Uran-Anomalie im Lyssbach
Vom Kanton Bern wurden wir 2012 mit der Aufgabe betraut, die Ursache der Uran-Anomalie im Lyssbach abzuklären. Mit dem Gewässerschutzlabor des Kt. Bern, mit dem Physiker Heinz Surbeck (nucfilm GmbH) und dem Drohnenpiloten der Firma Birdview picture GmbH ist uns dies gelungen.
The water and soil protection laboratory of the Canton of Bern detected anomalous high uranium concentrations in the creek “Lyssbach” at the locality of Lätti between between Lyss and Schönbühl (canton of Bern) as part of the standard water monitoring programm. Values up to 45 μg/l of dissolved uranium in creekwater and at up to 400 μg/l in groundwater samples have been measured. The average concentration of dissolved uranium in Swiss creeks is in the range of a few μg/l (Baertschi & Keil 1992).
Airborne radiation mapping
Water samples were collected from the “Lyssbach” and from groundwater inflows in the creek to explore the possible uranium source. Two suspicious contaminated sites were evaluated using a radiation detector as a payload of a octocopter (Figure 1). Airborne radiation mapping turned out to be a very effectiv and low budget instrument to detect anomalous radiation aereas within short time.
Scanning of 100’000 squaremeters
It was possible to scan several 100’000 m² within a day with a resolution of approximately 10 m2 and a detection limit of the flying Na(Ti) detector 50 cps. In order to increase the resolution to 2 m2 within the resulting anomalous radiation, the area was mesured with the same detector by foot. Soil samples, taken from core drillings, were analysed by gammaspectrometry and X‑ray fluorescence spectroscopy, watersamples by alphaspectrometry. In addition, piezometer measurements were made. The resulting radiation map is shown in Figure 2. The obtained uranium concentrations of the soil samples showed a max. value of 220 ppm U at a depth from 0.60 m. The uranium content of the watersample from the piezometer (420 μg U/l) showed the same value as earlier (Schmidt 2013) measurements from the drainagewater.
Evaluation of uranium sources
Several possible uranium sources could been evaluated, based on a historical investigation: disposal sites, fertilisers / waste of fertiliser production or geogene origin. The deposition age of tht solid uranium compounds in the soil could be estimated to 10’000 years b.p., based on the ratio of Ra-226 and Th-234. Therefore any present-day anthropogene origin of the uranium compounds can be excluded. However, during in the past 150 years the redox conditions may have changed by draining the swampy fields to gain agricultural land. This could have caused the input of oxygene into the soil to remobilze the uranium.
Autoren:
Simon Werthmüller, Geologische Beratungen Geologik AG
Büttenenhalde 42, 6006 Luzern (simon.werthmueller@geologik.ch)
Heinz Surbeck, Nucfilm GmbH,
Fineta, 1792 Cordast
Rico Ryser, Amt für Wasser und Abfall des Kantons Bern (AWA), Gewässer- und Bodenschutzlabor (GBL),
Reiterstrasse 11, 3011 Bern
