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Is my lot size large enough to permit a septic system?

Is my lot size large enough to permit a septic system?

  • The answer to this question depends on whether your property is located within the Groundwater Protection Zone (“GPZ”), or outside the GPZ.  See the section above titled “Is my property located above the aquifer?” for information on how to make this determination.
  • Minimum lot size over the aquifer (within the GPZ):  19,200 square feet (1,784 square meters). Per the Zoning Law at 21 GCA §61501(c), lot sizes above the aquifer are established by the Guam Environmental Protection Agency (GEPA).  The Guam Water Quality Standards at 22 GAR §5101(c)(1)(B) requires that “high-density residential development, more than one (1) dwelling per one-half (1/2) acre, should not occur without adequate public sewer service.”  GEPA implemented this requirement through the establishment of minimum lot sizes, based on the existing requirements of the Zoning and Subdivision Laws.  Within the aquifer, as mapped by the Department of Land Management in 1997 in their Groundwater Protection Zone (GPZ) Overlay, the minimum residential lot size on which a septic system may be constructed (for a single dwelling unit) is 19,200 square feet (1,784 square meters), or approximately one-half acre, based on 21 GCA §61501(a). See GEPA minimum lot size determination Memoranda here:  1997 & 2009
  • GEPA’s prior determinations for minimum lot sizes over the aquifer included an allowance for a smaller size of 9,600 square feet (892 square meters) for lots subdivided under the Zoning Law’s “Parental Division of Property” clause at 21 GCA §62140(b).  This exception to the half-acre requirement of the Guam Water Quality Standards is currently under legal review.
  • Minimum lot sizes outside the aquifer (outside the GPZ): 10,000 square feet (929 square meters).  Outside the aquifer, as mapped by the Department of Land Management in 1997 in their Groundwater Protection Zone (GPZ) Overlay, the minimum residential lot size on which a septic system may be constructed (for a single dwelling unit) is determined by Guam’s Zoning and Subdivision Laws, but generally speaking is not less than 10,000 square feet (929 square meters), based on 21 GCA §61501(a) and 21 GCA §62105(a).  See GEPA minimum lot size determination Memoranda here:  1997 & 2009
  • As with the lot sizes inside the aquifer, GEPA’s prior listing of minimum lot sizes outside the aquifer included an allowance for a smaller size of 9,600 square feet (892 square meters) for lots subdivided under the Zoning Law’s “Parental Division of Property” clause at 21 GCA §62140(b).

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