Senators Baucus (D-Mont.) and Grassley (R-Iowa) of the Senate Finance Committee have written to the 136 U.S. colleges with endowments of $500 million or more, asking a series of questions about endowment growth and spending on student aid. The senators are seeking answers in light of a National Association of College and University Business Officers study showing explosive college endowment growth, a news release said. The study, released Jan. 24, reported double-digit endowment growth at hundreds of colleges over the past year. Federal law requires most private foundations to pay out 5 percent of their assets each year toward their charitable purpose, but there is no such requirement for university endowments.