I think most of those estimates were based on installing a flame diverter (not easily possible with the base being so close to the water table) and having the r

I think most of those estimates were based on installing a flame diverter (not easily possible with the base being so close to the water table) and having the rocket-grade concrete cure over a number of months. The original pad they had did take many months to cure. Now, they have a stainless steel block (with holes to squirt water up out of) over the replacement concrete. Hopefully that system can cope with the pressure from the rocket exhaust.