Concrete Septic Tank

About Concrete Septic Tanks

Concrete septic tanks are the most widely installed tank type in the United States, accounting for the majority of all residential installations. They are manufactured at local precast concrete plants using high-strength concrete with a typical compressive strength of 4,000 PSI or higher. The manufacturing process involves pouring concrete into steel forms around a reinforcing cage of rebar, then curing the tank for a minimum of 28 days before delivery. Concrete tanks are available as single-piece units up to approximately 1,500 gallons, and as two-piece (top and bottom) or multi-section units for larger sizes. The joints between sections are sealed with butyl rubber or hydraulic cement to prevent infiltration and exfiltration. Quality concrete tanks include precast inlet and outlet baffles, access risers, and inspection ports as integral parts of the design.

Available Sizes and Costs

The table below shows the available sizes for concrete septic tanks with estimated purchase costs and annualized costs based on the expected 40-year lifespan. The annualized cost divides the purchase price by the expected service life to show the true yearly cost of ownership, which is the most meaningful way to compare tank materials of different lifespans. Delivery, excavation, and installation labor are not included in these prices and typically add $1,000 to $3,000 to the total installed cost.

Advantages

• Extremely durable and long-lasting with a lifespan exceeding 40 years when properly maintained
• Heavy weight resists flotation in high water table areas without additional anchoring
• Widely available from local precast concrete manufacturers in most regions
• Can be repaired if minor cracks develop using concrete patch or epoxy injection
• Available in the widest range of sizes from 500 to 2500 gallons and larger
• Resistant to root damage and soil pressure from heavy equipment above

Disadvantages

• Extremely heavy requiring crane delivery and placement which adds to installation cost
• Susceptible to cracking from ground settling, tree roots, or heavy vehicle traffic overhead
• Concrete can deteriorate from hydrogen sulfide gas produced by anaerobic decomposition
• Difficult to access for inspection and repair compared to lighter tank materials
• Not suitable for remote locations without crane access roads
• Joints between sections can leak if not properly sealed during installation

Installation Considerations

Concrete tank installation requires a crane or boom truck capable of lifting 4,000 to 10,000 pounds depending on tank size. The excavation must be sized to provide at least 12 inches of clearance on all sides for backfill. The hole bottom should be level and compacted to prevent settling. Multi-piece tanks require careful alignment and thorough joint sealing. After placement, the tank is backfilled with clean fill material compacted in lifts to prevent voids that could cause future settling. Risers should be installed at ground level for future access.

Regardless of tank material, all installations must comply with state and local code requirements for setback distances from wells, property lines, buildings, and water bodies. A licensed installer familiar with local requirements should perform or supervise all tank placement and connection work. Post-installation inspection by the permitting authority is required before the tank can be backfilled and put into service. Keep accurate records of the tank location, size, material, and installation date for future maintenance reference and potential property sale disclosure requirements.

Frequently Asked Questions

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