Under orders from the U.S. Environmental Protection Agency, owners of the H. Kramer and Co. smelter at 21st and Throop streets are paying to remove the top few inches of soil from at least 54 yards in the low-income, predominantly Latino neighborhood. The EPA sent workers out this week to clean up four of the yards, in part to persuade skeptical property owners to participate but also to signal the federal agency is serious about completing the work.