Mound Septic Systems: When and Why They Are Needed, Installation, and Cost Implications

Introduction

A mound septic system is an alternative to conventional septic systems, typically used in areas where the soil conditions are unsuitable for the installation of a standard drain field.

In particular, mound systems are designed for sites with poor soil drainage, shallow soils, high water tables, or other factors that make it difficult for a traditional septic system to function properly.

In this post, we’ll explain when and why mound systems are needed, how they are installed, and what homeowners can expect in terms of cost implications.

What Is a Mound Septic System?

A mound septic system is a type of elevated drain field that allows for proper wastewater treatment in areas where the soil is not deep enough or well-drained enough to support a conventional system.

Instead of placing the drain field underground, the effluent (liquid waste) is treated in a raised bed of sand and gravel that is built above the natural soil level.

This raised mound provides additional filtration and allows for better treatment of wastewater before it enters the environment.

When and Why Is a Mound System Needed?

Mound systems are often used when site conditions make it impossible to install a conventional septic system. These conditions may include:

1. High Water Table

In areas where the water table is close to the surface, there is not enough depth for a traditional drain field to safely treat wastewater before it reaches groundwater. Installing a mound system raises the drain field above the water table, allowing the effluent to be properly treated in the raised mound of sand and gravel.

Example: In Florida, many areas have high water tables due to the state’s low elevation and proximity to coastal waters, making mound systems a common solution in such regions.

2. Poor Soil Drainage

Conventional septic systems rely on the soil to filter and treat wastewater as it percolates through the ground. However, in areas with clay soils or other types of poorly drained soils, the wastewater may not be able to filter properly, leading to contamination of nearby water bodies.

Example: If a site has clay-heavy soil that prevents proper drainage, a mound system can provide the additional filtration needed for the system to function effectively.

3. Shallow Soils

In areas where the natural soil layer is too thin, there may not be enough space to install a conventional drain field. Mound systems provide a raised area for the effluent to filter through, allowing for proper treatment even when the soil depth is limited.

Example: Homes built on rocky terrain or shallow bedrock may not have enough soil depth for a traditional septic system, making a mound system the best solution.

4. Environmentally Sensitive Areas

In regions near lakes, rivers, or coastal waters, it’s crucial to protect water quality by ensuring that septic systems properly treat wastewater before it reaches the environment. Mound systems provide an additional layer of protection by raising the drain field and improving filtration, reducing the risk of nutrient pollution and contamination.

Example: In areas like Florida’s coastal zones, where water quality is a major concern, mound systems can help prevent nutrient runoff into sensitive ecosystems.

Installation of a Mound Septic System

The installation of a mound system requires careful planning and consideration of the site conditions. The process involves creating a raised area of soil, sand, and gravel, into which the treated effluent from the septic tank is distributed for further filtration.

Steps in the Installation Process:

Site Evaluation: A professional will conduct a thorough evaluation of the site to determine soil type, depth, drainage capacity, and the water table level. Based on this assessment, they will design the mound system to meet the specific needs of the property.
Excavation and Preparation: The top layer of the existing soil is removed to prepare for the mound. The soil from the excavation is sometimes used to help build the mound.
Construction of the Mound:
- A layer of sand is placed on top of the excavated area, followed by a layer of gravel.
- Distribution pipes are placed within the gravel layer, where they will distribute the effluent from the septic tank.
- The mound is covered with topsoil to support vegetation and prevent erosion.
Effluent Pumping: The septic system will be equipped with a pump to transport the treated effluent from the septic tank to the raised mound, where it will undergo further treatment as it filters through the sand and gravel layers.
Final Grading and Landscaping: Once the mound is built, the area is graded and landscaped to blend with the surroundings. It is important to ensure that the mound is protected from erosion and other damage by planting grass or shallow-rooted vegetation on the surface.

Cost Implications of Mound Systems

Mound systems are generally more expensive to install than conventional septic systems due to the additional materials and construction required.

The costs can vary widely depending on factors such as the size of the system, the complexity of the installation, and the site conditions.

Factors Affecting Cost:

Site Evaluation and Design: The cost of hiring professionals to conduct a site evaluation and design the mound system can range from $1,000 to $2,500, depending on the complexity of the project.
Materials: The cost of sand, gravel, piping, and other materials required for the mound system can add significantly to the total cost.
Installation: Labor costs for excavation, mound construction, and system installation can vary, but installation of a mound system typically ranges from $10,000 to $20,000, depending on the size of the system and local conditions.
Pump System: Mound systems require a pump to transport the effluent to the elevated drain field, adding to the overall cost. The pump system and its installation can range from $1,000 to $2,500.

Total Cost Estimate:

Basic Mound System: $15,000 – $25,000
Larger or More Complex Mound Systems: $25,000 – $40,000 or more

Maintenance Considerations

Mound systems require regular maintenance to ensure they continue to function properly and to avoid costly repairs or failures. Key maintenance tasks include:

Pump Inspections: The pump should be inspected regularly to ensure that it is working properly and that the effluent is being transported to the mound efficiently.
Regular Pumping: Just like conventional systems, mound systems require the septic tank to be pumped every 3-5 years to prevent solids from clogging the system.
Vegetation Maintenance: The surface of the mound should be kept clear of deep-rooted plants or trees, as their roots can damage the system. Grass and shallow-rooted plants are ideal for preventing erosion and maintaining the integrity of the mound.
Protecting the Mound: Avoid parking or driving vehicles on the mound, as this can compact the soil and damage the system. Ensure that rainwater or runoff is diverted away from the mound to prevent oversaturation.

Conclusion

Mound septic systems are an essential solution for properties with poor soil conditions, high water tables, or environmentally sensitive locations. While they are more expensive to install than conventional systems, they offer reliable wastewater treatment in areas where traditional systems would fail. With proper installation and regular maintenance, mound systems can provide effective, long-term wastewater management that protects both the property and the surrounding environment.

If you’re considering a mound system for your property or need expert advice on installation and maintenance, contact us for professional assistance.

Mound Septic Systems Overview

Factor	Details
When Needed	– High water table – Poor soil drainage – Shallow soils – Environmentally sensitive areas
Why Used	Provides additional filtration in areas where conventional systems can’t function effectively
Installation Steps	– Site evaluation – Excavation and preparation – Mound construction – Effluent pumping – Final grading and landscaping
Cost Estimate	– Basic System: $15,000 – $25,000 – Larger/Complex Systems: $25,000 – $40,000+
Maintenance Requirements	– Regular pump inspections – Septic tank pumping every 3-5 years – Vegetation maintenance – Protect mound from damage (e.g., vehicles, rainwater)
Advantages	– Suitable for poor soil conditions – Reduces risk of groundwater contamination – Can be installed in sensitive areas