Sec. 8.5. (a) As used in this section, "lot" means the parcel of real property on which:
(1) a one (1) family or two (2) family dwelling; or
(2) two (2) single family dwellings located on the same property with a combined design daily flow of not more than seven hundred fifty (750) gallons per day;
have been constructed or are proposed for construction.
(b) A residential onsite sewage system may be installed in a lot described in subsection (a) if at least one (1) site on the lot is determined to be suitable for the installation of the residential onsite sewage system.