Workreport 2019-43



Results of Monitoring at Olkiluoto in 2018 - Hydrology and Hydrogeology


Vaittinen, T., Hurmerinta, E., Nummela, J., Pentti, E., Tammisto, E., Turku, J., Karvonen, T.



Page count:



The impact of the construction of ONKALO is monitored by measuring and observing numerous different parameters related to hydrology, geochemistry, environment, rock mechanics and foreign materials. The Hydrological Monitoring Programme consists of the following parameters: groundwater level, hydraulic head, flow conditions in open drillholes, transverse flow, hydraulic conductivity, precipitation (including snow), sea-water level, surface flow (runoff), infiltration, ground frost, leakages in tunnels, and water balance in the tunnel system and in Korvensuo Reservoir. This Report focuses on hydrogeological parameters. Other parameters, like precipitation, ground frost etc. are reported in the Monitoring Report of the Environment. From year 2014 on, the parameter groundwater salinity (in situ EC) has been reported in the Monitoring Report of Hydrogeochemistry.

The updated monitoring programme was introduced at the beginning of 2012. The updated programme will be used for the period before repository operation. Only minor changes were implemented. Monitoring has been carried out according to plan. This Report presents the results for the year 2018.

The excavation of the access tunnel was completed in 2012 and excavations related to the demonstration area in 2013. In the technical facilities, excavation continued in 2016. Shaft ONK-KU2 was raise bored down to final level of –437 m during the autumn of 2010 and shafts ONK-KU1 and -KU3 down to the final level of −455 m during the spring of 2014. Raise boring of shat ONK-KU5 proceeded from the ground surface down to the depth of –290 m and the lowest part from the final depth of –437 m up to the depth of –387 m during 2018. The construction project of ONKALO finished and the construction of the final disposal repository started in December 2016.

Total inflow into ONKALO down to chainage 4580 m including shafts ONK-KU2 down to level −437 m, ONK-KU1 and -KU3 down to level −455 m and ONK-KU5 down to level −290 m was on average 24–35 L/min in 2018, but the exact range is difficult to determine due to the construction activities carried out in ONKALO and interrupted leakage measurements in the lowest shaft sections of ONK-KU1 and -KU3 (−290…−455 m). The mapping of water leakages and moisture conditions on the tunnel walls and ceiling has been continued. The general pattern of leakages has remained rather similar during the construction of ONKALO. The most significant differences are caused by seasonal effects like condensation of warm ventilation air on tunnel walls and ceiling.

The changes observed in groundwater level in the observation tubes in the overburden and in the shallow drillholes in the bedrock are not necessarily caused by the construction of ONKALO. However, weak indications of a local decrease in groundwater level have been observed. The effects on the head deeper in the bedrock have earlier been both short-term and long-term. In 2018, short-term effects were related to the drilling of pre-grouting holes in canister shaft ONK-KU5. Long-term changes, i.e. a decrease in heads near ONKALO have remained at the same level as in 2017. On average, drawdown in heads varies between 10 and 12 m within the HZ20 system and between 0.5 and 1.5 m within the HZ19 system. Due to the intersection of the HZ056 zone and a few local features, long-term drawdowns of over 20 m have occurred and the water level has decreased below the measurable drillhole depth in 13 monitoring sections during 2018. In addition, in one monitoring section head has increased to measurable depth due to technical problem.

Flow-based monitoring with the PFL DIFF-tool and PFL TRANS-tool was carried out in six drillholes in 2018. No major changes were noted in the results. PFL DIFF measurements were carried out in drillhole OL-KR41. Slug tests were performed in 13 shallow holes. The interpreted hydraulic conductivity was in agreement with previous results, except in OL-PP71, where apparent packer leaks lead to erroneously high values in most measured sections.


Hydrogeological monitoring, groundwater, groundwater level, hydraulic head, groundwater flow, hydraulic conductivity


WR 2019-43_web (pdf) (80.6 MB)
Appendix_01_web (pdf) (38.8 KB)
Appendix_02_web (pdf) (53.2 KB)
Appendix_03_web (pdf) (63.4 KB)
Appendix_04_web (pdf) (4.2 MB)
Appendix_05_web (pdf) (100.4 KB)
Appendix_06_web (pdf) (345.5 KB)
Appendix_07_web (pdf) (1.9 MB)
Appendix_08_web (pdf) (11.4 MB)
Appendix_09_web (pdf) (1.4 MB)
Appendix_10_web (pdf) (4.1 MB)
Appendix_11_web (pdf) (6.6 MB)
Appendix_12_web (pdf) (38.9 MB)
Appendix_13_web (pdf) (9.5 MB)
Appendix_14_web (pdf) (14.8 MB)
Appendix_15_web (pdf) (3.2 MB)
Appendix_16_web (pdf) (29.7 KB)
Appendix_17_web (pdf) (26.2 KB)
Appendix_18_web (pdf) (33.7 KB)


Share article:
This website stores cookies on your computer. These cookies are used to improve our website and provide more personalised services to you.


To make this site work properly, we sometimes place small data files called cookies on your device. Most big websites do this too.

1. What are cookies?

A cookie is a small text file that a website saves on your computer or mobile device when you visit the site. It enables the website to remember your actions and preferences (such as login, language, font size and other display preferences) over a period of time, so you don’t have to keep re-entering them whenever you come back to the site or browse from one page to another.

2. How do we use cookies?

A number of our pages use cookies to remember your actions and preferences (such as login, language, font size and other display preferences.)

Also, some videos embedded in our pages use a cookie to anonymously gather statistics on how you got there and what videos you visited.

Enabling these cookies is not strictly necessary for the website to work but it will provide you with a better browsing experience. You can delete or block these cookies, but if you do that some features of this site may not work as intended.

The cookie-related information is not used to identify you personally and the pattern data is fully under our control. These cookies are not used for any purpose other than those described here.

3. How to control cookies

You can control and/or delete cookies as you wish – for details, see You can delete all cookies that are already on your computer and you can set most browsers to prevent them from being placed. If you do this, however, you may have to manually adjust some preferences every time you visit a site and some services and functionalities may not work.