Septic Installation & Cesspool Conversion in Kaumana
We install septic systems and convert cesspools in Kaumana, mauka of downtown Hilo along Kaumana Drive, about 25 minutes from our equipment yard in Keaau. A good part of Kaumana is built on lava that was still moving in 1881, and that young rock (and the lava tubes running through it) is what we plan every job around.
Kaumana in numbers
- Part of the Hilo CDP. Kaumana is not its own Census place. Two Hilo census tracts carry its name: “Kahuku-Kaumana” (about 1,760 housing units) and “Piihonua-Kaumana” (about 2,850 housing units), per ACS 2020 to 2024 estimates. Tract lines don’t match the neighborhood exactly.
- Kaumana Hawaiian Home Land: a small DHHL tract here had 119 residents in 2020.
- Built on the 1880 to 1881 Mauna Loa flow. The eruption started in November 1880 on the northeast rift zone, and the flow front stopped advancing on August 10, 1881.
- Several hundred homes sit on that flow’s pahoehoe, according to the USGS Hawaiian Volcano Observatory.
- Kaumana Cave is a lava tube about 2 miles long that formed during the same eruption. It carried lava toward Hilo.
- Kaumana Drive is the Hilo end of Route 200 (Saddle Road). It passes the cave near mile 4 and is narrow and winding, with blind corners and hidden driveways.
- Hilo Bay priority area. DOH’s 2017 report lists Hilo Bay as a Hawaii Island priority area with about 8,700 cesspools. Check your own parcel on the UH prioritization tool.
Rock gardens and thin soil
The Hawaiian Volcano Observatory gives a simple way to spot a home on the 1881 flow: the “rock garden.” Soil hasn’t had time to form on that pahoehoe, so many yards are mostly bare lava with plants tucked into the cracks.
For a wastewater system, little soil means little natural treatment. Effluent needs soil to filter through before it reaches groundwater. Where the profile shows fractured lava, HAR 11-62 calls for a soil replacement system: we excavate into the rock, bring in suitable fill, and build the disposal area in that, with at least 3 feet of separation to groundwater. Mounds are reviewed case by case. Some owners choose an aerobic treatment unit, which needs a service contract with inspections every six months.
Breaking pahoehoe takes time and the right equipment, and imported fill has to be trucked up Kaumana Drive. Expect a rock lot to cost more than a lot with deep soil. Our conversion cost guide explains why rock moves the price.
Lava tubes under the yard
The 1881 lava reached Hilo largely through tubes, which let it travel a long way down a gentle slope. Kaumana Cave is the best-known one. USGS says the later pahoehoe was carried largely through tubes, and some sections and entrances of the Kaumana tube itself lie on private property.
A lava tube is a fast lane for water. Wastewater that reaches a tube can travel through open rock with no soil to treat it. We could not find a rule in HAR 11-62 or a county guidance document that addresses lava tubes by name, so we treat them as a site condition for the engineer and DOH to handle:
- Tell us and your engineer if you know of a tube, skylight or hollow-sounding area on the property.
- The 5-foot profile and percolation test come first. If the excavation opens into a void, the layout changes.
- The leach field or bed goes over solid ground, with the soil replacement layer doing the treatment.
- DOH Wastewater Branch reviews the plan before we dig and issues an approval to use when it’s done.
If an old cesspool in this rock seems to drain fast, that is not the same as treatment. It may simply mean the effluent found a crack or a tube.
Homes along Kaumana Drive
Kaumana is a residential area that climbs the hill along Kaumana Drive and its side streets. The projects we expect here:
- Cesspool conversions on older homes, especially when an addition or remodel brings the system under DOH review.
- New homes, where DOH reviews the wastewater plan before the county building permit is signed off.
- Ohana units. One system can serve up to five bedrooms and 1,000 gallons a day. On a rock lot, fitting a larger system is mostly a digging question.
Getting a machine up the hill
Kaumana Drive is a working highway with blind corners and hidden driveways, so we schedule deliveries of fill and equipment with traffic in mind. On a hillside, driveways can be steep. Before we quote, we look at whether an excavator can get in, where a truck can unload, and whether rock walls or plantings are in the way.
Slope also affects layout. Setbacks are 5 feet to buildings and property lines (9 feet for a seepage pit) and 50 feet to streams. On a sloped lot the engineer needs a level, stable spot for the disposal area.
The flow that nearly reached Hilo
In late March 1881 the flow was about seven miles from Hilo, above Kaumana. By June it was within five miles, and late that month it got into stream channels and sped up. It stopped in August about 1.5 miles from Hilo Bay, just north of today’s UH Hilo campus. USGS says no lava had come that close to the bay in more than a thousand years.
An earlier flow, in 1855 to 1856, stalled about six miles from Hilo Bay, just above what is now the Kaumana City subdivision. In 1984, Mauna Loa sent another flow toward upper Kaumana. It stopped about 5.3 miles short of Country Club Road, off Kaumana Drive. If you’re building new, ask the county about lava hazard designations for your parcel.
Deadlines and help with costs
The statewide deadline is January 1, 2050 for every cesspool, with no earlier date for priority areas (Act 125 explained). Since 2016, no new cesspools can be built. On funding, HGIA plans to open the Act 204 loan fund around the end of 2026, and USDA Section 504 may help lower-income owners, so check eligibility. See our grants and loans guide.
Other Hilo neighborhoods we cover
Get a plan for your rock
Tell us where you are on Kaumana Drive or the side streets and what you’re planning. We’ll look at the rock, the slope and the access, and tell you what kind of system the site will likely need. Request a free estimate
Frequently Asked Questions
My yard is mostly bare pahoehoe. Can I still have a septic system?
Yes, but usually a soil replacement system rather than a standard leach field. We excavate into the rock and build the disposal area in imported fill.
There’s a lava tube on my property. Is that a problem?
It can be. A tube can carry wastewater away untreated, so the system can’t drain into one. Tell your engineer about it at the start so the layout avoids it.
My old cesspool never backs up. Why convert it?
State law requires it by 2050. In rock this young, a cesspool that never fills may be draining into a crack or tube with little treatment along the way.
Is it harder to install a system on Kaumana Drive?
Access takes more planning. The road has blind corners and hidden driveways, so we check truck and excavator access before quoting.
Is Kaumana on county sewer?
We don’t state sewer status for specific streets. Ask the County Department of Environmental Management whether sewer is available at your address before designing a septic system.
Does building on the 1881 flow change the permit process?
The steps are the same: engineer’s design and percolation test, DOH review, licensed installer, and approval to use. The difference is the system type the rock calls for.