Results of monitoring at Olkiluoto in 2009: Hydrogeochemistry

Teea Penttinen, Anne-Maj Lahdenperä, Turo Ahokas, Sami Partamies, Petteri Pitkänen, Seppo Kasa

    Research output: Book/ReportReport


    The construction work of underground research facility ONKALO started in the autumn 2004. Possible changes caused by the construction of the disposal facility in the chemical environment in shallow and deep groundwaters are monitored on a regular basis. This report presents the hydrogeochemical monitoring measurements and observations made in 2009.

    A total of 31 shallow groundwater samples were taken in monitoring programme and 49 shallow groundwater samples in the Infiltration experiment area in 2009. The sampling points of shallow groundwaters were divided into groups on a basis of their typical geological and geographic features. The seasonal variation in concentration levels was now clearly observed in OL-PVP3A, OL-PVP13, OL-PVP14, OL-PVP17, OL-PVP18A, OL-PVP20, OL-PP39 and OL-PP56. This behaviour is related to high naturally fluctuating concentrations in these sampling sites. The effect of Korvensuo on the groundwater of OL-PVP30 appeared. No straight connection can be made with the ONKALO construction work and the observed changes in shallow groundwater concentrations.

    47 deep groundwater samplings were carried out during the year 2009 from 19 different drillholes and 30 groundwater samples were taken from ONKALO. 10 gas samples have been analysed and collected from 6 open drillholes during the year 2009 and 5 are from sampling points of ONKALO. The results from ground surface based monitoring campaign in 2009 show indications of changes in groundwater compositions, which are most probably caused by high hydraulic gradient of ONKALO. The 2009 results show slight but clear systematic dilution (in all species) in two monitoring points (OL-KR4_T76 and OL-KR37_T165, both intersections of HZ19) relative to the previous samplings. Of the monitored intersections of hydraulic zone HZ20B the OL-KR10_T326 have continued dilution trend (after packering) and OL-KR9_T468 and OL-KR23_T424_have become more saline. Particularly the start of salinity increase in OL-KR9_T468 is a signal of saline groundwater upconing along HZ20B feature. The results of the monitoring programme in ONKALO during the year 2009 have followed the predictable behaviour and remained mainly unchangeable in terms of samples collected from ONKALO. The gas results from monitoring campaign of the year 2009 are more scattered than earlier, but does not show any remarkable changes compared to the baseline data.

    In 2009, noisy soundings were removed (15) and 3 new points were selected from the area to the east of ONKALO for the Sampo-EM monitoring programme. Comparing the 2004-2009 ARD curves, some of the new sounding curves have been slightly changed. Mostly the differences are caused by new man-made structures (Jokinen et al. 2009). According to Jokinen et al. (2009) the other changes due to for example altered ground water conditions are very small, the modelling carried out by GTK later shows that some results indicate possible changes also in the groundwater conditions (Korhonen 2010). For instance the level of saline groundwater may be sinking in the eastern part, while it is rising on the western part.
    Original languageEnglish
    Number of pages296
    Publication statusPublished - 2010
    MoE publication typeD4 Published development or research report or study

    Publication series

    SeriesPosiva Working Report


    • ONKALO
    • monitoring
    • hydrogeochemistry
    • analysis results
    • Gefinex S400


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