Ether Jones wrote:

Just dug up the septic tank to get it pumped and I cannot lift the
concrete access cover. It is "frozen" in place (more like "chemically
bonded" I would say).

The tank is concrete and the access cover is concrete. The access
cover is rectangular in shape, about 12"x18". It has an iron handle
cast into the center. The sides of the cover are slightly angled so
that the cover fits snugly down into the access hole...

You might use a tripod or a 55 gallon drum on each side with a beam and
a comealong to put (say) 500 pounds of uplift on the cover handle for
a few hours while sprinkling hot water around the edge and bonking it
with a 4x4. You could measure the cable tension by pulling it sideways
with your hand or a fish scale. A 4' cable with 500 pounds of tension
would move sideways about 1/2" with a 20 pound force in the middle.

Nick