While its hard to fire civil servants, its not hard if done correctly. Write the supervisor's job description exactly as to what is acceptable performance. If, he exceeds the performance give a bonus (government bonuses are usually $5,000 to $10,000, annually for high ranking supervisors). If they don't exceed performance, but meet it, they get to keep their job. Small deficiencies -- no raise. As the deficiency increases -- then demotion or firing. Spell it all out to them.
If, they falsify federal documents -- fire and prosecute.