MEMPHIS (AP) — Health and environmental officials say they are investigating how high levels of arsenic and lead were found in groundwater under a Tennessee coal power plant.

Shelby County Health Department director Alisa Haushalter said in a statement the agency is working with the Tennessee Department of Environment and Conservation to monitor the probe into how toxins appeared in wells that check for pollution coming from coal ash ponds at Allen Fossil Plant in Memphis.

The Commercial Appeal reports the Tennessee Valley Authority told regulators that arsenic measured at levels more than 300 times the federal drinking-water standard were found.

TDEC officials say they believe the pollution doesn't threaten an aquifer that provides Memphis' water. TVA spokesman Scott Brooks said the company does not know if the toxins came from ash ponds.