Guidelines on remediation of contaminated sites
2. Strategy
2.1 Division of efforts into phases
The choice of strategy is determined by the objectives of the investigations. An investigation may be carried out in connection to the purchase/sale of property, for the purpose of listing the site as contaminated or for the purpose of remediating the site. These guidelines deal primarily with investigations carried out in connection with risk assessments of human health and the environment, and with possible subsequent remediation with regard to the established risk.
When choosing which strategy to apply, it is appropriate to divide the process into the following stages:
 | The initial survey phase |
| The investigation phase |
| The remediation phase |
| The operation and evaluation phase |
The division into phases is a good way in which to divide the work that is to be done. After each phase, the need for further measures is assessed. The division thus aims at optimising the use of information obtained in one phase for the planning of subsequent actions.
The reporting of activities that have been implemented does not necessarily follow the division of phases. Several phases can be reported at the same time (e.g. the initial survey phase and the investigation phase), and several reports can be made in one phase (e.g. following both the preliminary and the supplemental portion of the investigation phase).
Much is already known about investigations and remediation within certain sectors. This entails that, in some sites, phases can be ‘grouped’. Furthermore, mapping information /1/ or listing investigations are already available at many sites, thus overlapping the initial survey phase and the investigation phase.
So as to implement investigations and remediation as rationally and appropriately as possible, the strategy, and therefore the choice of phase division, is based on the available knowledge regarding the site. In some instances, it can be practical to implement investigations and remediation in accordance with the procedures applied in ordinary building and construction projects /2/. In the following, the contents of the four phases will be described briefly.
The connection between the four phases and the sections in these guidelines are shown in figure 2.1.
Fig. 2.1
Division of activities into phases.
2.2 The initial survey
The objective of this phase is to obtain the best possible basis for implementing the investigation of a contaminated site.
In the initial survey, information about the site which can support further measures should be collected. This should include information from existing charts and maps. In this phase, a historical review of the site should be prepared with the purpose of advancing a hypothesis regarding which contaminants may be present and where contamination can be expected.
2.3 The investigation phase
2.3.1 Objective
Investigations of contaminated sites typically aim at describing:
| The collection of representative data to be used in risk assessment. |
| The extent and intensity of soil contamination. |
| Indoor air problems in buildings due to evaporation of hazardous substances. |
| Risk of explosions in buildings and installations due to landfill gas. |
| Spreading of contaminants in superficial and deeper groundwater and possibly to a surface water recipient. |
The investigation phase comprises:
| Investigations |
| Risk assessment |
| Reports |
| Outline project |
Investigation techniques include boring, collection of soil, water and air samples, characterisation of samples and chemical analysis of samples.
Sampling should be planned in accordance with the investigation’s objective to ensure that the number and the selection of samples ensure that the objective can be met. This has been described in further detail in Guidelines for Sampling and Soil Analysis /3/.
If it is possible to foresee a remediation project before the investigation phase is put into action, then the investigation should be planned so as to be aimed towards this project.
Field and laboratory investigations should be planned so as to be aimed at collecting data which can be used in risk assessments of groundwater, land use and surface water recipients.
Investigations and risk assessments should always be reported. If investigations are carried out in several stages, such as preliminary and supplemental investigations, these should be reported independently of one another. However, all results should be taken into account in the overall risk assessment.
In cases where remediation is necessary, the investigation phase should be concluded by drawing up an outline project. Several different proposals for remediation techniques are typically discussed with the authorities before the outline project is drawn up.
2.3.2 Preliminary investigations
The objective of preliminary investigations is to test the hypothesis put forward in the initial survey, and to obtain an impression of how contaminated the site is.
The strategy for preliminary investigations should be based on information that has been gathered in the initial survey.
Soil borings should typically be placed at locations where contaminants are likely to be found, and should determine the extent of previously known contamination. Soil borings should be placed in such a manner as to cover areas with contamination-sensitive land use as well as other areas, where contamination may be found.
Placement of number of soil borings are dealt with in more detail in Chapter 4 and in Guidelines for Sampling and Analysis of Soil /3/.
When preparing for water sample collection, it is advisable to construct wells in the source area or immediately down gradient in order to determine the contamination strength of the source. When estimating the strength of the source, the distance between the well and the source of contamination - and thus the preceding dilution - should be taken into consideration.
Sometimes it is possible to take water samples in the sand fill around a tank or pipeline so as to establish the strength of the source.
The final sampling strategy is based on data collected in the initial survey and an analysis programme should be prepared.
The analysis programme in a preliminary investigation is typically quite general in nature. In supplemental investigations, when the problems have been identified, a more narrowly targeted programme can be applied.
Preliminary investigations should be concluded with an assessment of whether sufficient evidence has been established which illustrates the site’s contamination and which enables reliable and representative risk assessment.
Should the preliminary investigations indicate that the site is so contaminated that more detailed information is required, a proposal for supplemental investigations should be prepared.
2.3.3 Supplemental investigations
The objective of supplemental investigations is to clarify problems which have been established in preliminary investigations.
The investigations should typically be performed in order to:
| Give a more detailed description of type, severity and extent of contamination in soil or groundwater near the surface. |
| Clarify land use possibilities. |
| Assess the risk of indoor air problems, including the risks from landfill gasses, in existing buildings and installations on and near the site (contaminants transported via the sewer system or groundwater). |
| Assess the possible effect of contaminants on deeper groundwater aquifers or nearby surface water recipients. |
| Prepare an outline project, if needed. |
If remediation is deemed necessary, supplemental investigations should lead to one or more outline projects. Outline projects should consist of an overall description of the fundamental technical solutions and include a rough estimate of the cost of such a solution and a time table.
2.3.4 Risk assessment
Risk assessments are assessments of the environmental and health consequences of a given contamination. The objective of risk assessments is to establish the need for remediation.
Risk assessments are based on specific situations and information on the contaminants, contaminant transport and exposure pathways, and the target group in question in the given situation. The risk related to land use, to evaporation and to groundwater should be assessed independently of one another.
Criteria for soil quality have been established to be used in risk assessments in relation to land use. Sites where the soil fully lives up to these criteria can be used without restriction for all purposes including those that are highly sensitive to contamination. Furthermore, a cut-off criteria has been established for several contaminants. These criteria state the level at which it is necessary to prevent all contact with the soil. Principles for remediation (such as clean-up depths) and principles for assessment of soil contamination are stated in Section 9.2. It should be noted that compliance with soil quality criteria does not necessarily ensure compliance with evaporation and groundwater criteria.
At contaminated sites, indoor air in buildings as well as outdoor air may be unacceptably affected by underlying contamination of soil or groundwater. The effect on the indoor and outdoor air should be assessed in stages by various methods that have been constructed. In several stages, theoretical calculation models are included. Risk assessment should be based on evaporation to the overlying air and must not exceed the acceptable contamination contribution.
The risk of methane gas explosions in buildings on or in the immediate proximity of landfill sites can also be assessed in stages.
Risk assessment of groundwater should be used to assess whether contamination of either soil or upper groundwater aquifer contributes unacceptably to the contamination of groundwater resources. Groundwater quality criteria have been established for use in risk assessments. Risk assessments should be based on the aquifer complying with groundwater criteria at all points. Risk assessment can be carried out in stages, starting with a simple assessment. If this assessment does not provide enough evidence of the lack of risk, more complicated calculations should be carried out. Sorption, dispersion and degradation of the contaminants should be taken into account in these calculations. Furthermore, the assessment of the effect on the groundwater should be used to perform a risk assessment for surface water recipients.
If the risk assessment establishes a risk to human health or the environment, residents on or in the proximity of the site should be advised as to how to act until remediation can be implemented.
2.4 The remediation phase
The objective of the remediation phase is to plan in detail and implement the required remediation. The aim of remediation is to remove contaminants, limit exposure or prevent the spread of contaminants to soil, water or air.
Remediation can be extremely varied. It can involve a simple excavation of soil near the surface, a long-term pump-and-treat technique for contaminated groundwater, or a complicated in-situ techniques.
In the course of detailed planning, it is often necessary to perform supplemental investigations that specifically aim at the chosen remediation technique. Investigations could, for example, include detailed mapping of the extent of contamination or a pump test for designing soil vapour extraction.
If the concentration of the contaminant is below cut-off criteria, the precautions stipulated in Guidelines Regarding Advice of Residents in Mildly Contaminated Areas /4/ can be carried out.
2.5 Operation and evaluation phase
The objective of the operation and evaluation phase is to check the effect of remediation.
Before the operation and evaluation phase is put into action, procedures for evaluating measured parameters should be prepared. These should include alarm values with a view to adapting the remediation and stop criteria with a view to stopping the operation and evaluation phase. Procedures should also describe the frequency and form of reports, in which operation and evaluation measures should continuously be assessed to ensure that the required environmental effect is achieved.
2.6 Strategy for distribution of information
Depending on the extent of the actions, residents who are affected by these should be informed of what is being done. This kind of information should be an integral part of the entire process. A high level of information can ensure that the planned activities can proceed as smoothly as possible.
The problem holder is responsible for providing residents with the necessary information. This can be done by sending letters of information. Residents in the area are best informed by holding information meetings supplemented by the letters of information.
Residents should receive information regarding the planned activities before the first measures are put into action. This information should be followed up throughout the entire process, informing the involved parties about planned actions, results, conclusions and consequences. Furthermore, the information should contain a time table for the entire operation, including plans for further information.