A Hampton Falls gas station is under investigation by the New Hampshire Department of Environmental Services after groundwater seeped into one of its gas tanks, causing some cars to break down after filling up.Penguin Gas in Hampton Falls has closed access to the contaminated tank as it works to empty and inspect it.State officials said it's a very unusual situation, but the gas station is being cooperative. DES officials said groundwater levels rose much higher than a number because of recent rain and snowmelt and leaked through a break on top of an underground holding tank."And what that caused was a phase separation of gasoline, where the water mixes with the ethanol," said Jim Martin, of DES. "That's in our gasoline, and it goes down to the bottom of the tank." When too much water is mixed in, the mixture can get pumped into a vehicle's gas tank.>> Download the free WMUR app to get updates on the go: Apple | Google Play <<Water in an engine can be very problematic for vehicles. Police said at least five cars broke down miles after driving away from Penguin Gas. Tim Cassidy said he took his car to a mechanic who found water in the tank, and he's concerned about what that will mean in the long term."They got to it immediately," he said. "They had to take the gas tank out of the car, wash the lines, replace the spark plugs. So, my concern is, if any long-term damage here has been done to the cars, and it doesn't have that many miles on it, so that would not make me very happy, if that were the case."Managers of the gas station declined to comment.DES officials said anyone whose car was affected should speak with the gas station. They said anyone who runs into problems can call the Consumer Protection Bureau of the attorney general's office.