Septic Systems on Small Lots Fact Sheet
This guidance document is advisory in nature but is binding on an agency until amended by such agency. A guidance document does not include internal procedural documents that only affect the internal operations of the agency and does not impose additional requirements or penalties on regulated parties or include confidential information or rules and regulations made in accordance with the Administrative Procedure Act. If you believe that this guidance document imposes additional requirements or penalties on regulated parties, you may request a review of the document.

Form #: 12-038 Guidance Documents Revised: 9/19/22

Title 124 - Onsite Wastewater Treatment Systems requires that an onsite wastewater treatment system installed on or after the effective date of the regulations must meet all applicable requirements. In addition, an existing onsite wastewater treatment system becomes subject to the design requirements of Title 124 if:
  • It endangers public health, fails, or discharges a prohibited or unauthorized discharge,
  • It is being replaced, reconstructed, altered or modified,
  • There is an adverse change in use such as an increase in the number of bedrooms, design flow or waste strength,
  • It begins to receive wastewater from a different dwelling or non-dwelling facility than it was originally constructed to serve,
  • It begins to receive wastewater from a dwelling or non-dwelling facility that is reconstructed or replaced following an event such as fire that renders the structure unsuitable for occupancy, or
  • The system owner creates or causes an encroachment on a setback distance identified in Chapter 25 of Title 124 by a change in a property line or construction of a new development feature such as a well, water line or foundation.

Consequently, if your septic system fails, or it is being replaced, reconstructed, altered, or modified, it is subject to all requirements of Title 124 including setback distances from the septic tank and soil absorption system or a lagoon to such items as surface water, water wells, water lines, property lines and foundations.

If your septic system fails and there is not enough room on your property to meet all of the setbacks, there are a number of options that may be available to you including:

  • Connecting to a public sewer, if available,
  • Obtaining an easement and constructing a new onsite wastewater treatment system on another parcel of property,
  • Connecting to the neighbor’s septic system (the combined system must meet all current requirements, including an easement),
  • Abandoning or moving the well that is causing the setback infringement to occur, or

There are no minimum lot size requirements in Title 124 for the installation of an onsite wastewater treatment system. It may be difficult, however, to site a standard septic system on a lot that is smaller than one-half (½) acre due to soils, setbacks, and other site conditions. In addition, some local jurisdictions may have requirements that include lot size limits or more restrictive requirements. Regardless of lot size, all septic systems must meet specific standards with respect to system design and setbacks to surface water, drinking water wells, water lines, property lines and foundations.