Bedömningar av föroreningars utbredning i mark med punktkällor – Utvärdering och erfarenheter från riktad provtagning vid nedlagda bensinstationer

Sammanfattning: Small-scale environmental soil surveys at assumed point sources are done through targeted sampling at a limited number of sampling locations which makes delineation of a contaminated area difficult. However, if a decision of remediation is taken due to the results of a small-scale environmental soil survey, the size of the contaminated area still has to be assessed. In this study I examined the accuracy of such estimations, when based on the results from small-scale environmental soil surveys. I did this by evaluating 39 remediation projects at former petrol stations where it was possible to compare the assessed amount of contaminated soil with the actual amount of contaminated soil that was excavated during the remediation. The excavated amounts of contaminated soil differed from the estimated amounts, ranging from 4 to 1150 percent. In 78 percent of the studied projects, the amount of contaminated soil was underestimated which in some cases meant that the ground was incorrectly assessed as clean. The error in the estimations, expressed as tons of contaminated soil, increased both with the actual amount of contaminated soil and with the number of petrol tanks installed at the former petrol stations. However, no correlation between the error in the estimations and the number of sampling locations could be demonstrated. A problem that occurred at a quarter of the soil surveys was that the sampling at some individual locations did not provide conclusive or representative results. Other problems were obstructed sampling as well as uncertainties in the localization of point sources.