Home » Septic Installation & Cesspool Conversion in Fern Forest

Septic Installation & Cesspool Conversion in Fern Forest

We install septic systems and convert cesspools in Fern Forest, usually a drive of half an hour or more from our Keaau equipment yard once you count the gravel roads inside. Fern Forest sits higher and gets more rain than Mountain View village, Fern Acres or Eden Roc. Its long, skinny lots and gravel roads create their own set of septic problems.

Fern Forest in Brief

• 1,150 residents and 575 housing units (2020 Census, Fern Forest CDP). The Census counted 480 people in 2000, so the population more than doubled in twenty years.
• About 12.5 square miles, with roughly 2,590 parcels. About 2,293 of them are close to 3 acres.
• Elevation from about 2,200 to 2,970 feet, well above Mountain View and Fern Acres. The ZIP code is 96785, the same as Volcano.
• Rain: about 200 inches a year by local estimates. The Rainfall Atlas of Hawaii runs its 200- and 220-inch lines across the area. The old South Glenwood rain gauge, at about 2,276 feet just outside the Fern Forest census boundary, averaged close to 197 inches.
• Lava: USGS names Fern Forest as one of the neighborhoods built on Kilauea’s Ailaau flows, which erupted in the 1400s. On the USGS hazard map, Fern Forest falls in lava Zone 3.
• Roads: graded dirt and gravel inside the subdivision, with paved roads along the outer edges, maintained through mandatory road fees.

The Spaghetti Lot Problem

Most Fern Forest lots are about 3 acres, and local listings describe most of them as long and narrow, the so-called spaghetti lots. One 3-acre lot on the market was 125 feet wide and 1,045 feet deep.

Land area isn’t the problem. Three acres is about 130,000 square feet, thirteen times the state’s minimum land area for one system. The shape is what drives the design:

• Width limits placement. The disposal area has to stay 5 feet off each side line, or 9 feet if it’s a seepage pit, and 5 feet from the house. On a 125-foot-wide lot, the house, catchment tank, driveway and leach field end up in a row down a narrow strip.
• Long driveways. If the house sits deep in the lot, equipment and trucks may travel hundreds of feet down a private driveway just to reach the work area. Soft or narrow driveways limit what can get in.
• Long pipe runs, if you’re not careful. The tank should sit close to the house, with the field placed to fit the slope and the rock. A bad layout on a long lot can mean a lot of extra trenching.

Rock, Rain and Altitude

Fern Forest sits on the same Ailaau lava as its neighbors to the east, roughly 600 years old and laid down by lava tubes that run toward the coast. Higher up the slope, though, it’s wetter and cooler. That combination usually means:

• Rock inside the test pit. The engineer digs and logs the top 5 feet and runs a perc test. On these flows, the pit often reaches lava before it reaches 5 feet.
• Imported fill. Fractured lava can’t treat effluent on its own, so the state rule calls for a soil replacement bed, keeping at least 3 feet between the bottom of the system and groundwater. Every load of that fill comes in by truck, over the same gravel roads.
• Very wet working conditions. At 200 inches of rain a year, there aren’t many dry spells. We plan excavation around the weather and protect open trenches and fill from washing out.
• Thick vegetation. Fern Forest is heavily wooded. Clearing a path and a work area is part of the job, and the engineer needs a clear spot to dig the test pit.

An aerobic treatment unit (ATU) is another option on some lots, but it requires a service contract with an inspection every six months. On a remote lot with gravel access, think about whether a service tech can get in reliably for years.

Typical Fern Forest Projects

Fern Forest went from 460 housing units in 2010 to 575 in 2020, so many homes here are fairly new. What owners usually need:

• A system for a new house. DOH reviews the wastewater plan before the county signs off on the building permit. Our septic requirements for a new home guide explains the sequence.
• Retiring an older cesspool. Hawaii stopped allowing new ones in 2016, and Act 125 sets January 1, 2050 as the date every existing one has to be gone. See our Act 125 explainer.
• Catching up after additions. A permit for added rooms can bring DOH into the picture. The state sizes systems by bedroom, and it treats nearly any room bigger than 70 square feet as one.

Getting There

Fern Forest sits between Mountain View and Volcano, just off Highway 11. Some people call the area Glenwood, after South Glenwood Road. Inside the subdivision, most roads are graded dirt and gravel kept up by the community association, and one lot recently listed for sale sat about 0.7 miles off pavement. A 2015 county report on Puna road connectivity listed a link from Fern Forest to Eden Roc (Kaleponi to Punahele) as a priority, because upper Puna’s subdivisions had no connections between them.

Before a site visit, tell us your street, how far the lot is from pavement, and the condition of the last stretch of road and your driveway. That decides what size excavator and trucks we can bring.

Costs and Help

Statewide, a typical conversion lands somewhere from $20,000 to $50,000, and rock plus long gravel access tends to push Fern Forest toward the top of that range. Against a median owner-occupied home value of about $171,000 (Census Bureau estimate, 2020 to 2024), the septic work can be a big share of what the house is worth. Our conversion cost guide breaks the numbers down.

If your income is very low, the USDA’s Section 504 repair program in Hilo is worth a call: 1 percent loans of up to $40,000, and grants of up to $10,000 if you’re 62 or older. A new state loan program under Act 204 (2026) is expected from the Hawaii Green Infrastructure Authority in late 2026 but hasn’t opened. For questions about sewer service, the county Department of Environmental Management is the place to ask.

Neighbors Up and Down the Mountain

• Eden Roc
• Mountain View
• Volcano Village
• All Puna septic services

Thinking About a Spaghetti Lot?

Send us your street and a rough idea of where the house sits on the lot. We’ll plan the access, look at the rock and help you work with your engineer toward a system that DOH will approve. Request a free estimate

Frequently Asked Questions

My Fern Forest lot is only about 125 feet wide. Is that enough for a septic system?

Usually. You need 5 feet of clearance from each side line (9 for a seepage pit), which still leaves plenty of width. The real work is lining up the house, tank, catchment and field down a long strip.

Can you reach a lot that’s well off pavement?

Often, yes, but the road and driveway decide what equipment can get in. Wet gravel and narrow driveways may mean smaller machines and more truck trips for fill.

Does Fern Forest’s rain change the system design?

It mostly changes how and when we build. Open trenches and stockpiled fill need protection, and roof and road runoff has to be steered away from the finished field.

Is Fern Forest on the same lava as Fern Acres and Eden Roc?

Mostly, yes. The USGS lists Fern Forest on the Ailaau flows from the 1400s, the same flow field under Fern Acres. Fern Forest just sits higher and gets more rain.

Should I consider an ATU at Fern Forest?

Maybe, but weigh the service contract. ATUs need an inspection every six months, so a service tech has to reach your lot twice a year for as long as you own it.