Most homeowners only go through a cesspool conversion once, so it’s normal not to know what happens when. The process has more paperwork than people expect, and a couple of steps can’t be skipped or done out of order. Knowing the sequence ahead of time saves a lot of waiting around.
Here’s how a conversion works in Hawaii from the first phone call to the day you’re legally allowed to use the new system. The requirements come from the state’s wastewater rules (Hawaii Administrative Rules, Chapter 11-62) and the Department of Health’s current forms.
Step 1: Figure out what you’re working with
Before anyone digs, answer three questions:
- Is it really a cesspool? Check permits or property records, or have it inspected.
- What’s its priority level? Look it up on the state’s prioritization map. Priority affects grant eligibility and hints at what your site might need.
- Is sewer nearby? A sewer line running past the lot can change the whole plan, because hooking up is sometimes the easier path. Call the county before you pay for design work.
Step 2: Bring in a licensed engineer
Hawaii doesn’t let homeowners design their own wastewater system. The plans have to be prepared by a professional engineer registered in Hawaii, and the engineer is the one who submits them to the Department of Health (DOH). DOH keeps a list of engineers who do this work on its individual wastewater systems page.
If you work with a contractor who handles conversions regularly, they’ll usually have engineers they work with and can coordinate the whole thing.
Step 3: Site evaluation and percolation test
This is the step that decides what kind of system you can have. The engineer does two things on your lot:
- Looks at the soil profile at least five feet down to see what’s there and where any rock, clay or groundwater starts.
- Runs a percolation test at least three feet down to measure how fast water soaks into the ground.
The results go on a DOH Site Evaluation Form that the engineer signs and stamps. Among other things, the engineer has to confirm there are at least three feet of suitable soil below where the leach field will go. If there aren’t, which is common on lava rock and in areas with shallow groundwater, the design has to account for that.
Step 4: Choosing the system
With the site data in hand, the engineer picks the system that meets the rules for your lot. The most common options are:
- A septic tank with a leach field. The standard choice where the soil and space allow.
- A septic tank with a seepage pit. Allowed only in specific situations, such as steep lots, sites where good soil sits under a deep limiting layer, or lots too small for a leach field.
- An aerobic treatment unit (ATU). Treats wastewater to a higher level. Often used where groundwater is shallow or setbacks are tight.
- Other options like soil replacement systems, raised mounds and sand filters, which DOH reviews case by case.
Our cost guide compares what each one typically costs.
Step 5: The DOH application
The engineer puts together the application package and submits it to DOH’s Wastewater Branch, usually online. A typical package includes:
- The application form and the engineer’s construction plans
- A site plan and the home’s floor plans
- The Site Evaluation Form
- An Owner’s Certification, which you sign
- An operation and maintenance manual and a plan for sludge disposal
- A service contract, if the design uses an aerobic unit
The filing fee is $100 for a new system. DOH says it reviews applications within 45 working days when staffing allows, and individual home systems have historically moved faster than that. If DOH finds something missing or has comments, the applicant gets 30 days to respond.
If your project also needs a county building permit, keep the timing in mind. DOH’s approval lapses if the county doesn’t issue the building permit within a year.
Step 6: Construction
Once the plans are approved, a licensed contractor builds the system. DOH only accepts certain license classifications for this work: A (general engineering), C-9, C-37, C-37a and C-43. Ask any contractor which license they hold.
Construction usually means digging and setting the tank, building the leach field or pit, running new piping from the house, and bringing the tank’s access lids up to ground level so the system can be serviced later. On rocky lots, excavation is often the longest part.
Step 7: Closing the old cesspool
Your old cesspool doesn’t just get forgotten. It has to be dealt with so it doesn’t collapse or keep taking wastewater. The usual approach is to pump it out and then fill it completely with earth, sand, gravel or concrete, which is what the plumbing code calls for when a cesspool is abandoned. The engineer records how the cesspool was handled on the construction inspection report.
People sometimes ask about reusing the old cesspool as a seepage pit behind a new tank. In limited cases DOH has accepted that, but only when the pit meets the same design rules as a new seepage pit. It isn’t automatic, and many old cesspools won’t qualify. Ask your engineer early if it’s something you’re hoping for.
Step 8: Final inspection
The engineer keeps an eye on construction and, within 30 days of finishing, files a final inspection report with DOH. It includes stamped as-built drawings, measured setbacks, and photos of the exposed tank, piping and leach field or pit before they’re covered up. That’s why your contractor won’t backfill everything right away. DOH can also inspect the work itself.
Step 9: Approval to use
This is the finish line. Under state rules, you can’t use a new wastewater system until DOH authorizes it in writing. DOH sends that “approval to use” letter once the final paperwork checks out. Until then, the system isn’t officially in compliance, even if it’s working.
Keep a copy of the approval with your property records. Grant programs ask for it, and future buyers will want to see it.
After you’re done
Your obligations don’t end at approval:
- Follow the operation and maintenance manual. The Owner’s Certification you signed binds you, and any future owner, to it.
- Pump the septic tank on schedule. Solids still build up and need to be removed every few years.
- If you have an ATU, keep the service contract active. State rules require a certified operator to inspect the unit at least every six months, check sludge levels, and keep a service log. A copy of the contract goes to DOH every year.
How long does it all take?
DOH review is often a matter of weeks, but the whole project takes longer once you add the site evaluation, design, any grant paperwork, construction and final inspection. Simple sites move fastest. Lava rock, tight lots, shoreline properties and anything that needs a variance take longer. Starting early, before the 2050 rush, is the best way to keep the timeline under your control.
We can coordinate every step, from the site visit and engineering through construction and DOH approval. Request a free estimate.
Frequently Asked Questions
Who can design a septic system in Hawaii?
Only a professional engineer registered in Hawaii. The engineer prepares the plans, does the site evaluation, and submits the application to the Department of Health.
Can I install my own septic system in Hawaii?
No. The system has to be built by a contractor holding one of the license types DOH accepts: A, C-9, C-37, C-37a or C-43.
How long does DOH take to approve a septic system?
DOH says it reviews applications within 45 working days when staffing allows, and home systems often move faster. Missing information or comments add time.
What is an approval to use?
It’s the written authorization from DOH that lets you start using your new wastewater system. You can’t legally use the system until you have it.
What happens to the old cesspool?
It’s normally pumped out and filled completely so it can’t collapse or keep taking wastewater. Your engineer documents how it was closed in the final inspection report.
Can my old cesspool be reused as a seepage pit?
Sometimes, but not often. It has to meet the same design rules as a new seepage pit, and DOH has to approve it. Ask your engineer whether your cesspool is a candidate.
Does an aerobic treatment unit need ongoing service?
Yes. State rules require an active service contract with inspections at least every six months, and a copy of the contract has to be sent to DOH every year.
