Researchers find sewage from an oceanfront Big Island community reaches nearshore waters
There are nearly 50,000 cesspools on the Big Island, with tens of thousands posing a risk to water resources, according to the Hawaiʻi Department of Health.
Along a 2.5-mile stretch of road on the South Kohala Coast, there's a small community called Puakō in the midst of figuring out how to deal with their sewage. Half the homes are built right up against the shoreline.
Puakō started as a small fishing village built on the basalt rock of an old lava flow. Several underground springs feed the brackish ponds in the area and flow underground to rise up in the ocean.
The village grew into a small shipping port after the arrival of sugar plantations in the late 1800s. But it wasn't until the 1950s that the original 163 house lots were developed.
Around the early 90s, the demand for beachfront property skyrocketed and old shacks were replaced with luxury homes. With the change came increased concern from residents on how their wastewater was impacting the shoreline ecosystem.
"We've all noticed that the reef is changing. We used to see more fish and I've noticed more algae. And I'm in the water surfing and snorkeling almost every day," said Puakō Community Association President Mike O’Toole. He and his family have lived in the community for nearly 30 years.
Using dye, University of Hawaiʻi at Hilo researchers have tracked where sewage travels once it enters a cesspool or septic tank.
"Almost every time we found where the dye came out at the shoreline, it's typically one or two springs right at the shoreline where the sewage from a home was coming out," said UH Hilo researcher Steven Colbert.
"Some homes, when sewage would go into the cesspool at high tide, it would come out at the shoreline at low tide. So about six hours later, it was that fast for the sewage to reach the shoreline," Colbert said.
For homes a bit further and higher from the shore, the flow to the shoreline could take up to 10 days, he said.
"We also looked at the differences in the water quality between cesspools and septic tanks. There was no difference in how fast the water took to reach the shoreline from those different sources. And the water quality at those different points was similar," he said.
"Back in 2014, the community asked us to determine if there was sewage present in their nearshore waters. And from that work, we found out that there was," said researcher Tracey Wiegner. "What we found, and they all agreed, was that the main place that the wastewater was entering into the water table was at the Puakō community."
The UH Hilo study concluded that an onsite sewage treatment plant is the best solution for Puakō.
"Septic tanks don't work as well in this environment because there's no soil. It's just very fractured basalt rock that the water just pours through so easily to contaminate the groundwater and then our shoreline," Colbert added.
Colbert said the state of Hawaiʻi and the county have invested in plans for a sewage treatment plant in the area.
"We know that the state gave the county some money and that they're working on matching funds to move this forward," O’Toole said. "If it were done and completed, we had a wastewater system here in 10 years, I'd be happy. But we just can't give up."
In 2015, Hawaiʻi banned the construction of new cesspools — the last state to do so following Rhode Island's ban in 1968. In 2017, Hawaiʻi passed legislation to replace all cesspools by 2050.