Alternative & Advanced Septic Systems

Beyond Conventional Drainfields

Alternative septic systems are non-standard treatment technologies used when conventional gravity drainfields won't work due to site constraints, soil limitations, or enhanced treatment requirements.

🎯 When Alternative Systems Are Needed

Common Scenarios:

Site Limitations:

Shallow soils (less than 48 inches to bedrock)
High seasonal groundwater (within 24 inches of surface)
Slow percolation rates (tight clay soils)
Fast percolation rates (very sandy/gravelly soils)
Steep slopes (greater than 30%)
Small lot size (insufficient separation distances)

Environmental Protection:

Near sensitive surface waters
Wellhead protection areas
Drinking water source zones
Nutrient-sensitive watersheds

Special Requirements:

High wastewater flows (commercial properties)
Variable flow patterns (seasonal businesses)
Difficult repair situations (limited replacement area)
Regulatory requirements (enhanced treatment mandates)

🌟 System Types Available in Idaho

1. Aerobic Treatment Units (ATUs)

⭐ Most Common Alternative System

What It Is: Mechanical treatment system that introduces oxygen to accelerate bacterial decomposition.

How It Works:

Air pump injects oxygen into treatment chamber
Aerobic bacteria consume organic matter faster than anaerobic
Produces clearer effluent with lower BOD (Biological Oxygen Demand)
Effluent then goes to drainfield (often smaller than conventional)

Advantages:

Better treatment - 85-95% BOD reduction vs 40-60% for septic tanks
Smaller drainfield - Reduced land requirements
Faster treatment - Less retention time needed
Higher flows - Can handle larger volumes

Disadvantages:

Electricity required - Power outage stops treatment
Regular maintenance - Quarterly to annual service contracts
Higher costs - $10,000-$20,000+ installed
Mechanical parts - Pumps and aerators can fail

Idaho Usage: Very common in Central District (Boise metro) for small urban lots and near Boise River tributaries.

Key Resource: Central District Health - Aerobic Treatment & Drainfields Brochure

2. Pressure Distribution Systems

Uniform Wastewater Distribution

What It Is: System that uses a pump to evenly distribute effluent across entire drainfield.

How It Works:

Effluent collects in dosing chamber with pump
Pump activates when chamber fills
Forces effluent through pressurized network of small-diameter pipes
Uniform distribution through holes (orifices) along pipes

Advantages:

Level drainfields not required - Works on slopes up to 30%
Uniform distribution - Every part of drainfield receives equal flow
Better treatment - Entire soil area utilized
Smaller area - More efficient than gravity systems

Disadvantages:

Electricity required - Pump failure stops system
Maintenance - Pump replacement every 5-10 years
Orifice clogging - Small holes can plug with solids
Design complexity - Requires proper pressure zone calculations

Idaho Usage: Required for many alternative drainfield designs. Very common in mountain areas with sloping lots.

Key Resource: North Central - Complex Installer Training Manual (Section 5)

3. Mound Systems

For Shallow Soils or High Groundwater

What It Is: Raised drainfield constructed above original ground surface using imported fill material.

How It Works:

Native soil is scarified (loosened) to improve infiltration
Sand fill is placed to create treatment zone (typically 24-36 inches)
Pressure distribution network installed in sand fill
More sand placed over pipes, then topsoil and grass cover
Effluent treated as it passes through sand into native soil

Advantages:

Overcomes shallow soils - Creates treatment depth where none exists
High water table solution - Raises system above groundwater
Good treatment - Sand provides excellent filtration
Proven technology - Decades of successful use

Disadvantages:

Visually prominent - 2-4 foot high "hill" in yard
Large footprint - Needs more area than gravity system
Highest cost - $15,000-$30,000+ due to materials and labor
Landscape impact - Permanent raised feature

Idaho Usage: Common in Teton Valley (high groundwater), mountain valleys, and areas with shallow bedrock.

Key Resource: DEQ Technical Guidance Manual - Mound Systems (Section 8)

4. Sand Filters

Enhanced Filtration Systems

What It Is: Treatment system using sand media for additional filtration before discharge.

Types:

Intermittent sand filters - Periodic dosing onto sand bed
Recirculating sand filters - Multiple passes through sand
Packed bed filters - Gravel and sand layers

How They Work:

Septic tank effluent pumped to distribution pipes
Effluent trickles through sand media (18-36 inches)
Treated effluent collected in underdrain system
Discharged to drainfield or (in some states) surface water

Advantages:

Excellent treatment - 90-99% pathogen reduction
Small footprint - Compact design possible
Reliable performance - Consistent treatment quality
Protective of water quality - Ideal near sensitive areas

Disadvantages:

Higher cost - $12,000-$25,000 installed
Maintenance - Sand replacement every 10-20 years
Clogging potential - Requires good pretreatment
Professional service - Not DIY-friendly

Idaho Usage: Less common; primarily used near sensitive water bodies or for commercial applications.

Key Resource: DEQ Technical Guidance Manual

5. Gravelless Drainfield Systems

⭐ Emerging Technology (2025)

What It Is: Drainfield using manufactured chambers or bundles instead of gravel aggregate.

Types:

Plastic chambers - Arched chambers with open bottoms
Pipe bundles - Wrapped corrugated pipe assemblies
Synthetic aggregates - Engineered media replacing gravel

How They Work:

Chambers or bundles create void space for effluent storage
Effluent infiltrates into surrounding soil from larger surface area
No gravel needed, reducing weight and material costs
Often shallower installation than conventional systems

Advantages:

Faster installation - Less excavation and material handling
Lighter weight - Easier transport to remote sites
More storage - Greater void space than gravel
Environmental - No gravel mining impact

Disadvantages:

Product cost - Chambers more expensive than gravel
Availability - Not all products approved in all districts
Long-term data - Newer technology, less track record
Installer training - Proper installation critical

Idaho Usage: Growing rapidly. South Central District issued guidance in May 2025 on gravelless systems.

Key Resource: South Central - May 2025 Gravelless Systems Guidance

6. Drip Irrigation Systems

Subsurface Wastewater Irrigation

What It Is: Shallow, pressure-dosed system using drip tubing to distribute effluent.

How It Works:

Effluent treated in septic tank or ATU
Pumped through filter to remove particles
Distributed through network of drip tubing (1-2 feet deep)
Small emitters release effluent slowly to soil

Advantages:

Very shallow - Works where deep excavation impossible
Large area coverage - Can utilize entire yard
Landscaping compatible - Under lawn or landscaped areas
Good for slow soils - Distributes load over large area

Disadvantages:

Emitter clogging - Requires excellent filtration and maintenance
Electricity required - Pump and controls needed
Complex management - Filters, flushing, monitoring
Highest maintenance - Regular filter cleaning essential

Idaho Usage: Limited use; primarily for difficult sites where other options won't work.

Key Resource: DEQ Technical Guidance Manual

7. At-Grade Systems

Modified Shallow Systems

What It Is: Drainfield installed at or slightly above original ground surface.

How It Works:

Similar to mound but with less fill height
Native soil may be suitable but shallow
Fill sand provides additional treatment zone
Grass cover over entire system

Advantages:

Less prominent than mounds - Lower profile
More economical - Less fill material needed
Good for marginal sites - Improves moderately suitable soils

Disadvantages:

Still visible - Slight raised area in yard
Site specific - Only works with certain soil types
Design constraints - Must meet specific criteria

Idaho Usage: Alternative to full mounds when site conditions allow.

8. Evapotranspiration (ET) Systems

Zero-Discharge Systems

What It Is: Sealed drainfield designed to evaporate and transpire all effluent with no infiltration.

How It Works:

Lined drainfield bed prevents soil infiltration
Effluent stored in gravel or chamber void space
Plants transpire moisture through leaves
Evaporation from soil surface

Advantages:

Works in impermeable soils - Clay, bedrock, hardpan
Aquifer protection - No groundwater discharge
Good for arid climates - Takes advantage of high evaporation

Disadvantages:

Climate dependent - Must evaporate >90% of flow
Limited Idaho use - Humid regions not suitable
Large area required - 2-3x conventional drainfield size
Seasonal performance - May struggle in wet periods

Idaho Usage: Very rare; only in southern Idaho's driest areas.

9. Large Soil Absorption Systems (LSAS)

Commercial & High-Flow Systems

What It Is: Systems designed for flows exceeding 1,500 gallons per day (commercial, multi-family).

Requirements:

Engineering design required
Professional installation only
Monitoring wells often mandated
Operational permits and reporting

Types:

Large conventional drainfields
Commercial ATUs with large dispersal
Advanced treatment with surface discharge
Package treatment plants

Idaho Regulations: LSAS systems have additional requirements for design, installation, monitoring, and reporting.

Key Resource: Southwest - Non-Residential Requirements

🔬 Treatment Level Comparison

System Type	BOD Removal	TSS Removal	Pathogen Removal	Nitrogen Removal
Conventional Septic + Drainfield	40-60%	60-70%	90-99%	0-20%
Aerobic Treatment Unit (ATU)	85-95%	85-95%	90-99%	10-30%
Sand Filter	85-98%	95-99%	99%+	20-40%
Recirculating Sand Filter	90-99%	95-99%	99.9%+	40-60%
Mound System	70-90%	80-95%	99%+	20-40%
Drip Irrigation	60-80%	70-85%	95-99%	30-50%

BOD = Biological Oxygen Demand, TSS = Total Suspended Solids

💰 Cost Comparison

System Type	Installed Cost Range	Annual Maintenance	Expected Lifespan
Conventional Gravity	$5,000 - $12,000	$200-400 (pumping)	25-40 years
Pressure Distribution	$8,000 - $15,000	$300-600	20-30 years
Aerobic Treatment Unit	$10,000 - $20,000	$300-800	15-25 years
Mound System	$15,000 - $30,000	$400-800	20-30 years
Sand Filter	$12,000 - $25,000	$400-1,000	15-25 years
Gravelless Chambers	$7,000 - $14,000	$200-400	20-30 years
Drip Irrigation	$12,000 - $22,000	$500-1,200	15-20 years

🎓 Usage Scenarios

For Homeowners on Difficult Sites

Your situation: Lot has shallow soils, high water table, or is near a lake.

Steps:

Review separation distances to identify constraints
Read about system types above to understand options
Hire qualified engineer for site evaluation
Budget 50-100% more than conventional system
Plan for ongoing maintenance contracts
Explore grant funding if eligible

Most Likely Systems: Mound, pressure distribution, ATU

For Installers Expanding Services

Your situation: Want to offer alternative system installation.

Steps:

Complete Complex Installer Training - North Central's 63-page course
Study DEQ Technical Guidance Manual - Sections 6-11
Obtain manufacturer certifications for specific products
Invest in specialized equipment (pumps, chambers, etc.)
Get bonded for higher-value installations
Market expertise to engineers and health districts

Key Skills: Pressure system hydraulics, pump sizing, chamber installation, manufacturer specs

For Engineers Designing Systems

Your situation: Client's site won't support conventional drainfield.

Steps:

Conduct comprehensive site evaluation (soils, groundwater, topography)
Review DEQ Technical Guidance Manual for design criteria
Consider multiple alternative system types
Perform cost-benefit analysis for client
Prepare detailed design drawings and specifications
Submit to health district for review
Specify qualified installers and maintenance providers

Resources:

Nutrient/Pathogen Evaluations for sensitive areas
Subdivision Engineering for multi-lot projects
District-specific design standards

For Health District Staff

Your situation: Reviewing alternative system applications.

Steps:

Verify site conditions warrant alternative technology
Check engineer qualifications and design completeness
Review hydraulic calculations and treatment estimates
Ensure monitoring and maintenance plans included
Inspect installation for compliance with approved plans
Require as-built drawings before final approval

Resources:

DEQ Guidance Memorandums for policy interpretation
IDAPA 58.01.03 for regulatory requirements

📚 Key Resources by District

⭐ North Central - Most Comprehensive

DEQ Technical Guidance Manual (350+ pages, 15 MB)

Authoritative statewide reference covering all alternative system types.

Complete design criteria
Installation standards
Maintenance requirements
Troubleshooting guidance

Plus:

Complex Installer Training (63 pages, 10 MB)
85 technical diagrams (300 DPI)
Approved products database

View North Central Resources →

⭐ South Central - Latest Updates

May 2025 Rule Changes & Gravelless Systems Guidance

Most recent regulatory updates and emerging technologies.

New gravelless system requirements
Updated design standards
2025 installer training course

View South Central Resources →

Central District (Boise)

Aerobic Treatment & Drainfields Brochure

Urban focus - small lots and sensitive surface waters.

ATU requirements for Boise metro
Reduced setbacks with enhanced treatment
Manufacturer approval process

View Central District Resources →

All Districts

Every health district's collection includes alternative system information relevant to local conditions.

Browse All Districts →

🛠️ Maintenance Requirements

General Maintenance for All Alternative Systems:

Annual Tasks:

Inspect electrical components (pumps, timers, alarms)
Check alarm functionality
Verify proper operation
Document system performance

Periodic Service:

Pump septic tank every 1-3 years
Service mechanical components per manufacturer schedule
Clean filters (ATUs, drip systems)
Replace worn parts (pumps typically 7-10 years)

Professional Service Contracts: Most alternative systems require maintenance contracts with certified service providers.

Typical Costs:

ATU service: $200-400/year
Pump inspection/service: $150-300/visit
Filter replacement: $50-200
Major repairs: $500-3,000+

📋 Regulatory Requirements

Idaho-Specific Rules (IDAPA 58.01.03):

Enhanced Treatment Systems:

Professional installation required
Maintenance contracts mandated
Monitoring may be required
Service provider certification needed

Design Requirements:

Licensed professional engineer for most alternative systems
Hydraulic calculations required for pressure systems
Treatment performance documentation
Manufacturer specifications must be followed

Inspection & Approval:

Health district pre-approval before installation
Mid-construction inspections (multiple stages)
Final inspection before covering
As-built drawings required

Ongoing Compliance:

Annual operation reports (some systems)
Monitoring well sampling (sensitive areas)
Maintenance records retention
Service provider certifications

🌍 Geographic Considerations

Mountain Areas (Northern & Central Idaho)

Common Challenges:

Shallow soils over bedrock
Steep slopes
Seasonal high groundwater
Cold weather impacts

Typical Solutions:

Mound systems
Pressure distribution on slopes
Insulated components for freeze protection

Snake River Plain (Eastern Idaho)

Common Challenges:

High groundwater (shallow aquifer)
Very permeable soils (rapid infiltration)
Aquifer protection requirements

Typical Solutions:

ATUs for better treatment before discharge
Monitoring wells common
Pressure distribution for uniform loading

Boise Metro (Southwest Idaho)

Common Challenges:

Small urban lots
Proximity to Boise River and tributaries
High property values (space constraints)

Typical Solutions:

ATUs with reduced drainfield size
Gravelless systems for smaller footprint
Variance petitions common

South-Central Idaho

Common Challenges:

Basalt bedrock at shallow depths
Variable soil types
Agricultural chemical concerns

Typical Solutions:

Mounds over bedrock
Enhanced treatment near water bodies
Site-specific engineering analysis

🔬 Emerging Technologies

Nutrient-Reducing Systems

New Focus: Nitrogen and phosphorus removal for watershed protection Technologies: Recirculating systems, denitrification filters, media filtration Idaho Status: Growing interest in sensitive lake watersheds

Advanced Oxidation

Technology: UV, ozone, or hydrogen peroxide disinfection Purpose: Pathogen reduction for near-surface discharge Idaho Status: Limited use; mostly commercial applications

Constructed Wetlands

Technology: Engineered wetland cells for tertiary treatment Purpose: Polishing effluent before discharge Idaho Status: Rare; experimental permits only

Remote Monitoring

Technology: Cellular/WiFi system monitoring with alerts Purpose: Early problem detection, reduce site visits Idaho Status: Increasing adoption for ATUs and commercial systems

⚡ Key Takeaways

Critical Points:

Alternative systems cost more - Budget 50-200% more than conventional
Maintenance is mandatory - Not optional; budget $300-800/year minimum
Professional design required - Hire qualified engineer
Electricity needed - Most alternative systems use pumps
Site evaluation critical - Understand your constraints before selecting system

System Selection Checklist:

Site Characteristics:

System Requirements:

Daily wastewater flow estimate
Treatment level needed
Electrical service available
Budget (installation + 20 years operation)
Maintenance commitment

Regulatory:

When to Hire Professional Help:

✅ Always hire engineer for:

High groundwater sites
Steep slopes (>15%)
Near sensitive water bodies
Commercial properties
Failed conventional systems

✅ Always hire certified installer for:

Any alternative system type
Systems with mechanical components
Pressure distribution systems
Manufacturer-proprietary products

📞 Get Expert Help

Design Engineers: Engineering Resources
Certified Installers: Installer Resources
District Staff: Find Your District
DEQ Technical Support: Idaho Department of Environmental Quality

Alternative systems make septic feasible on sites where conventional systems fail. They cost more and require ongoing maintenance, but they protect water quality and allow development on challenging properties. Invest in professional design, quality installation, and regular maintenance for long-term success.