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Workreport 2018-44

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Name:

Monitoring at Olkiluoto in 2017, Hydrogeochemistry

Writer:

Vuorio, M., Lamminmäki, T., Pitkänen, P., Penttinen, T., Tiensuu, K., Komulainen, J., Wendling, L., Yli-Rantala, E., Partamies, S., Ahokas, T.

Language:

English

Page count:

348

Summary:

Possible changes in the chemical environment in shallow and deep groundwaters caused by construction of the disposal facility and underground research facility ONKALO are monitored on a regular basis. This report presents the hydrogeochemical monitoring measurements and observations made 2017.

Shallow groundwater: pH (field) values varied from acidic (5.4 in OL-PP5) to alkaline (8.3 in OL-PP56 L1). The maximum TDS value was 1748 mg/L (OL-PP56 L1). High sulfate concentrations were still measured in OL-PP56 L3, OL-PVP17 and OL-PVP18A. On the basis of the isotope results of δ18O and δ2H, the waters of OL-PVP12, OL-PVP30 (not sampled in 2017) and OL-PP3 have been affected by the Korvensuo reservoir water. The sampling points OL-PVP4A and OL-PP2 locate near or within Natura preservation area. In both sampling points, TDS has shown a long term increasing trend. In the basis of results 2016–2017, the increase of TDS (Na, Cl) has stopped in both points, but the trend has included temporary stops also earlier.

Deep groundwater and ONKALO: The results from the ground surface based monitoring campaign showed some indications of changes in groundwater composition, which in many cases were most probably caused by the high hydraulic gradient of the underground tunnels. Elevated sulfide concentrations were again observed in a few sampling locations, as has been observed in previous years. A dilution was still observed via the hydraulic zone HZ20. The results of the monitoring programme in the underground tunnels and facilities in general behaved predictably and remained unchanged or were in a state of slow change. The long-term dilution in ONK-PVA2 was still ongoing and ONK-KR4 followed the stabilised trend observed last year. The sulfate concentration in ONK-KR1 continued the steep increasing trend. The increase in SO42- content was also noticeable in ONK-PVA3, while ONK-KR2, ONK-KR3 and ONK-PVA2 showed only slight rise.

Gas samples and Sampo: The monitoring results of dissolved gases from deep drillholes using the PAVE technique corresponded well with the earlier data from the Olkiluoto site. The Sampo electromagnetic soundings give information of the resisitivity changes in the bedrock. The main result of this survey was that no or only weak changes were detected in the resistivity values of different layers. The results differ somewhat from the earlier results, one of the reasons for this is that the interpretations presented in this report were carried out using updated hydrogeological models which were fitting at some stations poorly to the electrically conductive layers.

Keywords:

Hydrogeochemistry, ONKALO, monitoring, groundwater, gas sampling, analysis results, Sampo electromagnetic soundings

File(s):

WR 2018-44_web (pdf) (29.3 MB)


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