oEPA
Unittd State*
Environmental Protection
Agency
Off ice of
Solid Waste and
Emergency Respon**
DIRECTIVE NUMBER: 9481.00_5D
TITLE: Alternate Concentration Limit Guidance
Based on Sec. S64.94(B) Criteria Part IT
- Info. Required in Ace Demo.
APPROVAL DATE: 9/1/86
EFFECTIVE DATE: 9/1/86
ORIGINATING OFFICE:
V FINAL
D DRAFT
STATUS: j j
[ 1
osw
A- Pending OMB approval
B- Pending AA-OSWER approval
C- For review &/or comment
D- In development or circulating
REFERENCE (other document*):
headquarters
OSWER OSWER OSWER
VE DIRECTIVE DIRECTIVE Dl
-------
EPA
. ..
Wasmngton. DC 20460
OSWER Directive Initiation Request
r.:-r n, O.i< .:..c ,-f,^e
9481.00-5Q
Name of Contact Person
Vernon. Myers
Code - Branch
WMD
Telephone Numoer
38'2-4495
Lead Olfice
D OERR
B osw
D OUST
D OWPE
d AA-OSWER
Approved (or Review
Signature ol Office Director
Oaie
Title
Alternate Concentration Limit Guidance Based on Sec. 264.94(8)
Criteria Part U- Information Required in Accumulation Demonstra-
tion
Summary of Directive
Describes factors involved in setting alternate concentration
limits at land disposal facilities. Written for State and
Regional permit writers and permit applicants.
Key Words:
Groundwater, Alternate Concentration Limit
Type of Directive (Manual. Policy Directive. Announcement, etc./
Status
i __
! U Drah
i O Final
i D New
I LJ Revision
Does this Directive Supersede Previous Directivels;' | j Yes [_J No Does It Supplement Previous Directive^!' [ | Yes | | No
If "Yes" to Either Question. What Oirective fnumber, title)
Review Plan
LJ AA-OSWER D OUST
D OERR D OWPE
LJ OSW Q Regions
D OECM
D OGC
D OPPE
D
Other /Specify!
This Request Meets .OSWER Directives System Format
Signature of Lead Office Directives Officer
: Date
Signature of OSWER Directives Officer
' Date
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OSV/Lfi POLICY DIRECTIVE NO.,
94x1 00-5D
ALTERNATE CONCENTRATION LIMIT GUIDANCE
BASED ON §264.94(b) CRITERIA
PART II
CASE STUDY C
DRAFT
Office of Solid Waste
Waste Management and Economics Division
U.S. Environmental Protection Agency
401 M Street, S.W.
Washington, D.C. 20460
March 1986
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DISCLAIMER
This report has not been formally reviewed by tha u.S.
Environmental Protection Agency, and it is ',.
y/ ana ic is not approved as an
official Agency publication. The contents do not necessarUv
r.«.ct the views and poiicies of the EPA. The .ention of
products or computer models is not to be considered as an
endorsement by EPA..
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PREFACE
This case study is one of a series of examples given
to demonstrate appropriate procedures for an Alternate Con-
centration Limit (ACL) application under 40 CFR, Part 264.94(b).
The case study was designed to serve as a model to aid in
implementing the draft Part I ACL Guidance Document (June 1985).
The case studies are developed from actual site reports that
have been submitted under RCRA or CERCLA for actual facilities.
Some information presented in the site reports has been changed
to create more suitable case studies, making the case studies
hypothetical examples of ACL demonstrations.
111
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CONTENTS
Preface iii
Figures v
Tables o . . . o vi
1. Introduction 1-1
2. Site Description 2-1
Land Use . . . . ;....... 2-1
Water Use and Users 2-1
Facility Operation . . . 2-3
Hazardous Constituents in the Waste 2-5
Hazardous Constituents in Ground Water. . . . 2-5
and Surface Water
3. Hydrogeology 3-1
Regional Geology 3-1
Site Geology . . 3-3
Precipitation 3-8
Surface Water Hydrology 3-8
Ground-Water Hydrology ............ 3-10
4. -Exposure Pathways 4-1
Potential Human Exposure . . 4-1
Potential Environmental Exposure . . ... . 4-4
Maximum Allowable Ambient Concentrations. . . 4-5
5. Flow and Transport Modeling 5-1
Conceptual Flow Model 5-1
Input Data and Assumptions 5-4
Model Setup 5-5
Model Results ..... 5-9
6. Alternate Concentration Limits ..... 6-1
Ground-Water Use Controls ..... 6-1
Alternate Concentration Limits . 6-3
References 7-1
Appendices
A Physical Properties and Environmental Fate of
Hazardous Constituents: 1,1,1-Trichloroethane
and Toluene A-l
B Typical Wetland Species for County in Which
Site C is Located B-l
C Description of RANDOM-WALK Solute Transport Model. C-l
D Ground-Water Elevations Simulated by RANDOM-WALK
Model for Local Grid . . D-l
IV
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FIGURES
Number Page
2-1 Land uses and offsite well locations 2-2
2-2 Site layout 2-4
2-3 Monitoring well locations ' 2-8
2-4 Isopleths for 1,1,1-trichloroethane . . . 2-9
3-1 Regional topography ......'.. 3-2
3-2 Boring location map 3-5
3-3 Cross section A-A1 ..... .3-6
3-4 Cross section B-B1 3-7
3-5 Ground-water contours . . 3-2
4-1 Flow diagram of pollutant, migration 4-2
5-1 Regional and local model areas . . . 5--2
5-2 Regional grid having a constant spacing of 200 feet. . 5-7
5-3 . Transfer of boundary conditions 5-8
5-4 Simulated 1,1,1-trichloroethane isopleths after .... 5-11
20 years
5-5 Simulated compliance point and receptor point. ..... 5-13
concentrations, over time
6-1 Ground-water Control Strategy 6-2
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TABLES " . '
Number Page
2-1 Inventory of wells within 1/2 mile of Facility C . . . 2-3
2-2 Hazardous constituents suspected to be present .... 2-6
at Facility C .
2-3 Analytical data in 1,1,1-trichloroethane 2-10
2-4 Analytical data for toluene 2-11
3-1 Monthly precipitation data 3-9
3-2 Estimated hydraulic conductivities for ........ 3-14
the site aquifer
4-1 Maximum allowable ambient concentrations ....... 4-6
5-1 Head calibration table ...... 5-10
5-2 Attenuation factors . 5-14
6-1 Alternate Concentration Limit Assumptions. ...... 6-4
6-2 Proposed alternate concentration limits 6-5"
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SECTION 1
INTRODUCTION
This document is an example application by Facility C for
Alternative Concentration Limits (ACLs) under 40 CFR 264.94 for.
hazardous constituents which have been detected in the ground
water near to the facility. The constituents are toluene and
1,1,1-trichloroethane.
Facility.C is located in northeastern glacial terrain
upgradient from a wetland area. There are no residences located
between the facility and the wetland area. There are no domestic,
commercial, or industrial uses of the ground water passing beneath
the facility before the ground water discharges to the wetland
area. The ACL application is based upon an examination of 'water
'quality criteria for toluene and 1,1,1-trichloroethane in two 0
wetland receptors. The relationship between receptor concentrations
and compliance point concentrations are simulated with a numerical
model which assumes that dispersion is the only mechanism for
attenuation between these points. The application demonstrates
that there are presently no human receptors and proposes ground-water
i*
use controls that will prevent future human exposures.
The application is presented in five sections following this
introduction. They are site characteristics, hydrogeology,
exposure pathways, contaminant transport model, and proposed
ACLs. The ACL factors listed in 40 CFR 264.94(b) are discussed
within these five sections.
1-1
-------
I
ro
Figure 2-1. Land use and offsite well locations.
-------
will show, all of these wells are located upgradient from the
facility. The three wells that are within 1/2 mile of the facility
are described in further detail in Table 2-1.
TABLE 2-1. INVENTORY OF WELLS WITHIN 1/2 MILE OF FACILITY C
Well Number
R-l
R-2
R-3
\
Use
domestic
domestic
domestic
Ground
elevation
(ft)
495
496
503
Well
depth
(ft)
20
20.
25
Approximate
depth to water
(ft) '
9
10
16 -
The cranberry bog located 1-1/4 mile to the southwest of the
facility is a water-intensive agricultural operation. The -bo.q
is irrigated with waters from Pond»A during harvest.and periods
of drought.
Pond A is used for sport fishing by local residents. Pond B
is larger and more accessable than Pond A, and is used for swimming,
boating, fishing and other water recreation.
FACILITY OPERATION
Facility C is currently, in post-closure operation. The
facility had consisted of four clay lined surface impoundments
which, between 1977 and 1982, received bulk and containerized
hazardous wastes generated by nearby industrial facilities. These
surface impoundments are shown in Figure 2-2. Ground-water con-
tamination by toluene and 1,1,1-trichloroethane was detected in
2-3
-------
-3-5Q
^ -560
r i IS // '
*'' \ f/r /
"'/ y&i
f ' JMW-I
0 Ifecrigff^
, M Va^l^
1 \ \
1 \
/ \
/ \
<
V A
\ > ~~
4 N
\ ^
\
m \
*/ \
\ A/^x \
* i > ^°
^^^^"^ff^^^fc^T "^
*"j
1
1
1
/
/
/
360
"00 200 300
SCALE, fttt
Figure 2-2. Site layout.
2-4
-------
1978, and appeared to originate from leaks in at least two of
the four units: the western disposal cell and the northwest
disposal cell. Efforts were made to contain the leaks in 1978,
1979, and 1980. The.units were removed from service in 1982,
when it was determined that the leaks could not be contained.
In 1983; the bulk and containerized wastes and sludges were
removed from the surface impoundments and the units were capped
and graded. However, some contaminated soils were not removed
i
and the ground-water quality did not return to background levels.
The incomplete source removal necessitated that the facility meet
post-closure requirements under §§264.117-264.120 including site
maintenance and" monitoring requirements. The post-closure monitoring
program has continued to detect 1,1,1-trichloroethane and toluene.
Furthe-r--details on the operating characteristics of the facility
are provided in the Part B application.
HAZARDOUS CONSTITUENTS IN THE WASTE
Accurate records were not maintained at the time that hazardous
wastes were deposited at this site. The list of constituents
suspected to be present at this site has been developed from
sampling-and analysis of waste materials removed from the site, and
)
soils on or near the site. The list of contaminants detected is
presented in Table 2-2.
HAZARDOUS CONSTITUENTS IN GROUND WATER AND SURFACE WATER
s
1,1,1-Trichloroethane and toluene have persisted in the ground
water beneath the site and in the downgradient surface waters.
2-5
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o*«-" QMw.7 ^,r
W MW-270 fC
Figure 2-3. Monitoring well locations.
2-8
-------
O.I MW-200 \M* !V£
W-9
Figure 2-4. Isoplechs for 1,1,1 trichloroethane (ppm)(Based on
maximum concentrations detected between 1978 and
1984).
2-9
-------
TABLE 2-3. ANALYTICAL DATA FOR 1,1,1-TRICHLOROETHANE
Sampling point
or monitoring
well
Background
MW-29
Compliance
MW-3
MW-4
MW- 9
MW-11
Northwest
Lobe
MW-5
MW-21
MW-27
MW-30
MW-31
MW-3 2
Southwest
Lobe
MW-16
MW-18
MW-22
MW-3 4
Surface Water
Samples
S-l
S-2
S-3
S-4
1978
ND
ND
ND
ND
ND
ND
NS
NS
. NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
1979
ND
ND
5.6
ND
ND
ND
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
Maximum
1980
ND
12.13
13.21
3.75
10.3
NS
NS
2.55
NS
2.81
1.87
NS
2.05
NS
NS
0.63
NS
NS
NS
concentration
1981
ND
1.78
2.45
3.44
8.8
8.02
NS
1.55
ND
1.80
.1.6
0.87
1.35
0.09
NS
1.64
0.76
NS
NS
1982
ND
0.24
1.72
0.62
2.4
6.08
3.6
1.28
ND
1.93
NS
0.61
0.42
0.07
ND
0.09
0.03
0.35
ND
(mg/1)
1983
ND
ND
. 1.4
0.15
1.06
1 . 77
NS
0.11
ND
0.21
NS
0.18
0.10
NS
ND
ND
ND
0.16
ND
1984
ND
ND
0.3
0.03
0.21
NS
NS
0.16
NS
0.25
0.12
ND
0.02
NS
NS
ND
NS
0.07
0.001
1985
ND
MD
0.06
0.03
0.02
NS
NS .
0.05
NS
0.07
0.05
ND
ND
ND
ND
ND
ND
ND
ND
ND Not detected (detection limit of 0.001 mg/1).
NS Not sampled. .
2-10
-------
TABLE 2-4. ANALYTICAL DATA.FOR TOLUENE
Sampling poin
or monitorin
well
Background
MW-29
Compliance
' MW-3
MW-4
MW-9
MW-11
Northwest
Lobe
MW-5
MW-21
MW-27
MW-30.
MW-31
MW-3 2
Southwest
Lobe
MW-16
MW-18
MW-22
MW-3 4
Surface
Water
S-l
S-2
S-3
S-4
t
g
1978
ND
107.6
1.7
3.7
ND
6.75
NS
NS
NS
NS
NS
,_
NS
NS
NS
.NS
NS
NS
NS
NS
Maximum concentration (mq/1)
1.979
ND
10.35
0.9
2.71
38.0
0.5
NS
NS
NS
NS
NS
NS .
NS
NS
NS
3.27
NS
NS
NS
1980
ND
5.02
1.20
4.03
47.1
NS
NS .
3.6
NS
20.57
2.95
NS
0.70
NS
NS
1.44
NS
NS
NS
1981
. ND
3.75
1.35
0.40
23.4
36.2
NS
3.35
ND
3.41
4.80
0.06
1.0
0.05
NS
3.81
2.43
NS
NS /
1982
ND
1.67
0.86
ND
8.62
7.3
9.05
1.39
ND
1.05
NS
0.01
ND
ND
ND
0.07
0.02
ND
0.001
' 1,983
ND
0.68
0.32
ND
2.1
0.6
NS
0.95
ND
0.83
NS '
0.007
ND
NS
ND
0.002
ND
ND
ND
1984
ND
ND
ND
ND
0.05
NS
NS
ND
NS
0.14
ND
ND
ND
NS
NS
ND
NS
0.001
ND
19.85
ND
ND
ND
ND
0.02
NS
NS
ND
NS
0.06
ND
ND
ND
NS
NS
ND
ND
0.002
ND
ND Not detected (detection limit of 0.001 mg/1).
NS Not sampled.
2-11
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their installation. Several important observations can be nade
from these tables; compliance concentrations since 1982 are
significantly less than those prior to that date; and contaminant
slugs can be observed to travel along both the northwest lobe and
the southwest lobe, taking several years to reach a surface water,
2-12
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SECTION 3
" HYDROGEOLOGY -
Facility C is located in glaciated terrain in the northeastern
United States. The local topography is characterized by small
hills and marshland. Figure 3-1 shows the location of the facility
on a hill overlooking two swamps. Constituents which have leaked
from the facility have been observed to migrate toward both
swamps. .
The geology and hydrology of this facility have been described
in detail in the Part B application. This section summarizes
the information on regional and site geology and hydrology that
is pertinent to this ACL application.
REGIONAL GEOLOGY
Surficial deposits in the site area are unconsolidated
materials of Pleistocene and Recent age which discontinuously
mantle an irregular bedrock floor. Pleistocene deposits are
glacial in origin. Recent deposits, being less abundant, consist
of stream and river alluvium, swamp deposits and talus. , During
the Pleistocene, the advancing ice sheet scoured away Pre-qlacial
soils and weathered bedrock, plucking considerable.-quantities of '
fresh rock as well. These debris were incorporated into the basal
ice. Deposition took place either directly, as lodgement till
beneath the advancing ice, or later as ablation during glacial
retreat. The latter materials were often reworked by meltwater
streams near the front of the ice sheet or adjacent to isolated
3-1
-------
OJ
I
K)
Figure,3-1. Regional topography.
-------
of sand and gravel. 'Postglacial deposits (Recent) are typically
strips of alluvial silt, sand and gravel which line stream beds.
Talus slopes are well developed at the base of cliffs where
frost action and chemical weathering have loosened weak materials
from higher elevation.. Swamp deposits are typically deposits of
organic debris silt and fine sand. Located -in topographic basins,
the swamp deposits may include layers of impure peat.
The bedrock is dominated by quartz, feldspar gneiss, though
other rock types are,present. Rock ages range from Precambian
to Pennsylvanian. The granite gneiss which dominates the quadrangle
and site area is a light gray biotite gneiss which .exhibits a
strong foliation. This foliation strikes generally northward
and dips westward, an attitude.which is present in beddina structures
in the other rock units. Locally, shear zones cross the above
foliation. In these zones, rocks are typically finer grained.
No major faults have been mapped in the quadrangle.
SITE GEOLOGY
The hill on which the site is located is composed of a .thick,
glacial deposit with many surface boulders (some reaching 5 to 8
feet in diameter). Many of the granite gneiss cobbles and boulders
exposed in pits near the site exhibit chemical weathering along
joints and between feldspar and biotite .grains (rottenstpne).
Borings indicate that the glacial deposit may be at a depth in
excess of 40 feet beneath the 8-acre disposal area, decreasing .
to approximately 20 feet near Swamp- A. Boring logs also indicate
many washed zones within the till which are comprised principally
3-3
-------
of sand and gravel. These zones of internal stratification were
clearly exposed just northeast of the disposal site. The hiqh
percentages of sand and gravel encountered in the boreholes and
exposures indicates a sandy ablation till.
Swamp A consists of some recent organic and lake deposits,
and is underlain by the same sandy, ablation till. Till in the
vicinity of Swamp B is shallow to bedrock, with occasional points
of ground-water discharge from bedrock springs.
Two geological cross sections were prepared using boring
logs compiled from field investigations. The orientation of
these cross sections is shown in Figure .3-2. The northeast-southwest
section A-A1 (Figure 3-3) runs from BRW-2 just southwest of
the disposal site, ending at MW-24. This section allows for a
subsurface interpretation adjacent to disposal 'areas and generally
perpendicular to ground-water flow. Borings MW-28 and MW-24 at
the north end of the section do not show the abundance of boulders
described in logs to the south. This absence/ of boulders may be
indicative of fine grained material deposited as outwash from
the ablation -till to the south. .However, a gravel pit 100 feet
to -the south of MW-28 exhibits many cobbles and large boulders.
Section B-B' (Figure 3-4). is roughly perpendicular to A-A1
and provides a subsurface interpretation along a ground-water
flow line typical of the northwest lobe. The section transects
the north end of the west disposal cell. A predominance of sand
and gravel in borings at the west end of section B-B1 suggests
deposition of washed material at lower elevations. Though some
3-4
-------
BEDROCK
SPRING
N
Figure 3-2. Boring locations.
3-5
-------
ElfVAIIOM FHOU
"HIUHAHr
WHCH UAHK
,.0«CTIO
WIST ciu.
cm
to* fftou TNI CAST
FACILITY c
'ftOPCHTY IIMC
A'
UW24
M C IAHO I OMAVtl UHAMIt OHf«
III' a»0-
HOMIlOIIIAt tCAti
COMTACI (OAIHCO WHCHt INftHMtOJ
NCFUIAL
f O» : I HO OF (ORMU
* : MfEHHEO 1AHO Una OH
MMOC* TOCOaHACMV
NO(f : TKl TVnCALLV tHOWN A*
A COlaiNAnON
-------
B
(VALUATION F*OM
INCH UANK
MWtl
CELL
Figure 3-4. Cross section B-B'
3-7
-------
pockets of fine sand and gravel exists in the borings higher on
the hill, they are 'expected to be very localized.
Fractured bedrock beneath the site has been recorded in
several borings. Boring log BRW-1 shows fractures at 45 feet
below ground surface with an associated pumping rate of 45 gpm.
Boring BRW-2 shows weathered gneiss at 85 feet with a pump rate
of 12 gpm.
PRECIPITATION
Thirty years of precipitation data are available -from a
meteorological station located 20 miles to the northeast of the
facility. The average annual precipitation is 42.6 inches and
varies relatively little from month to month. The monthly average
precipitation is shown in Table 3-1.
SURFACE WATER HYDROLOGY
Surface water runoff from the disposal site enters two
subbasins of the Brook A watershed. The Swamp A watershed
is separated from the watershed to the east by a surface
water divide (see Figure 3-1). Most surface runoff flows
towards the Swamp A subbasin. _Water entering Swamp A flows
to Pond A and into the cranbery bog (see Figure 2-1). A
much smaller amount of.site surface runoff flows to the
southwest in a small subbasin which drains to Swamp B.
Water entering Swamp B flows to Pond B and into the cranbe-ry
bog (see Figure 2-1).
3-8
-------
TABLE 3-1. MONTHLY PRECIPITATION DATA
Mean
Mean Days with
Precipitation Precipitation
(inches) over 0.01 inch.
Length of Record (yrs) 30 14
January , . 4.03 11
February 3.76 11
March 4.05 11
April 3.86 11
May . 3.35 .11
June 2.70 10
July ' 2.8'5 10
August 3.96 - 10
September 3.44 9
October . 3.00 8
November 4.03 11
December . 3.57 11
Total 42.60 124
Sources U.S. Department of Commerce.
3-9
-------
GROUND-WATER HYDROLOGY
. Ground water beneath the site flows in two, hydraulically
interconnected water-bearing formations. The upper portion of
the aquifer consists of unconsolidated, sandy glacial till and
swamp deposits, which' is underlain by approximately 30 feet of
fractured bedrock. Hydraulic conductivities for the unconsolidated
deposits range from 1.0 x 10~4 to 3.0 x 10~3 cm/sec, with
similar values for the bedrock. Vertical movement of water from
one formation to the other is governed by local differences in
conductivity between till and bedrock, and by differences in
hydrostatic pressure between the two units.
In the upland area of the disposal site, piezometric head
elevations from wells screened in bedrock are lower than elevations
measured in nearby overburden wells. This difference refl.e-c.tsa
downward component of flow, and consequently the disposal site
represents an area of ground-water recharge. For lowland
areas, the gradients are reversed and ground water discharges into
the swamp deposits. Evidence to support this conclusion can be
obtained from water level records taken from nested piezometers
(MW-35 and MW-33) in the vicinity of Swamp A. This scenario is
typical of the 'glaciated terrain in the northeast. In the vicinity
of Swamp B, the till is shallow to bedrock, resulting in occasional
points of ground-water discharge. The bedrock spring noted in
Figure 3-1 is an example of this mechanism.
Data obtained from the monitoring well network currently
established at the site were used to develop a ground-water
3-10
-------
contour map (Figure 3-5). The upland area immediately west of
the site between Swamp A and Swamp B (see Figure- 3-1) -is believed
to act as a ground-water divide due to its elevation and relatively
low permeability (10-5 to 10~4). Because of the site's
location on a convex hill slope, and the presence of ,a possible
ground-water divide through the disposal area'/ contaminants
introduced at the site have been observed to miqrate as two
lobes to the northwest and southwest. The regional, surface
water divide to the east (Figure 3-1) is believed to correspond
to a similar ground-water divide. Under natural conditions, the
flow directions dictated by the local and regional divides are
believed to remain throughout the seasons.
1
Although no bedrock boring logs exist for the area to the
west of Swamp A to determine the ext.ent of weathering/fracturing
at depth, seismic profiles indicate a water table surface that
follows bedrock topography. The northern-most seismic data
points in the west profile show a higher water table elevation
in the west bedrock outcrop than that of Swamp A. This implies
ground-water flow from the west towards Swamp A.
Almost all of the ground water which flows from the site
originates from precipitation. Due to its proximity to a ground-
water divide (believed to coincide with the surface water divide
of Figure 3-1), the site represents an upland headwaters area
where the regional ground-water flow contribution.is expected
to be limited. . In the Swamp A subbasin, virtually all of the
water leaves as evapotranspiration and runoff to the swamp.
3-11 '
-------
WATER SURFACE
477.Q fttl
Figure 3-5. Ground water contours (feet above msl).
3-12
-------
Under natural conditions with no major water diversions, there
is no interbasin -transfer of water.
The aquifer properties of principal interest to the analysis
in Section 5 are hydraulic conductivity, effective porosity, and
dispersivity. The results of field and laboratory tests to
determine these parameters are described in detail .in the Part B
application and are summarized below.
Hydraulic Conductivity
Field data available for a determination of hydraulic
conductivity include: '
0 Aquifer tests performed at wells BRW-1 and BRW-2;
0 An- analysis of grain-size distributions for soil
samples obtained during installation of wells MW-8,
MW-9, and MW-19; and
0 A minimum of five slug tests at each of the fallowing
wells: MW-27 (bedrock) and MW-5 and MW-15 (overburden).
Table 3-2 summarizes this data. Conductivity values are generally
within one order of magnitude in the two major water-bearing
formations.
Effective Porosity
The field data available for analysis of effective porosity
are the two aquifer tests at BRW-1 and BRW-2, where the calculated
values were 0.25 and 0.10, respectively. Well BRW-1 stressed
primarily overburden whereas the test at BRW-2 stressed primarily
bedrock. The resulting calculated values were consistent with
published ranges for fractured gneiss (BRW-2) and unconsolidated
sands and gravel (BRW-1).
3-13
-------
TABLE 3-2. ESTIMATED HYDRAULIC CONDUCTIVITIES FOR-THE SITE AQUIFER
Method of Analysis
Hydraulic Conductivity
feet/day cm/sec
Aquifer Test
BRW-ia
BRW-2a
8.
9.
2
1
2.
3.
9
2
X
X
10-3
10-3
Grain-size Distribution
Slug
MW-8
MW-9
MW-19
Testb
MW-27a
MW-5
MW-15
0.
5.
7.
0.
3.
2.
8
0
7
6
4
2
2.
1.
2.
2.
1.
7.
8
8
7
1
2
8
X
X
X
X
X
X
10-4
10-3
10-3
10-J
10-3
10-4
a Bedrock wells.
b Average values.
Dispersivity
A chloride tracer study was performed at the site and is
documented in the Part B application. Data obtained from the
tracer study provides calculated dispersivities of 208 feet
(longitudinal) and 53 feet (transverse). These values are within
published ranges for sites of similar scale.and aquifer
characteristics (Freeze and Cherry, 1979).
3-14
-------
SECTION 4
EXPOSURE PATHWAYS
Contaminants leaching from Facility C will generally follow
the fate and transport paths outlined in Figure 4-1. The northwest
lobe of contamination flows toward Swamp A and on to Pond A and
the cranberry bog, all the while being diminished by a variety
of physical/ chemical and biological mechanisms. The southwest
lobe of contamination flows toward the bedrock spri.ng and then
to Swamp B, Pond B and the cranberry bog. Exposures to contaminants
released from the facility may occur at various po-ints along
these paths, but due to the probable attenuation of the
plume by dilution and volatilization, the more critical points
of exposure will tend to be closer to the source.
This 'analysis of potential exposures te the hazardous constituents
considers both human and environmental receptors.. No current Human
exposures to contaminants from this facility have been identified,
but humans could be exposed to contaminants through contact with'
ground water, air, the swamp or pond surface waters, or through a
contaminated food chain. Ecosystems in the swamps, ponds, or
cranberry bog are all potential contaminant receptors.
POTENTIAL HUMAN EXPOSURE
Exposure to Contaminated Drinking Water
At'this time there are no wells in the ground water passing
.beneath the site; however, there are no local or State laws to
prevent a person from drilling a well into the contaminant plume.
4-1
-------
NORTHEAST
CELL
NORTHWEST NORTHWEST
CELL AGROUND WATER
LOBS
SOUTH
CELL
SOUTHWEST
GROUND WATER-
LOBE
ADSORPTION
ONTO SOIL
BIODEGRADATION
DISCHARGE TO
SWAMP A
SURFACE WATER
VOLATILIZATION TO
AMBIENT AIR
ADSORPTION
ONTO SOIL
BIODEGRAOATION
DISCHARGE TO
SWAMP B
SURFACE
WATER
BEDROCK
SPRING
DISCHARGE TO
POND A
VOLATILIZATION TO
AMBIENT AIR
DISCHARGE TO
POND B
CRANBERRY
BOG
Figure 4-1 Flow diagram of pollutant migration pathways/fate.
4-2'
-------
Regular ingestion of water from such a well could pose a significant
health risk, since 1,1,1-trichloroethane and toluene are recognized
i
by EPA to be systemic toxicants.
The likelihood of future drinking water exposure to the
contaminated ground water is small because the high water table
and poor load-bearing capacity make the land unsuitable for residential
structures. Section 6 proposes controls which will assure that no
such well is constructed. .
Exposure to Contaminated Food Chain
Both of the constituents addressed in this application have
water quality criteria derived by EPA. The criteria established
to protect human health from toxic properties of 1,1,1-trichloroethane
ingested, through water and contaminated aquatic organisms or
ingested through contaminated aquatic organisms alone, are 18.4 mg/1
and 1.03 gm/1 respectively. The criteria established to protect human
health fronr the toxic properties of toluene ingested through water and
contaminated aquatic organisms,.or ingested through contaminated aquatic
organisms alone, are 14.3 mg/1 and 424 mg/1, respectively (EPA, 1980).
Direct Contact
Direct contact with contaminated surface water is a potential
route of exposure, since contaminated ground water from Facility
C discharges to Swamp A, where it flows as surface water into
Pond A. Similarly, contaminated ground water also discharges to
Swamp B where it flows into Pond B. Pond A is used by local
residents for sport fishing. Pond B, being larger and more
accessible than Pond A, is used for fishing, boating, and swimming.
4-3
-------
There is a possibility that people may come into contact with
the waters of Pond A while fishing and the waters of Pond B through
swimming, boating, fishing, or other recreational activities.
However, the.potential for nearby residents to come into contact
with soils, sediments or water in the swamps must be weighed
against the probability of people gaining access to these areas.
Aerial photographs of the site (presented in the Part B applica-
tion) show dense vegetation. Investigation teams have also
reported difficulty accessing some areas of the swamp. The'
controls presented in Section 6 will take further steps to prevent
access.
POTENTIAL ENVIRONMENTAL EXPOSURE
Three types of environments were initially- considered at risk
of exposure: the marshes, ponds, and cranberry bog. However/
sampling data (shown in the Part B application) reveals that the
cranberry crop is not at risk of exposure to contaminants from
this site for several reasons. Contaminants from the site are
discharged to the swamps where they are volatilized, biodegraded,
and adsorbed onto peat. Very small amounts, of contaminants have
been detected in the inlet to Pond A, from Swamp A. Those .
contaminants are further degraded, diluted, and volatilized in
the pond water. Contaminants from the site have not and are not
expected to reach the cranberry crop at the south side of Pond A.
No contaminants have been detected in Pond B. '
4-4
-------
Assessment of-hydrogeologic data available.for the site
indicates that ground water from the site is discharging into
the Swamp A, Swamp B, and the bedrock spring. The major impact
will be on organisms in or using these surface waters.
The swamp environments contain plant and animal organisms
that may be adversely affected by site contaminants. While no
detailed ecological data have been gathered on the biota inhabiting
the Swamp A, it is possible to identify species that are known
to occur in nearby marsh areas. This information may be.useful
in tracing possible pathways of contaminant migration. The
information provided in Appendix-A was supplied by the U.S. Fish
and Wildlife Service. The data are extracted from the New England
Animal Species Data Base for the county JLn which the site is
located. Three distinct habT&at types are given: 1) emergent
wetland (Table B-l); 2) scrub/shrub wetland (Table B-2); and 3)
forested wetland (Table B-3). The aerial photographs taken of
the site show swamp maple and other trees. There is no reported
evidence of gross vegetative stress at the site.
Endangered Species
No endangered species have been identified in the vicinity
of Facility C and none are suspected to inhabit the area. The
U.S. Fish and Wildlife Service has provided a letter to this
effect that is included in the Part B application.
MAXIMUM ALLOWABLE AMBIENT CONCENTRATIONS
The maximum ambient concentrations xare based on environmental
exposure in the swamp areas. Human exposure to contaminants in
4-5
-------
SCALE, Utt
Figure 5-1. Regional and local areas.
5-2
-------
of ground water-can no longer be transmitted through tight bedrock
joints and fractures. Surface water bodies are represented as
constant head boundaries. The other boundaries represented
in a plan view of the model area are represented by no-flow
streamlines.
The conceptual aquifer is thus represented as a single layer
unconfined aquifer where flow is horizontal. Although vertical
gradients have been measured at the site, they are generally
small and should not -significantly invalidate an assumption of
horizontal flow. The single-layer approach also assumes similar
aquifer characteristics for both till and bedrock. Data obtained
from these two water-bearing formations support this assumption.
The"RANDOM-WALK model was selected to simulate the two-dimensional
flow and contaminant transport characteristics of'thi.s site.
The RANDOM-WALK technique of Modeling contaminant transport
has been proven to be a sound engineering tool through many
years of testing. This model first generates a flow field
utilizing the finite-difference method. From the flow field,
velocities are calculated and particles introduced to the system
are "tracked" through the aquifer in response to the processes
of advection and dispersion. . For a more detailed discussion of
this model, see Appendix C.
Some important characteristics of 'the RANDOM-WALK technique
include: (1) an ability to represent the dynamics of a two-
dimensional flow field and the effects of recharge due to rainfall,
and (2) dispersion coefficients are randomly modified to accommodate
5-3
-------
uncertainties associated with a range of possible dispersivity
values, and (3) "due to the random nature of particle movement,
some judgment is required when reviewing model output. For example,
where concentration is very low, one node within the model may
exhibit no contamination whereas surrounding nodes may reveal
contamination. The random particle movement effects the precision
of the simulation, but not its suitability for the ACL demonstra-
tion. With properly conservative input assumptions and cautious
interpretation of the output, this model is an appropriate tool
for ACL demonstrations.
INPUT DATA AND ASSUMPTIONS
The critical input data and assumptions for the RANDOM-WALK
model include aquifer properties, bou-ndary conditions, and pre-
cipitation recharge. The measured aquifer properties are presented
in Section 3. The hydraulic conductivity was shown to range
from. 2.lxlO~4 cm/sec (bedrock well), to 3.2xlp~3 cm/sec. For the
purpose of this model, the conductivity was set at 1.5x10"^ cm/sec
in all areas except the hill to the west of the site which lies
between the two lo'bes. The conductivity in that area was .set at
1.5xlO~4. The loSxlO"3 value lies in the middle of the range
observed for the path of the northwest lobe.
The measured values for effective porosity were 0.10 in the
fractured bedrock and 0.25 in the overburden. The model used a
value of 0.20. The relationship between effective porosity and
dispersion is inversely proportional (i.e., as effective porosity
5-4
-------
increases, both-the interstitial velocity and porosity decrease).
Thus, a conservative approach which leads to less dispersion and
higher plume concentrations will be to employ an effective porosity
near the upper end of the measured range.
The measured values for dispersivity were .208 feet (longitudinal)
and 53 feet (transverse). Following the rationale noted in the
previous paragraph, conservative values were obtained by reducing
the measured dispersivities. The model used a longitudinal
dispersivity of 100 feet and a transverse dispersivity of 25
feet.
The boundary conditions were set as constant head at the
swamps and along the low lying northeastern boundary and as
no-flow along the other"boundaries. All flow into-the model
grid was as.sumed to be via precipitation. Precipitation recharge
to the ground water was estimated by taking 30 percent of the
42.6 inch mean annual precipitation, or 12.68 inches, then roundina
down to 12 inch/yr. This 30 percent recharge value was estimated
from water budget data presented in the Part B application.
MODEL SETUP .
A three-step procedure was employed to achieve a' realistic
(but conservative) simulation of the site. The three steps are:
1) construct a regional flow model; 2) construct a local flow
model using the regional flow information to establish local
*
boundary conditions; and 3) simulate contaminant transport within
the local flow system.
5-5
-------
First, a regional flow field was defined covering the
conceptual model area shown in Figure 5-1. Constant head values
were assigned along the model boundaries comprised of surface
water bodies. To the east, an arbitrary, no-flow streamline was
established at a distance sufficiently far from the source such
that the flow field near the area of interest is practically
unaffected by the uncertainty associated with the position and
shape of this boundary. A sensitivity analysis on the no-flow
boundary showed that repositioning to different locations had no
adverse impacts on the head distribution near the area of interest,
Figure.5-2 shows the nodal discretization scheme necessary for
the finite-difference solution of regional ground water flow.
Within the regional model, aquifer properties were assumed
-ta-Jbe__c.onst'ant/ except near the topographic high west of the
site where conductivities are substantially less and ground
water mounding occurs. Uniform recharge was assumed over the
entire model area at 12-inches per year of infiltrating rainfall.
In the second step, output from the regional flow model was
used as input to a local model. The local model exhibits a
finer discretization scheme around the source area to enhance
resolution for transport modeling. Calculated head values at
selected, interior nodes were chosen as boundary conditions for
the local model, as shown in Figure 5-3. Constant head values
assigned at those nodes not present in the regional grid were
determined through linear interpolation from surrounding nodes,
but aquifer characteristics and recharge values were not changed.
5-6
-------
01
0
KEY«
BOUNDARY OF
FIXED HEAD
NODES
SITE
BOUNDARIES
BEDROCK
SPRING
200
urf-«H
Scole.feet
N
Figure 5-2. Regional grid having a constant spacing of 200 feet.
-------
FIXED BOUNDARY HEAD
FIXED HEAD FROM
REGIONAL MODEL
HEAD VALUE INTERPOLATED
FOR LOCAL MODEL
REGIONAL MODEL
AREA
LOCAL MODEL AREA
SITE BOUNDARIES
Figure .5-3. Transfer of boundary conditions from regional to local model.
5-8
-------
Thus, the overall approach maintains continuity between the
regional and local models. Table 5-1 presents a comparison
be.tween the calibrated head values and the mean observed values
at corresponding monitoring wells. The head values in the flow
model are somewhat low at several upgradient nodes (wells MW-3,
MW-28, and MW-29) and high at the lower portion of the southwest
lobe (wells MW-16, MW-22, MW-23, and MW-34). These departures
from the observed ground-water contours do not significantly
effect flow simulation between the compliance point and the .two
receptor points. Furthermore, these important flow characteristics
are reproduced in the model:. 1) predominant flow- is to the
northwest; 2) a smaller flow component travels from the site
toward the southwest; and 3) ground-water mounding is shown to
the east of the site. -
. ' *
In the third step, ground-water flow velocities were
determined from the head values in the local model. Constant 1(,
contaminant loading rates were assumed as a conservative repre-
sentation of landfill failure. Loading concentrations were set
equal to each constituents maximum solubility, which assumes
instantaneous equilibrium with source contaminants and infiltrating
rainwater. The simulation was carried out over 20 years, or until
steady state concentrations were observed at the contaminent
receptor points.
MODEL RESULTS
The model output provides contaminant distributions at each
time .step for which the model is run. Figure 5-4 presents the
5-9
-------
TABLE 5-1. HEAD CALIBRATION TABLE
Well
MW-13
' MW-4
MW-5
MW-6
MW-9
MW-13
MW-15
MW-16
MW-17
MW-19
MW-20
MW-21
MW-22
MW-23 .
MW-24
MW-25
MW-26
MW-28
MW-29
MW-31
MW-34
Nearest node3
(x,y)
17,17
17,19
' 19,20
20,19
17,15
17,13
21,10
12,10
13,19
17,24
14,16
15,21
6,8
9,6
22,27
21,15*
23,31
20,24
28,10
12,26-
5,5
Mean observed
well elevation
(ft)
497.6
495.9
496.2
500.3
497.7
498.5
502.7
483.1
488.9
490.0
490.5
490.4
465.2
467.9
491.6
503.2
487.3
495.3
517.8
, 478.7
449.6
Node
elevation
(ft)
"495.40
494.02
495.75
497.83
496.35
496.82
503.28
487.41
488.73
489.03
492.04
489.56
469.04
475.01
491.72
501.75
487.91
492.94
513.23
478.64
457.80
Difference
in elevation
(ft)
2.2
. 1.9
0.5
2.6
1.4
1.7
-0.6
-4.3
0.2
1.0
-1.5
0.8
-3.8
-7.1
-0.1
1.5
-0.6
2.4
4.6
0.06
-8.2
a Node coordinates relate to local grid shown in Figure 5-3.
5-10
-------
CONSTANT HEAD 80UNOARY
ACTUAL SWAMP
CONSTANT HEAD BOUNDARY
ACTUAL SWAMP B BOUNDARY
Figure 5-4. Simulated 1,1,1 trichloroethane isopleths after
20 years (ppm).
5-11
-------
simulated 1,1,1-trichloroethane plume for year 20. The geometry
of this plume approximates generally the observed plume geometry
shown in Figure 2-4.
The key outputs of the RANDOM-WALK model are the steady
state relationships between contaminant concentrations at the
compliance point and those at the designated receptors. Figure
5-5 presents the concentrations over time at these points. The
values in this graph represent the mean concentrations for the
sets of grid nodes which represent the compliance point and the
receptors. These concentrations are not associated with any
particular constituent/ and since the effects of dispersion do
not vary among constituents, the results can be applied to both
I/1,1-trichloroethane and toluene releases.
Table 5-2 presents the attenuation factors between the
compliance point and the two receptors. The concentration levels
at each point are average concentrations estimated from between
year 10 and year 20 of the simulation model. (Year 10 is shown
in Figure 5-5 to be the approximate time at which steady state
is reached at the furthest receptor point.) This table shows
that dispersion reduces concentration by a factor of 10.80 between
the compliance points and the bedrock spring, and by a factor of
2.2 between the compliance point and the edge of Swamp A. These
attenuation factors are rounded down to 10 and 2, respectively,
for the ACL calculations in Section 6.
The results in Table 5-2 are conservative estimates of the
expected attenuation because they do not consider the degradation
5-12
-------
I
t-~
CJ
COMPLIANCE POINT
BEDROCK SPRING
Figure 5-5. Si.ul.ted compliance point and receptor point concentrations, over tin*.
-------
that would occur,during the time required for a contaminant to
travel-from the point of compliance to Swamp A. The analytical
data in Tables 2-3 and 2-4 suggest that the true attenuation may
be greater. The maximum 1,1,1-trichloroethane concentration at
the compliance point (13.2 mg/1) is roughly 5 times the maximum
concentration at the edge of Swamp A (2.81 mg/1) and 8 times the
maximum surface water concentration (1.64 mg/1). The maximum
toluene concentration at the point of compliance (107.6 mg/1) is
also roughly 5 times the maximum concentration at the edge of
Swamp A (20.57 mg/1) and 28 times the maximum surface water
concentration (3.81 mg/1).
TABLE 5-2. ATTENUATION FACTORS
Mean
concentration3
(mg/1)
Attenuation
factorb
Compliance point
Bedrock spring
Swamp A
13.72
1.27
6.2
10.80
2.21
a Mean concentration observed at each point between year 10
and 20.
b Attenuation factor equals compliance point concentration
divided by receptor concentration.
5-14
-------
SECTION 6 '. '
ALTERNATE CONCENTRATION LIMITS
The ACLs requested for this site are based upon the contaminant
thresholds proposed in Section 4 and the attenuation factors
estimated in Section 5. The analyses presented in those sections
include the following features:
0 The critical environmental receptors are .identified as
Swamp A and tire bedrock spring.
0 There are currently no human exposure pathways, and future
human exposure will be prevented by a proposed strategy
for ground-water use. controls.
8 The transport model estimates contaminant attenuation due
to dispersion only. The roles of degradation and soil
retardation were not considered, nor was'the effect of
dilution in the receiving surface waters. Omission of
these other attenuation mechanisms produces a more
conservative result.
\
GROUND-WATER USE CONTROLS
The State considers all ground water within the State to be
subject to the prior appropriation doctrine of water rights. Under
the doctrine, the State has the authority to allocate ground-water
rights and regulate ground-water use. These ground-water rights
can be bought and sold.
To assure that no humans are exposed to contaminants released
from the facility, the owners propose to implement ground-water use
6-1
-------
Figure 6-1. Ground-water Control Strategy.
6-2
-------
controls on-a 100 acre parcel of land surrounding the facility.
The owners are currently negotiating a transfer of water rights.
for the 100 acres as shown in Figure 6-1. The area includes
Swamp A, the bedrock spring/ parts of Swamp B, and all lands
between the facility and these potential receptors. By purchasing
the water rights, the facility owners will be able to. prohibit
all uses of this ground water which could lead to human exposure
to contaminated water. Should the negotiation efforts fail, the
owners will pursue an alternative strategy of purchasing the
land and the water rights. The State Attorney General's office
has been contacted by the facility owner and has ruled that the
efforts of the facility owner are allowable under State law.
Enforcement of the ground-water use controls will be the
-responsibility of the State EPA. .
ALTERNATE CONCENTRATION LIMITS
The proposed Alternate Concentration Limits for this site
are calculated by multiplying the attenuation factors determined
in Section 5 by the allowable levels shown in Section 4. Because
these values are based upon environmental guality criteria (and
not protection of human health), they are contingent upon successful
implementation of the ground-water use controls specified above.
The important assumptions that went into calculating the ACLs are
listed in Tab.le 6-1. Most of the assumptions are conservative
in nature because of the lack of both site-specific and contaminant-
specific data. Due to these assumptions, the amount of contaminant
6-3
-------
TABLE 6-1o IMPORTANT- ACL ASSUMPTIONS
Factor
Data
Assumption
1. Contaminant Attenuation
Biodegradation
Adsorption
Dispersivity
2. Ground-water flow
Conductivity
Porosity
3. Contaminant Transport
Loading concentration
Attenuation between
POCa and POE&
4. Allowable surface water
concentrations
Acute/chronic toxicity
ratio
No site data
No site data
Site-specific data
Site-specific data
Site-specific data
No site data
Calculated based
on site jnodel
No data
Not considered
Not considered
Set at half the
measured values
Set at mid-range
of values
Set at upper-range
of values
Set at solubility
limits
Set at lowest
calculated values
Set at highest
calcualted value
a POC - Point of compliance
b POE - Point of exposure
6-4
-------
attenuation that is occurring at the site, is probably underestimated..
Likewise, the acceptable toxic effect levels of the contaminants in
the swamp are probably underestimated.
The ACLs are shown in Table 6-2. Contaminant flow toward
Swamp A is attenuated less than flow to the bedrock sprinq; therefore,
the ACLs were determined by flow to the swamp. The proposed
ACLs are 3.6 mg/1 for 1,1,1-trichloroethane and 0.35 mg/1 for
tolu'ene. The 3..6 mg/1 for 1,1,1-trichloroethane and the
0.35 mg/1 for toluene are higher than current concentrations observed
at the site. Since concentrations have been diminishing at the
site and since the major source of the contamination was removed
in 1983, the proposed ACLs are not expected to be exceeded at
any time in the future.
TABLE 6-2.
PROPOSED ALTERNATE CONCENTRATION LIMITS
Constituent
Receptor
Maximum
allowable
concentration3
(ppm)
a From Table 4-1
b Fran
Carpi iance
point Proposed
Attenuation concentration ACL
factor0 (ppm) (ppm)
1,1,1-Tri-
chloroe thane
Toluene
Swamp A
Bedrock
Spring
Swamp A
Bedrock
Spring
1.8
1.8
0.175
0.175
2.0
10.0
- 2.6
10.0
3.6 3.6
18
0.35 0.35
1.75
6-5
-------
REFERENCES
Freeze, R.A. and J. A. Cherry, 1979. Groundwater. Prentice-Hall, Inc.,
Englewood Cliffs, N.J.
Prickett, T.A., R.G. Naymik, and C.A. Lonnquist, 1981. A
"Randomwalk" Solute Transport Model for Selected Ground-Water
Quality Evaluations. Illinois State Water Survey, Bulletin
65, Urbana, Illinois
U.S. Environmental Protection Agency, 1979. Water-Related Fate
of 129 Priority Pollutants, Volume II. EPA-440/4-79-029b.
U.S. Environmental Protection Agency, 1980. Water Quality
Criteria Documents'; Availability. Federal Register 45:
79318-79357, November 28, 1980.
U.S. Environmental Protection Agency,- 1985.- Alternate
Concentration Limit Guidance Based on §264.94(b) Criteria;
Part I: Information Required in ACL Demonstrations, Draft.
June 1985.
7-1
-------
.APPENDIX A
CHEMICAL, PHYSICAL, AND BIOLOGICAL
PROPERTIES OF TOLUENE AND 1,1,l^TRICHLOROETHANEl
Excerpted from: Chemical, Physical, and Biological Properties
of Compounds present at Hazardous Waste Sites, Final Report.
Office of Waste Programs Enforcement. September 27, 1985.
A-l
-------
TOLUENE
Summary
Toluene has been shown to be embryotoxic in experimental
animals, and the incidence of cleft palate increased in the
offspring of dosed mice. Chronic inhalation exposure to high
levels of toluene caused.cerebellar degeneration and an irreversibL
encephalopathy in animals. In humans, acute exposure depressed
the central nervous system and caused narcosis.
CAS Number: 108-88-3
Chemical Formula: CgH^CHj
IUPAC Name: Methylbenzene
Important Synonyms and Trade Names: Toluol, phenylmethane
Chemical and Physical Properties
Molecular Weight: 92.13
Boiling Point: 110.68C
Melting Point: '-95«C
v
Specific Gravity: 0.8669 at 20°C
Solubility in Water: 534.8 mg/liter
Solubility in Organics: Soluble in acetone, ligroin, and carbor
disulfide; miscible with alcohol,
ether, benzene, chloroform, glacial
acetic acid, and other organic solvents
Log Octanol/Water Partition Coefficient: 2.69
Vapor. Pressure: 28.7 mm Bg at 25°C
Vapor Density? 3.14
Plash Point: 4.4»C
A-2
-------
Tcanspoct and Fate
Volatilization appears to be the major route of removal
of toluene from aquatic environments, and atmospheric reactions
of toluene probably subordinate all other fate processes (USEPA
1979). Photppxidation is the primary atmospheric fate process
for toluene, and benzaldehyde is reported to be the principal
organic product. Subsequent precipitation or dry deposition
can deposit, toluene and its oxidation products into aquatic
and terrestrial systems. Direct photolytic cleavage of toluene
is energetically improbable in the troposphere, and oxidation
and hydrolysis are probably not important as aquatic fates.
The log octanol/water partition coefficient of toluene
indicates that sorption processes may be significant. However,
no specific environmental sorption studies are available, and
the extent to which adsorption by sedimentary and suspended
organic material may interfere with volatilization is unknown.
Bioaccumulation is probably not an important environmental
fate process. Although toluene is known to be degraded by
microorganisms and can be detoxified and excreted by mammals,
the available data, do not allow estimation of the relative
importance of biodegradation/biotransformation processes.
Almost all toluene discharged to the environment by industry
is in the form of atmospheric emissions.
Health Effects
There is no conclusive evidence that toluene is carcino-
genic or mutagenic in animals or humans (USEPA 1980).. The
National Toxicological Program is .currently conducting an in-
halation carcinogenicity bioassay in rats and mice.
Oral administration of toluene at doses as low as 260 mg/kg
produced a significant increase in embryonic lethality in mice
(USEPA 1980). Decreased fetal weight was observed at doses
as low as 434 mg/kg/ and an increased incidence of cleft palate
was seen at doses as low as 867 mg/kg. However/ other researchers
have reported that toluene is embryotoxic but not teratogenic
in laboratory animals. There are no accounts of a teratogenic
effect in humans after exposure to toluene.
Acute exposure to toluene at concentrations of 3-75-1., 500 mg/ra
produces central nervous system depression and narcosis in
humans (ACGIH 1980). However, even exposure to quantities
sufficient to produce unconsciousness fail to produce .residual
organ damage. The rat oral LD-Q value and inhalation LC-Q
value are 5,000 mg/kg and 15,000 mg/m, respectively. Cnronic
inhalation exposure to toluene at relatively high concentrations
produces cerebellar degeneration and an irreversible encephalopathy
in mammals.
A-3
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Toluene in sufficient amounts appears to have the poten-
tial to alter significantly the metabolism and resulting bio- '
activity of certain chemicals. For example, coadministration
of toluene along with benzene or styrene has been shown to
suppress the metabolism of benzene or styrene in rats.
Toxicity to Wildlife and Domestic Animals
Of five freshwater species tested with toluene/ the clado-
ceran Daphnia majna was most resistant to any acute effects
(USEPA 1980). The ECSQ and LC5Q values for all five species
range from 12,700 to 313,000 ugyliter. No chronic tests are
available for freshwater species. The two freshwater algal
species tested are relatively insensitive to toluene with- EC,-n
values of 245,000 ug/liter or greater being reported. For
saltwater species, EC Q and LC5Q values range from 3,700 Mg/
for the bay shrimp to3I,050 mg/liter for the Pacific oyster.
The chronic value in an embryo-larval test for the sheepshead
minnow is reported to be between 3,200 and 7,700 (jg/liter,
and the acute-chronic ratio is between 55 and 97. In several
saltwater algal species and kelp, effects occur at toluene
concentrations from 8,000 to more than 433,000 ug/liter.
Regulations and Standards
Ambient Water Quality Criteria (USEPA):
Aquatic Life .
The available data are not adequate for establishing cri-
teria'. However, EPA did report the lowest concentrations
of toluene known to be toxic in aquatic organisms.
Freshwater
Acute toxicity: 17,500 Mg/liter
Chronic toxicity: No available data
Saltwater
Acute toxicity: 6,300 Mg/liter
Chronic toxicity: 5,000 ug/liter
Hunan Health.
Criterion: 14.3 mg/liter
NIOSH Recommended Standards: 375 mg/m? TWA
560 mg/m STZL
A-4
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OSHA Standards: 750 rag/ra3 .TWA
1,120 mg/ra Ceiling Level
REFERENCES
AMERICAN CONFERENCE OF GOVERNMENTAL INDUSTRIAL HYGIENISTS (ACGIH).
1980. Documentation of the Threshold Limit Values. 4th ed.
Cincinnati, Ohio. 488 pages
'NATIONAL INSTITUTE FOR OCCUPATIONAL SAFETY AND HEALTH (NIOSH) .
1973. Criteria for a Recommended StandardOccupational
Exposure to .Toluene. Washington, D.C. DHEW Publication
No. (NIOSH) HSM 73-11023
NATIONAL INSTITUTE FOR OCCUPATIONAL SAFETY AND HEALTH (NIOSH).
1983. Registry of Toxic Effects of Chemical Substances.
Data. Base. Washington, D.C. October 1983
NATIONAL RESEARCH COUNCIL (NRC). 1980. The Alkyl Benzenes.
National Academy Press, Washington, D.C.
SAX, N.I. 1975. Dangerous Properties of Industrial Materials.
4th ed. Van Nostrand Reinhold Co., New York. 1,258 pages
U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1979. Water-
Related 'Environmental Fate of 129 Priority Pollutants.
Washington, D.C. December 1979. EPA 440/4-79-029
U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1980. Ambient
Water Quality Criteria for Toluene. Office of Water Regu-
lations and Standards, Criteria and Standards Division,
Washington, D.C. October 1980. EPA 440/5-80-075
U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1984. Health
Effects Assessment for Toluene. Final Draft. Environmental
Criteria and Assessment Office, Cincinnati, Ohio. Sep-
tember 1984. ECAO-CIN-H033
WEAST, R.E., ed. 1981. Handbook of Chemistry and Physics.
62nd ed. CRC-Press, Cleveland, Ohio. 2,332 pages
A-5
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1,1,1-TRICHLOROETHANE
Summary
Preliminary results suggest that I,I,1-trichloroethane
(1,1,1-TCA) induces liver tumors in female mice. It was shown
to be mutagenic using the Ames assay, and it causes transforma-
tion in cultured rat embryo cells. Inhalation exposure to
high.-concentrations of 1,1,1-TCA depressed the central nervous
system; affected cardiovascular function; and damaged the lungs,
liver, and kidneys in animals and humans. Irritation of the
skin and mucous membranes has also been associated with human
exposure to 1,1,1-trichloroethane.
1
CAS Number: 71-55-6
Chemical Formula: C
IUPAC Name: 1,1,1-Trichloroethane
Important Synonyms and- Trade Names: Methyl chloroform, chloro-
thene, 1,1,1-TCA
Chemical and Physical Properties
Molecular Weight: 133.4
Boiling Point: 74.1»C '
Melting Point: -30.4°C
Specific Gravity: 1.34 at 20°C (liquid)
Solubility in Water: 480-4,400 rag/liter at 20°C (several divergent
values were reported in the literature)
Solubility in Organics: Soluble in acetone, benzene, carbon
tetrachloride, methanol, ether, alcohol,
and chlorinated solvents
Log Octanol/Water Partition Coefficient: 2.17
Vapor Pressure: 123 mm Hg at 20*C
Vapor Density: 4.63
A-6
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Transport and Fate ,
1,1,1-Trichloroethane (1,1,1-TCA) disperses from surface
water primarily by volatilization. Several studies'have indic-
ated that 1,1,1-trichloroethane may be adsorbed onto organic
materials in the sediment, but this is probably not an.important
route of elimination from surface water. 1,1,1-Trichloroethane
can be transported in the .groundwater/ but the speed of transport
depends on the composition of the soil.
' .Photooxidation by reaction with hydroxyl radicals in the
atmosphere is probably the principal fate process for this
chemical.
Health Effects
1,1,1-Trichloroethane was retested for carcinogenicity
because in a previous.study by NCI (1977), early lethality
precluded assessment of carcinogenicity. Preliminary results
indicate that 1,1,1-TCA increased the incidence of combined
hepatocellular carcinomas and adenomas in female .mice when
administered by gavage (NTP 1984). There is evidence that
1,1,1-trichloroethane is mutagenic in Salmonella typhimurium
and causes transformation in cultured rat embryo cells (USEPA
1980). These data suggest that the chemical may be carcinogenic.
Other toxic effects of 1,1,1-TCA are seen only at concen-
trations well above those likely in an open environment. The
most notable toxic effects of 1,1,1-trichloroethane in humans
and animals are central nervous system depression, including
anesthesia at very high concentrations and impairment of coordi-
nation, equilibrium, and judgment at lower concentrations (350
ppm and above); cardiovascular effects, including premature
ventricular contractions, decreased blood pressure, and sensiti-
zation to epinephrine-induced arrhythmia; and adverse effects
on the lungs, liver, and kidneys. Irritation of the skin and
mucous membranes resulting from exposure to 1,1,1-trichloro-
ethane has also been reported. The oral LD.Q value of 1,1,1-
trichloroethane in rats is about 11,000 mg/Kg.
Toxieity to wildlife and Domestic Animals
The acute toxicity of 1,1,1-trichloroethane to aquatic
species is rather low, with the LC_Q concentration for the
most sensitive species tested being 52.8 rag/1. No chronic
toxicity studies have been done on 1,1,1-trichloroethane, but
acute-chronic ratios for the other chlorinated ethanes ranged
from 2.8 to 8.7. 1,1,1-Tricholoroethane was only slighty bio-
accumulated with a steady-state bioconcentration factor of
nine and an elimination half-life of two days.
A-7
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No information on the toxicity of 1,1,1-trichloroethane
to terrestrial wildlife or domestic animals was available in
the literature reviewed.
Regulations and Standards
Ambient Water Quality Criteria (USEPA)':
Aquatic Life . .
The available data are not adequate for establishing criteria.
However, EPA did report, the lowest values of the two
trichloroethanes (1,1,1 and 1,1,2) -known to be toxic in
aquatic organisms.
Freshwater
Acute toxicity: 18 mg/liter
Chronic toxicity: 8.4 mg/liter
Saltwater
Acute toxicity: 31.2 mg/liter
Chronic toxicity: No available data
Human Health
Criterion:- 18.4 mg/liter
3!
Level
NIOSH Recommended Standard:. 350 ppm (1,910 mg/m )/IS min Ceiling
OSHA Standard: 350 ppm (1,910 mg/m3) TWA
REFERENCES
INTERNATIONAL AGENCY FOR RESEARCH ON CANCER (IARC). 1979.
IARC Monographs on the Evaluation of the Carcinogenic
Risks of Chemicals to Humans. Vol. 20: Some Halogenated
Hydrocarbons. World Health Organization, Lyon, France.
Pp. 515-531
NATIONAL CANCER INSTITUTE (NCI). 1977. Bioassay of 1,1,1-
Trichloroethane for Possible Carcihogenicity. CAS No. 71-
55-6. NCI Carcinogenesis Technical Report Series No. 3.
Washington, D.C. DHEW Publication No. (NIH) 77-803
A-8
-------
NATIONAL INSTITUTE FOR OCCUPATIONAL SAFETY AND HEALTH (NIOSH).
1976. Criteria for a Recommended Standard Occupational
Exposure to 1 , 1 ,1-Trichloroethane (Methyl Chloroform).
Washington, D.C. DHEW Publication No. (NIOSH) 76-184
NATIONAL INSTITUTE FOR OCCUPATIONAL SAFETY AND HEALTH (NIOSH).
1983. Registry of Toxic Effects of Chemical Substances.
Data Base. Washington, D.C. October 1983
/
NATIONAL TOXICOLOGY PROGRAM (NTP) . 1984. Annual Plan for
Fiscal Year 1984. Research Triangle Park, N.C. DHHS
Public Health Service. NTP-84-023
U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA) . 1979. Water-
Related Environmental Fate of 129 Priority, Pollutants.
Washington, D.C. December 1979. EPA 440/4-79-029
U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1980. Ambient
Water Quality Criteria for Chlorinated Ethanes. Office
of Water Regulations and Standards, Criteria and Standards
Division, Washington, D.C." October 1980. EPA 440/5-80-029
U.S. ENVIRONMENTAL PROTECTION AGENCY (USEPA). 1984. Health
Effects Assessment for 1, 1, 1-Trichloroethane. Environmental
Criteria and Assessment Office, Cincinnati, Ohio. September
.1984. ECAO-CIN-H005 (Final Draft)
VERSCHUEREN, K. 1977. Handbook of Environmental Data on Organic
Chemicals. Van Nostrand Reinhold Co., New York. 659 pages
, P.P.-, ed. iggi^L, Handbook_pf Chemistry and Physics.
62nd ed. CRC Press, Cleveland, Ohio. 2,332 pages
A-9
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APPENDIX B
TYPICAL WETLAND SPECIES FOR
COUNTY IN WHICH SITE C IS LOCATED1
^-Provided by che U.S. Fish and Wildlife Service.
B-l
-------
TABLE B-l. TYPICAL SPECIES IN A PALUSTRINE, EMERGENT WETLAND
Plants
Herbivores
Omnivores
Carnivores
Cattail
Arrowhead
Rushes
Burweed
American Widgeon
Canada Coose
Beaver
.Insects
CO
I
Sona Sparrow
Swamp Sparrow
Spotted Turtle
Wood Turtle
Mallard
King Rail
Virginia Rail
Sora
American Woodcock
Red-Winged Blackbird
Short-Tailed Shrew
White-Footed Mouse
Meadow Vole
Southern Bog Lemming
Meadow Jumping Mouse
Black Duck
Common Crackle
Star-Nosed Mole
Muskrat
Mute Swan
Belted Kingfisher
Common Snapping Turtle
Northern Spring Peeper
Common Yellowthroat
Pickeral Frog
Northern Black Racer
Eastern Smooth Green Snake
Black-Crowned Night Heron
Sedge Wren
Marsh Wren
Water Shrew
Red Spotted Newt
Green Frog
Great Egret
Green-Backed Heron
American Bittern
Bullfrog
Stinkpot
-------
TABLE B-2. TYPICAL SPECIES IN A PALUSTRINE, SCRUB/SHRUB WETLAND
Plants
Herbivore
Omnivore
Carnivore
Alder
Button Bush
Myrica
Willows
Eastern Cottontail
New England Cottontail
White-Tailed Deer
Insects .
to
i
Carolina Wren
Veery
White-Eyed Vireo
Yellow Warbler
Rose-Breasted Grosbeak
Eastern Bluebird
Yellow-Billed Cuckoo
Yellow-Breasted Chat
Song Sparrow
American Goldfinch
Racoon
Wood Turtle
Eastern Box Turtle
Marsh Hawk
American Woodcock
Red-Winged Blackbird
'Short-Tailed Shrew
White-Footed Mouse
Meadow Vole
Meadow Jumping Mouse
Black Duck
Common Snipe
Cray Catbird
Common Crackle
Blue Grey Ghatcatcher.
Yellow Throated Vireo -
Nashville Warbler
American Redstart
Long-Tailed Weasel
Northern Spring Peeper
Common Yellowthroat
Swamp Sparrow
Northern Brown Snake
Eastern Ribbon Snake
Northern Black Racer
Eastern Smooth Green Snake
Eastern Milksnake
Black Crowned Night Heron
Cooper's Hawk
Water Shrew
Eastern Garter Snake
Red-Tailed Hawk
Canada Warbler
Henslow's Sparrow
Green Frog
Mink
River Otter
Bullfrog
Green Frog
-------
TABLE B-3. TYPICAL SPECIES IN A PALUSTRINE, FORESTED WETLAND
Plants
Herbivores
Omnivores
Carnivores
Red Maple
Elm
Ash
Swamp-White Oak
Swamp Oak
Eastern Cottontail
New England Cottontail
White-Tailed Peek
Insects
CO
Red-Headed Woodpecker
Great Crested Flycatcher
Black-Capped Chickapee
Tufted Titmouse
Veery
Cedar Waxwing
Scarlet Tanawer
Brown Carpenter
pood Thrush
Scarlet Tanager
Wood Turtle
Eastern Box Turtle
Mallard
Marsh Hawk
Virginia Opossum
Mea'dow Vole
Grey Fox
Wood Duck
Black Duck
Mallard
Belted Kingfisher
I
Eastern Wood Pewee
Blue Grey Gnatcatcher
Nashville Warbler ,
Silver Haired Bat
Eastern Pipistrelle
House Wren
Four-Toed Sachmandek
Wood Frog
Northern Brown Snake
Northern Redbelly Snake
Eastern Ribbon Snake
Eastern Hognose Snake
Eastern Worm Snake
Northern Black Racer
Eastern Smooth Green Snake
Eastern Milk Snake
Cooper's Hawk
Red Shouldered Hawk
Barred Owl
Long-Eared Owl
Water Shrew
Northern Spring Peeper
Fowler's Toad
Timber Rattlesnake
Thrush
-------
APPENDIX C
DESCRIPTION OF RANDOM WALK
SOLUTE TRANSPORT MODEL1
Ground
Illinois State WateVsurvey^Urbana^nr' ^ ^^ "* ^ Lon^ui«-
C-l
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ABSTRACT
A generalized corapucer code is given that can simulate a large class
of solute transport problems in groundwater. The effects of convection,
dispersion and chemical reactions are included. The solutions for
groundwater flow includes a finite-difference formulation. The solute
transport portion of the code is based on a particle in a cell technique
for the conveccive mechanisms, and a random'walk technique for the
dispersion effects.
The code can simulate one- or two-dimensional nbnsteady/steady flow
problems in heterogeneous aquifers under water table and/or artesian or
leaky artesian conditions. Furthermore this program covers time-varying
pumpage or injection by wells, natural or .artificial recharge, the flow
relationships of water exchange between surface waters and the groundwater
reservoir, the process of groundwater evapotranspira.tion, the mechanism of
possible conversion of storage coefficients from artesian to water-table
conditions, and the flow from springs.
In addition, the program allows specification of chemical constituent
concentrations of any segment of the model including, but not limited to,
injection of contaminated water by wells, vertically averaged salt-water
fronts, leachate from landfills, leakage from overlying source beds of
differing quality than the aquifer, and surface water sources such as
contaminated lakes and streams.
Further features of the program include variable finite-difference
grid sizes and printouts of input data, time series of heads, sequential
« '
plots of solute concentration distributions, concentrations of water
C-2
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flowing CTito sinks, and the effects of dispersion and dilution or mixing of
waters li.iving .various solute concentrations. .
The discussion of the vligital technique includes the necessary
mathematical background, the documented program listing, theoretical, versus
computer comparisons, sample input data, and explanations of job setup
procedures and one field application.
INTRODUCTION
Presently, there .ire four classes of problems of concern in studies of
solute transport in groundwater: 1) Chemical problems such as predicting
TDS, Cl, nitrates, etc. as when dealing wich sea water intrusion, excessive
fertilizer applications, hazardous waste leachate, and injection of
chemical wastes into the subsurface using disposal wells; 2) Bacterial
problems associated with cesspools, artificial recharge, sanitary
landfills, and waste injection wells, etc.; 3) Thermal problems involving
injection of hot water into the groundwater reservoir, development of
^eothermal energy, and induced infiltration of surface water having varying
temperatures; and 4) Multi-Phase problems arising from such situations as
development of steam-wacer systems, secondary recovery of water by air
injection, and possible air-waCer interfaces due co o.ver-puraping. Although
this transport program may be extended, the emphasis of this report is
placed on the chemical problems.
One form of the governing equation for solute transport in one-
dimension is:
C-3
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. _ t c i ) = m
Ki( ..x * <
:iii.:!'!;!'.;.;ro.'; - a:,\vi;t.T[0.v; i iv'oiHji.Trox - !.;IIM.[TV
where: D =* coefficient of hydrodynamic dispersion
0 = ^ V * D*
. .». = dispersivicy
V «« interstitial velocicy
D* a coefficient of molecular diffusion (neglected in che following
developmenc)
x a space dimension
Rj " retardation factor
CSQ « source or sink function having a concentration Cg
C 3 concentration
Problems including solute transport in groundwater involve solving
equation I in one, two, or rarely three-dimensions. For the derivation of
the equation and further explanation refer to Freeze and Cherry (1979),
Bear (1972), and Ogata (1970).
In our opinion, the most popular numerical technique presently used
for solving- tlie above equation is the method of characteristics (MOC), or
the part icle-in-a-cel I method. MOC treats the above equation in two parts.
First, the convective term containing the velocity, V, is solved with an
adaptation of the usual finite-difference flow type of model. Then the
dispersive term is solved by using another finite-difference grid
associated with the concentration distribution. A large number of .
computer-generated particles move about by the velocity vectors which are
solved in the flow model, and carries the concentration information between
C-4
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the convection .uicJ >i ispersion terms during che solution of che above
ifquacion. The inscription of che MOC is straight forward , but the computer
code is highly involved, very expensive to operate, and requires a large
computer to effect a solution. While the MOC seems to be popular at this
time, many researchers, including us, are looking for a more efficient and
more direct way to solve problems concerning solute transport in
groundwater. The conceived ramdom walk method follows.
The 'random walk' technique is based on dispersion in porous media
being a random process. On a microscopic basis, dispersion may be as shown
in figure I. As shown, dispersion can take place in two directions even
though the-mean flow is in one direction to the right. The idea unfolds by
studying diagram (1-c). A particle, representing the mass o.f a specific
chemical constituent contained in a defined volume of water, moves through
an aquifer with two types of motion - one notion is with the mean flow
(along streamlines determined by finite differences) and another is with
random motion, governed by scaled probability curves related to flow length
and the longitudinal and transverse dispersion coefficients. Finally, in
the computer code, sufficient numbers of particles are included such that
their locations and density, as they move through a flow model, is adequate
to describe the distribution of the dissolved constituent of interest.
The advantages of this random walk technique over the MOC or, for that
matter of fact, over many other numerical schemes are many:
1) There is no dispersion equation to solve. The dispersion part of
.equation 1 is solved in this computer code by the addition of only
* 11 Fortran statements attached to the solution of the convection
part of equation 1.
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Mean Flow
TRANSVERSE
DISPERSION
Mean Flow
LONGITUDINAL
DISPERSION
Convective
Component
Random
Component
Normal
Distribution
Curves for
Dispersion
Figure 1. Hasic concepts of 'random walk' co
computer program
C-6
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2) There -is only one finite-difference grid involved in solving the
conveccive portion of aquation I: The particle movement takes
place in continuous spacu.
3) Concentration distribution needs only to be calculated when it is
of interest. In the MOC, after each particle is moved, new
concentrations are assigned on the basis' of the solution of the
dispersion term in the above equation for every time step of the
simulation.
4) Computer CPU time is drastically reduced. There is not one
simulation in Part 4 of this report that took more Chan a few
seconds, including compiling and loading on a- CDC CYBER 175.
5) Particles are needed only where water quality is of interest.
These particles are not needed everywhere in che model as wich the
MOC. .
/
6) Solutions .ire additive. If not enough particles are included for
adequate definition in one run, a second run can be done and the
results- accumulated. This is not true of the MOC where possible
spar.se areas of particles may occur, causing loss of accuracy.
7) This method is particularly suited for time-sharing systems where
velocity fields can be stored and manipulated in conjunction with
an on-line particle mover code.
8) .In the traditional sense of the words, finite differencing
phenomena associated .with 'overshoot' and 'numerical dispersion1
are eliminated.
Although there .iro numerous advantages to this technique, there are
also some disadvantages.
C-7
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. I) Us wich ch« MOC, concentrations greacer Chan inicial condicions are
possible especially when coarse discrecizing' is used.
2) A princout of concentrations may noc be pleasing Co che eye when
Che number of particles is small. (A Calcomp ploccing and
smooching roucine could be added co chis model co eliminate chis
problem, however chis is beyond che scope and objectives of this
report.)
3) The method may cake an unusually large number of particles Co
produce an acceptable solution for some problems. No more than
5,000 particles are used in chis reporc, however.
4) More often than not, engineering judgment is an absolute
requirement Co be added co che computed results in arriving at an
acceptable solution. This is because of the 'lumpy1 character of
the output. Therefore, experience with this technique is*needed
before one can apply che code successfully to a field situation.
'The main objective of this report is to present a generalized computer.
code that will simulate a large class of solute transport problems
involving convection and dispersion. . tn the present version, the effect of
density induced convection is not included. This complication is necessary
only when a vertically averaged concentration distribution is inadequate.
The class of problems that require a vertical averaged concentration
distribution is sufficiently large that the inclusion of density
differences will wait for some further publication.
C-8
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ACKNOWLEDGMENTS
This roporC w.-is prepared under Clio general supervision of
Dr. William 0. Ackermann, former Chief, and Mr. Stanley A. Changnon, Chief
of the Illinois Scace Water Survey. R. J. Schichc, Assistant Chief, and
J. P. Gibb-, Head of the Groundwater Section, in- particular, made useful
suggestions with regard to this material. ' ' .
The helpful comments of Adrian P. Visocky, Hydrologist, and Robert A.
Sinclair, Head of the Data and Information Management Unit, are appreciated
as well as the support from the Analytical Chemical Laboratory Unit.
Thanks are also due Mrs. Pan Lovett for typing the manuscript;
f ' .
Mrs. "J. Loreena lyen^ for final editing; and John W. Brother, Jr., Linda Jo
Riggin, and William Motherway, Jr., for preparing the .illustrations.'
C-9
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_ I'AKT 1. Mathematical Background
The computer codu contained in this report can be broken Lnco two
parts. The first part relates to the "flow model" and the second part to
the.particle moving section which is termed the "solute transport model".
v
Some sort of model is needed to provide the velocity vectors of an
aquifer clow system in order to calculate the convective movement of
particles. In most of the situations to follow, a finite-difference scheme
is used to generate the head distribution. From this head distribution a
velocity field is derived. The velocity field then provides the means of
moving the particles advectively in the aquifer. Details- of this follow.
Calculations of Flow
Three methods for head calculations are written into the computer
code. The idea is to generate a head distribution which can then be used
to calculate a velocity field. Two of these head calculations are
analytical and ch« third is a finite-difference method. For a brief
background ot" the finite-difference scheme for producing a head
distribution consider the following:
The partial differential equation (Jacob, 1950) governing the
nonsteady-state two-dimensional flow of groundwater may be expressed as:
(kxh ''^) > -._ (K.I, '±) , s :'il *. .)
/ j y - c
where
Kxb a Tx a aquifer transraissivity in the x direction
Kyb = Ty a aquifer transraissivity in the y direction
Kx = aquifer hydraulic conductivity in the x direction
Ky a aquifer hydraulic conductivity in the y direction
C-10
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S » aquifer -storage coefficient
h =» he.id .ibovo base of .iquifer
b 3 s.-itur;itt?d thickness of .iquifer
c a time
Q = source or .sink functions expressed as nee flow races per
unic area
A numerical solution of equation 2 can be obtained through a
finite-difference approach. The finite-difference approach first- involves
replacing the continuous aquifer system parameters with an equivalent set
of discrete elements. Secondly, the equations governing the flow of
groundwater in the discretized model are written in finite-difference form,
Finally, the resulting set of finite difference equations is solved
numerically with Che aid of a digital computer.
A finite-difference grid is superposed over -a map of an aquifer as
illustrated in fi^ur* 2. The^aquifer is Chus subdivided into volumes
having dimensions m^xuy, where m is Che saturated thickness of the aquifer.
The di f ferent ials c x and i y are approximated by the finite lengths £ x and
Jy, respectively. The areadxijy should be small compared with the total
area o,f the aquifer to the extent chat the discrete model is a reasonable
representation of Che continuous system. The intersections of grid lines
are called nodes and are referenced with a column (i) and row (j)
coordinate system colinear with the x and y directions, respectively.
The general form of die finite difference equation governing Che flow
of uroundwater in the disc ret ized model is then given by
C-ll
-------
-h
,/th
KUW
\
i or x
i-\,,i
OELX(I)
:th
Ax,
COLUMN
|i,,/-l
i,J
W+l
^
Ax 2
NODE
IX
I,./
DELX(I) = ?j
OELY(J) = «a
Figure 2. Finite difference grid
C-12
-------
r.
3 aquifer transmissivity between nodes.* , and/ ,.*! calculated
ns ?ERMX.:' , times h where PERM is hydraulic conductivity
*
T <: : ; = .iquifer transraissivi ty between nodes x ,^_ andx. + 1, ' calculated
' V as P'£RMx' - times h where PERM is hydraulic conductivity
h^ = calculated heads at nodes '/. , at the end of a time increment
measured from an arbitrary reference level
hr a calculated heads at nodes > ,' at the end of the previous rime
increment measured from the same reference level defining
h ^ i
A t = time increment elapsed since last calculation of heads
S . a %qui-fer storage coefficient at nods ^ , . .
Q 3 nee withdrawal rate if positive, .or net accretion rate if
negative at node.*. ,;
Since there is an equation of the same form as equation 3 for every
node.of the digital model, a large set of simultaneous equations must be
solved for the principal unknowns h^,f . The modified iterative alternating
direction implicit method (MIADI) g-iven by Prickett and Lonnquist (1971) is
used to solve the set of simultaneous equations.
Briefly, the MIADI method involves first, for a given time increment,
reducing the large sec o'f simultaneous equations down to'a number of small
sets. This is done by solving the node equations, by Gauss elimination, of
.in individual row of die model while all terms related to che nodes in the
two adjacent rows are held constant. After all row equations have been
processed row l.y row, attention is focused on solving the node equations,
again by Gauss elimination, of an individual column while all terms related
C-13
-------
to che two adj-ncenc columns are held conscanc. Finally, afcer all
liquations have been solved column by column, an 'iteration' has been
completed. The above process is repeated a sufficient number 'of times to
.ichieve convergence, and this completes the calculations for the given time
increment. The calculated heads .ire then used as initial conditions for
the next time increment. This total process is repeated for successive
time increments until the desired simulation is completed.
Equation 3 may be rewritten to illustrate che general form for
calculations by rows. As a first simplification it is assumed that the
finite difference grid is made up of squares such chatty aAx. (The case
whereby does not equal ^x is treated in the code Chat follows as outlined
by Pri-cketc and Lonnquisc, 1971.) Equation 3 is Chen expanded, Che signs
reversed, and terms of h^- grouped together to yield
(I)
liquation 3 is of the form
where
01) = (S. .;..x-/.\t ).!>;,. .. > T. . ,
.\,\ = -T. , . '"* ? .,'-1,1
"'"'- ' ' ('l;° h- - , *T. - h
' ' '
,'-1.1 * ^../^VAC
n -
-------
program'"given by Prickett and Lonnquist, 1971. The report by P.rickecc and
Lonnquist should be a companion report Co this one, .is many details of flow
modeling are taken directly from there for use in this report.
Let us emphasize again that several methods can be used to produce
head distributions from which velocities can.be calculated. As will be
explained later, you can enter heads from theoretical distributions, field
data, or other techniques involving totally different methods for
numerically generating heads.
Once a head distribution is defined for all the nodes of the finite
difference <
-------
Solace Transport Calculations
The basis, for die transport of dissolved.conscituents in this computer
code is thac the distribution of the concentration of chemical constituents
of the water in an aquifer can be represented by the distribution of a
finite number of discrete particles. Each of these particles is moved by
groundwater flow and is assigned a mass which represents a fraction of the
total mass of chemical constituent involved. In the limit, as the number
of particles gees extremely large and one approaches the molecular level,
one arrives at the exact solution to the actual situation. However, ic is
our experience that relatively few particles are needed to arrive at a
solution that will- suffice for many engineering applications.
There are two prime mechanisms which can change contaminant
concentration in groundwater. First, the effects of mechanical dispersion
as 'the fluid spreads through the pore space of the porous medium are
described by the first and second terms on the left hand side of
equation 1. Secondly, the effects of dilution and mixing are expressed in
the second .ind third terms on the left hand side of equation I.
Dispersion
To illustrate the details of the random walk technique, as it relates
to dispersion, consider Che progress of a unit slug of tracer-marked fluid,
placed initially at x"0, in an infinite column of porous medium with steady
flow in the x direction. With CgQ equal to zero, equation 1 describes
the concentration of the slug as it moves downstream. Bear (1972)
describes the solution as .
«>
C-16
-------
vhere
C " concencracion
>IL a longitudinal ilispersivi ty
V = interstitial velocity
t = time
x = distance along the x axis
The shapes of the curves C(x',t) are shown in figure 3 where x'ax-Vt.
Based upon concepts found in comprehensive statistics books (for
example see Mood and Graybill, 1963) a random variable x is said to be
normally distributed if its density function, n(x), is given by
where
-* = standard deviation of the distribution
u » mean of the distribution
Mow, let us equate the following terms of equations 6 and 7 as
C -~-2dLVt~ (8)
u - Vt (9)
n(x) - C(x,t) (10)
With the identities of equations 8 through 10 taken into account, you will
\
note that equations 6 and 7 are equivalent.
Realizing that dispersion in a porous medium can be considered a
random process, tending to the normal distribution is the key to solute
transport as described in this report. There is nothing new here, as a
very complete discussion of statistical models of dispersion and how it
effects water quality has been given, for instance, by Bear (1972) and
Fried (1975). What may be new here is the method by which this statistical
C-17
-------
3-2-1 0
4 5
Figure 3. Progress of a slug around the nean flow
C-18
-------
approach gets inco the computer code and is applied co transport problems.
That explanation follows.
Consider now' figure 4A which is a representation of how particles are
moved in the computer code when the flow is in the x direction and one
considers only longitudinal dispersion. During a time increment, DELP, a
particle, with coordinates xx,yy is first moved from an old to a new
position in the'aquifer by convection according to its velocity at the old
position Vx. Then, a random movement in the +x -or -x direction is added
to represent the effects of dispersion. This random movement is given the
magnitude:
~l'2dLDX x ANORM (0) (11)
where
**« """" """
OX '2dTV DELP
^ [ U X
ANORM(O)-"* A number drawn from a normal di scrjh'iP inn Of numbers
between -6 and +6, that distribution having a standard
deviation of I and a mean of zero.
The new position of the particle of figure 4A is the old position plus
a convective term (Vx DELP) plus the effect of the dispersion terra,
' 2dLDX ANORM(O).
If.the above experiment was repeated for numerous particles, all
having the same initial position and convective term, a map of the new
positions of the particles could be created having the discrete density
distribution . . ^ . _ _N_ _ _^_ .^j
/ "'(.x-V . l>l:Lr): .'
. <-'.V|J I i~j^"^r . (1-)
where dx a incremental distances over which N particles are found
NO 3 total number of particles in the experiment
C-19
-------
(A) LONGITUDINAL DISPERSION
du >0
dT=0
Normal distribution of probable
new petition in x direction
Old particle position
V
xx.yy
Example new
particle position
RLMDX
V/DELP
y
- Where:
R L OX - ^/2d^DX ANORM(0)
New position « Old position + Convection + Dispersion
xx = xx * DX + RL.DX
yy a yy
(B) TRANSVERSE DISPERSION
dL * 0 (to avoid a zero divide check SET to 10 ~30)
cJT >0
Old particle
position
xx.yy
RT»DX
DISPERSE
Example
new particle
xx.yy position
CONVECT
DX = VX»DELP
\/2dDX
y
Where:
nT =-DlSPT
New position = Old position » Convection * Dispersion
xx * xx + DX + 0
yy 3 yy » 0 - RT*DX
Figure 4. Computer code scheme for convection and longitudinal (A)
and transverse (B) dispersion along x axis
C-20
-------
Equations 6', 7, and 12 are equivalent, with che exception chac equations 6
.ind 7 are continuous distributions >ind equation 12 is discrete. As
illustrated in figure 4A, the distribution of particles around the mean
position, VXD£LP, is made to be normally distributed via the function
ANORM(O). The function ANORM(O) is generated in the computer code as a
simple function involving a summation of random numbers. Probable
locations of particles, however, are only considered out to 6 standard
deviations either side of the mean. This is done since, on a practical
basis, the probability is low of a particle moving beyond that distance.
One further emphasis is appropriate concerning the so called "density
function1 of -equations 6, 7, and 12.
The equivalent density functions C(x,t) and N/dx provide the means for
relating the concentration of a contaminant in a field problem to the
concentration of particles found in portions of a finite-difference model.
Various density functions will be defined later, by example,' as they are
needed for application purposes.
Figure- &B illustrates the extension of this method to account for
dispersion in a direction transverse to che mean flow and how the aquifer
transverse dispersivity, dc, is included. Figures 5A and 5B illustrate
the algebra involved when the flow is not aligned with the x-y coordinate
system. And finally, figure 6 shows both longitudinal and transverse
dispersion taking place simultaneously and the appropriate vector algebra.
Dilution, Mixing, Retardation, and Radioactive Decay
Consider the one-dimensional flow problem in figure 7A in which the
flow and concentrations of the sources are given. With dispersion set to
zero and retardation set to one, the distribution of concentrations in the
system are simply a result of pure mixing as illustrated in figure 7B.
C--2.1
-------
(A) LONGITUDINAL DISPERSION
Old particle
position \
xx.yy \
dL
dy
> 0
= 0
DY = V 'DELP-
DO
DISPERSE RL»DD
DX * VX»D£LP
Where:
RL'OD
RL'OY J * *. New particle
RL»OX position
xx.yy
'2dLOD ANORM (0)
New position = Old position * Convection + Dispersion
xx xx + DX * RL'DX
yy yy + DY -c RL»DY
(8) TRANSVERSE DISPERSION
0 (to avoid a zero divide in code
DISPL * 10-30)
0
Old particle _ DX - VX»DELP
position
DO
DY - Vy»OELP
DISPERSE { RT»DD
L, -RT.
DX
New position
xx
VV
* Old position + Convection + Dispersion
DX + RT'OY
OY - RT.OX
xx
w
«
+
Figure 5. General scheme for convection and longitudinal (A)
and transverse (B) dispersion
C-22
-------
Old position
xx,yy
LONGITUDINAL AND
TRANSVERSE DISPERSION
RL'DX RT'DY
New position
xx,yy
RL'DY
-RT'DX
RL'DD = >/2dLDO~ ANORM (0)
RT'DO = v^dDO ANORM (0)
Longitudinal Transverse
New position = Old position » Convection * Dispersion.- ± Dispersion
.xx = xx + DX + RL'DX + RT'DY
yy yy * DY + RL'DY - RT'DX
Figure 6. General scheme for convection and dispersion
C-23
-------
(A)PROBLEM
0 200.000 .|i»l
of tOO ing/1
f
U - 200.000 oixl
Jt concentration
.11 JOQ mad
Hplative velocity
Q lOO.OOOtiixJ
at ' concentration
!
I
Q - > Q - >
C ' ' C '
0* '
Caoesntrat.on '
V > >
(B> SOLUTION
Q 200 000 qixi
C ' 300 mq/l
I
Q * 1 00.000 gpd
C ' 200 mg/l
V' 5
0 200.000
Q 400,000 qpd
C 200 mq/l
V vl unm
V * 2
Q « 300.000 gpa
* C « 200 mg i
V 1.5
(C)
N - 30/dav
f
N ' 10/dav
t
(h 1 UdMicie 10 mq/l
Time density of particles m computer model 20-
N/V " 20 -»
Space density of |)articlcs in computer model on any particular day
Figure 7. Mixing and dilution effects in water quality problems
C-24
-------
Now,. li«c us assume th.it we can arrange in 'che computer model Co have
one parcicel represenc 10 mg/ L . Then figure 7C shows whac Che cime densicy
of Che particles. in Che computer model would be for Che input data of
figure 7A.. Figure 7D shows whac che space densicy of parciclas in che
computer mode.l would be on any particular day. Once Che space densicy of
particles is known, a multiplication by che particle mass yields the
concentration of the flowing water.
In equation 1 che retardation factor (R
-------
WATER LEVEL ELEVATIONS
o
N>
1
2
3
4
5
6
.......
8
9
IO
1 1
12
13
14
15
16
17
IB
19
20
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26
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