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A new study says that so many more undocumented immigrants now live in America than the last time Congress created a large-scale forgiveness program that officials need to think carefully about the impacts that would create on states.

For example, the Immigration Reform and Control Act of 1986 allowed 2.7 million undocumented immigrants to become legal residents, and 85 percent of them lived in just five states, according to a study released Wednesday by the Pew Charitable Trusts.

Now, an estimated 11.2 million unauthorized immigrants live in the nation, and they are scattered in large numbers throughout most states.

For example, the number of undocumented immigrants in Utah in 1990 was estimated at 15,000. That number grew to an estimated 110,000 in 2010 — more than a seven-fold increase in 20 years, the study said.

So the report says as Congress debates immigration reform, it should think through how federal, state and local governments would need to work together to provide services a big group would need as its seeks legalization — and how to pay for it.

The paper looked at the 1986 act and the more recent Deferred Action for Childhood Arrivals (DACA) program — which has allowed 500,000 unauthorized immigrants who arrived as children to remain — to identify services likely needed.

Among programs needed would be ones to help teach English and U.S. civics to aid immigrants in qualifying for residency and citizenship; outreach to inform them about steps they need to take; help in obtaining documents to prove their residency over required periods; and protection from fraud.

The study said the federal government in the past provided some of those services itself or provided grants to states. In some cases, states and local governments sometimes simply decided to step up and help in other instances.