Thurston County planning staff used a work session to brief the Planning Commission on geologically hazardous areas and related implementation issues for the county's Critical Areas Ordinance (CAO) update, focusing on life-safety risks, ecological functions and how new mapping tools may make permitting clearer for applicants.

A county presenter said critical aquifer recharge areas cover substantial portions of the county and that most of the roughly 24,000 private wells in the county pump from those recharge zones, making the areas central to both water supply and CAO considerations. "In other words, they are crucial to our primary water supply," the presenter said, noting overlapping protections and the risk that streamflows are declining because groundwater that once fed streams has been increasingly tapped.

The presenter referenced the Tri Lakes groundwater study (completed two to three years earlier), saying it showed significant groundwater contamination in some North County areas and that septic systems likely account for a large share of those contamination detections (staff estimated roughly 60270 percent in parts of North County). The presenter added that the human-health implications of many detected consumer chemicals remain poorly evaluated.

Commissioners pressed staff on mitigation and authority: staff said many contamination and design details are addressed through the stormwater manual and the health department rather than through the planning code, although the CAO can restrict certain land uses in sensitive recharge areas. Staff also warned that, as connections to public water become harder, there could be a rise in permit-exempt wells and that mitigation for new uses is increasingly difficult for water providers to secure.

On geologic hazards, staff reviewed hazard categories (landslide, erosion, marine bluff, seismic, volcanic and mine hazards) and recommended using new DNR lidar-based landslide maps and other high-resolution data to distinguish true landslide hazards from adjacent terrain. Staff described implementation tools the county could expand, including requiring geologic hazard acknowledgments to appear on property records for some hazards and more clearly defining what level of geotechnical investigation is needed at the permitting counter.

Natalie, a planning staff reviewer, told the commission that applicants do not need to submit a geotechnical report to file a critical area review permit; the planner will indicate whether a report is required and existing tools cannot always specify the length or level of detail such a report should include. Mark Beaver, the county's geotechnical engineer, reviews reports that are submitted and staff said that increased transparency about report expectations is a priority to reduce applicant uncertainty.

Commissioners also discussed the difficulty of balancing tree protection and wildfire mitigation, the prospects for using upper-basin forest management to increase streamflow, and the trade-offs inherent in requiring increasingly detailed site studies. Staff said future meetings will bring DNR to present landslide mapping and additional implementation guidance.

What happens next: the commission will continue the CAO update at future work sessions, including a scheduled presentation from Washington DNR on high-resolution landslide maps and a January follow-up on critical aquifer recharge concepts.