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Will it poison the wells ?

Right now I imagine people in the far east are very nervous about the events which continue in Japan.

One deep worry which I suspect the general population have regards drinking water. I think that the tidal wave in Japan has the potential to cause contamination of drinking water by waste water and sewage. This is clearly not good. I am not an expert on the subject of microbiology so I can not comment any further on this issue.

I am sure that some people may be asking questions about the radioactive contamination of drinking water by the fallout from the Japanese reactor accident. While we do not know how much radioactivity will leak from the stricken reactor site, so far compared with Chernobyl the release has been small.

If an intense cloud of fallout was to be released and washed out of the sky by rain, then it would not be a good idea to drink that water. I hold a view that where possible rain water collected from your roof or garden should not be used as drinking water during a nuclear accident, however a well in the garden is much more likely to be safe to drink from.

I think that the key isotopes to consider are the iodines and cesiums.

This is because the water in the well is likely to be older than the rainwater, even if the accident was carry on releasing short-lived iodine isotopes forever* at the same rate the water in a garden well would be older than the rain water. If water requires 32 days to trickle from the surface of the garden through the soil into the well, then ignoring chemical effects the level of shortlived nasties such as iodine-131 will be lower. In the case of iodine-131 94 % of it would have decayed, so if the rainwater contains 1000 Bq of I-131 per litre while the garden well would have 63 Bq per litre. This simple model assumes that it rains at a constant rate and that everything is constant.

The next big thing which protects the garden well is that as the water passes through the soil it will be chemically processed by the soil. Many soils have a great deal of clay minerals in them, these clay minerals are able to remove cesium by an ion exchange process. As a result cesium is not very mobile in soil, the cesium tends to bind to the soil particles. As a result the cesium will stay in the top layers of the soil.

* Thankfully te release of iodine-131 can not go on forever, the production of iodine-131 stopped almost a week ago, and the half life of this isotope is eight days.

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