Sampling and characterisation of groundwater colloids in ONKALO at Olkiluoto, Finland 2009-2010

The purpose of this study was to estimate the concentration of colloids and composition of the colloid phase on the basis of the water chemistry results of filtered and unfiltered water samples and to compare the results with the previous ones. The water samples were collected from groundwater stations ONK-PVA1 in December 2009 and ONKPVA5 in June 2010. The colloid concentrations were determined from scanning electron microscopy (SEM) micrographs taken from the filters. The change in the water chemistry due to filtration was also analysed. The decrease of element concentrations due to filtration would possibly reflect the composition of the colloid phase. Because the concentration of the colloids is very low, three parallel water samples were analysed three times with an Inductively Coupled Plasma - Mass Spectrometry (ICP-MS) analyser so that the chemical differences between the filtered and unfiltered water could be evaluated. The colloid concentration in ONK-PVA1, determined by the single particle analysis of SEM micrographs, was 0.5 μg/l while the colloid concentration in ONK-PVA5 was 0.15 μg/l. The colloid phase composition could not be reliably determined due to the low colloid concentration. (orig.)