In Guam, the use of onsite wastewater disposal systems (commonly referred to as ”septic systems”) is regulated through a number of laws and regulations. The Guam Environmental Protection Agency (GEPA) Administers the Toilet Facilities and Sewage Disposal Act (10 GCA Chapter 48), and its two implementing regulations: the Individual Wastewater Disposal System Regulations (22 GAR Chapter 12) and the Connection to Public Sewer Regulations (22 GAR Chapter 25). This law and its regulations cover the specific requirements for the permitting, design and construction of septic systems in Guam. In addition, lot size and sewer connection requirements are also incorporated into Guam’s Water Quality Standards (22 GAR Chapter 5), the Zoning Law (21 GCA Chapter 61) and the Subdivision Law (21 GCA Chapter 62). The questions and answers below are meant to step you through the application of these various requirements to the design, permitting, and construction of a septic system for a single family dwelling.
Additional Resources & Information
General Septic System Information
The US Environmental Protection Agency has excellent septic system resources.
The USEPA’s Frequently Asked Questions is a good start: https://www.epa.gov/septic/frequent-questions-septic-systems
Design Guidance
The USEPA design manuals offer a more in-depth look, and do not replace GEPA’s regulations, but can be used to supplement and provide excellent advice for designers on issues such as construction precautions, the most effective geometry for septic tanks, and other information:
1980 manual:
https://www.epa.gov/sites/default/files/2015-06/documents/septic_1980_osdm_all.pdf
2002 manual update:
https://cfpub.epa.gov/si/si_public_record_Report.cfm?Lab=NRMRL&dirEntryID=55133
Soils Information
The USDA’s Natural Resources Conservation Service maintains the official soil survey maps for Guam. The soil survey can provide a good first look at the soil conditions that might be on any particular lot, but site-specific investigation is still required because soils typically vary even within small distances.
NRCS Web Soil Survey main page (includes links to guides on how to use the information on the soils survey):
https://www.nrcs.usda.gov/resources/data-and-reports/web-soil-survey
The University of Guam hosts a pdf copy of the original print edition, which may not be the most up-to-date in terms of latest revisions to the map, but some users may find it easier to use than the online soil survey:
https://www.uog.edu/_resources/files/wptrc/guam.pdf
Percolation Testing
Wetlands
The official wetland map for Guam is the US Fish and Wildlife Service National Wetland Inventory Map, per Executive Order 90-13, included as Appendix B of the Guam Water Quality Standards 22 GAR Chapter 5. The USFWS NWI online mapping tool can be accessed here:
https://fwsprimary.wim.usgs.gov/wetlands/apps/wetlands-mapper/
On-site wetland determinations performed by a GEPA professional are still required if work will be performed near a wetland, but this site provides useful information for planning because of the 300 foot setback required between a septic system and a wetland.
Waters of the Territory
Flood Zones
You can view the latest Flood Hazard Areas designated for Guam on the Federal Emergency Management Agency’s (FEMA’s) Flood Rate Insurance Map (FIRM) viewer here: https://msc.fema.gov/nfhl
Northern Guam Lens Aquifer
The official aquifer map, for the purpose of interpreting GEPA laws and regulations, is the 1997 Department of Land Management Groundwater Protection Zone (GPZ) Overlay. A scanned copy of the official map can be downloaded here:
Add link to GPZ Map
You can also view the GPZ in GEPA’s interactive map service, which allows you to see the GPZ boundaries in relation to other features to help pinpoint the location you are looking for. The GEPA Interactive Map also allows you to view flood plains, wetlands, and other Waters of the Territory:
Under Construction
The University of Guam, Water and Environment Research Institute (WERI) also maintains a detailed map of the Northern Guam Lens Aquifer, which is the best reference available for determining groundwater flow direction, aquifer thickness, and a host of additional hydrologic data. However please note that the GPZ map is the “official” map of the aquifer, to be used when determining compliance with requirements of GEPA laws and regulations related to the “aquifer”.