.2 Methods for Interpreting Results
Hypothetical risks are calculated for monitoring points A/
C, and D to determine the incremental contributions made by the
•
hazardous waste management units. After this calculation, the
potential for actual human exposure to ground-water at points A,
C, and D is assessed. The known or modeled spatial distribution
of the plume over this distance is compared with the hydrogeologic
characteristics of the site to determine whether the plume is
associated with geologic units that have a reasonable chance of
serving as a source of drinking water, of transmitting the plume
to surface waters, or of entering nearby streams.
The lateral extent of the plume (as determined by the loca-
tion of Point D) at steady-state conditions also serves as an
indicator of the potential for exposure. These distances are
compared qualitatively for a variety of geologic settings to des-
cribe those settings that offer the greatest and least potential
for exposure. Sites are grouped into two categories. The first
consists of those at which a potential for exposure exists and
in which ground-water quality poses an adverse risk to a hypo-
thetical user. The second consists of sites at which the plume
3-23
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will remain entrained for a very long time in a geologic unit
that is not a reliable source of water and at which the other
pathways of exposure do not appear to be significant. These
ratings are compared with the TOTioo values calculate for the
cases to evaluate how well the TOT^QO test results correlated
with these categories. This comparison is used to refine the
definition of vulnerability.
The hydrogeologic information and data used in the case
study evaluations are not all-inclusive. That is, the information
presented may not necessarily describe the entire facility«area.
For instance, only one or two "representative" cross-sections
were used in each case study. Because there are on-going
investigations at these sites, full sets of data are not yet
available. The case study interpretations and evaluations are
»'
not meant to replace or be equivalent to comprehensive Part B
permit application reviews for meeting the ground-water protection
requirements of 40 CFR Part 264, Subpart F.
3.2.3 Results of Preliminary Exposure and Health Risk Assessments
OSW is compiling and studying information drawn from a
collection of 228 hazardous waste management facilities across
the U.S. and is categorizing these facilities by geologic setting.
This study will include an examination of flow patterns and an
assessment of current and future health risk to potential ground-
water users. Time of Travel and the maximum potential dimensions
(distance between the unit and point D) of plume growth for
facilities representative of the various settings will also be
estimated.
3-24
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Section 3.3 presents information for six facilities. Health
risk assessments for potential ground-water users at five of
these facilities were made using actual monitoring data. An
analytical model has been used to describe potential contaminant
concentrations at the sixth site and to supplement the moni-
toring data at one of the other sites.
3.3 CASE STUDIES: HEALTH RISK ASSESSMENT
The following case studies discuss the health risk
assessments using the detailed assessment methodology described
in Section 3.2, primarily for the ground water pathway. However,
when exposure through surface water or the basement seepage
pathway is possible, this- fact is noted.
Summary of Case Studies
The case studies presented below describe a range of TOT^QO3
and exposure potentials. Case study D-l illustrates horizontal
flow in a shallow glacial till aquifer where a long TOT]_QO and
naturally saline ground-water correspond'to a very low exposure
potential. Case study D-2 describes a plume that travels through
an alluvial aquifer and discharges to a nearby river; TOTj.00 ^s
short, and potential exposure via the first pathway would be high
except for the restricted aquifer use and an industrial setting.
The full impact on the second pathway is unknown. Case study D-3
shows how a very long TOT^QO through a thick chalk sequence yields
a very low exposure potential for all pathways. A short TOTioo
through an unconfined upper aquifer is illustrated in case study
D-4; however, exposure is limited due to surrounding land use.
Case study D-5 shows how a short TOTiQO *n an unconfined aquifer
3-25
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causes contamination of a nearby bay and a high exposure
for the first two pathways. Case study D-6 shows a complex
setting of a recharge zone where fractured bedrock strongly
affects ground-water flow, and where a short TOT^oo corresponds to
known exposures through the first pathway to nearby residents.
Although the case studies do not include an example of a
long TOT^oo setting where exposure potentials are high, EPA is
investigating further. The possibility exists that a site initially
characterized as a long TOT^oo location could have exposure potentia
due to unforeseen channeling of ground-water through the third
pathway. This channeling could occur through thin sand lenses,
fissures, and manmade conduits. Although thorough characterization
of the hydrogeology of the site should preclude this happening, a
long TOTj.00 setting may need further evaluation to eliminate the
possibility of exposure through a hidden pathway.
3-26
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3.3.1 Case Study D-l ^ . Q Q
Facility Description
The facility is located near a major river in'~"the Great
Lakes Region and has been used since 1942 for a variety of
industrial purposes including commercial hazardous waste disposal.
The site was used during 1942 and 1943 for the manufacture of
trinitrotoluene (TNT). Subsequently, it was used for: the stor-
age and transport of chemicals and ammunition, the storage and
burial of radioactive materials, and the burial and burning of
wastes from the development of high energy fuels. Figure 3.3-1
depicts some of the waste unit locations .
The current facility operations include the treatment,
recovery, disposal and transfer of hazardous and industrial
wastes. The waste units include a waste receiving area, metal
hydroxide storage ponds, chemical treatment facilities, biolo-
gical treatment lagoons, transfer stations and nine landfills,
one of which is presently in operation. The operating landfill
is the major source of potential ground-water contamination.
Leachate data from the landfills indicate that the most
common organic constituents are methylene chloride, toluene,
trichloroethene, 1, 1,1-trichloroethene, benzene, tetrachloroethene
and chloroform. Methyl ethyl ketone, tetrahydrofuran, phenol and
some PCB compounds were also detected.
3-27
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^^rsi^r• • *^ • i • f * H • ^ •
~
:;Ix&Wmtf'.' * v ••
»»^*^^^^» ^ • •• c. ~^^^ • • ^ » • ^^/ • •
NO. 8 ;il^::?W^ *M
J^MIjtox^v U> ^-
!.. ••^*--X>»z *•*'_!Iv/ r.^
O-^-. A'^-^rS
j^ ---•» «••
8r ..^4
?fc'" -5.1
v ' •.••• Jj3
\K>L^^.
^fP^?
N'POND
POND N0-7
POND
PONDS
SECURE LANDFILLS 2-6
SN^5 LAGOONS 1,2,5,6
FIGURE 3.3.1 WASTE UNITS
3-28
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Topography/Climate
The facility lies on the lowland area of a lake plain. The
lake plain has a gentle slope of approximately 0.3 percent toward
the north; the slope begins at an elevation of 375 feet at the
base of an escarpment and drops to an elevation of 275 feet. The
plain varies in width from about 6.5 miles to 10 miles. The
facility is located in an area of low relief. The site slopes
between 0.1 and 0.2 percent toward the north; surface drainage is
generally the north through several small creeks.
Precipitation is fairly uniformly distributed throughout the
year; the wettest month is August, which accounts for approxi-
mately 12 percent of the total precipitation. Data for the area
indicate about 31.5 inches of precipitation for water year 1983,
while the potential evapotranspiration was estimated at 25.4
inches for the same year.
Regional Geology/Hydrology
The bedrock units in this region are comprised of a series of
Upper Devonian to Silurian aged shales, limestones and dolostones.
The rock units are relatively flat-lying with a regional dip of
approximately 0.75% south - southwest.
The unconsolidated deposits include alluvium overlying
glacial deposits from several major periods of glaciation. In
some areas, these deposits have been re-distributed by streams.
In addition, the irregularity of the glacial deposits has led
to a varied drainage pattern with many lakes, ponds, bogs and
marshes. The major drainage direction in the region is toward
the Great Lakes and the St. Lawrence River.
3-29
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The glacial deposits constitute the best aquifers within the
region; limited ground water is available from bedrock aquifers
in areas where the unconsolidated deposits are absent, thin, or
of low permeability.
Site Geology
The geology of the site area has been characterized by
information gathered during several field investigations. More
than 450 borings and test pits from several site studies were
used by the permit applicant to describe the geology of the area.
Figure 3.3-2 is a geologic cross section drawn from the northwest
to the southeast portion of the^site.
Surficial Geology
The facility is underlain by about 30 to 60 feet of glacial
deposits overlying shale bedrock.
The uppermost unit at the site is a low permeability glacial
till sequence that is about 10-25 feet thick in the site area.
The till is underlain by a glaciolacustrine clay, 20-30 feet thick
in most areas, which is in turn underlain by a glaciolacustrine
silt/sand unit. Beneath these units is a lodgement till that
overlies the shale bedrock.
At the northwestern portion of the site the glaciolacustrine
clay unit is divided into an upper and lower member by a silt till
that was apparently deposited during a local oscillation of the
advancing glaciers.
3-30
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FIGURE 3.3-2 GEOLOGIC CROSS SECTION
to
10
NORTHWEST
ELEVATION
FEET MSL
320 _,
BOREHOLE LANDFILL NO. 7
G-8 AND NORTH POND
300
280 J
260 J
240 J
220 H
200 J
SOUTHEAST
UPPER ALLUVIUM
LAGOON'S
UPPER
UPPER CIACIOLACUSTRIME CLA»
MIDDLE SILT TILL
PARTIALLY WEATHERED
SHALE BEDROCK
(QUEENSTON FORMATION)
_ 260
L 240
U220
L200
HORIZONTAL SCALE IN FEET
VERTICAL EXAGGERATION 30 TIMES
NOTE: This figure Is a schematic representation
of the geologic stratigraphy made by straight
line Interpolation between boreholes G-l and
G-8. Some of the strata shown are
discontinuous.
-------
Bedrock Geology
Bedrock encountered during drilling in the site area is a
reddish-brown shale that is approximately 1000 feet thick. Rock
samples were cored from some of the borings on the site. The
cores reveal that the rock is generally a red fissile shale that
has occasional bands of green shale ranging from 1/2 to 24 inches
thick, and gypsum nodules 1/2 inch to 1 inch in diameter.
The top 5 to 10 feet of the shale unit is highly weathered
and fragmented. Although some cores showed that the shale was
broken parallel to bedding, it was difficult to determine whether
this'was due to natural bedding features of the rock or if it was
induced by drilling. Some high angle joints which were not a
result of drilling were observed in some of the unweathered cores.
The surface of the bedrock is undulating; it slopes from an
elevation of about 275 feet MSL, in the southeastern part of the
site, to 250 feet MSL in the northwestern portion of the site.
.The average values for hydraulic conductivity are 1 x 10~5
cm/sec in the shallow rock and 5 x 10"^ cm/sec in the deeper rock
zones.
Site Hydrology
Shallow ground water occurs in the upper glacial till
sequence at a depth of about 3 to 5 feet. Potentiometric contours
in the upper glacial till indicate that the shallow ground water
moves horizontally north - northwest. Vertical flow in the
upper glacial till is minimal due to the underlying less permeable
glaciolacustrine clay. The glaciolacustrine clay is the main
retarding layer to downward vertical flow in the site area.
3-32
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Vertical gradients across the glaciolacustrine clay unit range
from 0.1 to 0.58 with a mean of 0.35.
Flow in the glaciolacustrine silt/sand aquifer is essentially
horizontal to the north and west. The most transmissive portion
of the aquifer is its thickest portion, where a coarser sub-unit
is present. As the ground water flows northward, it moves toward
the areas of higher transmissivity. Figure 3.3-3 depicts flow
directions in the glaciolacustrine silt/sand aquifer.
Flow within the basal red till is controlled by pressure
differences within the glaciolacustrine silt/s"and aquifer and the
underlying bedrock. The shallow bedrock exhibits flow that is
predominantly horizontal toward the north and west, similar to
flow in the glaciolacustrine silt/sand aquifer. The shallow bed-
rock has low hydraulic conductivity and is not considered a sig-
nificant water-producing zone when compared to the glacial aquifer.
The average values for flow rates for the geologic units
at the site as presented in the Part B application are given in
Table 3.3-1. The flow velocities were calculated using values
for hydraulic conductivities, hydraulic gradients, and effective
porosity. Conductivities of the geologic formations were
determined in the field .through variable head tests and in the
laboratory. Gradients were established using ground-water level
measurements obtained from wells and piezometers at the site.
A value of oil for effective porosity was supplied by the applicant
and is applied to all the units. Since it is unlikely that all
the units would have the same effective porosity, TOT values
3-33
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OJ
J,
•U I
FIGURE 3.3-3
Glftclolacustrine Aquifer
•
Potentionetric Contour*
'*~~l t ^'^M^'^t-'r-^^^^
^-.js^-' >.- . . • •• »«*a».»MM»<..
C^^^<--*-l^niteiF=^v=::::K:ijl;:P •
"*^" I TJT^'l 1 MBkAVV TT ' • J-a . •-. • •» l'l >1*^> •
^ .TT^yy*^*-^—rivj.^id.iTit.^l.fj^r*.
^M;_:-.- I - g
—T.~ ^ ft J
' Jl . ' • 1: ^^•"^
•IrJ^X X^-y^^tkJ^^jP^^f
•/••'•^v&^.'iP-*-*.. •- -•/
/.- :.•.,•:.%;•'/•£ -./..- JT
/.....-.•.•...• .•• -r"^ ^._ ..»•••*... •• i- •WHT=»C?H
-------
TABLE 3.3-1 ESTIMATED FLOW RATES AND VOLUMES
U)
OJ
01
GEOLOGIC*1* PERMEABILITY,
FORMATION (cm/s)
UGT
GC
MST
GSS
BRT
SR
NOTES
(1)
Horizontal Vertical
2x10~6 6x10~7*6*
5x!0"8 2xlO"8
3x10 Ixio"7
4xlO~8 3xlC"8
Ixio"5
Formation Designations
K GRADIENT, 1
(ft. /ft.)
Horizontal Vertica
0.002 0.012
0.001 0.35
0.005 0.07
0.007 6x10 l
0.00/4 0.0/4
0.004
*
•
FLOW AREA, A
(ft.2)
1 Section*3*
80,000
40,000
60,000
7* 90,000
40,000
160, OOO*9*
Plan
I6x106
I6xl06
7x10
I6xl06
15xlOb
-
FLOW VOLUME ****
Q. (ft.Vday)
Horizontal
1.0
0.006
3
360
0.02
18.1
Vertical
320
320
50
60
-
FLOW RATE, v*5*
(ft./yr.)
Horizontal Vertical
0.04 0.07
0.0005 0.07
0.16 0.07
14.5 0.01
0.002 0.01
0.4.
UGT - Upper Glacial Tills
GC - Glaciolacustrlne Clay
MST - Middle Silt TIM
GSS - Glaclolacustrine Silt/Sand
BRT - Basal Red Till
SR - Shallow Rock
(2) Exit gradient from property.
(3) Cross section area along.north or north and west perimeter for each formation.
CO Q = klA.
(5) V - kl/n . with n - O.I.
(6) k
V
(7) Estimated to maintain continuity.
(8) Coarse portion of aquifer with k
(9) Assumed 20 feet thick.
kl/n , with n
e-7
6x10 cm/s due to structural discontinuities. (See text Sections 7.1 and 8.3.)
-------
calculated with this input should be considered to be only estimates
A second TOT has been calculated using default values for effective
porosity for each unit.
A contaminant can be traced from the point of release at the
surface through the geologic formations in the site area. Hori-
zontal and vertical flow rates can be added, using vector addition,
to get the resultant flow rate vector through the different units
(see Figure 3.3-4). Figure 3.3-4 also depicts two different
profiles of flow, for the northwest and the southeast sides of
the facility. Ground-water time of travel through the geologic
units varies between these opposing sides of the facility because
of different unit thicknesses and the presence of the middle silt
till at the northwest side of the facility. The middle silt till
is absent at the southeast side of the facility.
At the southeast side of the facility, the upper glacial .
till layer is thinner (approximately 11 feet thick) than at the
northwest side (approximately 16 feet thick). Using average flow
rates derived from vector addition, the ground water would take
150 years to flow through that layer. At the northwest side, the
ground water would take 230 years to flow through the upper
glacial till unit, because of the greater unit thickness.
Flow within the upper glacial till is toward the north-
northwest. Assuming that a particle is released and will be
carried with the ground water without being affected by advective
or dispersive forces, after 100 years, the particle will still be
traveling through the upper glacial till layer toward the north-
northwest. The time that the particle would take to reach the
3-36
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WATER TABLE
0.081 FT/YR
230 YEARS
20'
0.07 FT/YR
100 YEARS
7'
0.17 FT/YR
220 YEARS
0.07 FT/YR kO YEARS
H.5 FT/YR 1000 YEARS TO
FLOW ACROSS THE AQUIFER
(1A.500 FT)
U)
\°
.01 FT/YR 500 YEARS
16' UPPER GLACIAL TILLS
UPPER GLACIO-
LACUSTRINE CLAY
15'
MIDDLE
SILT
TILL
3'LOWER GLACIOLACUSTRINE
" CLAY
10 ' CLACIOLACUSTRINE SILT/SAND
AQUIFER
N
3' BASAL RED TILL
0.4I FT/YR
BEDROCK
1 WATER TABLED
\ 0.12 FT/YR
NJ50 YEARS
X. 13'
0.0? FT/YR
290 YEARS
YEARS TO flOVI AC*
IFER (725 FT.)
tOSS THE ~]
I 0.01 FT/YR
\ 500 YEARS
UPPER GLAC
GLAC 10-
LACUSTRIN
20' CLAY
1« US FT/YR
J GLAC IOLACUS TRINE SI
3 'BASAL RED TIL
TILLS
0.<«1 FT/YR
BEDROCK
NORTHWEST SIDE OF FACILITY
(Velocities from TABLE 2.3-1
Scale - 1" = 10' HOR.
I" = 10' VER.
SOUTHEAST SIDE OF FACILITY
(Velocities from TABLE 2.3-1 except
UPPER GLACIAL TILLS and AQUIFER
velocities based on horizontal
gradients 0.005 and 0.0007
respectively)
Scale - 1" = 10' HOR.
I" = 10' VER.
FIGURE 3.3-4 SCHEMATIC FLOW DIAGRAM
-------
glaciolacustrine silt/sand aquifer is 590 years for the northwest
side of the facility and 440 years for the southeast side of the
facility.
TOTiQO Calculation
TOT^oo can b® calculated by adding the number of years as
shown in Figure 3.3-4 to travel through the geologic units under-
lying the site. It wil~l~'take 590 years to travel 55 feet along a
flow path to the glaciolacustrine silt/sand unit at the northwest
side of the facility. When it reaches this unit, the ground water
moves horizontally at a rate of 14.5 ft/year. To complete the
total distance of 100 feet, ground water must travel an additional
45 feet through the unit. At a rate of 14.5 ft/year, the added
travel time is three years. Thus, the total estimated travel time
over 100 feet at the northwest side of the facility is 593 years.
TOT^QO calculation using ne default values
Effective Porosity
Default Values TOT
Upper Glacial Tills 0.05 115 years
Upper Glaciolacustrine Clay 0.01 10 years
Middle Silt Till 0.10 220 years
Lower Glaciolacustrine Clay 0.01 4 years
Glaciolacustrine Silt/Sand 0.15 4.5 years
TOT100 = 353.5 years
Using default values of effective porosity (see Table 3.2-2 of
the main text) for each layer rather than a constant effective
porosity of 0.1 throughout produced a difference in TOT^QQ of
239.5 years. As such the percent error involved is too large
3-38
-------
N
, r
r . TA
l] .; -i r**4«- . ... '-U? mW!) *\
Ki: •,,••!. .••-, •• , x \i£
i1- •« • *••! - - ' JL __JlW3CSS^ij£.- *-.. t .:.^**-J)«J^ »j
^^^te^^iw7^^':^^^
!-iii>~ ;^^^TOK»^'^ ^v-?n
.••^: -.. dF« - »^mKrf* •.- .. • t-r -:
l^fEM^py
^^:C^S»H
r-r
••/i; o
• rniantTiii at VKL
3Ill:iATt01
• rtltontTit 01 vtu LOCit:
>oti«T;aii iti!:inT:;t
arrtt »ALBTICII
BCT crm euetAi
CC CIACIOIACIITIIM IlI/IASD
IIT lilAL 1CJ TtLt
it iiAiiov toes
oi :tu laa
lOtt: »-• «OT LOCtTIO.
SCALE IN
FIGURE 3.3-5
WELL AND PIEZOMETER LOCATION
PLAN AND FORMATION INTERVALS
3-39
-------
(when using a constant effective porosity value) to recommend its use
Plume Information
The monitoring well network at this site consists of over
50 shallow and deep wells located to serve a detection monitoring
function. The shallow wells draw from the upper glacial till
layer and the deep wells draw from the various deeper formations.
Ground-water monitoring has been performed on a monthly basis for
two years, drawing samples from a selection of the monitoring
wells on the site. There is no conclusive evidence of a contam-
inant plume at this site, but isolated contamination has been
observed at individual wells.
Only one well has shown contamination in repeated samples
that is not explained by laboratory error or solvents used in well
grouting materials. This well, shallow well Z-3 (screened in the
upper glacial till), is considered to be point C in this case
study. The nearest downgradient well, point A also screened in
the upper glacial till aquifer, is represented by well Z-21,
300 feet north of Z-3. These wells are located between secure
landfill (SLF) 7 and SLF 11, shown in the upper portion of
Figure 3.3-5. The observed contaminant levels at these well are
presented in Table 3.3-2.
There are no suitable wells to represent points B or D. No
wells are located offsite or far enough downgradient from the
facility to characterize contaminant migration. However, since
no contaminant plumes have been detected, this is not necessary.
3-40
-------
Likewise, no wells are located far enough upgradient from the
potential sources of contamination to serve as background wells.
However, background concentrations for the constituents reported
in Table 3.3-2, are clearly below the limits of detection.
Health Risk Assessment
Of the two contaminants observed at well Z-3, one is recog-
nized as a carcinogen and the other is a systemic toxicant.
Trichloroethylene is a carcinogenic substance with a potency,
recommended by the Carcinogen Assessment Group (CAG), of 1.9 x
10~2. Lifetime ingestion of 2 liters per day of water with an
average trichloroethylene concentration of 668 ppb (the average
of the three samples) represents a 3.6 x 10~4 probability of
contracting cancer.
The acceptable daily intake for 1,2-trans-dichloroethylene
•'
is 0.001 mg/kg/day. The highest of the concentrations observed
at well Z-3 corresponds to an exposure of 0.0027 mg/kg/day and a
hazard index of 2.7. This concentration would therefore pose an
unacceptable health risk if it were present in a drinking water
supply.
Several of the deeper wells on the site showed barium
concentration in excess of the 1 ppm, National Interim Primary
Drinking Water Standards value. However, these concentrations
appear to be a background condition since some of these wells are
located upgradient of the hazardous waste management units, and
since the travel time to some of the deep wells is over 500 years.
3-41
-------
Exposure Assessment
The exposure potential at this facility is considered to be
very low. There is no known contaminant plume, the TOT is very
long, and the ground-water beneath the facility is very saline,
in excess of state drinking water standards. The ground waters
are not currently used as a source of drinking water, and no such
use is expected in the future.
Table 3.3-2: Contaminant Concentration (ppb)
Point C Point A
Constituent (Well Z-3) (Well Z-21)
1,2
Tri<
Trans-dichloroethylene
rhloroethylene
6/84
ND
1290
11/84
60
496
12/84
95
258
6/84
ND
. ND
11/84
ND
ND
12/8
ND
ND
ND denotes not detected. The limits of detection were 10 ppb.
3-42
-------
3.3.2 Case Study D-2
Facility Description
The facility started operations in 1952 and covers an area
of approximately 2.4 sq. miles in the southeastern U.S. (see
Figure 3.3-6). This area contains manufacturing facilities in
conjunction with past, present, and proposed waste treatment,
storage, and disposal units. Some of the units currently onsite
consist of an incinerator, numerous storage tanks, a landfill,
and a biological sludge landfill.
No information was available concerning the types of wastes
disposed of in the landfill unit. However, it is known that ope-
rations at this facility have contaminated the uppermost alluvial
aquifer? therefore, the facility is implementing a Corrective
Action Plan as specified under 40 CFR 264.100. This plan proposes
closure of many of the units in an attempt to eliminate the source
or sources of contamination and installation of a pumping well
system to contain contaminant migration.
Site Topography
The site consists of rolling topography with gentle slopes to
the southeast toward the river. Many small streams and drainage
ditches dissect the site. Surface water flow from northwest of
the property is diverted through drainage ditches to the east
into the river. Surface flow from within the site follows the
site topography to the southeast into the river.
3-43
-------
Site Climate
The climate of the area is very humid and sub-tropical.
There are very long, hot, and humid summers with mild wet winters.
The average annual precipitation is 59 inches, with December
through April being the wettest and August through November being
the driest. The average temperature for this area is 65°F January
averages 498F while July averages 80*F.
Regional Geology
The site is located in the Gulf Coastal Plain Physiographic
province adjacent to the river. The area is underlain by alluvium
and terrace deposits of Pleistocene age. Deposits also included
in this area are undifferentiated Miocene sand, clay, and gravelly
sand. Total thickness of these unconsolidated flood plain terrace
deposits are over 700 feet.
Site Geology
Data from previous and recent test drilling indicate that
the plant site is built on a flood plain terrace, whereas the
lower portion of the facility located near the river is built on
flood plain deposits. A pervasive clay layer is reported at the
surface of the facility. This is reportedly well documented from
previous reports; however, the large distances between wells as
shown in Figure 3.3-7 indicate that very little control in the
form of wells or borings is available for interpretatipn of the
j
cross sections. Cross section locations are shown on Figure 3.3-8.
Directly below this surficial clay are lenticular deposits of silt,
sand, and clay. Previous reports (May 1981) allude to the fact
that there may be a hydraulic connection through the clay between
3-44
-------
liiiiiiiilMil PLANT SITE
FIGURE 3.3-6 FACILITY LOCATION
3-45
-------
to
•
u>
-J
o
70
O
CD
CT
•— i
OJ O
£ <">
o
CD
I
CO
"
"
-------
WELL LOCATION, NUMBER, AND
o... WATER SURFACE ELEVATION IN
•••° FEET ABOVE MEAN SEA LEVEL
-,0 PRODUCTION WELL LOCATION
/-'4 CONTOUR INTERVAL IS 1 FOOT
FLOW LINE SHOWING DIRECTION
OF GROUND WATER MOVEMENT
FIGURE 3.3-8 FLOW NET ANALYSES FOR THE ALLUVIAL AQUIFER, AUGUST 1984
3-47
-------
the water table and fluids in the reservoir. The basis for this
statement is reportedly from water level data, but these data
were not available for review.
The surficial clay materials are underlain by Recent and
Pleistocene shallow terrace and alluvial deposits. As shown in
the cross sections (Figure 3.3-7), this unit is the uppermost
aquifer and consists of alternating, interbedded layers of sand, .
gravel, and clay. Underlying this alluvium is a sequence of
Miocene clays and sandy clays with thicknesses ranging from 30 to
more than 100 feet. Below these clays are alternating layers of
Miocene age sand, clay, and gravel over 700 feet thick. This
unit is the second aquifer identified in the area. There is no
mention of the bedrock underlying this facility. The Miocene
clay layer is reported to be a confining layer separating the
upper alluvial aquifer from the lower Miocene sandy aquifer.
Site Hydrology
Ground water parameters have been defined at the site through
the use of many existing wells (M series wells) from previous
studies and through the installation of nine 2 inch diameter
observation wells (OW-1 through OW-9). Most of the observations
contained in this report are directed at the uppermost alluvial
aquifer. The only mention of the surficial clay layer is that
permeabilities range from 0.7 x 10~° to 1.9 x 10~' cm/sec. There
is no discussion in the report addressing to what extent the clay
layer impedes flow into the alluvial aquifer. However, the
application indicates a "water surface" in the cross-section
(Figure 3.3-7) which is described as the alluvial aquifer water
3-48
-------
table. It can be seen in the cross section that an area labeled
effluent stream is in direct contact with the alluvial aquifer.
This may be a pathway for migration as evidenced by elevated
contaminant concentrations in well M-6.
Ground water in the uppermost aquifer is reported to be under
semi-confined conditions and flowing to the southeast towards the
river (see Figure 3.3-8).
The underlying Miocene aquifer is also confined and reported
to contain highly mineralized water. Due to the overlying low
permeability Miocene clay layer (10~"^/sec) the applicant states
that the upper alluvial and Miocene aquifers are not hydraulicaLly
connected. Therefore, contamination in the uppermost aquifer
would not migrate to the Miocene aquifer for a long time.
Due to pumping from wells at the facility and adjacent
»' . '
property, the hydraulic head.in the Miocene and alluvial aquifers
have been greatly impacted. Prior to ground-water development,
the potentiometric surface in the Miocene aquifer was higher than
that in the alluvial aquifer. Today, the Miocene potentiometric
•surface elevations are below that of the upper alluvial aquifer.
Flow directions in the Miocene aquifer are also reported to be
somewhat influenced due to its development as a ground-water
resource.
Field tests were performed in an attempt to define the
hydraulic parameters of the alluvial aquifer. Twelve hour
specific capacity tests were performed on wells M-3, M-4, M-6
and M-12, with results ranging from 14.15 to 25.5 gallons per
minute per foot of drawdown.
3-49
-------
Aquifer (pump) tests (96 hours) were performed on wells W-3
and W-12 in order to define transmissivity, hydraulic conductivity
and coefficients of storage. A summary of the test results is
presented in Table 3.3-3. These wells are reported to be screened
in the uppermost alluvial aquifer, and, therefore, listed para-
meters are indicative of this unit.
Time of Travel
A worst case TOTiQO was calculated for flow in the uppermost
alluvial aquifer using the following parameters:
Default Value
Worst case Average (Freeze &
K Value K Value Cherry, 1979)
Hydraulic Conductivity (K) 288 ft/day 90 ft/day 10~1cm/sec
Time drawdown and
recovery tests (Pump
tests)
Hydraulic gradient (i)
water level
measurements
Effective Porosity
EPA default value
.01
.20
.01
.20
.01
.20
Ground water velocity (v) 14.4 ft/day 4.5 ft/day 14.2 ft/day
TOT10o
7 days
7 days 22 days
The above TOT^QO does not take into account the surficial
clay layer due to the fact that the effluent stream shown in the
cross sections (Figure 3.3-8) is in direct connection with the
alluvial aquifer. Due to this feature, contamination could reach
the alluvial aquifer without moving through the clay layer.
However, there are hazardous waste units located in the clay that
do not breach through to the alluvium. Therefore, a TOT incorpor-
ating the clay is presented below:
3-50
-------
TABLE 3.3-3 SUMMARY OF PUMPING TEST RESULTS
U)
I
Well
Number
M-3
M-4
M-6
M-12
MW-11
Distance
from . ,
Discharge PW to EW -
Q r
(gpm) (feet)
78
78
78
90
88
75.5
75.5
75.5 22.5
Saturated
Tb ickness
m
(feet)
38
-
-
25.8
34.56
22
22
AVERAGE :
Coeff i cient
of
Transmi ss i vi ty
T
(gpd/ft)
1,117
3,973
8,939
55,751
49,200
4,326
9,832
18,026
18,895.5
Coefficient
of
Permeab i 1 i t
K
(gpd/ft )
29
104
235
2,161
1,424
197*
447
819
676.8?
Coefficient
of
y Storage
S
(-) Remarks
Time- drawdown
T 1 me- d rawdown
Ti me- recovery
Time- drawdown
Time-drawdown
Time -drawdown
Time- recovery
6.33 x 10 Time-drawdown
— PW, pump ing well;
EW, evaluation well
-------
K = 1.9 x 10~7cm/sec Permeability value stated in
(lab methods) the May 1981 report.
n = .01 Default value from EPA location
guidance for effective porosity.
i = 1.0 Assuming vertical flow through
the clay layer (worst case).
Using the expression, v = Ki , a velocity of .05 ft/day was
ne
calculated. Assuming that the clay unit is 20 ft. thick it would
take approximately 400 days for groundwater to travel through
this unit into the uppermost aquifer.
Plume Information
The indicator parameters used to delineate the plume consist
of specific conductance, total organic carbon (TOC) and total
organic halogen (TOX). Figure 3.3-9 shows results of the specific
conductance testing, while Figure 3.3-10 shows locations of wells
tested and compliance point monitoring wells. From the various
monitoring results there appears to be a line of contamination
with two lobes of increased contamination. One appears to be
concentrated near the manufacturing area with its source presum-
ably being an abandoned effluent pond. There is no discussion
concerning the nature of this pond and, therefore, very few
conclusions can be drawn concerning the contamination. Due to
the fact that contamination is lower in OW-1 than OW-2, it is
possible that the plume has past and there is not a continued
source. However, without historical monitoring data, no definite
conclusion can be drawn concerning this issue. The other plume
appears to be in the area of the effluent stream (Figure 3.3-9).
3-52
-------
OWT WELL LOCATION, NUMBER, AND
•"•• GROUND-WATER SPECIFIC
CONDUCTANCE IN
. CONTOUR INTERVAL IN pMHOS
jS AS SHOWN (DASHED WHERE
I INFERRED)
NOTE: Ground-water collection data
M Wells: June 13-21,
OW Wells: July 17-20, 1984
•00 ItOO ItOO
KALI IN rut
FIGURE 3.3-9 ISO-SPECIFIC CONDUCTANCE MAP FOR THE
ALLUVIAL AQUIFER, JULY-JUNE 1984
3-53
-------
LINE OF
COMPLIANCE
\ POINTS
'** LOCATION AND NUMBER OF 300 GPM
O MAXIMUM CAPACITY OEWATERING WELLS
••-« LOCATION AND NUMBER OF 200 GPM
O MAXIMUM CAPACITY OEUATERING WELLS
..-• LOCATION AND NUMBER OF 100 GPM
O MAXIMUM CAPACITY OEWATERING WELLS
c»-i LOCATION AND NUMBER OF MONITORING
6 WELL FOR CORRECTIVE ACTION PROGRAM
-• LOCATION AND NUMBER OF COMPLIANCE
O POINT MONITORING WELL
FIGURE 3.3-10 GROUND-WATER DEWATERING PLAN AND LOCATION OF
CORRECTIVE ACTION AND COMPLIANCE POINT MONITORING. WELLS.
3-54
-------
It is interpreted that contamination has been released from
various waste management units in this area.
Well M-2 is located upgradient of the facility and is
designated as well B (background) in the A, B, C, D configuration,
Since there are two plumes or plume sources, wells OW-1 (point
C-l) and OW-2 (point A-l) will be used to identify the plume from
the manufacturing area while well M-6 (point C-2) and well M-12
(point A-2) will be used to identify the plume on the eastern
side of the facility. No D wells at this facility have been
designated. Table 3.3-4 shows contaminant concentrations at
*
selected wells.
B. Health Risk Assessment
Several hazardous constituents have been observed in the two
plumes originating at this site. Table 3.3-4 presents concentra-
tions of hazardous constituents observed in selected monitoring
wells M-2 (point B) OW-1 (point C-l), OW-2 (point A-l), M-6
(point C-2) and M-12 (point A-2).
Carcinogenic constituents were observed in wells M-6, OW-2
and M-12. The carcinogenic risks are tabulated in Table 3.3-5
for each of these wells. The most significant risk at each of
these well is due to high levels of arsenic. (Arsenic has been
associated with skin cancer in epidemiological studies.) The
highest risk, 4.6 x 10~2 was observed at well OW-2, a few hundred
feet downgradient from the compliance well near the manufacturing
facility. In the plume originating at the hazardous waste manage-
ment unit, the compliance point (M-6) shows a carcinogenic risk
3-55
-------
TABLE 3.3-4 CONTAMINANT CONCENTRATIONS AT SELECTED WELLS (ppb)
Constituents M2
(6/8*0
Purge & Trap Compounds
Benzene ND
Carbon disulfide NO
Chloroethane NO
Chlorobenzene NO
Chloroform ND
1,2-Trans-dichloroethylene ND
Methylene chloride ND
trans-1,3-Dichloropropene ND
Methyl ethyl ketone ND
Carbon tetrachloride ND
Toluene ND
Trichloroethylene ND
Tetrachloroethylene ND
M6 M6 M12
(*/8*) (6/8*) (*/8*)
118
*0.6
*3.8
NO
1*0.8
<10
*0.*
ND
11*.*
ND
93**
3*.5
NO
OW2
(6/8*)
838
ND
29*69.6
938.8
ND
10.2
2*.6
306.6
17
ND
Acid/B/N/Pest Compounds
Aniline ND
bis(2-Ethylhexyl)phthalate ND
1 ,3,5-Trichlorobenzene ND
2,3f5,6-Tetrachlorophenol ND
2,3,*,5-Tetrachloropheno.l ND
o-Cresol ND
a+p-Cresol ND
Di-n-butyl phthalate ND
1 ,2-Di chlorobenzene ND
1 ,3-Di chlorobenzene ND
1 ,*-Di chlorobenzene ND
Aldicarb ND
Nap tHa lene ND
Nitrobenzene ND
Phenol ND
1, 2, *-Tri chlorobenzene ND
ND
10
ND
3*
ND
ND
ND
ND
1*7
ND
13
ND
ND
ND
ND
ND
ND
ND
96
< 1-9
28*
ND
ND
87
ND
< 1.9
Pest..& Herb. Compounds
A-BHC ND
G-BHC NO
ND
ND
ND
6.0
DAI HPLC Compounds
Haleic hydrazide
Nicotine acid
ND
ND
ND
ND
ND
<900
3-56
-------
TABLE 3.3-4 (continued)
Const!tuents
Extractable HPLC Compounds
Benzidine
3 ,.3' ~Di ch 1 orbenzi dene
3.3'~Dimethoxybenzidene
m-phenylenediamine
p-pheny1ened i ami ne
To 1 uene- 2 ,_3- D i am i ne
Metals & Cyanides
Aluminum
Arsen ic
Barium *
Be ry 1 1 i urn
Cadmium
Calcium
Chromi urn
Copper
Total Cyanide
I ron
N i eke 1
Osmium
Potass ium
Sodi urn
S t ron t i urn
Thai 1ium
Vanadi urn
Zinc
M2
(6/8'
NO
<25
<25
NO
NO
NO
NO
20
NO
NO
2800
NO
NO
<25
NO
<20
<800
590
1*300
NO
NO
NO
10
M6
*) (V8i»
--
--
--
—
""
50
200
—
5
--
530
--
—
550,000
—
--
—
3,273,000
--
--
--
--
M6
) (6/81*)
NO
NO
NO
NO
NO
NO
61,500
20
110
6
-------
•00-2A
TABLE 3.3-5: Tabulation of Carcinogenic RisksJ
Constituent
Well Numbers (hypothetical exposure points)
M2 (B) OW1 (Cl) OW2 (Al) M6 (C2) M12 (A2)
Benzene ND
Chloroform ND
Methylene Chloride . ND
Carbon Tetrachloride ND
Tetrachloroethylene ND
Arsenic ND
NA 1.2xlO-3 1.8xlO-4 NA
NA 1.9x10-3 2.8x10-4 NA
NA 1.8xlO-7 7.3xlO-7 NA
NA 1.1x10-3 ND NA
NA ND ND NA
NA 4.2x10-2 1.5x10-2 7.7x10-3
*Risk measurements based upon average of observed concentrations
ND - constituent analyzed, but not detected or below detection
limits.
NA - not analyzed.
3-58
-------
of 1.5 x 10~2 while the downgradient well (M-12) has a risk of
7.7 x 10-3.
Systemic toxicants have also been observed in both plumes.
The tabulation of hazard indices for these wells is shown in
Table 3.3-6. Well OW-2 has a very high concentration of chloro-
benzene. This level of contamination relates to a hazard index
of 84.2, or more than 80 times the maximum acceptable level.
Well M-6 has high levels of toluene, chromium and barium. The
total hazard index depends upon the valence state of the chromium.
If the chromium is hexavalent, the HI is 28.2, as shown in
Table 3.3-6, but if it is trivalent, the HI is 21.1. In either
case a toxic risk is posed.
Both plumes pose significant carcinogenic risks, and contain
unacceptable levels of systemic toxicants. The plume originating
at the manufacturing facility has no compliance point data, but
the downgradient well, OW-2, has high levels of arsenic and
chlorobenzene. In the plume originating at the hazardous waste
management unit, both the compliance point well and the down-
gradient well would pose significant health risks if used as
sources of drinking water. Monitoring has not been done to
determine the downgradient extents of these plumes.
A simple analytical model was used to describe contaminant
transport toward the river. The model results show that steady
state concentrations at 100 feet are reached in one week. Steady
state concentrations at the river edge are reached in roughly
one year. The steady state concentrations are extremely dependent
3-59
-------
TABLE 3.3-6 TABULATION OF HAZARD INDICES FOR SYSTEMIC TOXICANTS
Const!tuent
Chlorobenzene
Methyl Ethyl Ketone
Toluene
1,2 Dichlorobenzene
1,4 Dichlorobenzene
Phenol
Ch rom i urn
Nickel
Barium
Zinc
Total
Wei 1 Numbers (hypothetical exposure points)
M2 (B)
ND
NO
ND
ND
ND
ND
ND
<.06
1.97
.001
OWI (Cl)
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
OW2 (Al)
84.2
.034
.002
.021
.08
ND
.93*
.257
1.67
.004
M6 (C2)
ND
.156
.921
ND
ND
.004
7.07*
.286
19.7**
.018
M12 (A2)
NA
NA
NA
NA
NA
NA
ND
NA
<9.85
NA
2.0
NA
8774
25.2
NA
NA - not avai table
* Assumed to be hexavalent. Report identifies only total chromium.
** Hazard .index based on the higher of the measured values.
3-60
-------
upon the dispersivity assumptions. With a dispersivity of 1.0 m,
the concentration at the edge of the river is 14.5 percent of that
at 100 feet. Because the concentrations of systemic toxicants at
points A-l and C-2 are both over 14.5 times the recommended ADI
for some constituents, the ground water at the river edge is
likely to exceed ADI for these constituents.
Exposure Assessment
The plumes originating at this facility will discharge into
the nearby river. Parts of these plumes will pass outside of the
facility property before discharging to the river; however they
will pass beneath the property of another chemical manufacturing
facility. No supply wells are in the path of the plumes. The
river is used as a source of drinking water, though the degree of
surface water contamination and the location of drinking water
intakes was not provided in the materials reviewed for this case
study.
From velocity values for the alluvial aquifer of 14.4 and
4.5 ft/day, it can be approximated that the contamination would
have traveled to the river (3600 ft) within a range of 250 days
to slightly more than 2 years. This assumes that all the water
in the aquifer discharges into the river, thereby preventing
underflow. Further analysis of ground-water flow in the area of
the river would be necessary in order to adequately characterize
its movement.
3-61
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3.3.3 Case Study D-3
Facility Description
A hazardous waste landfill has been operated at this site
since 1977 on approximately 300 acres of the site's 2500 acres
(see Figure 2.3-11). Previously, wastes were disposed of in
trenches ranging in depth from 30 to 50 feet. Current practice
consists of burial of non-liquid containerized and
non-containerized wastes in trenches up to 175 feet deep and up
to 8 acres in area. It is believed that most listed hazardous
wastes have been disposed in this facility.
Climate
Average precipitation in the area is about 50 inches/year.
Monthly average precipitation ranges between about 6.2 inches in
the winter and spring months to about 2.2 inches in the late
summer to early fall. Watersheds in the area are characterized
by high amounts of evapotranspiration and widely varying amounts
of runoff depending on the surficial geology. Area temperatures
are moderate with below freezing temperatures occurring only
during short periods. Therefore, accumulations of snow and ice
are not a consideration in runoff or water balance calculations.
Regional Hydrogeology
The site is located in the Coastal Plain physiographic pro-
vince. The rocks in this area generally consist of Upper Cretaceous
sediments which dip to the southwest. The facility is located
on chalk/marl which is a relatively homogeneous low permeability
unit. The chalk was presumably deposited in a clear sea of
3-62
-------
NOTE: Borings from State
Inventory Wei 1
1
0123
•i
SCALE IN MILES
FIGURE 3.3-11 LOCATION OF DEEP WELL BORINGS AND GEOLOGIC SECTIONS
3-63
-------
moderate depths. The uppermost aquifer lies directly beneath
the chalk/marl and local ground water is believed to flow east to
northeast. The uppermost aquifer is the first stratigraphic unit
with the ability to transmit groundwater at a sufficient rate and
yield to be used as a water supply.
Site Geology
The chalk/marl group (650-750 feet thick) consists of a
chalky limestone with a minerologic makeup of 50% calcium
carbonate, 44% clay minerals and approximately 6% sand. The
lower member of the group is a uniform thin bedded chalky marl
with a thickness of approximately 250 feet. The chalk/marl, as
previously stated, is reported to be quite homogeneous with very
little structure and a low permeability. There is some discussion
in the application concerning faulting in the chalk/marl group.-
The presence of faulting or fractures could greatly effect the
migration of contaminants within the chalk/marl group.
The uppermost aquifer formation is approximately 400 feet
thick beneath the site and generally consists of thin clay and
sand beds with thick and coarse sand and gravel beds at its base.
This formation is divided into three units with the upper 100 feet
being a sand member. Figures 3.3-12 and 3.3-13 represent schematic
sections in the area of the site.
Site Hydrology
The potentiometric surface of the chalk/marl is generally 10
to 30 feet below the ground surface. However, because evaporation
is greater than precipitation, dry trenches have been excavated
to over 100 feet. From water level measurements in the uppermost
3-64
-------
sw
u>
&
tn
N-3
NE
o
z
500 _
0 _
-500 -
-1000
-1500 -
3 -2000 -
i—
-2500-
-3000-
EL.-2225
NATURAL GROUND LEVEL
1-8
A1
EL. 110
UPPERMOST] AQUIFER FORMATION
EL.-1770
NOTE: See FIGURE 2.3-11 for Location of Section and Scale
r 500
- 0
- -500
-1000
-1500
-2000
-2500
-3000
m
r~
m
o
FIGURE 3.3-12 GEOLOGIC SECTION A-A1 NORMAL TO STRIKE
-------
NW
J-]k
SE
N-8
00
cr>
500 -,
0 -
-500 .
-1000 -
EL.
EL.-465
EOB
o
z
^ -1500
-2000 -
-2500 -
-3000 -
-3500 J
NATURAL GROUND LEVEL
CHALK/MARL
UPPERMOST AQUIFER FORMATION
'
ITE: See FIGURE 2. 3-11. for Location of Section and Scale
B'
EL 200
EL. -510
ft _ft~7fi
tL . -0/U
Cl 1 1f\f\
tL . - 1 3UU
ci -on^n
EOB
- 500
- 0
. -500
m
m
<:
--1000 ^
z
--1500 ^
-H
-?nnn 1^
--2500
--3000
--3500
FIGURE 3.3-13 GEOLOGIC SECTION B-B'
PARALLEL TO STRIKE
-------
aquifer, a downward gradient into the aquifer was observed from
the chalk/marl in the eastern portion of the site. In the western
portion of the site, however, an upward gradient from the upper-
most aquifer into the chalk/marl was observed. Head differences
reach a maximum of 80 feet in the eastern portions of the site
and a maximum of 20 feet in the site western portions. Although
the application states that vertical gradients do exist (approxi-
mately .11) and ground-water movement occurs, the actual movement
is believed to be negligible. Field permeability values are
reported to range from 5.7 x 10"^ to 1 x 10"^ cm/sec. Also, a
laboratory determined effective porosity of 33.4% was reported.
Plume Information
There was no information available concerning existing
monitoring well locations, nor were any monitoring data presented.
However, considering the low permeability values and thickness
of the chalk/marl, migration into the uppermost aquifer may be
unlikely except over extremely long time periods. This statement
appears true even though much of the actual waste disposal occurs
below the water table in the chalk/marl unit.
There is some discussion in the application regarding
proposed monitoring well installations in the chalk/marl. Sixteen
core holes will be placed around the unlined trenches used during
interim status. These core holes will be completed as wells
screened across selected fractures in the chalk. An additional
18 wells will be screened below the base of adjacent trenches.
This shallow monitoring system will encircle the landfill trenches.
Two background wells away from active landfilling will also be
3-67
-------
installed to depths of 100 feet.
Time of Travel
Using the following application-supplied values, a vertically
downward ground-water velocity was calculated. (K values were
obtained from packer and well recovery tests).
Hydraulic Conductivity (K) 1 x 10""^ cm/sec
Hydraulic Gradient (i) .11
Effective Porosity (ne)_ .33
Ground Water Velocity (V) .034 ft/yr
From a ground water velocity of .034 ft/yr a TOT]_QO °f approxi-
mately 3000 years can be expected. There is 550 feet between the
uppermost aquifer and the base of the waste management unit at
the site. Considering the previously listed velocity, the
contamination would take approximately 16,200 years to reach the
uppermost aquifer.
Health Risk Assessment
The contaminant plume at this facility is hypothetical. The
simulation model assumed a steady state source release rate of
1.0 g/yr of benzene from a point at the facility. The resulting
concentrations and hypothetical health risks are shown in
Table 2.3-8 at distances of 100 feet and 550 feet. At 100 feet,
the plume reaches steady state after 7500 years with a concentra-
tion- of 0.805 ppb and a hypothetical carcinogenic risk of 1.1 x
10~5. At 550 feet, the plume reaches steady state after 33,000
years with a concentration of 0.87 ppb and a risk of 1.24 x 10"^.
The health risk indicated in this table is the hypothetical
risk associated with the small 1.0 g/yr assumption. At 1 x 10"^,
the steady state risk is approximately at the threshold of
acceptability at both 100 and 550 feet.
3-68
-------
Table 3.3-7: Results of Benzene Plume Simulation
Time (years)
500
1000
5000
7500
8000
10,000
15,000
20,000
30,000
33,000
Benzene Concentration (ppb) Health
100 ft 550 ft Risk
0
3.72 x 10-3 5.3
6.33 x 10-1 9.0
8.05 x 10-1 1.15
6.58 x 10-5 9.4
1.04 x 10-2 1.49
1.68 x 10-1 2.4
5.74 x 10-1 8.2
8.61 x 10-1 1.23
8.68 x 10-1 1.24
0
x
X
X
X
X
X
X
X
X
10-9
10-7
10-6
10-11
10-8
10-7
10-7
10-6
10-6
3-69
-------
Exposure Assessment
Based on available information, there is no plume at this
facility. If one does develop, it will not pose much of a risk
because the hydraulic conductivity of the chalk/marl is so low
that it would take an extremely long time for exposure to occur.
Such a plume would travel very slowly, on the order of one foot
in 300 years and would not be expected to reach the uppermost
aquifer for over 15,000 years. Furthermore, the chalk/marl for-
mation is not pumped for any domestic, commercial, or agricultural
purposes.
3-70
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3.3.4 Case Study D-4
Facility Description
A plume of ground water contaminated by liquid metal-plating
effluent has formed downgradient from an industrial park on Long
Island, New York. Discharges from the plant to the shallow
aquifer began in the 1940s. Waste water treatment was installed
in 1958, and the operations ceased in 1970. While the facility
was in operation the plume contained elevated chromium and cadmium
concentrations extending approximately 4,300 feet downgradient
from the waste disposal basins and discharged into a small creek.
Hydrology
The area is underlain by the upper glacial (water table)
aquifer, and the Magothy aquifer, which supplies all the drinking
water to the area. The aquifer of concern is the upper glacial
aquifer which, in the study area, ranges from 80 to 140 feet
thick. The water table in the area ranges from 0 to 25 feet
below land surface. This aquifer consists chiefly of medium to
coarse sand with lenses of fine sand and gravel. Locally, beneath
and immediately west of the stream, the rate of movement of the
leading edge of the plume may be as low as 0.5 feet/day, owing
to the smaller hydraulic gradient in that area. The TOT for
100 feet is therefore less than 200 days.
Plume Information
Maximum concentrations of hexavalent chromium determined
during successive investigations ranged from 40 mg/1 in 1949 to
10 mg/1 in 1962. Cadmium concentrations ranged from 0.01 to
10 mg/1, but in most places, were less than 1 mg/1. Maximum
3-71
-------
observed concentrations of cadmium and chromium in the creek were
0.1 and 2.9 mg/1, respectively. Concentrations of both cadmium
and hexavalent chromium in most of the plume and in part of the
the creek exceeded the limits of 0.01 and 0.05 mg/1, respectively,
as stated in the National Interim ,Primary Drinking Water Standards.
The location of the monitoring wells is depicted in
Figure 3.3-14. No background well was available. Point D, the
leading edge of the plume, is interpreted as Well #62. Well #2
was chosen as point A, even though it lies 700 feet along the flow
line. No monitoring well was installed at compliance point C.
Analysis of the single samples taken in the fall of 1975 from
the observation wells at the site are reported in Table 3.3-8.
Well #2, the closest well to the disposal basins, showed the
highest concentration of contaminants. Figure 3.3-15 presents a
cross-section of the area and the plume, along the axis of flow
toward the creek.
Health Risk Assessment
The concentrations of the constituents used in the following
assessments may not represent the largest values passing through
the hypothetical exposure points, because ground-water quality
sampling has occurred between 10 and 20 years after waste water
treatment operations had reduced the concentrations of hazardous
constituents entering the ground water.
No oral carcinogens were identified at this site. Cadmium
and chromium VI have been identified as inhalation carcinogens,
but no oral carcinogenic risks have been demonstrated. Cadmium,
chromium VI and chromium III are all recognized as systemic
3-72
-------
500 looo FCET
100 iee 100 MI Tins
FIGURE 3.3-14 WELL PATTERNS AND PLUME OUTLINE
3-73
-------
Table 3.3-8: CONCENTRATION OF METALS IN MONITORING WELLS (ppb)
Compound
Trivalent chromium
Hexavalent chromium
Cadmium
Point D
(Well 162)
110
0
440
Point A
(Well #2)a
366
24
6,900
aWell #2 is located approximately 700 feet from the disposal
basins.
3-74
-------
MA* SHOWING LOCATION Or SCCTION
t'U
FIGURE 3.3-15 CROSS-SECTION OF GROUND-WATER PLUME
3-75
-------
toxicants on EPA's listing of ADI's. The remaining constituents
appearing at elevated concentrations (iron, manganese and zinc)
are neither carcinogenic nor recognized systemic toxicants.
The hazard indices for cadmium and chromium are presented
in Table 3.3-9. This table shows that the concentrations of
cadmium represent a significant toxic hazard, because ingestion
of 2 litres per day of water at the contamination levels observed
at points A or D represents a cadmium ingestion of many times the
ADI. The hazard index for point D is 25. Neither hexavalent nor
trivalent chromium concentrations have hazard indices in excess
of 1.0.
Exposure Assessment
Prior to discovery of the contaminant plume in the early
1940's, the shallow aquifer was widely used as a source of
»*
drinking water. The yield probably exceeds 10 gallons.per minute
in nearby shallow local wells. In addition, the contaminated
portion of this aquifer underlies an area of approximately
77 acres. The leading edge of the plume appears to be influenced
by the position of the creek, although Figure 3.3-15 suggests
that part of the plume may flow under and beyond the Creek.
Use of this contaminated ground water for drinking purposes
does not appear to occur because the many residences overlying
the plume are served by municipal water. If the area were not
urbanized, there would be a greater chance that the ground water
would be used for drinking purposes. Also, because the plume is
well documented, potential users would likely be warned by local
authorities to avoid consuming this ground water.
3-76
-------
Table 3.3-9: Tabulation of Hazard Indices
Constituent
ADI Exposure (mg/kg/day) Hazard Index
(mg/kg/day) A D A D
Cadmium
.0005
0.197
0.0126
394 25.2
Chromium III
1.60
.0105
.0031
.0066 .0019
Chromium VI
.0021
.0007
.33
Total
394 25.2
3-77
-------
Conclusions
The cadmium concentration at points A and D represent
significant toxic risk if they are ingested in drinking water.
The exposures that would result from drinking water use exceed
acceptable daily intake thresholds by a factor of 394 at point A
and a factor of 25 at point D.
This case demonstrates that a large-scale plume can develop
within a hydrogeologic setting that fails the TOTiQO criterion.
The potential for exposure to this plume is high because the
plume occupies a large portion of an aquifer that has a large
sustained yield. An opportunity for large-scale, direct exposure
to this plume appears to be prevented only by the highly urban
character of this area. Were the site more rural in character,
significant use of the ground water would be expected. Impact
on stream quality has not been assessed in this case study.
3-78
-------
3.3.5 Case Study D-5
Facility Description
This case study concerns ground-water contamination associated
with several unlined surface impoundments containing creosote
wastes in Florida. The site began operation in 1902; operations
ceased around 1981. Figure 3.3-16 shows the locations of the
facility and the monitoring wells used in this assessment.
Figure 3.3-17 is a hydrogeologic cross-section of the site. As
shown by monitoring data, the plume extends approximately
1,000 feet from the impoundments towards a bay. The plume length
9
for .phenols is considerably less than anticipated by theoretical
calculations. [Such calculations project the. phenol plume to have
migrated 4 to 5 kilometers downgradient from the site beneath the
bay.] However, there are no apparent monitoring wells "beyond
300 meters south of the site that verify these calculations.
Although many of the expected waste components are absent or
extremely dilute near the bay, a dark sludge band has been
observed on the beach at low tide. This suggests transport to
the bay through the ground-water system.
Hydrogeology
The site overlies an upper sand and gravel aquifer that is
approximately 90 meters thick at the site area. The water table
is within 1.2 meters of the land's surface near the impoundments.
Contamination has been found only within the upper 30 meters of
the aquifer, due probably to the retarding influence of the silt/
clay lens shown in the cross-section at a depth of approximately
10 feet. TOTjLoO ^s estimated to be 25 days.
3-79
-------
PLANT
OVERFLOW PONDS
0 50. 100 150 METERS
i i
6
1.5
MONITORING SITE AND NUMBER
ALTITUDE OF WATER TABLE. CONTOUR
INTERVAL 0.5 METER. DATUM IS SEA LEVEL
•A* GEOLOGIC SECTION LINE A -A1
FIGURE 3.3-16 LOCATION OF MONITORING SITES (WELLS)
3-30
-------
FIGURE 3.3-17 HYDROGEOLOGIC CROSS-SECTION OF SITE
(January 1984)
SEA LEVEL
3 PONDS
A1
METERS
r-10
.ju;—~-r CLAY rj
-SEA LEVEL
-10
Mo
GENERALIZED SECTION. NOT TO SCALE
k MULTIPLE DEPTH WELL SITE
•* *
•2.0 ALTITUDE OF POTENTIOMETRIC SURFACE,
CONTOUR INTERVAL 0.5 METER. DATUM
IS SEA LEVEL. DASHED WHERE
APPROXIMATE
3-81
-------
Plume Information
Monitoring data are available for 33 chemicals falling into
five groups. These groups are: phenols, polycyclic aromatic
hydrocarbons, nitrogen heterocyclics, sulfur heterocyclics, and
oxygen heterocyclics. These data are presented for six well loca-
tions in Table 3.3-10. For the purpose of this analysis, well 1
is designated as point B, well 3 as point C (compliance), well 4
as point A (although it lies some 250 feet from the compliance
point) and well 7 as point D, the downstream edge of the plume.
The location of these wells is shown in Figure 3.3-20.
Health Risk Assessment
These monitoring data are analyzed for adverse health risks
to hypothetical users in accordance with established toxicity
factors for carcinogens and systemic toxicants, and by analogy
with constituents with unknown toxicities to similar constituents
with known toxicities. The latter method is used here because
extremely high levels of a compound are present for which no
toxicity values are available.
1. Standard procedure-
a. Carcinogens
Of the constituents listed in Table 2.3-10, only
Benzo-(a)-pyrene is known to be carcinogenic,
and it was not detected at any of the wells.
b. Toxicants
Several of the constituents have known toxic
risks, and include: phenol, biphenyl,
pentachlorophenol, and fluoranthene. The
estimated Hazard Index for each of these is as
follows:
3-82
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TABLE 3.3-10 CHEMICAL ANALYSES FOR SELECTED ORGANIC CONTAMINANTS
IN GROUND WATER AT A DEPTH OF 18.3 METERS AT SITES
1 AND 3 THROUGH 7*
Compound
Phenols
Phenol
2-methyl phenol
2, 4-dimethyl phenol
3, 5-dimethyl phenol
2,3,5-trimethylphenol
1-naphthol
2-naphthol
Pentachlorophenol
Total phenols
Polycyclic aromatic
hydrocarbons
Indane
Naphthalene
2-methyl naphthalene
1-methyl naphthalene
Biphenyl
Acenaphthene
Fluorene
Phenanthrene
Anthracene
Fluoranthene
Pyrene
Benzo(a)pyrene
Total polycyclic
aromatic hydrocarbons
Nitrogen heterocycles
2,4-dimethylpyridine
Qu incline
2-methlyqu incline
2-quinolinone
Acridine
Carbazole
Acridinone
Total nitrogen
heterocycles
Well
1
B
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
1 numbers/hypothetical exposure points
3 4 5 6 7
C A D
13.3
456
1,835
1,666
317
360
317
11.6
4,976
19.0
1,976
159
91.1
22.0
157
82.1
57.2
3.2
2.8
1.6
ND
2,571
ND
3.5
ND
1,217
1.0
339
12.4
1,573
ND
7.8
623
548
36.5
ND
ND
ND
1,215
ND
27.3 1
1.1
0.5
--
1.2
1.2
1.6
ND
0.2
0.2
ND
33
ND
ND
ND
125
ND
13.5
ND
139
ND
15.9
83
13.5
35.9
111
2.4
ND
262
54.7
,038
87.3
44.7
7.8
44.9
17.3
2.9
ND
ND
ND
ND
1,298 1
ND
ND
ND
214
ND
52.5
2.2
?69~~
ND
44.7
178
999
218.8
216
13.3
ND
17770
435
271 1
437
260
53.2
246
103.4
49.4
3.0
ND
ND
ND
,858 1
ND
ND
2.7
517
ND
299
11.4
S30~
ND
2.3
405
6.6
60.9
138
81.1
ND
694
186
,072
156
81.3
15.4
75.9
34.5
12.5
ND
ND
ND
ND
,634
ND
ND
ND
94
ND
104
2.4
Ioo~
Concentrations in micrograms per liter; ND, not detected.
3-83
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TABLE 3.3-10 CHEMICAL ANALYSES FOR SELECTED ORGANIC CONTAMINANTS
IN GROUND WATER AT A DEPTH OF 18.3 METERS AT SITES
1 AND 3 THROUGH 7 (Continued)*
Well numbers/hypothetical exposure points
1 3 4 56 7
Compound B C A D
Sulfur heterocycles
Benzo(b)thiophene ND 268 6.0 82.7 442 157
Dibenzothiophene ND 3.6 0.5 4.9 4.4 1.1
Total sulfur ND 272 7 88 446 158
heterocycles
Oxygen heterocycles
Dibenzofuran ND 89.3 O.J 15.1 101.1 31.4
Total oxygen ND 89 1 . 15 . 101 31
heterocycles
* Concentrations in micrograms per liter; ND, not detected
3-84
-------
A B C D
Biphenyl ND ND .013 .009
Phenol ND ND .004 ND
PCP ND ND .011 ND
Fluoranthene .006 ND .013 ND
Total Hazard Index .009 ND .25 .12
ND - not detected
2. Estimation of unknown toxicities by analogy
Extremely high concentrations of 2,4-dimethylphenol,
3,5-dimethyiphenol, and 2,3,5-trimethylphenol have
been observed at this site, but these compounds do
not have assigned EPA toxicity values. EPA does,
however, list ADIs for 2,6-dimethylphenol and
3,4-dimethylphenol of 0.00019 and 0.00044 mg/kg/day,
respectively. We have chosen the lower of the two,
0.00019, as a conservative estimate of the ADI for
2,4-di, 3,5-di, and 2,3,5-trimethylphenol.
A B C D
Total Concentration (mg/1) 1.20 ND 3.83 0.47
Hazard Index 185 ND 588 72.3
Exposure Assessment
The potential for exposure to contaminants at this site could
be great due to the potentially high yield of the aquifer as shown
by nearby production wells (e.g., 5,500 gallons per minute) and
the areal extent of the plume (approximately 7.4 acres). There
is, however, no present indication that ground water in the area
of the plume is being used for drinking water purposes. A study
is underway to determine if there have been any detrimental
environmental effects to the bay.
3-85
-------
Conclusions
The evidence of significant toxic risk at this site is
convincing, although the substances of concern are not explicitly
represented on the ADI list for systemic toxicants. The EPA list
of ADIs shows 2,6-dimethylphenol to be one of the most toxic
substances on that list, with an ADI of.. 0.00019 mg/kg/day.
Application of this toxicity threshold to chemically similar
2,4-dimethylphenol, 3 , 5-dimethylphenol and 2, 3-, 5-trimethylphenol
observed at this site is a reasonable procedure, though it is
conservative and may tend to overestimate risk. However, the
•
concentrations at this site are so high that" even an ADI of
0.0019 mg/kg/day (i.e., 100 times less toxic than
2,6-dimethylphenol) would show significant risks.
The ground water characterized by this risk extends for a
substantial distance from the site (approximately 1,000 feet).
The opportunity for exposure is high; the sustained yield of the
geologic unit containing the plume can exceed 5,500 gpm. The
site clearly fails the proposed TOT]_oo criterion.
3-86
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3.3.6 Case Study D-6
Facility Description
A facility which handled hazardous wastes is located at a
former sand and gravel pit operation. The facility's operations
have resulted in the release of hazardous constituents to the
ground water beneath the site. The facility currently consists
of a fenced enclosure with an incinerator, a concrete block
building, and an asphalt lined lagoon (see Figure 3.3-24).
Outside of the fenced enclosure is an undeveloped area partially
enclosed by second fence constructed to restrict vehicular access.
Prior to 1972 the site was a sand and gravel pit, which was
allegedly used to store and dispose of contaminated by-products
from tank cleaning.
The on-site asphalt lagoon was originally constructed in 1972
»'
to accommodate waste generated by a marine oil spill of
100,000 gallons of industrial fuel. The existing incinerator was
also upgraded at that time. In addition to the oil spill wastes,
the owner also accepted tank bottoms of number 6 and number 4 oil,
septic tank wastes, and industrial process wastes. Approximately
100,000 to 200,000 gallons were received annually by the facility
between 1972 and 1977.
The facility was operated as a transfer station for the
wastes listed above. Initially, the incinerator with afterburners
and pollution control equipment was used to dispose of oil
impregnated refuse (seaweed from the oil spill, rags, etc.).
However, the incinerator was not used after 1975. The typical
method of operation was to accumulate wastes in large tanks until
3-87
-------
sufficient quantities were obtained for shipment to refiners or
off-site disposal. Contents of the lagoon were then transferred to
the large tanks. Subsequently, the tanks leaked. Also, numerous
accounts allege that rinse waste and oily wastes were applied directly
to the ground surface. The area between the inner fenced area and
the adjacent road was once allegedly used for dumping and burning
and contains buried drums. This area has since been filled to
grade by the site owner.
Environmental Setting
The topopgraphy of the site is relatively flat west of the
adjacent road witn" the fenced enclosure and the areas to the
west and north lying in a excavated area. Off-site, the land
slopes steeply eastward to the river. Elevations range from
approximately 300 feet mean sea level (MSL) at the site to less
than 200 feet MSL at the river, approximately 3/4 mile due east.
Site area surface and groundwater discharge to the river and
its tributary brook. The State's department of environmental
protection has classifed the river as B-2, acceptable for
recreation, including water contact. Class B-2 waters may also
be used for industrial and potable supply after treatment.
Site surface drainage is contained on-site and the water
either evapotranspirates or percolates into the soil. The
percolation rates through the contaminated soils at the site
are likely to be approximately twice as high as usual for the
state, creating little or no run-off.
3-88
-------
(MONITORING
WELL ITTPI
WATER
IWELL
*| S3 SAL. DRUMS
ASPHALT i— GATE
RAMP
VERTICAL TANK (7YP.)
I CHAIN LINK
I FENCE
BOTTOM OF SLOPE
'TOP OF SLOPE
APPROXIMATE SCALE: |"= 100*
TRUE
SITE PLAN
FIGURE 3.3-18
3-89
-------
HAND
• GRAVEL PIT
1*=1000'
LOCATIONS OF OFF-SITE MONITORING WELLS
MAP FnOM U9Q8 QUAOnANQLE)
N
FIGURE U-19
-------
• I • —••».«
I II III II I \L I I I I I
KEY
DOMING LOCATIONS
i i i riii i i i i i 'i i
___.«_-.
ON-SITE SUB SURFACE SOIL BORING LOCATIONS AND
LOCATIONS OF SITE SOIL SECTIONS
f\J
TRUE
~~1
FIGURE 3.3-20
-------
SITEECTION A-A'
FI
1.3-21
-------
MO DETECTABLE TOTAL VOLATILE onOANICO
-------
TABLE
2.3-n
B-l
B-l
B-2A
. B-2S
B-2C
B-3 (soil)
B-3 (rodO
B-4
B-5 (soil)
B-5 (rocO
SSSSaSL&ai
.209.0 - 224.8
188.6 - 204.9
131.5 - 1«.5
153.9 - I50'8 •
187.5- IV'*
171.2- IBS-1
145.6.- 161-6
28.5 - 65-1
150.5 - 153.4
132.5 - 1*7.6
Groundwater
Elevation
(ft HSL)
3/6/8A
1.7 x 10~4
4 5 x 10" -
^ • »
8.3 x 10"6
TO'2
» 10
,n-3
1.7. x 10
1 4 x 10"4
1 • ^ *^
2.6 x 10"5
fa • ^
.5
9.3 x 10 .
2.8 x 10'5
. - - ,n-5
223.6
. 219.*
192.1
200.9
frozen
176.8
170.3
99.8
170.5
170.4
224.1
21&.8
193.4
203.0
203.1
176.5
.153.9
97.0
171.0
170.9
3-94
-------
Surficial Geology
The study area is located on a glacial outwash plain comprised
of stratified sand, gravel, and boulders. Three major subsurface
units are noted to be present near the site. These units consist
of glaciomarine fine sands and gravels, reported overlying glacio-
fluvial (deltaic) stratified sands and gravels. Glacial till is
noted to underlie the stratified sands.
Beneath the site the predominant soil type is a medium grained
sand with lenses of silt and clay (see Figure 3.3-26 through 3.3-28)
Approximately forty feet of these medium coarse grained sands
beneath the site are unsaturated. An effective porosity of 0.2
(default value) was used for these sediments when saturated.
The glaciomarine fine sands, silts and clay silts reportedly
overlie the sand and till along the steep slopes that lie adjacent
to the river and its tributary brook. It was noted that the clayey
glaciomarine deposits have apparently presented a barrier to
ground water flow from the sand and gravel deposits (sand and till).
Springs and seeps were noted to occur where this ground water
flowing from the sand and gravel escapes to the surface through the
clayey deposits.
Bedrock Geology
The topography of the bedrock surface generally slopes to the
east, toward the river as shown in Figure 3.3-32. The bedrock
surface forms a broad northeast-trending trough to the west of
the site; the surface rises south of the site. This peculiar
topography of the bedrock surface is a significant factor, which
results in movement of groundwater toward the north away from the
3-95
-------
site.
The bedrock beneath the site is reportedly composed of granit^
pegmatite or schistose migmatite, possibly transected locally by
thin, tabular mafic dikes. Cores from the monitoring wells drilled
in 1984 show moderately to heavily fractured rock with softening
and iron staining due to weathering along the fractures. It was
noted that ground water is transported through the bedrock apparently
to the northwest in fractures, and to the north/northeast along the
dikes. Calculated permeabilities from falling head permeability
*
tests in the upper zone of the bedrock were reported to vary from
10~5 to 2.5 x 1CT6 cm/sec.
Site and Near Site Hydrology
General information on the ground water hydrology of the
surficial and bedrock aquifers in the vicinity of the ^site was
noted to be given in a previous report, conducted in 1982. A
study conducted in 1984 was designed to better define the
ground water flow and to verify the inferences made relative to
the hydrogeologic parameters of the area from the 1982 study.
To this end, five monitoring wells were installed (B1-B5), in
addition to the four previous monitoring wells installed
in 1982 (B101-104). Figure 3.3-25 shows the location of the
monitoring wells from both studies. Also note Table 3.3-16 on
Well Data (1984).
Wells Bl through B5 were installed in order to expand and
address the need for further well data. This well information
was intended to confirm the presence and migration of the
contaminant plume, to delineate areas of high permeability, to
3-96
-------
assist in model calibration, and define areas of low permeablility
thought to exist near the site.
The general path of ground water flow in the surficial aquifer
was noted"to be northwestward from the site, eventually turning
eastward through an east-west trending coarse gravel deposit toward
the "springs" (see Figures 3.3-29 and 3.3-30). Figure 3.3-31 gives
the inferred bedrock potentiometric surface; flow direction was
inferred to move to the northwest, as indicated by the arrows.
The aquifers are hydraulically connected as indicated by
the presence of contaminants in the bedrock aquifer. Downward
vertical gradients (i.e. a recharge zone) through the surficial
aquifer were indicated by all the 1984 boring sites with multiple
well installations.
Plume Information
»•
The path of contaminants leaving the site appears" to be in a
north-northwesterly direction; the contaminants then appear to
take a larger radius turn (larger then that predicted by the 1982
study), before curving eastward and finally southeastward to
intersect the river at the springs. Refer to the section on site
and near site hydrology for well data used to confirm the contam-
inant plumes path. Also see Figures 3.3-29 through 3.3-32. The
report also noted that most of the bedrock ground water that
originates at the site is discharged to the overlying gravel
deposits in the vicinity of the springs.
3-97
-------
;-'
.,
/~V o' sorf IOOQ' (
.^) » '"^ ./ *
INFERRED SURFICIAL AQUIFER PLUME FROM
•becAw ^-^l
N
FIGURE 3.3-23
-------
LEGEND
.3- 30IL IIOnillQ LOCATION - - WITIIOnAWAL WELL l.OCATIOII
- onoiiMowAicn LEVEL .... ....... APPROXIMATE TOP OF IIEOIIOCH
WATER SAMPLE
-TAKEN AT OEPIII
06 pp»» 1.1.1-TIIICIILOnOETIIAHC.
1.000 ppb TCE
HO-OELOW DETECTAULE LEVELS
SPRIIIQS-i
III
RIVER
1000
2000
3000 I'EET 4000
6000
0000
sunsunrAcn CROSS^GECTION A-A FROM SITE TO
(ooo rifliiro2.323for Croao-Socllon Locnllon)
FIGURE 3.3-24
-------
&
- c
— •. •
q •>• .-- 7
; •
-188* POTENTIOMETER ;-
"SURFACE ELEVATION (f««O
INFERRED BEDROCK POTENTIOMETRIC
SURFACE FROM (1982) WITH
1984 DATA. SUPERIMPOSED
,j± -. • ~. ---', FIGURE 3.3-25
3-100
-------
SC/UE
.a
* mr
/'•• . s. - DM .
LEGEND
MONITORING WELL DG
1004 CONCENTRATION
(6ppb)
0EDROCK AQUIFER PLUME FROM 1^02
WITH THE 1004 1,1,1-TniCIILOnOETIIANE ODQEHVED DATA OUPEniMPOBED |
FIGURE 3.3-26
-------
Time of Travel-TOT]_QO
Approximately 40 feet of unsaturated medium-textured sands a
encountered cirectly beneath the site. The analytical approach to
solving for TOT within the unsaturated zone was based on a
single-layered system of a single material type. This solution
assumes that the hydraulic gradient is equal to 1.1 A steady state
flow of moisture through the unsaturated zone is also assumed.
Steady state flux (q) is assumed to be equal to net precipitation
where evapotranspiration and run-off are assumed nonexistent. This
provides the maximum flux for the site.
>
0 Unsaturated Zone
TOTunsat.= L0 L = Length of unsaturated column
q 0 = Volumetric water content
approximately equal to porosity
q = Flux
TOTllr,a_«. = (1.22 x 103 cm) (0.395 cm3/cm3)
unsciu. , _ _ /
107 cm/year
TOTunsat.= 4'5 years
0 Saturated Zone
V = Ki K « 3.28 x 10~4 ft/sec (default value)2
ne i = 0.02 average from field data
ne = 0.2 (default value)
V= 3.28 x 10"5 ft/sec
TOT100 = 100 ft = 3.05 x 106 sec = 9.67 x 10~2 yrs
3.28 x ID"5 ft/sec
TOT100 = TOTunsat. + TOTsat.
TOT]_oo = 4.6 years
1 - Derived from Technical Support for Developing Guidance for
Calculating Time of Travel (TOT)in the Unsaturated Zone;
December, 1984, Section 3.
2 - Default value for hydraulic conductivty taken from Freeze & Cherry,
1979. K selected for clean sand is 1 x 10~2 cm/sec. Conversion
factor for ft/sec = 3.28 x 10"2.
3-102
-------
Health Risk Assessment
This health risk assessment characterized hypothetical risks
associated with the lifetime consumption of ground water contaminated
with trichloroethylene (TCE) and 1,1,1-trichloroethane, the major
contaminants for this site. While actual contamination of private
well water supplies near the site has occurred, these data were not
available for use in this case study and therefore the potential
risks to residents who were exposed to contaminated drinking water
will not be evaluated here.
Hypothetical risks associated with the lifetime consumption
of ground water containing TCE and 1,1,1-trichloroethane (two
potential human carcinogens) will be based on the maximum contaminant
concentrations identified in 1984 in a bedrock monitoring well (B-l)
located in the centerline of the plume. Figure 3.3-33 shows the
»*
location of B-l and Table 3.3-17 contains the sampling-results.
Contaminant concentrations are generally higher in the bedrock
aquifer than in the surficial aquifer. Well B-l is located
*
off-site at roughly 1000 feet northeast of the si.te; it corresponds
to a well location between points A and D on Figure 3.2-1. Well
B-l data were collected in 1984. Drinking water has been obtained
from both the bedrock and surficial aquifers. Thus, using the
data available in the RI for this, site, worst-case risk estimates
will be produced.
For 1,1,1-trichloroethane, and additional risk esimate was
made based on the maximum isoconcentration line shown in
Figure 3.3-33; the concentration gradients shown in Figure 3.3-33
apply to the surficial aquifer and are based on historical and
3-103
-------
(-.
o
LEGEND
|fll MONITOniNQWELLD1
•'if70 I 100^ CONCENTRATION.
lsocon:*.i TPII
;>iriovc-ii**ii'.!l.te02>j •*
'' • x 'I /•;-••>
j : 1 -,j. j. ' ..-../ . • . . .
'^[ii:. INFERRED SUnFICIAL AQUIFER PLUME FROM 1983 T>AT&
WITH THE 10IM 1,1,1-TIlllcnUOnOETIIAHE OD3ERVED DATA OUPEniMPOSED,
• .*
N
FIGURE
3.3-27
-------
TABLE 3.3-12
LABORATORY ANALYTICAL RESULTS
OF GROUNDWATER QUALITY MONITORING
Location
B-l (shallow soil)
B-l (bedrock)
B-2 (shallow soil)
B-2 (deep soil )
B-2 (bedrock)
B-3 (shallow soil)
B-3 (bedrock)
B-4 (deep soil ) '
5-5 (deep soil )
B-5 (bedrock)
Date
(1984)
3/21
3/21-
3/22
3/22
3/22
3/20
3/20
3/21
3/20
3/16
1,1,1 Trichlo'roethane
(oob)
170** (230)
470** (500)
9
16
5
65
3
ND
NO (ND)*
7 (8)*
Trichloroethylene (TCE)
(oob) . '
16,000
29,000
91
160
56
1,800
120
ND
ND (ND)*
190 (177)*
duplicate
ND « not detected .
These samples were diluted for the analysis of trichloroeth/lene. The
companion results in parentheses for 1,1,1-trichloroethane are for the;
•undiluted sample. . • '
3-105
-------
TABLE 3.3- 13. INCREMENTAL CARCINOGENIC RISK ASSOCIATED WITH LIFETIME
CONSUMPTION OF TCE AND 1,1,1-TRICHLOROETHANE CONTAMINATED GROUND WATER
Average Daily CAG Potency Incremental
Concentration Lifetime Dose* Estimate Carcinogenic
Contaminant (ppb)
Trichloroethylene 29,000
1,1,1-Trichloroethane 500
1,000
(mg/kg/day)
0.83
0.014
0.028
(mg/kg/day )'1
1.9 x 10'2
1.6 x 10'3
1.6 x 10"3
Risk
1.6 x ID'2
2.2 x 10'5
4.4 x 10'5
* Assumes lifetime ingestion of 2 liters/day of drinking water by a 70 kg.
adult
3-106
-------
current (1984) data.
The carcinogenic risks associated with the lifetime consumption
of TCE and 1,1,1-trichloroethane are given in Table 3.3-18. The
risk from TCE ingestion over a lifetime is estimated at 1.6 x 10~2,
which is extrememly high. For 1,1,1-trichloroethane, the estimated
risk is 2.2 and 4.4 x 10"5.
While the concentrations of contaminants found in the sixteen
private wells that were closed in 1977 are not reported in the RI,
it can be assumed that by virtue of the wells being capped, the
risks were considered to be unacceptable. ,
•
Exposure Assessment
Exposure to ground water contaminants from this site has
occurred. As previously stated, 16 private wells in the path
of the plume -were closed in 1977.' In 1978 a public water supply
was provided as replacement for these wells. Future exposure via
ground water ingestion is unlikely because of the provision of
this new water supply. However, unless land use controls are
instituted to prevent utilization of the contaminated aquifer,
exposure could occur in the future from well water installatipn.
The plume is migrating to the north and northwest and
eastward to a river and brook. Based on data in the site RI report,
no contamination has been found in these downgradient surface
waters. Potential future risks associated with the river and
brook would depend on the remedial actions taken on the site, where
significant soil contamination exists that could contribute to
overland flow and infiltration to ground water. The brook (as Class
B-2 water) could theoretically, under state regulations, be used for
3-107
-------
drinking water if treated. Relatively low-level contamination of
a spring adjacent to the river has occurred, the spring being a
discharge point for the contaminated ground water. The potential
for exposure to contaminants in the spring is not known from
information provided in the RI.
3-108
-------
4.0 ESTIMATING THE NUMBER OF FACILITIES LOCATED IN
VULNERABLE GROUND-WATER SETTINGS
The analytical approach and methodology followed to
estimate the number of hazardous waste land treatment, storage,
and disposal (TSD) facilities located in vulnerable ground-water
settings, and the results obtained, are discussed in this
Section.
The optimal approach to determine the number of hazardous
waste TSD facilities in vulnerable settings would be to eval-
uate the ground-water vulnerability of each facility in the
U.S. on a facility-specific basis. However, an evaluation of
all facilities was not possible due both to the lack of available
hydrogeologic data on TSD facilities and to the time constraint
placed on the completion of the analysis. As a result, a praq-
matic approach was developed necessarily that uses only currently
available data.
4.1 METHODOLOGY
Ground-water vulnerability is evaluated in terms of
TOTiQOf the time of travel of ground water along a 100-foot
flow line originating at the water table at the base of the
hazardous waste unit. In the absence of facility-specific
information for all facilities in the U.S., other readily
available databases containing information useful for the
analysis were identified. Several databases were reviewed
for hydrogeologic information that could be used to calculate
and evaluate ground-water vulnerability.
4-1
-------
As described in detail in the guidance criteria, the
calculation of TOTiQO requires data on hydraulic conductivity,
hydraulic gradient, and the effective porosity of the geologic
media underlying the facility. These data are explicitly
required in a Part B application, and are used to calculate the
average linear velocity (V) of ground-water flow. Based upon
the criteria outlined in the guidance, travel distance is set
at 100 feet; therefore, ground-water velocity essentially
dictates whether a facility pases the TOTiQO criteria.
Additional data requirements for the analysis were EPA
facility ID number, address, and latitude and longitude. These
data are necessary to identify facility location and ascertain
overlap between the various databases. The following databases
were identified as being potentially useful for characterizing
ground-water vulnerability:
0 HWDMS database - the hazardous waste data manage-
ment system database includes information on
process codes based on Part A permit application
data, and regional updates. This database
provides the best representation of the "universe"
of RCRA hazardous waste TSD facilities, including
landfills, surface impoundments, and waste piles.
0 1982 GCA Study - GCA Corporation prepared a
comprehensive database of geographical, geological,
and hydrological variables to characterize the
hydrogeology of 346 sites.
4-2
-------
0 1983 G&M Study - Geraghty & Miller designed 18 flow
field scenarios to correspond to the 18 generic
hydrogeologic settings developed by GCA Corporation
(1982) based on data for 346 existing sites. G&M
established a rational basis for simulating flow
rates and patterns by applying flow system theory,
professional experience, and literature reviews.
Selected pairs of flow fields having similar hydro-
geologic characteristics were clustered into flow
systems, reducing the total number of flow systems
from 18 to 14.
0 WA23 Database - EPA's Office of Solid Waste (OSW)
and Pope-Reid Associates collected data from Part B
applications to develop a worst-case hydrogeologic
scenario. Sufficient data were collected from
163 hazardous waste disposal facilities nationwide
to create a computer database. The database
contains two files; a ground-water characteristics
file and a stratigraphic (soil) conditions file.
0 1985 GCA Study - GCA is currently conducting a
study for OSW. They have collected data on approx-
imately 225 sites (RCRA, CERCLA, USGS, municipal)
and are analyzing the data for quantitative
information that can be used in calculating TOT,
and risk or environmental performance criteria.
Approximately 60 of the sites have been analyzed,
of which 37 are RCRA facilities.
4-3
-------
0 EPA Case Studies - case studies for 10 RCRA-permitted
hazardous waste land TSD facilities and one Superfund
remedial action site were developed and included as
Technical Methods for Evaluating Facility Locations:
Technical Resource Document.
The databases were evaluated in terms of the information
that they could provide on hydrogeology on the sites, aquifer
type, ground-water quality, location, and facility type.
Facility types analyzed are limited to landfills, surface
impoundments (treatment, storage, and disposal), and waste
piles. Other facility types such as deep well injection, are
not considered.
A review of available information and relevant databases
revealed three potential approaches for determining TOT^go-
The first approach, to review all available RCRA hazardous
waste land TSD facility Part B permit applications and calculate
TOT100 f°r eacl-1 facility, would have yielded the most accurate
*
results because it employed detailed facility-specific data.
However, it was rejected for two reasons: (1) the relatively
small number of Part B applications available (roughly 150);
and (2) the time necessary to carry out the approach. Gathering
the needed data from EPA Regional Offices would have required
more time than was available for this analysis.
The second approach was to use the,1982 GCA and 1983 G&M
studies to calculate TOT^oO f°r ^ aquifer flow regimes, based
on data from the 346 land TSD facilities, and project the
4-4
-------
findings for these facilities to the HWDMS universe by
statistical methods. This approach was also rejected because
it was based entirely on the generic flow regimes for the
determination of TOT^QQ, an<^ failed to employ any facility-
specific data.
The third approach, which was selected, was to augment the
second approach by combining 173 generic TOT^QO calculations
with as many (55) facility-specific determinations as could be
made from available data, short of analyzing Part B applications.
This approach balances the desire to maximize the number of
facilities measured" with the need to rely as heavily as possible
on facility-specific data.
All three approaches are less than ideal in that they
require the extrapolation of results from a facility sample
to estimate the number of facilities that are in vulnerable
settings. The statistical validity of any such extrapolation
is unclear since insufficient information exists to determine
what would be a hydrogeologically representative sample of
facilities. However, the third approach has the advantage of
employing both facility-specific and flow regime classification
data. This approach allowed evaluation of the more generic
flow regime approach by comparing the results of the flow
regime analysis to the results of the facility-specific analysis,
while making the best use of the available data. Therefore,
the third approach was judged to be the best available procedure
for estimating the total number of facilities potentially
subject to the ground-water vulnerability criterion.
4-5
-------
The vulnerability designation was determined by comparing
EPA vulnerability guidelines to the TOTioo of the facility. A
designation of vulnerable, non-vulnerable, or non-vulnerable
(storage) was assigned to each facility.
"Vulnerable" facilities are those for which TOTioo is less
than on the order of 100 years for disposal facilities or, for
treatment facilities, for which TOTioo is too short to implement
a Corrective Action Plan. "Non-vulnerable" facilities were
divided into two categories. "Non-vulnerable (storage)" repre-
*
sents those treatment or storage facilities located over ground
water in settings where TOTioo exceeds the time in which a
Corrective Action Plan can be implemented. "Non-vulnerable"
represents the remainder of non-vulnerable facilities, i.e.,
those in settings where TOTioo exceeds oh the order of 100 years
4.2 RESULTS
TOT^oo was determined for 228 facilities including 55
facilities for which facility-specific data were used and 173
for which the G&M flow regimes served as the basis for generic
TOTioo calculations. However, some of these facilities have
lost interim status (LOIS) as a result of failure to certify
compliance with certain ground-water monitoring requirements
of the Hazardous and Solid Waste Amendments of 1984. The
HWDMS database provides information on facilities that have
survived LOIS. A July 21, 1986 HWDMS printout indicated that
171 of the 228 facilites for which TOTioo was determined were
still accepting wastes. Table 4-2-1 presents by EPA Regions
the vulnerability status of these 171 facilities.
4-6
-------
TABLE 4.2-1 DISTRIBUTION OF FACILITIES BY REGION (VULNERABLE,
NON-VULNERABLE, NON-VULNERABLE (STORAGE))
Region tVulnerable ftNon-vulnerable #Non-vulnerable (storage
1
2
3
4
5
6
7
8
9
10
11
7
10
18
17
26
5
8
14
4
-
1
2
1
8
19
1
-
2
1
-
-
-
1
10
4
-
-
1
_
Totals 120 35 16
4-7
-------
The results indicate that the majority (120, or 70%) of
the 171 facilities are located in vulnerable ground-water
settings. The vulnerability status may be affected by errors
in the TOT100 calculations and errors that may be caused by
variations in the quality of hydrogeologic data in the databases.
Some errors in classification have already been identified and
are being corrected. TOTioo values for the sites included in the
analysis vary from much less than one year to more than 1000
years, but insufficient information is available to warrant the
9
rigorous construction of a distribution of TOTiQO values, which
would perhaps allow the effect of TOTiQO on vulnerability to be
evaluated stochastically.
4.3. CONTINUING EFFORTS
The EPA will continue to examine specific hazardous waste
land TSD facilities in various hydrogeologic settings to further
the facility location standards development program. Currently,
a preliminary classification scheme has been designed for the
purpose of selecting the possible settings that may adequately
correspond to a wide range of TOTioO3- Therefore, rather than
covering all hydrologic/physiographic/hydrogeologic provinces,
the scheme covers all the physical settings that govern TOT^go
from the surface to the uppermost aquifers or close receptors.
The classification scheme considers two basic systems: an
unconsolidated overburden (Regolith) and an underlying bedrock
system. As applied to the TOT^QO concept, each system is classified
according to its ability to allow water to flow through it.
4-8
-------
TABLE 4.3-1 GEOLOGIC SETTINGS
Regolith Systems
Bedrock System
1. Thin or absent
2. Alluvium/Aeolian
3. Alluvium/Aeolian with confining
layer
4. Clay
5. Clay over unconsolidated aquifer
6. Unsaturated sand
7. Permeable Glacial
8. Impermeable Glacial
a) Aquifer
b) Aquitard
a) Aquifer
b) Aquitard
a) Aquifer
b) Aquitard
a) Aquifer
b) Aquitard
a) Aquifer
b) Aquitard
a) Aquifer
b) Aquitard
a) Aquifer
b) Aquitard
a) Aquifer
b) Aquitard
4-9
-------
TABLE 4.3-2
Regolith Systems
(Unconsolidated soils sediment cover overlying bedrock)
1. Thin or absent: Is not a factor in water infiltration
2. Alluvium/ Aeolian: Unconsolidated material overlying bedrock.
Capable of allowing water to infiltrate
and be stored or move. Deltaic, fluvial,
coastal, aeolian sands, gravel, loam, -
non-glacial in origin. May contain silt/
clay lenses, overbank deposits. Can be
the uppermost aquifer, and also reach
great thicknesses.
»
Alluvium/Aeolian with confining layer: Similar to (2) above,
but with a confining layer (Unconsolidated)
between it and bedrock, such that it will
restrict flow to bedrock locally.
Clay: Any considerable thickness of clay size material
overlying bedrock. Can be saprolite, lake deposits,
peat, etc. It impedes infiltration to bedrock.
3.
Clay over Unconsolidated aquifer:
Similar to (4) above. The
implication is that it is
not a recharge area for
the underlying aquifer.
Unsaturated sand:
Permeable glacial
Similar in texture to (2) above, but lack
of recharge makes it unsaturated.
Glacier related sediments with varying
degree of permeability. Includes outwash,
eskers, stratified drift, sandy/bouldery
till, glaciofluvial, glaciomarine, brittle
glacial till, etc.
8. Impermeable glacial:
"Tight" glacial deposits such as clayey
till, lacustrine deposits, etc.
4-10
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TABLE 4.3-3 BEDROCK SYSTEMS
A. Bedrock Aquifers
1. Includes sedimentary and crystalline rocks that exhibit
secondary porosity due to:
- Faults
- Fractures, joints, and cleating (coal)
- Foliation and schistocity
- Karst (limestone, dolomite, gypsum)
- Weathered horizons (& unconformities)
- Narrow intrusion (dikes)
2. Poorly cemented and bedded sandstone and carbonate
rocks
3. Thin bedded sequences of sedimentary rocks
4. Basalt flows
B. Bedrock Aquitards
1. Well cemented, unaltered elastic and chemical sediment
2. Unaltered crystalline rock
4-11
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Table 4.3-1 shows the eight different classes in the Regolith
system and the two classes of bedrock that can be applied to
each overburden class. Table 4.3-2 presents the conceptual
definition of each Regolith class/ and Table 4.3-3 presents the
conceptual definition of each Bedrock Class.
These preliminary combinations cover a wide range of TOTjoo3
Since the classification scheme is not based on geographical
location, a site can be furt-her described as belonging in a
specific location, such as the "glaciated Appalachian Region."
One may find a second case study that fits the same TOT^QQ classi-
fication, but is located in the "glaciated Central Region." In
such a case, there will be no need to include both sites as case
studies since that specific TOTlOO setting is represented by
either one.
The intent of this continuing effort is to determine
whether case study or modeled characterizations exist for each
of the major geologic categories. If characterizations are
lacking, they will be formulated and refined during the location
standards development process.
4-12
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5.0 REFERENCES
GAG (Carcinogen Assessment Group), 1984. Relative Carcinogenic
Potencies Among 54 Chemicals Evaluated by the Carcinogen
Assessment Group as Suspect Human Carcinogens, Health
Assessment Document for Polychlorinated-Dibenzo-pDioxins.
EPA-600/8-84-041A, May 1984.
Freeze, A. R. and J. A. Cherry, 1979. Groundwater. Prentice
Hall, Inc., Englewood Cliffs, N.J.
Todd, David K., 1959. Ground Water Hydrology, John Wiley & Sons,
New York, 336 pp.
Theis, C. V., 1935. The relation between the- lowering of the
piezometric surface and the rate and duration of discharge of
a well using ground-water storage, Trans. Amer. Geoph. Union,
volume 16, pp. 519-524.
Thiem, G., 1906. Hydrologische Methoden, Gebhardt, Leipzig, 56 pp,
U.S. Environment Protection Agency, 1980. Water Quality Criteria
Documents; Availability. Federal Register 45:79318-79357,
November 28, 1980.
U.'S. Environment Protection Agency, July 1983. Liner/Locational
Analysis Project. Prepared by: Ertec Atlantic, Inc.
5-1
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ATTACHMENT 1
APPLICATION OF LINER LOCATION MODEL TO
THE ANALYSIS OF TIME-OF-TRAVEL CRITERIA
FOR SITING OF NEW LAND DISPOSAL FACILITIES
Prepared by Geraghty i Miller, Inc.
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Geraghry & Milic:. Inc.
APPLICATION OF LINER-LOCATION MODEL
TO THE ANALYSIS OF TIME-OF-TRAVEL CRITERIA
FOR SITING OF NEW LAND DISPOSAL FACILITIES
DRAFT FINAL REPORT
Prepared For:
U.S. ENVIRONMENTAL PROTECTION AGENCY
LAND DISPOSAL BRANCH
OFFICE OF SOLID WASTE
Washington, D.C. 20460
EPA CONTRACT 68-01-6871
WORK ASSIGMENT NO. 34
By:
GERAGHTY & MILLER, INC.
ANNAPOLIS/ MARYLAND 21401
January 1985
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Gcraghty Sc Miller, Inc
PREFACE
This report was prepared by Geraghty & Miller, Inc.
(G&M) in fulfillment of work Assignment 34 under the U.S.
Environmental Protection Agency (EPA) Contract 68-01-6871.
It will be incorporated by GCA Corporation into a larger
report that will deal with the technical issue of selecting
criteria that control the siting of new hazardous waste land
disposal facilities. The work is being performed for the
Office of Solid Waste (OSW) which has the objective of
establishing a scientific basis for a working definition of
the term "vulnerable ground water". The present working
definition is based on a time-of-travel (TOT) to a standard
distance measured along a ground-water flow line. Ground
water under landfills and disposal surface impoundments is
considered non-vulnerable if the TOT is equal to or greater
than 100 years. Ground water under storage impoundments and
waste piles is considered non-vulnerable if the travel time
is equal to or greater than 10 years.
Both hypothetical studies and real site case studies
are being developed in order to examine the health risks of
exposure to various chemicals and a range of hydrogeologic
settings that would bracket the above TOT criteria. G&M and
ICF, Inc., are performing model studies with .the liner-
location model, while Geotrans is performing site-specific
model studies to assist GCA in their analyses.
The EPA technical project monitor for this study was
Mr. Seong Hwang of the Land Disposal Branch (LOB) under
the direction of Mr. Arthur Day. The Project Manager and
Quality Assurance Officer for G&M were Don A. Lundy and
Jeffrey P. Sgambat, respectively. Other members of the G&M
team included Messers. Glenn Duffield and Robert Wright.
G&M also acknowledges significant input from the Project
Manager at GCA Corporation, Mr. Alfred Leonard and at ICF,
Mr. Baxter Jones.
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Geraghty 6t Miller, Inc
TABLE OF CONTENTS
Page
PREFACE i
SUMMARY 1
INTRODUCTION 4
CONCLUSIONS 6
METHODOLOGY 7
Scenario Development 7
Randon-Walk Model Development 13
RESULTS 22
Random-Walk Model Output. ...» . 22
Liner-Location Model Output .......... 22
Relationship Between Ground-Water
Velocity/Time-of-Travel and Peak
Concentrations 24
REFERENCES 29
APPENDICES
A. TABLES OF RANDOM-WALK MODEL OUTPUT A-1
B. GRAPHS OF RANDOM-WALK MODEL OUTPUT B-1
11
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Gcraghty & Miller, Inc.
LIST OF FIGURES
1. Orientation of a Generic Flow Field With
Respect to the Contaminant Source and the
Surface Water Outflow Boundary
(From Geraghty & Miller, 1984) 8
2. Nine Generic Ground-Water Flow Fields
Used in the Liner-Location Transport
Model Scenario 9
3. Six Generic Flow Fields Used to Study
the Time-of-Travel Criteria 11
4. Examples of Standard Breakthrough Curve
and How It May Be Adjusted to Simulate
Larger Mass Inputs and Biodegradation 19
5. Comparison of Random-Walk Model Output
With Two Analytical Solutions 21
6. Plot of Contaminant Concentrations vs.
100-ft TOT for Standard Mass Load Input
Scenarios 26
7. Plot of Peak Contaminant Concentration
vs. 100 ft. TOT for Adjusted Load (Flow
Field-Controlled) Input Scenarios . 27
iii
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Gcraghty & Miller, Inc.
LIST OF TABLES
Face
1. Contaminant Velocities, Dispersivities,
and Effective Porosities for Twelve
Transport Model Scenarios. . . 12
2. Source-Term Characteristics for Six
Generic Flow Fields 16
3. Critical Times and Peak Concentrations
of Breakthrough Curves and 100-ft TOTs
for Twelve Scenarios 23
iv
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Gcraghty & Miller, Inc.
SUMMARY
Geraghty & Miller, Inc., (G&M)-worked with ICF, Inc.,
and GCA Corporation to adapt and apply an existing set
of computer models developed for the 1984 liner-location
project of the Economics Analysis Branch of OSW for the
assessment of health risks associated with a range of time-
of-travel (TOT) conditions on hypothetical sites.
G&M developed six generic vertically-oriented ground-
water flow fields and a standardized contaminant source
term for simulation of contaminant mass transport to a
downgradient monitor well. A range of ground-water velo-
cities was selected to represent a range of TOTs to a well,
i.e., for travel along a 100-ft ground-water flow line that
originates at the center of the source and terminates at a
monitor well.
The source term is conceptualized as a line source
with dimensions of 1-foot wide and 32.8 ft (10 m) long.
This source has mass loading characteristics of either a
generic landfill or a storage surface impoundment. The
source life and strength for the landfill source is e^ti-
mated assuming an original mass in storage of 6 kg/ft , a
leaching rate determined by an assigned contaminant concen-
tration in the concentration in the leachate and ^facility
leakage rate controlled by ground-water velocities in the
underlying flow field. The source life for the surface
impoundment source is arbitrarily set to 30 years; source
strength is controlled by an assigned contaminant concen-
tration and a leachate release rate dictated by the flow
field.
To simulate these conditions, G&M used the Random-Walk
particle tracking code of Prickett, et al. (1981). A stan-
dard mass input of one kilogram over a one-year time step
produces a standard breakthrough curve of concentration
vs. time at the well for each flow field. Contaminants
are assumed to have one of two mobilities based on earlier
work in the liner-location project. , Each mobility class
represents three specific contaminants selected by GCA for
risk analyses:
Mobility Class 1 Mobility Class 2
(Rd = 1.3) (Rd - 32)
Acrylonitrile Benzene
Phenol Xylene
Chromium VI Nickel
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Gcraghty & Miller, Inc.
With input from G4M, ICF adjusted the standard break-
through curves to account for the following:
Concentration in the leachate
(either equal to saturation or 1/10 saturation
concentration)
Leachate release rate
(controlled by the underlying flow field)
. Dispersion in the third dimension
(at a right angle to the vertical plane of the flow
field)
Attenuation and time delays caused by transport through
the unsaturated zone and biodegradation in the saturated
zone are ignored in the analysis. With a modified liner-
location model code, ICF simulated contaminant concentra-
tions and individual health risks at the end of the fol-
lowing time periods: 50, 100, 200, 500, and 1000 years, and
at steady state, for the landfill and surface impoundment
sources with the above two source concentration assumptions.
•*
G&M studied the relationship of peak concentrations to
ground-water velocities and TOT under both equal and flow
field-controlled mass input conditions. Equal mass inputs
could be controlled by either the facility design/failure
mode or an underlying unsaturated zone. Unequal flow field
controlled inputs would be the expected result of a low-
permeability and/or low-flux environment.
For all hydrogeologic settings considered, except those
involving diffusion-controlled transport with large (two-
orders-of-magnitude) contrasts between multilayer veloci-
ties/ peak concentrations produced by equal mass releases at
the source are inversely related to velocity and positively
related to TOT. Where mass releases are controlled by
the flow field/ concentrations are positively related to
velocity and inversely related to TOT for all settings,
including diffusion-controlled transport with high velocity
contrasts.
The apparent reversal of relationships between con-
centration and velocity/TOT points up the importance of
the source term in the model. It also raises an issue
concerning to what degree low-velocity flow fields will
actually limit mass loadings from facilities located in
these settings. G&M believes that in most cases mass
loading rates are controlled by the underlying flow field.
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Gcraghcy & Miller, Inc.
Prom this modeling study, it is clear that the lowest
concentrations are associated with settings that involve
very low velocity surficial layers (with diffusion-con-
trolled transport) overlying an aquifer that would otherwise
have received higher inputs of contaminants and would not
have met current TOT criteria.
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Gcraghty & Miller, Inc.
INTRODUCTION.
This report will document the application of a Random-
Walk mass transport model for estimating concentrations of
contaminants at hypothetical wells downgradient of a leaking
generic landfill or storage surface impoundment. The model
application is an extension of an earlier modeling study by
G4M which constituted part of Phase I of the liner-location
project for the Economic Analysis Branch (EAB) -(Geraghty &
Miller, Inc., 1984). The current study for Land Disposal
Branch (LDB) draws heavily from the previous study which is
now documented in a draft final report entitled "Liner-
Location Risk Analysis Model". Several significant changes
were required in applying the model to the current study, as
documented below.
Model scenarios developed in the liner-location project
were based in part on a national survey of water-supply
aquifer characteristics. Ground-water velocities assigned
to model flow fields in that project ranged from about 1.6
to 33,000 ft/yr (0.5 to 10,000 m/yr). For that reason,
they essentially represented 100-ft time-of-travel (TOT)
scenarios that would have ranged from 0.003 to 63 years.
New scenarios developed for the current study represent
100-ft TOTs that range from about 10 to 1083 years. Based
on data generated in G&M's aquifer survey, these new sce-
narios represent underdeveloped aquifers in arid regions
associated with low recharge settings, or what is more
likely, low-permeability non-aquifers in all climatic
settings.
Within the constraints of this project, low-velocity
hydrogeologic settings had to be conceptualized as being
composed of one or two layers of homogenous, isotropic
porous media. Real-world complexities such as natural
variations in layer geometry and permeability were not
simulated. The processes of flow and transport within
an unsaturated zone were also not simulated.
Our modeling effort is further limited by significant
assumptions concerning the source of contamination. Sources
behave in simple predictable ways, and do not alter the
assumed natural rate of ground-water flow through the model
flow fields. Moreover, sources are small with simple
geometries, and do not create the magnitude of mass loadings
that could be simulated for large areal sources.
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Miller, Inc.
The models used in this study are limited in repre-
senting all complexities that can be observed on real
sites. However, they are very useful in a comparative
analysis which has the objective of identifying general
and fundamental relationships between velocity/TOT and
concentrations/risks.
There are two primary objectives to G&M's scope of
work. The first objective was to develop new scenarios and
provide ICF with model output that would be used in the
liner-location model (or some derivative of that model) that
would provide numerical estimates of health risks to a
hypothetical exposed population. The second objective was
to establish the general relationships between TOT and
concentration of contaminants observed at a specified
distance downgradient. The specified distance was set at an
arbritary 100-ft length measured along a centrally located
flow line orignating from the source of contamination and
terminating at a monitor well. Because the ground-water
velocity (not the contaminant velocity) is the key model
variable that controls TOT, the relationship between
velocity and concentration is equally important • and was
studied.
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Gctaghty & Miller, Inc.
CONCLUSIONS
Liner-location model runs by G&M indicate a very wide
range of concentrations resulting from six ground-water
contaminants emanating from two contaminant sources located
within six hydrogeologic settings. Based on Random-Walk
transport model simulations, the following conclusions can
be drawn concerning TOT/ ground-water velocities and peak
contaminant concentrations:
1. Peak concentrations decrease with increasing TOTs
(with decreasing ground-water velocities) when the
contaminant mass input is rate-limited by the
underlying ground-water flow field, all other
parameters held equal.
2. Peak concentrations increase with increasing TOTs
(with decreasing ground-water velocities) when mass
input at the source and all other model parameters
are held equal.
3. A low-velocity, near-surface layer can signifi-
cantly increase the TOT from a facility to any
given distance in an underlying uppermost aquifer
and also decrease peak concentrations in the same.
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eraght? i"c Miller, Inc.
METHODOLOGY
The technical approach used by G&M- to meet the project
objectives proceeded through the following four steps:
Developed new model scenarios with input from LDB
Examined the existing liner-location models to see
if they were suitable in present form for applica-
tion to the new scenarios
Made model changes, performed the simulations, and
delivered output to ICF for their risk estimates
Analyzed the output from the Random-Walk model and
identified basic relationships between TOT/ground-
water velocity and peak contaminant concentrations
and breakthrough times.
Scenario Development
Scenarios are identified in this project by- the same
characteristics that were used in the previous liner-
location project. A mass transport model scenario is
identified on the basis of three characteristics -- a
generic ground-water flow field, a contaminant mobility
class, and a distance to an exposure point.
The flow field is conceptualized as a two-dimensional
vertical plane extending beneath the contaminant source to
a depth that represents the base of shallow ground-water
circulation beneath the site. ' Unlike the flow systems of
the liner location project, the unsaturated zone is elim-
inated in the current analyses. The velocity field within
the generic flow system was not simulated, nor was it based
on a national survey as was done with the liner-location
project. Rather, a range of velocities and dimensions
were arbitrarily assigned to the generic settings in order
to bracket the TOT criteria currently under consideration
by LDB.
Figure 1 shows the conceptual orientation of a flow
field with respect to a source area and a generic exposure
point developed in the liner-location project. Figure 2
shows the nine generic flow fields used in the liner-
location project; these were developed from a survey of 67
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MODEL
SOURCE AREA>
TOTAL FACILITY
SOURCE AREA
PARTICLE PLUME;
te ___
Figure 1.
Orientation of a Generic Flow Field with Respect
to the Contaminant Source and the Surface Water
Outflow Boundary (from Geraghty & Miller, 1984).
8
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OIM/Y
MM
IO M/Y • .
1 M/Y
MM
IOOM/Y • i
10 M/Y
MM
lOOOM/Y • .
IOOM/Y
30 M
10,000 M/Y -. .
1000 M/Y
ISM
MM
x Voos M/Y — y /.//' .
IOOM/Y
\
t M/Y
EXPLANATION
50 M
tOM
1
1
:OM/Y
I
01 M/Y
boundary
)OM
-
Woitr toblt boundary
\
IM/Y
boundary
No-llOw '
boundort
ISM
15 M
\ M/Y
1
1M/Y
MM
MM
MM
IOM/Y •
O.S M/Y
IOOM/Y
AVERAGE UNEAR GSCUNOwATER VELOCITY VECTORS
^ETERS/YEifl) THROUGH £iCM LitER OF SATURATED
MATERIAL WITH CONSTANT THICKNESS (METERS).
CROSS-HATCH USES INDICATE LAYER IS A NON-AQUIFER.
I M/Y
Figure 2. Nine Generic Ground Water Flow Fields Used in
the Liner-Location Transport Model Scenarios.
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uglny -& Miller, Inc.
case studies of regional water-supply aquifers in all major
ground-water regions of the U.S. (as defined by the U.S.
Geological Survey; McGuiness, 1963). Although useful for
studying risks of ground-water exposure from contaminated
aquifers, the generic settings in Figure 2 all have TOT
values to 100-ft distances that are less than 100 years.
Figure 3 shows six additional generic flow fields devel-
oped for the current study. Two generic flow fields shown
in Figure 3 were developed to provide a way of testing
risks at the TOT values that are equal to the proposed
criteria of 100 years for landfills and disposal surface
impoundments, and 10 years for storage surface impoundments
and waste piles (flow fields K, L, respectively). Four
other new flow fields were created to provide concentration
and risk estimates for TOT values that were larger than
these (flow fields J, M, N, and 0).
Three ground-water contaminants from each of two
mobility classes were selected by GCA for the current
analysis. In Mobility Class 1, defined by a retardation
factor (Rd) equal to 1.3, acrylonitrile, phenol, and chro-
mium VI were selected. In Mobility Class 2, having a Rd
equal to 32, GCA selected benzene, xylene, and nickel.
The six generic flow fields and two mobility classes
combine to make 12 mass transport model scenarios for
simulation. Table 1 shows additional model parameters that
were used for these scenarios. Contaminant velocities were
calculated with the ground-water vel .cities shown in Figure
3 and the two Rd factors discussed above. Dispersivities
are estimated on the basis of literature values and work
performed in the liner-location project, allowing for some
adjustment of low velocity, diffusion-controlled movement to
be discussed later. Effective porosities are also based on
work done in the liner-location project (Geraghty & Miller,
1984). \s shown in Table 1, "Layer 1" refers to the single
layer of flow fields J, K, and L, or the upper layers of
flow fields M, N, and 0. This layer is consistently equal
to 20-ft thick in the single layer classes and 10-ft thick
in the double layer classes. Layer 2, the underlying layer
in flow fields M, N, and 0, is consistently set to 20-ft
thick.
10
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Gcraghty-& Miller, Inc.
K
FT/YR
t.OI FT/YR
1 FT/YR
t
1 FT/YR
10 FT/YR
t
1 FT/YR
20 ft
M
N
.01 FT/YR
n
1 FT/YR
" I
.01 FT/YR
.1 FT/YR
.1 FT/YR
I.I FT/YR
1 FT/YR
f.l FT/YR
1 FT/YR
- 1 1 FT/YR
10 FT/YR
t.l FT/YR
10 ft
20 ft
EXPLANATION
War* taut.
Out-flow «4-
Boundory
10 FT/YR.
Contaminant Source
— Ground-water Velocity
I FT/YR
10 ft Layer thickness
-f- In-flow Boundary
^•No-flow Boundary
Figure 3. Six Generic Flow Fields Used to Study the
Time-of-Travel Criteria.
11
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TABLE 1.
CONTAMINANT VELOCITIES, DISPERSIVITIES, AND EFFECTIVE
POROSITIES FOR TWELVE TRANSPORT MODEL SCENARIOS
Scenario
Gratification
Horizontal
Contaminant Velocity
Dispersivity
Effective Porosity
Number3
J-1-100
J-2-100
K-1-100
K-2-100
L-1-100
L-2-100
tt-1-100
l*-2-100
N-1-100
N-2-100
0-1-100
0-2-100
Layer 1
(ft/yr)
7.7x10"^
3.1x10"-*
7.7x10*2
3.1x10"
7.7
3.1x10"'
7.7x10"^
3.1x10~4
7.7x10",
3.1x10"-*
7.7x10"!
3.1x10"^
Layer 2
(ft/yr)
—
_
— —
—
—
7.7x10"}
3.1x10"^
7.7x10"!
3.1x10"^
3!lx10"1
Laver 1
Long. Trans.
(ft) (ft)
6.6
6.6
6.6
6.6
6.6
6.6
1.0
1.0
.33
.33
6.6 •
6.6
6.6
6.6
6.6
6.6
6.6
6.6
.70
.70
.13
.13
.66
.66
Layer 2
Long. Trans.
(ft) (ft)
i
__
—
__
—
6.6
6.6
6.6
6.6
6.6
• 6.6
-
— —
—
^_
—
.66
.66
.66
.66
.66
.66
Layer 1
(percent)
10
10
20
20
.20
' 20
, 5
5
10
10
20
20
Layer 2
(percent)
—
^^
—
__
—
20
20
20
20
20
20
* Identification number = flow field - mobility class - exposure point distance, in feet
Long. * Longitudinal dispersivity, in direction that is parallel to ground-water flow
Trans. » Transverse dispersivity, in direction that is orthogonal to ground-water flow
12
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Gcraghty _& Miller, Inc.
To maintain some consistency for comparison with
the liner-location model runs, the source term is treated
as a line-source positioned at the upgradient end of the
flow field (Figure 3). The source is arbitarily set at
32.8 ft (10m) long and one ft wide. In the Random-Walk
model runs, a standard mass input of one kilogram (Kg)
(represented by 1,000 particles) is input over a 1-year
time step. Breakthrough of the one Kg mass of contaminants
is tracked through the flow fields to the hypothetical
exposure well which fully penetrates the layer of interest
(the higher velocity layer in two-layer flow fields).
Random-Walk Model Development
Because of several significant differences between
the previous and current application of the mass transport
and liner-location models, both G&M and ICF were required
to further develop the models before they could be run.
The following discussion will focus on those changes that
were made in G&M's particle tracking code which utilizes the
Random-Walk model of Prickett, Naymik, and Lonnquist • (1981).
Minor code changes were required because of the low
velocity generic flow fields and because the source terms
are handled differently from the liner-location application.
More specifically, the changes were made in order to handle
the following factors:
Longer simulation times
Shorter exposure distances
Slower ground-water velocities
Generic flow field-limited mass loading
Changes in scaling factors.
Longer simulation times and short exposure distances
were handled with trivial changes and require no further
discussion here. The effects of slower velocity on the
dispersion term and changes in the scaling factors applied
by ZCF were non-trivial and are discussed below.
13
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Gcraghty-& Miller, Inc.
Velocity and Dispersion
The spreading of contaminants through subsurface
materials is caused both by mechanical dispersion and
molecular diffusion. Under most aquifer conditions, where
ground-water velocities are greater than one foot per
year, the molecular diffusion component can be ignored.
Such was the case in the previous application for the
liner-location project. At very low velocities, such
as those seen in Figure 3 for flow field M, mechanical
dispersion is negligable relative to molecular diffusion
and this must be accounted for in the mathematical model
(Freeze and Cherry, 1979).
Because the Random-Walk model generally assumes that
diffusion is negligable, and relies on only a dispersivity
term, it was necessary to define a new term called "effec-
tive dispersivity" defined as follows:
ae
where:
a » Effective dispersivity (L)
a = Longitudinal (or tranverse) dispersivity, (L)
V = Average linear ground-water velocity (L/T)
* 2
D » Diffusion coefficient, (L /T)
In the current scenario simulations, only flow field
M was significantly affected by the diffusion coefficient.
Values of dispersivity listed in Table 1 include the dif-
fusion term.
Source Term
In the previous liner-location project, a separate
submodel developed by Pope Reid Associates was used to
simulate the stochastic process of facility failure and
mass release of contaminants from a hypothetical facility.
14
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Gewghty. & Miller, Inc.
Release rates from the Pope Reid model were generally small
enough so that the project team could ignore hydraulic
changes in the underlying generic flow fields. it was
assumed that leachate drained freely from the liner system
and, while delayed by passing through the unsaturated zone,
the leachate release rate was not limited by underlying
earth materials or by low ground-water velocities. This
methodology was considered acceptable since generic flow
fields A through I (Figure 2) had relatively large values of
velocity.
ICF's original liner-location model reads the standard
breakthrough concentrations from G&M's model output and
scales the data according to the size of the facility. It
then creates future scenarios by adding the adjusted stan-
dard concentration curves in a sequence determined by the
failure and leakage history of the Pope Reid model. ICF
modified this code to by pass the Pope Reid simulation and
assume a more simplified life expectancy of the source term.
They also deleted the scaling factor for the facility size
and added a new term to handle dispersivity in the third
dimension oriented at right angles to the vertical flow
fields.
In the current application by ICF, the Pope Reid model
was replaced with an assumption that the underlying hydro-
geologic materials would have a control on the volumetric
release rate of leachate from the source. Time and*'re-
sources did not permit simulating this rigorously under a
set of hydraulic parameters and boundary conditions.
Rather, we assumed that the vertical leakage rate from
the source was equal to the vertical seepage velocity
within the underlying flow field.
Table 2 lists for each of the six flow fields the
critical source term characteristics.that affect the leach-
ate release rate from the 32.8 ft area. As shown/ we
assumed a contamination concentration of 100,000 mg/1 in the
leachate in order to show how the mass load can range over
three orders of magnitude (from .045 to 18 kg/yr). This
high concentration is slightly larger than the most soluable
species considered, phenol (with solubility of 93,000 mg/1),
and therefore the mass loading rates represent a conserva-
tive upper-bound estimate.
To meet G&M's project objectives, it was necessary to
evaluate the effects of both the standard and flow field-
adjusted mass load source strengths. The interpretation
15
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Gcraghty, & Miller, Inc
TABLE 2.
SOURCE-TERM CHARACTERISTICS FOR SIX GENERIC FLOW FIELDS
Flow
Field
J
K
L
M
N
0
Vertical
Ground-Water
Velocity
(ft/yr)
.01
.1
1.
.01
.1
1.
Effective
Porosity
(percent)
10
20
20
5
10
20
Recharge
Per Unit
Area
(ft/yr)
.001
r
.020
.200
.0005
.010
.200
Leachate
Release
Rate
(ftVyr)
.033
.656
6.560
.016 .
.328
6.560
Mass .
Loading
(kg/yr)
.092
1.8
18.
.045
.92
18. -
Release rate is the flow field-controlled volumetric discharge
of leachate over a strip source area with dimensions of
1 ft x 32.8 ft.
Hypothetical examples assuming a contaminant concentration of
100/000 mg/1 in the leachate.
16
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Geraghty .«Sc Miller, Inc
of these two conditions deserves some discussion. The
standard mass input to all flow field scenarios can be
conceptualized as one of the following:
. The facility is engineered and fails in a consistent
way that creates an equal release of mass that is
input directly to the saturated zone of each flow
field.
. An unsaturated zone serves to spread, dilute, atten-
uate, etc. releases of different magnitudes and
thereby converts them all to equal inputs to the
saturated zone.
The flow field-controlled, adjusted mass input can be
conceptualized as follows:
. The facility is engineered and fails in a variety
of ways, however, a low rate of flux through the
cover materials or a low permeability of host mater-
ials coiGterols the actual release of mass and the
subsequent direct input to the saturated zone.
. An unsaturated zone serves to convert releases of
equal magnitude to inputs of variable magnitude that
are controlled by the low-flux, low-permeability
setting.
In G&M's opinion, the flow field-controlled situations will
be more common in low-velocity settings.
The source life for the landfill strip was calculated
by assuming an initial total mass and storage per unit
area and calculates the time to deplete the mass through
leaching. Based on mail survey data studied by ICF in the
liner-location project, G&M and ICF assumed an average
contaminant density in landfilled wastes of 0.30 kg/ft .
The average thickness of landfilled waste was assumed to be
20 feet, thereby creating a mass storage per unit area of 6
kg/ft . The leaching rate was set equal to the product of
the seepage velocity of the underlying flow field, the area
of the source, and the concentration of the particular
chemical constituent. The life of the storage surface
imp9undment source was assumed to be 30 years. Mass release
was assumed to be the product of seepage velocity of the
underlying flow field, area of the source, and concentra-
tions assumed for the particular contaminant.
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Geraghty &. Miller, Inc.
The standard breakthrough curve generated from a 1-kg
input of contaminant mass at the source is adjusted to fit
the particular mass loading conditions for each contaminant.
Figure 4 shows how the amplitude of the breakthrough curve
can be adjusted upward to simulate a loading rate of 1 .8
kg/yr, corresponding to a leachate with a contaminant
concentration of 100,000 mg/1 for flow field K (Table 2).
Figure 4 also shows this effect of biodegradation on
concentrations of the standard breakthrough curve. The
example shown is for a species that was loaded at the
standard rate of 1 kg/yr but has biodegraded with a half-
life of 20,000 days. As shown, the peak concentration is
not only smaller but occurs earlier in time. For most of
the small velocity scenarios considered in our study, a
relatively slow rate of biodegradation could yield signi-
ficant reductions in concentration at hypothetical exposure
points. Unfortunately, time and resources did not permit
establishing a half-life for the organic species which are
known to biodegrade, especially benzene and acrylonitrile.
The estimates of concentrations are, therefore, conserva-
tively large for these species.
Transverse Dispersion
One of the limitations of the earlier application of
the Random-Walk model is that dispersion of contaminants
was limited to the vertical plane and transverse dispersion
at right angles to the plane was not simulated. Because
the exposure points are centrally located along an axis
that divides the source area into two equal parts, this
does not read to major errors with large areal sources
(simulated in the liner-location project). For the current
application, however, it is necessary to consider dispersion
in the third direction.
A correction factor was determined empirically. This
was accomplished by comparing several analytical solutions
to the Random-Walk model output. The solutions for an
instantaneous mass input at a point source for one- and
two-dimensional cases (Hunt, 1978) are used for this pur-
pose. The one-dimensional equation can be converted to
a quasi two-dimensional solution by dividing the concen-
tration by the thickness of the aquifer in question. Figure
5 illustrates how, for scenario K-1-100, the 1-0 solution
adjusted by thickness is a very close match to the Random-
Walk output (scatter of points). The two-dimensional equa-
tion can similarly be converted to quasi three-dimensional
18
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\
o
6
C
o
*>
0
C
«*
C
f>
u
C
o
u
Scenario K-1-IC3
ground water velocities (ft/
horizontal- 1
v«rt tea!- .1
retardation factor- 1.3
EXPLANATION
• Ooia computed by moaii
—— Standard Srtonthrougn eurv«
^— — Source-ierm adiusted curvt
— • — Biod«qrca«d curve
450
t ime (years)
Figure 4. Examples of Standard Breakthrough Curve and How
It May be Adjusted to Simulate Layer Mass Inputs
and-Biodegradation.
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Geraghcy. & Miller, Inc
by dividing by thickness. Figure 5 illustrates the break-
through curve for the 2-D solution adjusted for vertical
thickness, which has a concentration that is small than
the quasi two-dimensional solution by a factor that ranges
from about 1/8 to 1/15. This relationship of concentrations
for the 1-D and 2-D cases appears to hold., for other velocity
fields considered in our analyses. For this reason, and
because risks are being examined at the order-of-magnitude
level, G&M advised ICF to adjust the Random-Walk model
standard curves downward by a factor of 1/10 to account for
dispersion in the third dimension.
20
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\
cj
c
o
c
0
u
c
o
u
Sc«n»rto K-1-IB0
~ — • •• D«ta gen«r»tad by
R»ndom-W»lk mod«1
(Rt1 solutions h«v« *»m« m»ss lotding
per unit «re», .830 kg/sq.ft)
as sa 75 laa 125 isa i?s zee 225 2se 2?s aea 325 ase 375 430
Ti me (yrs)
Figure 5. Comparison of Random-Walk Model Output With
Two Analytical Solutions.
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Gcraghcy. £ Miller, Inc.
RESULTS
Appendix A includes tables of output produced by
the Random-Walk model which show concentration vs. time
resulting from a standard 1-Kg mass input for 12 scenarios.
Mass loading to a surface stream is included for each
scenario as a check on the concentration breakthrough.
Appendix B presents the same output in graphical format and
includes the best fit curve to the scatter of data which is
typical of"particle tracking code output.
Random-Walk Output
Table 3 shows .the critical times and peak concentra-
tions of. the standard breakthrough curves and for break-
through curves resulting from an adjusted, flow field-
controlled mass release (Table 2). Table 3 also shows for
each of the 12 scenarios, the TOT to the 100-ft exposure
point. Under the proposed TOT criteria, flow fields L and 0
constitute vulnerabl-e conditions for landfills and disposal
impoundments. All flow fields would meet the TOT criteria
for non-vulnerable conditions for storage impoundments and
waste piles.
The adjusted load breakthrough curves represent data
used by ICF in their simulations of future concentrations.
It is important to note that the critical time of starting,
ending, and peaking of the curves are not adjusted, only the
magnitude of the concentration is adjusted.
General observations based on the one-yr mass input to
the flow fields should hold true for other transient cases
involving longer simulation times. If time is considered to
be a relevant measure of risk, scenarios involving the
lowest velocities and least mobil constituents must be
associated with the lowest risks. If concentration is the
major control on risk, Table 3 suggests that the hydrogeo-
logic setting/mobility combination, which is best suited for
reducing risks, is also sensivitive to the strength of the
source term.
Liner-Location Model Output
The original liner-location model developed by ICP
simulates a concentration and corresponding risk profile
over a 400-year simulation period. Individual risks are
computed on the assumption of a 70-year lifetime with a dose
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craghcy. & Miller, Inc
TABLE 3.
CRITICAL TIMES AND PEAK CONCENTRATIONS OF BREAKTHPOUGH
CURVES AND 100-ET TOT'S FOR TWELVE SCENARIOS
Critical Times
Scenario
Identification
J-1-100
J-2-100
K- 1-1 00
• K-2-100
L-1-100
L-2-100
^M-1-100
M-2-100
N-1-100
N-2-100
0-1-100
0-2-100
Start
(yr)
300
8,000
35
800
4
80
250
8,000
120
3,000
5
150
Peak Concentrations K Time of Travel
End Peak Time Standard Load" A
(yr) (yr) ' (mg/1)
5,000
110,000
450
11,000
53
1,100
120,000
360,000
800
20,000
120
3,500
1,250
32,270
115
3,000
12
320
1,360
33,000
260
6,440
21.5
550
42.4
1.80
19.5
.92
20.5
.87
1.2
.048
14.7
.63
9.9
.45
d justed Load"
(mg/1)
3.9
.17
35.
1.7
370.
16.
.054
.0022
4.8
.21
65.
2.9
To 100-ft
(yr)
1000
1000
100
100
10
10
1083
1083
186
186
18.6
18.6
a Standard mass load of one kilogram for one year ever the strip source area (32.8 ft )
Standard mass load adjusted by flow field-controlled leachate relase rates (Table 2).
23
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Geraghty & Miller, Inc.
based on a running average concentration over any 70-year
period. In the current study, simulation times were much
longer than 400 years and it seemed reasonable to compute
concentrations at greater intervals, assuming that the point
of concentration represents a 70-year average.
In this study, concentrations and risks are provided
by G&M and ICF, respectively, for landfills and surface
impoundment sources at the following time intervals: 50,
100, 200, 500, and 1,000 years and at steady state. Al-
though the calculated source life of both source types is
limited to several thousand years, it was necessary in some
cases to extend this in order to reach the hypothetical
steady-state case. The project team composed of G&M, GCA,
and LDB personnel agreed that the time factor begins to take
on more importance than concentrations beyond 1,000 years,
and no additional time steps between 1,000 years and the
hypothetical steady-state case are calculated.
Concentrations and risks vary over many orders-of-
magnitude and represent a total of 72 separate scenarios (2
source strength terms x 2 source types x 6 contaminants x 6
flow fields x 6 time intervals). GCA Corporation will
discuss the significance of these with respect to the TOT
criteria^.
Relationship of TOT and Velocity to Peak Concentrations
The relationships of TOT and velocity to peak concent
tratiorvs are highly depended on the source term. trus
is because the advection-dispersion-retardation models
(both analytical, numerical and particle tracking) require
that the concentration at any downgradient location is
directly proportional to both contaminant concentration
and volumetric release rate of leachate at the source.
Because the assumption of the concentration of contaminants
at the source being equal to the saturated concentration (in
pure water) is considered highly conservative, an additional
set of runs were created where the mass in storage and
contaminant concentration in the leachate is reduced by a
factor of ten. This yields a 10-fold decrease in concentra-
tions for all 72 scenarios.
Changing the concentration at the source impacts peak
concentrations but is completely independent of TOT and
velocity. The other half of the source term, the volumetric
leachate release rate can be related to TOT and velocity.
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Gcraghty- & Miller, Inc.
For the somewhat limited instances where mass loading is
independent of the setting (i.e., the same for each sce-
nario), two relationships are observed. First, in single-
layer flow systems, the concentration tends to decline with
increasing velocity to a certain point, beyond which the
concentration becomes essentially steady and the potential
exposure time decreases with increased velocity. Second,
when a lower velocity layer is positioned above the aquifer
of interest (compare settings M and N to K; and compare 0
to L), peak concentrations are reduced because of the
slow, controlled release of contaminants to the underlying
layer in which the hypothetical well is screened.
For the more prevalent situations where the mass input
is allowed to be controlled by the hydrogeologic setting and
the adjusted leachate release rates prevail, the relation-
ship of velocity to concentration changes somewhat. In
single-layer cases, peak concentrations increase in direct
proportion to increased horizontal velocities. If low
velocity layers are positioned above higher velocity layers,
peak concentrations within the latter are reduced, as they
are with the standard load input.
Figures 6 and 7 show the general relationships between
peak concentrations and TOTs for the standard and adjusted
mass load input scenarios. Figure 6 shows that peak concen-
trations generally increase with increasing TOT. A note-
worthy exception to this relationship is apparent for
scenarios involving flow field M. The order-of-magnitude
decrease in peak concentration for scenarios M-1 and M-2 is
attributed to diffusion-controlled transport in the upper
layer and to the two order-of-magnitude contrasts in veloci-
ty between the upper and lower layers of the flow field.
When these conditions prevail, peak concentrations become
less sensitive to the mass loading rate.
Figure 7 shows a more consistent relationship where
peak concentrations decline with increasing TOT values. The
change in slope of the line between scenarios 0 and N to
scenarios involving flow field M is attributed to the same
characteristics identified above. Apparently, flow field M
has a distinct advantage for minimizing contaminant concen-
trations in an underlying velocity layer. This observation
is consistent with previous work done for the liner-location
project in which it was shown that the effect of adding low
velocity layers above the aquifer of interest is to greatly
reduce peak concentrations and spread out the breakthrough
curve over longer periods of time.
25
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«*•
0
c
o
+*
10
i.
C
I)
o
c
o
u
m
u
D.
\
O)
X
O)
o
k
X
CQ
T3
10
0
•0
t.
•o
c
U)
100
10
.1
.01
001
.0001
. J-l
. L-l
\.J-2
M-2
e1
10
100
1000
10000
Time o-f Travel to 100 ft (yrs)
Figure 6. Plot of Contaminant Concentrations vs. 100-ft
TOT for Standard Mass Load Input Scenarios.
26
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O
(0
I
O
C
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O
ID
•)!
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Gerighcy,& Miller, Inc.
The apparent reversal of relationships between TOT/
velocity and concentrations is largely a function of the
source term in the model. It also raises an issue con-
cerning to what degree low-velocity flow fields will act-
ually limit mass loadings from facilities located in these
settings. However, it is clear that the lowest concentra-
tions are associated with settings that involve very low
velocity surficial layers (with diffusion-controlled trans-
port) overlying an aquifer that, by itself, would not have
an acceptable velocity to meet current TOT criteria.
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Gcraghty & Miller, Inc.
REFERENCES
Freeze, A.R., and Cherry, J.A., 1979; Groundwater, Prentice-
Hall, Englewood Cliffs, New Jersey.
Hunt, B., 1978; Dispersive Sources in Uniform Ground-Water
Flow. Journal of the Hydraulics Division, ASCE 104:
75-85.
Geraghty "& Miller, Inc., 1984; Appendix B-Subsurface Trans-
port Modeling, in Liner Location Risk Analysis Model,
report prepared by Sobatka & Co. fo'r OSW under EPA
Contract No. 68-01-6621, Work Assignments 51 and 53, 61
pp.
McGuiness, C.L., 1963; The Role of Ground Water in the
National Water Situation, U.S. Geol. Survey, Water
Supply Paper 1800, 1121 pp.
Prickett, T.A., Naymik, T.C., and Lonnquist, C.G., 1981;
A "Random-Walk" Solute Transport Model for Selected
Groundwater Quality Evaluations; Bulletin 165, 111.
State Wtr. Sur., 103 pp.
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