Vapor Mitigation Systems: How They Work & When to Use Them

Invisible Vapors, Real Risks

You can’t see them, smell them, or touch them, but vapor intrusion can silently affect the air you breathe and the safety of your property.

In New Jersey, where decades of industrial activity, fuel storage, and solvent use have left their mark, vapor intrusion has become a significant environmental concern. Invisible gases can migrate through soil and groundwater, enter buildings, and expose occupants to harmful chemical vapors.

That’s where vapor mitigation systems (VMS) come in. These systems prevent hazardous vapors from seeping indoors, protecting people’s health and preserving property value.

This article explains how vapor mitigation systems work, when they’re needed, and how Oak Environmental helps New Jersey property owners, buyers, and developers install compliant, effective systems to ensure clean air and regulatory peace of mind.

What Is Vapor Intrusion?

Vapor intrusion occurs when chemical vapors from contaminated soil or groundwater migrate upward through the subsurface and infiltrate buildings.

These vapors enter through cracks in concrete slabs, utility conduits, or sump openings, mixing with indoor air and potentially exposing occupants to volatile chemicals.

Common Sources of Vapor Intrusion

• Leaking underground storage tanks (USTs)
  

• Historic dry cleaning operations using solvents like PCE or TCE
  

• Former industrial facilities or machine shops
  

• Fuel spills or unremediated Brownfield sites
  

• Contaminated groundwater beneath structures
  

Typical Contaminants

• Volatile Organic Compounds (VOCs) such as benzene, trichloroethylene (TCE), and perchloroethylene (PCE)
  

• Petroleum hydrocarbons from fuel or oil
  

• Chlorinated solvents are used in manufacturing or cleaning processes
  
  

Why It Matters

These vapors can accumulate indoors at concentrations that pose both health and safety risks. Chronic exposure may contribute to respiratory issues, neurological symptoms, or increased cancer risk.

From a property standpoint, vapor intrusion can lead to regulatory scrutiny, transaction delays, and reduced market value unless addressed proactively.

How Vapor Mitigation Systems Work

When vapor intrusion is confirmed or suspected, a vapor mitigation system (VMS) provides a protective barrier between the contaminated subsurface and indoor air.

1. Sub-Slab Depressurization (SSD): The Most Common System

• Works much like a radon mitigation system.
  

• A small fan connected to a vent pipe creates negative pressure beneath the slab, pulling vapors from the soil and venting them safely above the roofline.
  

• This prevents vapors from entering through cracks or gaps in the building foundation.
  

SSD systems are proven, effective, and widely approved by the NJDEP for both residential and commercial applications.

2. Sub-Membrane Depressurization (SMD)

• Ideal for crawl spaces or buildings without concrete slabs.
  

• A durable plastic membrane is laid over the soil, with vent piping installed underneath to collect and vent vapors.
  

• The system can operate passively or actively with a fan.
  
  

3. Passive Venting Systems

• Installed during new construction.
  

• Use natural pressure differences (without fans) to vent vapors safely outdoors.
  

• Can later be upgraded to an active system if needed.
  

4. Sealing and Vapor Barriers

• Vapor-resistant liners or sealants are installed below foundations or slabs to block vapor migration.
  

• These are commonly used for preventive protection in new developments built on former Brownfield sites.
  

5. Ongoing Monitoring

• To maintain NJDEP compliance, systems are tested periodically to confirm that negative pressure is maintained and vapors remain below screening levels.
  
  

When Are Vapor Mitigation Systems Needed?

Vapor mitigation isn’t just for contaminated sites it’s often required anytime soil or groundwater contamination could pose an indoor air risk.

1. During Environmental Remediation

When a Phase II ESA or remedial investigation identifies volatile contaminants, NJDEP requires mitigation to protect occupants until cleanup is complete.

2. For Existing Buildings

Older buildings built above contaminated soil or shallow groundwater may need retrofit systems once vapor intrusion is confirmed.

3. During New Construction

Developers often install preventive vapor barriers and venting systems beneath new buildings on former industrial or Brownfield sites. This is far more cost-effective than retrofitting later.

4. In Real Estate Transactions

Lenders, insurers, and buyers frequently require vapor mitigation assessments before closing deals involving industrial or commercial properties.

5. Regulatory Compliance

Under NJDEP’s Vapor Intrusion Guidance, if vapor concentrations exceed safety thresholds, mitigation must be implemented immediately, regardless of property use.

Benefits of Installing a Vapor Mitigation System

1. Protects Occupant Health

Eliminates exposure to harmful vapors, ensuring safe indoor air quality.

2. Preserves Property Value

A compliant mitigation system provides long-term protection and reassurance to future buyers and lenders.

3. Reduces Legal and Regulatory Risk

Demonstrates due diligence and compliance with NJDEP and EPA standards, minimizing liability.

4. Enables Redevelopment

Makes it possible to safely repurpose impacted properties or Brownfields.

5. Builds Lender and Buyer Confidence

Verified vapor control is often a prerequisite for financing and occupancy approval.

How NJDEP Regulates Vapor Mitigation

New Jersey’s Vapor Intrusion Technical Guidance (VI Guidance) provides a clear framework for identifying, testing, and mitigating vapor risks.

Key Requirements

• Screening Levels: NJDEP defines safe contaminant limits for soil gas and indoor air.
  

• Triggering Conditions: If test results exceed these limits, mitigation is mandatory.
  

• System Design: Must be engineered by qualified professionals using approved materials and methods.
  

• Performance Verification: Post-installation testing ensures the system effectively controls vapor intrusion.
  

• Ongoing Monitoring: Periodic checks confirm sustained system performance and compliance.
  

Failure to comply can delay case closure or trigger enforcement actions.

Oak Environmental’s Expertise in Vapor Mitigation

At Oak Environmental, we provide end-to-end vapor mitigation solutions — from investigation to design, installation, and verification.

Our Core Services

• Vapor Intrusion Assessment & Testing
  Comprehensive soil gas and indoor air sampling following NJDEP protocols.
  

• System Design & Engineering
  Custom sub-slab or sub-membrane systems tailored to building type and contamination profile.
  

• Installation & Commissioning
  Certified technicians ensure every system meets NJDEP performance standards.
  

• Ongoing Monitoring & Maintenance
  Regular inspections and data reporting for regulatory compliance.
  

• Regulatory Documentation & Case Closure
  Complete reports and certifications for submission to NJDEP and lenders.
  

Our Competitive Edge

• Licensed Subsurface Evaluators (SSEs) and environmental engineers with extensive NJDEP experience.
  

• Expertise in both retrofit and new construction mitigation systems.
  

• Rapid turnaround times to meet tight closing or occupancy deadlines.
  

• Clear, transparent communication with property owners, attorneys, and regulators.
  

With Oak Environmental, you get more than compliance — you get confidence that your air is clean and your property is safe.

Real-World Example: Vapor Risk Resolved

A commercial property in central New Jersey was undergoing redevelopment when indoor air testing revealed elevated vapor concentrations of PCE and TCE from historical dry-cleaning operations nearby.

Oak Environmental quickly designed and installed an active sub-slab depressurization system tailored to the site’s layout. Within two weeks of installation, follow-up testing confirmed a 95% reduction in vapor concentrations, meeting NJDEP indoor air standards.

The project achieved case closure on schedule, enabling the client to secure financing and commence occupancy without delay.

Key Takeaways: Managing Vapor Risks Effectively

1. Test Early: Always include vapor intrusion screening in Phase II ESAs.
   

2. Act Quickly: Address vapor issues as soon as they’re identified.
   

3. Hire Licensed Experts: Only NJDEP-certified professionals can design and verify compliant systems.
   

4. Plan for Long-Term Maintenance: Monitoring ensures systems continue to perform safely.
   

5. Integrate Vapor Mitigation into Redevelopment Plans: Building vapor mitigation into new construction saves time and money in the long run.

Clean Air, Safe Properties

Vapor intrusion may be invisible, but its risks are very real. Whether you’re buying, selling, developing, or occupying a property in New Jersey, proper vapor mitigation protects not only your investment but the people who live and work within it.

Oak Environmental provides the knowledge, certification, and field experience to identify vapor risks early, design effective systems, and verify compliance — ensuring clean air and safe properties for years to come.

Take Action Today

Don’t let unseen environmental risks jeopardize your real estate transaction. Oak Environmental provides fast, compliant, and reliable due diligence services to help you identify and manage potential issues before they impact your deal. Schedule your Phase I ESA consultation today at oaknj.com/contact and secure your property’s future with confidence.

Oak Environmental — ensuring safe, compliant, and transparent real estate transactions across New Jersey.