The Administrator shall make grants to States to provide assistance to municipalities with a population of five thousand or less, or counties with a population of ten thousand or less or less than twenty persons per square mile and not within a metropolitan area, for solid waste management facilities (including equipment) necessary to meet the requirements of section 6945 of this title or restrictions on open burning or other requirements arising under the Clean Air Act [42 U.S.C. 7401 et seq.] or the Federal Water Pollution Control Act [33 U.S.C. 1251 et seq.]. Such assistance shall only be available—