This outdoor Slab on grade job took an unusual turn. The slab was about 20 feet by 30 feet. We needed to locate the depth of the slab and if there was rebar and if so the spacing. This patio slab held two storage tanks. My guess would have been 6 to 8 inches and wire mesh. So we took out the 2600 Mhz rig and start rolling and can't see the bottom of the slab, so we moved to a 1600 Mhz, 900mhz and then finally on the 400 Mhz antenna we found the bottom of this small slab on grade area at over 3 feet deep and rebar 1 foot on center 15 inches deep. This is deeper than footers I have seen in large hospital buildings. My guess for each tank would be somewhere between 4 to 6 tones. My guess for the strength of the concrete slab supporting them 13,500 to 27,000 tones. So to the question at hand, will it hold the added weight of a new tank? It should do an ok job at supporting the weight for the next 100,000 years or so.