The difference between staying consistently or generally below emissions targets could save taxpayers “millions” of dollars on the North End sewage plant upgrade, according to the city’s finance chairperson. On Thursday, Coun. Scott Gillingham told reporters that’s why the city is lobbying the province to adjust its rules and let treated wastewater from the North End plant meet maximum ammonia limits on a “rolling average,” rather than the current rule, which is to “never exceed” the stipulated limit. Gillingham said during Thursday’s finance committee the city’s chief administrative…