MEMPHIS, Tenn. (AP) - Memphis residents are as proud of their sweet-tasting water as their barbecue and blues. The water - drawn from the Memphis Sand aquifer beneath this Tennessee city - is so revered that a city utility called it a "community treasure" in an online report on its cleanliness.

So alarms went off after state environmental officials and the Tennessee Valley Authority revealed this week that high levels of arsenic and lead had been found in groundwater beneath the coal-fired Allen Fossil Plant in southwest Memphis. The toxins were detected in wells where pollution is monitored from ponds that hold coal ash - the dirty byproduct left from burning coal to generate electricity.

One well had arsenic at levels more than 300 times the federal drinking-water standard. The monitoring wells run about 50 feet (15 meters) deep and are about a half-mile (.8 kilometer) from far deeper wells drilled by the TVA directly into the Memphis Sand aquifer. Next year, the TVA plans to pump 3.5 million gallons (13.2 million liters) of water out of the aquifer per day to cool a natural gas power plant that is replacing the aging Allen coal plant.

The Tennessee Valley Authority's coal-burning Allen Fossil Plant on Friday, July 14, 2017 in Memphis, Tenn. Groundwater in wells at the plant have tested for excessive levels of arsenic and lead. (AP Photo/Adrian Sainz)

A layer of clay lies between the groundwater and the aquifer. This prompted the Tennessee Department of Environment and Conservation, through spokesman Eric Ward, to state that it is "confident the contaminants found in TVA wells at the Allen Fossil Plant are not impacting drinking water."

Nonetheless, the department has asked Memphis Light, Gas & Water - the city's water utility - to test treated drinking water. It also told the TVA, which has a history of difficulties handling coal ash, to pinpoint where the toxins came from.

Spokesman Scott Brooks said the TVA, the nation's largest public utility, doesn't know the source of the toxins and is cooperating with the state.

Still, the mere existence of toxins - and their proximity to other deeper wells burrowing into the aquifer - drew a sharp response from Mayor Mark Luttrell of Shelby County. His county is home to more than 900,000 residents and has Memphis as its seat.

"The levels of arsenic in the water samples are not acceptable to our community," he said in a statement.

The Sierra Club has demanded more tests and said TVA should immediately contract with Memphis Light, Gas & Water to use municipal water to cool their new plant.

An advocacy group called Protect Our Aquifer also expressed concern.

"We suspected the groundwater beneath the Allen plant was already contaminated, but this is even worse than we had imagined," Ward Archer, the group's president, said in a statement. "TVA's plan to pump Memphis Sand Aquifer water from beneath this contaminated site is irresponsible and endangers our drinking water supply."

Jerry Collins, president and CEO of Memphis Light, Gas & Water, said an analysis of drinking water test results should be ready in coming days.

"We are very confident that the analysis will show that the concentrations of arsenic and lead, if they can find any at all, will be well below any drinking-water standards" of the Environmental Protection Agency, he said.

Collins acknowledged the public alarm, adding, "They are very proud of the drinking water here in Memphis."

Part of the concern is the TVA's history of handling coal ash ponds. The utility has been sued by environmental groups that allege that coal ash ponds from its coal-fired power plant in Gallatin, Tennessee, are seeping pollution into the Cumberland River, violating the Clean Water Act.

Environmental groups want the waste at the 1950s-era Gallatin Fossil Plant dug up and taken elsewhere. TVA has said it's cheaper and may be safer and more environmentally friendly to keep it where it is

A trial was held earlier this year, and a decision is pending.

Also, a 2008 coal ash disaster at TVA's Kingston Fossil Plant in Tennessee sent more than 5 million cubic yards of sludge into the Emory and Clinch rivers that year, destroying homes. The TVA since has invested billions of dollars in safer ways to store coal ash.

The TVA's Brooks said finding the source of the toxins could take months of investigation, noting "there are a lot of questions."

As the investigation continues, Memphis residents like Bennie Howie await answers. Howie said word of the toxins is "extremely upsetting," especially after the lead-tainted water crisis in Flint, Michigan.

"This is a big deal," Howie said, adding afterward, "Did we not learn something from Flint, Michigan?"

Just last year, Memphis officials announced with fanfare that 12,000 bottles of their prized water from the Memphis Sand aquifer were being sent northward to help Flint residents.