Septic Drain Fields and Leach Fields
A drain field, also called a leach field, disperses liquid wastewater into the ground. The septic tank holds back most of the solids. The soil beneath the field does much of the remaining treatment.
This guide starts with a conventional gravel-trench field fed by a distribution box. We’ll update it with diagrams and explanations of other layouts, including chamber, mound, and drip systems.
Watch how a drain field works
Follow the blue flow from the septic tank through the distribution box. The animation switches between two trench lines every six seconds so you can watch the soil wetting and draining. Both lines can receive flow at the same time in a gravity-fed system.
Swipe the diagram sideways to see all the labels.
The liquid leaving the tank is called effluent. It flows by gravity to the distribution box, which divides it among the trenches. Effluent leaves through small openings in each pipe, passes through gravel, and seeps into the soil. Soil particles and naturally occurring microorganisms help remove contaminants as the effluent moves through unsaturated soil. EPA septic system types
How many gallons per day is a drain field designed for?
In Ohio, most household systems are designed for 120 gallons per day per bedroom, with a minimum of 240 gallons per day. A three-bedroom home generally starts at 360 gallons per day and a four-bedroom home at 480 gallons per day. Your approved septic plans show the design flow for your property. Ohio design-flow rule
The designer combines the daily flow with how much effluent the soil can accept per square foot. Two homes with the same number of bedrooms can need different field sizes. Slow-draining soil can require more trench area. Shallow groundwater or bedrock can call for a different layout. Ohio soil absorption standards
What kind of soil works best?
Well-structured, well-drained loamy soil can be a good fit. It has pore spaces that let effluent soak in and air reach the soil. Dense clay or compacted soil can absorb water slowly, causing it to collect in the trenches or surface in the yard. Very coarse sand or gravel can let liquid move too quickly for adequate treatment, especially where groundwater is shallow.
A soil evaluation looks below the surface at soil layers, their structure, and the depth to seasonal groundwater or bedrock. That helps the designer determine whether conventional trenches fit your property. Ohio soil absorption standards
Protect your drain field
- Keep vehicles and heavy equipment off it. Cars, trucks, trailers, and construction equipment can compact the soil, closing the spaces that let effluent soak in. The weight can crush pipes or shift the distribution box, sending too much flow to one trench.
- Keep buildings and pavement off it. Sheds, garages, patios, and driveways can make lines hard to inspect or repair. Construction can compact soil, and concrete or asphalt can reduce evaporation and the oxygen soil microorganisms need.
- Keep trees and large, deep-rooted plants back. Roots can grow into pipe openings and joints, restrict flow, and damage lines. Grass or shallow-rooted ground cover is a better fit over the field. Tree planting distance depends on the species and your layout.
- Send rainwater away from it. Downspouts and sump pump outlets can saturate the soil, leaving less room for it to take in and treat effluent.
Before putting in a driveway, shed, or landscaping, check your septic permit or layout drawing so you can locate the field. EPA drainfield care guidance