Sand Mounds
A sand mound system is an on-site sewage disposal system that is elevated above the natural soil surface in a suitable sand fill material. Gravel-filled absorption beds are constructed in the sand fill, and effluent from a double-compartment septic tank or BAT unit is pumped into the absorption area through a pressure distribution network. The use of an effluent filter in the outlet end of the septic tank is required when a BAT unit is not required. Pretreatment of sewage occurs in the septic tank or BAT unit, and additional treatment occurs as the effluent moves downward through the sand fill and into the underlying natural soil.
The purpose of the design is to overcome site limitations that prohibit the use of conventional trench on-site sewage disposal systems.
The design can overcome the following site limitations:
- High water tables
- Shallow soils over fractured bedrock
- Slowly permeable soils
Presently in Maryland, sand mound systems that meet conventional on-site sewage disposal criteria are designed to overcome high water tables or shallow soils over fractured bedrock and are approved for routine use. Sand mound systems on slowly permeable soils, with rates of 60-120minutes per inch, are currently nonconventional (alternative) and may be installed in repair situations or on certain existing lots of record
Components of a Sand Mound System
- Septic Tank: Pre-treats the wastewater by allowing solids to settle and anaerobic digestion to occur.
- Pump Chamber: Holds the effluent and pumps it to the sand mound.
- Sand Mound: Consists of layers of sand, gravel, and soil where further treatment occurs.
- Distribution Network: Pipes that evenly distribute effluent across the sand mound.
- Observation Ports: Allow for monitoring the system’s performance.
Benefits of Sand Mound Systems
- Adaptability: Suitable for areas with poor soil conditions or high water tables.
- Environmental Protection: Provides effective treatment, reducing the risk of groundwater contamination.
- Longevity: With proper maintenance, sand mounds can last for decades.
- Cost-Effective: Often less expensive than connecting to a municipal sewer system in rural areas.
Construction and Design
Site Evaluation
Before installation, a thorough site evaluation is conducted to assess soil conditions, topography, and local regulations. This ensures the system is designed to meet the specific needs of the location.
Design Considerations
- Size of the Mound: Determined by the volume of wastewater and soil absorption capacity.
- Slope and Orientation: The mound should be oriented to maximize sun exposure and minimize erosion.
- Materials: High-quality sand and gravel are essential for effective filtration.
Installation Process
- Site Preparation: Clear the area of vegetation and level the ground.
- Septic Tank Installation: Install the septic tank and connect it to the house plumbing.
- Mound Construction: Layer sand and gravel according to design specifications.
- Distribution System: Install pipes to distribute effluent evenly.
- Final Covering: Cover the mound with topsoil and vegetation to prevent erosion.
Maintenance of Sand Mound Systems
- Regular maintenance is crucial for the longevity and effectiveness of sand mound systems:
- Inspection: Regularly check the septic tank, pump chamber, and distribution network.
- Pumping: Periodically pump the septic tank to remove sludge and prevent overflow.
- Vegetation Management: Maintain grass cover on the mound to prevent erosion and ensure proper insulation.
