Septic Companies and Contractors in St. Louis, MO

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Where does septic actually start in the St. Louis metro?

The sewer district says where the line is. The Metropolitan St. Louis Sewer District describes its service area as all of St. Louis City and 90 percent of St. Louis County, with Highway 109 as the general western boundary and the Missouri, Mississippi and Meramec rivers as the others. East of that line you are almost certainly on a public sewer. West and south of it, through the Meramec valley and Wildwood, Glencoe, Grover, Pond and Melrose, and across the collar counties, homes treat their own sewage.

The highway is only a rough line. The rule that decides your property is a distance. St. Louis County code says a sanitary sewer is available when a sewer line sits within 200 feet of any part of the property, and where it is available the building connects to it. So a parcel west of 109 is not automatically septic ground, and a house that has been on septic for 40 years can lose the right to stay there when a main is extended past the lot.

Pockets break the pattern. Eureka sits inside the western unsewered area and is not septic ground at all: the city states that Missouri American Water provides its water and sewer service. Going the other way, MSD publishes what connecting costs, $1,126.00 for a single-family residence plus a $75.00 connection permit, and a possible $300.00 tap fee where no wye exists, and says the permit to abandon the old septic system comes from the county, not from MSD.

MSD defines its service area as all of St. Louis City and 90 percent of St. Louis County, with Highway 109 as its general western boundary and the Missouri, Mississippi and Meramec rivers as the others. Source: Metropolitan St. Louis Sewer District (MSD Project Clear), Glossary, Service Area, read 2026-08-27.

A sanitary sewer is deemed available when a sanitary sewer line is within 200 feet of any part of the property, and every building with plumbing fixtures must connect to a public sewer where one is available. Source: St. Louis County Revised Ordinances, Chapter 610, Section 610.080, read 2026-08-27.

The county Plumbing Code repeats the 200-foot rule from the septic side and adds that the Code Official shall require connection where a public sanitary sewerage system is legally and economically available. Source: St. Louis County Revised Ordinances, Chapter 1103, adopted Uniform Plumbing Code Chapter 22, Section 22.1.3, read 2026-08-27.

Eureka is inside the western unsewered pocket but is not on septic. Missouri American Water provides the city's water and sewer service. Source: City of Eureka, Missouri, Utility Information, read 2026-08-27.

MSD publishes its connection costs: a $1,126.00 connection fee for a single-family residence, a $75.00 connection permit, and a possible $300.00 tap fee where no wye exists. The septic abandonment permit comes from the city or county, and where no sewer is adjacent the owner pays to extend it. Source: MSD Project Clear, Customer FAQ, How do I connect my house to the public sewer?, read 2026-08-27.

Who issues the septic permit where I live?

Not one office, and not one kind of office. The state health department states the rule: in most Missouri counties the local health department issues onsite wastewater construction permits, and in the rest it is another agency, such as a sewer district, building department, or planning and zoning department. In this metro the state's own county lookup puts all six counties under authority type Ordinance, each with its own onsite wastewater ordinance and the state's note that it may go past the state minimum. Only some of the six are health departments. The rest are a building department, a code enforcement office and a community development division, which is why assuming the health department wastes a week.

The state permit rule is not absolute, and this is the part most pages get wrong. Missouri requires a construction permit before a new system, a major modification or a major repair, but the statute opens with an exception. The owner of a single-family residence lot of three acres or more, or of a residential lot of 10 acres or more that meets a separation and density test, is excluded from sections 701.025 to 701.059 and the rules under them. The conditions are strict: every point of the system more than 10 feet off any adjoining property line, no effluent leaving the property, no contamination of surface water or groundwater, no nuisance. The exclusion does not reach lots next to a lake operated by the Corps of Engineers or by a public utility. And it does not free you from your county, which can require a permit under its own ordinance regardless. All six counties here do. Treat the exclusion as a state-law question to raise with your permit office, not as a reason to skip the office.

City limits can change the answer too. Some incorporated areas inside an ordinance county fall outside the county's permit authority and go back to the state. Wildwood, the metro's main septic city, is not one of them: the city runs first with its own Zoning Authorization, which for new construction in the NU Non-Urban Residence District wants a percolation test and the septic field drawn on the plot plan inside the clearing limits, and then St. Louis County issues the permit, under a contract by which the county also does the building inspections. Wildwood's own planning department describes the standard as complying with State and St. Louis County regulations.

St. Louis County, MO: the state names the county Plumbing Department and the county Department of Public Health, and the county's plumbing code puts enforcement in the Office of Plumbing and Sewer Inspection, inside Public Works, not the health department. The septic rules sit in the county Plumbing Code, and the installer needs a county master drainlayer license on top of state registration.
St. Charles County, MO: Community Development, Building and Code Enforcement Division. A minimum of three acres is required for a new system, new lagoons are not allowed, and a property on a private system cannot transfer until a county-licensed inspector has passed it.
Jefferson County, MO: Code Enforcement in Hillsboro, again not a health department. The county licenses the soil evaluator, designer and installer itself, each license carrying a $25,000 bond and liability insurance.
Franklin County, MO: the Building Department in Union. The county's onsite sewage ordinance was replaced effective October 1, 2025, and no fee schedule is published online.
Lincoln County, MO: the county Health Department in Troy. A public sewer within 300 feet is grounds for denial, and there are no county building permits outside city limits, so the septic permit carries the build.
Warren County, MO: the Environmental Health Office at the county health department in Warrenton, where the Sanitarian runs the process. The permanent electric sticker is released only after the system passes final inspection. The permit is $200.00 and expires in one year.

In most Missouri counties the local health department issues onsite wastewater construction permits, and in the rest the authority is another agency such as a sewer district, building department, or planning and zoning department. Where authority rests on a local ordinance, the regulation can be more restrictive than the state standard. Source: Missouri Department of Health and Senior Services, Onsite Wastewater Treatment, read 2026-08-27.

The Missouri DHSS county permit authority lookup lists every one of the six St. Louis metro counties under authority type Ordinance, each carrying the note that the county has its own onsite wastewater ordinance and may have additional requirements beyond the state minimum construction standards. The agencies it names are the St Louis County Plumbing Dept. and the St Louis County Department of Public Health, St Charles Community Development Building and Code Enforcement Division, Jefferson County Code Enforcement at 725 Maple St, Hillsboro, the Franklin County Building Dept. at 400 E. Locust St, Union, the Lincoln County Health Dept. at #5 Health Department Dr, Troy, and the Warren County Environmental Health Office (Health Dept.) at 105 S Market Street, Warrenton. Source: Missouri Department of Health and Senior Services, OWTS Construction Permit Required, county lookup, read 2026-08-27.

St. Louis County's own plumbing code puts septic enforcement in the Office of Plumbing and Sewer Inspection, which sits inside the Department of Public Works. Source: St. Louis County Revised Ordinances, Section 1103.P-122, read 2026-08-27.

An installer in St. Louis County must hold both a Missouri DHSS registration for private sewage systems and a county master drainlayer license, and permits are issued only to bonded and insured licensed masters. Source: St. Louis County Revised Ordinances, Sections 1103.P-148(2) and 1103.P-126, read 2026-08-27.

St. Charles County requires a minimum of three acres for a new onsite system and does not allow new lagoons. It also requires a compliance inspection before a property served by a private sewage system transfers, by an inspector holding the county's own Onsite Wastewater Treatment System Inspector Business License. Source: St. Charles County, Onsite Wastewater Treatment Systems FAQ, with the change-of-ownership inspection in the 2021 Private Sewage Disposal Code amendments, read 2026-08-26.

Jefferson County issues its own onsite soil evaluator, designer and installer licenses on top of Missouri registration, each requiring a $25,000 bond with the county as obligee and liability insurance naming the county. Source: Jefferson County, license registration packets, read 2026-08-26.

Franklin County's onsite sewage ordinance was adopted and amended September 23, 2025 with an effective date of October 1, 2025, and the Building Department publishes no fee schedule online. Source: Franklin County Building Department, read 2026-08-26.

Lincoln County denies a construction permit where a public sewer is available within 300 feet, and the county issues no building permits outside city limits. Source: Lincoln County Health Department onsite application packet, and Lincoln County Planning and Zoning, read 2026-08-26.

In Warren County the permanent electric sticker is released only after the septic system passes final inspection by the Sanitarian. The septic permit fee is $200.00, the permit is not issued the same day, and it expires one year from issuance. Source: Warren County Sanitarian, On-Site Sewage System Installation/Major Repair Steps, Rev 02/25, and Warren County Schedule of Fees effective February 3, 2026, read 2026-08-27.

Except as provided in section 701.031, no person may construct or make a major modification or major repair to an onsite sewage disposal system without first notifying the city, county or department, completing the application, paying the fee that city, county or department has set, and obtaining a construction permit. Source: Section 701.046, Revised Statutes of Missouri, read 2026-08-26.

The owner of a single-family residence lot of three acres or more, or of a residential lot of 10 acres or more with no single-family residence onsite sewage disposal system within 360 feet of any other and no more than one single-family residence per 10 acres in the aggregate, is excluded from sections 701.025 to 701.059 and the rules made under them, including the provisions on construction, operation, major modification and major repair. The exclusion does not reach lots adjacent to lakes operated by the Corps of Engineers or by a public utility, and it applies only when all points of the system sit more than 10 feet from any adjoining property line and no effluent enters an adjoining property, contaminates surface water or groundwater, or creates a nuisance as determined by a readily available scientific method. Source: Section 701.031, Revised Statutes of Missouri, read 2026-08-26.

Some incorporated areas inside an ordinance county fall outside the county's permit authority, and the permit process returns to Missouri DHSS. Source: Missouri Department of Health and Senior Services, OWTS Construction Permit Required, read 2026-08-27.

Wildwood issues the Zoning Authorization first, and its submittal requirements for new construction in the NU Non-Urban Residence District include five copies of a percolation test and the septic field drawn on the plot plan inside the clearing limits. The city has contracted with St. Louis County to issue building permits and perform building inspections, and four stamped copies go to the county once the city has issued the zoning authorization. Source: City of Wildwood, Zoning Authorization Guidelines, New Construction WITHIN the NU (Non-Urban Residence District), and City of Wildwood Inspections page, read 2026-08-27.

Wildwood's own Department of Planning describes the wastewater standard on an unsewered lot as complying with State and St. Louis County regulations, and asks for a soil morphology report from a qualified soil scientist plus an engineered design where the soils percolate poorly. Source: City of Wildwood Department of Planning, Determination of Issues and Findings of Facts, Board of Adjustment Case B.A. #33-22, public hearing of November 17, 2022, read 2026-08-27.

Wildwood requires packaged wastewater treatment plants in large-lot single-family subdivisions in areas not served by public sanitary sewers, and a developer must seek a waiver to use individual household systems instead. Wildwood issues its own zoning authorizations for septic systems, one of which appears in the city's March 2026 development report. Source: City of Wildwood, Missouri, Department of Planning report to the City Council, Recent Development Trends within the City of Wildwood, March 25, 2026, read 2026-08-27.

What makes St. Louis County, MO different from every collar county?

One rule rewrites the design. St. Louis County requires that all water-carried sanitary sewage pass through an approved mechanical sewage treatment plant before it is discharged into the soil, and it defines an individual system as that plant discharging into an approved subsurface field. The plain septic tank feeding a gravity absorption trench field, which is what the state rule is built around, is not this county's standard design. The full plant specification, the NSF standard it has to meet, the sizing rule and the access depth are set out on the aerator and pump replacement page and in the St. Louis County record.

Two consequences a homeowner feels. The unit has a motor, so a St. Louis County system carries an aerator and a pump, and with them a wear-out and service need a gravity tank-and-field system does not have at all. And the county publishes the permit cost: a minimum of $284.00, covering plan review, processing and up to four inspections. Minimum lot size is 20,000 square feet on public water, 30,000 without.

The ground is why the code reads this way. Western St. Louis County is Mississippian limestone under loess, till and residuum, exposed mainly in the river bluffs, and the county code carries sinkhole setbacks and a ban on discharging into a sinkhole or rock crevice: 50 feet from the edge of a surficial sinkhole to a sewage tank, 100 feet to the disposal area, and no discharge into any crevice or opening in rock. The state geological survey gives the reason. Sinkholes often serve as direct conduits for surface water into the aquifer underneath.

All water-carried sanitary sewage in St. Louis County shall pass through an approved mechanical sanitary sewage treatment plant prior to discharge into the soil, and an individual system consists of that plant discharging into an approved subsurface disposal field. Source: St. Louis County Revised Ordinances, Chapter 1103, adopted Uniform Plumbing Code Chapter 22, Sections 22.1.7 and 22.3.4, read 2026-08-27.

The state minimum construction standards build around the absorption trench, requiring at least one foot of vertical separation between the bottom of a trench and the limiting layer or seasonal high water table for standard systems, and four feet to groundwater or bedrock in highly permeable soils and in cherty clay soils in areas of severe geological limitations. Source: 19 CSR 20-3.060(5)(A)2., Missouri Code of State Regulations, read 2026-08-26.

The minimum fee to install a septic system in St. Louis County is $284.00, made up of a $96.00 permit processing and plan review fee plus $188.00 for up to four inspections. Each additional inspection is $47.00. Source: St. Louis County Revised Ordinances, Chapter 1100, Section 1100.200 and Table 1100.200, read 2026-08-27.

Minimum lot size for an individual system is 20,000 square feet where the premises are served by a public water main, and 30,000 square feet where they are not. Source: St. Louis County Revised Ordinances, Chapter 1103, adopted UPC Chapter 22, Section 22.4.1, read 2026-08-27.

Setbacks from the edge of a surficial sinkhole are 50 feet for the sewage tank and 100 feet for the disposal area, tanks and absorption systems should never be located in the drainage area of a sinkhole, and the code forbids discharging sewage into any crevice, sinkhole or other opening in a rock formation. Source: St. Louis County Revised Ordinances, Chapter 1103, adopted UPC Chapter 22, Table 22.4.3 with note 4, and Section 22.1.5, read 2026-08-27.

Bedrock under the St. Louis area is Mississippian limestone beneath Quaternary loess, glacial till, residuum and fluvial deposits, exposed mainly in river bluffs, road cuts and quarries. Source: U.S. Geological Survey Map I-2533, Bedrock Geologic Map of the St. Louis 30' x 60' Quadrangle, Missouri and Illinois, read 2026-08-27.

Sinkholes often serve as direct conduits for rapid surface water infiltration into the underlying groundwater aquifer, and contaminants near or at the surface can quickly enter the aquifer and pollute drinking water. Source: Missouri Department of Natural Resources, Missouri Geological Survey, Sinkholes, read 2026-08-27.

What kind of work do septic contractors in this metro actually do?

The work splits along the same line as the geography. In St. Louis County the code requires a mechanical treatment plant, so the machine itself is part of the job: aerator and pump replacement, service and inspection. In the collar counties it is more often a tank feeding a field, so the calls are tank replacement, drainfield replacement and pumping. New installation runs the same sequence everywhere: soil evaluation, then a design the soil can take, then the permit, then machines.

New septic system installation, on a lot that has never had one.
Septic tank replacement, for a rusted steel tank, a crumbling lid or collapsed baffles.
Drainfield replacement, when the field is failing rather than the tank.
Septic repair, where the classification decides everything: replacing the tank or building a new absorption field is a major repair under state law, which normally means a permit, subject to the large-lot exclusion in section 701.031 and to your county's own ordinance. The septic tank replacement page carries that rule in full.
Aerator and pump replacement, the St. Louis County specialty, because the county's required plant is a mechanical one and runs on a motor.
Septic inspection, including the compliance inspection St. Charles County requires from a county-licensed inspector before a private-system property transfers.
Septic design and soil evaluation, the step that decides what the county approves.
Septic tank pumping, the routine maintenance work.
A maintenance contract. The maintenance page carries the ongoing obligation, what a contract holds, and what happens when the property changes hands.

Missouri defines a major modification or major repair as redesigning and altering an onsite sewage system by relocating the system or a part of it, replacing the septic tank, or constructing a new absorption field. That definition is what pulls a tank replacement or a new lateral field into permitted work. Source: Section 701.025(6), Revised Statutes of Missouri, read 2026-08-26.

What should I have ready before I call?

Eight answers, and they are the difference between a useful first call and a second one.

Your county, and whether the address is inside a city limit. In Wildwood that means two offices: the city's Zoning Authorization first, then the county permit.
Whether a sanitary sewer runs within 200 feet of any part of the lot. In St. Louis County that makes it a connection, not a system.
The bedroom count. A system is sized by bedrooms, at 120 gallons per day each in St. Louis County, not by square footage.
Lot size, and whether you are on public water. In St. Louis County that pair sets the 20,000 or 30,000 square foot minimum.
Whether a soil evaluation has been done, and by whom. Warren County wants one from a soil scientist meeting state requirements before anything else moves.
Any paperwork on the existing system: the original permit, the as-built drawing, the last pumping date.
In Warren County, what the counter asks for: a recorded warranty deed if you bought within six months, a 911 address assignment, and photo ID.
Machine access. Where a truck can reach, how far the tank sits from the house, what is in the way.

Design flow for a single-family dwelling in St. Louis County is 120 gallons per day per bedroom, and the plant is sized by an engineer at no less than that or 1,000 gallons, whichever is greater. Source: St. Louis County Revised Ordinances, Chapter 1103, adopted UPC Chapter 22, Table 22.3.7 and Section 22.9.3, read 2026-08-27.

Warren County requires a soil evaluation by a soil scientist meeting Missouri DHSS requirements before anything else, and the permit application asks for the request form, a recorded warranty deed if the property was bought within the last six months, a 911 address assignment, the soil evaluation and photo ID. Source: Warren County Sanitarian, On-Site Sewage System Installation/Major Repair Steps, Rev 02/25, read 2026-08-27.

How does a request on this page reach a contractor, and what should I ask?

You call or send the form, and the request goes to an independent local septic contractor who works your county. This site explains Missouri septic permitting and routes requests to the people who do the work. It does not perform septic work, and it does not check any individual contractor's credentials, so it will never tell you that one has been checked.

Check them yourself instead. This is the list for the whole site: the service pages send you here for it, and every question below has a rule behind it.

Are you registered with Missouri DHSS to install onsite sewage systems? The state requires it of any person installing them, at a basic or an advanced level depending on the system.
May I see the registration identification card? That, or a call to the Onsite Wastewater Treatment Program on (573) 751-6095, is the check. The state's online list is filterable by county, but being on it is optional and the state says it is not all inclusive, so absence from the list proves nothing either way.
Was that registration issued by a county? A county registration under sections 701.053 to 701.055 counts as a state registration and is valid anywhere in Missouri.
In St. Louis County: are you a master drainlayer? The county requires that license on top of state registration and issues permits only to bonded and insured licensed masters. The county's homeowner permit covers small interior plumbing only, so it will not carry a septic installation.
In Jefferson County: do you hold the county's own installer, designer or soil evaluator license? Each one carries a $25,000 bond with the county as obligee and liability insurance naming the county.
In Warren County: are you a county registered installer? Anyone paid for any part of the installation has to be.
Who pulls the permit, and from which office? Name the office back to them from the list above.
Who does the soil work? A percolation test is for an engineer, sanitarian, registered geologist, soil scientist or a department-certified person. A soil morphology evaluation is for a soil scientist, unless the others have special training and field experience.

Any person installing onsite sewage disposal systems shall be registered to do so by the Missouri Department of Health and Senior Services, at a basic or an advanced level depending on the system. That requirement sits in the same statute as the large-lot exclusion. Source: Section 701.031, Revised Statutes of Missouri, and Missouri DHSS, Onsite Wastewater Treatment, read 2026-08-26.

The state publishes a county-filterable list of registered onsite wastewater installers. Being listed is optional and the state says the list is not all inclusive. To check an installer who is not on it, ask to see the registration identification card or call the Onsite Wastewater Treatment Program on (573) 751-6095. Source: Missouri DHSS, registered OWTS installers list, read 2026-08-26.

A person may not represent himself as a registered onsite sewage disposal system contractor in Missouri unless registered by a county or the department, and a registration issued by a county in compliance with sections 701.053 to 701.055 counts as a state registration and is valid in all political subdivisions of the state. Source: Section 701.053, Revised Statutes of Missouri, read 2026-08-26.

St. Louis County requires an installer to hold Missouri DHSS registration and a county master drainlayer license, and the county's homeowner permit is limited to small interior plumbing work, so it does not cover a septic installation. Source: St. Louis County Revised Ordinances, Sections 1103.P-148(2) and 1103.P-130, read 2026-08-27.

In Warren County, if any person is paid for any portion of installing the system, they must be a Warren County registered installer. Source: Warren County Sanitarian, On-Site Sewage System Installation/Major Repair Steps, Rev 02/25, read 2026-08-27.

Percolation tests are to be conducted by an engineer, sanitarian, registered geologist, soil scientist, or a person trained and certified by the department. A soil morphology evaluation is to be conducted by a soil scientist, unless an engineer, registered geologist or sanitarian has had special training and field experience. Source: 19 CSR 20-3.060(2)(D)1. and 2., Missouri Code of State Regulations, read 2026-08-26.

The work, page by page

Towns covered in depth

Wentzville, MO St. Charles County
Warrenton, MO Warren County
Wright City, MO Warren County
House Springs, MO Jefferson County
De Soto, MO Jefferson County
High Ridge, MO Jefferson County
Wildwood, MO St. Louis County
Washington, MO Franklin County

Need the job done, not just the rule explained