Workreport 2019-44



Results of Monitoring at Olkiluoto in 2018, Hydrogeochemistry


Penttinen, T., Wichmann, A., Ripatti, K., Nummela, J., Yli-Rantala, E., Wendling, L., Partamies, S., Lamminmäki, T., Pitkänen, P., Vuorio, M., Ylöstalo, R.



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Possible changes in the chemical environment in shallow and deep groundwaters caused by construction of the final disposal facility are monitored on a regular basis. This report presents the annual hydrogeochemical monitoring results and observations for 2018.

The effect of works on ground surface was seen in analysis results of many groundwater pipes. Elevated sulfate concentrations were detected in OL-PP56 and OL-PVP17, which are located between the site of the Encapsulation plant and and the previously built parking area, in OL-PVP42A and OL-PVP42B located on the construction site of the encapsulation plant. Increasing sulfate concentrations were also seen in the upper part of ONKALO (ONK-KR1, ONK-KR2, ONK-KR3). In the shallowest sampling section of OL-PP56 and in OL-PVP42A pH decreased clearly from the values of the previous year. In the points between Olkiluoto main road (Olkiluodontie) and Natura nature reserve, OL-PVP4A and OL-PP2, the long increased salinity (TDS) values had remained stable since 2016.  Infiltration from Korvensuo water reserve affected the composition δ18O ja δ2H isotopes in the water of OL-PVP12 and OL-PVP30.

Changes that in most cases are related to the hydraulic gradient caused by open underground spaces were observed in deep groundwaters. Downward movement of sulfate rich groundwater along either hydrological zones (BFZ045, HZ056) or open drillhole (OL-KR45, open from 2007–2015) was seen in elevated sulfide concentrations. Dilution of the water in HZ20 structure was still detected. In an intersecting sampling section of OL-KR4 an increase in sulfate was seen, respectively. Elevated sulphate concentrations were observed also in the underground monitoring points at the final disposal depth. Dilution of ONK-PVA2 continued and changes in ONK-KR4 and ONK-PVA1 were stabilised. Gas samples collected with PAVE and PFL devices corresponded to previus gas sampling  results from Olkiluoto. Instead, samples collected with SWA technique indicated lower gas contents.

Sampo electromagnetic soundings were not carried out in 2018 because the broken device could not be fixed during the year.


Hydrogeochemistry, final disposal facility, ONKALO, monitoring, groundwater, gas sampling, analysis results


WR 2019-44_web (pdf) (8.2 MB)
Appendices 1-25_web (pdf) (6.4 MB)


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