Thanks for the ideas all. Looks like we are going to use a 4 inch sewer test plug a foot below our cut. Then inert the area if needed. We will use our PID to see if its required. We will cut with a portable bandsaw. The shear idea would be great if this wasnt for a finished product.
On top of this schedule 40 stainless pipe we have to install and valve assembly. Pressure in the well itself is not an issue, and this is a vapor recovery well, it has no pressure, or suction on it yet. Once cut down and our valve is in place, we well fire up the blow system and start removing product from the well, along with 10 others on site. This one is a thorn in our side, since the drillers were supposed to cut the casing to grade, but no one caught that they were 6 inches high until two weeks after they left, so we are stuck cutting it while its in the ground, and is full of explosive product at the bottom.