What actually happens when you replace a cesspool?

Most people who own a cesspool have never seen it. It’s a lid somewhere in the yard, or not even that, just a patch of grass the mower goes over. So when you hear that every cesspool in Hawaiʻi has to be upgraded, converted, or connected to sewer by 2050, the honest first question isn’t about law or deadlines. It’s simpler and a little uneasy: what are they actually going to do to my yard? Who shows up, what gets dug up, and how do I know it was done right?

The answer is less mysterious than it sounds. A cesspool is just a hole in the ground that takes everything from your toilet, shower, and sinks and lets it soak into the rock below, with no treatment along the way. Replacing it means putting something between your house and the ground that actually treats that water first. On most of Hawaiʻi Island there’s no sewer line to connect to, so that something is usually a septic tank or an aerobic treatment unit, plus a place for the treated water to soak in.

Deadline for every cesspool in the State (HRS §342D-72)

2050

Deadline for every cesspool in the State (HRS §342D-72)

Cesspools on Hawaiʻi Island (State estimate)

about 48,600

Cesspools on Hawaiʻi Island (State estimate)

Typical DOH plan review, depending on how complete the paperwork is (DOH)

2 days–2 weeks

Typical DOH plan review, depending on how complete the paperwork is (DOH)

The path runs through the same handful of people and the same order on almost every property. It looks like this.

First, someone has to read the ground

The first person to walk your property is a Hawaiʻi-licensed civil engineer. The Department of Health requires one to design the new system, and you hire them directly. They’ll want your property’s TMK number, the tax map key the State and County use to track permits for your parcel, so it helps to have it handy.

Then they look at the things you never think about: how big the lot is and how steep, how deep the soil goes before it hits groundwater or solid rock, whether you’re in a flood zone, and how far you are from wells, streams, and the shoreline. They dig a test hole and time how fast water drains out of it. That’s the percolation test, and on young lava rock or thin soil, which describes a lot of this island, it matters more than anything else.

Those results decide what kind of system you can have. Some lots can take a standard septic tank. Others need an aerobic treatment unit (ATU), which pumps air into the tank so bacteria break the wastewater down more thoroughly before it leaves. The test also sets how large the disposal area has to be, usually trenches or a bed of gravel where treated water seeps slowly into the ground. In limited situations, such as a very steep lot, deep suitable soil under a shallow limiting layer, or not enough land for trenches, a seepage pit (a deep, lined hole) is still allowed.

Your soil decides the design. Everything after that is paperwork, digging, and checking.

Then the State has to say yes, on paper

Your engineer turns the site work into plans and submits them online to the DOH Wastewater Branch. The package includes an application, an owner’s certification form, the site evaluation, an operation and maintenance plan, and a $100 filing fee. If the design uses an ATU, a signed maintenance contract goes in too.

DOH’s own guidance says review can take roughly two days to two weeks, and the deciding factor is how complete the paperwork is. A missing form doesn’t get rejected so much as it gets stuck. Nothing can be built until DOH approves the plans in writing. It’s also worth checking with Hawaiʻi County’s Building Division about any plumbing or building permits needed to reconnect your home’s drain line.

This is the quietest part of the whole process, and often the most frustrating, because nothing is visibly happening. It’s also where small gaps, like a form unsigned or a document never forwarded, quietly add weeks.

The loud part: a crew in the yard

Once the plans are approved, a licensed contractor builds what the engineer designed. DOH accepts only contractors holding one of five Hawaiʻi license classes: A, C-9, C-37, C-37a, or C-43. Ask to see the license, and check that it’s one of those. Depending on the job, you may also need a licensed plumber and electrician, particularly for an ATU, which runs on power.

This is the stage that looks like construction. There’s an excavator, a hole for the tank, trenches or a bed for the disposal field, and pipe running back to the house. The old cesspool gets handled in the same job. It’s pumped out, and then either filled in completely with earth, sand, or gravel so it can’t collapse under someone later, or, if the approved plan calls for it, pumped, cleaned, and reused as a seepage pit for the new system.

Timing matters here in a way most homeowners don’t expect. Before everything is buried, the engineer needs to see it, and DOH’s inspection report asks for photos of the treatment tank with its piping connected to the distribution box and the leach field or seepage pit, all still exposed. If the crew backfills before the engineer has inspected and photographed, the work may have to be uncovered again.

Checking the work, and the letter that ends it

When construction is done, your engineer inspects it against the approved plans. They measure setbacks to buildings, property lines, streams, wells, and the ocean’s vegetation line, confirm there are at least three feet of suitable soil beneath the trenches or bed, and record how the old cesspool was closed. Within 30 days they send DOH a construction inspection report, the contractor’s certification, stamped as-built plans, and the photos. DOH may also visit.

That report isn’t a rubber stamp. The engineer has to say whether the system was built exactly to plan, whether changes were made and resolved, or whether it can’t be accepted as built. If the contractor departed from the design in a way the engineer won’t sign off on, that gets fixed before anything moves forward.

Then DOH issues a written approval to use. Until that letter arrives, the new system can’t be put into service. It is the piece of paper that says your cesspool is officially behind you.

Until the approval-to-use letter arrives, it isn’t finished. It just looks finished.

With an ATU, there’s one more thing, and it doesn’t end. You’ll keep an active service contract, with an inspection at least every six months, and send DOH a copy every year. Whatever the design, the new system does something the cesspool never did: it treats the water before it goes back into the ground.

So how long does it take?

Honestly, it depends on how many people are waiting on each other. The engineer’s calendar, the completeness of the DOH submittal, the contractor’s schedule, getting the inspection done before backfill, and the final report all line up end to end. None of those steps is especially long on its own. What stretches a conversion out is usually the space between them: a document that sat in an inbox, a call nobody returned, a crew that couldn’t start because approval hadn’t been forwarded.

That’s the part ʻĀina Force works on. We don’t engineer, permit, or build anything, and we don’t quote prices or promise funding. Licensed independent engineers evaluate and design, DOH reviews and approves, licensed independent contractors install, and DOH issues the approval to use. Our role is to keep information, introductions, documentation, and communication moving between all of them, so the homeowner has one place to ask “where are we?” and get a straight answer.

Because a cesspool conversion isn’t really hard. It’s just a lot of hands passing one project along.

If you’d like to see where your own property stands, you can check your property. It shows your parcel and its State cesspool priority area, and we’ll follow up about what it may involve.