Q2 reports that a former chemist at the city of Billings Water Treatment Plant laboratory is accused of contaminating water test samples in 2015, costing the city its state certification.

35-year-old Michelle Henderson was scheduled to appear in Yellowstone County Justice Court Wednesday on one count of tampering with public records or information. Henderson worked in a lab with two other chemists, who separated testing duties.

A supervisor determined the chemist was conducting tests properly. Henderson was captured on surveillance video contaminating a fellow chemist’s samples with an unknown substance.