United States
Environmental Protection
Agency
Office of
Research and
Development
Office of Solid
Waste and
Emergency
Response
EPA/540/S-96/500
December 1995
?>EPA Engineering Forum Issue
DETERMINATION OF BACKGROUND
CONCENTRATIONS OF INORGANICS IN
SOILS AND SEDIMENTS AT HAZARDOUS
WASTE SITES
R. P. Breckenridge1 and A. B. Crockett1
INTRODUCTION
The National Engineering Forum is a
group of U.S. Environmental Protection
Agency (EPA) professionals representing
EPA Regional Offices, committed to the
identification and resolution of engineering
issues affecting the remediation of
Superfund sites. The forum has identified
the need to provide remedial project
managers (RPMs) and other state or private
personnel working with hazardous waste
sites a thought-provoking, technical-issue
paper on how to determine background
concentrations of inorganics in soils and
sediments at hazardous waste sites. Mr.
Frank Vavra and Mr. Bob Stamnes,
Engineering Forum members, provided
technical guidance and direction in the
development of this Issue paper.
This paper was prepared by R. P.
Breckenridge and A. B. Crockett. Support
for this project was provided by the National
Exposure Research Laboratory's
Characterization Research Division with the
assistance of the Superfund Technical
Support Project's Technology Support
Center for Monitoring and Site
Characterization. For further information,
contact Ken Brown, Technology Support
Center Director, at (702) 798-2270, or R. P.
Breckenridge at (208) 526-0757, U.S.
Department of Energy, Idaho National
Engineering Laboratory.
1 U.S. Department of Energy, Idaho National Engineering Laboratory.
Technology Support Center for
Monitoring and Site Characterization,
Characterization Research Division
Las Vegas, NV 89193-3478
Lechnology Innovation Office
Office of Solid Waste and Emergency Response,
U.S. EPA, Washington, B.C.
Walter W. Kovalick, Jr., Ph.D., Director
Printed on Recycled Paper
764asb95
-------
PURPOSE AND SCOPE
The purpose of this paper is to provide RPMs and
others investigating hazardous waste sites a summary
of the technical issues that need to be considered when
determining if a site (i.e., hazardous waste site/area of
concern) has elevated levels of inorganics relative to
the local background concentrations. This issue paper
is narrowly focused and is for educational use only
by project managers. It is not meant to be a formal
guidance document or "cookbook" on determination
of background concentrations of inorganics at
hazardous waste sites. This issue paper provides the
investigator with information needed to determine
whether activities conducted at a site have resulted in
elevated concentrations of inorganic contaminants in
soils or sediments compared with naturally occurring
and off-site anthropogenic concentrations of the same
contaminant.
The first portion of this paper provides a definition
for and discusses factors that influence background
concentrations. The second portion is separated into
Part A, "Comparing the Concentrations of Inorganics
in Soils and Sediments at Hazardous Waste versus
Background Sites," and Part B, "Guidance for
Addressing High Background Concentrations of
Inorganics at CERCLA (Comprehensive
Environmental Response, Compensation, and
Liability Act) Sites." Part A is a modification of the
State of Michigan guidance on conducting soil
surveys (Michigan 199la, 1991b) and discusses
issues that need to be considered by investigators
attempting to establish background concentrations for
hazardous waste sites. It can be used to provide
potentially responsible parties a summary of issues
they need to consider when determining whether a
hazardous waste site has elevated concentrations of
inorganics compared to a background site. Part B
presents a summary of a draft issue paper titled,
"Options for Addressing High Background Levels of
Hazardous Substances at CERCLA Sites" (EPA
1992a) and includes updated information and
approaches.
This paper addresses technical issues for scientists
and engineers faced with how to determine
background concentrations. It is not intended to
address agency policy-related decisions on how to use
background data to achieve cleanup levels or achieve
applicable or relevant and appropriate requirements
(ARARs). Technical issues discussed here include
selection of background sampling locations,
considerations in the selection of sampling
procedures, and statistical analyses for determining
whether contaminant levels are significantly different
on a potential waste site and a background site. How
to statistically define background for purposes of
remediating a hazardous waste site to background
levels is not addressed.
This paper focuses on inorganics and, in particular,
metals. Radionuclides are not specifically addressed;
however, metals with radioactive isotopes (e.g.,
cobalt-60) that may be encountered at hazardous
waste sites are included. This paper does not
specifically address background concentrations of
organics at a site, but the approach would be very
similar in many respects (except for partitioning), and
some unique aspects regarding organics are noted.
Statistics play a major role in establishing
background concentration levels, and methods vary
widely in their degree of complexity. No specific
recommendations regarding statistical techniques are
provided because they could be misused or have
policy implications. However, some general guidance
is presented to acquaint the reader with issues that
should be discussed with a statistician early in the
design of a study. Statistics should be used
throughout the development of a sampling plan in the
same manner as quality assurance. Sampling
objectives, design, data analysis, and reporting can all
be influenced by statistical considerations.
To provide recommendations that can be used at a
variety of sites, information was gleaned from several
different approaches to the background issue. The
approach employed by the State of Michigan
(Michigan 1990, 1991b) provides one of the most
straightforward and scientifically sound strategies
that, in combination with EPA documents (EPA
1989a, 1989b) and scientific literature (Underwood
1970; Kabata-Pendias and Pendias 1984), form the
basis for this issue paper. This paper discusses the
generic issues from various strategies that should be
-------
considered when addressing the background issue.
However, information presented here may need to be
modified to meet site-specific soil and sediment or
data-quality objective concerns.
STATEMENT OF ISSUE
Hazardous waste sites may pose a threat to human
health and the environment when toxic substances
have been released. The hazardous substances at a
site may originate from either "on-site" (i.e., resulting
from releases attributable to site-specific activities) or
"off-site" (i.e., resulting from sources not on-site).
These "off-site" substances may result either from
natural sources (e.g., erosion of naturally occurring
mineral deposits) or anthropogenic sources (e.g.,
widespread lead contamination from auto-mobile
exhaust in urban areas) (EPA 1992a). To determine
the appropriate action to take at a hazard-ous waste
site, EPA must distinguish between substances
directly attributable to the hazardous waste site (i.e.,
"site" contaminants) and those attributable to
"natural background" concentrations.
Definitions
Soils and sediments for this issue paper are defined
as all mineral and naturally occurring organic material
located at a site and will mostly be related to the
material <2 mm in size because it is usually the finer
material that has a greater affinity for inorganic
contaminants. The U.S. Department of Agriculture
and the International Soil Science Society use the 2-
mm breakpoint to differentiate between soils or
sediment (consisting of sands, silts, and clays) and
gravel (Breckenridge et al. 1991; Lewis et al. 1991).
When establishing background concentration levels,
it is usually more cost effective to focus on the finer
materials; however, some bias is introduced. Large
particles can be rinsed and the rinsate analyzed if
necessary. Soils and sediments are heterogeneous and
contain a wide range of sizes from fine clays to larger
gravel and coarse fragments (Soil Science Society of
America 1978).
In the soils literature, the term "background" usually
refers to areas in which the concentrations of
chemicals have not been elevated by site activities. In
the sediment literature, terms such as "background
sediment" (in the Code of Federal Regulations
(CFR)—40 CFR 131.35-91) and "reference
sediment" (ASTM 1990) are used in similar manners
and are often interchangeable.
To minimize confusion, the term "background
concentration" is defined in this document as the
concentration of inorganics found in soils or
sediments surrounding a waste site, but which are
not influenced by site activities or releases. A
"background site" should be a site that is geologically
similar and has similar biological, physical, and
chemical characteristics (e.g., particle size, percent
organic carbon, pH) as the contaminated site (ASTM
1990) but also should be upstream, upgradient, or
upwind of the site. Samples taken from a site to
determine background concentrations will be referred
to as background samples.
Almost anyone involved with hazardous waste site
evaluations will at some time be involved in
determining background concentrations of inorganics
at a site. There are two issues to be considered when
addressing background. The first is whether the site
and local area have a high natural variability in
concentrations of inorganics. The second is to
differentiate between natural and anthropogenic
sources at a site with high background concentrations
(e.g., lead in soil due to automobile emissions). The
broad range in concentrations of naturally occurring
inorganics may lead to the erroneous conclusion that
an area has been contaminated with inorganics.
Establishment of background concentrations based on
adequate site-specific sampling data and comparison
to normal background ranges for a specific area and
land use can help resolve the confusion.
EPA in its Risk Assessment Guidance for Super-
fund: Volume I, Human Health Evaluation Manual
(Part A) (often referred to as RAGS) (EPA 1989c)
discusses two categories of background:
-------
1. Naturally occurring—substances present in the
environment in forms that have not been influenced
by human activity.
2. Anthropogenic-natural and man-made sub-
stances present in the environment as a result of
human activities not specifically related to the
CERCLA site.
Figure 1 shows the relationship between the on-
site-related and off-site-related "populations" of
substances that contribute to concentrations at a site.
In some locations, the background concentrations
resulting from naturally occurring or anthropogenic
sources may exceed contaminant-specific standards
promulgated to protect human health (EPA 1992a).
The background concentration defined in this
document includes both the naturally occurring and
local/regional anthropogenic contributions (see
Figure 1).
Background concentrations are needed when
deciding whether a site is contaminated. Knowledge
of background concentrations helps address issues
such as (a) the effects of past land use practices on
levels of inorganics in soil and sediment, and
(b) establishing lower limits when conducting risk
assessments for soil and sediment contamination.
Figure 2 illustrates a process for determining
whether contaminant concentrations in soil and
sediments at a hazardous waste site are elevated
relative to background concentrations.
Determining the effect of past land use practices
on levels of inorganics in soils and sediments is an
important initial step towards quantifying the
potential threat to human health and the environment.
Information obtained from this step can provide the
first indication that background concentrations may
be elevated. Preliminary site investigations should be
carefully planned so that high-quality data can be
gathered to gain an understanding of the nature and
degree of threat posed by a site and to determine
whether immediate response is required.
Usually, remedial action is taken only on sites that
exceed a 10~4 incremental cancer risk or exceed a
hazard index of 1.0 for systemic effects. Superfund
cleanups are generally conducted to 10~6 incremental
cancer risk or to a safe hazard index. However, many
states have developed statutes (ARARs) that require
more stringent cleanup levels than risk-based levels
and sometimes require cleanup to natural background
concentrations.
It is often best to compare mean concentrations
between groups of similar samples from the
hazardous waste and background sites. Mean values
can be developed for a soil series or an operable unit.
The operable unit is usually the smallest area that
would be considered under a remediation plan (e.g.,
10 m * 10m if a bulldozer is used to remove the top
6 inches of soil). However, there may be cases when
it is important to know if a single sample has a high
probability of exceeding background. In this case, the
single value can be compared to the background
maximum limit (mean background concentration plus
three standard deviations), which is discussed later.
Background Concentration
Numerous natural and anthropogenic sources
influence background concentrations and need to be
accounted for during an initial hazardous waste site
investigation. Proper accounting of these sources is
important when establishing cleanup standards and
are critical if discussions about ARARs develop.
It is not feasible to establish a single universal
background concentration for soils or sediments; it is
more useful to discuss the range of background
concentrations for a contaminant. Single values are
hard to establish because concentrations vary
depending on how physical, chemical, and biological
processes, and anthropogenic contributions have
affected parent geological material at a site. If a site
has various soil or sediment textures (e.g., sands,
loams), a range in inorganic concentrations should be
developed for different soil series or textural
groupings. Thus, physical and chemical parameters
need to be identified when investigating a site to
ensure that soils or sediments with similar parameters
are compared. This is important because there are
often different soil types at a site, and sediments differ
depending on where (e.g., in a pool or main channel)
and when samples are collected. The following
parameters should be similar when
-------
ON-SITE
Total
On-site
Concentrations
CONCENTRATION
FROM
SITE-RELATED
ACTIVITIES
ON-SITE
BACKGROUND CONCENTRATIONS
ANTHROPOGENIC
SOURCES
(Local, Regional
or Global)
NATURALLY
OCCURRING
SOURCES
BACKGROUND
AREA
Background
Concentrations
OFF-SITE
BACKGROUND CONCENTRATIONS
ANTHROPOGENIC
SOURCES
(Local, Regional
or Global)
NATURALLY
OCCURRING
SOURCES
Figure 1. Relationship between on- and off-site concentration groupings when defining background concentrations
for hazardous waste sites.
comparing paired hazardous waste site samples to
background samples:
• pH/Eh
• salinity
• cation exchange capacity (CEC)
• percent organic carbon
• particle size and distribution
• thickness of horizon (soil)
• soil type, structure (soil)
sample design
depth of sampling
sampling equipment and compositing regime (if
applicable)
number of samples
digestion/analytical method
acid volatile sulfide concentrations (sediment)
simultaneously extracted metal concentrations
(for determining sediment toxicity)
-------
Verify the Assumptions
of Start [sties I Test
DEFNE DATA
QUALFTY
QBJECTWES
POR
BACKGROUND
EVAL UATDN
Figure 2. Process for determining if contaminant concentrations at a hazardous waste site are above background concentrations in soil and sediments.
-------
At times some of these soil parameters such as
percent organic carbon, pH and salinity may be
altered by hazardous waste site activities. These
changes in soil chemistry could falsely imply that the
hazardous waste site and background site
soil/sediment matrices are totally very comparable.
For example, if oil were released at a hazardous waste
site where mercury is of a concern the percent organic
carbon values could be much higher than at ths
background site. This could lead to an incorrect
conclusion that the sites are not similar for
comparison of inorganic concentrations.
Many of these soil parameters can be obtained by
contacting the local Natural Resources Conservation
Service (NRCS) Office and requesting a soil survey
report for the county (usually free of charge) where
the site is located. Most soils on private lands in the
U.S. have been mapped by the NRCS. By using a soil
survey report, the field personnel can evaluate how the
soils were originally classified and gain access to
average values for the soil series located at the site.
By consulting with a soil scientist and comparing
current site soils to those previously mapped, an
assessment can be made of the amount of change and
disturbance that has occurred to the soil profile.
Aerial photographs used to map soils are also helpful
in evaluating past land use, locating stream channels,
determining parent material for sediment loading, and
determining site factors that affect movement of
contaminants (e.g., low percolation rate). More detail
on how and why to characterize soils at hazardous
waste sites can be found in a companion issue paper
(Breckenridge et al. 1991).
A special case occurs for hazardous waste sites
that contain fill. "Fill areas" may be present around
construction or disposal areas and should be sus-
pected if the site is located in areas frequently in-
undated with water. Sites where dredge material (e.g.,
sediments from shipping areas) is suspected to have
been used as fill should be given additional attention
because the dredge material may have elevated levels
of contaminants. A soil scientist can usually identify
fill locations and areas disturbed by construction
because of the disturbed nature of the soil profile.
Natural and Regional Anthropogenic
Contributions to Background Concentrations
Table 1 presents concentration ranges and mean
values of inorganics in selected surface soils of the
United States. Most of this contribution is due to
natural and regional/global anthropogenic sources
The soil types presented are general, but cover many
of the major categories found in the United States
There is one omission from the table and that is for
cadmium, since cadmium mobility is strongly
dependent on soil pH and percent organic carbon
The mean global content of cadmium in soils is
between 0.07 and 1.1 ppm (ppm-dry weight • mg/kg
for SI units); for the United States, values range from
0.41 to 0.57 ppm, but values of up to 1.5 ppm haw
been documented in some forest soils (Kabata-
Pendias and Pendias 1984). In all cases, the higher
cadmium values reflect anthropogenic contributions
(from local and regional sources) to topsoils. Table 2
provides average, range, and no-effect levels fa-
selected inorganics in sediment and soils that can be
used to compare to background concen-trations for a
site. The no-effect levels are the metal concentrations
in sediment that have a low proba-bility of causing a
measurable impact on benthic populations. The
control values for soils and sedi-ments approximate
the average concentrations of metals contributed by
natural and anthropogenic (local and global) values
(Lee et al. 1989; EPA 1992b). These values should
not be used as back-ground concentrations but can be
used to guide investigators in determining whether
elevated levels of contaminants may be present at a
hazardous waste site.
Local Anthropogenic Sources that Influence
Background Concentrations
Note: Some of the activities discussed here may
not be waste handling or disposal activities; however,
they could qualify as releases under Superfund (e.g.,
mining activities may result in releases that can be
addressed under Superfund).
Numerous local anthropogenic activities can
contribute to the inorganic concentrations at a
hazardous waste site yet aie not directly related to site
activities. Local soils and sediments may be
contaminated by ore deposits or mining, by
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TABLE 1. CONCENTRATION OF INORGANICS IN SURFACE SOILS OF THE U.S. [IN PPM-DRY WEIGHT, DW), EQUIVALENT TO
mg/kg-dw] (SOURCE: KABATA-PENDIAS AND PENDIAS 1984).
Elements
Soil
Sandy soils and lithosols on sandstones
Light loamy soils
Loess and soils on silt deposits
Clay and clay loamy soils
Alluvial soils
Soils over granites and gneisses
Soils over volcanic rocks
Soils over limestones and calcareous rocks
Soils on glacial till and drift
Light desert soils
Sitty prairie soils
Chernozems and dark prairie soils
Organic light soils
Forest soils
Various soils
As
Range
<0. 1-30.0
0.4-31.0
1.9-16.0
1.7-27.0
2.1-22.0
0.7-15.0
2.1-11.0
1.5-21.0
2.1-12.0
1.2-18.0
2.0-12.0
1.9-23.0
<0. 1-48.0
1.5-16.0
<1. 0-93.2
Mean
5.1
7.3
6.6
7.7
8.2
3.6
5.9
7.8
6.7
6.4
5.6
8.8
5.0
6.5
7.0
Ba
Range
20-1500
70-1000
200-1500
150-1500
200-1500
300-1500
500-1500
150-1500
300-1500
300-2000
200-1500
100-1000
10-700
150-2000
70-3000
Co
Mean
400
555
675
535
660
785
770
520
765
835
765
595
265
505
560
Range
0.4-20
3-30
3-30
3-30
3-20
3-15
5-50
3-20
5-15
3-20
3-15
3-15
3-10
5-20
3-50
Mean
3.5
7.5
11.0
8.0
9.0
6.0
17.0
9.5
7.5
10.0
7.5
7.5
6.0
10.0
10.5
Cr
Range
3-200
10-100
10-100
20-100
15-100
10-100
20-700
5-150
30-150
10-200
20-100
15-150
1-100
15-150
7-1500
Mean
40
55
55
55
55
45
85
50
80
60
50
55
20
55
50
Cu
Range
1-70
3-70
7-100
7-70
5-50
7-70
10-150
7-70
15-50
5-100
10-50
10-70
1-100
7-150
3-300
Mean
14
25
25
29
27
24
41
21
21(a)
24
20(a)
27
15
17(a)
26
Hg
Range
<0.01-0.54
0.01-0.60
0.01-0.38
0.01-0.90
0.02-0.15
0.01-0.14
0.01-0.18
0.01-0.50
0.02-0.36
0.02-0.32
0.02-0.06
0.02-0.53
0.01-4.60
0.02-0.14
0.02-1.50
Mean
0.08
0.07
0.08
0.13
0.05
0.06
0.05
0.08
0.07
0.06(a)
0.04(a)
0.10
0.28
0.06(a)
0.17
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TABLE 1. (CONTINUED)
Soil
Sandy soils and lithosols on sandstones
Light loamy soils
Loess and soils on silt deposits
Clay and clay loamy soils
Alluvial soils
Soils over granites and gneisses
Soils over volcanic rocks
Soils over limestones and calcareous rocks
Soils on glacial till and drift
Light desert soils
Sitty prairie soils
Chernozems and dark prairie soils
Organic light soils
Forest soils
Various soils
Mn
Range
7-2000
50-1000
50-1500
50-2000
150-1500
150-1000
300-3000
70-2000
200-700
150-1000
200-1000
100-2000
7-1500
150-1500
20-3000
Ni
Mean
345
480
525
580
405
540
840
470
475
360
430
600
260
645
490
Range
<5-70
5-200
5-30
5-50
7-50
<5-50
7-150
<5-70
10-30
7-150
<5-50
7-70
5-50
7-100
<5-150
Mean
13.0
22.0
17.0
20.5
19.0
18.5
30.0
18.0
18.0
22.0
16.0
19.5
12.0
22.0
18.5
Elements
Pb Se
Range
<10-70
<10-50
10-30
10-70
10-30
10-50
10-70
10-50
10-30
10-70
10-30
10-70
10-50
10-50
<10-70
Mean Range
17 0.005-3.5
20 0.02-1.2
19 0.02-0.7
22 <0. 1-1.9
18 <0. 1-2.0
21 O.1-1.2
20 0.1-0.5
22 0.1-1.4
17(a) 0.2-0.8
23 <0. 1-1.1
21 (a) <0. 1-1.0
19 <0.1-1.2
24 <0. 1-1.5
20(a) <0.1-1.6
26 <0. 1-4.0
Mean
0.5(a)
0.33(a)
0.26(a)
0.5
0.5
0.4
0.2
0.19(a)
0.4
0.5
0.3
0.4
0.3
0.4
0.31
Sr
Range
5-1000
10-500
20-1000
15-300
50-700
50-1000
50-1000
15-1000
100-300
70-2000
70-500
70-500
5-300
20-500
7-1000
Mean
125
175
305
120
295
420
445
195
190
490
215
170
110
150
200
Zn
Range
<5-164
20-118
20-109
20-220
20-108
30-125
30-116
10-106
47-131
25-150
30-88
20-246
<5-108
25-155
13-300
Mean
40.0
55.0
58.5
67.0
58.5
73.5
78.5
50.0
64.0(a)
52.5
54.3(a)
83.5
34.0
45.7(a)
73.5
a. Data for whole soil profile.
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TABLE 2. AVERAGE RANGE AND LOW- TO NO-EFFECT LEVELS OF SELECTED INORGANICS
IN SEDIMENTS AND SOILS (mg/kg UNLESS OTHERWISE NOTED).
Media and source Ag
SEDIMENTS'"
Non-polluted, Great Lakes —
(U.S. Army Corps of Engineers 1977)
No effect level (Persaud et al. 1989)" —
0.5
Effects range low, marine sediments (Long 1.0
et al. 1995)"
No adverse biological effects, marine 6. 1
sediments (WDOE 1991)"
Control sediments, Southern California 0.06-2.0
(Lee et al. 1989)'
Control sediments, Puget Sound (Lee et al. 1.2
1989)'
Control sediments, Yaquina Bay 0.55
(Lee et al. 1989)'
No effect threshold, freshwater sediments b —
(Environment Canada 1992)
Lowest effect level, freshwater sediments 0.5
(Persaud et al. 1992)
Threshold effect levels for freshwater —
sediments (Environment Canada 1994)
Threshold effect levels for marine 0.73
sediments (Environment Canada 1994)
Effects range low, freshwater (Ingersoll et —
al. 1995)
SOILS (control values)"
Average and common range in natural 0.05
soils (summarized in Shields 1988) „„. -
Average concentration in earth's crust —
(Merck 1989)
Average concentration in earth's crust 0.07
(CRC 1992)
Relative abundance in soils 0.05
(Martin and Whitfield 1983)
As
<3
4.0
8
8.2
57
3-15
3-15
—
3.0
6
5.9
7.24
13
5
0.1-40
0.5
1.8
6.0
Ba Cd
<20 —
— 0.6
— 1.0
— 1.2
5.1
— 0.001-2
— 3.1-18.3
— 0.47
— 0.2
— 0.6
— 0.596
— 0.676
— 0.70
430 0.06
100-3500 0.01-7
500 0.1-0.2
425 0.2
— 0.35
Cr
<25
22
33
81
260
6.5-40
20.9
19.3
55
26
37.3
52.3
39
100
5-3000
100-300
100
70
Cu
<25
15
28
34
390
2.8-30
10-50
6.3
28
16
35.7
18.7
41
30
2-100
70
55
34
Fe% Hg Mn Ni
<1.7 <1.0 <300 <20
2.0 0.1 400 15
— 0.1 — —
— 0.15 — 20.9
— 0.41 — —
— <1.0 — <20.0
— 0.02-0.12 — 13.0
— — — 14.5
— 0.05 — 35
— 0.2 460 16
— 0.174 — 18.0
— 0.13 — 15.9
20 — 730 24
— 0.11 600 40
— 0.01-0.8 100-4000 5-1000
5 0.5 850 180
5.63 0.08 950 75
4.0 — 1000 50
Pb
<40
23
21
46.7
450
<10.0
8
5.5
23
31
35.0
30.2
55
10
2-200
20
12.5
35
Zn
<90
65
68
150
410
<70.0
—
26.3
100
120
123.1
124
110
50
10-300
200
70
90
a. Control values approximate natural background.
b. No-effect refers to no measurable impact to benthic organisms when exposed to sediments with stated levels of metals.
-------
agricultural application of pesticides or sewage
sludge, and by emissions from motor vehicles. In
urban areas, sites may become contaminated by air
emissions from home heating, automobiles, and
industry. Table 3 provides ranges of contaminant
levels in surface soils from some local anthropogenic
sources of inorganics that could contribute to
background concentrations at or near a hazardois
waste site. Table 4 provides a review of some of the
more common agricultural sources of inorganics
associated with practices such as sludge, pesticides,
and fertilizer applications.
These tables identify elements that could be
associated with different land uses at or around a
hazardous waste site. For example, if the site is
located in an area with high agricultural chemical
usage, elevated background concentrations of arsenic,
bromine, lead, vanadium, and zinc could be expected.
To determine what background concen- trations might
be without the agricultural contribution, the
investigator needs to rely on some investigative skills.
These skills are detailed in Part A of this document.
Accessing Data and Methods for Establishing
Background Concentrations
The previous discussion presented information on
ranges of background concentrations that could te
expected for inorganics of greatest concern eL
hazardous waste sites. Additional information
sources that should be consultedinclude soil scientists
from the NRCS and county extensbn agents who may
have conducted soil surveys that describe the natural
soils' physical, chemical, and biological status.
However, many of these surveys were conducted for
purposes such as mineral development, farming, and
soil conservation; the data focus on properties of
soils. The NRCS maintains the SOILS-5 data base
that provides attributes of soils (e.g., texture, pH,
CEC, salinity, clay content) that can be accessed at
the local NRCS Office or through tie NRCS Office of
Technology, Cartography and Geographic
Information System Division at (202) 447-5421.
Many data sets are available on World Wide Web
(WWW). The U.S. Geological Survey (USGS)
Global Land Information (GLI) system is another
source for most land-based data and can be located on
WWW at http://edcwww.cr.usgs.gov/glis/glis.html.
The Agricultural Stabilization and Conservation
Service can also be a good source of acrid
photographs for hazardous waste site assessment.
Information on soil surveys, aerial photographs, and
other sources that may be useful for identifying soil
types and land use in the United States is presented in
Table 5.
Several large projects have been conducted t)
address the issue of characterizing background soi
concentrations. For example, the Oak Ridge
Reservation (a U.S. Department of Energy facility)
conducted a background soil characterization project
to establish a database, to recommend how to use the
data for contaminated site assessments, and to provide
estimates of the potential health and environmental
risks associated with the background levd
concentrations of potentially hazardous constituents
(see Table 5, ORNL 1993). This source provides a
detailed approach for those faced with conducting a
detailed background investigation.
Approach for Establishment of Background
Reference Values
The approaches described in this document, for
the most part, combine discussion of issues generic to
soils and sediments. However, when warranted
attributes unique to the two different media ae
discussed in separate sections. One such section
discusses sediments that require sampling through
overlying water.
PART A
COMPARING THE CONCENTRATIONS OF
INORGANICS IN SOILS AND SEDIMENTS
AT HAZARDOUS WASTE VERSUS
BACKGROUND SITES
The objective of Part A is to determine whether
hazardous waste site-related activities have caused an
increase in the levels of inorganic contaminants in
soils and sediments compared to background
concentrations.
SOILS
Step 1—Evaluation of Land Use History and
Existing Data
Purpose: This effort is designed to identify land
use history both on and near the hazardous waste site
(i.e., within the air and watershed connected D
11
-------
TABLE 3. INORGANIC CONTAMINATION OF SURFACE SOILS, AVERAGE VALUES
FROM VARIOUS ANTHROPOGENIC SOURCES IN THE UNITED STATES
(PPM-DW)a (SOURCE: KABATA-PENDIAS AND PENDIAS 1984).
Element
Site and pollution source
Mean or range of content
Arsenic (As)
Cadmium (Cd)
Cobalt (Co)
Copper (Cu)
Lead (Pb)
Mercury (Hg)
Zinc (Zn)
Metal-processing industry
Application of arsenal pesticides
Metal-processing industry
Urban garden
Vicinity of highways
Mining or ore deposit
Metal-processing industry
Roadside or airport area
Urban gardens, orchards, and parks
Sludged farmland
Metal processing industry
Urban garden and urban vicinity
Roadside soil
Non- ferric metal mining
Hg mining or ore deposit
Urban garden, orchard, and parks
Non- ferric metal mining
Metal processing industry
Urban gardens and orchards
10-380
31-625
26-160
0.02-13.6
1-10
13-85
42-154
7.9
3-140
90
500-6,500
218-10,900
960-7,000
15-13,000
0. 1-40
0.6
500-53,000
155-12,400
20-1,200
a. Equivalent to mg/kg-DW.
or in proximity to the site) to determine
contribution the anthropogenic activities from
previous land use at or near the hazardous waste site
have had on background concentrations.
Approach: Early in a hazardous waste site
investigation, site history should be determined by
examining available records and by interviewing
personnel familiar with the site. This information can
be used to assess the types of contaminants associated
with past operations that may be of concern and may
be compared to Appendix IX, Superfund and Priority
Pollutant Compounds, lists which identify the
inorganic contaminants of concern. Evaluation of site
history can provide important data when determining
those compounds for which background
concentrations need to be established. For example,
if releases of cadmium and lead are suspected at a
hazardous waste site and the site is located in a
heavily industrialized area, there is high potential that
metals like mercury, lead, and cadmium may be
present and elevated in soils and sediment from off-
site contributions. An initial evaluation of on-site
data should be sensitive to the issue of elevated
background so that off-site contributions can be
properly accounted for.
Another advantage of evaluating existing
hazardous waste site data is to determine if pre-site
operation values are available for inorganics in
sediments or soil. These data can be obtained from
site records or other existing sources discussed later
in this paper. NRCS soil surveys should be checked
both for aerial photographs that show previous land
use on or near the site and for average physical and
chemical properties for soils at and around ths
12
-------
hazardous waste site.
Local county agricultural
TABLE 4. AGRICULTURAL SOURCES OF INORGANIC CONTAMINATION IN SOILS (PPM DW)a
(KABATA-PENDIAS AND PENDIAS 1984).
Element
As
B
Ba
Be
Br
Cd
Ce
Co
Cr
Cu
F
Ge
Hg
In
Mn
Mo
Ni
Pb
Rb
Sc
Se
Sn
Sr
Te
U
V
Zn
Zr
Sewage sludges
2-26
15-1,000
150-4,000
4-13
20-165
2-1,500
20
2-260
20-40,600
50-3,300
2-740
1-10
0.1-55
-
60-3,900
1-40
16-5,300
50-3,000
4-95
0.5-7
2-9
40-700
40-360
-
-
20-400
700-49,000
5-90
Phosphate fertilizers
2-1,200
5-115
200
-
3-5
0.1-170
20
1-12
66-245
1-300
8,500-38,000
-
0.01-1.2
-
40-2,000
0.1-60
7-38
7-225
5
7-36
0.5-25
3-19
25-500
20-23
30-300
2-1,600
50-1,450
50
Limestones
0.1-24.0
10
120-250
1
-
0.04-0.1
12
0.4-3.0
10-15
2-125
300
0.2
0.05
-
40-1,200
0.1-15
10-20
20-1,250
3
1
0.08-0.1
0.5-4.0
610
-
-
20
10-450
20
Nitrogen fertilizers
2.2-120
-
-
-
185-716
0.05-8.5
-
5.4-12
3.2-19
<1-15
-
-
0.3-2.9
-
-
1-7
7-34
2-27
-
-
-
1.4-16.0
-
-
-
-
1-42
-
Manure Pesticides (%)
3-25 22-60
0.3-0.6
270
- -
16-41 20-85
0.3-0.8
-
0.3-24
5.2-55
2-60 12-50
7 18-45
19
0.09-0.2 0.8-42
1.4
30-550
0.05-3
7.8-30
6.6-15 60
0.06
5
2.4
3.8
80
0.2
-
45
15-250 1.3-25
5.5
a. Equivalent to mg/kg-DW.
-------
TABLE 5. SOURCES OF INFORMATION FOR IDENTIFYING SOIL TYPES, LAND USE,
AND DETERMINING BACKGROUND LEVELS OF INORGANICS IN SOILS
AND SOME SEDIMENTS IN THE U.S.
Source
Supporting background
information
Locations
Contact point
Bureau of Land
Management—BLM
Provides data on areas in the country
that have naturally occurring substances
that pose a hazard to humans or the
environment.
Mostly
western U.S.
BLM Service Center
Denver Federal Center
Lakewood, CO 80225
(303) 236-0142
National Park Service
(NFS)
Inventory and monitoring of trace levels
of inorganics in soils in natural areas.
Nationwide Local NFS Headquarters
U.S. Geological Several reports on the concentration of
Survey inorganics in the environment;
Nationwide Water Resources Information Center:
(703)648-6818
Background geochemistry of some
rocks, soils, plant, and vegetables in the
conterminous U.S. "Geological
Survey," professional paper 574-F,
1975—Summary of determination
between natural and anthropogenic
contributions—shows natural values
vary widely and are highly site specific
and regionally dependant.
Nationwide National Technical Information Service
(NTIS)
U.S. Department of Communication:
(703) 487-4650
An accounting of pesticides in soils and
ground water in the Iowa River Basin,
1985-88 (IA 86-055).
Midwest
NTIS
U.S. Geological
Survey
Aerial photographs of sites.
Nationwide USGS, Salt Lake City ESIC
8105 Federal Bldg.
125 South State St.
Salt Lake City, UT 84138-1177
(801) 524-5652/Fax: (801) 524-6500
USDA-Agricultural
Stabilization and
Conservation Service
(ASCS/SCS)
Aerial photographs of current and
previous land use and soils types
including erosion potential.
Nationwide ASCS/SCS
Aerial Photography Field Office,
P.O. Box 30010
Salt Lake City, UT 84130-0010
(801) 975-3503/Fax: (801) 975-3532
National Ocean Coastal and Geodetic Surveys including
Service (NOS) aerial photographs.
Coastal areas National Ocean Service
Coast and Geodetic Survey Support
Sec. N/CG236
SSMC#3,Rm. 5212
1315 East-West Highway
Silver Spring, MD 20910
(301) 713-2692/Fax: (301) 713-0445
14
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TABLES. (CONTINUED)
Source
Supporting background
information
Locations
Contact point
National Archives
Research Administra-
tion/National Air
Survey
(NARA/NASC)
Series of infrared Landsat photographs
for mid-1970s by state.
Nationwide NARA/NASC
National Air Survey
4321 Baltimore Ave.
Bladensburg, MD 20710
(301) 927-7180/Fax: (301) 927-5013
U.S. Forest Service
(FS)
U.S. Department of
Energy (DOE)
Often have data on trace elements as
part of soils inventory and monitoring
program.
Collects and publishes data on trace
metals and radionuclide concentrations
around DOE facilities and for reference
sites.
Nationwide Nearest FS experiment station
Nationwide Nearest DOE office, Environmental
Monitoring Division
Oak Ridge National
Laboratory
The background soil characterization Local -
project provides background levels of Roane
selected metals, organic compounds, and County, TN
radionuclides in soils from
uncontaminated sites at the Oak Ridge Approach
Reservation. Also a good approach for useful
evaluating background for use in nationwide
baseline risk assessments
D.R. Watkins
Oak Ridge Reservation
Environmental Restoration Div.
P.O. Box 2003
Oak Ridge, TN 37831-7298
(615)576-9931
See ref ORNL 1993.
National Climatic Data
Center
Provide data on wind roses and climate
parameters for most areas of the
country.
Nationwide
User Service Branch
Asheville, NC
(704) 259-0682
EPA
Most complete source of data that
includes EPA and other Agency
information on Hazard ID, Dose-
Response, and Risk Characterization.
STORET (physical and chemical
parameters in soils and sediments).
Nationwide EPA/540/1-86/061 (EPA 1986)
EPA Office of Water and Hazardous
Material
(202) 382-7220
Commercial product—more user friendly,
Earthlnfo: (303) 938-1788
Journal Articles Can provide local, regional, or national
background concentration values. Can
be accessed via literature searches, but
usually need to be searched by element
or media.
Local to Selected references: (1) Metals in
National Determining Natural Background
Concentrations in Mineralized Areas, 1992
(Runnells et al. 1992), and (2) Sediment
Quality and Aquatic Life Assessment
(Adams et al 1992).
15
-------
agents and state, county, and federal environmentd
quality officials are also sources of information on
local emissions or previous sampling data that may be
used to establish background concentrations. EPA or
state regulators of chemical storage, use, and emission
data bases of local industries may be a good source of
chemicals used or stored in the local area. EPAs
STORE! data base should be checked
Step 2—Establishment of Data Quality
Objectives
Purpose: The purpose of Step 2 is to establish
data quality objectives (DQOs) (EPA 1993) for the
decision-making process.
Approach: The DQO process is described in
"Standard Practice for Generation of Environmentd
Data Related to Waste Management Activities:
Development of Data Quality Objectives" (ASTM
1995) and is summarized in a companion issue paper
titled, "Characterizing Soils for Hazardous Waste Site
Assessments" (Breckenridge et al. 1991). The
companion issue paper explains how to classify soils
when faced with different classification systems and
what soils data need to be considered when
establishing DQOs. EPA's external working draft,
"Guidance for Data Quality Assessment" (EPA
1995), is helpful in discussing the role of statistics in
the DQO process. This document has a companion
PC-based software program to help support the
document. Since this is designed as a "living
document," contact the Quality Assurance Division
[Fax number (202) 260-4346] in the Office of
Research and Development (401 M Street, S.W,
Washington, D.C. 20460) to obtain the latest version.
Step 3—Determining Sample Location and
Numbers to Collect
Purpose: The purpose is to design a statistically
valid approach that yields representative samples
from areas of concern andfrom background areas and
to factor judgement (bias sampling) into selecting
sampling locations to maximize the possibility of
detecting elevated levels of contaminants on-site.
Approach: There are a number of options in
sampling design that determine where to colled
samples from a hazardous waste site to compae
against a background site. The investigator needs to
discuss the DQOs with a statistician to select the
appropriate design. Numerous design options are
available. One option is for those areas where the
sites' soil and sediment matrix and distribution of
suspected contaminants appear to be homo-geneous.
Establishing a consistent grid (i.e., systematic
sampling grid) across the entire site and sampling at
set locations should provide a reasonable
characterization of the contamination values across
the site. A second option may apply if certain parts of
a site are suspected of being contaminated due to
historical use. In this case, bias sampling or
intensifying the grid in highly suspected areas could
be considered. This approach maximizes the
possibility of determining whether contaminart
concentrations at a site are above background and
minimizes the risk of not taking action at a hazardous
waste site.
There is a wealth of guidance on soil sampling.
One document that is useful because of its coverage
of soil sampling methods and design for reducing
various sources of sampling error is titled,
"Preparation of Soil Sampling Protocols: Sampling
Techniques and Strategies" (EPA 1992c). This
document also provides information for those
uncertain about sampling design options and
composite collection techniques.
The following discussion points should be
considered when selecting and designing the sampling
plan.
Point A—For a given site, there may be several
areas of concern based on known or suspected pat
site activities. Once these areas are identified, a
sampling plan can be developed. Historical data
should be identified and evaluated early in the process
to determine their use in identifying areas of concern
or if the entire site needs to be sampled. Historicd
and land use information identified from Step 1 plays
a key role in determining the degree ofbias in the
sampling plan. Factors such as location of tanks,
piping, staging areas, disposal ponds, and drainage
areas (e.g., sumps) should be considered when
designing a sampling plan. Several soil properties or
processes that govern the mobility of contaminants
can also bias sample location:
Soil pH: A quick check using a field test kit can
identify if the pH of the soil is in a range to mobilize
contaminants. In acid soils (pH <6.5), inorganics
such as zinc, manganese, copper, iron, cobalt, ard
boron are easily leached. However, if soil pH is
16
-------
above 7.0, these inorganics form stable compounds.
Other inorganics, such as molybdenum and selenium,
are mobilized in alkaline soils, whereas in acid soils
they become almost insoluble. Thus, pH and
contaminants of concern need to be factored into the
selection of sampling depth in soils.
Soil Texture: Most soils are a combination of the
following grain sizes:
Medium to large grain size material has moderate
to high porosity (15 to 40 percent) and low capacity
for adsorbing inorganics. These soils have low
capacity to hold contaminants in the grain interstices
due to low cation exchange capacity and low capillary
action. Investigators should look for surface staining
and consider sampling at deeper depths.
Fine sands to silt materials have a stronger
capillary action, and silts are capable of sorbing
inorganics. Special attention should be given to
sampling at the interface between fine material layers
and larger grains, or where fine sand lenses are mixed
in clay soils (these often form conduits for
contaminant movement).
Clays are fine particles and possess a net negative
charge, and most have high cation exchange
capacities. This may cause heavy metal cations (e.g.,
Cr+6, Cd+2, Pb+2) to adsorb to the clay surface. Clays
also form large cracks and fractures due to
shrink/swell and freeze/thaw effects. Investigates
should look at the profile in clay soils to determine if
inorganics (e.g., iron and manganese) have oxidized
or been reduced in fractures causing a color change
(e.g., under oxidation, iron changes to a
red/yellow/brownish color compared to the naturi
blue/gray color). The sample design should consider
these factors by collecting samples from fractures and
especially from areas that show signs of oxidation.
Soil Organic Carbon Content: Organic carbon
content plays a key role in the sorption of
contaminants. Special attention should be given to
sampling layers that have excessive organic carbon
(e.g., darker soils, upper soil layers, peat).
of the solid soil phase to exchange cations is one of
the most important soil properties governing
movement of inorganics in soils. In general, the CEC
is related to the surface area of tie soils and sediments
(Kabata-Pendias and Pendias 1984). Soils and
sediments that have larger surface areas (e.g., clays)
have a greater CEC, while those with smaller surface
areas (e.g., sands) have a lower CEC.
Transport: The transport of dissolved or
colloidal inorganics takes place through the soi
solution (diffusion) and with the moving soil solution
(leaching) (Kabata-Pendias and Pendias 1984).
Investigators should be aware that in cool, humil
climates, inorganics generally leach downward
through the profile; in warm, dry climates and hot,
humid areas, the movement is often upward
However, specific soil properties, mainly the soil's
CEC and moisture availability, control the rate of
migration of inorganics in a soil profile.
Point B—A grid system can be used to establish
the locations to be sampled. A grid will also help
define the total population from which a subset may
be selected using a statistical approach (e.g.,
systematic random, random, or stratified random) to
identify the specific sample population. If the site has
excavations or steep depressions, sample points along
both sidewalk and the base of any excavations should
be included in the grid. If samples are collected from
excavations, similar soils (i.e., same depth, type, and
horizon) should be sampled from the background site
for evaluation. However, soils are heterogenous and
spatial patterns do exist. Some soil types exhibit
spatial correlations that should be considered by the
project's statistician. The area represented by each
grid point should be proportional to the size of the
area for equal weighting and be equal to or greatff
than the operable unit (discussed earlier). One of the
following equations may be used to determine grid
intervals for three different size categories (Michigan
1991b):
GI
Small site
(0 to 0.25 (1)
acre)
Cation Exchange Capacity (CEC): The ability
17
-------
GI
Medium site
(0.25 to 3
acre)
(2)
Intensified grid
GI
Large site (3)
(>3.0 acre)
where:
GI = grid interval
A = area to be gridded (in square feet)
GL = length (or longest side) of area to IE
gridded.
For example, for a 1.5-acre site (the longest sids
being 280 feet), and given that 1 acre = 43,560 square
feet, substituting values in Equation (2) above, we
have:
^/65,340/3.14
4
36 feet betweengrid points
Grid systems are useful but have limitations. An
option is to select a sampling area that is equal to an
operable unit (i.e., the size of the smallest remedial
action unit) and divide the site into equal units.
Samples can then be collected, following a statistical
design that represents the unit.
Point C—After the grid point interval is
determined, a scaled grid overlay can be made and
superimposed on a map of both the hazardous waste
and background sites. Some specified point (e.g., the
southwest corner) should be designated as the (0,0)
coordinate. The grid can then be oriented to
maximize sampling coverage. Some grid orientation
may be necessary for unusually shaped areas. Also,
the site can be subdivided with different calculated
grid intervals so that proportional sampling can be
intensified for suspect areas, such as sumps or sinks
or low-lying drainage areas where contaminants have
a higher probability of concentrating. The following
is an example of a grid:
Point D—Several options exist for collecting
samples: (a) collect a sample at all (or a minimum of
four) grid points as discussed under Point B, (b) use
the systematic random sampling approach referenced
in SW-846, Third Edition, Section 9.1.1.3.3, or
(c) use a stratified random design with an intensified
grid for suspected problem areas. The selected
number of sample locations are determined by
sampling objectives, number of analytes to be
evaluated per sample, the analytical techniques to be
used, and budget constraints.
Point E—The determination of depth sampling
increments are dependent on DQOs and the capacity
of different soil layers to hold (sorb) metals.
Recommended dspth sampling increments are for the
following: clay and organic soils on-site, 0.25 to 0.5
feet or by major horizon; silts and loams, 1.0 to
2.5-foot intervals or by master horizons; and sands,
1.0 to 5.0 feet. The selection of depth sampling
increments also depends on the suspected amount of
contamination released, mobility of contaminant,
amount of water or liquid awlable for transport (e.g.,
ponding), and funding. Samples collected from
specified depths can be either single or in multiple
replicates, depending on the statistical method used
for background data comparison (see Step 5). A
locations where soil type is tie same, compositing can
be considered to save costs and more precisey
estimate the mean value. However, compositing may
be a concern if the data are used for futuE
enforcement purposes.
Point F—For a background site, a minimum of
four samples collected from the same soil type are
needed to establish "background" concentration for a
soil type (Michigan 1991a). These sample numbers
will help account for natural constituent occurrences
and inherent variability (i.e., range) within each
18
-------
distinctive soil type. When determining if
contaminants have moved into a profile (i.e., by
depth), samples should be taken at comparable depths
from similar soil types for both the background site
and the hazardous waste site. If site environmental
conditions have resulted in leaching of contaminants
into the soil profile, the major soil horizons (i.e., O, A,
and B) for a soil type may need to be sampled at both
the contaminated and background site. If the site E
sampled by major horizon, a minimum of four
samples should be collected from each horizon) (see
Figure 3). Sample size (e.g., weight) at all locations
at the hazardous waste and background sites should
be the same.
GROUND SURFACE
1st major horizon — Brown
medium-coarse SAND
2nd major horizon — Lt. brown
silty fine SAND
3rd major horizon — Gray silty
CLAY w/trace of fine-medium
sand
4 samples
4 samples
4 samples
Figure 3. Approach for sampling sites where compar-
ison is needed between major soil horizons
or layers within a soil type.
Point G—Background samples should be taken
from areas unaffected by site activities. If similar
soils cannot be found in areas unaffected by site
activities, possible locations for determining back-
ground are areas on-site, such as under stationaiy
objects like storage sheds or porches, large flagstones,
and old trees.
Point H—Wind rose data can be used to identify
background sample locations in the predominant
upwind direction from the hazardous waste site
Wind rose data usually provide monthly averages
(based on hourly observations) on the percentage cf
time the wind blew from the 16 compass points or
was calm. Wind rose data can be obtained for ths
area from the local weather station or the Nationi
Oceanic and Atmospheric Administration (NOAA).
Generally, if airborne deposition is the primary
method of contaminant release from sites in arid
environments, the investigator should focus on
sampling the soils near the surface. However,
consideration must be given to the mobility of the
contaminant and texture of the soil.
Step 4—Sample Collection, Preservation,
Handling, Analysis, and Data Reporting
Purpose: The purpose is to ensure that all samples
are handled in a manner that protects their integrity
and are analyzed using comparable, standard
methods.
Approach:
approach:
The following is the recommended
1. All sample collection, preservation, preparation,
handling, and analytical methods should follow
standard methods [e.g., U.S. EPA SW-846, "Test
Methods for Evaluating Solid Waste,
Physical/Chemical Methods" (EPA 1986)]. It B
important that all samples are handled using
comparable methods when preparing for and during
analysis. For example, using different digestion
methods can change results significantly.
2. For inorganics, it is recommended to use a tota
metals procedure with results reported in mg/kg (or
percent for iron) on a dry weight basis. This
minimizes additional sources of variation, since these
constituents are often naturally occurring. To assess
the bioavailability of metals in anoxic sediments, acid
volatile sulfide and simultaneously extracted metals
should be determined (Di Toro et al. 1990, 1992).
Step 5—Statistical Comparison of Hazardous
Waste and Background Sites
Purpose: The objective is to determine f
concentrations of inorganics from a hazardous waste
site are elevated compared to those from a back
ground site.
Approach: The following discussion outlines some
basic statistical concepts in the context of background
data evaluation. A general statistics textbook such as
Statistical Methods for Environmental Pollution
Monitoring (Gilbert 1987) should be consulted for
additional detail. Also, the following list of published
statistical guidance may be useful (Figure 4). There
are numerous statistical approaches that are
applicable when collecting, assessing, and analyzing
background data. The approaches presented hee
have been adopted by the State of Michigan
(Michigan 1990, 1991b) and modified based on the
authors' experience. They are readily understandable
and easy to use. However, it is recommended thfc
investigators consult a statistician to assist in the
design or review of a sampling plan prior to collecting
19
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samples.
1. Careful consideration must be given to the
selection of a statistical procedure based on site-
specific factors. These include the size of ths
background data base and the number of samples
available for comparison, variability of soil type, and
coefficient of variation of data. The following aie
some statistical methods that can be used if data
from the site follow a normal distribution. Some
environmental sample sets are normally distributed.
However, the majority of environmental contamin-
ation data sets are not normally distributed. Some of
the more commonly used tests of normality aie
presented in Table 6. Tests should be conducted en
all data to determine if the data meet the assumption
of normality. If the data are not normally distributed,
log or other types of transformations should be
conducted to approximate normality prior to using the
data sets in statistical comparisons, such as t-tests or
analysis of variance procedures (ANOVA).
If the data cannot be normalized, additional
attention needs to be given to selecting appropriate
statistical tests, and the situation needs to be
discussed with a statistician. Special statistical
consideration may be warranted if samples are
composited and the data are needed to suppot
regulatory requirements discussed in Part B.
Statistical Methods Guidance3
Basic
Statistical Methods for Environmental Pollution Monitoring , Van Nostrand Reinhold Company (Gilbert 1987).
Guidance for Data Quality Assessment (EPA 1995).
Soils Sampling Quality Assurance Guide (EPA 1989d).
Guidance for Conducting Remedial Investigations and Feasibility Studies under CERCLA (EPA 1988).
EPA's Guidance Manual: Bedded Sediment Bioaccumulation Tests, pp. 82-91 (Lee et al. 1989).
Statistical Guidance for Ecology Site Managers , Washington State Department of Ecology (WDOE 1992).
Risk Assessment Guidance for Superfund, Volume 1: Human Health Evaluation Manual (Part A) , pp. 4-5 to 4-10
(EPA1989c).
Advanced
Estimation of Background Levels of Contaminants (Singh and Singh 1993).
Statistical Analysis of Ground-Water Monitoring Data atRCRA Facilities (EPA 1992d).
Background and Cleanup Standards
Methods for Evaluating the Attainment of Cleanup Standards, Volume 1: Soils and Solid Media (EPA 1989b)
(detailed statistical discussion).
alf time and resources are limited, Gilbert (1987), Hardin and Gilbert (1993), and EPA (1995) provide some of the
most relevant statistical information.
Figure 4. Statistical Methods Guidance.
20
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TABLE 6. TESTS FOR EVALUATING NORMALITY OF DATA SETS, SOURCE: EPA (1995).
Test3 Sample Size (N) Notes on Use Reference
Shapiro Wilk W Test
Filiben's Statistic
Studentized Range Test
Lilliefors Kolmogorov-
Smirnoff Test
Coefficients of Skewness
and Kurtosis Tests
Geary's Tests
Coefficient of Variation Test
• 50
• 100
• 1000
>50
>50
>50
• 50
Highly recommended
Highly recommended
Highly recommended
Useful when tables for other tests
are not available
Useful for large sample sizes
Useful when tables for other tests
are not available.
Use only to discard assumption of
Gilbert (1987)
EPA(1992c)
EPA (1995)
EPA (1995)
Madansky(1988)
EPA (1995)
EPA (1995)
EPA (1995)
Chi-Square Test
normality quickly.
Largeb Useful for group data and when the Introductory Statistics
comparison distribution is known. Books
aBy order of Recommendation.
bThe necessary sample size depends on the number of groups formed when implementing this test
Each group should contain at least five observations.
When comparing a contaminated site with a
background site, a null hypothesis should be
developed. For example, a null hypothesis could be:
There is no difference between the mean
contaminant concentration of the hazardous waste
site and background site. The alternate hypothesis
would be: The mean concentration for the
contaminated site is different from that of th e
background site. If parametric statistics are used for
this assessment, such as a t-test or ANOVA, the data
can be normalized to selected parameters (e.g,
organic carbon, particle size). Many parametric and
non-parametric statistical procedures exist to compare
a background site with one or more hazardous waste
sites. A variety of such procedures are reviewed n
Lee et al. (1989), EP'A's Risk Assessment Guidance
for Superfund, Volume 1 (EPA 1989c), and EPA's
Guidance for Data Quality Assessment (EPA 1995).
The latter source provides examples and a discussion
of most of the tests needed to conduct comparisoB
between data sets.
a. Empirical Rule. (Note: Many of the foliowirg
calculations can be performed using calculators that
are preprogrammed.) Use mean (• b) and variance
(Sb) of background concentrations to establish an
"upper limit"for delineating significant
concentrations, such as:
1) Calculate the background mean (• b) by dividing
the sum of the total background readings by the total
number of background readings for each element of
concern:
n
2) Calculate the background variance (Sb ) by taking
the sum of the squares of the difference between each
reading and the mean, and dividing by the degrees of
freedom (the total number of background samples
minus one):
Xb)2
Xb)2
(Xn ' Xb)2
3) Calculate the background standard deviation (SJ
by taking the square root of the variance:
4) T
21
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Coefficient of Variation Test (CV) where CV =sb i *b
is used to evaluate data distribution. The background
data should have a CV of less thanO.5 for sandy soils,
less than 0.75 for finer soils, or an explanation
accounting for higher CV values. The maximum
recommended CV is 1.00. If the data distribution
exceeds a CV of 1.00, then a thorough evaluation
should be made to account for this variability (e.g,
laboratory QA/QC, soil classification, sample
location, outlier classification, and sample location),
and the outlier data addressed (see EPA 1989c)
Additional samples may need to be analyzed to ensure
that a sufficient data base population (n) is achieved.
There are several classical procedures (Gilbert
1987; EPA 1995) and robust outlier tests (Singh and
Nocerino 1994) available in the statistical literature.
Consult Outliers in Statistical Data by Barnett and
Lewis (1994) for a full account of this issue. Outliers
often distort statistical estimation, and resulting
inferences and can lead to incorrect conclusions. The
solution is to consult a statistician who understands
outliers and knows how to use robust procedures
-------
procedures could be used with any of the precedirg
statistical methods:
a. For any
-------
and the higher the organic carbon, the greater tte
potential for accumulating metals. Toxic effects are
less likely as the organic carbon content increases for
a given non-ionic organic contaminant level. For
metals, toxic potential is reduced as particle size
decreases or organic carbon increases. If the particle
size or organic carbon content of the background and
contaminated site sediments differ significantly, it is
not appropriate to directly compare contaminart
residue levels without normalizing the data. Some
organic contaminants can be normalized to organic
carbon by dividing by the fraction of organic carbon
(Adams et al. 1992); the same approach has been
used for divalent cationic metals—lead, nickel,
copper, cadmium, and zinc. Metals data can be
normalized to acid volatile sulfide levels (Di Toro
et al. 1990, 1992), a key element such as aluminum
(Schropp and Windom 1988; Daskalakis and
O'Conner 1995), or particle size (NOAA 1988). EPA
is also refining its equilibrium partitioning approach,
which could be used to normalize contaminant levels
among different sediments (Adams et al. 1992; EPA
1992b). Further discussion of these procedures E
beyond the scope of this paper, and expert assistance
should be obtained.
Step 2—Comparison of On-site Data to Sediment
Quality Criteria
Simply comparing the level of metals in bulk
sediments, deposited under similar conditions,
upstream and downstream from a suspected facility
can provide an indication that a facility may have
contaminated the downstream site. These data,
however, proude no indication of bio availability that
may justify remediation. Indeed, bulk sediment
contamination is only poorly correlated with adverse
impacts. For metals, the key parameter h
determining toxicity is the pore water concentration of
a metal. In situations where no background site data
exist, yet contaminated site data do, it may be useful
to compare sediment contamination levels to various
sediment quality criteria.
EPA is developing sediment quality criteria for
metals, but the factors determining bio availability are
complex, and an approach has yet to be selected
(Ankley et al. 1994). Research has shown that h
anaerobic sediments, toxic impacts due to cadmium,
copper, lead, nickel, and anc are not present when the
sum of the molar concentrations of these metab
divided by the AVS concentration is less than ore
(Di Toro et al. 1990, 1992). Essentially, when excess
sulfide is present, the metals are complexed and metal
concentrations in pore water are low.
While bulk sediment contamination levels do not
correlate well with toxic effects, a number of
statistically based, sediment-quality indices have been
developed. If resources are limited, and useful
background site data do not exist, concentrations £
the contaminated site can be compared with metd
concentrations in bulk sediment known to have a low
probability of causing adverse impacts on benthic
organisms. Several "no-effect" levels are presented in
Table 2. NOAA developed effects-based guidelines
including no-effects, possible effects, and probable-
effects levels (Long and Morgan 1990) based on
National Status and Trends Program data, and
MacDonald (1992) used the same approach with
additional data to develop similar marine guidelines.
The guidance for marine sediments was further
updated by Long et al. (1995). The most recert
guidance on metals is presented in Interim Sediment
Quality Assessment Values (Environment Canada
1994), in which NOAA National Status and Trends
Program data and spiked-sediment toxicity tests were
used to develop threshold effects values for fresh and
marine waters, presented in Table 2. If the
contaminated site levels are below the no-effecte
levels, further investigation may not be required even
if the site has been contaminated. If the no-observed-
effects levels are exceeded, further investigation may
be justified. Bulk sediment guidelines have also been
developed by EPA Region V (U.S. Army Corps of
Engineers 1977) for classifying sediments of Great
Lakes harbors. The Ontario Ministry of Environment
(Persaud et al. 1989) and other guidelines are
summarized in EPA's Guidance Manual: Bedded
Sediment Bioaccumulation Tests (Lee et al. 1989).
In addition, these and other guidelines have been
reviewed and summarized by Giesy and Hoke (1990).
In areas where an entire watershed has been
impacted, such as from mining activities, it may not
be possible to select a suitable background site, b
such situations, historical data (Runnells et al. 1992)
or archived samples may be the best source of data
Another approach would be to sample surficial
sediments and compare them to deeper
uncontaminated sediments (those laid down prior to
the watershed being impacted).
No specific rules can be provided regarding the
use of existing background reference data fa-
sediments or soils. Judgement should be made witi
full knowledge of the specific objectives of ths
investigation, data limitations, and qualifications and
24
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with the help of appropriate experts (e.g., chemists,
hydrologists, statisticians, benthic ecologists, and
sampling experts).
Step 3—Selection of Sites for Collection of
Background Sediment
The ideal background site data for comparison
with contaminated site data are obtained frcm
samples:
1. Collected immediately upcurrent of the
contaminated site in an area not impacted by the
suspected contaminant source.
2. Collected at the same time the contaminated
sediment is sampled.
3. Having very similar particle size and organic
carbon content.
4. Collected using identical sampling equipment.
5. Collected using the same statistically based
sampling design (i.e., numbers and configuration) and
compositing handling procedures (if any).
6. Analyzed using identical analytical methods.
When comparing data sets, it is important that
everything about the sampling and analytical
procedures for the background and contaminated site
sediments be as similar as practical. If both fine and
coarse sediments are available for sampling at the
contaminated site and the background site, the finer
sediments are preferred because they have a greatar
affinity for metals.
The ideal situation is seldom achieved, and
compromises may have to be made. For streams, i
may be practical to sample directly opposite from the
contaminant or contaminant source or even
downstream as long as the background site is not
impacted by the plume of concern. Contaminated and
background site sediment characteristics will be most
alike where the currents are similar, with fines being
deposited in areas of low currents aid coarser material
being associated with faster currents. A significant
complication of sampling streams is the potential for
severe erosion, which may remove massive amounts
of sediments during flood conditions. Thus, even the
contamination observed in the sediments directly
downstream of a pint source may not be attributable
to the existing source. The surface sediments after a
flood may represent contamination deposited from
upstream sources or historical contamination from
another facility previously operating at the hazardous
waste site. Knowledge of a suspected contaminatd
source's effluent, the processes generating ths
effluent, and historical stream flow information can be
helpful to link the suspected source and the
contaminated site's metal concentration. Since it is
difficult to establish a background reference site after
a major flood event has occurred, previous data or
deep sediments may be the best source for
background reference data.
For estuarine and marine sites, selection of a
similar but unimpacted background site also can be
difficult. The process may involve the use of
hydrologic models to simulate tides and currents to
avoid areas impacted by the contaminated plume. It
may be necessary to select distant background sites
when currents are highly variable. The same
considerations need to be addressed in lakes witi
wind-driven currents. When questions arise about site
selection, it is best to consult with an expert who E
familiar with the hydrology of the area.
When it is not possible to obtain background
sediment with the same particle size and organic
carbon content, normalization procedures, discussed
previously, should be considered. While it is beyond
the scope of this document to recommend specifc
sampling and assessment methods, excellent
comprehensive references for such information are
Procedures for the Assessment of Contaminate d
Sediment Problems in the Great Lakes (IJC 1988),
Assessment and Remediation of Contaminated
Sediments (ARCS) Program, Assessment Guidance
Document (EPA 1994b), and Manual of Aquatic
Sediment Sampling (Mudroch and Azcue 1995).
Additionally, EPA's Office of Science and
Technology within the Office of Water is developing
a methods manual that will cover all aspects of
sediment monitoring, from sample collection to
analytical methods to assessment techniques (EPA
1994c).
PARTB
APPROACHES FOR DETERMINING
BACKGROUND LEVELS OF INORGANICS
THAT CAN BE COMPARED WITH
CONCENTRATIONS OF INORGANICS AT
CERCLA SITES
Part B was developed to addrss issues that need
to be considered when the establishment of
background under CERCLA is required. Part B also
25
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provides a summary of technical issues rather than an
in-depth statistical evaluation of the topic. Those
needing an in-depth level of statistical evaluation
should seek the expertise of a statistician and may
benefit from a paper that addresses estimation of
background concentrations of contaminants, for
example Singh and Singh (1993) or Hardin and
Gilbert (1993).
Step 1—Conduct On- and Off-site
Reconnaissance as Preliminary Assessment
Phase of CERCLA
Purpose: The initial reconnaissance is
performed to identify concerns associated with on-site
or off-site activities that may have resulted in
contributing to enhanced inorganic background
concentrations.
Approach: See Step 1 under Part A (a similar
approach should be considered).
Step 2—Collect Preliminary Information and
Samples About Background Levels of Concern
Purpose: During the preliminary assessment/site
investigation (PA/SI) stage, existing soil and sediment
analytical data for contaminated sites and background
sites can provide initial information to identify
problems that might be encountered with establishing
background values.
Approach: The PA/SI stage is not designed to
evaluate all concerns at the site. However, an initial
site visit can be advantageous to evaluate site con
dition, assess analytical data, or collect samples of
equal number (i.e., number from contaminated site =
number from background site) from media that have
similar physical (e.g., texture) and chemical (e.g., pH,
percent organic carbon, CEC) properties. During the
SI phase, sufficient information is needed to support
the hazard ranking score (HRS) to identify if a
contaminated site should be nominated for inclusion
to the National Priority List (NPL) due to high threat
to humans or the environment (HRS scores • 28.5 are
usually nominated for inclusion to the NPL). The SI
stage may present the first opportunity to actual^
measure background con-centrations for assessing if
observed releases have occurred. Section G of the
preamble to the HRS final rule (55 FR 5/546) on
"Observed Releases" states that an observed release
is established when a sample measurement that equals
or exceeds the sample quantitation limit is at least
three times the background level (EPA 1992a, p. 2-3).
Step 3—Determine Potential Magnitude of a
Problem by Combining Information from Steps
land!
Purpose: Combining information on past land
use and site operations with data from local, regional,
and global contributions can help alert investigators
that the issue of background concentration might
require more attention when developing a sampling
and analysis plan during the remedial investigation
(RI) process.
Approach: Information sources other thai
chemical analysis (e.g., information or data obtained
from other sources or Steps 1 and 2) may be used for
characterizing the background concentrations fora
site. A multi-tiered approach is often helpful to lump
background concentrations, such as:
1. Global contributions—mostly atmospheric
contributions from wet and dry deposition.
2. Regional contributions—influence of geological
formations (e.g., increased selenium in western
regions).
3. Local contributions—contributions due to land
use (e.g., high arsenic, lead, andmercury values due to
pesticide use in fruit production), local air emission
sources, and nearly all industrial activities.
Step 4—Establish a Clear Statement of the
Problems at the Site and Develop RI Sampling
Strategy
Purpose: The RI process is the time to conduct
detailed measurements of background concentrations
at CERCLA sites. Section 300.430(b)(8) of the
National Contingency Plan requires that a sampling
and analysis plan (SAP) be developed during the
scoping phase of the RI process.
Approach: A number of EPA guidance docu-
ments discuss the need to characterize background
concentrations as part of the SAP formulation step.
For example, according to the Guidance for Data
Use ability in Risk Assessment (Data Useability
Guidance) (EPA 1989a), the SAP should be
developed to resolve four fundamental risk assess-
ment decisions, one of whbh is to determine "whether
site concentrations are sufficiently different from
background." Similarly, the Guidance for
Conducting Remedial Investigations and Feasibility
Studies under CERCLA (RI/FS Guidance) (EPA
1988) states that when determining the nature ard
26
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extent of contamination at a site, background
sampling should be conducted to help identify the
respective areas of both site-related contamination
and the background concentrations.
Step 4a—Confidence Interval Determination
Purpose: The purpose is to develop confidence
intervals for determining mean metals values and
problem statements for a contaminated site.
Approach: Literature sources such as those
presented in Table 5 can be useful to determine if a
site has a potential contamination problem. However,
literature values should be used only to support or
help evaluate data from contaminated and background
site samples. Site variability must be accounted for
when conducting a characterization. Some sites have
fairly homogenous soils, sediments, and areas
impacted by emissions. More often, a site has a high
degree of variability, and the problem statement and
SAP need to reflect this For many sites, a 95 percent
confidence interval of the mean metals concentrations
would be reasonable (i.e., if the mean for lead is 20
ppm-dry weight ±4, the 95 percent confidert
background value would be between 16 and 24 ppm-
dry weight). However, if the site is complex due D
different soils/sediments and areas of concern, a 90
percent confidence interval may be more acceptable
due to an increased number of samples and cost
Once a confidence interval is developed, a problem
statement for the site can be formulated to guide
further effort. An example of a problem statement
could be: "Are on-site concentrations of mercury
lead, arsenic, and zinc statistically different from off-
site background concentrations?"
Step 4b—Develop Hypotheses for Testing
Purpose: EPA's RAGS "provides guidance on
developing hypotheses to frame a problem in a
manner that can be tested."
Approach: There are two types of hypothesB
most often used: null hypothesis (a) — the site-related
concentration is less than or equal to the background
concentration, and null hypothesis (b) — the site-
related contaminant concentration is greater than cr
equal to the background concentration. Additioni
guidance on selecting hypotheses is presented in the
Risk Assessment Guidance for Superfund, Volume I
(EPA 1989c).
Step 4c—Determine Level of Precision
Purpose: RI/FS guidance is that the level of
precision be determined before sampling and
analysis strategies are developed. This will guide the
number and location of samples.
Approach: Determining the level of precision
early in the development of a SAP will minimize
many future problems. Two types of statistical errors
are encountered when testing hypotheses aboit
differences between on-site and off-site
concentrations. The following definitions are true
only if the null hypothesis (a) is used, but not with (b).
1. Type I error (•) (false positive): "Rejecting the
null hypothesis when it is true." Because of the
uncertainty related to sampling variability, an
individual could falsely conclude that the site-related
contaminant concentration is greater than background
concentration whenit actually is not. In this case, the
null hypothesis is rejected, and the site-related
concentration is consideredto be statistically different
from the background concentration.
2. Type II error (•) (false negative): "Accepting
the null hypothesis when it is false." Alternatively, an
individual might accept the null hypothesis that the
contaminated site-related concentration is less than or
equal to background concentration when it actually is
not. In this case, the null hypothesis is accepted and
the site-related concentration is considered to be no
different from the background concentration.
A decision based on a Type I error could result
in unnecessary remediation, while a Type II errcr
could result in the failure to dean up the contaminated
site when remediation is necessary. The Greek letter
alpha (•) is used to represent the probability of a false
positive, and beta (•) is used to represent the
probability of a false negative decision.
Precision associated with hypothesis testing is
defined by the parameters of confidence level and
power. These are defined in EPA (1992a) and EPA
(1989a) as:
1. Confidence level (100 percent - •)—One
hundred percent minus the confidence level is the
percent probability of concluding that the
contaminated site-related concentration is greater than
background when it is not (Type I error or "fals
positive"). As the confidence level is lowered (cr
alternatively, as • is increased), the likelihood of
committing a Type I error increases.
27
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2. Power (100 percent - •)—One hundred percent
minus the power is the percent probability of
concluding that the site-related concentration is less
than or equal to background when it is not (Type I
error or "false negative"). As the power is lowered (or
alternatively, as • is increased), the likelihood of
committing a Type II error increases.
Although a range of values can be selected for
these two parameters, as the demand for precision
increases, the number of samples and cost will
generally also increase. The Data Useability
Guidance states that for risk assessment purposes, the
minimum recommended performance measures are
Confidence, 80 percent (• = 20 percent) and Power,
90 percent (• = 10 percent). These values can be
interpreted to mean the following:
1. Confidence level = 80 percert—In 80 out of 100
cases, contaminated site-related concentrations would
be correctly identified as being no different
(statistically) from background concentrations, while
in 20 out of 100 cases, site-related concentrations
could be incorrectly identified as being greater than
background concentrations.
2. Power = 90 percent—In 90 out of 100 cases,
site-related contaminants would be correctly identified
as being greater than background concentrations,
while in 10 out of 100 cases, site-related
concentrations would be incorrectly identified as
being less than or equal to background concentrations.
If the site situation requires a higher level of
precision to reduce the probability of committing a
Type I or II error, it can only be accomplished b/
increasing the number of samples and overall cost
[see guidance in EPA (1995)]. These decisions need
to be made on a site-specific basis and are primarily
related to remediation and risk reduction goals.
Step 5—Develop a Sampling Approach That Will
Answer the Problem Statement and Meet the
Established Level of Precision
Purpose: The environmental scientist can
develop a range of costs and options for differert
ranges of probability values of committing either a
Type I or II error. The guidance developed in Step 1
of conducting a preliminary background evaluation
can be expanded, with the assistance of a statistician,
to determine the number of samples, location of
samples, and statistical test to employ.
Approach: Developing a full-scale SAP directed
at determining if there is a difference between
contaminated site and background values requires
knowledge about how theinorganics of concern move
in the environment, site variability, and level of
precision. The environmental scientist should initially
seek the support and guidance of scientists and a
statistician familiar with the issues. A SAP can then
be devised to evaluate questions about background
where off-site concentrations are elevated due to off-
site anthropogenic contributions. Guidance fa-
reaching decisions in these cases can be obtained from
the Draft Issue Paper (EPA 1992a).
CONCLUSIONS AND RECOMMENDATIONS
The issue of establishing background concen-
trations for inorganic metals for comparison to levels
at a potentially contaminated site can be complicated
by natural and anthropogenic contributions to totd
background concentrations. The issues presented h
this paper are designed to provide investigators with
sufficient knowledge to assess whether concentrations
of inorganics at a hazardous waste site are statistically
above background concentrations. There are also
discussions on how to approach background
determinations at a hazardous waste site if there is a
high potential for regulatory enforcement action.
There are a wide variety of methods that ae
available in the literature and in various EPA
documents for evaluating background. Each method
is slightly different, but there are a number of
common issues that are presented in this paper. The
most important factor to consider when determining
background concentrations is to ensure that the
physical, chemical, and biological aspects of the
media to be sampled at both the contaminated site and
the background site are as similar as possible. There
are references and data included in this paper that
provide average concentrations and reference values
for selected soils and sediments in the United States.
Most of the values in the literature are fa-
concentrations that include natural and global
anthropogenic contributions. These should be
considered but should not take theplace of conducting
a thorough site-specific investigation to determine the
previous land use both on and in the vicinity of the
hazardous waste site to detemiine local anthropogenic
contributions. The time spent using well-documented
investigative skills to identify unaffected background
sites that are similar geologically to the contaminated
site will be of great value when establishing
background concentrations. This paper presents the
issues that are important to consider when comparing
28
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if inorganics at a hazardous waste site are statistically
different from those found at a background site areas.
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