Public works: Sienna Hills chip‑seal issues traced to material and application; city to increase sweeping and consider fog coat

Caldwell — City Public Works staff addressed resident complaints about loose rock after a 2024 chip‑seal operation in Sienna Hills and surrounding streets. Staff told council an analysis found two contributing problems: a lower quantity of asphalt emulsion applied during the operation and a batch of aggregate that lacked the fracture characteristics necessary to embed consistently.

Public Works Director Bruce Mills told council that crews have stepped up sweeping and removal of loose rock and that most loose aggregate has already been collected. Mills said the city has changed materials and application practices for 2025, and he reported improved performance on streets treated this year. He offered two corrective options: a focused fog‑coat on the Sienna Hills area (estimated roughly $80,000–$90,000) or fog‑coating the entire chip‑seal area (an estimate around $440,000). Mills cautioned that these are corrective, backward‑looking expenditures and recommended aggressive sweeping and improved specifications for future chip sealing instead of a full retrofit unless council directs otherwise.

Councilors asked whether the city’s chip‑seal schedule had applied the treatment to relatively new streets; Mills said the city is adjusting its approach and will avoid treating very young neighborhood streets and will space chip‑seal applications to get longer life. Staff committed to continue sweeping in affected neighborhoods and to provide a follow‑up if council requests additional corrective work.