If you own a home or business in Fresno, Clovis, Madera, or the surrounding Central Valley, chances are your property relies on a septic system for wastewater treatment. While most people are familiar with leach lines, many aren’t aware of another common alternative—drainwells (also called dry wells). Understanding the differences between these systems can help you make the best choice for your property’s septic needs.
At Sequoia Pumping, we’ve installed and maintained both leach lines and drainwells for decades, and we’re here to break down their differences, how they work, and when one might be a better option than the other.
What’s the Difference Between a Drainwell and a Leach Line?
Both drainwells (dry wells) and leach lines serve the same essential function—disposing of liquid wastewater from your septic tank. The difference lies in how and where they disperse that wastewater:
- Leach Lines: A series of perforated pipes that allow wastewater to slowly absorb into the soil over a large area.
- Drainwells (Dry Wells): A deep, vertical pit filled with gravel or crushed rock that allows wastewater to seep directly into deeper soil layers. Older drain wells, which are still common in the Central Valley, are commonly brick-lined, but not rock-filled. Therefore, they can post a safety issue or even collapse over time.
The type of system you need depends on your soil type, lot size, and local groundwater levels.
Leach Lines: How They Work & When They’re Used
Leach lines, also called leach fields or drain fields, are the most common method for septic system drainage. Here’s how they work:
- Septic tank collects wastewater and separates solids from liquids.
- Effluent (liquid waste) flows into a distribution box.
- The box directs flow to multiple perforated pipes buried in trenches filled with gravel.
- Wastewater slowly filters into the surrounding soil, where natural bacteria help break down contaminants.
Components & Installation
- Trench Depth: Usually 18-36 inches deep, depending on soil conditions.
- Pipe Size: Typically 4-inch perforated PVC pipes.
- Gravel Base: A 12-24 inch layer of crushed rock or gravel supports the pipes.
- Distribution Box: Ensures even wastewater flow to all lines.
When Are Leach Lines Used?
Leach lines are best suited for properties with:
✔ Sandy or loamy soil that absorbs water well.
✔ Adequate space for multiple trenches.
✔ Low groundwater levels to avoid contamination.
Leach lines can be placed in several formations, and the size, length, and number of leach lines will be determined by the engineer responsible for their installation. Here’s an example of a top-view diagram of leach lines and the property they serve.
Drainwells (Dry Wells): A Space-Saving Alternative
In areas with clay-heavy soil, high water tables, or limited space, a drainwell (dry well) may be a better option. Instead of dispersing wastewater horizontally like leach lines, drainwells send it deep underground.
How Drainwells Work
- Effluent from the septic tank is directed into a large vertical pit lined with crushed rock.
- Water seeps downward through the gravel, filtering into lower soil layers.
- The surrounding soil naturally absorbs and processes the wastewater.
Components & Installation
- Well Depth: Usually 5-30 feet deep, depending on soil conditions.
- Diameter: Ranges from 3-6 feet wide.
- Gravel or Rock Fill: Provides space for wastewater to collect and seep down.
- Concrete or Plastic Liner (Optional): Some systems use pre-cast wells for added stability.
When Are Drainwells Used?
✔ Clay-heavy soil that doesn’t absorb water well.
✔ Small properties without space for long leach lines.
✔ High groundwater areas where traditional leach fields might fail.
How Drainwells & Leach Lines Are Arranged in a Septic System
Depending on the property layout, either system can be installed in different configurations:
- Straight-Line System: Leach lines or drainwells placed in a row for even distribution.
- “V” or “Horseshoe” Layout: Two leach lines or drainwells connected with a valve to control flow.
- Multiple Drainwells: If one drainwell fills too quickly, a second (or third) is added downstream to handle excess wastewater.
Each design is customized based on soil conditions and space availability.
Which System is Right for You?
Choosing between a leach line and a drainwell depends on:
✅ Soil Type – Sandy soil? Use a leach line. Clay-heavy? A drainwell may be better.
✅ Space Available – Large property? Leach lines work well. Small lot? Consider a drainwell.
✅ Local Regulations – Some areas require one system over the other.
✅ Water Table Levels – If groundwater is high, a drainwell could be a better option.
Need Help? Call Sequoia Pumping!
Whether you need a new septic system installed, repairs, or routine pumping, Sequoia Pumping has been serving Fresno, Clovis, Madera, and the Central Valley for generations. Our team can assess your property, determine whether a leach line or drainwell is best, and ensure your septic system runs smoothly for years to come.
📞 Call us today at (559) 233-2400 to schedule a consultation!
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