Figure 3. Schematic of the Mound System (After Converse and Tyler, 1990).
Conventional septic tank-absorption field systems rely on suitable soil and site conditions to treat wastewater onsite. Mound systems are only slightly different in principle from a wastewater treatment aspect. Mound systems are elevated absorption beds and utilize suitable sand fills to partially treat wastewater before it reaches natural soil. Mound systems are used to augment natural soil for complete treatment and disposal.
A mound system consists of a septic tank, a dosing tank, distribution pipes, and a mound, as shown in Figure 3. The septic tank allows the solids in wastewater to settle and degrade. The septic tank effluent is filtered by an effluent filter and discharged to a dosing tank. The dosing tank is equipped with a pump to deliver the septic tank effluent through the distribution system to the mound. The distribution system normally consists of small diameter pipes and allows for even wastewater application under low pressure on the mound.
Figure 3. Schematic of the Mound System (After Converse and Tyler, 1990).
Most of the wastewater pollutants are removed as the wastewater flows through the sand layer in the mound. The natural soil underneath absorbs the partially treated wastewater from the mound and removes pathogens to complete treatment and disposal.