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.
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)
⭐ 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 tanksSmaller drainfield - Reduced land requirementsFaster treatment - Less retention time neededHigher flows - Can handle larger volumes Disadvantages:
Electricity required - Power outage stops treatmentRegular maintenance - Quarterly to annual service contractsHigher costs - $10,000-$20,000+ installedMechanical 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
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 flowBetter treatment - Entire soil area utilizedSmaller area - More efficient than gravity systems Disadvantages:
Electricity required - Pump failure stops systemMaintenance - Pump replacement every 5-10 yearsOrifice clogging - Small holes can plug with solidsDesign 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)
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 existsHigh water table solution - Raises system above groundwaterGood treatment - Sand provides excellent filtrationProven technology - Decades of successful use Disadvantages:
Visually prominent - 2-4 foot high "hill" in yardLarge footprint - Needs more area than gravity systemHighest cost - $15,000-$30,000+ due to materials and laborLandscape 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)
Enhanced Filtration Systems
What It Is: Treatment system using sand media for additional filtration before discharge.
Types:
Intermittent sand filters - Periodic dosing onto sand bedRecirculating sand filters - Multiple passes through sandPacked 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 reductionSmall footprint - Compact design possibleReliable performance - Consistent treatment qualityProtective of water quality - Ideal near sensitive areas Disadvantages:
Higher cost - $12,000-$25,000 installedMaintenance - Sand replacement every 10-20 yearsClogging potential - Requires good pretreatmentProfessional service - Not DIY-friendly Idaho Usage:
Less common; primarily used near sensitive water bodies or for commercial applications.
Key Resource: DEQ Technical Guidance Manual
⭐ Emerging Technology (2025)
What It Is: Drainfield using manufactured chambers or bundles instead of gravel aggregate.
Types:
Plastic chambers - Arched chambers with open bottomsPipe bundles - Wrapped corrugated pipe assembliesSynthetic 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 handlingLighter weight - Easier transport to remote sitesMore storage - Greater void space than gravelEnvironmental - No gravel mining impact Disadvantages:
Product cost - Chambers more expensive than gravelAvailability - Not all products approved in all districtsLong-term data - Newer technology, less track recordInstaller 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
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 impossibleLarge area coverage - Can utilize entire yardLandscaping compatible - Under lawn or landscaped areasGood for slow soils - Distributes load over large area Disadvantages:
Emitter clogging - Requires excellent filtration and maintenanceElectricity required - Pump and controls neededComplex management - Filters, flushing, monitoringHighest 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
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 profileMore economical - Less fill material neededGood for marginal sites - Improves moderately suitable soils Disadvantages:
Still visible - Slight raised area in yardSite specific - Only works with certain soil typesDesign constraints - Must meet specific criteria Idaho Usage:
Alternative to full mounds when site conditions allow.
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, hardpanAquifer protection - No groundwater dischargeGood for arid climates - Takes advantage of high evaporation Disadvantages:
Climate dependent - Must evaporate >90% of flowLimited Idaho use - Humid regions not suitableLarge area required - 2-3x conventional drainfield sizeSeasonal performance - May struggle in wet periods Idaho Usage:
Very rare; only in southern Idaho's driest areas.
Commercial & High-Flow Systems
What It Is: Systems designed for flows exceeding 1,500 gallons per day (commercial, multi-family).
Requirements:
Engineering design requiredProfessional installation onlyMonitoring wells often mandatedOperational 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
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
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
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
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
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:
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:
⭐ 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 →
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+
Alternative systems have mechanical components that WILL fail without proper maintenance. Budget for ongoing costs or you'll face expensive emergency repairs and potential regulatory violations.
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
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
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
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
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
New Focus: Nitrogen and phosphorus removal for watershed protection
Technologies: Recirculating systems, denitrification filters, media filtration
Idaho Status: Growing interest in sensitive lake watersheds
Technology: UV, ozone, or hydrogen peroxide disinfection
Purpose: Pathogen reduction for near-surface discharge
Idaho Status: Limited use; mostly commercial applications
Technology: Engineered wetland cells for tertiary treatment
Purpose: Polishing effluent before discharge
Idaho Status: Rare; experimental permits only
Technology: Cellular/WiFi system monitoring with alerts
Purpose: Early problem detection, reduce site visits
Idaho Status: Increasing adoption for ATUs and commercial systems
Alternative systems cost more - Budget 50-200% more than conventionalMaintenance is mandatory - Not optional; budget $300-800/year minimumProfessional design required - Hire qualified engineerElectricity needed - Most alternative systems use pumpsSite evaluation critical - Understand your constraints before selecting system
Site Characteristics:
System Requirements:
Regulatory:
✅ 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
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.
