I would like to know the calculation.
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I understand your dose calculation and the derivation of number of liters of rain water required to achieve an ede of 5mrem, the equivalent of a cross-country flight.
What I don't understand is why you have chosen this particular methodology to illustrate that the amount of particles in the rain water is safe.
According to the current EPA regulations, the Maximum Contaminant Level of co-occurring beta/photon emitters in drinking water is 4mrem/year ede. (see http://water.epa.gov/lawsregs/rulesregs/sdwa/radionuclides/upload/2009_0... and http://www.federalregister.gov/articles/2000/12/07/00-30421/national-pri...).
EPA's drinking water collection and sampling methodology can be found here: (http://water.epa.gov/lawsregs/rulesregs/sdwa/radionuclides/upload/2009_0...).
It references a "relatively high" level for gross beta-particle activity at above 25pCi/L(0.925Bq/L). That is to say, according to EPA, if this rain water that you measured was actually drinking water, it would've been well (few times, actually) above the maximum allowable contaminant levels for co-occuring beta particles activity.
Of course, we shouldn't be implying that consuming any amount of rain water would be safe in the first place, regardless of presence of radionuclides.
I guess I disagree with your approach of illustrating the impact of the Fukushima plume in the Bay Area. If you are talking about consuming water, then drinking water is what you should be testing.
Thank you for your hard work and making these results available to the public.
I would agree that if we are talking about consuming water we may want to use the drinking water standards, however, these standards are set for long-term exposures and we did not see this as the same situation. We are measuring rain water, so consuming it is the most conservative dose estimation and that is what we present. It is important to mention that rain water is not drinking water and water supplies will have a large dilution fraction from this runoff. We will be taking readings from water supplies and other pathways to attempt to quantify the dilution, but this will be difficult considering the half-life of I-131 and the very low concentration we are seeing.
While there will indeed be large dilution in the water supply, won't there be additional isotopes with longer half-lives such as Cesium-137 that is added to the water table in California as storm systems from the Pacific continue to roll in over the coming weeks and months?
A number of media reports talk about the dilution that occurs as the radioactive isotopes move east from Japan, but isn't there a risk that these particles will make their way into subsequent storm systems? Not trying to be alarmist--just try to get a realistic picture of what our longer-term outlook is for ingested and inhaled radiation exposure here in California.
Thanks for all the time that you're putting in to distributing accurage information...it's a true public service mission.
This has to do the the volatility of Cs137 which is actually quite low. Cs137 will not just reside at the surface but will diffuse into the bulk of the ocean and very little, if any, will be at the surface. Once it hits the ocean, I think it is safe to say it effectively disappears with respect to rain. There are other pathways like sea life and quantifying this will also be very hard. There is a whole science in defining these pathways and quantifying the transport. The best place to do this is Japan because the Cs137 will be detectable for quite a long time. Here on the West Coast, I expect the Cs137 to dilute below our detection limits much sooner.
Is there any chance the radioactive particles can sink into the deep crevices of the ocean and cause an ancient sea creature to mutate and awaken? Also, can such a mutation cause such a creature to grow to enormous size and start attacking our cities? If so, have scientists possibly figured out a way to control Godzilla enough to get him to defeat aforementioned ancient sea monster?
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