If you need to construct a mounded septic system rather than a conventional system to handle waste water and sewage on your property, be prepared to pay quite a bit. A mounded system costs a lot more than a conventional septic system, due to environmental constraints. As the name implies, the mound system leaves a large hill-like structure on the site, which can't be camouflaged with landscaping on or around it because the roots can interfere with the system.
Mounded septic systems are installed on sites with marginal soils or other site limitations, where traditional septic systems would not work. One reason for the higher cost is that a mounded system requires more sophisticated construction than a conventional system, including electric pumps.
According to the Ohio State University Extension Service, a mound system costs approximately twice the amount of the same-sized conventional septic system, because of the amount of labor involved and cost of the sand. "The higher cost is necessary, however, if the site or soil condition makes it impossible to use a subsurface soil absorption system," according to the OSUES. Although installation costs vary depending on septic size and location, a mounded septic can run between $30,000 to $50,000 to construct. The actual mounds consist of large amounts of gravel and sand, brought to the site. The electric pumps require regular replacement, and you must purchase a generator to keep the system operating during a power failure. In addition, mounded systems fail more frequently than conventional septic systems.
Depending on the type of soil in your area, mounded septic systems can last many years, although not usually as long as traditional systems. According to the University of Minnesota, typical yearly costs for a mounded septic system might run as much as $500 as of the time of publication, including the costs of replacing pumps in these systems. A mounded system should be pumped out more often than conventional septics, depending on the number of people occupying the house or type of use in a commercial property. While annual pumping may not be necessary, the mounded system should be pumped at least biannually.
Once the mound system is installed, proper care can increase the life of the system, saving you money in the long term. Don't park vehicles or leave any heavy objects on top of the mound, and don't pave over it. Use water wisely: Don't take overly long showers, and limit full wash loads to once a day. Install low-flow toilets and other water-saving devices. Plant grass or other vegetation over the mound to prevent soil erosion.