Broken sprinkler pump has been removed. But the power line is still there. It
Runs to a 30amp breaker. The wire is short, I would have to extend it to the pump
Perhaps 20”. The wire is very heavy gauge possibly 220- 10 gauge and difficult to splice.
Is there an electric fitting to join two heavy gauge wires together

What kind of wire or cable do you have? Each type has it's own unique connection method and set of materials.