Assistant Administrator for EPA's Office of Air and Radiation, Gina McCarthy (Melina Mara/The Washington Post)

Looks like it could be Gina McCarthy’s big day. The assistant administrator for air and radiation at the Environmental Protection Agency is the White House’s pick to head that agency — and the long-expected announcement could come as soon as Wednesday, we’re hearing.

McCarthy is replacing Lisa Jackson, who stepped down earlier this month.

It’s long been expected that whoever the nominee was would face tough questions on Capitol Hill — after all, the agency’s portfolio includes flashpoint issues like climate change, a key priority for the White House. Jackson’s tenure was marked by plenty of testy Hill exchanges.

It looks like oil and several other industries regulated by EPA won’t make a fuss over the president’s selection, with the coal folks being the possible exception. But several Senate Republicans, including Sen. David Vitter (R-La.), have made rumblings about McCarthy, signalling her nomination won’t exactly be a cakewalk.