You should look at the definition that you referred to, more...

You should look at the definition that you referred to, more closely. It is the specific gravity of dry soil! The material that is being drilled by Quasar/ags is actually an aquifer with a large percentage of interstitial water which at SG 1.00 will bring your overall SG down considerably to 1.6-1.9

Look up wet sand and wet clay, average them and tell Rupert.

http://www.csgnetwork.com/specificgravmattable.html