A Maryland judge is considering whether to grant class-action status to a lawsuit stemming from a leak at an Exxon gas station that contaminated the wells of about 150 families and businesses. In a hearing Monday, attorneys for the plaintiffs argued that the suit should be treated as a class action because the gas station was the major source of the contamination and because the leak affected an aquifer common to all plaintiffs. Earlier this month, a Maryland jury awarded $150 million to residents affected by a separate gasoline leak.