The University of Texas will independently review a study that found no link between hydraulic fracturing and water contamination after learning the lead author is a paid board member of a company that uses the drilling method.

Charles “Chip” Groat, a professor of geologic sciences and associate director of the university’s Energy Institute, is also a board member of Plains Exploration and Production Co.

Plains, like many other companies, uses hydraulic fracturing to drill into impermeable layers of rock to extract natural gas and oil. Groat received from Plains more than $413,000 in cash and stock in 2011. Groat did not disclose his position with Plains to supervisors or in the study.

Critics of hydraulic fracturing, or fracking, believe it harms the environment. Industry leaders insist it is safe.