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Håndtering af lettere forurenet jord - Fase 1

Summary and conclusions

In order to support the development of new Danish regulations on the utilisation of lightly contaminated soil, a study has been carried out to determine the feasibility of using limit values for the content of contaminants in the soil instead of limit values for leaching of the contaminants, while still maintaining a safe level of protection of the groundwater. The study has investigated whether a combination of a sufficiently low level of solid content of contaminants in the soil and certain requirements on the way the soil is utilised can ensure that a utilisation project will not cause an unacceptable impact on the quality of the downstream groundwater.

Approach

The study, which has been based on existing data, has included collection and evaluation of corresponding determinations of solid content and leaching properties of a number of inorganic and organic contaminants for a substantial number of soil samples from Denmark, Sweden and Belgium. Limit values, which may be expected to ensure that the impact on groundwater at the point of compliance (POC) downstream of the project will not exceed a level determined by the Danish Environmental Protection Agency (DEPA), have been calculated for a number of utilisation scenarios. For inorganic contaminants, the limit values for release from the soil refer, e.g., to batch leaching test EN 12457-1 at L/S = 2 l/kg, whereas the limit values for release of organic contaminants refer the so-called equilibrium column test at L/S = approx. 1 l/kg. The scenario calculations have followed the same principles as those upon which the development and implementation of the EU leaching acceptance criteria for waste to be landfilled were based.

In addition to the contamination parameters that are currently included in the definition of lightly contaminated soil, the study has included parameters which will be part of the future requirements on soil and waste to be disposed of at landfills for inert or mineral waste.

The project scenarios considered in the study are listed below:

The relationship between the solid contents and the leaching properties of the contaminants for the collected datasets for contaminated and uncontaminated soil has been evaluated and compared to the calculated limit values for release of contaminants for a number of different project scenarios where the height, surface area and the rate of infiltration, as well as the distance to the POC have been varied. By showing this relationship and the calculated leaching limit values graphically and inserting the proposed limit values for the solid content of the contaminants, it has been evaluated whether the latter can be expected to ensure, under various conditions, that the downstream criteria for groundwater quality set by the DEPA will not be exceeded at the POC. The limit values for solid content of contaminants in DEPA’s proposals for utilisation of lightly contaminated soil are shown below:

The study has resulted in a number of recommendations concerning the conditions for design and location of lightly contaminated soil utilisation projects and a number of conclusions and recommendations concerning the contaminants studied, as well as the quality of the available data upon which the study was based. As a general rule, it is recommended that the future regulation on lightly contaminated soil utilisation, if it is based on solid content of contaminants, includes an option if one or more of the solid content limit values are exceeded instead of using leaching tests and comparing the results with appropriate leaching limit values.

Recommended conditions for design and location of lightly contaminated soil projects

Based on the above as well as other considerations, a number of design and location conditions intended to protect the environment and, in particular, the groundwater quality can be proposed for utilisation of lightly contaminated soil:

• The maximum size of a single utilisation project is 100 m by 100 m. This will ensure that the groundwater quality criteria are not exceeded 100 m downstream in any direction from the project (the diagonal distance of a 100 m by 100 m area will be 140 m, but this falls within the safety margins of the calculations).
• All utilisation projects exceeding 100 m in one direction will, therefore, require submission of a specific permit application which documents that no unacceptable impacts on water extraction wells from secondary or primary aquifers in the area will result from the project.
• In order to protect single groundwater extractions, utilisation projects must not be placed less than 100 m from an existing groundwater extraction wells or installations.
• The maximum project height without infiltration-reducing measures and without a separate permit application is 1 m.
• If it is required to apply greater heights than 1 m (without restrictions of the area size), a corresponding reduction in the rate of infiltration through the material must be accounted for, e.g., for a height of 2 m, the net rate of infiltration must be reduced to half its original value (to 175 mm/year), for example, by changing the properties of the top layer. Alternatively, a separate permit application must be submitted.
• The sizes and number of projects must be seen in the context of a surface area of maximum 1% of the total surface area of a catchment area, a municipality or other relevant segments.

When applying the above listed guidelines, problems may arise with utilisation of lightly contaminated soil for projects of other dimensions such as, e.g., roads and noise barriers.

A road will normally be long and relatively narrow and will generally have a dimension longer than 100 m. Hence, there is a risk that the use of lightly contaminated soil in construction of roads may cause an impact of the groundwater 100 m downstream in certain directions that exceeds the groundwater quality criteria. In many cases the use of lightly contaminated soil for road construction will reduce the rate of filtration through the soil and will, thereby, reduce the impact on the groundwater. It may be necessary to set up special requirements for utilisation of lightly contaminated soil for road construction.

It may also be necessary to set up special requirements for utilisation of lightly contaminated soil for sound barriers. Sound barriers with heights exceeding 1 m could possibly be allowed if the area extension was restricted. The requirement on the area extension of the utilisation project will be a function of the restrictions placed on the leaching of contaminants from and/or the content of contaminants in the soil, which will probably again, to a certain extent, depend on the leaching criteria eventually set for acceptance of soil at landfills for inert or mineral waste.

Considerations and recommendations concerning limit values based on solid content of contaminants

Inorganic contaminants

Extensive data exist for As, Cd, Cu, Ni, and Pb, and they seem to indicate that the risk of exceeding leaching criteria that correspond to a utilisation scenario with a 100 m extension in the direction of the groundwater flow, a distance of 100 m to the POC and a height of 1 m (scenario 3) and the EU limit values for acceptance of waste at inert landfills (Inert-LFD) is rather low if the limit values for solid content proposed by the DEPA are used, in particular, if they are supplemented by a requirement that the pH of the soil in a slurry with water must remain between 6 and 9. The same seems to be the case for Hg, albeit on the basis of a more limited number of datasets.

Extensive data also exist for Cr and Zn, but there seems to be a higher risk of exceeding the leaching criteria here, including when there are requirements placed on the pH range. As far as chromium is concerned, it might be worth considering to replace the solid content limit value with a limit value on leachable Cr(VI). It might also be worth considering to place specific restrictions on soil from sites where the contamination originates from wood impregnation activities (and other sites where Cr is known to be part of the contamination). For Zn, a lower limit value for the solid content, e.g., 100 mg/kg, could be considered. This would provide a far higher probability that the release will be acceptable. At the same time, the data seem to indicate that uncontaminated soil generally has a content of Zn below 100 mg/kg.

At the moment, no proposals for solid content criteria exist for Ba, Mo, Sb and Se in connection with utilisation of lightly contaminated soil. For Ba, the number of datasets is considerable, and there seem to be no problems for compliance with the leaching limit values corresponding to scenario 3, scenario 4 and Inert-LFD. In contrast, the number of available datasets for Mo, Sb and Se is very low. For solid contents of Se of up to 10 mg/kg, no conflicts with the leaching limit values corresponding to scenario 3 and scenario 4 and Inert-LFD are observed, whereas all datasets exceed these limit values for Sb. For Mo, the small set of data (8 samples) indicates that a solid content limit value of 10 mg/kg could possibly ensure a low probability of exceeding the relevant leaching criteria.

The DEPA has also proposed solid content limit values for total cyanide and acid dissociable cyanide. No available data for evaluation of these contaminants have been found.

It is recommended that the data material be improved (i.e., that the number of corresponding determinations of solid content and leachability performed on appropriate soil samples be increased), in particular, for Cr/Cr(VI), Mo, Sb and Se, as well as for total cyanide and acid dissociable cyanide, if a qualified investigation has to be carried out in order to determine the possibility of setting an upper limit for the solid content that can ensure compliance with the selected leaching criteria for lightly contaminated soil. For Sb, perhaps a review of the background for establishing the groundwater and leaching criteria should be carried out in order to ensure that the very low limit values are based on realistic information (and if this is not the case, it should be considered if they need to be changed).

Organic contaminants

As far as organic contaminants are concerned, it must be stated, to begin with, that the number of relevant datasets available, particularly for the hydrocarbons, is too limited to provide sufficient information on the possibility of setting an upper limit for the solid content that can ensure compliance with leaching criteria for lightly contaminated soil, that correspond to certain selected utilisation scenarios.

Based on the existing available data, it appears that establishing such an upper limit may be problematic for total hydrocarbons, gasoline and gas oil with the proposed solid content limit values (but as mentioned, the data material is very limited).

For PAHs, including naphthalene, it may be possible to establish an upper limit of solid content that can provide a high probability that the leaching will not exceed certain limit values that correspond to selected scenarios. With the proposed solid content limit values, nearly all datasets comply with the leaching limit values as defined by scenarios 1 and 2, and most datasets also comply with those defined by scenarios 3 and 4. This picture can be upset somewhat by the fact that PAHs from “old” contaminations are often less mobile then PAHs from “newer” contaminations.

For BTEX and gasoline, no useful data material has been found. It should be noted that the EU has set a limit value of 6 mg/kg for the solid content of BTEX in waste to be accepted at landfills for inert waste. Until a possible background for determining a solid content limit value based on the risk of leaching and subsequent impact on groundwater is established, it is recommended to replace the solid content limit valued for BTEX proposed by DEPA (10 mg/kg) with the EU value (6 mg/kg) in order to preserve the consistency between different regulations affecting soil management.

It is strongly recommended to establish a much better basis for evaluating the feasibility of applying relatively safe solid content limit values for utilisation of lightly contaminated soil for both hydrocarbons and PAHs.

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Version 1.0 Maj 2009, © Miljøstyrelsen.