After your methane test is complete, you will receive results classifying your property into one of five Site Design Levels. This classification determines what type of mitigation system your project requires and significantly impacts your construction budget and timeline. Understanding what each level means helps you plan effectively.
How Site Design Levels Are Determined
LADBS assigns Site Design Levels based on two primary measurements taken during testing: methane concentration and gas pressure. The concentration is measured as a percentage of the Lower Explosive Limit, while pressure readings indicate whether methane is actively migrating through the soil.
Your property is assigned the level corresponding to the highest readings recorded at any probe location during any measurement session. Even if most of your property shows minimal methane, a single elevated reading will determine your overall classification.
Level 1: Minimal Hazard
Test Results Criteria
Level 1 classification requires methane concentrations below 1,000 ppm (less than 2% of LEL) and gas pressure at or below atmospheric levels. These readings indicate minimal methane presence and no active gas migration. The midwilshire methane zone analysis further supports these findings by highlighting the consistent stability of methane levels across various sampling sites. Continuous monitoring has confirmed that the conditions remain conducive to maintaining safe atmospheric pressure, minimizing the risk of gas migration. This ongoing assessment is crucial for ensuring environmental safety and compliance with regulatory standards.
Mitigation Requirements
For properties in the Methane Zone with Level 1 results, basic passive mitigation is still required. This includes a standard thickness vapor barrier membrane, typically 10-mil polyethylene or equivalent, a sub-slab ventilation system consisting of perforated pipe in a gravel blanket, and a passive vent riser extending above the roofline.
For properties in the Methane Buffer Zone with Level 1 results, you may qualify for exemption from mitigation requirements. Submit your test results to LADBS with a formal exemption request. Proper adherence to Playa Vista methane testing procedures ensures that your property is evaluated accurately and meets all necessary safety standards. It is essential to keep abreast of any updates in regulations concerning methane exposure to maintain compliance. Failure to follow the proper procedures may lead to penalties or hinder your eligibility for exemptions.
Typical Mitigation Costs
Level 1 passive mitigation for a typical residential project runs approximately $5,000 to $12,000 depending on building size and complexity. Commercial projects vary more widely based on square footage.
Level 2: Low Hazard
Test Results Criteria
Level 2 applies when methane concentrations range from 1,000 to 12,500 ppm (2% to 25% of LEL) with gas pressure still at or below atmospheric levels. This indicates methane presence but without active pressure-driven migration.
Mitigation Requirements
Level 2 mitigation builds upon Level 1 requirements with enhanced specifications. Requirements include a gas-resistant membrane with documented methane permeation rates, enhanced sub-slab ventilation with specified pipe spacing and gravel depth, a vent riser with passive or active capability, and methane detection devices at the lowest occupied level.
Typical Mitigation Costs
Level 2 systems typically cost $10,000 to $20,000 for residential projects and $15,000 to $35,000 for commercial projects, depending on building size and design complexity.
Level 3: Moderate Hazard
Test Results Criteria
Level 3 classification applies when methane concentrations reach 12,500 to 25,000 ppm (25% to 50% of LEL) or when positive gas pressure is detected at lower concentration levels. The presence of pressure indicates more active subsurface conditions.
Mitigation Requirements
Level 3 adds significant requirements beyond Level 2. These include a higher-specification membrane with lower permeation rates, more extensive sub-slab ventilation system, mechanical room ventilation requirements for enclosed utility spaces, enhanced detection and alarm systems, and provisions for future active ventilation if conditions warrant.
Typical Mitigation Costs
Level 3 mitigation typically ranges from $18,000 to $30,000 for residential projects and $30,000 to $60,000 for commercial projects.
Level 4: High Hazard
Test Results Criteria
Level 4 applies when methane concentrations reach 25,000 to 50,000 ppm (50% to 100% of LEL) or when significant positive gas pressure is measured. These conditions indicate substantial methane presence with active migration potential.
Mitigation Requirements
Level 4 typically requires active mitigation in addition to passive systems. Components include all Level 3 passive system elements, an active (powered) ventilation system with automatic activation, continuous methane monitoring with building management system integration, audible and visual alarms at specified locations, and documented maintenance and inspection requirements.
Typical Mitigation Costs
Level 4 systems typically range from $30,000 to $50,000 for residential projects and $50,000 to $100,000 or more for commercial projects due to the active system components.
Level 5: Severe Hazard
Test Results Criteria
Level 5 is the highest hazard classification, applying when methane concentrations exceed 50,000 ppm (above 100% of LEL) or when high positive gas pressure is measured. These conditions represent the most severe methane hazard scenarios.
Mitigation Requirements
Level 5 requires the most comprehensive mitigation systems. Requirements include redundant active ventilation systems with backup power, continuous monitoring with automatic controls and remote notification, the most stringent membrane specifications available, comprehensive detection and alarm systems, ongoing monitoring and maintenance throughout building life, and periodic retesting and system verification.
Typical Mitigation Costs
Level 5 mitigation for residential projects may run $50,000 to $75,000 or more. Commercial projects often exceed $100,000 to $200,000 depending on building size and complexity. The ongoing maintenance and monitoring requirements also add to lifetime costs.
Appealing or Retesting Your Results
If you believe your test results do not accurately represent site conditions, you have options:
Requesting Retesting
You may request additional testing if you have reason to believe the original test was conducted improperly or if site conditions have changed. However, LADBS will use the highest readings from any valid test to determine your classification. Retesting is not a way to shop for better results.
Investigating Anomalies
In some cases, localized methane sources such as decomposing organic matter, damaged sewer lines, or isolated contamination can cause elevated readings that do not represent overall site conditions. If you suspect this is the case, discuss with your testing agency whether additional investigation is warranted. High methane levels implications extend beyond localized issues and can indicate broader environmental challenges. Elevated methane concentrations contribute significantly to climate change, making it essential to assess the potential sources thoroughly. Addressing these high levels requires a strategic approach to mitigation and ongoing monitoring to safeguard local ecosystems and public health.
Understanding Your Results and Next Steps
Once you have your Site Design Level, the path forward involves engaging a methane mitigation designer to prepare plans meeting LADBS requirements for your level, incorporating mitigation costs into your project budget, coordinating the mitigation design with your architect and structural engineer, and planning construction sequencing to accommodate mitigation installation and inspection.
Sway Features provides both testing and mitigation design services, allowing us to guide you seamlessly from test results through design and construction. Contact us at 888-949-7929 to discuss your results and next steps.