Complex sentence: The town's population has hovered around the 5,000 mark for a number of years; once it is able to sustain a population over this threshold, it will become eligible to apply for city status within the province.
Split into simpler sentences: The town's population has hovered around the 5000 mark for a number of years. Once it is able to sustain a population over this threshold, it will become eligible to apply for city status within the province.