Databank

Workreport 2007-19

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Name:

Groundwater Sampling at Olkiluoto, Eurajoki from the Borehole OL-KR6 During a Long-Term Pumping Test in 2006

Writer:

Hirvonen, H., Hatanpää, E. & Ahokas, H.

Language:

English

Page count:

83

Summary:

A long-term pumping test at borehole OL-KR6 at Olkiluoto was initiated in 2001. Since then, flow and in situ EC measurements as well as groundwater sampling from specific sampling sections have been performed yearly. The aim of this study was to obtain information on the potential connections via fractures both to the sea and to deep saline groundwater during long-term pumping of the open borehole. In 2006, four groundwater samples were collected from four different sampling depths (98.5-100.5 m, 125-130 m, 135-137 m and 422-425 m). The groundwater samples were taken in stages using PAVE equipment.

The water types found in the groundwater samples from OL-KR6 were Na-Ca-Cl (for samples from depths of 98.5-100.5 m and 125-130 m) and Na-Cl (for samples from depths of 135-137 m and 422-425 m). The sample from depth 422-425 m was saline (TDS> 10000 mg/l), while other waters were brackish (1000 mg < TDS <10000 mg/l).

This study presents the sampling methods and analysis results of groundwater samples from deep borehole OL-KR6, and draws a comparison between the results of the in situ EC measurements and the EC results measured during groundwater sampling. This report also contains a short comparison of the results obtained from the long-term pumping test conducted between 2001-2006.

In situ EC results and EC results measured in laboratory are in quite good agreement. At sampling depth, 422-425 m, EC increased between 2004-2006. At a depth of 423 m, much variation in situ EC-values indicates that routes of groundwater may change during long-term pumping due to the limited storages of different aquifers or the heterogeneity of the content of groundwater in different locations in the bedrock. The minor systematic difference between in situ and sampling EC at a depth of 136 m was probably due to the different flow fields during flow logging and water sampling.

The dominant gas in the groundwater samples was nitrogen. Carbon dioxide was the second dominant gas, except for the OL-KR6/125-130 m sample, where argon was the second dominant. All sample vessels were argon treated before sampling so contamination by argon was possible.

In 2006, dissolved gas concentrations were higher in OL-KR6 samples than in the two previous years. Higher concentrations were noticed in nitrogen, carbon dioxide and argon (contamination possible) contents at all sampling depths.

One of the conclusions from this and previous studies is that the changes in the three upper sampling points were most remarkable in 2001-2002 just after pumping started. Otherwise, water compositions were invariable.

Keywords:

long-term pumping test, in situ EC-measurement, salinity, groundwater, sampling, analysis, chemical analysis results

File(s):

Groundwater Sampling at Olkiluoto, Eurajoki from the Borehole OL-KR6 During a Long-Term Pumping Test in 2006 (pdf) (1.4 MB)


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