Precast Concrete Septic Tanks

Precast Concrete Septic Tank Solutions: The AJFoss Brand Experience

Family Values & Support from a Local Team That Cares

For moAJFoss logo stamped on septic than five decades, the family-owned and operated team at A.J. Foss has provided quality precast concrete septic tank solutions with consistent value and exceptional service. As one of New Hampshire’s first precast concrete manufacturers, we are proud that our family of loyal clients has grown to include residential and commercial neighbors throughout New Hampshire, Maine, and northern Massachusetts.

We live and work among the people we serve – who range from homeowners to professionals such as engineers, designers, general contractors, and construction managers – and we care about the success of each and every project. Our team welcomes the opportunity to apply our vast knowledge of precast concrete septic tank construction, installation and service, to solve your unique project challenges with prompt attention and consistent support.

Polylok pan poured cover into tank.Our durable, watertight, easy to install precast concrete septic tanks provide a dependable and environmentally-friendly, “green” component to your septic system. Each customizable septic tank is crafted with high-quality 5,000 psi concrete that we regularly test using ASTM C31 and C39 quality testing guidelines. Our Type III high early strength cement is tested each month to ensure that it complies with ASTM Standard C 150 and AASHTO M 85 requirements. Each tank also meets the pertinent requirements of ASTM C 1227 for concrete strength, reinforcement, size, capacity, water-tightness, and identification with the A.J. Foss logo.

We are proud to be one of the oldest members of the National Precast Concrete Association, Read on, to learn more about our process and commitment to providing you with an excellent experience.

The Role of a Septic Tank

A key component of your plumbing system, a septic tank is a single or multi-compartment holding chamber that collects wastewater (septic influent) from drains and toilets. The natural biochemical treatment of solid and liquid influent begins in the treatment chamber, and liquid sewage (effluent) is discharged to a drain field (also called a leach field or effluent dispersal area) covered by soil, below the surface of your yard.

In the tank, heavy solids settle on the bottom, while light materials such as oils, greases and fats float to the surface. Lighter solids, such as laundry lint and hair, also float near the surface.

Anaerobic Versus Aerobic Septic Systems

Anaerobic septic systems do not use oxygen to treat wastewater, so 30 to 40 percent of the treatment happens inside the tank, while 60 to 70 percent happens in the effluent dispersal area that serves as the drain field or leach field. This process requires a larger leach field footprint than aerobic systems. Anaerobic systems do not require electricity or service on mechanical components, yet the anaerobic chambers must be professionally pumped out every 3 to 4 years. This type of system typically costs less to purchase, install and maintain than an aerobic system – ranging from $6,000 to $12,000, depending on where you live.

Aerobic systems use oxygen to treat wastewater. Aerobic bacteria consume more organic solids in septic tanks than anaerobic bacteria do, so up to up to 90 percent of the treatment happens in an advanced treatment septic tank, while approximately 10 percent happens in the drain field effluent dispersal area. This process reduces the leach field size requirement by 50 percent or more, since the effluent that leaves an aerobic tank is much cleaner. Aerobic systems, such as Singulair by Norweco, require electricity and servicing of mechanical parts such as the aerator that aids aerobic digestion. This type of system typically costs more to purchase and maintain than an anaerobic system – ranging from $10,000 - $20,000 depending on where you live – but it’s a worthwhile investment for homes near water bodies or with small lots that require smaller leach fields.

Septic Tank Design and Structure

A quality septic tank is manufactured with concrete, fiberglass and steel rebar, is located underground, and ranges in size from 500 gallons for small septic systems to thousands of gallons for larger systems.

The most common septic tank size range is 1,000 to 1,500 gallons for a typical residential septic system.

A septic tank design can include a single treatment chamber, or multiple treatment chambers, depending on the system requirements. The treatment chamber has one inlet for septic influent, and the final chamber has one outlet, positioned lower than the inlet to enable the one-way flow of septic effluent out to the leach field soil treatment area.

A.J. Foss offers the option to install a plastic riser and aesthetically-pleasing dark green cover to bring the tank to grade level to create a watertight connection from the top of the tank to ground level, thus mitigating any ground water infiltration.

Below, we discuss the materials used to build quality septic chambers, and factors that influence the structural integrity of a precast concrete tank, as well as weight load designs, and the manufacturing requirements for septic tanks as mandated by the State of New Hampshire.

Materials Used to Build Quality Precast Concrete Septic Tanks

Septic tank rebarThe three main materials used to build quality precast concrete septic tanks include:

  • Concrete - 5,000 psi
  • Fibers - used for secondary reinforcement and crack control
  • Steel Reinforcing Bar (Rebar) - used to increase tensile strength. Rebar has a much higher tensile strength than concrete, so the two products complement each other when used together.

Components of Concrete

In its simplest form, concrete is a mixture of paste and aggregates, or rocks. The paste, composed of cement and water, coats the surface of the fine (small) and coarse (larger) aggregates. Through a chemical reaction called hydration, the paste hardens and gains strength to form the rock-like mass known as concrete.

The components of concrete include air, water, and four other materials: Cements , supplementary cementing materials , aggregates , and chemical ad mixtures.

Factors That Influence the Structural Integrity of Precast Concrete Products:

  • Grade of steel ( Grade 40 yields a min. 40,000 lbs. / sq. in . ; Grade 60 yields min. 60,000 lbs /sq. in. )
  • Size and spacing of steel reinforcing bar (rebar sizes #3, #4, #5 , and #6)
  • Location of steel in concrete (in the top, bottom, and walls)

Why Steel Rebar Spacing is Critical

Concrete has high compression strength, but low tensile strength. Proper integration of steel reinforcing bar (rebar) into a concrete structure improves its tensile strength, enabling it to withstand tension in areas where compression occurs the most. A structure’s design specifies where the steel rebar should be placed to improve strength and ensure that the concrete will not crack or fail. Rebar may be specified every 8 inches or every 18 inches, depending on the load design, and is typically specified the most in the bottom third of the tank cover where the tension is greatest.

Compressive Versus Tensile Strength

Steel reinforcing bar (rebar) helps concrete products withstand the load of tension (pressure). Rebar is placed where the concrete is forced to stretch or bend under load, since concrete can crack when torqued or twisted.

The compressive strength of 5,000 psi concrete means it can handle a load of 5,000 lbs. of compressive force, or squeeze, for every square inch of surface area. Concrete’s compressive strength is ten times greater than its tensile strength, however, so concrete with a compressive strength of 5,000 psi only has a tensile strength of 500 psi. It ultimately takes 10 times the weight, or force, to crush concrete than it does to pull it apart.

Cracked, inferior septic tank

This large septic tank failed because the reinforcing bar was set at 48-inches apart, instead of the optimal 8-inches on center. It’s important to know how a tank is constructed, and not simply shop for best price, as illustrated by the failure of this poorly-constructed, inexpensive tank that cost the homeowner more money, time and frustration.

H-10, HD, & H-20, and HS-20 Structural Load Designs

Precast concrete tanks designed for H-10 structural loading are for non-traffic use. They are designed for 3-ft. of earth cover plus 300 lbs. per square foot of live load. Most tanks fall into this category.

The HD versions of our tanks are for non-vehicular traffic, but are designed for 5’ of earth cover plus 300 lbs. per square foot of live load.

Often a precast concrete septic tank must be installed below a vehicular traffic area, requiring an H-20 or HS-20 traffic-rated loading. A.J. Foss manufactures precast concrete septic tanks designed to handle H-20 and HS-20 loading.

Each traffic-rated precast concrete tank is manufactured with our high-quality 5,000 psi concrete using Type III cement, as well as thicker side walls, bottom and top slabs to meet loading requirements.

Septic tanks designed to handle traffic-rated loads have thicker side walls and bottom and top slabs, and require specialized equipment to handle their additional weight.

H-20 Loading is defined by the American Association of Highway and Transportation Officials (AASHTO) as a vehicle load with an 8,000 pound front axle and one rear axle weighing 32,000 pounds representing a 16,000 pound wheel load.

HS-20 loading is defined as a vehicle load with an 8,000 pound front axle and two rear axles weighing 32,000 pounds each representing two 16,000 pound wheel loads.

For each traffic-rated precast concrete tank that A.J. Foss builds, we provide our clients with a diagram and documentation of the tank’s design and testing to verify that the structure can withstand HS-20 loading. This assures clients that our precast concrete tanks are designed and built to exact specifications, using the proper rebar size, grade, lengths, bends, and placement to ensure successful performance.

State of NH Septic Tank Manufacturing Requirements

Some of the key points specified in the State of New Hampshire’s Code of Administrative Rules are listed below. These design parameters apply to all types of septic tanks in New Hampshire, whether manufactured with precast concrete, fiberglass, or steel.

Env-Wq 1010.06 - Septic Tank Design Requirements

  • The outlet of a septic tank shall be at least 2 inches but not more than 4 inches below the inlet to the septic tank.
  • Any septic tank made of concrete shall be certified by its manufacturer or distributer as meeting or exceeding the following design strength requirements:
    • If the septic tank will not be subjected to vehicular traffic and the top of the septic tank will be 3 feet or less below finished grade, the septic tank shall be designed for a minimum live load at the surface of 300 pounds per square foot plus the weight of 3 feet of unsaturated earth;
    • If the septic tank will not be subjected to vehicular traffic and the top of the septic tank will be more than 3 feet but 6 feet or less below finished grade, the septic tank shall be designed for a minimum live load at the surface of 300 pounds per square foot plus the weight of 6 feet of unsaturated earth;
    • If the septic tank will be subjected to vehicular traffic or if the top of the septic tank will be more than 6 feet below finished grade, the septic tank shall be designed to meet AASHTO H-20 specifications or better; and
    • The minimum compressive strength for the concrete shall be 4,000 pounds per square inch at 28 days.
  • Any precast concrete septic tank shall be certified by its manufacturer or distributer as meeting the applicable requirements of ASTM C1227.
  • Any septic tank fabricated from material other than concrete shall be certified by its manufacturer or distributer as being designed for loads that are equivalent to those specified in (b)(1)-(4), above.

Env-Wq 1010.07 Inlet and Outlet Baffles

Each septic tank shall have an inlet baffle and an outlet baffle that are:

  1. Plumb and level;
  2. Solvent welded/glued and secured to the inlet pipe or outlet pipe, as applicable, using stainless steel screws; and
  3. Plastic vented tees that extend above the liquid line to not less than one inch from the interior of the top of the septic tank or cover

Not All Concrete Septic Tanks Are Created Equal

Similar to a mattress, you cannot see inside a precast concrete septic tank, so it’s critical to know how your tank is manufactured. All A.J. Foss precast concrete products conform to ASTM C31 and C39 quality testing guidelines.

Wise contractors, designers, and homeowners understand the ultimate negative impact of sacrificing quality for cost or speed, and they all benefit from the A.J. Foss team’s commitment to efficiently providing quality products at fair prices.

Comparison of Precast Concrete Septic Tank Features, Safety, and Value

High-quality 5,000 PSI ConcreteYesNo
Reinforcing Bar Built into Every Tank, Whether or Not it is H-20 RatedYesNo or Not Always
Traffic Rated H-20 Tanks Include Engineered DrawingsYesNo or Optional
Reinforcing Fiber Built into Every TankYesNot Always
Same or Next Day DeliveryYesNo
1-hour Delivery WindowYesNo
Advanced Treatment Unit (ATU) Supplied Norweco UnitsYesNo
In Stock Tank SelectionYesNot in Busy Season
Optional Built-in Plastic Risers (A.J. Foss was First in NH to offer this)YesSometimes
Compliant with ASTM C-1237YesNo
Follows NPCA’S Best Practices Manual for Quality Concrete ManufacturingYesNo


Differences Between Monolithic and Mid-Seam Tanks

Monolithic precast concrete septic tank.

Monolithic precast concrete septic tank

A monolithic precast concrete tank is built with the sides and bottom poured as one U-shaped piece, and a cover is added to the top. The tank cover can be manufactured with a lip to help it stay fastened to the top of the tank. A.J. Foss is one of the few manufacturers that offers a lipped cover.

Also called a top seam tank, a monolithic tank is ideal for high water table locations because the joint (or seam) that connects the two pieces together is at the very top of the structure, where the water table typically doesn’t reach. If for any reason the tank is not completely watertight, the water level will not get high enough to cause water to leak into or out of the tank. Depending on the tank-size, the water level inside the tank is usually around 12 inches below the top of the tank.

Mid-seam precast concrete septic tank

Mid-seam precast concrete septic tank

A mid-seam precast concrete tank is designed with a joint (or seam) in the middle. The top and sides are poured in one u-shaped piece, and the bottom and sides are poured in another u-shaped piece. This allows for optimal distribution of tension and weight throughout the tank.

On a mid-seam tank, the water level can reach the middle seam, and if it is not watertight, water can leak into or out of the tank if it is not properly sealed according to NPCA Best Practice Guidelines. Tanks designed for larger than 2,000 gallons are usually casted in multiple pieces designed to be stacked and sealed together with a butyl product to create a watertight seam.

The Benefits of Precast Concrete Septic Tanks

Why Contractors and Septic System Designers Choose A.J. Foss Precast Concrete Septic Tanks

For more than five decades, A.J. Foss has been known as The Signature of Quality Precast because we consistently manufacture, install, and service quality precast concrete products at fair prices.

We are proud to be one of the oldest members of the National Precast Concrete Association,

12 Reasons Why Contractors & Septic System Designers Choose A.J. Foss Precast Concrete Septic Tanks

Easy Access to Drawings
All product drawings are maintained in Autocad or PDF format, for ease of reference.

In-Stock, Ready to Install Products
In-stock products eliminates wait times, once the contractor is ready to install.

Several Traffic Rated Tank Loading Types
Enables designers to specify H-10, Heavy Duty (car or truck), or H-20 loading

Large Selection of Sizes
Choose from single compartment, two- and three-compartment tanks, in-stock and ready for delivery

We can Pre-package the Pumps that Designers Specify for Contractors
We pride ourselves on our ability to support designers in specifying the appropriate pump and accessories for their projects. We can also do rail systems, which are a cost-effective method versus engaging a third-party, post-installation, to try to install a rail system.

We Offer Built-in Plastic Risers to Keep the Septic Tank Watertight From the Top Down
You can have a lot of infiltration through the concrete covers because they can’t be watertight. This is the reason to specify your tank with plastic built-in and A.J. Foss was the first to offer it to our customers

We Offer an In-stock ATU (Advanced Treatment Unit) for Use with the Norweco Singulair System
To accommodate small lots, waterfront properties, and nitrogen-reduction areas, A.J. Foss offers NSF 40 & 245 certified in-stock Advanced Treatment Units (ATUs) at very competitive prices. For example, a system for a 4-bedroom home would cost approximately $6,100. This includes the pre-treatment and treatment all in one tank, up to 5 bedrooms, then just a small tank in front as you go to 6-8 bedrooms.  Norweco Article

Flexibility of Design
We provide flexibility of design, enabling designers to plan for effluent leaving the tank from the side or end of the tank (3 inlets, 3 outlets)

Ease of Service
We provide 24-inch diameter access points for servicing or pumping of the tank

We Supply a “Guide for Caring for Your Septic System”
With every tank we sell, we strive to educate homeowners on how their system works, and best practices for increasing its life. This EPA-produced guide is a great starting point.

We Install Tanks in One Piece, Up to 1750 Gallons
Our one-piece installation takes half of the time it would take to install in two pieces. The tank is assembled at the plant prior to delivery, which eliminates the need to place the bottom piece of the tank into the ground, then seal the seam (joint) with butyl rubber, then set the top piece on top of it. This saves valuable time for contractors, by eliminating the wait for the required 50% compression of the joint before backfilling the tank.

Our Famous One Hour Delivery Window
Choose your delivery time – same day or next – and we will work to be there within the one-hour delivery window, to keep your project moving forward.

Large In-Stock Selection of Precast Concrete Septic Tanks

A.J. Foss is your go-to resource for precast concrete septic tanks, with 20 acres of in-stock products ready for rapid delivery throughout New Hampshire, Maine and northern Massachusetts. We offer the area’s largest selection of in-stock residential septic tanks up to 3,500 gallons, and can often deliver on the same day you order – with our renowned one-hour delivery window – to support your project sequencing and maximize your productivity.

Popular Precast Septic Tank Sizes & Features

Our non-traffic rated precast concrete septic tank sizes range from to 300 to 3,500 gallons. Our traffic-rated precast concrete septic tank sizes range from 600 to 8,000 gallons. Choose from Single CompartmentTwo Compartment, and Three Compartment tanks. Custom tanks are also available.

Click here for our Quick Reference Precast Tank Dimension Guide.

Top 13 Precast Concrete Septic Tank Sizes and Features

A.J. Foss Delivers Know-How With Each Product

We pride ourselves on providing clients with detailed information about the design, installation and care of our A.J. Foss-crafted precast concrete septic tank.

With every delivery, we supply clients with a colored folder that includes:

  • diagram of their new precast concrete septic tank, including the size, structural load design (H-10, H-20, or HS-20) and the access-cover size and its location on the tank. These details are important for the long term, so if the tank ever needs to be pumped out or if a pump inside the tank ever fails, that information will help to streamline servicing and maintenance.
  • Septic Smart brochure - A homeowner’s guide to use and care of their septic system.
  • Information about the benefits of concrete, and our A.J. Foss contact information for reference.

Clients can also be assured that we maintain internal records for each size of traffic-rated tank that we sell, including in-depth drawings that detail rebar placement, calculated stress loads, and more.

Support for Contractors and Designers

Septic Tank Sizing Tools for Builders, Designers and Contractors
To ensure that builders, designers, and contractors specify the proper tank size and install to the proper dimensions, we provide these professionals with our proprietary in-house designed A.J. Foss Septic Tank Size Guide. This valuable tool enables a user to slide up or down on the size-chart to locate the values that correspond to a particular A.J. Foss tank size. This weather-resistant chart is designed to be easy for contractors to leave in their trucks and equipment, so when they need to dig a hole, there is easy access to the dimension chart.

A.J. Foss also supports design professionals by providing these tools for all precast products:

  • A USB drive that contains the product’s drawing files in AutoCAD and PDF formats
  • A Pump Station package that details system dimensions, features, control panel and components (for multi-compartment tanks as well) See an example
Concrete Septic Tank Components, Add-ons and Accessories