In the case of a public water system which serves a population of not more than 3,300 persons and which needs financial assistance for the necessary improvements, an exemption granted under § 142.50(b) (1) or (2) may be renewed for one or more additional 2-year periods, but not to exceed a total of 6 additional years, if the public water system establishes that the public water system is taking all practicable steps to meet the requirements of section 1416(b)(2)(B) of the Act and the established compliance schedule.