The federal government notified the Maine Department of Health and Human Services on Wednesday that it is terminating Riverview Psychiatric Center's Medicare Provider Agreement, essentially shutting off some $20 million in annual federal funding at the state-run Augusta hospital. The issue has been simmering for months and in August caused a scramble in the Legislature to correct the problem. At issue is the federal Centers for Medicaid and Medicare Services' contention that the hospital, which is run by the state, is overcrowded, inadequately staffed and using improper methods such as handcuffs and Tasers to subdue violent patients.