DUNN, N.C. — Authorities said what looked like an ammonia leak at Dunn's water treatment plant was actually someone stealing the chemical to make methamphetamine.

The Harnett County Sheriff Office said 28-year-old Steven Matthews broke into the water plant several times in the last eight months. Investigators said he climbed the fence at night, then used a hose to fill propane tanks with anhydrous ammonia, getting five to six pounds each trip.

Water plants use anhydrous ammonia in small amounts to purify your drinking water. For meth makers, it is a key ingredient for their drug.

Investigators traced the equipment left behind back to Matthews, who allegedly confessed to the crime.

Authorities said the ammonia can go for as much as $500 a pound on the black market.