Conventional gravity field
Tank plus gravity-fed trenches or bed. Requires suitable soils with adequate separation to limiting conditions. Simplest to own.
Michigan site work planning
Septic System Types
Site conditions choose the system. Knowing the options helps you read a design and understand what you are agreeing to maintain.
The county and the designer select the system. This page explains what the names mean.
(734) 476-1098Plan the next conversation
Use the guide below to organise questions, then confirm the details for the actual parcel and scope.
Explore excavation servicesA mound system is the design people hear about when a parcel will not support a conventional field, usually because groundwater or a restrictive layer sits too close to the surface for the required separation.
It is one of several alternatives to a conventional gravity system, and the choice is not a preference. Soil evaluation results, setbacks, available area, and the county's standards determine which design can be approved.
This septic system types guide explains the common designs, the conditions behind them, and the maintenance obligations an owner takes on with each. Septic system types guide.
Conventional first, alternatives when the site demands
A conventional system uses a tank for settling and a gravity-fed field where effluent infiltrates through suitable soil. It is the simplest to build and maintain, and it works where soils accept effluent at an acceptable rate with enough vertical separation to groundwater or a restrictive layer.
When that separation is not available, designs raise or improve the infiltrative surface. Elevated and mound designs build the field above natural grade in imported material. Pressure distribution uses a pump and a network to dose the field evenly rather than relying on gravity. Advanced treatment units reduce the strength of the effluent before it reaches the soil, which can allow a smaller or shallower dispersal area.
Each step away from a conventional gravity design adds components and obligations. Pumps, alarms, filters, and treatment units need power, monitoring, and service, and some counties tie ongoing operating permits or monitoring requirements to particular system types. Those obligations belong in the decision, not just in the installation cost.
Common designs and what drives them
Elevated or mound system
Field built above natural grade in imported material to achieve separation. More material, larger footprint, often a pump.
Pressure distribution
A pump doses the field through a distribution network for even loading. Adds electrical supply, controls, and an alarm to maintain.
Chamber or gravelless systems
Alternative media replacing stone in the field, used where the design or the county's standards permit.
Advanced treatment units
Pretreatment before dispersal, which may reduce field size. Typically carries service contracts and monitoring obligations.
Reserve area
Not a system type, but part of every design: protected land for a future replacement, kept clear of traffic and structures.
How the design gets chosen
1. Soil evaluation
Depth to groundwater and restrictive layers, soil texture and structure, and the loading the soil can accept.
2. Site constraints
Available area, setbacks to wells, water, structures, and property lines, along with slope and access.
3. Design flow
The load the system must handle, for a home usually driven by bedroom count under the county's standards.
4. County standards
What the county approves and under what conditions, including any engineer involvement for alternative designs.
5. Ownership obligations
The maintenance, monitoring, and any operating permit the chosen design carries, understood before it is built.
Limits of this guide
Which designs are approved, and under what conditions, varies by county and changes over time. The design for a specific parcel comes from the soil evaluation and the county's current standards, not from a list of options.
West Branch Builders does not design septic systems or hold an installer or evaluator certification. Design is the responsibility of the county-recognised designer or engineer, and installation is performed by a credentialed installer.
Alternative systems carry ongoing obligations. Pumps fail, alarms need power, filters need cleaning, and treatment units need service. Where a design adds components, find out what maintenance and monitoring the county expects before you agree to it.
Official sources — confirm current requirements with the office named for the parcel.
- Washtenaw County: installing a septic system — County application, evaluation and inspection process
- Washtenaw County time-of-sale program — Property-transfer evaluation requirements
- Livingston County septic permits — County application, evaluation and inspection process
- EGLE groundwater discharge and onsite wastewater unit — State-level onsite wastewater program context
Turning this into a project conversation
If a design has already been approved for your parcel, the practical questions are construction sequence, access, material, and how the field and reserve are protected during the rest of the build.
If you are still at the evaluation stage, the system type is the output of that process. Send the county and parcel details and the conversation can start from what the site supports.
Related pages: Contact Us.
Questions to carry into the review
Why would my parcel need a mound or elevated system?
Usually because groundwater or a restrictive soil layer is too close to the surface to give the required vertical separation beneath a conventional field. Raising the infiltrative surface in imported material restores that separation, at the cost of a larger footprint and usually a pump.
Are chamber systems better than stone-and-pipe fields?
They are an alternative medium, not automatically an upgrade. What matters is whether the county approves the design for your soils and flow, and how the system performs over time. The design decision belongs to the designer and the county rather than to product preference.
What ongoing maintenance does an alternative system need?
It depends on the components. Pumps, alarms, filters, and treatment units all need periodic attention, and some systems carry service or monitoring obligations attached to an operating permit. Ask the county and the designer what applies before the system is built.
Can I choose a different system than the one the county approved?
Changes go back through the county. The approved design reflects the soil evaluation, setbacks, and the standards in force, so a substitution needs review and approval rather than a field decision during construction.