New oil and gas drilling is probably the most visible activity people associate with threats to groundwater in Texas. But it's not usually the source of known contamination, according to state records.

Instead, old or abandoned oil and gas wells, petroleum storage facilities and even existing water wells are most frequently identified as problems.

A Texas Groundwater Protection Committee report, presented to the Legislature last year, said there were 4,729 active groundwater contamination cases documented or under enforcement in 2008. Of those, 395, or 8.4 percent, were "attributed to oil and gas exploration and production activities," but "no producing oil and gas wells" were listed as groundwater-contamination sources, Texas Railroad Commission spokeswoman Ramona Nye said. The state has more than 281,000 oil and gas wells, Nye said.

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