Guidelines on remediation of contaminated sites
6. Quality criteria for soil, air and groundwater
6.1 Background and objectives
In recent years, the Danish EPA has recommended a number of criteria for selected chemical substances by issuing several publications and by background work /9, 10, 19, 20, 21, 22, 23, 24, 25/.
The objective of this chapter is to review the various criteria for soil, air, and groundwater. The basis for setting these criteria and their application will briefly be described.
The criteria for the three media – soil, water, and air – have been designed independently of each other in that they are based on exposure to each of the three media. Each criteria should thus be complied with simultaneously. Compliance with soil criteria, for example, does not automatically imply compliance with criteria for water and soil.
It should be emphasised that the soil and groundwater criteria do not represent a risk analysis. A specific risk analysis should take account of the local geological conditions and the sensitivity of land use.
6.2 Quality criteria for soil
The Danish EPA has prepared toxicological quality criteria for soil for a large number of selected chemical substances.
Criteria are always based on the assumption that it should be possible to use the site for very sensitive purposes (e.g. private gardens or day-care centres). As a starting point, soil-quality criteria should be complied with from the surface to a depth of 1 m, however, see also Section 5.2.3. In addition to health considerations, the criteria are also based on aesthetic and hygiene considerations (smell/appearance/taste).
As a supplement to, or instead of, soil-quality criteria, quality criteria for evaporation apply for several substances. Air-quality criteria are described in Section 6.6.
In most cases where contamination is to be assessed, ecotoxicological considerations are not taken into account. The current ecotoxicological quality criteria are listed in Table 6.1.
For most of the substances reviewed, quality criteria for the top soil are based on acceptable/tolerable daily exposures. If it is known that exposure to contamination components occurs from other sources (e.g. food or air), the criteria will take account of this and ensure that total exposure does not exceed the ADI/TDI values (acceptable daily intake / tolerable daily intake).
Table 6.1 lists quality criteria for soil in connection with very sensitive land use. To aid risk analysis (Section 5.1), the table also shows whether the reason for setting the quality criteria is the acute or the chronic effect of the substance. If individual values significantly exceed the soil quality criteria (+100%), the need for mapping the extent of the high value/hot spot should be assessed.
The statements of acute and chronic effects in Table 6.1 do not mean that a threshold criterion can be derived for a substance where the level is based on the chronic effect.
Table 6.1 also states zero values for selected organic components. Zero values are defined as calculated pore-water concentrations for clay and sand (Table 1 in Appendix 5.3) which do not exceed the quality criteria for the groundwater.
Table 6.1
Quality criteria for soil in areas with very sensitive land use, ecotoxicological
quality criteria and background levels /3/. The methods
of analysis for individual substances appear in the guidelines on sample-taking and
analyses /3/. All units are in mg/kg dry weight (DW)
Substance |
Soil quality criteria |
Eco-toxicological soil quality criteria4 |
Background level |
Acetone |
8 |
|
|
Arsenic |
201(2) |
10 |
2-6 |
Benzene |
1.5*2 |
|
|
BTEX, total |
10*2 |
|
|
Cadmium |
0.52 |
0.3 |
0.03 – 0.5 |
Chloroform |
50*2 |
|
|
Substance |
Soil quality criteria |
Eco-toxicological soil quality criteria4 |
Background level |
Chlorophenols, total |
3*2 |
0.01 |
|
Chromium, total |
500 |
50 |
1.3 – 23 |
Copper |
5001 |
30 |
13 |
Cyanide, total |
500 |
|
|
DDT |
1 |
|
|
Detergents, anionic |
1,5002 |
5 |
|
1,2-dibromomethane |
0.022 |
|
|
1,2-dichloroethane |
1.42 |
|
|
1,1-dichloroethylene |
52 |
|
|
1,2-dichloroethylene |
852 |
|
|
Dichloromethane |
82 |
|
|
Fluorides, inorganic |
201 |
|
|
Gas oil |
100 |
|
|
Lead |
402 |
50 |
10 – 40 |
Mercury |
1 |
0.1 |
0.04 – 0.12 |
Molybdenum |
5 |
2.0 |
|
MTBE |
5002 |
|
|
Nickel |
301 |
10 |
0.1 - 50 |
Nitrophenols |
|
|
|
PAH, total |
1.52,3 |
1.0 |
|
Petrol (C5-C10) |
25* |
|
|
Petrol (C9-C16) |
25* |
|
|
Phenols, total |
70*1 |
|
|
Phthalates, total |
2502 |
1.0 |
|
Styrene |
40*2 |
|
|
Turpentine, mineral |
25* |
|
|
Tetrachloroethylene |
5*2 |
|
|
Tetrachloromethane |
5*2 |
|
|
1,1,1-trichloroethane |
2002 |
|
|
Trichloroethylene |
5*2 |
|
|
Substance |
Soil quality criteria |
Eco-toxicological soil quality criteria4 |
Background level |
Vinyl chloride |
0.4*2 |
|
|
Zinc |
500 |
100 |
10 - 300 |
Note: For several substances (marked *), criteria for evaporation are stated (see Table 6.5).
| 1 | Based on acute effect. |
| 2 | Based on chronic effect. |
| 3 | PAH, total defined as the sum of individual components: fluoranthene, benzyl(b+j+k)fluoranthene, benzyl(a)pyrene, dibenzyl(a,h)anthracene, and ideno(1,2,3-cd)pyrene. |
| 4 | See also /53/. |
| 5 | For hydrocarbons greater than C35, see /3/. |
6.3 Cut-off criteria for soil
In the guidelines from the Danish EPA on ‘Advice to Residents in Slightly Contaminated Areas’, cut-off criteria for soil contamination in the upper soil stratum have been set for ten selected substances /4/.
The cut-off criteria state the level of soil contamination at which it is necessary to completely cut off all contact with the soil, for example by remediation or excavation, if the area is to used for very sensitive purposes.
The Guidelines include a number of rules which aim at reducing exposure to the same level as for areas where the soil-quality criteria are not exceeded. The cut-off criteria for soil are listed in Table 6.2.
Table 6.2
Criteria for necessary contamination cut off, mg/kg dry weight (DW).
Substance |
Level where contamination cut off is necessary |
Arsenic |
201 |
Cadmium |
52 |
Chromium |
1,000 |
Copper |
5001 |
Lead |
4002 |
Mercury |
3 |
Nickel |
301 |
Zinc |
1,000 |
PAHs |
152 |
Benzo(a)pyrene |
12 |
Dibenzo(a,h)anthracene |
12 |
1
: Based on acute harmful effects2: Based on chronic harmful effects
If contamination in the upper soil stratum is not more than the cut-off criteria, and there are no clumps or hot spots with high concentrations of contamination, then the completed surveys (the initial (historical) survey and analyses of soil samples) provide evidence that the criteria described in these guidelines have been complied with /4/.
As it can not be ruled out that contamination near the surface may represent a threat to the groundwater, these criteria can be supplemented with other criteria or specific risk assessments, cf. Section 5.4. Furthermore, contamination should not contain substances which are problematic because they evaporate into the indoor and/or outdoor air, cf. Section 5.3.
If a larger area is slightly contaminated, i.e. concentrations are less than the cut-off level, situations may arise where remediation is carried out at lower concentrations, for example the soil-quality criteria. For example, this may occur in situations where an enforcement notice has been issued or where limitations on land use following remediation, are undesirable (corresponding to de-listing a contaminated site).
6.4 Criteria for soil from other sources
A distinction is made between acceptable residual concentrations in soil which is brought in from other sources and acceptance criteria for untouched soil.
Soil which is filled in an excavation at a contaminated site, for example, can originate from other parts of a site, from off-site, or from soil remediation. With regard to soil from other sources, land use or the depth at which the soil is to be laid is not considered.
Therefore, the overall requirement is that soil from other sources is clean, or has previously been cleaned to the extent that soil-quality criteria are complied with to the bottom of an excavation.
It should be emphasised, that mixing contaminated soil with clean soil with a view to complying with acceptance criteria is in direct conflict with the intentions of environmental legislation. Dilution in this way is unacceptable, irrespective of whether it arises in required excavations or through mixing soil from the same site.
Use of soil from other sources must always be approved separately for each specific case.
6.5 Quality criteria for groundwater
Table 6.4 shows quality criteria for groundwater. The quality criteria stated in the Table correspond to ‘requirements for groundwater for normal aeration and filtration’ in the ‘Guidelines on Well Control at Water Works’ /26/. These guidelines also include requirements for a number of other substances and parameters.
In connection with the preparation of health-based quality criteria, a data sheet has been prepared for a large number of the substances mentioned in Table 6.4, where the most important data and conclusions from the background documentation are described. These data sheets have been collected in a report called ‘Toxicological Quality Criteria for Soil and Drinking Water’ /9/.
Table 6.4
Quality criteria for groundwater beneath contaminated sites. 1)Sum of
fluoranthene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene,
benzo(g,h,i)perylene, indeno(1,2,3-cd)pyrene
Substance |
Groundwater quality criteria, µg/l |
Background level, µg/l |
Acetone |
10 |
|
Arsenic |
8 |
0.1->8 |
Benzene |
1 |
|
Boron |
300 |
10->300 |
Butylacetates |
10 |
|
Cadmium |
0.5 |
0.005->0.5 |
Chlorinated solvents |
1 |
|
Chloroform |
As low as possible |
|
Chromium, total |
25 |
0.04-10 |
Chromium VI |
1 |
|
Copper |
100 |
0.1->50 |
Cyanide, total |
50 |
|
DEHP |
1 |
|
Detergents, anionic |
100 |
|
1,2-dibromomethane |
0.01 |
|
Diethylether |
10 |
|
Isopropyl alcohol |
10 |
|
PAH 1) |
0.2 |
|
Lead |
1 |
0.1->1 |
Methylisobutylketone |
10 |
|
Methyl-tert-butylether (MTBE) |
30 |
|
Mineral oil, total |
9 |
|
Molybdenum |
20 |
0.2-20 |
Naphthalene |
1 |
|
Nickel |
10 |
0.1->10 |
Nitrophenols |
0.5 |
|
Pentachlorophenol |
Not measurable |
|
Pesticides, total Pesticides Pesticides, persistent chlorinated |
0.5 0.1 |
|
Phenols |
0.5 |
|
Substance |
Groundwater quality criteria, : g/l |
Background level, : g/l |
Phthalates (not DEHP) |
10 |
|
Styrene |
1 |
|
Toluene |
5 |
|
Vinyl chloride |
0.2 |
|
Xylenes |
5 |
|
Zinc |
100 |
0.5->10 |
The quality criteria for groundwater have been set on the basis of a total assessment of
the water’s route to the consumer. Groundwater which is to be used as drinking water
must be of such a quality that, after all influences to which it is exposed before it
reaches the consumer, the water still complies with the requirements for drinking water.
The physical-chemical conditions and the vulnerability of the groundwater aquifer determine the spread from the source to the groundwater aquifers, and thus influence the quality requirements.
Quality criteria must be fulfilled in the major groundwater aquifers. The quality requirements must also be fulfilled in minor, upper groundwater aquifers which may be the cause of significant spreading of contamination, or which may be used for drinking-water supplies.
An important stage of risk assessment (Chapter 5.4) is therefore to establish an acceptable level for residual contamination in relation to an influence on the groundwater at the site.
6.6 Quality criteria for air
In connection with assessing evaporation of highly volatile components from contaminated sites, there is a distinction between the terms ‘evaporation criteria’, and ‘limit values for air’. A definition of these terms appears in Table 6.5.
Table 6.5
Definitions of criteria for air
Evaporation criteria
Limit value for air |
An air-quality criterion for evaporation to air is a contribution value which is generally set equal to the limit value for air (see below). The Danish EPA lays down limit values for air on the basis of toxicological assessments. The limit values for air are used for setting maximum permissible contributions of contaminating industries of substances to the air as immission (B values). They are also used in setting air-quality criteria for evaporation into the overlying air. |
A number of criteria for evaporation from soil have been laid down. These criteria can be
applied in assessing non built-up areas, and in assessing evaporation to the indoor air in
overlying buildings.
As a general rule, evaporation of chemical substances from a contaminated site should not give rise to a higher contribution to the overlying air than laid down in the evaporation criteria. Air-quality criteria for evaporation to the overlying air generally correspond to the limit values for air issued by the Danish EPA.
Table 6.6 lists the quality criteria for evaporation to the overlying air.
Table 6.6
Quality criteria for evaporation from contaminated sites.
Substance |
Air-quality criteria for evaporation to the overlying air mg/m3 |
Acetone |
0.4 |
Aromatic hydrocarbons |
|
Benzene |
0.000125 |
Butylacetates |
0.1 |
Chloroform |
0.02 |
Cyanides, volatile acidic |
0.06 |
Diethylether |
1 |
Isopropanol |
1 |
Hydrocarbons, total |
0.1 |
Methylisobutylketone |
0.2 |
MTBE |
0.03 |
Naphthalene |
0.04 |
Phenols |
|
Chlorophenols, sum of chlorophenols,
dichlorophenols, trichlorophenols, and tetrachlorophenols |
0.00002 |
Nitrophenols |
0.005 |
Styrene |
0.1 |
Tetrachloromethane |
0.005 |
Tetrachloroethylene |
0.00025 |
Toluene |
0.4 |
Trichloroethylene |
0.001 |
Vinyl chloride |
0.00005 |
Xylenes |
0.1 |
Limit values for air have been established for many more substances than mentioned in
Table 6.6. These values can be extracted from the background documentation to the list of
B values cf. the four substance categories below. In addition, the Danish EPA regularly
sets limit values for air for other substances, and the values already listed are
regularly revised.
When implementing limit values for air to B values, there are four different categories /19/.
 | Substances where only the total dosage and thus, in reality, the average concentration of the substance, is decisive for an effect. In these cases the B value is set at 40 times the limit value for air. |
| Substances with acute or sub-acute effects. In these cases B values are set at the limit value for air. |
| Substances where smell is the limiting factor. In these cases B values are set at the limit value for air. |
| Substances which have an immediate acute effect. Here the B value is set at 1/10 of the limit value for air. |
Refer also to the background documentation on setting B values /21/.
6.7 Use and limitations of quality criteria
It should be noted that groundwater criteria are independent of soil criteria in that compliance with soil-quality criteria does not automatically ensure compliance with criteria for water.
Similar to groundwater criteria, evaporation criteria are also independent of soil criteria, in that compliance with soil criteria does not automatically imply compliance with evaporation criteria.
Of course, it would be very practical if it were possible to have overall criteria for soil which could also ensure that evaporation or leaching did not occur to a significant degree. At the moment, this is not possible.
Situations can arise where it is necessary to ignore quality criteria. For example, soil-quality criteria should not be applied if the natural background level for a given heavy metal is higher than the soil quality criteria. Similarly, there may be areas where the groundwater has a naturally elevated content of chloride or organic substances.