Contaminated sediment
Guidance on certain aspects of working with contaminated sediments where issues and methods differ between contaminated sites on land and in sediment.
Efforts to address pollution-damaged sediment sites follows the same principles and largely the same legislation as corresponding work with contaminated sites on land. This guidance primarily refers to Chapter 10 of the Environmental Code, but other relevant legislation related to sediments is also addressed.
This page is intended for
Municipalities and county administrative boards, operators and property owners who have a responsibility for remedial actions, developers and consultants within remedial actions.
Useful information
Multiple agencies have responsibility for work with contaminated sediments. Each agency has different areas of responsibility and goals linked to this work. The agencies have collaborated to produce improved guidance for improving the degree of pollution in Swedish sediments. These agencies are the Swedish Environmental Protection Agency (EPA), the Swedish Geotechnical Institute, Geological Survey of Sweden, the Swedish Agency for Marine and Water Management, and the County Administration Boards.
Legislation
Chapter 10 of the Environmental Code deals with polluted sites. The Government has adopted five ordinances on topic and issued the following statutes based on the Environmental Code:
Ordinance on Serious Environmental Damage (2007:667) (riksdagen.se)
Ordinance on Environmental Risk Areas (1998:930) (riksdagen.se)
Ordinance on Government Grants to Fund Remediation of Contaminated Sites (2004:100) (riksdagen.se)
Environmental quality standards and water management
Environmental quality standards for water and the status of Swedish water bodies can be used as tools when identifying and conducting inventories of contaminated sediment sites and to prioritise work with polluted sites both on land and in water.
Environmental quality standards for water include surface water (lakes, streams and coastal waters) and groundwater. The purpose of the standards is to ensure Sweden’s water quality. The standards are binding. An environmental quality standard for water describes the quality a Swedish water body is to have achieved at a specific point in time. The main rule is that all water bodies must achieve what in water management is called good status. A standard specifies a minimum permitted level. The total environmental impact on the water body must not lead to reducing the quality below the status specified in the standard. The non-deterioration ban requires that the status not deteriorate or affect the possibility of improvement.
Factors that affect a water body’s state, and thus its status, include chemical, ecological and quantitative parameters. In many water bodies, pollution sources with significant dispersal need to be addressed to achieve a good status. A pollution source can be both a polluted site on land or contaminated sediment site. Ongoing economic operations are different types of sources, while runoff from agriculture and forestry operations and air emissions are examples of diffuse sources.
Other relevant regulations not dealt with here:
Environmental Quality Standards for Bathing Water (Swedish Agency for Marine and Water Management)
Responsibility for contaminated sediment sites
Legal questions are central to working with contaminated sites, particularly responsibility for investigations and measures. Relevant legislation is based on Chapter 10 of the Environmental Code, but other parts of the Environmental Code, regulations and directives also impact this work.
Since the 1990s, Sweden has had experience in investigating contaminated sites on land. When investigating liability for contaminated sediments, it is very valuable to have the previous experience from investigating liability based on the “polluter pays principle” for pollution on land, as the legal questions are the same. Pollution damage in sediments may come from many different sources, resulting in a more complex process, but the principles are still the same. The EBH portal (database with potential polluted areas, a joint website provided by the County Administration Boards for guidance and information on contaminated sites) provides guidance for liability studies that can largely be applied here.
When assessing liability for pollution in sediments, however, there may be different issues from those for pollution on land due to the prevailing conditions of dispersion in water areas.
Special circumstances may exist for:
- Initial study and inventory
- Risk assessment
- Source tracking
- Scope
- Assigning liability
- Impacted properties
Linking the pollution to the correct source
There are straightforward cases where one or more contaminants in the sediments can be clearly linked to a single potential source. In these cases, the process does not differ significantly from the investigating liability for other contaminated sites. This can be because the contaminant is specific for an operator and/or dispersion pathway and/or because the location-specific conditions of the contaminant’s source mean there are no other possible sources for that contaminant.
In other instances, it is more difficult to link one or more known contaminants to one or more sources. For example, this can apply to commonly occurring pollutants, such as PAH in areas where there are several possible sources of the substance. A port area can have various industries, stormwater discharges, draining watercourses with industries upstream or ship traffic that can affect sediments.
Differences between liability studies for sediment and for other contaminated sites
Often this involves which documentation is needed and which approach may be needed to produce the documentation. New information can also lead to decisions on who requirements are imposed on. A liability study for contaminated sediments may thus require re-assessment to gain the full picture of liability.
Examining liability can contribute to better information about current sources and thus opportunities to remedy these.
Inventory and priorities
There are contaminated sediments in many places around Sweden, and it is important to identify these and prioritise which to investigate in more detail.
Prioritisation of contaminated sediments is based on the same assumptions as for contaminated soil. A site can be prioritised for remedial measures if there are acute risks to human health and the environment, if there are important objects for protection at the site or if there is an unacceptably high dispersion of a prioritised substance from the site.
Before remediation of a contaminated sediment site is conducted, remediation of contaminated soil sites that risk adding contamination to the sediments should be prioritised to prevent recontamination of the sediments after a potential remediation. It is also important to stop other ongoing releases that can pollute sediment sites before the sediment is remediated.
Remediation of contaminated sediment sites should be based on the impact analysis and action plans that the water authorities draw up for each registered water body. Both of these analyses are based on water body status and established environmental quality standards.
Studies and investigations
Investigations are needed to determine the degree of contamination and to assess risks and the need for action for a sediment site.
The Undersökningsportalen (translation: The Investigation Portal) provides practical support on investigating contaminated sites, including separate information on sediments.
Undersökningsportalen (fororenadeomraden.se)
Investigations and remediation of contaminated sediments also require knowledge of conditions and applicable methods for aquatic environments.
The Swedish EPA provides guidance on questions related to contaminated sites in general and on environmentally hazardous activities that may be relevant, for example, when handling dredged masses on land.
Survey releases from ongoing and previous economic operations
An important part of the initial investigation is charting ongoing or previous releases to sediment from economic operations. If pollution from one activity has spread to a larger area where emissions from other activities have also been added, it is important to gain an overall picture of the impact on the larger area.
Obtain information on bottom and water current conditions
In the next step, it is important to obtain information about bottom conditions, such as areas where sediments and pollutants can accumulate and where there are erosion or transport areas from which sediments and possible pollutants can disperse.
It is also important to investigate whether there are water currents in the area that could transport particles with pollutants. The sediments can then be sampled and analysed based on different chemical parameters, depending on which pollution sources may have existed or exist in the catchment area.
Investigate the pollution situation
There are several potential reasons for sampling, such gaining an overview of the pollution situation or to more accurately define the dispersion of pollution and identify hotspots before taking action. Thus, it may be necessary to sample the area multiple times.
Knowing what substances are found at different sediment depths is important for understanding how pollution dispersion varies over time and the associated risks. The surface sediments on an accumulation bed reveal which pollutants are being added at the time of sampling and can provide evidence of current sources negatively impacting the sediments. The ecosystem of the water may also need to be studied to assess risk and define potential measures.
Risk assessment
The overall purpose of risk assessment in the context of remediation is to estimate associated risks and how much the risks need to be reduced to mitigate negative effects on the environment, health and natural resources for current and future generations.
The risk assessment is based on the Swedish EPA’s basic assumptions for contaminated sites, including contaminated sediment sites. These assumptions include protecting human health and the environment at the site and in surrounding areas. It is not permitted for dispersion of pollution from a polluted site to lead to elevated background levels or to releases that risk impacting groundwater and surface water quality. The risk assessment provides the basis for investigating which potential measures should be taken to achieve an acceptable level of risk. The results are also used as a basis for investigating which measure is most suitable and for developing measurable targets before a remediation.
A risk assessment may also be needed to prepare for work in water, if contaminated sediments are affected, even when the primary purpose is not remediating the contaminated sediments. This can apply to dredging of sea lanes or maintenance dredging in a port. The risk assessment can provide the basis for evaluating such aspects as risks for spreading pollution during dredging and assessing which protective measures are needed.
When assessing risks with a sediment, several factors has to be considered. In addition to levels of various substances, their bioavailability and the risk of dispersion need to be assessed.
Assessment criteria
Assessment criteria help in assessing the level of contamination in sediments. Assessments can have different purposes. For example:
- Determine whether the site should be classified as a contaminated site, as per Chapter 10 of the Environmental Code and, in case of remediation, produce threshold values (remediation).
- Assess whether special precautionary measures are needed when dredging, as per Chapter 11 of the Environmental Code (water activities).
- Assess whether dredged masses are contaminated, in connection with the exemption application from the dumping ban, as per the Waste Ordinance (Chapter 15 of the Environmental Code).
- Assess whether “good status” has been achieved, as per the Water Management Ordinance (VFF) and HVMFS 2019:25 (water management).
- Assess whether “good environmental status in the marine environment” has been achieved, as per the Marine Environment Ordinance and HVMFS 2012:18 (marine environmental management).
- Decide whether measures or requirements are necessary (such as threshold values) to ensure that a specific operation contributes to fulfilling standards, as per chapters 9 and 26 of the Environmental Code and associated ordinances and regulations (review and supervision of environmentally hazardous activities).
- Evaluate monitoring data from a more general perspective to draw conclusions about whether the environmental quality objectives can be achieved or whether there is a general problem with specific substances, what the trend looks like and so on (environmental quality objective follow-up).
When presenting the results of the pollution situation assessment, it is important to be clear about what the purpose of the assessment has been and how the results are intended to be used.
Effect-based and indicative threshold values as support
Effect-based threshold values can be helpful in gaining a basic picture of the risks associated with a sediment site. Sweden has effect-based threshold values for certain priority substances (anthracene, fluoranthene, cadmium, lead and tributyltin) in sediments for assessing chemical status. These are listed in regulation HVMFS 2019:25 from the Swedish Agency for Marine and Water Management. There are also assessment criteria for specific pollutants (siloxanes, D4 and D5, and copper) in sediments and which are used in the assessment of ecological status.
The Swedish Agency for Marine and Water Management also provides indicative values. See report 2018:31 for an indication of where follow-up investigations may be needed, such as for identifying significant sources.
Reference values for organic environmental toxins and metals in sediments
The Swedish EPA, together with the Geological Survey of Sweden, has produced a table presenting the distribution of organic environmental toxin levels in Swedish marine sediments. There is also a table of the distribution of concentrations of metals in Swedish limnic sediments (see below). The values in these tables can only be used for comparative descriptions of contaminated sediment sites, e.g., to assess whether the contaminant levels in a sediment site are above national background levels. A classification using the values in the table says nothing about the presence of negative effects in the environment.
Please note that the general threshold values for soil are not suitable for use when evaluating sediment data.
Read more about assessment of contaminated sediments at:
Table: Organic environmental pollutants in marine sediments
The corresponding table was previously published in the Swedish EPA’s report 4914 (1999) Assessment Criteria for Environmental Quality – Coast and Sea.
The updated table includes samples taken between 1986 and 2014 in marine sediments and more substances than before, including organotin compounds and PBDEs. The database for limnic sediments is not yet large enough to produce a similar table. A more detailed description of the update is found in the SGU report 2017:12.
The table can serve as a reference tool when assessing a sediment’s pollution content. For most substances, the levels have been divided into five classes, from very low to very high. A classification involves judging whether the content is low or high in relation to other samples and says nothing about the presence of negative effects in the environment. For status classification within water management, use the assessment criteria found in HVMFS 2019:25.
The table below shows the distribution of organic environmental toxins in marine sediments in Swedish sea areas and economic zones (µg/kg dry weight). These levels should not be normalised for carbon content, and these levels and class limits are not linked to effect-based values.
The boundary between class 1 (Very low content) and class 2 (Low content) has been set at the 5th percentile of all data, the boundary between class 2 and class 3 (Medium content) at the 25th percentile, the boundary between class 3 and class 4 (High content) at the 75th percentile, and the boundary between class 4 and class 5 (Very high content) at the 95th percentile. This means that half of the values fall into class 3, ranging from the 25th to the 75th percentiles. Other percentile limits apply to tin compounds (see the background report). All data have been used, even samples with concentrations below the reporting limit. In cases where many data points are below the reporting limit, one or more of the lower classes are missing, as the 5th percentile, or sometimes even the 25th percentile, of data is below the reporting limit. In such cases, a sample may be classified as class 1–2 or 1–3.
The boundary between class 1 and class 2 roughly corresponds to the lowest concentrations in samples taken in areas far from local sources, such as in the open sea, while samples from areas with a high degree of pollution, often close to the coast, are given class 5.
The following table shows the distribution of organic environmental toxins in marine sediments in Swedish sea areas and economic zones (µg/kg dry weight) for the period 1986–2014.
|
Substance |
Class 1 |
Class 2 |
Class 3 |
Class 4 |
Class 5 |
|
Very low content |
Low content |
Medium high content |
High content |
Very high content |
|
|
Naphthalene |
<4,9 |
4,9-19 |
19-63 |
>63 |
|
|
Acenaphthene |
<5,5 |
5,5-33 |
>33 |
||
|
Fluorine |
<2,0 |
2,0-9,4 |
9,4-35 |
>35 |
|
|
Phenanthrene |
<7,0 |
7,0-17 |
17-50 |
50-150 |
>150 |
|
Anthracene |
<1,0 |
1,0-3,1 |
3,1-11 |
11-45 |
>45 |
|
Fluoranthene |
<18 |
18-45 |
45-140 |
140-390 |
>390 |
|
Pyrene |
<12 |
12-30 |
30-100 |
100-380 |
>380 |
|
Benz(a)anthracene |
<7,5 |
7,5-19 |
19-62 |
62-180 |
>180 |
|
Chrysene |
<11 |
11-26 |
26-67 |
67-200 |
>200 |
|
Benz(b)fluoranthene |
<32 |
32-69 |
69-200 |
200-440 |
>440 |
|
Benz(k)fluoranthene |
<11 |
11-28 |
28-79 |
79-180 |
>180 |
|
Benzo(a)pyrene |
<12 |
12-31 |
31-99 |
99-240 |
>240 |
|
Dibenz(ah)anthracene |
<4,4 |
4,4-8,9 |
8,9-27 |
27-79 |
>79 |
|
Benzo(ghi)perylene |
<22 |
22-62 |
62-180 |
180-400 |
>400 |
|
Indeno(1,2,3-cd)pyrene |
<24 |
24-76 |
76-220 |
220-530 |
>530 |
|
Total PAH 11 |
<170 |
170-440 |
440-1200 |
1200-2800 |
>2800 |
|
Total PAH 15 |
<250 |
250-440 |
440-1200 |
1200-4700 |
>4700 |
|
Total PAH M1 |
<57 |
57-110 |
110-320 |
320-1700 |
>1700 |
|
Total PAH H2 |
<180 |
180-320 |
320-940 |
940-2600 |
>2600 |
|
Hexachlorobenzene |
<0,020 |
0,020-0,15 |
0,15-0,45 |
0,45-1,6 |
>1,6 |
|
PCB 28 |
<0,066 |
0,066-0,30 |
0,30-1,3 |
>1,3 |
|
|
PCB 52 |
<0,12 |
0,12-0,40 |
0,40-1,9 |
>1,9 |
|
|
PCB 101 |
<0,10 |
0,10-0,34 |
0,34-1,1 |
1,1-5,5 |
>5,5 |
|
PCB 118 |
<0,084 |
0,084-0,31 |
0,31-0,84 |
0,84-3,6 |
>3,6 |
|
PCB 138 |
<0,21 |
0,21-0,67 |
0,67-2,0 |
2,0-9,1 |
>9,1 |
|
PCB 153 |
<0,20 |
0,20-0,61 |
0,61-2,0 |
2,0-7,9 |
>7,9 |
|
PCB 180 |
<0,081 |
0,081-0,29 |
0,29-0,90 |
0,90-4,9 |
>4,9 |
|
Total PCB 7 |
<0,81 |
0,81-2,5 |
2,5-7,6 |
7,6-34 |
>34 |
|
α-HCH |
<0,006 |
0,006-0,04 |
0,04-0,17 |
0,17-0,36 |
>0,36 |
|
β-HCH |
<0,003 |
0,003-0,11 |
0,11-0,57 |
0,57-1,2 |
>1,2 |
|
γ-HCH |
<0,006 |
0,006-0,034 |
0,034-0,12 |
0,12-0,30 |
>0,30 |
|
Total HCH |
<0,025 |
0,025-0,21 |
0,21-0,87 |
0,87-2,0 |
>2,0 |
|
γ-chlordane |
<0,018 |
0,018-0,090 |
0,090-0,39 |
>0,39 |
|
|
α-chlordane |
<0,006 |
0,006-0,082 |
0,082-0,30 |
>0,30 |
|
|
trans-Nonachlor |
<0,021 |
0,021-0,088 |
0,088-0,30 |
>0,30 |
|
|
Total chlordane |
<0,063 |
0,063-0,27 |
0,27-0,81 |
>0,81 |
|
|
p,p'-DDT |
<0,019 |
0,019-0,29 |
0,29-2,0 |
>2,0 |
|
|
p,p'-DDD |
<0,029 |
0,029-0,32 |
0,32-1,7 |
1,7-5,3 |
>5,3 |
|
p,p'-DDE |
<0,057 |
0,057-0,32 |
0,32-1,2 |
1,2-3,6 |
>3,6 |
|
Total DDT |
<0,32 |
0,32-0,89 |
0,89-3,5 |
3,5-10 |
>10 |
|
PBDE 47 |
<0,045 |
0,045-0,11 |
0,11-0,37 |
>0,37 |
|
|
PBDE 100 |
<0,041 |
0,041-0,14 |
>0,14 |
||
|
PBDE 99 |
<0,047 |
0,047-0,13 |
0,13-0,47 |
>0,47 |
|
|
PBDE 85 |
<0,15 |
0,15-0,55 |
>0,55 |
||
|
PBDE 209 (Deca) |
<2,4 |
2,4-13 |
>13 |
||
|
EOCl |
<200 |
200-830 |
830-2700 |
2700-5600 |
>5600 |
|
EOBr |
<180 |
180-590 |
590-1900 |
1900-3000 |
>3000 |
|
EPOCl |
<100 |
100-560 |
560-2100 |
>2100 |
|
|
EPOBr |
<88 |
88-480 |
480-700 |
>700 |
|
|
monobutyltin (MBT) |
<1 |
1-10 |
10-20 |
>20 |
|
|
dibutyltin (DBT) |
<1 |
1-10 |
10-26 |
>26 |
|
|
tributyltin (TBT) |
<1 |
1-19 |
19-55 |
>55 |
1PAH M = five PAH with medium molecular weight
2PAH H = eight PAH with high molecular weight
Choosing remedial action
Sediment is part of the water environment and is partly covered by different regulations and environmental and sustainability goals than what applies on land. When designing overall and measurable goals for measures, it is important to take this into account.
The methods for remediating contaminated sediments are different from methods on land. Before choosing a remedial method, the conditions on the site need to be well investigated. Such factors as water depth, bottom slope, objects on the bottom and dispersion of the contamination greatly influence which method is suitable. The area’s current and future use can also be decisive for which measures can and need to be taken.
The Åtgärdsportalen (the measures portal) provides more information about various remedial methods to clean up contaminated sediment sites.
Support and regular guidance
The Swedish EPA, SGU and the Swedish Agency for Marine and Water Management regularly are consulted by supervisory authorities and other stakeholders regarding contaminated sediments. This is done based on each authority’s routines. Additionally, SGI provides special support from experts that is funded by the remediation appropriation.
If SGI is asked for expert support not related to SGI’s area of expertise, SGI forwards these questions to the relevant authority.
Read more about expert support on contaminated sediment (sgi.se)
Guidance from the Swedish Agency for Marine and Water Management
The Swedish Agency for Marine and Water Management provides guidance on water activities, dredging and handling of dredged masses, dumping of dredged masses and environmental quality standards for surface water.
Dredging and digging and filling (havochvatten.se)
Environmental quality standards for surface water (havochvatten.se)
Collective knowledge and tools
At renasediment.se, you can find knowledge, facts and tools for more efficient handling of contaminated sediments. The action portal includes comprehensive information on remedial treatment of contaminated sediments and a separate report on the current state of knowledge on fibre banks.