Engineer & Designer Resources

Technical Guidance for Professional System Design

This page provides comprehensive resources for engineers, soil scientists, designers, and environmental consultants designing septic systems across Idaho's diverse terrain and regulations.

🎯 Essential Technical Resources

📘 DEQ Technical Manual

350-Page Authoritative Reference

The most comprehensive technical guidance for:

Complex system designs
Alternative treatment technologies
Site-specific engineering solutions
Performance-based designs

View DEQ Resources

📏 Separation Distances

Complete Setback Requirements

District-specific distance tables for:

Wells and water sources
Property boundaries
Surface water bodies
Soil absorption systems

View All Distance Tables

⚙️ Alternative Systems

27+ System Types Documented

Technical specifications for:

Aerobic treatment units
Pressure distribution
At-grade systems
Mound systems
Advanced treatment

Browse Alternative Systems

🧪 Soil Evaluation

Site Assessment Standards

Guidance on:

Percolation testing
Soil profile analysis
Groundwater evaluation
Site constraints

Find in DEQ Manual

📐 System Design Workflow

Phase 1: Site Assessment

Preliminary evaluation
- Property boundaries and easements
- Topographic survey
- Utility locations
- Access considerations
Soil investigation
- Test pit excavation (minimum 2 pits)
- Soil profile description
- Seasonal high water table determination
- Percolation or infiltration testing
Site constraints analysis
- Separation distance compliance
- Slope limitations
- Bedrock or impervious layers
- Seasonal flooding potential

Phase 2: System Selection

Design flow calculation
- Bedroom count method (standard)
- Fixture unit method (commercial)
- Actual use data (if available)
- Peak flow considerations
Treatment level determination
- Standard soil treatment adequate?
- Enhanced treatment required?
- Discharge limitations?
- Sensitive area considerations?
System type selection
- Conventional gravity system (if suitable)
- Pressure distribution (uniform dosing)
- At-grade or mound (poor soils)
- Alternative treatment (site constraints)

Phase 3: Design Documentation

Site plan requirements
- Scale drawing (1"=20' or better)
- All existing and proposed structures
- Septic system components and locations
- Separation distances clearly marked
- Easements and property lines
System design details
- Component sizing calculations
- Hydraulic profile
- Construction specifications
- Materials list
- Installation sequence
Supporting documentation
- Soil investigation report
- Percolation test results
- Design flow calculations
- Professional seal (if required)

📋 Permit Submittal Requirements

Standard Submissions (Most Districts)

Completed application form (district-specific)
Site plan meeting district standards
Soil investigation report
Design calculations
Construction details
Applicable fees

Enhanced Requirements (Complex Systems)

Central District (Boise Metro) may require:

Professional engineer seal on designs
O&M (Operations & Maintenance) manual
Monitoring plan
As-built drawings after installation

Check with your district for specific requirements.

🗺️ District-Specific Engineering Resources

Urban Districts (Higher Complexity)

Central District Health (CDH)

Most stringent review process
Professional seal often required
Alternative systems common due to lot constraints
Higher permit fees

View CDH Resources

Rural Districts (Site-Specific Solutions)

North Central District

Extensive DIY homeowner installer program
Detailed training materials available
Flexible approach for difficult sites
Strong technical support

View North Central Resources

Panhandle District

Lake and shoreline considerations
Cold climate design factors
Seasonal water table challenges
Bedrock and steep slope solutions

View Panhandle Resources

🛠️ Common Design Challenges

Challenge 1: Limited Separation Distances

Problem: Property boundaries, wells, or surface water too close

Solutions:

Proprietary advanced treatment units
Drip irrigation dispersal (smaller footprint)
Engineered fill systems
Shared systems (if permitted)

Key Resource: Alternative Systems Guide

Challenge 2: Poor Soil Conditions

Problem: Tight soils (clay), shallow soils, or high water table

Solutions:

At-grade or mound systems
Pressure distribution for uniform loading
Imported fill material (certified)
Soil modification (limited conditions)

Key Resource: DEQ Technical Guidance Manual Chapter 5

Challenge 3: Steep Slopes

Problem: Terrain >25% grade, downslope seepage concerns

Solutions:

Upslope tank placement
Pressure distribution mandatory
Curtain drains for groundwater control
Terracing and retaining walls

Key Resource: DEQ Technical Guidance Manual Chapter 7

Challenge 4: Commercial or High-Flow Applications

Problem: Restaurants, offices, subdivisions with large flows

Solutions:

Advanced treatment required
Flow equalization tanks
Redundant system components
Professional O&M contracts

Key Resource: DEQ Pre-Treatment Requirements

📊 Design Standards by District

Conventional System Minimums (Typical)

Component	Minimum Requirement	Notes
Septic Tank	1,000 gallons (residential)	1,500+ for garbage disposal
Soil Depth	18-24" unsuitable material	Below drainfield bottom
Absorption Area	Varies by percolation rate	See district tables
Tank Access	6" minimum risers to grade	Required for inspection

Separation Distances (Most Restrictive)

Wells: 100 feet minimum (some districts 150')
Property lines: 5-10 feet (varies by district)
Surface water: 50-100 feet (varies)
Buildings: 5-10 feet minimum

Always verify current requirements with local district.

💡 Professional Practice Tips

Best Practices for Smooth Approvals

Pre-application consultation
- Meet with district staff before design
- Discuss site constraints early
- Clarify documentation requirements
- Confirm fee schedules
Conservative design approach
- Use safety factors on critical dimensions
- Plan for future expansion if feasible
- Consider replacement area requirements
- Document design assumptions clearly
Clear communication
- Label all plan components clearly
- Provide calculation summaries
- Include construction notes
- Specify inspection requirements
Professional relationships
- Maintain good rapport with district staff
- Respond promptly to review comments
- Attend pre-construction meetings
- Ensure installer understands design intent

📚 Technical References

Idaho State Resources

IDAPA 58.01.03 - Idaho Individual/Subsurface Sewage Disposal Rules
DEQ Technical Guidance Manual - Chapter-by-chapter system design guidance
DEQ Guidance Memorandums - 20 policy interpretations (1993-2021)

Industry Standards

NSF/ANSI Standards - Product certification requirements
ASTM Standards - Materials and testing methods
Soil Science Society of America - Soil classification guidance

Continuing Education

Many districts offer:

Annual training workshops
New technology seminars
Regulatory update sessions
Complex system design courses

🏘️ Subdivision & Large System Design

Multi-Unit Considerations

Shared vs. individual systems
- District policies vary significantly
- Maintenance responsibility structure
- Easement and access requirements
- Long-term management plans
Capacity planning
- Conservative flow estimates
- Peak demand analysis
- Future expansion provisions
- Reserve areas required
Community system requirements
- Professional O&M mandatory
- Monitoring and reporting
- Financial assurance mechanisms
- Homeowner association covenants