Hawai'i’s volcanic landscape channels water, and millions of gallons of wastewater from coastal cesspools, quickly through networks of cracks and lava tubes directly into the ocean. Untreated sewage that reaches the coast is rich in nitrogen and phosphorus, which can harm coral reefs by fueling fast-growing algae that blocks sunlight from reaching the corals. There are risks to human health too, as untreated wastewater can contaminate drinking water with harmful bacteria and viruses, such methicillin-resistant Staphylococcus aureus (MRSA). To better understand this risk, Pacific Islands CASC supported researchers are evaluating water pollution from cesspools in Kahalu'u Bay, on the western coast of Hawai'i Island. They are studying how sea-level rise might impact sewer infrastructure, cesspools, and water quality by conducting field surveys, collecting samples, performing dye tracer tests, and analyzing sea-level rise projections. 

In August 2024, the researchers conducted a dye test that traced wastewater from a coastal cesspool to Kahalu'u Bay in just six hours, which doesn’t allow enough time for the wastewater to be diluted or to break down naturally. Initiated through Pacific Islands CASC’s Manager Climate Corps (MCC) program, this research is a response to community members voicing concerns about the cesspools. The project aims to improve adaptation planning and investments for coastal wastewater infrastructure across the state of Hawai'i. 

This work is supported by the Pacific Islands CASC Project “Predicting Sea Level Rise Impacts to Coastal Wastewater Infrastructure and Water Quality for Adaptive Planning and Coastal Habitat Resilience."