AUSTIN — Democratic gubernatorial nominee Bill White earned more than $2.6 million serving on the board of a gas well servicing company that now is part of a congressional investigation into possible groundwater contamination.

White, who made cleaning Houston's polluted air a hallmark of his tenure as Houston's mayor, has been on the board of BJ Services Co. since 2003, the year he was elected, earning more than $627,000.

White also received almost $830,000 in stock and another $245,000 in stock options. He will receive an additional $180,000 in stock and a retirement payout of $783,000 if the firm's merger with Baker Hughes is approved by shareholders Friday.

The issue of White's involvement with BJ Services came to light after he refused a Houston Chronicle request for his tax returns during his tenure as mayor. The relationship was disclosed in personal financial disclosure statements. White's campaign provided details on his BJ Services earnings Tuesday.

The U.S. House Energy and Commerce Committee is investigating Houston-based BJ Services Co., Halliburton and several other oil field service companies to see if the gas extraction method known as hydraulic fracturing, or fracking, is a hazard to groundwater drinking supplies in Texas, Arkansas, Colorado, New York, Oklahoma and Pennsylvania.