Within the aquifer (as defined by the GPZ), the only building types that may be served with a septic system are single family dwellings and duplexes, based on the combined requirements of the Guam Water Quality Standards (22 GAR Chapter 5) and the Individual Wastewater Disposal System Regulations (22 Gar Chapter 12).
Outside the aquifer, other building types may be served with septic systems, but in no case may anything other than “domestic wastewater” be disposed of on-site.  Domestic wastewater refers to wastes coming only domestic-type sources such as toilets and sinks.  Guam’s Water Quality Standards effectively prevent the disposal of wastewaters generated by industrial or other commercial uses, all of which could reasonably be expected to exceed groundwater quality criteria for land disposal, which are based on drinking water standards, even outside the aquifer.
In addition, the Guam Regulations provide design criteria only for septic tanks associated with single family dwellings, duplexes, and apartments up to a maximum of four units.  The design of onsite wastewater disposal systems any other type of building must be based on engineering methods approved by GEPA on a case-by-case basis, and effluent from such systems must meet Guam Water Quality Standards criteria.