FAQs • St Charles County, MO • CivicEngage

Who can design the Onsite Wastewater Treatment System (OWTS)?: System options are determined by a soil morphology evaluation conducted by an approved soil evaluator (view a list of approved soil evaluators). Alternative systems must be designed by a profession engineer licensed in the State of Missouri. Conventional systems are often designed in accordance with Private Sewage Disposal Code of St. Charles County by OWTS installers licensed with St. Charles County.

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Community Development - Onsite Wastewater Treatment Systems (OWTS)

1. Is an Onsite Wastewater Treatment System (OWTS) a “septic” system?: A septic system was the primary system used for years to treat sanitary sewage. In the past 30-40 years, many new options for treatment of sewage were developed and allow for systems to be located in difficult areas and smaller locations. Septic systems are a type of OWTS, but they are no longer used.

2. When is a permit required for an OWTS in St. Charles County?: A permit is required for the installation, modification, alteration, addition to, or repair of any OWTS that treats 3,000 gallons or less of waste per day.

3. How do you determine the gallons per day of treatment?: St. Charles County utilizes the State of Missouri Department of Health and Senior Services “Green Book” for determining flow rates for sewage (specifically Table 4).

4. Can I install a lagoon?: No. St. Charles County does not allow for the installation of new lagoons.

5. Can I discharge sewage to a ditch or other location?: No. St. Charles County does not allow the surfacing of sewage regardless of property ownership.

6. Can I install a Low-Pressure Pipe (LPP) system?: Yes. Provided the site and the soil allow, St. Charles County allows all types of conventional and alternative systems (other than lagoons and wetlands) including gravel and pipe, gravelless, EPS gravelless, chamber, dosing, sand filter, peat/bio filter, mound, and subsurface drip distribution (SDD).

7. Can I install my own OWTS?: Maybe. Determining whether you can install a system depends on many factors. First, alternative systems, as determined by soil morphology, must be designed by a professional engineer and installed by a licensed OWTS installer. Soils suitable for a conventional system, as determined by soil morphology, may be installed by an owner/occupant of a residential property provided a level of competency is present (determined by testing or interviewing as necessary) and at the sole discretion of the Building Official.

8. Who can design the Onsite Wastewater Treatment System (OWTS)?: System options are determined by a soil morphology evaluation conducted by an approved soil evaluator (view a list of approved soil evaluators). Alternative systems must be designed by a profession engineer licensed in the State of Missouri. Conventional systems are often designed in accordance with Private Sewage Disposal Code of St. Charles County by OWTS installers licensed with St. Charles County.

9. How much property is required to install an Onsite Wastewater Treatment System (OWTS) (often referred to as a “septic” system)?: A minimum of 3 acres is required for the installation of a new OWTS.

10. Can I use a septic system (actually, an Onsite Wastewater Treatment System) to service my property?: A minimum of 3 acres is required for the installation of a new Onsite Wastewater Treatment System (OWTS). Also, if a viable public sewer is within 200 feet of the property, you must connect to public sewer.