Enlighten me... engineering wise

I know this is a fairy tale and all, and the answers to my question might be in the film but wasn't paying attention to it... but anyway:

how could you built a warehouse/wholesale market in the middle of a semi-developed area without knowing that there runs a shallow underground body of water under it(six feet to be exact)? wouldn't the state environmental law officers have informed them of that prior to building? and wouldn't they discover it, if not foretold, that there is an underground river while digging for its foundations? if so, the river would have been diverted, if not relocating the establishment for risk of subsurface water contamination. i'm not familiar with california state architecture laws though, hence it could be possible. but i say, they -- costco -- have one bad environmental analyst/surveyor (in a fictional sense). It's just a thought though, not in anyway trying to bash the plot.

Anyway, i loved the movie nonetheless. A fine fairy tale, like i said. And great acting by all major characters.