Septic systems are like miniature waste treatment plants. They’re most common in rural areas, where public sewer access is not readily available. Several types of septic systems are used across the country, but the most common is the septic tank/absorption field system. In this type of system, waste leaves the house through a drain and travels to the septic tank, which is buried underground. Waste stays in the tank long enough for solids to settle out as sludge and for grease and oils to float to the surface as scum. Specially designed outlets in the tank hold back sludge and scum, while allowing the relatively clear middle layer — known as effluent — to enter the drain field. Microbes in the soil digest or remove most contaminants from waste water before it reaches groundwater.

The size of the septic tank system needed depends on the size of your home and the number of people living there; a 6-bedroom home, for example, requires a much larger system than a 2-bedroom home. Because septic tank systems are tasked with moving biodegradable wastes to a place where they can naturally break down, the installation of these systems is best left to a pro. Sure, a do-it-yourselfer may save money tackling this large-scale project, but if the system fails, remediation could cost a bundle.

The cost to build a septic tank system varies widely, depending on your location. According to SepticTankGuide.com, a standard or conventional gravity system for a 3-bedroom home on a level site with good soil would likely cost from $1,500 to upward of $4,000. Getting bids from qualified local contractors is the only way to determine a true cost for your project, but this breakdown — based on a conventional gravity system for a single-family home — should provide some general financial information:

Tank

Most septic tanks are made of concrete, but you may also find them made from steel, fiberglass or polyethylene. A 1,000-gallon precast concrete tank — adequate for a 3-bedroom home — generally costs $600 to $1,000.

Drain gravel

Gravel trenches are the most common type of septic soil absorption field used in the United States. According to the Purdue University Extension Service, a typical gravel trench soil absorption field is made of a 36-inch-wide trench containing 10 to 12 inches of gravel and is installed 12 to 36 inches deep from the ground surface. The gravel in each trench holds a perforated distribution pipe in place for distribution of wastewater throughout the trench. The spaces between the rocks allow wastewater to move through the trench into the soil. Expect to pay $12 to $30 for 1 ton of drain gravel.

Pipes, risers

Piping carries waste from your house to your septic tank and then from your tank into the drain field. Costs will vary according to the size and design of the system. For reference, 100 feet of 4-inch perforated PVC piping costs $65 to $80. A septic tank riser allows above-ground access to your tank and can considerably reduce the cost of maintaining your system. Septic tank risers are commonly made from polyethylene, PVC or concrete. Concrete risers are the cheapest (approximately $100), but they’re heavy and can be difficult to install. A riser made from polyethylene or PVC will typically cost $200 or more, depending on size.

Permits

Depending on where you live and the complexity of your project, you may need a building permit. A permit may add several hundred — or even several thousand — dollars to the cost of your overall project, but it and its accompanying inspections will help ensure your tank is installed according to code.

Design and installation

A soil test (generally $100 to $400) will be necessary to determine the soil’s drainage capability, the average high groundwater mark and signs of bedrock. Understanding these soil conditions, as well as terrain, home placement and well placement will enable an experienced engineer to design a septic system appropriate for your site. A qualified septic contractor can then use those design plans to install a system that conforms to local regulations and performs efficiently and effectively.

If you need help identifying skilled septic professionals in your area, you may want to contact the National Onsite Wastewater Recycling Association; your local sanitation office may also be a good resource. Again, costs will vary greatly depending on your location and the scope of your project. Nationally, design and installation costs generally fall within the $1,500 to $4,000 range.

Maintenance matters

The Environmental Protection Agency recommends regular maintenance for septic systems or they may fail. To prevent buildup, sludge and floating scum need to be removed through periodic pumping of the septic tank. Regular inspections and pumping as necessary, generally every 3 to 5 years, are the best and cheapest ways to keep your septic system in good working order.