Springdale planners weigh requiring slope‑stability assessments in geotechnical reports

The Springdale Planning Commission discussed May 7 draft ordinance language that would require slope‑stability assessments be added to the town’s required geotechnical reports when excavations are close to neighbors.

Planning staff said the town engineer recommended the assessment be required when the horizontal distance from an excavation edge to a property line is less than twice the excavation depth — for example, a 5‑foot excavation within 10 feet of a property line would trigger the analysis. "The engineer recommended that a slope stability assessment should be required in situations where the horizontal distance from the edge of an excavation to a property line is less than twice the depth of the excavation," Nile Connolly, a staff member, told the commission.

Why it matters: Commissioners said the change is intended to reduce the risk that deep residential excavations — notably for swimming pools and "infinity" pools — undermine neighbor properties or create public‑safety hazards. Commissioners pressed staff on whether the draft language would actually bind mitigation and who would judge whether mitigation was adequate.

Commission discussion and substance

Commissioners and staff focused on three linked issues: (1) the triggering metric for a required slope assessment (horizontal distance less than twice excavation depth); (2) how the assessment’s mitigation recommendations would be enforced; and (3) whether the policy should explicitly cover other sensitive areas such as 30% slopes, riverbanks and dry washes.

Staff said geotechnical reports are already required for most new buildings and that the slope‑stability item could be added as an element of those reports. "The place where we think the slope stability assessment would fit would be within the geotechnical report, which the town already requires for new buildings," Nile Connolly said. Staff also acknowledged swimming pools sometimes do not require a full geotechnical report under current code and recommended adding language to close that gap.

Several commissioners asked what happens if a geotechnical assessment finds an impact that cannot be mitigated. One commissioner asked, "Who says that those mitigation efforts are adequate?" and cautioned that a report that merely "includes recommendations to mitigate these impacts" does not guarantee implementation. Connolly answered that geotechnical reports are prepared and stamped by licensed geotechnical engineers and flagged that staff typically review routine reports while the town engineer reviews complex cases. He proposed adding process language to send these reports to the town engineer in high‑risk cases and adding a clear requirement that necessary mitigation must be implemented.

Scope and related hazards

Commissioners discussed whether the draft should be broadened to address steep natural slopes (commonly called 30% slopes), riverbanks and dry washes. Staff and commissioners agreed the erosion hazard overlay zone and the town’s River Management Plan already address many riverbank and high‑slope concerns, but they recommended staff consult the town engineer and consider a separate paragraph in the ordinance for cliffs/mesas and steep slopes. Staff also noted that, by policy, 30% slopes are typically protected from disturbance; where disturbance is allowed, geologic hazards (landslide, rockfall) are already considered in geotechnical reports.

Next steps

The commission asked staff to revise the draft to: add explicit language that required mitigation must be implemented where necessary; clarify that developments such as swimming pools that currently fall outside geotechnical reporting will be captured when they meet the excavation trigger; and consult with the town engineer about whether and how to add a separate statement addressing 30% slopes, riverbanks, mesas and dry washes. No formal vote or ordinance adoption occurred; this agenda item was non‑action and will return to the commission after staff revisions and the town engineer’s input.

Ending note

Commissioners agreed the draft was a reasonable first step but asked staff to return with clarified, enforceable wording and a recommendation on handling 30% slopes and riverbank/dry‑wash edges.