Summary and conclusions

Håndtering af lettere forurenet jord - Supplerende data for udvaskning af uorganiske og organiske stoffer fra jord

Background

In order to support the preparation of new regulations on reuse of lightly polluted soil, a study has been carried out to investigate the feasibility of setting limit values based on solid content that, in combination with certain restrictions on the reuse conditions, would ensure sufficient protection of the groundwater downstream of the utilisation application. The study considered both inorganic and organic contaminants, but for a number of these the data available (corresponding results of analyses of solid content in and testing of leachability from soil samples) were too limited to allow a proper evaluation. To improve this situation, the Danish EPA has initiated a supplementary study aimed at providing new data on total content and leachability for both inorganic and organic contaminants for a number of lightly polluted soil samples.

As part of the new study, 38 lightly polluted soil samples were collected, 12 of which were polluted with both inorganic and organic substances. The remaining soil samples were either polluted with inorganic (13 samples) or organic substances (13 samples). The soil samples collected were intended to represent a range of Danish soil types as well as different types of pollution. The samples were analysed for solid content of inorganic and organic substances and leaching tests were carried out for inorganic (EN 12457-1) as well as organic substances (DHI, 2003).

The results of the study are presented in this report. The same methods and principles that were used to evaluate the results in the previous study have also been used in this study. A detailed description of the methodology applied may be found in DHI (2007a). In this report the previously collected data have been included, and the evaluation is based on both new and “old” data.

Inorganic substances

A considerable amount of data exists for As, Cd, Cu, Hg, Ni, and Pb, and the new data confirms the conclusions drawn in the report “Management of slightly polluted soil” (DHI, 2007a). The data show that leaching criteria set in scenarios 3 and 4 (scenario with a length of 100 m in direction of the groundwater flow, 1 m in height and distances of 100 m and 30 m, respectively, to the point of compliance (POC)) and the EU waste acceptance criteria (WAC) for landfilling of waste at a landfill for inert waste, will be met in most cases, if the limit values for solid content suggested by the Danish EPA for these substances are applied, especially if a further requirement that the pH in the soil-water-slurry is to be between 6 and 9 is enforced.

A considerable amount of data also exists for Cr and Zn. However, for these two pollutants there seems to be a higher risk of the leaching criteria being exceeded, even if the solid content limit values suggested by the Danish EPA are combined with a requirement that 6<pH<9. For both Cr and Zn, the risk of exceeding the leaching criteria would be considerably reduced if the suggested total content limit value was lowered from 1,000 mg/kg to e.g. 100 mg/kg. The limit value should be combined with a ban on the use of soil from wood preservation sites that may potentially have a high Cr contamination. Even under these conditions the leaching criteria corresponding to scenarios 6 and 7 may still be exceeded, particularly in the case of Zn.

The Danish EPA has currently not suggested any limit values for solid content in soil for Ba, Mo, Sb and Se in connection with the reuse of lightly polluted soil. For Ba, a considerable amount of data exists, based on which it should be possible to set a safe soil reuse limit value for solid content of e.g. 500 mg/kg which would ensure sufficient protection of the groundwater. For Mo, Sb and Se the amount of data points have been increased, and the evaluation is now based on 38, 42 and 36 sets of data, respectively. Nonetheless, it seems rather problematic to set a limit value for solid content for Mo and Sb. For Mo, a solid content limit value lower than 1 mg/kg would be required to ensure with a reasonable certainty that the leaching criteria for scenarios 5, 6 and 7 can be met. Still, this could be problematic in relation to unpolluted soil, since the natural content of Mo typically is 0.2-5 mg/kg. For Sb, the limit value for total content should be even lower (e.g. < 0.1 mg/kg) to ensure that the risk of exceeding the leaching criteria for the most restrictive scenarios is minimised. If a certain risk that the leaching of Se may exceed the leaching criteria defined by scenario 7, and possibly by scenario 5, is acceptable, it seems reasonable to set a limit value of e.g. 2 mg/kg for Se. Based on the present data and conditions, this should guarantee reasonable groundwater protection. The natural soil content of Se is typically 0.02-2 mg/kg.

An overview of the suggested limit values can be seen in table 0.1.

Table 0.1
Suggestions for limit values for inorganic substances.

Parameter	Limit value, suggested by the Danish EPA (mg/kg DW)	Suggested limit value/ proposed amendment (mg/kg DW)
As	20
Ba	-	500
Cd	5
Cr	1,000	100
Cu	1,000
Hg	3
Mo	-	(lower than 1)
Ni	30
Pb	400
Sb	-	(0.1)
Se	-	2
Zn	1,000	100

Suggestions in parentheses are considered to be problematic in practice.

Organic substances

For the organic substances the data for the evaluation of criteria for solid content has been improved considerably, compared to the previous study (DHI, 2007a). Nevertheless, the amount of data points is still relatively limited (maximum 56 sets of data) compared to the amount of data available for the inorganic compounds.

Collecting soil samples for testing a range of the different soil types that exist in Denmark was represented in combination with different types of pollution and age of pollution.

Based on the existing data and the applied evaluation principles it is not possible to set up criteria for solid content, neither for total hydrocarbons (THC), nor for fraction of hydrocarbons (C₆-C₁₀, C₁₀-C₂₅ and C_25-C₃₅), which to a sufficient degree would guarantee groundwater quality for reuse scenarios 100 m long in the direction of groundwater flow, and 1 m or more high (corresponding to scenario 3 and 4). A considerable amount of the soil samples shows leaching of the hydrocarbons that exceed the leaching criteria set up for scenarios 3 and 4, even for very low solid contents. The leaching criteria for scenario 3 and 4 are however very low and at the same level as the test detection limit for the hydrocarbon.

For similar reuse scenarios it would be necessary to tighten the requirements for naphthalene and sum of 7 PAHs substantially, if the leaching criteria are to be fulfilled for all soil samples. The limit values that the Danish EPA has suggested for benzo(a)pyrene and dibenz(a,h)anthracene, are presumably sufficient to guarantee groundwater protection.

For smaller reuse scenarios (e.g. scenario 1 and 2 at 10 m long and 1 m high) table 0.2 shows the suggestions for limit values as set up by the Danish EPA. The limit values are for each compound discussed in the table. Provided that it can be accepted that a few soil samples show leaching characteristics that exceed the leaching criteria, the data suggests that the limit values are sufficient to guarantee groundwater protection, but only for reuse scenarios that do not exceed the dimensions used in scenarios 1 and 2.

Table 0.2
Comments for limit value of solid content for reuse projects with dimensions limited to maximum 10 m in length in direction of groundwater flow, and 1 m in height.

Parameter	10 m long and 1 m high (scenarios 1 and 2, correspon ding to the smallest reuse scenarios used for discussion)
	Limit value	Comments
Total hydrocarbons	200 mg/kg DW	The limit value for sum of hydrocarbons is based on the limit values for the fraction of hydrocarbons. All limit values must be fulfilled at the same time
C₆-C₁₀	35 mg/kg DW	Data suggests that the limit value is acceptable, provided that it can be accepted that a few results exceed the leaching criteria
C₁₀-C₂₅	75 mg/kg DW	Data suggests that the limit value is acceptable, provided that it can be accepted that a few results exceed the leaching criteria
C₂₅-C₃₅	200 mg/kg DW	All soil samples fulfil the leaching criteria for scenarios 1 and 2. The limit value suggested by DEPA is based on these data being acceptable
PAH	40 mg/kg DW	Data suggests that the limit value is acceptable, provided that it can be accepted that a few results exceed the leaching criteria.
Naphthalene	5 mg/kg DW	Data suggests that the limit value is acceptable, provided that it can be accepted that a few results exceed the leaching criteria
Benz(a) Pyrene	3 mg/kg DW	All soil samples fulfil the leaching criteria for scenarios 1 and 2. The limit value suggested by DEPA is based on these data being acceptable
Dibenz(a,h) anthracene	3 mg/kg DW	All soil samples fulfil the leaching criteria for scenarios 1 and 2. The limit value suggested by DEPA is based on these data being acceptable