A mound septic system is used in locations where conditions don't allow a conventional septic system. The three main conditions that indicate the need for a mound system are soils that drain too quickly or too slowly, shallow bedrock and a high water table. Mound septic systems cost substantially more than conventional septic systems.
The potential cost of a mound septic system can vary widely from $9,000 all the way up to $25,000, according to the website Eco-Nomic. Variables that affect cost include the conditions of the land where the mound septic will be placed, the size of the home, including number of bedrooms, and the choice between a plastic and cement septic tank, with plastic being more expensive.
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A mound septic system that is built onto a slope is more expensive because the mound has to be made much larger to make up for the sloped land. If you are faced with a choice between a sloped site and a flat site when situating your mound septic system, you can save a lot of money by choosing the flat site even if it means running pipes a longer distance from the house.
Most of the cost of a mound septic system is in hiring large machinery and the people who run them. Backhoes, graders and bulldozers are expensive to run. The more excavators there are in your immediate area, the more competition there is likely to be between them, and the lower their fees are likely to be. Shop around and talk to all the excavating companies in your area to determine who can offer you the best deal.
A mound septic system has the same components as a conventional septic system, but the leach field is contained within the mound of soil rather than being buried underground. Much of the cost of a mound system is for the septic tank, pipes and excavation. The cost that is above and beyond a conventional system is because of the added excavation and work required to build the mound, a process that is more complex than simply digging a hole and filling it in.