Hmm. I honestly cant think of anything else besides contaminates from the runoff. IMO, the OP is leaving something out of the equation or we are just looking at simple things that we are used to seeing. Many of us ( at least me) havent dealt with a tank of that size and any problems that occur with tanks of this size. The OP might have better luck posting in other forums as well just to see what other communities have to say.
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