GAO estimates $124.7 billion in improper payment in FY2014 in testimony here.
The Department of Agriculture (USDA) reported that section 281 of the Department of Agriculture Reorganization Act of 1994 precluded the use of recovery auditing techniques>Specifically, the agency reported that section 281 provides that 90 days after the decision of a state, a county, or an area committee is final, no action may be taken to recover the amounts found to have been erroneously disbursed as a result of the decision, unless the participant had reason to believe that the decision was erroneous. This statute is commonly referred to as the Finality Rule, and according to USDA, it affects the Farm Service Agency’s ability to recover overpayments.In 2013 GAO dinged NRCS and RMA for not checking SSA death files. Situation hadn't changed by March 2015.
The bulk of the testimony points out problems relative to the SSA death files.
Seems to me Congress could fix many of the problems by changing the laws in several instances: permit SSA to pass on state-provided death data (eliminating the need for separate files), easing the ability to share the data with agencies, forcing state agencies to use the data (in the case of TANF)