The average cost of a septic system starts at approximately $20,000. That includes perk test, engineering, and installation. Some soils, like Haiku, have a lot of clay. It takes a long time for water to seep down through the clay, so more leach lines are required. The more leach line the system requires, the more it costs. The opposite is true in Hana. The soil mixed with cinders there allows water to run right through it.
Cost to pump a septic tank - starts at $200.00.
The appraisal on a property is greatly increased with an engineered and D.O.H. approved septic system.
Each septic system is individually engineered for your lot. The number of bedrooms. the size and configuration of the lot, and perk rates are all used to determine final system design.
The state will only allow one Individual Wastewater System (IWS) per 10,000 square foot lot. And, there can be only five bedrooms per IWS. The state determines wastewater flows based on the number of bedrooms in a dwelling. You can build on an existing lot that has less than 10,000 sf so long as it was in existence before state IWS rules became law in September of 1991. If you want more than five bedrooms, you must have 20,000 sf or more land. You would be required to install two septic systems. The state requires floor plans to be submitted for their review. An examination is made to determine that a "den, study, rumpus room, etc" cannot be readily converted into a bedroom.
If you think you will be adding a two bedroom cottage to your three bedroom house, you may want to consider having the system designed to handle the additional flows.
* New Federal E.P.A. rules and guidelines supercede State guidelines mentioned above. The information has remained in report in order for reader to recognize the major changes which affect all cesspool owners in Hawaii today.