Cost to Install a Septic System in St. Louis [2025 Data]
Septic system installation costs between $7,055 and $17,187 in St. Louis, Missouri, with an average of $12,121. Your septic pro will consider the system type, size, and location for a personalized quote.
Missouri’s high prevalence of clay soil and risk of groundwater contamination can increase the costs of this project.
Many St. Louis properties need an alternative or advanced septic system to combat these issues.
Contractors are licensed by the state, and permits are granted by the county.
You need to disclose known septic issues prior to selling your home, which can impact its value.
The cost to install a septic system in St. Louis, Missouri, is $12,121, with most homeowners spending between $7,055 and $17,187. St. Louis is home to some of the oldest sewers in the country, and most properties located in the city center and inner suburbs use them. As you travel further out into St. Louis County, you’ll start finding more and more septic systems.
Before taking on a septic system project and planning out your budget, review the major cost factors.
Septic System Installation Cost Factors
Septic system installation in St. Louis is unique because many properties have difficult clay soil that doesn’t have sufficient absorption. Because of the gravel and fractured bedrock, the area is particularly susceptible to groundwater contamination, which can require costly advanced treatment systems. A local septic tank pro can help you navigate these intricacies, but here are some significant factors that impact the price.
Tank Size
St. Louis regulates septic tank size based on the number of bedrooms in your home. The minimum tank size in Missouri is around 1,000 gallons for a residence, but it varies from county to county. A 1,000-gallon septic tank costs $900 to $2,100 for the tank alone.
While small septic systems cost the least, larger houses require larger systems because they have more sinks, toilets, bathtubs, and other wastewater sources that flow into the septic tank. As tank size increases, so do costs.
| Tank Size (Gallons) | Number of Bedrooms | Average Cost (Tank Only) |
|---|---|---|
| 1,000 | 1–3 | $900–$2,100 |
| 1,250 | 4 | $1,000–$2,500 |
| 1,500 | 5 | $1,500–$3,000 |
| 2,000 | 6+ | $2,500–$5,000 |
Materials
Septic tanks are commonly made of plastic, concrete, or fiberglass, with fiberglass being the most expensive. Here’s how much a tank costs based on each material.
| Material | Average Cost (Tank Only) | Pros | Cons |
|---|---|---|---|
| Concrete | $700–$4,000 | The most common type in St. Louis, highly durable | Prone to cracks, precast versions are not watertight |
| Plastic | $1,000–$3,200 | Lightweight and easy to install, budget-friendly | Least durable |
| Fiberglass | $1,500–$5,000 | Easy to install, resists cracking and algae growth | Most expensive |
Type of Septic System
There are two main types of septic systems. Each comes with its own set of pros and cons. While anaerobic systems are relatively low-maintenance, they aren’t great for small properties and may not be an option if you live in an area of St. Louis County that’s vulnerable to groundwater contamination. Anaerobic systems can do well in small spaces but require extra work.
| Anaerobic | Aerobic |
|---|---|
| Anaerobic bacteria break down waste | Aerobic bacteria break down waste |
| More affordable | More expensive |
| Uses fewer chemicals | More efficient |
| Needs a larger leach field | Good for smaller properties |
Anaerobic: Anaerobic systems are more common and cost $3,000–$8,000. They’re less costly than aerobic systems and don’t need extra power or chemicals, but they’re less efficient and require a larger leach field. A pipe runs from the house to the septic tank, where another pipe runs into the leach field. Anaerobic bacteria break down solid waste before the system distributes the wastewater into the soil.
Aerobic: Aerobic septic systems utilize oxygen pumped into the tank to activate bacteria that feed on the solid waste. They’re more expensive at $10,000–$20,000 and require electricity to run, but they’re more efficient and work well on smaller properties.
Alternative or Advanced Systems: If you’re battling high water tables, challenging soil conditions, and groundwater vulnerabilities, you may need to install an alternative or advanced septic system that incorporates a pretreatment solution—like an aerobic treatment unit (ATU) or recirculating media filter (RMF). Mound septic systems are one of the most popular ways to combat clay soil. Alternative systems cost $7,000 to $20,000, depending on the build.
Site Prep
With the prevalence of clay soil and potential groundwater contamination from limestone deposits, you’ll need to do specific site prep before your septic tank installation. This includes surveying the land and testing the soil before designing and installing the drain field.
Land Survey: You’ll need to get a land survey before installing a septic system to ensure your plans fall within property lines and aren’t too close to buildings, bodies of water, and other obstructions that could cause issues. Expect to spend $330–$900 to hire a licensed land surveyor.
Percolation Test: Before the installation, you need a local perc test pro to perform a percolation test. The test measures water drainage in the soil, soil type, and the height of each sediment layer on your property to determine the best type of septic system for you. The cost to test your soil is $700–$2,000.
Leach Field Installation: Septic tank systems consist of a septic tank and a trench referred to as a leach field or drain field. This section of the system transports the wastewater back to the soil. Drain field installation costs $5,000–$12,000.
Septic System Installation Pro Costs
In St. Louis, septic system contractors are licensed by the state, and permits are obtained through the county. Labor is a significant cost that rises with more complicated installations.
Labor
Labor accounts for 50% to 60% of the total cost of your septic tank installation. You’ll need to hire a licensed septic installer in St. Louis, Missouri—this is not a DIY project. The Missouri Department of Health and Senior Services (DHSS) regulates these licenses.
Permits
You’ll need a permit from St. Louis County Transportation and Public Works to install a septic system, which costs a minimum of $274 and includes:
Permit processing and plan review fee: $86
Inspections (up to four): $188
Additional inspections cost $47 each.
Does a Septic System Increase Home Value?
A working septic system doesn’t have a positive impact on your home value. That said, your septic system can decrease your home’s value if it’s damaged, at the end of its lifespan, or doesn’t meet state requirements.
Missouri requires you to disclose septic and plumbing issues when selling your home, so it’s a good idea to call a pro to fix your septic issues or replace your system before putting your home on the market.
Pumping your septic tank every three to five years is one of the most important septic maintenance tasks. When you combine that with flushing only approved items (toilet paper and waste) and avoiding driving over your drain field, you have a recipe for a long-lasting septic system.
How Angi Gets Its Cost Data
Home is the most important place on earth, which is why Angi has helped more than 150 million homeowners transform their houses into homes they adore. To help homeowners with their next project, Angi provides readers with the most accurate cost data and upholds strict editorial standards. We survey real Angi customers about their project costs to develop the pricing data you see, so you can make the best decisions for you and your home. We pair this data with research from reputable sources, including the U.S. Bureau of Labor Statistics, academic journals, market studies, and interviews with industry experts—all to ensure our prices reflect real-world projects.
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