Hawaii & Alaska
Trista McKenzie et al., 2021

HI - Sea-level rise drives wastewater leakage to coastal waters

When people think of sea level rise, they usually think of coastal erosion. However, recent computer modeling studies indicate that coastal wastewater infrastructure, which includes sewer lines and cesspools, is likely to flood with groundwater as sea-level rises.

A new study, published by University of Hawai'i (UH) at Manoa earth scientists, is the first to provide direct evidence that tidally-driven groundwater inundation of wastewater infrastructure is occurring today in urban Honolulu, Hawai'i. The study shows that higher ocean water levels are leading to wastewater entering storm drains and the coastal ocean -- creating negative impacts to coastal water quality and ecological health.

The study was led by postdoctoral researcher Trista McKenzie and co-authored by UH Sea Grant coastal geologist Shellie Habel and Henrietta Dulai, advisor and associate professor in the UH Manoa School of Ocean and Earth Science and Technology (SOEST). The team assessed coastal ocean water and storm drain water in low-lying areas during spring tides, which serve as an approximation of future sea levels.

To understand the connection between wastewater infrastructure, groundwater and the coastal ocean, the researchers used chemical tracers to detect groundwater discharge and wastewater present at each site. Radon is a naturally occurring gas that reliably indicates the presence of groundwater, while wastewater can be detected by measuring specific organic contaminants from human sources, such as caffeine and certain antibiotics.

"Our results confirm that indeed, both groundwater inundation and wastewater discharge to the coast and storm drains are occurring today and that it is tidally-influenced," said McKenzie. "While the results were predicted, I was surprised how prevalent the evidence for these processes and the scale of it."

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Read also Sea‐level rise drives wastewater leakage to coastal waters and storm drains, Trista McKenzie et al., Feb. 25, 2021

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