KHON2: Dye study raises questions about wastewater reaching Shark’s Cove tide pools

PUPUKEA, Oahu (KHON2) — A new dye study at one of Oahu’s most popular North Shore swimming spots is revealing a potential connection between the public restrooms at Pupukea Beach Park and the waters below at Kapoo, or Sharks Cove, tide pools.

Malama Pupukea Waimea partnered with Wastewater Alternatives and Innovations, WAI, to determine whether wastewater from the park’s septic system could be seeping into the marine ecosystem below.

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Researchers placed a harmless fluorescent green dye into the plumbing system of the public restrooms and monitored the surrounding waters.

The dye began showing up in the tide pools within a few days.

Denise Antolini with Malama Pupukea Waimea said the study was designed to make something that normally happens underground visible.

“We specifically wanted to look at the septic system and see if there was leakage. So that’s what this current study is about, where Malama Pupukea Waimea partnered with WAI to put dye into the septic system at Pupukea Beach Park to see if we have a problem,” Antolini said.

The dye was placed into a bathroom sink over about nine to ten hours. Researchers said instruments began detecting it in the water roughly two days later, and by Saturday it was visible to the naked eye. 

Antolini said the strongest readings were found in areas where people enter the water.

“The hot spots that we detected where there’s the most amount of leakage are right below the lifeguard tower and right at the entry where most of the tourists go in right at the tide pools,” Antolini said. It’s definitely in areas where people are swimming and using the water, so it’s very concerning.”

Christina Comfort, WAI’s Water Quality Program Manager, said the dye was detected at relatively high concentrations near the rocks underneath the lifeguard stand.

“What we’re finding is that yes, we are seeing the dye in the tide pools, and we’re seeing it in pretty high concentrations right by the rocks, just under the lifeguard stand, under where the bathrooms are, and then we’re also seeing it in lower concentrations outside the walls of the tide pools as well.”

Researchers also detected lower-level readings farther out in the ocean.

Comfort said the wastewater flows from the restrooms into septic tanks before reaching a seepage pit, where wastewater can leach into the surrounding ground.

“That pit is basically leaching into the tide pools, and potentially it looks like it’s also leaching underneath the tide pools and out via groundwater flow out into the open ocean, so it is wastewater contaminated.”

The dye itself is not the concern

The researchers emphasize that the fluorescent dye used in the study is safe for people and the marine environment.

The concern is what else may be traveling through the same pathway.

Jenny Yagodich with Mālama Pūpūkea-Waimea said the dye study was only the first step.

“We did see dye in the water, and the instruments that are used to sense the dye also picked up readings. So yeah, now that it’s in there, it’s just going to become what’s next. So the next steps will be doing further testing for things like enterococcus and other bacteria to see if it’s just clean water getting through or if the water is contaminated or not. So phase by phase.”

That distinction is important: the dye study does not establish that the tide pools are contaminated with harmful bacteria or pathogens.

Routine water-quality testing is already conducted in the area.

Yagodich said the Surfrider Foundation’s Blue Water Task Force monitors the location twice a month, while the state Department of Health conducts monthly testing and issues public notifications when bacteria levels are elevated.

“Our study just picked up the dye, the color that came out, indicating that there is a connection between the two. But those studies actually pick up the bacteria, and so it hasn’t been terrible. There are days when it’s definitely – the health department has said brown water over here, but we’re not seeing that all the time.”

Comfort said the relatively short travel time of the dye is one reason researchers want to conduct additional testing.

“When we’re getting those fast travel times of only, in this case, a few days. What that means is there’s really not a lot of time for the microbes in, for instance, soil or in the ground to break down any pathogens or take up any nutrients. So you’re pretty much just getting raw wastewater that’s flowing right into the ocean.”

She said the septic system does provide some primary treatment by separating solids, but researchers want to determine what is ultimately reaching the marine environment.

The additional testing will look for bacteria such as E. coli and enterococcus, as well as nutrients that could affect marine life.

Antolini said sewage can be particularly concerning in a marine conservation district because excess nutrients can contribute to algae growth and affect the ecosystem.

“Sewage is not good for marine life, particularly not good for corals for a bunch of reasons. It can create kind of nuisance algae growth. You don’t get the right kind of limu growing in the area if you have an overload of nitrogen and phosphorus. And also the pathogens are a big concern as well.”

Researchers said wastewater seepage from septic systems and cesspools is an issue in many coastal areas across Hawaiʻi.

Comfort said WAI conducted a similar dye tracer study in May at Kealakekua Bay on Hawaiʻi Island. In that case, dye injected into a home’s cesspool reached the shoreline in about 24 hours.

“We found that the dye was reaching the shoreline in about 24 hours. So that was a really, really fast flow, and it diluted a lot in the groundwater on its way there. But it was flowing constantly out through the groundwater through the Punavi for about four days.”

Unlike a cesspool, the Pūpūkea Beach Park system includes a septic tank that separates some solids before wastewater reaches the seepage pit.

Still, researchers said the study demonstrates the need for more investigation.

Mālama Pūpūkea-Waimea said it has been working to protect the area’s marine ecosystem for more than two decades.

The group said it wants to work with the City and County of Honolulu’s Department of Parks and Recreation and the state on possible solutions, which could include additional treatment or filtration, improved monitoring or better communication about water conditions.

Antolini said the dye study was deliberately designed to make the potential pathway visible.

“We deliberately wanted it visible because that’s the best way for all of us to have a conversation and to see what’s happening in our oceans. And Operation Grinch Water has so far been very successful in educating us and the public and our partners about what’s going on down there.”

For now, researchers said the dye provides evidence of a connection between the park’s wastewater system and the surrounding marine environment.

The next question is whether bacteria, pathogens or excess nutrients are traveling through that same pathway—and additional water-quality testing will be needed to determine that.

In a statement, the City’s Department of Parks and Recreation said:

The City and County of Honolulu’s Department of Parks and Recreation appreciates working with Mālama Pūpūkea Waimea and Wastewater Alternatives & Innovations towards recognizing this issue, and taking the appropriate action. We are looking forward to further testing of the nearshore water to determine if remediation is necessary, and exploring what options are available towards continuing to be good stewards of our share public spaces.

Currently, we are beginning the design phase of a cesspool to Individual Wastewater System conversion for the now closed comfort station at Kalaeloa Beach Park, and can explore options available for Pūpūkea Beach Park should the need arise.

In a statement, the state Dept. of Health said:

It has not yet received the findings from the wastewater dye tracer study conducted at Pūpūkea Beach Park. Once the study’s results and supporting information are provided to the department, DOH will conduct a thorough examination of the methods and findings. DOH’s coastal water quality programs rely on established, science‑based protocols and DOH’s own sampling data to determine when public health advisories are necessary.