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Doesn't sound like it would be a problem to me if it is that shallow. But I am not an engineer!Quite a drain you have next to the tub! Good place to dump the water I suppose. Unless that is the entrance to your bomb shelter!
BTW, do you ride a street bike too or just a track bike?
Keep in mind that once you put your hot tub down, the water won't be able to get underneath it.Concrete is pourous. How long did it stay pooled up like that? I wouldn't worry about it at all.