The Federal Emergency Management Agency (FEMA) is working to get back part of the aid distributed to 4,500 households in the aftermath of Hurricane Sandy, an Associated Press investigation found.

The households, through systemic flaws rather than efforts to dupe the system, may have received improper payments, like two members of the same household who were each given aid, or owners of vacation homes and homes whose damage was covered later by insurance. The agency has asked around 850 recipients to return a total of $5.8 million, with an average request of nearly $7,000.

For some recipients, that could be tough. Around half of the households make less than $30,000 a year. For a household of four, the federal poverty line is $23,850.

Throughout New York and New Jersey, around 179,000 households received federal aid in the aftermath of the storm that flooded and destroyed much of the Northeast coast.

It’s not the first time FEMA is looking for recipients to return payments. After Hurricane Katrina, the agency asked 90,000 households for refunds, many from households who had already spent the money and couldn’t afford to pay it back. Congress ended up allowing FEMA to forgive much of the debt.

The aid distribution effort continues, two years after the storm. In June 2014, a study found that tens of thousands had not received aid, many whose New York City homes were damaged. Another report by the Fair Share Housing Center found that the Hurricane Sandy relief program disproportionately rejected Black and Latino aid applicants. To try to increase transparency, New Jersey introduced the Sandy Bill of Rights to clarify aid status for those still waiting for checks, or their application to be approved. Governor Chris Christie vetoed the bill in May.