CONCORD, N.H. – Day one of what is expected to be a marathon pollution trial over the gasoline additive MTBE ended Monday with lawyers for New Hampshire and two big oil companies heatedly accusing each other of misleading jurors.

The judge denied demands for a mistrial made by Citgo’s lawyer, Nathan Eimer.

The state is seeking more than $700 million from Citgo and ExxonMobil to cover the cost of monitoring and treating MTBE-contaminated wells.

Lawyers for the state argue that the MTBE gasoline is a defective product and that oil companies failed to warn the state of its potential for groundwater contamination.

After jurors were dismissed for the day, Eimer accused the state’s lawyer, Jessica Grant, of using what he described as a fabricated document in arguing that Citgo knew the groundwater contamination potential of MTBE.

Grant countered that the opening statement by ExxonMobil attorney James Quinn was rife with falsehoods.

Merrimack Superior Court Judge Peter Fauver stressed to the lawyers that they were at the start of what is expected to be a four-month trial. He advised them to come up with something “that’s not too inflammatory or accusative” when preparing their written suggestions of what he should tell jurors.

Grant told jurors the state will base its case largely on the oil companies’ own documents detailing how MTBE contamination is more widespread and costly to clean up than gasoline without MTBE.

Quinn said that MTBE came into use in the 1970s, when the federal government ordered oil companies to remove the lead from gasoline.

“MTBE makes gas less dangerous,” Quinn said, noting that by some estimates it saved 2 million lives by replacing toxic pollutants.

Grant told jurors the state’s experts estimate more than 40,000 wells in the state are probably contaminated by MTBE.

Ten gallons of gasoline treated with MTBE could contaminate 62 million gallons of water — the amount in Echo Lake in Conway, Grant said.

Quinn described Grant’s account as “courtroom fiction.”

New Hampshire banned the use of MTBE – methyl tertiary butyl ether – in 2007.

The lawsuit, filed in 2003, is the only one brought by a state to reach trial on the issue of MTBE contamination.

Most other MTBE cases brought by municipalities, water districts or individual well owners have all been settled or dismissed, except one.