United States
                 Environmental Protection
                             Office of
                             Research and
Office of Solid
Waste and
December 1995
&EPA    Engineering  Forum  Issue
                 WASTE SITES
                 R. P. Breckenridge1 and A. B. Crockett1

                  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.
                  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
U.S. Environmental Protection Agency
Region 5, Library (PL-12J)
77 West Jackson Boulevard, 12th Floor
Chicago, IL  60604-3590
                                      Technology Innovation Office
                                      Office of Solid Waste and Emergency Response,
                                      U.S. EPA, Washington, D.C.

                                      Walter W. Kovalick, Jr., Ph.D., Director

                                           Printed on Recycled Paper


  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
  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 of
data-quality objective concerns.

  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.


  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)-^0  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

   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 1, 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 x 10 m 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

                                                     BACKGROUND CONCENTRATIONS

  (Local, Regional
    or Global)
(Local, Regional
or Global)
 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
                       number of samples
                       digestion/analytical method
                       acid volatile sulfide concentrations (sediment)
                       simultaneously extracted metal concentrations
                       (for determining sediment toxicity)



    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
the 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
have 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 for 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

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 are not directly related to
site activities. Local soils and  sediments may be
contaminated  by  ore deposits or mining,  by





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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 hazardous
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
be expected for inorganics of greatest concern  at
hazardous  waste sites.    Additional  information
sources  that should  be  consulted include  soil
scientists from the NRCS and county extension
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 the 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 aerial 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 to
 address the issue of characterizing background soil
 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
 level  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 are
 discussed in separate sections.  One such section
 discusses sediments that require sampling through
 overlying water.
                   PART A

    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
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 to

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
  a. Equivalent to mg/kg-DW.
or  in  proximity  to the site) to determine what
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 DC,
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 the
            hazardous waste site.   Local  county  agricultural


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                               AND SOME SEDIMENTS IN THE U.S.
    Supporting background
          Contact point
Bureau of Land
National Park Service
Provides data on areas in the country
that have naturally occurring
substances that pose a hazard to
humans or the environment.

Inventory and monitoring of trace
levels of inorganics in soils in natural
Mostly       BLM Service Center
western U.S.   Denver Federal Center
             Lakewood, CO 80225
             (303) 236-0142

Nationwide    Local NPS Headquarters
U.S. Geological
U.S. Geological
Stabilization and
Conservation Service
 National Ocean
 Service (NOS)
Several reports on the concentration of
inorganics in the environment;

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.

An accounting of pesticides in soils
and ground water in the Iowa River
Basin, 1985-88 (IA 86-055).

Aerial photographs of sites.
Aerial photographs of current and
previous land use and soils types
including erosion potential.
Coastal and Geodetic Surveys
including aerial photographs.
                                                        Coastal areas
Water Resources Information Center:

National Technical Information Service
U.S. Department of Communication:
(703) 487-4650
             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

             Aerial Photography Field Office,
             P.O. Box 30010
             Salt Lake City, UT 84130-0010
             (801) 975-3503/Fax: (801) 975-3532

             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

                                      TABLES.  (CONTINUED)
     Supporting background
Contact point
National Archives
Research Administra-
tion/National Air
Series of infrared Landsat photographs
for mid-1970s by state.
Nationwide    NARA/NASC
              National Air Survey
              4321 Baltimore Ave.
              Bladensburg, MD20710
              (301)927-7180/Fax: (301) 927-5013
U.S. Forest Service
U.S. Department of
Energy (DOE)
Often have data on trace elements as
pan of soils inventory and monitoring

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
The background soil characterization     Local -
project provides background levels of     Roane
selected metals, organic compounds,      County, TN
and 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
              See ref.ORNL 1993.
National Climatic       Provide data on wind roses and climate   Nationwide
Data Center            parameters for most areas of the
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).
Journal Articles         Can provide local, regional, or national   Local to
                      background concentration values. Can   National
                      be accessed via literature searches, but
                      usually need to be searched by element
                      or media.
                                                   User Service Branch
                                                   Asheville, NC
                                                   (704) 259-0682
                                    Nationwide     EPA/540/1-86/061 (EPA 1986)
                                                  EPA Office of Water and Hazardous
                                                  (202) 382-7220
                                                  Commercial product—more user
                                                  friendly, Earthlnfo: (303) 938-1788

                                                  Selected references: (1) Metals in
                                                  Determining Natural Background
                                                  Concentrations in Mineralized Areas,
                                                  1992 (Runnells et al. 1992), and (2)
                                                  Sediment Quality and Aquatic Life
                                                  Assessment (Adams et al 1992).

agents and state, county, and federal environmental
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.  EPA's STORE! data base should be checked

  Step  2—Establishment  of  Data   Quality

    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 Environmental
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

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 and from 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  collect
samples from a hazardous waste site to compare
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  contaminant
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 past
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.
Historical and land use information identified from
Step 1 plays a key role in determining the degree of
bias 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, and
boron  are easily leached.  However, if soil pH is
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

   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., Cr4*, 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.  Investigators
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 natural
blue/gray color). The sample design should consider
these factors by collecting samples from fractures
and  especially  from  areas  that show  signs of

   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).
   Cation Exchange Capacity (CEC): The ability
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 the 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 soil
solution  (diffusion) and with  the  moving soil
solution (leaching) (Kabata-Pendias and Pendias
1984).  Investigators should be aware that in cool,
humid   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 sidewalls 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 greater than the
operable  unit (discussed earlier).   One of the
following equations may be used to determine grid
intervals for three different size categories (Michigan
        = GI
Small site
(0 to 0.25

        = GI
                     Medium site
                     (0.25 to 3
Large site

(>3.0 acre)
                                                                            Intensified grid

     GI = grid interval
      A = area to be gridded (in square feet)
     GL = length (or longest side) of area to be

   For example, for a 1.5-acre site (the longest side
being 280  feet), and  given that 1  acre  = 43,560
square feet, substituting values in Equation (2)
above, we have:
v/65.340/3.14  =
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 comer) 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:
                                                   •    •••••
                                                                 •    •    •
                                                        •    •     •    •    •
                                                                  •    •    •
                                                                                  * * *
                              (0.0)   •
  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, 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 depth 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 available 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).  At locations where soil type is the same,
compositing can be considered to save  costs and
more precisely estimate the mean value.  However,
compositing may  be a concern if the data are used
for future 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 199la).   These  sample
numbers will help account for natural constituent
occurrences and  inherent variability (i.e., range)

 within each 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 is 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.
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
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 stationary
objects like storage sheds  or porches, large flag-
stones, 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 of
time the wind blew from the 16 compass points or
was calm. Wind  rose data  can be obtained for the
area from the local weather station or the National
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

   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 is
 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 total
 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 (Da Toro et
 al. 1990, 1992).

 Step 5—Statistical  Comparison  of Hazardous
 Waste and Background Sites

    Purpose:   The objective  is to  determine if
 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 here 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  that  investigators  consult a

statistician to assist in  the design or review of a
sampling plan prior to collecting samples.

1.  Careful consideration  must  be given to  the
selection of a statistical procedure based on site-
specific factors.   These include the  size of  the
background data base and  the number of samples
available for comparison, variability of soil type, and
coefficient of variation of data.  The following are
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  are
presented in Table 6. Tests  should be conducted on
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

  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 support
regulatory requirements discussed in Part B.
                                  Statistical Methods Guidance3

 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 (Pan A), pp. 4-5 to 4-10
 (EPA 1989c).
 Estimation of Background Levels of Contaminants (Singh and Singh 1993).
 Statistical Analysis of Ground-Water Monitoring Data at RCRA 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).
 "If 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.

following procedures could be used with any of the
preceding statistical methods:

a.  For any 

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 contaminant
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 is beyond the scope
of this  paper, and expert assistance should  be

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, provide no  indication of bioavailability
that may justify remediation. Indeed, bulk sediment
contamination is only poorly correlated with adverse
impacts.   For metals,  the  key  parameter  in
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 bioavailability
are complex, and an approach has yet to be selected
(Ankley et al. 1994).  Research has shown that in
anaerobic sediments, toxic impacts due to cadmium,
copper, lead, nickel, and zinc are not present when
the sum of the molar concentrations of these metals
divided by the AVS concentration is less than one
(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 at
the contaminated site can be compared with metal
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 recent 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-effects 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
     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.  In
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 for
sediments or soils. Judgement should be made with
full  knowledge of the specific objectives of the
investigation, data limitations, and qualifications and
with the help of appropriate experts (e.g., chemists,


   	Test*	Sample Size (N)	Notes on Use          	Reference
  Shapiro Wilk W Test

  Filiben's Statistic

  Studentized Range Test

  Lilliefors Kolmogorov-

  Coefficients of Skewness
  and Kurtosis Tests

  Geary's Tests

  Coefficient of Variation

  Chi-Square Test
 z 50         Highly recommended

 z  100         Highly recommended

z 1000        Highly recommended

 > 50         Useful when tables for other tests
              are not available

 > 50         Useful for large sample sizes

 > 50         Useful when tables for other tests
              are not available.

 ^ 50         Use only to discard assumption of
              normality quickly.

Large6         Useful for group data and when
              the comparison distribution is
Gilbert (1987)

EPA (1995)

EPA (1995)


EPA (1995)

EPA (1995)

EPA (1995)
Introductory Statistics
  "By order of Recommendation.
  "The 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  the
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  in  Lee  et  al. (1989), EPA's Risk
Assessment Guidance for Superfimd, 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 die tests
needed to conduct comparisons between data sets.

a.   Empirical Rule. (Note: Many of the following
calculations can be performed using calculators that
are Dreprogrammed.)  Use mean (xb)  and variance
(Sb) of background concentrations to establish an
                  "upper    limiffor    delineating    significant
                  concentrations, such as:

                  1)  Calculate the background mean (x b) by dividing
                  the sum of the total background readings by the total
                  number of background readings for each element of
                  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):
                 s,2  =
                  3)  Calculate the background standard deviation (Sb)
                  by taking the square root of the variance:

4)  The Coefficient of Variation Test (CV) where
CV = s, / *, is used to evaluate data distribution. The
background data should have a CV of less than 0.5
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 to identify multiple outliers.

  If an outlier is  found, an option  is to take a
substitute sample, have it analyzed, and repeat the
statistical process.  (To  avoid costly delays, it is
recommended to collect extra samples for laboratory

  For example,  four background samples  are
collected  from a site for lead analysis.   The lead
values from the laboratory analysis were 56, 25, 18,
and 35 mg/kg.  The investigator wants to examine
the data set to determine  if the 56-mg/kg sample is
an outlier.  The summary statistics for these samples
       xb (mean) =
                   56 1- 25 +  18  + 35
                                    = 33.5
 Sb (variance) - I (56 - 33.5)2 * (25 - 33.5)2 + (18 - 33.5)2

           * (35 - 33.5)2 }  /3 = ^|1 = 273.67
 Sb (standard deviation) =

CV (coefficient of variation)  = -^  =
   The test for a single outlier in a normal sample
 with the population mean and variance unknown
 (Barnett and Lewis 1994, p. 218-222) is appropriate
 for the above identified sample. The test statistic is:
            xm»- *    56-33.5
   The theoretical cut-off point (Barnett and Lewis
(1994), Table XIH, p. 485) for « = 0.05 is  1.46.
Since the calculated value of the test statistic (1.36)
is less than the theoretical cut-off point (1.46), the 56
mg/kg sample is not an outlier.
   Background concentrations should be determined
for major soil types at the hazardous waste site.  If
this  is  not  feasible,  then  a mean  background
concentration should be determined on the soil type
at the hazardous waste and background sites with the
lower absorption capacity (usually the sandiest soil)
and  those  with the  higher absorption capacity
(usually silts and clays). The finer-texture soils (silts
and clays) will usually sorb the most contaminants
and provide  a good value for comparison.  If the
mean concentration from the fine textured soils from
the hazardous waste site is above similar values for
the background site, there is a high probability that
the site is contaminated.
   Once a   mean  background  concentration  is
established,   similar  statistical  tests  should  be
conducted on the data from the hazardous waste site.
After the data sets  have met the assumptions for
normality or have been corrected (see Figure 2), then
statistical comparisons can be made between the site
and background data sets.
b.  t-Test.  Any t-test should be discussed with a
statistician prior to use since there are a number of
variations and  assumptions that can apply.   The
Gosset Student T-test has good  application when
comparing    background   sites    to   potentially
contaminated sites (Michigan 199la).
c.  Cochran's Approximation to the Behrens-Fisher
Student's t-test.  This test is also available for
evaluating background variance versus exceedances
(i.e.,  contamination)  as referenced in  40  CFR
Part 264, Appendix IV.  Note that this  statistical
comparison method does require that two or  more
discrete samples be taken at each sampling location.
d.  In some cases, it may be of interest to establish an
upper limit of background for the site. This would
be useful if the investigator wanted to compare
single values for a soil type from the hazardous
waste site  with the background population  for a
similar soil.  The mean background concentration
(xb) plus three standard deviations (3Sb) comprises
a reasonable maximum allowable or upper limit.
2.  Procedures for non-detect values. If more than
50 percent of the background analytical values are
below  the  detection  limit  (DL),  either  of the

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 from

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 greater
affinity for metals.
     The ideal situation is seldom achieved, and
compromises may have to be made. For streams, it
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 and 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 point
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 contaminated source's
effluent, the processes generating the 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 with
wind-driven currents.  When questions arise about
site selection, it is best to consult with an expert who
is 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 specific
sampling  and  assessment  methods,  excellent
comprehensive references for such information are
Procedures for the  Assessment  of Contaminated
Sediment Problems in the Great Lakes (UC 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
              CERCLA SITES
     Part B was  developed  to address issues that
need to be considered when the establishment of
background under CERCLA is required. Part B also
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

     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  (MRS)  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 2 28.5 are usually nominated for inclusion to
the NPL).   The SI stage may present the first
opportunity to actually 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 1 and 2

     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 than
chemical analysis (e.g., information or data obtained
from other sources or Steps 1 and 2) may be used for
characterizing the background concentrations for a
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, and mercury 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

     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
Useability in  Risk  Assessment (Data  Useability
Guidance)  (EPA  1989a),  the SAP should be
developed to resolve four fundamental risk assess-
ment decisions, one  of which 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 and
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  confident  background  value would  be
between 16 and 24 ppm-dry weight).  However, if
the site is complex due to 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

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 hypothesis
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 or equal to the  background concentration.
Additional  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
about  differences between  on-site and off-site
concentrations.  The following definitions are true
only if the  null hypothesis (a) is used, but not with

1.   Type I error (a) (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 when it actually is not. In
this case, the null hypothesis is rejected, and the site-
related concentration is considered to be statistically
different from the background concentration.

2.   Type n error (P) (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

     A decision based on a Type I error could result
in unnecessary remediation, while  a Type n error
could  result  in the  failure to  clean  up  the
contaminated site when remediation is necessary.
The Greek  letter alpha (a) is used to represent the
probability of a false positive, and beta (P) 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

1.   Confidence  level (100  percent -  a)—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
"false positive").  As the confidence level is lowered
(or alternatively, as a is increased), the likelihood of
committing a Type I error increases.

2.   Power (100 percent - P)—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 n
error or "false negative"). As the power is lowered
(or alternatively, as P is increased), the likelihood of
committing a Type n 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  (a = 20 percent) and
Power, 90 percent (P = 10 percent).  These values
can be interpreted to mean the following:

1.   Confidence level = 80 percent—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

     If the site situation requires a higher level of
precision  to reduce the probability of committing a
Type I or n error, it can only be accomplished  by
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 different
ranges of probability values of committing either a
Type I or n 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 the inorganics 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 for reaching decisions in these cases can
be obtained from the Draft Issue Paper (EPA 1992a).
     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 total
background concentrations. The issues presented in
this paper are designed to provide investigators with
sufficient knowledge to  assess  whether concen-
trations 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 are
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 for
concentrations  that  include natural and global
anthropogenic contributions.   These  should  be
considered  but   should  not take the  place  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 determine
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  if  inorganics at  a
hazardous waste site are statistically different from
those found at a background site areas.
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