CONCORD, N.H. – New Hampshire shouldn’t have had to trade water quality for cleaner air, a former state official told a jury in a trial over whether ExxonMobil contaminated the state’s groundwater with a gasoline additive.

Kent Colburn, former director of the air resources division of New Hampshire’s Department of Environmental Services, testified Monday in state court in Concord that it wouldn’t have participated in a federal clean-air program called Reformulated Gasoline, or RFG, if Exxon had warned of the risks of the additive, methyl tertiary butyl ether, or MTBE. The trial began Jan. 14.

“DES was not in the business of transferring pollution from one medium to another,” said Colburn, who served from 1995 to 2002. Although the RFG program “created numerous health benefits,” MTBE wasn’t the reason for the air quality improvement, he said. Former DES commissioner Robert Varney testified last week that he was “shocked” to learn Exxon was aware of MTBE’s risks before adding it to gasoline sold in the state.

New Hampshire could be seeking more than $200 million from ExxonMobil, the last defendant on trial in the $816 million lawsuit filed in 2003. This is one of scores of cases involving MTBE filed since 2000 against refiners, fuel distributors and chemical makers.

Robert Larkins, a former vice president of marketing for Exxon in the 1980s, said in taped testimony played in court last week that he approved the use of MTBE despite a colleague’s recommendation in a mid-1980s memo against using it because of its risk to groundwater. The colleague had been asked by ExxonMobil to conduct a study of MTBE.

“She did not say that you cannot or should not put it in there,” Larkins said, referring to the memo. “She said there were some concerns and she recommended against it.”

ExxonMobil has argued that it was complying with federal regulations that pre-empt state law. They said MTBE was added to gasoline to make it burn more thoroughly and thus reduce air pollution, as required under the 1990 Clean Air Act.

James Quinn, a lawyer for the company, said the state was aware of the risks of MTBE when it opted into the RFG program in 1991 because there had been documents and data about the additive for several years. New Hampshire decided to re-enter the clean-air program in 1997.

Cross-examining Colburn, Quinn referred to a report from Maine that Colburn received in 1995 that said MTBE had been detected in groundwater for more than 10 years and that “increased surveillance” of the chemical in water was required. Maine was petitioning the Environmental Protection Agency to get out of the RFG program in 1999.

New Hampshire has said that about 40,000 wells are contaminated with MTBE, including about 5,590 at levels determined to be unfit for drinking.

The number of contaminated wells is a factor in deciding monetary damages if ExxonMobil is found liable. The state is also seeking damages based on market share of gasoline sales in New Hampshire during the period covered by the lawsuit.