Look, first things first. Drinking water limits and limits for milk are two very different things.
The limits for drinking water are 3 pCi/L that is 3 picocuries per liter, and assumes long term exposure. The average person doesn't drink as much milk as water, nor do you bathe in it, brush your teeth with it, cook (as much) with it etc. The amount is minute because it assumes constant exposure to potable, drinkable water.
The milk they sampled contains 18 pCi/L which would be 6 times the limit for drinking water but not 6 times for milk for I-131. (The limit for milk is 4,700 pCi/L or 261 times higher.) For Cesium-134 they found 24 pCi/L, and for Cesium-137 19 pCi/L, which would be 8 times and 6 1/3 times over the limit for WATER respectively.
This translates into 600%, 800% and 633% for each of the three isotopes respectively; however you CANNOT then ADD the percentages and come up with 2033% over the limit. What kind of math is that? It's not a cumulative total for radiation in general, and besides it's milk, NOT drinking water. No one isotope was 2033% over the limit for water or milk.
That said, how did the radioactive isotopes get into the cow to get into the milk? I would assume from drinking water and eating grass contaminated with those isotopes. We have no measurements for rainwater in Hawaii available to the public.
What is the ratio of isotopes in pCi/L that a cow has to consume to produce milk that has a pCi/L of the isotopes. I doubt it's one to one, because the "experts" have constantly repeated how poorly the uptake for those isotopes is in humans and animals. Now, I don't know what the ratio is and though I bet there is a study or two on the subject I have yet to find it.
If for example, if the ratio is 2 to 1 then the cow would have had to consume 36 pCi/L of water/grass I-131. For Cesium-134 48 pCi/L, and for Cesium-137 38 pCi/L...if it's 3 to 1 or 4 to 1 you can hopefully do the math yourself. Maybe it's 10 to 1: I don't know. Were the cows drinking straight undiluted rainwater? Doubtful. Was the grass soaked in rainwater that just contained 48 pCi/L of Cesium-134...again doubtful. I would think that the rainwater that fell on the cows had many multiples of 3 pCi/L of I-131 because it would be diluted in water troughs and on the grass and feed that they consumed. This is all conjecture on my part. I have no numbers with which to work, only a little logic, reasoning and critical thinking skills of which certain bureaucrats seem to be blissfully bereft.
I look at rainwater readings elsewhere and find them to be in the from 79 pCi/L in MA to 543 pCi/L in CA (San Fransisco) for I-131 but in all cases they also found Cesium and Te-132. On the day they measured 543 pCi/L of I-131 they found 13 pCi/L of Te-132 and Ce-137 in San Fransisco along with a few other isotopes. The point is, for it to show up in the milk it has to be in the rainwater in many multiples of what it is in the milk, but we have no measurements for rainwater in Hawaii that I have seen. NONE. ZIP. NADA. ZILTCH. ZED. ZERO. Not any. Squat.
All I can gather from the exceedingly limited data I can find is that it has been more than 18 pCi/L of I-131 in the rainwater. I doubt it was 500 pCi/L of I-131, on the other hand I doubt it was only 36 pCi/L of I-131. I am thinking the range is some where between 100 and 400 pCi/L of I-131 in our rainwater but that's a guess. Problem is rainwater IS drinking water for some of the state where catchment and surface water make up a good deal of the water supply.
Again the amounts are minuscule in the main water supply because even so the contaminated water mixes with the drinking water in ratios that would knock down the pCi/L count by factors: Waikamoi Reservoir is a 30 million gallon (MG) reservoir and Kahakapao Reservoir is 100 MG. One gallon is 3.7854 liters. So doing a little math even if 100,000 liters of contaminated rainwater got directly into the reservoir when it was only about half full it would be diluted far below the 3 pCi/L for the isotopes. It makes for some nice math problems: 100,000 liters of 200 pCi/L I-131 water mixes with 200,000,000 liters of uncontaminated water...assuming a somewhat even distribution what is the new contamination level?
I just made these numbers up to make the math easy. We have had a wet winter and the reservoirs are better than half full and 100,000 liters would be an extremely heavy rainfall so that would be a conservative (read unlikely) guesstimate using made up numbers erring on the side of contamination. Possible but not plausible and you'd still be 30 times under the limit for drinking water. A thought exercise for the sake of example.
After all that, people on catchment do not have the luxury of large numbers, and rainfall directly on you is not diluted...100 to 400 pCi/L of I-131 and even the smaller amounts of the other isotopes that are basically here permanently due to their much longer half lives are not amounts to be flippantly ignored. Cesium accumulates. It also bio-accumulates. Stay out of the rain for a while and don't drink rainwater. Especially if you are pregnant or a small child.
This is FRANCE where the numbers are smaller and they are much farther away:
The people who have catchment tanks should have been warned, one good rainfall can take a tank from 3/4 full to full and then the dilution is only 1:4. I know quite a few people who use catchment
Up until March I collected rainwater on Maui for watering plants and occasionally for drinking...fresh vog free rainwater is delicious. This is no longer the case. Over time the longer lived isotopes could be cause for concern in our drinking water but right now this is not the case. It is indeed cause for caution when it comes to direct exposure to rainwater. The "nothing to worry about" mantra becomes annoying.
It would be nice if our government would do it's (expletive removed) job and inform the people of the measurements in the rainwater instead of just the lack thereof. Still, it's better than Canada were they aren't even testing the milk because they are so certain there is no cause for concern. The point is it's not the milk itself but the amount of radiation it took to get the cows to produce contaminated milk in the first place. Also to be noted is not all the rain has radiation in it all the time, but obviously it has had some in it recently or they wouldn't be detecting it in the milk and that's the problem: we don't know how much or when.