For the purposes of this chapter:
(a) “Local agency” means any of the following entities:
(1) A city, county, or city and county.
(2) A special district formed pursuant to general law or special act for the local performance of functions regarding onsite sewage treatment systems within limited boundaries.
(b) “Onsite sewage treatment systems” includes individual disposal systems, community collection and disposal systems, and alternative collection and disposal systems that use subsurface disposal.