Posiva publishes Working Reports and Posiva Reports. From the year 2006 nearly all the reports have been published on our webpage and they can be found in the databank. In the databank you can also find our Annual Reviews and some other publications as well. You can also find print-quality pictures and useful links in the databank.

Recent publications

Workreport 2020-44



Results of Monitoring at Olkiluoto in 2019 Hydrogeochemistry


Yli-Kaila, M., Ylöstalo, R., Penttinen, T., Wichmann, A., Pulkkinen, P., Lamminmäki, T., Pitkänen, P.



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Possible changes in the chemical environment in shallow and deep groundwaters caused by construction of the disposal facility are monitored on a regular basis. This report presents the annual hydrogeochemical monitoring results and observations for 2019.

The effect of works on ground surface was seen in analysis results of many shallow groundwater sampling points. High sulfate and NO3 concentrations were detected in OL-PVP42A and OL-PVP42B, which located at the area of encapsulation plant construction. High sulfate concentrations were still analysed in OL-PVP17 and OL-PP56, near encapsulation plant site. High sulfate concentrations were also observed in north side of the island, probably due to natural changes in hydrological conditions and land use during construction of new power line. In the sampling points between Olkiluoto main road (Olkiluodontie) and Natura nature reserve, OL-PVP4A and OL-PP2, the long increased salinity (TDS) values increased slightly again, after more stable period 2016−2018. Infiltration from Korvensuo water reserve affected the composition δ18O and δ2H isotopes in the water of OL-PVP12 and OL-PP3.

Changes that in most cases are related to the hydraulic gradient caused by open underground spaces were observed in deep groundwater. Dilution of the water in HZ20 structure was still detected, e.g. in OL-KR7 and in OL-KR25. The groundwater in ONK-PVA12 (HZ19) and ONK-PVA13 (HZ20) was notably diluted and tritium results were high, which indicate young meteoric water origin. In addition, open period of drillhole OL-KR28 was seen in the groundwater results of 2019, for example in ONK-PH22_60.

Elevated sulfide and acetate concentrations were observed, especially in OL-KR45 and OL-KR46. The highest sulfide concentration in underground facilities, 7.4 mg/L, was measured in ONK-PH22_34. Effect of cement contamination (e.g high pH) was seen in the results of ONK-PH17.

The results of pilot holes ONK-CTPH6.1 and ONK-PH30, as well as the results of new borehole ONK-PR91, corresponded well to previous view of the baseline conditions at repository depth. In OL-KR20_T140_0219 (HZ20B) very light δ2H vs. δ18O isotope composition was analysed, which indicates significant glacial water fraction in the sample.

Gas samples collected in 2019 corresponded to previous gas sampling results from Olkiluoto, however, samples collected with SWA method indicated lower gas contents.

Sampo electromagnetic soundings were not carried out in 2019 because the broken device could not be fixed during the year.


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


WR 2020-44_web (pdf) (11.7 MB)
APPENDICES 1-25_web (pdf) (8.3 MB)


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