The powers granted and procedures prescribed by §§ 6-3-1 to 6-3-7, inclusive, shall be in addition to and not in derogation of any other powers conferred by law upon any of the participating subdivisions to make agreements, to appropriate and expend money, and to issue bonds for the same or similar purposes, or any other methods prescribed by law for the accomplishment of such purposes, and no existing law shall be deemed to be repealed hereby.
SDCL 6-3-8