SUMMARY GUIDANCE ON
SOIL SCREENING LEVELS
Version 1 - December 2013
SOIL SCREENING LEVELS
This guidance addresses the selection and use of “screening levels” in prioritising
contaminated sites for remediation efforts.
KEY POINTS
a. Soil Screening Levels (SSLs) are used in remediation programmes and projects to provide
a reference point for priority setting in relation to possible interventions. They are used to
“screen out” sites (or areas within sites) which are a low priority in terms of risk.
b. There are a number of well established SSL systems internationally, all in industrialised
countries. They are based on similar approaches: health data for a particular chemical is
combined with assumptions about typical exposures and with policy judgements about
acceptable levels of risk, to provide guidance on acceptable levels of contaminants in soils.
c. The range of systems and SSLs has been reviewed by Blacksmith Institute, in the context
of updating the priority ranking component of the Toxic Sites Identification Program (TSIP).
There is a very wide variation in the values adopted in different systems and the spread of
SSL values does not allow “consensus” values to be identified.
d. The USEPA system is comprehensive and has been rationalised and updated relatively
recently. It has a high degree of credibility, given the scientific expertise and decades of
experience which underlie it. It has therefore been used as the basis for the SSLs applied
to the Toxic Sites Identification Program.
e. In order to derive a system that is more widely applicable in the global context of TSIP,
some adjustments were made to the EPA values, particularly in relation to a number of
substances categorised as possible carcinogens, where the high risk factors applied in the
USA result in stringent levels that may not be as appropriate in other countries.
f.
For agricultural use of land, where USEPA SSLs are not available, relevant values from
Canadian and UK systems have been used. Work continues to developed more detailed
guidance on pesticide screening levels.
g. It is a long and complicated process to develop a new set of SSLs. In the absence of
national values, authorities who are responsible for remediation efforts may wish to use the
values assembled here in their initial screening or may adopt values from one of the
established systems. It is important to ensure that any such use takes full account of
national and local conditions and circumstances.
h. On this basis, SSLs for the most frequently occurring substances in the toxic sites work are
provided in this Guidance Note (see Table in Annex). Links are provided to the systems
referenced.
GAHP Guidance Notes provide information on international good practices and regulations in remediation.
They are prepared to assist GAHP members in dealing with practical problems of remediation of polluted sites
and are intended to assist readers to identify key points that should be taken into account in reviewing or
approving any proposal. Guidance notes reflect the views of individual GAHP specialists and of invited outside
experts and do not necessarily represent the views of any specific government or agency. Additional
background and material may be found on the GAPH website.
SOIL SCREENING LEVELS
Version 1 - December 2013
CONTEXT
The context for this guidance is support for the implementation of national or sub-national remediation
programmes, based on the identification of contaminated sites and the setting of priorities for remediation
interventions. Remediation programmes typically use risk based approaches, given the high costs of major
remediation projects and the limited human, technical and financial resources that are normally available.
Essential first stages in a remediation effort are to build of a list of potentially contaminated sites and to
establish a process to identify which sites should be priorities for investigation and intervention. The list and
the priorities will continue to evolve as more and better information is obtained and as experience is gained
in the process.
Guidance Notes are intended to be used in a dialogue between GAHP members and the agencies involved
in remediation programmes and projects. Further context on the purpose and development of these
Guidance Notes is provided on the GAHP website.
SCREENING AS PART OF PRIORITY SETTING
Decisions on which interventions to undertake are almost always based on a “triage” process: immediate
attention has to be given to sites which are clearly high priority (based on aspects such as visibility, public
concern, and health impacts); sites presenting little risk are excluded from short term consideration; and the
remaining sites have to be investigated further.
Screening
“Screening” is the process of quickly identifying those sites which pose little or no risk, so that they can be
given low priority in the remediation programme.
Such “screening out” usually involves simple
sampling/testing for key pollutants and comparison with defined “screening values” or “screening levels”.
Soil Screening Levels (SSLs), as discussed and presented here, are intended to help identify those
sites which can be considered low risk in terms of health and pollution impacts and which can
therefore be given lower priority in initial remediation efforts.
Screening values, in the present context, are established on the basis of health effects data and of
assumptions about soil conditions and possible pathways, together with policy positions and assumptions
related to acceptable levels of risk. The approach is to set out the levels of contamination in the soil below
which there is an acceptably low risk of health impacts, using clear assumptions about the use of the land
and the typical exposure patterns for people on and around the site. (Screening values can also be
developed on the basis of ecological effects but that approach is probably not relevant at present for most
developing economy governments.)
Development of screening values from scratch is a long process, requiring considerable amounts of local
data and high levels of relevant expertise. A number of countries/agencies around the world have
established different screening systems and levels. They are specific to the individual country circumstances
and conditions and they vary considerably. They are subject to revision as data improves or as assumptions
are refined. The differences in various systems, which reflect individual circumstances, mean that there is no
clear set of “consensus” values and it is not appropriate to simply adopt a set of external values without
careful review. Nevertheless, reference to such existing systems can be a practical approach for countries
which have not yet developed their own systems.
Focus of sampling/screening
The basic risk model is based on the concept of Source-Pathway-Receptor. The screening process normally
is focused on the source: the contaminant must be present in quantities and concentrations sufficient to
GAHP Guidance Notes provide information on international good practices and regulations in remediation. They are prepared to
assist GAHP members in dealing with practical problems of remediation of polluted sites and are intended to assist readers to
identify key points that should be taken into account in reviewing or approving any proposal. Guidance notes reflect the views of
individual GAHP specialists and of invited outside experts and do not necessarily represent the views of any specific government
or agency. Additional background and material may be found on the GAPH website.
2 SOIL SCREENING LEVELS
Version 1 - December 2013
present a hazard. Sampling and screening are carried out at the source: if the source is not significant, in
relation to established screening levels, then the overall risk is inherently low. Sampling at the receptor,
where the contamination may come into contact with people, is not necessarily part of the screening stage.
In the context of contaminated or polluted sites, the main focus is usually the level of contamination in the
soil and how this may impact people on or close to the site. For this reason, this Guidance is focused on soil
parameters and on direct pathways that impact people.
Another common area of high concern is the
impact on groundwater. This may require more extensive consideration and investigation of the site than is
assumed here, which would normally be carried out once the overall level of contamination at a site is
determined to be serious.
Range of parameters
In order to have a practical and low cost screening system, the set of parameters to be used must be limited
and easy/inexpensive to sample and test.
It is better to have screening values for groups of similar
compounds, or for representative compounds, wherever possible. The requirements of the screening
process have to match the personnel and the facilities that are available for implementing the process.
Sampling and testing procedures
Clear and consistent analytical procedures are required for sampling and testing, in order to ensure
consistent results, within resource constraints. It is not within the scope of this Guidance Note to address
such procedures. It is important that the sampling procedures define how the number and location of
samples is to be established, for different sizes and categories of sites. Prior information on the past use
and the extent of the site should inform the type and number of samples to be collected and the
contaminants for which the samples are to be tested. Given the costs of testing, the requirements should be
narrowed as far as is reasonable, at the screening stage.
Clear Quality Assurance and Quality Control (QA/QC) protocols should be applied to both sampling and
testing.
Laboratories used for testing should be certified for working at the level of accuracy and
consistency required.
EXISTING SOIL SCREENING SYSTEMS
Screening systems with specific values to address soil contamination have been developed in a number of
countries including the Netherlands, the USA, Canada, Australia, the UK and Brazil. (The European Union is
still in the process of developing a common approach.) The Netherlands (Dutch) system provides both
Target Values based on background and potential risks to ecosystems and Intervention Values for sites
based on risks to humans. In federal systems, individual states/provinces have sometimes taken the lead in
developing and implementing systems. In the US many states have local systems, with the EPA more
recently establishing consistent standards for federal application. In Canada, the systems were mainly
developed at Provincial level, with some Canada-wide values. In Australia, there are national values which
are broadly used by the States. In Brazil, the state of Sao Paulo has adopted standards ahead of the
Federal Government.
All these systems are based on the same approach: use of scientific data on acceptable levels of uptake of
chemicals by people, animals and plants, combined with structured scenarios for typical exposure levels of
humans in different contexts (residential, industrial, etc.) and with relevant risk factors established for
protection of health and environment.. However, there are many differences between the parameters and
values used across the systems. In some cases, there are formulas given for developing the site specific
values, rather than specific numbers. The actual values for any given parameter can vary by up to two
orders or magnitude (or even more). This demonstrates both the inherent variability in geological conditions
and in health status between countries and also the effects of different detailed assumptions and
approaches.
GAHP Guidance Notes provide information on international good practices and regulations in remediation. They are prepared to
assist GAHP members in dealing with practical problems of remediation of polluted sites and are intended to assist readers to
identify key points that should be taken into account in reviewing or approving any proposal. Guidance notes reflect the views of
individual GAHP specialists and of invited outside experts and do not necessarily represent the views of any specific government
or agency. Additional background and material may be found on the GAPH website.
3 SOIL SCREENING LEVELS
Version 1 - December 2013
SELECTING SOIL SCREENING VALUES
A detailed comparison of values for the most common chemical contaminants has been carried out by
Blacksmith Institute for the purpose of defining soil screening values for use in the Toxic Site Identification
Programme (TSIP), which is supported by GAHP. The systems included in the review were the US EPA,
Canada, Australia, the Netherlands and UK. Annex 1 and additional information on the GAHP website
provide details of the specific sets of values examined.
The review compiled the published screening values for about 90 contaminants which have been reported in
the TSIP process, looking separately at values for residential, industrial and agricultural land use. Not all the
systems had values for all of the contaminants and all of the uses. In a few cases, especially for complex
organics, the values in the systems for the different chemical forms are not readily comparable. This review
confirmed the variation across systems, with no consistent pattern which might reflect a more or less
conservative approach. There is little clustering about a central values for any contaminant, which might
have reflected consensus about appropriate values for a given substance.
From the point of view of finding an international point of reference for screening levels, the most
comprehensive system is that of the US EPA. This has a strong analytic base, wide coverage (in terms of
the substances included) and it has recently been reviewed and revised in order to achieve consistency
across the different EPA Regions. These “Regional Screening Levels” (RSLs) are a very good starting point
for any other system.
As a result, Blacksmith Institute has adopted for its own use a hierarchy of
references, starting with values from the published USEPA RSL tables (with one exception, as discussed
below), and then using Canadian data or UK data for substances where there is not a relevant USEPA
value.
The US, Canadian and UK data were developed in the specific context of their national systems and
regulations. Care must be taken in adapting them for use in other systems. However, they are based on
careful science and rigorous analysis and therefore provide a very good basis from which to work.
One notable adjustment applied in this Guidance to the published RSL values is in relation to possibly
carcinogenic contaminants. The RSLs specifically reflect US conditions and approaches and use a relatively
conservative “one in one-million additional case” risk criterion for a wide range of possibly carcinogenic
substances. This results in relatively stringent screening values for such substances. Blacksmith Institute
follows this approach for substances which are clearly established as carcinogenic. The criterion used is
that the cancer based SSLs are used for those substances categorised by the International Agency for
Research on Cancer (IARC – part of WHO) as human carcinogens (“Group 1”) or probable human
carcinogens (“Group 2A”). However, for other substances, including those categorised lower on the IARC
listings, the relevant non-carcinogen hazard value is adopted.
In practice, this distinction applies to a limited number of substances but does resolve some of the apparent
major inconsistencies between values in different country systems. The main set of compounds for which
this distinction is relevant are pesticides. Many of the pesticides covered in this Guidance are in IARC Group
3 - "not classifiable as to its carcinogenicity to humans". This category is used for agents for which IARC
deems there is not adequate evidence on carcinogenicity, noting that further research may be needed.
Selection of Screening Levels for pesticides can be complex, given the variety of chemicals used in pesticide
formulations and the range of degradation products that can occur in the soil over time. Work continues
under GAHP to address these concerns and updated or separate guidance will be provided in due course.
Contamination of agricultural land is outside the scope of the RSLs and therefore soil screening values from
other systems have been selected for addressing agricultural land. These values are generally from
Canadian systems, with UK values used in a cases where no Canadian values are quoted. These values as
used here are intended for localised areas contaminated by a specific source and are not intended to apply
GAHP Guidance Notes provide information on international good practices and regulations in remediation. They are prepared to
assist GAHP members in dealing with practical problems of remediation of polluted sites and are intended to assist readers to
identify key points that should be taken into account in reviewing or approving any proposal. Guidance notes reflect the views of
individual GAHP specialists and of invited outside experts and do not necessarily represent the views of any specific government
or agency. Additional background and material may be found on the GAPH website.
4 SOIL SCREENING LEVELS
Version 1 - December 2013
to apply to broad areas of land affected by non-point or distributed pollution. (Some national systems, such
as China, do address in detail quality standards for agricultural soils of different types and in different uses.)
Work continues under GAHP to identify practical and efficient approaches to screening sites which have
been contaminated by pesticides.
Selected values
On the basis of the above approach a set of SSLs have been selected for use in the Toxic Site Identification
Program (TSIP) which is supported by GAHP. These SSLs cover the most common pollutants identified in
the TSIP work and provide reference values for different current uses of the land. This compilation has been
prepared by GAHP staff on the basis of published information from different sources. They are tabulated in
Annex 2.
Screening values are given for different current uses of a site. The different values reflect the exposure
patterns associated with these different uses. Where there is effectively unrestricted access to a site, then
the residential values should be used. Where the site is not open to widespread use by the public, then the
industrial values are normally more appropriate.
BEYOND SCREENING
For those sites with contamination levels which are above the screening level, further decisions have to be
taken about the priority of each site for remediation. Conceptually, it would be helpful to have a set of
“Response Levels” above which remediation had to be undertaken. However, this concept is not easy to
operationalise. Three broad approaches are possible.
o
Action Levels: This would be a set of values which represent an unacceptable level of risk and which
allow a decision to be made, on the basis of the limited initial data, that short-term actions had to be
taken to reduce the risk. There are serious practical difficulties in defining, in a simple but fully analytic
manner, the specific levels at which the risk posed by a site would be unacceptable.
o
Multiples of Screening Levels: This approach would use a multiple of the screening level as a
threshold to require remediation to be undertaken. The approach is heuristic rather than analytical
and therefore simpler to establish but has little real justification, especially since dose response
relationship are not the same for all substances. In practice, however, most decision makers would
understand higher multiples as inherently riskier. Pragmatic assumptions (such as 3-10 times the
Screening Level) are sometimes used to guide priorities for more detailed investigations.
o
Hazard Ranking: This could be done simply in terms of the multiples of the Screening Level (i.e.
highest multiple has highest priority) but this again does not take into account the differences in
contaminants and in the site circumstances.
A number of simplified forms of a Hazard Ranking
System have been developed (e.g. the Blacksmith Index), which take into account both the source and
the population at risk. These can provide a more objective basis for setting relative priorities across a
number of sites.
GAHP Guidance Notes provide information on international good practices and regulations in remediation. They are prepared to
assist GAHP members in dealing with practical problems of remediation of polluted sites and are intended to assist readers to
identify key points that should be taken into account in reviewing or approving any proposal. Guidance notes reflect the views of
individual GAHP specialists and of invited outside experts and do not necessarily represent the views of any specific government
or agency. Additional background and material may be found on the GAPH website.
5 SOIL SCREENING LEVELS
Version 1 - December 2013
ANNEX 1
Soil Screening Levels considered.
The reviews on which this Guidance Note are based examined the specific screening values of national
authorities in USA, The Netherlands, Canada, United Kingdom, and Australia. Links to the original sources
for these values are provided on the GAHP website, under Technical Advisory Group Guidances.
A number of other systems were also reviewed in less detail, including other European countries, New
Zealand, China and sub-national authorities in USA, Canada, Australia, and Brazil.
EPA source documents
The latest version of the USEPA tables of values used in the GAHP Guidance Note are provided at:
http://www.epa.gov/reg3hwmd/risk/human/rb-concentration_table/Generic_Tables/
That page presents several tables based on different target risk figures and have been developed in the
context of specific EPA regulations. The guidance and caveats provided with these tables should be
reviewed carefully before using values for screening.
Canada
Guidance has been developed mainly at the Provincial level, with the national guidance for a limited set of
substances at: http://www.ccme.ca/publications/ceqg_rcqe.html
United Kingdom
Soil Guideline Values for a small number of substances and a framework and calculation model to assist in
assessments are available at: http://www.environment-agency.gov.uk/research/planning/33714.aspx
GAHP Guidance Notes provide information on international good practices and regulations in remediation. They are prepared to
assist GAHP members in dealing with practical problems of remediation of polluted sites and are intended to assist readers to
identify key points that should be taken into account in reviewing or approving any proposal. Guidance notes reflect the views of
individual GAHP specialists and of invited outside experts and do not necessarily represent the views of any specific government
or agency. Additional background and material may be found on the GAPH website.
6 SOIL SCREENING LEVELS
Version 1 - December 2013
ANNEX 2 - SOIL SCREENING LEVELS FOR SELECTED COMMON CONTAMINANTS (in ppm unless
otherwise defined)
The substances tabulated are those occurring most commonly in the GAHP data. For substances not
listed, the references in Annex 1 can be consulted.
Pollutant
Residential
Industrial
Agric.
0.61
2.4
12
Cadmium
70
800
1.4
Chromium - Total
64
87
64
Chromium - Hex
0.29
5.6
0.4
Lead
400
800
70
Mercury - Elemental
10
43
26
Mercury - Inorganic
23
310
6.6
Mercury - Methyl
7.8
100
Uranium (soluble salts)
230
3,100
23
Asbestos
1% in soil
1 % in soil
1% in soil
Cyanide
22
140
0.9
Dioxin - mixed
9.4x10-5
3.9x10-4
4x10-6
Dioxin - 2,3,7,8-TCDD
4.5x10-6
1.8x10-5
Fluoride
3,100
41,000
200
PCBs - "high risk"
0.22
0.74
0.50
18,000
180,000
3.8
0.06
1.7
0.029
1.0
Chlordane
35
40
DDT
36
430
Dieldrin
3.1
31
Endosulfan
370
3,700
Endrin
18
180
Hexachlorobenzene
(Benzene Hexachloride)
49
490
Lindane (Gamma Hexachlorocyclohexane)
21
240
1,200
12,000
Methyl bromide (bromomethane)
7.3
32
Methylparathion
15
150
METALS
Arsenic
NON-METALS
Phenol
Vinyl Chloride
PESTICIDES
Aldrin
Malathion
GAHP Guidance Notes provide information on international good practices and regulations in remediation. They are prepared to
assist GAHP members in dealing with practical problems of remediation of polluted sites and are intended to assist readers to
identify key points that should be taken into account in reviewing or approving any proposal. Guidance notes reflect the views of
individual GAHP specialists and of invited outside experts and do not necessarily represent the views of any specific government
or agency. Additional background and material may be found on the GAPH website.
7 SOIL SCREENING LEVELS
Version 1 - December 2013
Parathion
370
3,700
Toxaphene
0.44
1.6
0.015
0.21
1.1
5.4
12,000
120,000
Hexane
570
2,600
Trichloroethylene (TCE)
0.91
6.40
0.01
22
110
0.1
5,000
45000
120
PAHs
Benzo[a]pyrene
ORGANICS
Benzene
Formaldehyde
Perchloroethylene/
tetrachloroethylene (PCE)
Toluene
0.07
NOTES TO TABLE:
o
The values are based on protection of human health. Values for ecological objectives are likely to
be different.
o
The values are based on the assumption of one dominant contaminant. Where multiple
contaminants exist, it may be appropriate to adjust individual component screening values
downwards to allow for possible synergistic or cumulative effects.
o
High precision in values is not appropriate: these values are generally rounded to two significant
figures.
GAHP Guidance Notes provide information on international good practices and regulations in remediation. They are prepared to
assist GAHP members in dealing with practical problems of remediation of polluted sites and are intended to assist readers to
identify key points that should be taken into account in reviewing or approving any proposal. Guidance notes reflect the views of
individual GAHP specialists and of invited outside experts and do not necessarily represent the views of any specific government
or agency. Additional background and material may be found on the GAPH website.
8