As the nation's largest electricity company prepares to plead guilty to violating the federal Clean Water Act, Duke Energy has started delivering bottled water to people with tainted wells close to its North Carolina coal ash pits.

Duke has long denied its 32 dumps in the state have contaminated the drinking water of its neighbors, suggesting any worrying chemicals found in the wells is likely naturally occurring.

But recent state-mandated tests found that more than 150 residential wells tested near Duke's dumps have failed to meet state groundwater standards, and residents have been advised not to use their water for drinking or cooking.

Many of the results showed troublesome levels of toxic heavy metals like vanadium and hexavalent chromium — both of which can be contained in coal ash. And some of the residents have retained lawyers.

Duke spokeswoman Erin Culbert told The Associated Press that any homeowner who gets a state letter warning of a tainted well will get safe bottled water from Duke, if they request it.

While denying responsibly for the problem, Culbert said Duke simply wants to provide the homeowners "peace of mind."

Duke is scheduled to plead guilty Thursday to nine environmental crimes as part of a negotiated settlement with federal prosecutors requiring it to pay $102 million in fines and restitution. The proposed settlement over years of illegal pollution leaking from ash dumps at five of Duke's plants has been sealed, so it wasn't clear before the hearing whether people with contaminated well water will benefit.