The former Dow Chemical Co. counsel once nominated to head the EPA’s Superfund office failed to gain Senate approval in 2018 because of a Democratic senator’s concerns about the nominee’s defense of a contaminant.

Peter C. Wright was the White House’s nominee to head the Environmental Protection Agency’s Office of Land and Emergency Management, but was left out of a group of nominees confirmed Jan. 2. Because the 115th Congress officially ended, the Trump...