Summary and conclusions

Olie i jord

Analysis for ”total petroleum hydrocarbons” is used in evaluation of contaminated soils, mostly including a fractionation of the hydrocarbons according to carbon number. A new method has previously been developed and evaluated for use in Denmark and in this report the results of previous validation and evaluation studies are integrated with further investigations in order to prepare an optimized method description, rules for method interpretation, and suggestions for soil quality and cut-off criteria.

The new method (the AnalyCen method) applies solvent extraction and quantification by GC-FID. The method performance has been improved compared to the previously applied method (the VKI method) with respect to precision, limit of detection and recovery of petroleum products from soils.

The method allows for GC-MS-SIM-based quantification of BTEX and PAH using the extracts prepared for the GC-FID analysis. Improved precision and reduced risk of false positives are obtained with limited additional costs.

The method includes a method for determination of biogenic hydrocarbons (uneven-numbered n-alkanes and selected phytosterols) also using GC-MS-SCAN and the extracts prepared for GC-FID. The principles of application and interpretation of biogenic hydrocarbon determination are given.

Attempts to interpret specific petrogenic hydrocarbons as unequivocal indicators of the presence or absence of petrogenic (contamination derived) hydrocarbons in soils were unsuccessful.

Rules were drafted for assigning hydrocarbons found in a soil quantitatively to petroleum product types (gasoline and similar products or unweathered diesel and similar products).

Suggestions for revised Danish soil quality criteria are given that reflect the increased recovery obtained with the new analytical method in order to maintain the same level of protection of the criteria.

The justification for establishing soil cut-off criteria was investigated by studying the mobility, the acute toxicity and the odour properties of hydrocarbons from petroleum-contaminated soils.

Leaching tests of 45 soils demonstrated limited leaching of heavy hydrocarbons from soil. By interpretation of the leaching of PAH from the same soils it was further inferred that the limit between heavy and light fuels could be changed from C₂₅ to C₂₀ if the limit is set based upon the leaching properties.

A range of NSO compounds was identified in the soils, and a high degree of leaching of the NSO compounds was demonstrated.

Model-based calculations of soil air and indoor air concentrations demonstrated that heavy hydrocarbons will not exceed air quality criteria in soil air, whereas volatile and light hydrocarbons may exceed the criteria. In indoor air, only volatile hydrocarbons will exceed the criteria to a significant degree.

Based upon a previous identification of NSO compounds and 1,3,5-trimethylbenzene as those most likely to be associated with acute toxicity, health-based screening criteria for soil and drinking water were calculated. The soil and leachate NSO concentrations found in this study did not exceed these criteria. Accepted, international guidelines or limit values for NSO in soil, drinking water and groundwater were not found.

Based upon a previous identification of NSO compounds as those most likely to be associated with odor of petroleum-contaminated soils, odor-based screening criteria for air were calculated. The model-based calculations of soil air and indoor air concentrations of NSO compounds did not exceed these criteria. The data material behind the evaluation of odour problems is less comprehensive than for the other parts of the study.

Integrating the data on occurrences, compound distribution, mobility, toxicity and odor properties of the soils studied, a set of revised soil quality criteria and a set of justified cut-off criteria were drafted, see Table 2.

Table 2
Draft soil quality and cut off criteria for soil hydrocarbons.

Hydrocarbon fraction	Volatile	Light		Heavy	Total
mg/kg d.w.	C₆-C₁₀	>C₁₀-C₁₅	>C₁₅-C₂₀	>C₂₀-C₄₀	C₆-C₄₀
Soil quality criteria	25	35	55	150	150
Cut off criteria	-	-	-	450	450

The draft criteria are based upon the preconditions that:

The analytical method prescribed by the Danish Environmental Agency (DEPA) must be strictly applied
All criteria for total and all fractions of hydrocarbons are met
Cut off criteria for heavy hydrocarbons and total hydrocarbons can only be applied, if the soil quality criteria for volatile and light hydrocarbons are met as well
Criteria for identified compounds occurring in petroleum products, including totals of such, as set by the Danish EPA must be met: benzene, 1,2-dibromo- and 1,2-dichloroethane, tetraethyl- and tetramethyllead, and finally PAH

It is allowed to:

Disregard contributions from biogenic hydrocarbons determined using the method prescribed by the Danish EPA

It should be noted that the Danish EPA has subsequently adjusted the cut-off criterion for the >C₁₀-C₁₅ fraction of light hydrocarbons to 40 mg/kg d.w.