During her four-year tenure as administrator of the EPA, Lisa Jackson was a true champion for public health and environmental justice.

One of her greatest legacies is the Mercury and Air Toxics Standard, a rule that will help Americans breathe a little easier since it sharply limits the amount of mercury and other toxic metals that can be emitted by coal-fired power plants. The rule finally requires the capture of mercury, arsenic, hexavalent chromium, nickel, selenium and other heavy metals at the plant smokestacks.

Improved air quality resulting from these new standards will yield significant health benefits, preventing an estimated 130,000 asthma attacks, 11,000 premature deaths and 4,700 heart attacks. Following the laws of physics, however, these toxic pollutants must go somewhere. As the rule cleans up our air it will also result in much greater quantities of deadly metals in solid waste—the coal ash and scrubber sludge generated by coal-fired plants—that ends up in massive dump sites across the U.S.

Therefore it is imperative that the Obama Administration finish the job and protect the nation’s most vulnerable communities from the increased volume and toxicity of coal ash resulting from this landmark rule.

Without standards to ensure safe coal ash disposal, these toxics will continue to build up in more than 1,040 coal ash dams and landfills across the country, entering our drinking water, lakes, streams and the air near these dumps. Arsenic, chromium, mercury and selenium have already contaminated the air and water of hundreds of sites across the U.S., threatening communities whose pleas for federal action to clean up coal ash have gone unanswered.

In the administrator’s statement, Jackson claimed that the actions taken on her watch mean “the ship is sailing in the right direction.” However, far too much remains undone, and the course is not clear. As toxic coal ash threatens clean water across the nation, Americans need a captain at the helm of the EPA who will finish the job started by Administrator Jackson.

Obama has a mandate, and the public wants protection. A 2011 Gallup poll shows that a majority of Americans worry a “great deal” about clean water, with water contamination by toxic waste and the pollution of rivers, lakes and reservoirs ranking as the top environmental concerns for 79 percent of respondents. Yet a strong coal ash rule is certain to encounter Congressional resistance, and the next administrator must navigate difficult waters and remain unwavering in the face of political winds that obstruct the agency’s duty to protect health and the environment.

After Jackson passes the torch, Americans will need a coal ash rule that prevents water contamination and catastrophic spills. Without a coal ash rule, the administration simply traded cleaning up our air for poisoning our water. Coal ash has contaminated water in 37 states, and that number is growing. Unless her successor wants to get us closer to 50, the new chief must deliver the long-delayed coal ash rule or risk a legacy of poisoned communities and dying rivers.