Iron County approves tier and zoning changes after septic-density study

The Iron County Commission on Monday approved a pair of amendments to the county general plan and matching zoning changes that shrink urbanizing “tier 3” areas around Summit and Newcastle and rezones surrounding parcels to reduce future septic density.

The move implements recommendations from a 2023 septic-density study and later reviews by county staff and the planning commission; commissioners voted to approve both the tier changes and corresponding zone-map revisions after a public hearing and planning commission recommendation.

County staff said the changes respond to groundwater nitrate sampling and a mass-balance analysis that identified the number of septic systems an area can sustain before modeled nitrate concentrations rise by about 1 milligram per liter above local baseline. The planning presentation explained that some study sites already have higher baseline nitrate levels and that the county set development limits in order to avoid further groundwater degradation.

The adopted changes reduce the geographic extent of tier 3 around Summit and remove commercial zoning in parts of Newcastle’s north side, replacing higher-density residential categories (R-1-Half) with larger-lot categories (R-5) and creating RA-20 buffers in places where the county wants to discourage intensive agricultural or industrial uses next to residential areas. The county also clarified code text to better handle leasing of multiple spaces on a single parcel and streamlined soil-suitability requirements for subdivisions that do not propose public improvements.

County staff and commissioners said the tiering and zoning changes are intended to protect aquifers while keeping a path open for future central sewer systems. Officials noted that central sewer or pretreatment systems can allow higher densities safely; for example, a pretreatment system that lowers nitrate loading by roughly half could permit smaller lot sizes under the county’s mass-balance framework. Commissioners and staff also said the long-term solution is coordinated sewer infrastructure and that the county is continuing work with municipalities and the Central Iron County Water Conservancy District on regional water and sewer planning.

At a public hearing, a member of the public asked where the underlying data and reports could be found; staff pointed attendees to the Utah Geological Survey website, which posts the detailed study reports and supporting data used in the county analysis.

The commission approved the tier-change general plan amendment and the related zone-map amendments in separate votes during the meeting. Planning staff said the changes follow yearslong work to update the tiering system and to apply recent technical data to areas that had zoning established decades earlier.

The county’s next step will be to continue similar reviews in additional growth areas, including a forthcoming review of Brian Head’s tier-2 boundaries and later items for Cedar City and Enoch.