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 2020-43



Results of Monitoring at Olkiluoto in 2020 - Hydrology anf 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, hydrogeochemistry, surface 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 in drillholes, hydraulic conductivity, precipitation (including snow), sea-water level, surface flow (runoff), infiltration, ground frost, leakages in underground facilities/openings, and water balance of ventilation 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. Since 2014 the parameter groundwater salinity (in situ EC) is reported in the Monitoring Report of Hydrogeochemistry.

In December 2003, a programme for monitoring at Olkiluoto during construction and operation of ONKALO was presented (Posiva 2003c). In 2012 the monitoring programme was updated to concern years 2012–2018 (Posiva 2012a). In 2016 the monitoring programme was updated again to concern years 2017–2019, and in 2019 for years 2020–21 as internal memoranda. Monitoring has been carried out according to prevailing programme, and this Report presents the results of 2019.

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 shaft 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 2019. The construction project of ONKALO finished and the construction of the final disposal facility started in December 2016. 

Total leakage into ONKALO down to 4580 m chainage including shafts ONK-KU2 and -KU5 down to level −437 m and shafts ONK KU1 and  KU3 down to level −455 m was 25–34 L/min in 2019, but the exact inflow is difficult to determine, because due to construction works parts of the underground opening were out of reach for the measurements. The mapping of water leakages and moisture conditions on the tunnel walls and ceiling has been continued. The general pattern of sizes and counts of leakage areas 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 2019, decrease in heads near ONKALO was caused by temporary inflows through pilot hole ONK-CTPH6.1. Typically drawdowns in heads vary between 10 and 12 m within the HZ20 system and between 0.5 and 1.5 m within the HZ19 system. Due to the hydraulic short-circuit between the HZ19 and HZ20 systems drawdowns were disturbed throughout year 2019. Inflow into ONKALO along the HZ056 zone and the repository-scale HZL10 zone caused long-term drawdowns of over 20 m. The water level had decreased below the measurable drillhole depth in 13 monitoring sections during 2018 and in 2019, one section more took place. 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 2019. PFL DIFF measurements were carried out in drillhole OL-KR23. There were significant changes in the PFL DIFF results. No major changes were noted in the PFL TRANS results. 


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


WR 2020-43_web (pdf) (90 MB)


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.