Japan starts release of Fukushima’s treated radioactive water

You're drawing some arbituary point of even more negligible dilution when mathematically, flat out dumping everything straight into Inawashiro is still merely 1% of WHO limit for safe drinking water. It would already be adequately diluted for human health. It's already likely sufficiently negligible considering the ratio of solution:solvent. Spread that over 30/50 or whatever years over water cycles and different locations and it's even less of an issue. It would be bloody diluted regardless, especially so when titrated on multi decade time scale. I'd happily drink it. And I am not being facetious.

Ultimately, regardless of feasibility, it's simply a solution which they didn't even consider, because again, as you recognized why would they. That's politically suicide even if it's deemed ecologically sound plan. Which circles back to your first point, does any country dump tritium in their local lake? Not publically, and Fukushima is notoriously public politics. But you know what most try to do with nuclear waste? They attempt to engineer supremely expensive local storage solutions, and frequently fail only to spend stupid resources to warehouses it domestically, instead of dumping that into the commons. It's 60 olympic swimming pools worth of water. It's trivial storage problem for nation state. Hence problem 1/2/3 isn't even a problem especially if they bothered with local dumping studies which again, is 3 tankers per day for 30 years. It's nothing. Desalinating 1.25m tons is also trivial, and not even that costly. A 10m gallon / day plant cost less than 100M and sort filter that in a month. Which is peanuts versus aggregate clean up cost, and even potential lost fishing revenue. Cost isn't driving this decision to release, politics is. And it's not regional geopolitics because JP isn't releasing this water out of spite for her neighbours. Let's not forget, it's not PRC but most of region as well as countries across the Pacific not pleased with this decision.

Which ultimately circles back to point 4, and my broader point. LOCALs don't like it. LOCALs vote. Can't risk LOCAL votes even if they're irrational, and EVEN worse if their rational distrust of TEPCO becomes reality down the line. IIRC even more containated water already leeched into ground water. Risk of future leaks, however "safe" this water is, and heads will roll. So the politically expedient solution is to dump into ocean and remove any potential risk. The political math is simple, they would never even consider local disposal or long term local storage due to the risks, so into the ocean it goes. Which again, is fine. Fine in the sense that it's a calculated decision. But let's just acknowledge that's whats actually driving decision making. Less science and more domestic JP politics. They didn't have to dump this water. A 5T economy can afford to store it indefintely and ignore geopolitical shit show. But domestic JP politics want that water gone from JP territory, so into the ocean it goes.

By considering the context of the OP and my response, which was the 80s. By not injecting partisan stuff. By adding something insightful or something we might not know already.

Why don't you just drink bleach instead of wiping down your countertop with it?

Seriously, I have a hard time assuming good will from your post if you do not try to differentiate the amount of dilution happening in a 100km2 50m deep lake vs a 100,000,000km2-sized 5,000m deep ocean.

Shit breaks down into food.

In the ocean: bacteria food -> plant food -> fish food.

It's not arbitrary, and I don't understand why you think it is. It's not even a mathematical issue. At it's core, it has always been an environmental issue.

Fundamentally, the complaint is that the tritium water will cause environmental damage. => And will lead to damage to humans. If we go down to the roots of the issue, it has not, and never was centered around whether the bq/L was below human drinking limits. It has always been about whether the bq/L amount is safe for the environment. That's why I brought up the natural range in the first place. If anything, claims about it being safe to drink have been a distraction brought up to placate protestors. (And it misses the point)

Therefore, the powerplant should be (and has been) required to reduce environmental effects. When it comes to controlling the Catastrophically F'd reactors, they've been less than capable to say the least. But that's not explicitly related to the tritium water we are discussing about right now.

So, the goal should be to minimize environmental damage. In order to better ensure that, the Tritium water should not cause a major change in composition of the water. Therefore, the bq/L of tritium in water, should preferably, not change beyond the naturally expected amount. (ie: 0.4–1.2 bq/L) Hence why I brought up how your solution violates that basic idea, while the sea release does not. I even showed you the very basic napkin math that made me come to that conclusion.

You do realize, one of the other proposed solutions was actually release by air? After all, Tritium is an isotope of Hydrogen. That plan was specifically dropped because the amount of expected tritium per cubic liter of air, would be greater than when released in water. The decision from the start, has been about minimizing the becquerels per cubic liter. Certainly, the government would accept nothing else.

I should point out, the water is more dangerous when stored. By default, the stored water has a significantly higher concentration until it is diluted. Certainly, higher than the safe level. A leak from the tanks would cause significantly more environmental damage. Just like with aircraft design, where every contingency is considered, we must also consider every contingency for when that containment fails. History has shown us multiple times, that inevitably, even the best built systems are destroyed by human error.

Quite frankly, your complaints are more arbitrary than mine. You are proposing that Japan should take the concerns of uninformed individuals, over the concerns and claims made by professionals.