When a collective bargaining contract is ambiguous, arbitrators can rely on an unequivocal past practice to find that the operative date is an employee's date of hire, as opposed to the collective bargaining contract's "effective date." In 2010, Town of Manchester workers requested that their names be removed from the "on call" list of employees who respond to emergencies after normal work hours. Each of the employees worked as a wastewater treatment plant operator or maintainer. The municipality denied the requests, and the union filed a grievance. The pertinent collective bargaining contract, which the union claimed was effective as of July 1, 2006, provides, "The Union agrees that at least four (4) Wastewater Treatment Plant Operators/Maintainers shall serve on a rotating basis as the weekly on-call person at all times outside of the regular working hours for the Wastewater Treatment Plant Group." The union maintained that because the employees were hired prior to the effective date of the collective bargaining contract, they were exempt. The town objected that each of the employees participated in the "on call" work assignments, without protest, for approximately 10 years, and that the operative date was the date of hire. Arbitrators found that the collective bargaining contract was ambiguous. The "past practice," wrote arbitrators, "was unequivocal and ascertainable over a reasonable period of time as a certain, fixed and established practice." For approximately a decade, workers who were hired after July 1, 1998 were required to participate in "on-call" work assignments, after normal work hours, as if the operative date was the date of hire. Each of the employees was hired after July 1, 1998. If arbitrators agreed with the union's claim, there would be insufficient operators or maintainers to respond to "after hours" emergencies, and essential wastewater treatment services might not be performed. Arbitrators denied the union's grievance. Saranne Murray represented the municipality. Wayne Marshall represented the union.