How Do You Convert 88,000 Cesspools to Modern Onsite Systems?

A massive wastewater upgrade plan in Hawaii requires new technology and a long time-horizon for cash-strapped homeowners.

How Do You Convert 88,000 Cesspools to Modern Onsite Systems?

Nicole Lowen

Interested in Onsite Systems?

Get Onsite Systems articles, news and videos right in your inbox! Sign up now.

Onsite Systems + Get Alerts

In 2017, the Hawaii Legislature passed a bill requiring the replacement of all cesspools by 2050. Gov. David Ige signed that bill, and now a state working group is digging into how the state can make that law work.

Hawaii is a state of about 1.4 million people and has approximately 88,000 cesspools. The number of cesspools isn’t certain. What is certain is that those cesspools are contributing pollution to the ocean surrounding the Hawaiian Islands. From 2006 to 2016, fecal bacteria counts along the islands’ beaches increased fivefold.

State Rep. Nicole Lowen, D-Kailua-Kona, represents a district on the western shore of the Big Island, and for her constituents, the issue is critical in more ways than one.

“We rely on healthy reefs for tourism. It’s a big draw, and it’s the bulk of our economy,” she says. But all drinking water comes from the island’s aquifers as well. “As an island, we can’t get water easily from elsewhere.”

As a member of the Cesspool Conversion Working Group, Lowen will have a direct hand in helping to change Hawaii’s dependence on cesspools as a means of wastewater treatment. On the working group are other legislators, a banker, a Realtor, people from government water and wastewater agencies, scientists and representatives from environmental advocacy organizations.

The group began meeting in 2018 and has a list of 14 tasks laid out by the Legislature. Among those are developing a long-range plan for the replacement of all cesspools, prioritizing the order of replacements, examining how this will be paid for and how much landowners can afford to pay, considering what technologies are best suited for the job and determining whether some areas should be exempt.


Although the 2017 law calls for replacement of all cesspools, in reality that may not be necessary, or it may not be necessary immediately. A major challenge will be finding the information needed to make that decision, says Sina Pruder, wastewater branch chief of the Hawaii Department of Health. “Because one of the things that group will do is actually divide cesspools into those that are impacting state waters as well as groundwater,” she says. The hope is to identify, and perhaps exempt, cesspools that aren’t doing either.

As with any other type of wastewater technology, geology will play a part in the decision. You can’t find a piece of land more than about 30 miles from the shore, but you can find parcels at high altitudes and maybe with a substrate where water doesn’t move quickly and is not near groundwater, Darren Lerner says. He holds a Ph.D. in biological sciences, directs the University of Hawaii Sea Grant College Program and is interim director of the university’s Water Resources Research Center. “Some of those places can be a lower priority in terms of conversion and may be suited for septic,” he says.

He also emphasized the island’s dependence on groundwater. “We have surface freshwater, but we do not have these perennial streams you would be familiar with on the continent. Many of those streams are flash. They exist when we have periodic rain,” he says. And because of the steep inclines on the islands, most water moves to the ocean very quickly.

There is a good deal of information telling scientists where pollution is happening, especially in terms of nitrogen and phosphorus, he says. But that’s different from knowing whether pollution from one particular cesspool is having an impact. It’s also possible there are acceptable cesspools if some are found to have no effect or minimal effect on the environment, he says.

Lerner sits on the working group’s subcommittees for technology and for data collection and prioritization. The other subcommittee will look at how to pay for the conversion. “You can’t go out and convert all 88,000 tomorrow. We’re talking in the billions of dollars,” he says.


Given the island’s topography and geology, finding a suitable technology to replace cesspools will be a challenge. Connecting to municipal sewer won’t solve the problem in every location, Lerner says. About 1 million of the state’s 1.4 million people live on Oahu, and while sewer service is available there, it is not fully established even in the populous area around Honolulu. The cost of extending it to the rest of the island would be significant, he says.

Yet because of geology and proximity to the ocean or groundwater, in some locations septic tanks and drainfields aren’t a much better solution than cesspools, he says.

“The technology we’re using for treatment is from, like, the Industrial Revolution,” Lowen says. She introduced a bill to start a pilot project with new technologies, in particular the Bill & Melinda Gates Foundation waterless toilet that turns feces into ash. Her bill passed the House but died in the Senate.

Ideally there will be a solution that has low installation and maintenance costs, Pruder says. Membranes or aeration blowers would preferably not be included because of the complexity they add. “We’ve found that a lot of homeowners don’t maintain their systems,” Pruder says. “I think one thing our state is looking at is some kind of breakthrough with passive systems.”

Especially interesting, she says, is some of the research happening on the U.S. East Coast, which has been grappling with water-quality problems from nitrogen pollution. Notable is Suffolk County, New York, on the eastern tip of Long Island, where the county and several municipalities now mandate advanced nitrogen-reducing systems as the solution for about 360,000 cesspools.

Better technologies would also bring better opportunities for water reuse, Lerner says. Nitrogen and phosphorus could be extracted and water could be recycled for purposes that can, but don’t have to, include potable use.

The Big Island will be especially affected by the replacement law, Pruder says. In 1991, the islands of Maui, Kauai and Oahu passed laws to prohibit new cesspools. The Big Island did not limit cesspools and people kept installing; and as a result, the island now has about 50,000, many next to the ocean shore.


When the law mandating conversion was newly passed, there was a sense of fear among the public, Lowen says. “I think people didn’t understand what the requirement would be or when it would come into play.” Once they understood there was a span of about 30 years before conversion would be required, that fear subsided.

Yet motivating people to pay the cost of conversions will be a difficult issue as well because in most places the cost of a cesspool is cheap, Lowen says. By contrast, the islands have many solar power installations because the high price of electricity gave homeowners an incentive to make upfront investments in solar that paid off with long-term savings. Converting a cesspool makes good sense for public health and the environment, but there is no financial incentive for homeowners, she says.

It’s a big task that Hawaii has set itself. Not only the Cesspool Conversion Working Group will be involved. In April the state Health Department posted two requests for proposal. One of those contractors will help the state evaluate technologies suitable for replacing cesspools, and the other will help determine what funding is available to help pay for all those conversions. Even converting a cesspool to a septic system can run $20,000 to $30,000 per household, and many homeowners cannot afford that, Lerner says. Parts of the islands are composed of “blue rock,” a basalt that is notably hard and very difficult to excavate, Pruder says.

“I think the positive is that the state is really committed to moving forward,” Lerner says. There is no need to convince the state of the existence of a problem. Everyone recognizes it and recognizes the need to work together.

None of this will happen immediately. In recognition of the size of the task, the Legislature passed a bill in the spring to extend the deadline for the group’s final report by two years, from 2021 to 2023.


Comments on this site are submitted by users and are not endorsed by nor do they reflect the views or opinions of COLE Publishing, Inc. Comments are moderated before being posted.