The E.P.A., as part of Mr. Biden’s new push, will revive a program that allowed companies to reduce the penalty on some violations in exchange for subsidizing initiatives that have a positive environmental impact. The Trump administration had scrapped that program.

But the E.P.A. is fundamentally a regulatory and rule-making agency. It has addressed racial issues, but it lacks the legal and investigative firepower of Mr. Garland’s department.

The Justice Department has a robust civil rights division responsible for enforcing the 1964 Civil Rights Act, including Title VI, which prohibits states, localities and universities that receive federal funding from discriminating against people “on the basis of race, color or national origin.”

Activists began pressuring the Justice Department to use Title VI on environmental cases during the Obama administration. But that effort stalled, and the Trump administration quickly jettisoned the policy.

That all changed in November, when Ms. Clarke announced, to the surprise of local officials, that she was opening a Title VI investigation into the actions of the Alabama Public Health Department and the Lowndes County Health Department.

The state government, controlled by Republicans, has done little to address the problem on its own over the years. But local residents have also complained about the actions of local Black officials who have failed to address a sanitation and water management system that routinely results in sewage backups in the streets of towns like Hayneville.

Catherine Coleman Flowers, a MacArthur fellow whose 2020 book, “Waste,” brings attention to the crisis in Alabama, praised the creation of the office. But she said the ultimate test would be whether Mr. Garland was willing to withstand the political blowback for getting tough on governments, especially in conservative-leaning states.

“Environmental justice has to be done like any other investigation the department does,” like a corruption case, said Ms. Flowers, who has been interviewed by investigators. “They can do settlements, but people need to be punished when they do something wrong. There needs to be real penalties, or there will be no fear of repercussions.”