City hears GeoPacific findings: Hemlock Street built on deep landslide mass, engineers urge fast action

GeoPacific Engineering told the Wheeler City Council on July 15 that Hemlock Street sits atop a deep, prehistoric landslide and recommended immediate, targeted work to reduce groundwater and slow movement.

The firm’s engineering geologist, Beth Rapp, said borings and monitoring show landslide debris extending roughly 35 to 45 feet below the roadway, with about "7 or 8 feet of roadway fill" above that material. Geotechnical engineer Ben Anderson said the firm believes movement is likely to continue “unless something is done to improve the conditions out there,” and that lowering groundwater in the slide mass would help.

The council heard that GeoPacific drilled two borings to 50 feet this winter and installed inclinometer pipes to measure slope movement. Readings taken in November, February and April showed measurable movement down in the deeper landslide debris — a pattern the consultants said is consistent with groundwater-driven slope…