Separation distances (also called setbacks) are minimum required distances between septic system components and various site features to protect public health, groundwater quality, and property rights.
Proper separation distances ensure:
| Feature | Minimum Distance | Notes |
|---|---|---|
| Wells (drinking water) | 100 feet | Most critical setback |
| Property lines | 5-10 feet | Varies by district |
| Buildings (foundation) | 10-20 feet | Depends on system type |
| Surface water (streams/lakes) | 50-100 feet | Varies by water body type |
| Septic tank to drainfield | 5 feet | Component spacing |
| Replacement area reserve | 100% of original | Future system space |
⭐ Eastern Idaho (Most Current)
Septic Separation Distances Chart (Sept 2025)
Quick-reference format perfect for field use. Most recent update in entire knowledgebase.
Updated: September 5, 2025 | Size: 492 KB
Central District (CDH)
Standard Distances for Septic Tank/Drainfield
Boise metro area requirements with urban/suburban context.
North Central District
DEQ Technical Guidance Manual (Section 4)
Authoritative statewide reference with detailed explanations.
All Other Districts
Every health district provides separation distance tables in their document collections.
Standard Requirement: 100 feet minimum
Why It Matters:
Special Considerations:
Exceptions: Some districts allow variance petitions for reduced distances with:
Standard Requirement: 5-10 feet minimum (varies by district)
Why It Matters:
Boundary Types:
Replacement Area: You must also have a 100% replacement area on your property meeting all setback requirements. This ensures future system repairs or replacements can be accommodated.
Standard Requirements:
Why It Matters:
Special Cases:
Standard Requirements:
Why It Matters:
Structures Included:
Septic System Internal Distances:
Why It Matters:
| Feature | Typical Distance | Purpose |
|---|---|---|
| Water supply lines | 10 feet | Prevent cross-contamination |
| Large trees | 10-20 feet | Prevent root intrusion |
| Slopes >30% | Avoid or engineer | Prevent system failure |
| Utility easements | Per utility requirements | Legal access rights |
| Cuts and fills | 10-20 feet | Soil stability |
Idaho regulations require 100% replacement area for all septic systems.
❌ Building a garage over the replacement area ❌ Installing a swimming pool in the replacement area ❌ Planting trees that will interfere in 10-20 years ❌ Paving over the replacement area
✅ Keep replacement area as lawn or landscaping ✅ Mark replacement area on property maps ✅ Inform future property owners of location
Before You Buy Property:
Field Reference:
Due Diligence Checklist:
Design Considerations:
From Septic Tank:
From Drainfield:
To Property Lines:
To Wells:
Most health districts allow variance petitions for reduced setbacks when:
Solutions:
Solutions:
Solutions:
Site Evaluation
Learn how to assess your property for septic system suitability.
Alternative Systems
When standard systems won't fit, explore alternative technologies.
Real Estate Resources
Pre-purchase guides for evaluating septic system feasibility.
Engineer Resources
Technical guidance for system design and variance petitions.
For official setback requirements in your area:
Setback requirements protect groundwater quality and public health. When in doubt, use greater distances - you can never be "too far" from a well or property line. Always verify current requirements with your health district before finalizing system plans.
