A mound septic system needs to have a great functional quality. It is important to get one of them approved, especially if it is located in ones premises. A standard gravity system is essential for the running of a mount septic tank and it costs between $3,500 and $6,500. Fees and designs are the other part of the expenditure on a septic mound tank. Including all expenses, the price of a working mound septic system is definitely less than $9,000.