Gradually more and more people build septic systems in Puna. Still many people think that septic systems and cesspools are the same. I will show you why this is not really true.
About ¾ of the population on the Big Island of Hawaii are served by cesspools. Experience has shown that cesspools are an inferior way to deal with sewage. The possible pollution of ground water (aquifer) and therefore contamination of present and future drinking water resources, plus the contamination of coastal waters, beaches and recreational areas (as the sewage will always find it’s way to the ocean) makes the usage of cesspools a big risk factor for public health. The Hawaii County office therefore prohibits the usage of cesspools in these areas and it will only be a matter of time until cesspools will no longer be permitted at all. It is said that this will not become an issue unless the number of residents and urbanization increases, (which it will). Stronger pollution controls will then need to be enforced.
Until then the basic formula in Puna is as follows:
Properties with a size under 1 acre must use septic systems in Puna.
Properties with a size over 1 acre can use either cesspools or septic systems.
What’s the basic idea behind these individual sewage treatment systems?
Basically both septic tanks and cesspools can be seen as settling basins. Heavy solids will drop to the bottom and form what is called ‘sludge’ while lighter solids will float to the top and create a layer of ‘scum’. Bacterial activity starts to decompose the solids and therefore liquefy and purify the sewage. Gases that occur due to bacterial activity escape through vents on the top.
Cesspools are a much simpler in structure. The liquid drains into the soil directly through holes in the bottom and in the sides of the tank while the sludge is retained on the bottom. In septic tanks the liquid is drawn from well below the scum layer through a pipe on the side and directed to a distribution box and then into a leech pit.
Why are cesspools inferior?
Direct discharge of raw sewage into the ground.
Clogs up easily, because the sludge doesn’t get decomposed properly.
Need to be cleaned out more often.
Sewage gets too far into the ground, aerobic bacteria (which decomposes sewage more quickly than anaerobic bacteria) is only present in the top 26 inches of soil.
The deeper the sewage goes into the ground the more likely it is to contaminate ground water before it is purified by bacterial decomposition.
They are more likely to contain a higher level of coliform bacteria (which is an indicator bacteria for pathogenic bacteria).
How does a septic system work?
A septic system basically consist of 4 parts:
Sewer line: This is the piping that connects the house plumbing with the septic tank.
Septic tank: A septic tank can be made of polyethylene, fiberglass or concrete. The price of a smaller tank (1-2 bedrooms) is not significantly cheaper than a bigger tank (5 bedroom) so you might want to consider buying a bigger one, especially if you are considering expanding your home at a later date.
Distributor box: This box distributes the run off from the septic tank evenly into the leech pit. The more evenly the distribution of the flow, the better the bacterial decomposition process. Uneven distribution might lead to overloading of one area, which can in turn bring the effluent too deep into the soil and therefore possibly contaminate the ground water.
Leech pit: Make sure that your leeching system is big enough for your daily flows (see below) and also that it will work even in times of heavy rain and surface flooding.
Home and Outdoor Living Water Requirements
Flow Rate GPM
Total Use - U.S. Gals.
Adult or child
Kitchen sink (a)
Shower or tub
Bathroom lavatory sink
Water softener regeneration
Outside hose faucet
Notes to Table: (a) water flow restricting valves and shower heads can reduce flow and water use by up to 50%. Source: USDA "Water Systems Handbook." (Thanks to Keith Oberg, ProfessionalHome Inspection Service, Binghamton, NY, for providing this information.)
Never install septic tanks under driveways or heavy equipment.
Always protect polyethylene tanks from puncturing with sharp objects.
Make sure to keep chemicals out of the septic systems in Puna as they will possibly reduce the activity of the bacteria.