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Resident warns council of groundwater, shows test-hole readings after 30-by-30-foot landslide
Summary
Longtime Preston resident Thane Corbridge presented photos and test-hole data to the council, described a 30-by-30-foot landslide on his property in September 2023, and said groundwater in test holes rose from 5 inches to 20 inches. He urged attention to surface and subsurface drainage as nearby development proceeds.
Thane Corbridge told the council he has lived on the family farm for decades and that groundwater in the area has long been high; he said a 30-by-30-foot landslide occurred along his east fence in September 2023. Corbridge showed a packet of photos and a map and described test holes he drilled: at one monitoring hole he said he found "5 inches of water" initially and "20 inches of water" a few days later, which he said was sufficient to trigger the slide.
Corbridge said city-installed surface drains appeared properly installed but that grades and grate placements do not always match the lowest field points, which may be forcing more water into the subsurface. He told the council he had talked with "someone" who contacted DEQ and was told groundwater responsibility rests with local municipalities; Corbridge said he had no written follow-up from DEQ to present. Council members and staff asked clarifying questions about grate locations, whether irrigation practice or overwatering could contribute, and whether a deeper or differently configured retention/pipe system could mitigate the risk. Staff and council thanked Corbridge and indicated they would keep the neighborhood informed as the related subdivision/planning items proceed.
