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Håndtering af lettere forurenet jord - Konsekvensvurdering

Summary and conclusions

This report presents the results of a project conducted by DHI on behalf of the Danish EPA. The study is based on the results obtained in previous studies reported in:

• DHI (2007) Håndtering af lettere forurenet jord. Slutrapport juni 2007.
• DHI (2008) Håndtering af lettere forurenet jord – supplerende data for udvaskning af uorganiske og organiske stoffer fra jord. Slutrapport februar 2008.

The Danish EPA has laid out the framework for this project, as seen in Annex A (in Danish).

The Danish EPA wish to regulate the re-use of soil by dividing the soil into two categories based on either the solid content of contaminants or the leaching of contaminants, as illustrated in Figure 0.1.

Figure 0.1. Definition of categories of soil for re-use.

The classification of soil can be based either on solid content or on leaching of contaminants. Soil classified as category 1 should be free for re-use in construction work without any additional restrictions. Soil classified as category 2 should be re-used in construction work under specified conditions.

This project is divided into three main parts:

1. Determination of limit values based on solid content for category 1.

2a. Determination of limit values based on solid content for category 2 when reused on a bottom liner.

2b. Evaluation of project sizes using soil classified as category 2 without a membrane.

3. Determination of limit values based on leaching for category 1 and 2.

The limit values calculated in this study are solely based on considerations concerning the protection of groundwater. The data collected in previous work, consisting of both solid content and leaching results (DHI 2007, 2008), constitute the basis of this study. The methods, results and conclusions are summarised for each part below.

Limit values based on solid content – category 1.

Limit values for category 1 must provide sufficient protection of the groundwater when re-using soil classified in this category. This is fulfilled if the concentrations of contaminants in the soil pore water do not exceed the groundwater quality criteria.

As a starting point, the Danish EPA has proposed the Danish soil quality criteria as limit values for category 1. For selected contaminants, it was evaluated if the concentrations of the contaminants in pore water could be expected to be lower or equal to the groundwater quality criteria.

Based on the results obtained from leaching test conducted on a number of different soils (DHI 2007, 2008), the pore water concentrations were calculated for each soil and each contaminant, assuming that the L/S ratio of 0.27 l/kg represents pore water.

It was decided by the Danish EPA that the proposed limit values should be evaluated allowing a minor part of the collected data to exceed the groundwater quality criteria. This was formulated in the following decision model:

Model 1:

The pore water concentration must be lower than the groundwater quality criteria for 85% of the data. The pore water concentration must be lower than 10 times the groundwater quality criteria for 100% of the data.

This model was tested for the following parameters:

As, Cd, Cr(total), Cu, Hg, Mo, Ni, Pb, Sb, Se, Zn, naphthalene, benz(a)pyrene, dibenz(a,h)anthracene and Sum of 7-PAH, hydrocarbons (C₆-C₁₀, C₁₀-C₁₅, C₁₅-C_20, C₂₅-C₄₀).

If the data for a given parameter could not fulfil the requirements in model 1, a lower limit value that meets the requirements was suggested (if possible). As regards inorganic compounds, the evaluation showed that it was necessary to add a supplementary requirement to the limit values based on the pH-value in the pore water. Thus, all data with pH below six and above nine in the eluates from the leaching test were removed from the data collection. Table 0.1 provides an overview of the results from the evaluation of soil quality criteria using model 1.

Table 0.1 Evaluation of soil quality criteria (JKK) as limit values for category 1. The evaluation is based on model 1.

As shown in table 0.1, the soil quality criteria fulfilled the requirements in model 1 only for a few compounds. It was not possible to find lower limit values that fulfilled the requirements for Pb and the hydrocarbons.

The Danish EPA decided to re-evaluate the soil quality criteria as limit values for category 1 using a less restrictive model;

Model 2

The pore water concentration must be lower than the groundwater quality criteria for 75% of the data. The pore water concentration must be lower than 10 times the groundwater quality criteria for 95% of the data.

The results of the re-evaluation are shown in table 0.2.

Table 0.2 Evaluation of soil quality criteria (JKK) as limit values for category 1. The evaluation is based on model 2.

The re-evaluation of the data using the soil quality criteria as limit values showed that the requirements in model 2 were fulfilled for most of the components, except for Pb and the hydrocarbons. For the fraction C₂₀-C₄₀, a limit value lower than the soil quality criteria was suggested but for the other fractions of hydrocarbons and Pb, it was not possible to fulfil the requirement in model 2 at all. For the fractions of hydrocarbons (C₆-C_10, C₁₀-C_15, C₁₅-C₂₀), this resulted in the proposal of limit values equal to the analytical detection limits. For Pb, a different approach for setting a limit value was needed.

Lead is a heavy metal which is strongly retarded in soil due to precipitation and sorption and thus the mobility of this metal in soil is generally low. Therefore, it would be reasonable to include these physical and chemical properties of the metal when setting up limit values for protection of groundwater. Based on model calculations performed in a previous study (DHI 2007), a limit value at 10 mg/kg TS could be proposed for Pb on condition that the dimensions of the construction work do not exceed 100 m in length and 5 m in height. If this condition is met, the groundwater quality will be unaffected at a distance of 30 m from the construction work.

Assuming that the conditions laid out in model 2 are acceptable, the soil quality criteria can be used as limit values for category 1 for most of the components. It was necessary to set up limit values lower than the soil quality criteria only for the hydrocarbons and for Pb. Table 0.3 shows the proposals for category 1 limit values.

Table 0.3 Category 1 limit values fulfilling the requirements in model 2 - except for Pb. The limit value suggested for Pb is based on model calculations allowing for retardation and dilution.

1. Limit value not based on leaching data but equal to the limit value of the fraction C₂₀ – C₄₀.
2. Proposal for limit values equal to analytical detection limit. For C₆-C_10, the analytical detection limit may be lower sometimes, but the limit value for this fraction is suggested to be 10 mg/kg TS.
3. The evaluation is based on very few data – only 8 soil samples.

Based on a database of solid content analyses for 6320 soil samples, it was calculated what percentage of these soils would comply with the proposed limit values for category 1 soil. However, it was not possible to evaluate the limit values suggested for the hydrocarbons as the analytical method had recently been changed. Based on the analysis results for Cd, Cr, Cu, Ni, Zn, sum of PAH, benz(a)pyrene and dibenz(a,h)anthracene, approx. 60% of the soil samples would be classified as category 1. If the suggested limit value for Pb (10 mg/kg TS) was included, approx. 13% of the soil samples would belong to category 1.

Based on model 2 for setting and evaluating the limit values for category 1, it was accepted that up to 25% of the soil sample data exceeded the groundwater quality criteria, and for 5% of the data, the excess could be more than 10 times the groundwater quality criteria. Therefore, a simple and conservative evaluation of the consequences of this model was conducted. It was assumed that up to 15% of an area could be covered by re-used soil classified as category 1. The results of the evaluation showed that the groundwater quality was affected by an order of 20 – 86% of the groundwater quality criteria, with the highest impact coming from Zn.

Limit values based on solid content – category 2. Re-use on bottom liners

Soil classified as category 2 may be re-used in construction work using a bottom liner. For this purpose, limit values are set up. These limit values must provide sufficient protection of groundwater, also when the functionality of the bottom liner is lost. Thus, the concentration of contaminants in pore water from the soil must not exceed the groundwater quality criteria when the bottom liner ceases to function.

During the active phase of a bottom liner, leachate will be collected and disposed of and when the functionality of the bottom liner is lost, the source term will be reduced.

The reduction in source term was calculated for eight different scenarios of re-use of soils on bottom liners. The scenario providing the lowest reduction in source term was used for evaluation of the category 2 limit values proposed by the Danish EPA. The limit values were evaluated on the basis of model 2, taking into account the source term reduction with time for each contaminant in question. New and lower limit values were proposed in case the requirements in model 2 could not be fulfilled. Table 0.4 lists the proposed limit values for category 2 soil re-used on a bottom liner.

Table 0.4 Proposed category 2 limit values. The limit values can be applied only to re-use of soil on a bottom liner.

1. Limit value not based on leaching data but equal to the limit value of the fraction C₂₀ – C₄₀.
2. The evaluation is based on very few data – only 8 soil samples.

Re-use of soil classified as category 2 without bottom liner

Based on the limit values proposed for category 2, it is tested whether it is possible to re-use a smaller amount of soil without using a bottom liner. The dimensions of construction projects were evaluated based on model calculations taking account of transport of contaminants (including sorption and dilution) and with point of compliance (POC) 30 m downstream from the project. It was decided that at POC = 30 m, 100 % of the data collected for different soil samples must fulfil the groundwater quality criteria. Based on these requirements for re-use of soil without bottom liner, only projects with dimensions less than 4x4x4 m could be allowed, as larger projects could not fulfil the placed   requirement.

Limit values based on leaching – Category 1 and 2

As an alternative to using limit values based on solid content analyses, limit values for both category 1 and 2 can be defined based on leaching of contaminants from the soil.

Leaching-based limit values calculated based on the proposal for category 1 are shown in Table 0.5. The intention is that the level of protection of the groundwater should be identical for both types of limit values (solid-content-based and leaching-based). However, the leaching-based limit values are determined directly on the basis of the groundwater quality criteria and they do not include a certain percentage of soil samples that exceed the groundwater quality criteria. Thus, the limit values based on leaching are in fact stricter than the values based on solid content. This can, however, be compensated when accepting soil for re-use in a certain project.

Table 0.5 Category 1 limit values based on leaching tests. The limit values must be supplemented with a requirement for a pH value in eluates of between 6 and 9.

Tables 0.6a and 0.6b present calculated leaching-based limit values for category 2 without using a bottom liner. These limit values depend on the dimensions of the project and the dimensions of the re-use project must not exceed these dimensions.

Table 0.6a Category 2 limit values based on leaching tests. The limit values are supplemented with a requirement for a pH value in eluates of between 6 and 9. The limit values can be applied to re-use of soil without using bottom liner.

Table 0.6b Category 2 limit values based on leaching tests. The limit values are supplemented with a requirement for a pH value in eluates of between 6 and 9. The limit values can be applied to re-use of soil without using bottom liner.

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Version 1.0 Maj 2009, © Miljøstyrelsen.