When vapor intrusion threatens indoor air quality, building owners and environmental professionals face a critical question: How do you protect occupants from toxic soil gases migrating upward through building foundations? The answer lies in a properly designed and installed vapor intrusion mitigation system (VIMS)—and getting it right the first time isn’t just about regulatory compliance. It’s about protecting human health.
At Clean Vapor, we’ve spent 38+ years answering this question across 1,200+ successful projects spanning more than 30 million square feet. We’ve learned that vapor intrusion mitigation systems aren’t one-size-fits-all solutions applied by general contractors with minimal training. They’re engineered protection systems that demand site-specific design, professional installation, and ongoing performance verification.
If you’re developing a brownfield site, managing an existing contaminated property, or designing new construction over impacted soils, understanding what a vapor intrusion mitigation system actually does—and what separates effective systems from costly failures—can save lives, money, and years of regulatory headaches.
Understanding Vapor Intrusion and Why Mitigation Matters
Vapor intrusion occurs when volatile organic compounds (VOCs) or other hazardous vapors migrate from contaminated soil or groundwater into buildings through cracks, gaps, and porous materials in foundations and floor slabs. These subsurface vapors follow the path of least resistance, often drawn upward by pressure differentials between the building interior and the soil.
The health risks are real. Depending on the contaminants present, long-term exposure to vapor intrusion can cause respiratory problems, neurological effects, and increased cancer risk. For property developers, the stakes extend beyond human health to include regulatory enforcement, property devaluation, transaction delays, and potential legal liability.
A vapor intrusion mitigation system is the engineered solution that prevents these harmful vapors from entering occupied spaces. But not all systems perform equally—and that’s where expertise, proper design, and proven installation methods make all the difference.
What Does a Vapor Intrusion Mitigation System Actually Do?
At its core, a VIMS creates a protective barrier and a venting pathway that prevents the upward flow of contaminants into the occupied space. These systems work through one or more of the following mechanisms:
Sub-slab depressurization creates negative pressure beneath the building’s floor slab, preventing soil gas from entering while safely venting it to the atmosphere above the roofline. This is typically the most reliable approach for active mitigation systems.
Vapor barriers are specialized membranes installed beneath floor slabs that block vapor migration. However, barrier selection matters tremendously—inexpensive polyethylene sheeting isn’t sufficient for chemically impacted sites. Professional-grade spray-applied barriers or high-performance geomembranes provide the durability and impermeability required for long-term protection.
Passive venting systems in new construction use properly designed aggregate layers, sub-slab conveyance plenums, and vent stacks that allow soil gas to convectively vent without mechanical assistance. When designed correctly by experienced professionals, passive systems can eliminate the need for fans and ongoing energy costs—but only if the design accounts for site-specific conditions.
The key word throughout is “site-specific.” Soil type, contamination levels, building design, climate conditions, and intended building use all influence which mitigation approach will work reliably over decades, not just months.
The Four Phases of Effective Vapor Intrusion Mitigation
Clean Vapor’s approach to VIMS follows a comprehensive four-phase process that ensures long-term system performance and human health protection.
Phase 1: Diagnose
Before any mitigation system can be designed, we must thoroughly understand the vapor intrusion risk. This diagnostic phase includes soil gas testing, indoor air sampling when appropriate, and comprehensive site assessment. We analyze contamination sources, soil characteristics, building construction, and site-specific conditions that will influence system design.
Tom Hatton, our founder and industry pioneer who helped write the ANSI/AARST soil gas mitigation standards, the NAVFAC Vapor Intrusion Mitigation documents, and AVIP’s Best Practices, has always emphasized one principle: you can’t design an effective system without understanding the problem you’re solving. Rushed assessments lead to over-engineered systems that waste money or under-designed systems that fail to protect occupants.
Phase 2: Design
This is where engineering expertise separates professional vapor intrusion specialists from general contractors who install “cookie-cutter” systems. Our PE-signed and sealed designs account for building-specific factors including foundation type, occupancy patterns, HVAC operations, and state regulatory requirements.
For new construction, we design passive systems that integrate seamlessly with building plans—eliminating future operational costs while meeting or exceeding performance standards. For Existing Buildings, we take a high-minded asymmetric approach to building evaluation where soils, structures, and building systems are evaluated against the physical forces that induce vapor intrusion. Once these variables are understood, Clean Vapor designs retrofit solutions that work within the limitations of the existing structure to deliver an effective Vapor Mitigation System.
Every design we produce is custom-engineered for the specific site. We’ve completed 500+ passive New Construction designs with zero failures requiring conversion to active systems—a nearly 40-year track record that demonstrates the value of precision engineering over guesswork.
Phase 3: Build
Even the best design fails if installation isn’t executed by trained, experienced professionals. Our installation teams are ANSI/AARST certified and trained specifically in vapor intrusion mitigation—not plumbers or general contractors adapting radon techniques to commercial applications.
We’re certified installers of Land Science, Epro and Cetco spray-applied gas barriers, which provide superior performance compared to traditional sheet membranes. Our sub-slab depressurization installations follow best practices for piping, fan selection, and atmospheric discharge locations that ensure systems operate efficiently for years.
Quality installation also means attention to details that inexperienced contractors overlook: proper sealing of penetrations, correct aggregate specifications, efficient conveyance plenums, adequate slope for condensate drainage, and strategic placement of collection points that account for soil permeability variations.
Phase 4: Monitor
A vapor intrusion mitigation system isn’t “install and forget” infrastructure. Ongoing monitoring ensures the system continues protecting building occupants as conditions change over time. We use Vapor Guardian telemetric monitoring systems—real-time, cloud-based platforms that track system performance 24/7 and alert property managers to any issues before they become health risks.
Response-driven controls allow systems to adjust automatically to changing conditions, reducing energy consumption while maintaining protective negative pressure beneath the slab. For property owners and environmental consultants managing long-term remediation sites, this continuous verification provides documentation for regulatory compliance and liability protection.
Active vs. Passive Vapor Intrusion Mitigation Systems
Choosing between active and passive systems depends on timing, contamination levels, regulatory requirements, and building design.
Passive systems rely on natural pressure differentials and properly designed vent pathways to manage soil gas. They work exceptionally well in new construction when designed by qualified professionals from the beginning. The advantages are clear: no ongoing energy costs, no mechanical components to maintain, and no fan noise. However, passive systems require precise design and proper installation during construction—retrofitting a passive system into an existing building is rarely feasible.
Active systems use fans to mechanically create sub-slab negative pressure. They’re the go-to solution for retrofit applications in existing buildings and for sites with high contamination levels where passive venting can’t provide sufficient protection. Active systems offer adjustable performance and easier verification of operation, but they require ongoing energy consumption and periodic fan maintenance.
At Clean Vapor, we’ve pioneered passive system design that has consistently eliminated the need for active conversion down the road. Our 500+ passive installations with zero failures didn’t happen by accident—this is the result of a trained team of engineers that are skilled in evaluating contaminants, soils, and structures, selecting the right materials, and implementing convective plenum design principles that account for worst-case scenarios, not just average conditions.
Why Professional Engineering Matters in VIMS Design
You wouldn’t hire a general plumber to design a hospital’s medical gas system. The same principle applies to vapor intrusion mitigation—human health protection demands science-based engineering expertise, not basic schedules borrowed radon mitigation techniques.
Licensed Site Remediation Professionals (LSRPs), environmental consultants, and property developers increasingly recognize that VIMS require PE-signed designs, especially in states like North Carolina where professional engineering certification is mandatory for commercial installations. Our Clean Vapor Engineering, P.C. division provides these stamped designs, giving regulators, lenders, and property owners the confidence that systems meet professional engineering standards.
Beyond regulatory requirements, proper engineering prevents the costly mistakes we’ve seen from less experienced contractors: undersized collection systems that leave portions of buildings unprotected, improper vapor barrier installations that allow preferential pathways, and fan selections that waste energy or fail prematurely.
With 100+ years of combined team experience and Tom Hatton’s role in establishing industry standards, Clean Vapor brings technical depth that simply isn’t available from contractors who occasionally install vapor systems between residential radon jobs.
Common Vapor Intrusion Mitigation System Failures—and How to Avoid Them
Not every VIMS performs as intended. We’ve been called to diagnose and repair failed systems installed by others, and the problems typically trace to a few recurring issues:
Inadequate site assessment leads to systems designed for the wrong contaminant profile or soil conditions. Without proper soil gas testing and understanding of contamination sources, even well-installed systems won’t deliver adequate protection.
Generic designs that don’t account for building-specific factors frequently underperform. Foundation type, slab thickness, sub-slab aggregate presence, and building pressurization all influence system requirements.
Poor installation quality undermines even good designs. Kinked piping, inadequate sealing, reverse slope piping, incorrect aggregate specifications, and improper vapor barrier installation create pathways for vapor intrusion despite the presence of mitigation infrastructure.
Lack of monitoring means failing systems go undetected until indoor air testing reveals problems—or until occupant’s experience health effects. Without continuous monitoring, property owners have no early warning that system performance has degraded.
The solution to all these failure modes is straightforward: work with vapor intrusion specialists who have decades of experience, proven methodologies, and the engineering credentials to deliver systems that protect human health reliably.
Regulatory Compliance and State-Specific Requirements
Vapor intrusion mitigation standards vary by state, with some jurisdictions adopting specific technical requirements while others reference ANSI/AARST standards or EPA guidance. New Jersey, New York, Pennsylvania, and North Carolina each have distinct regulatory frameworks that influence VIMS design and documentation requirements.
Professional environmental consultants understand these requirements, but they often need qualified mitigation contractors who can translate regulatory standards into functional systems. Clean Vapor works regularly with LSRPs, PEs, and environmental consultants to ensure installed systems satisfy both the engineering principles of effective mitigation and the documentation requirements of state programs.
For brownfield redevelopment projects seeking state remediation funding or regulatory closure, VIMS documentation becomes especially critical. Our PE-signed designs and comprehensive monitoring data provide the technical foundation for regulatory approval and long-term liability management.
Choosing the Right Vapor Intrusion Mitigation Partner
When human health and regulatory compliance are on the line, choosing your vapor intrusion mitigation partner is one of the most consequential decisions in brownfield redevelopment or contaminated site management.
Look for specialists, not generalists. Vapor intrusion mitigation isn’t a side business for Clean Vapor—it’s all we do. We’re not HVAC contractors, plumbers, or general environmental remediation firms that occasionally install vapor systems. Our exclusive focus for 38+ years means we’ve encountered every conceivable site condition, building type, and contamination scenario.
Verify credentials and experience. ANSI/AARST certification, PE-licensed engineers on staff, and a track record measured in millions of square feet successfully mitigated—these credentials separate professionals from pretenders.
Demand site-specific design. If a contractor offers to provide a quote without thorough site assessment or proposes a “standard” system configuration, keep looking. Effective vapor intrusion mitigation requires engineering, not guesswork.
Understand the full lifecycle approach. Design and installation are just the beginning. A qualified partner provides monitoring, maintenance support, and long-term performance verification that protects your investment and your occupants.
Protecting Human Health Through Better Indoor Air
At Clean Vapor, every vapor intrusion mitigation system we design and install serves one ultimate purpose: protecting human health by ensuring safe indoor air quality. After 38+ years and 1,200+ successful projects, we’ve learned that achieving this goal requires more than equipment and installation techniques—it demands engineering expertise, obsessive attention to detail, and a commitment to doing things right the first time.
Whether you’re planning a new brownfield development, managing an existing contaminated property, or navigating regulatory requirements for VI mitigation, the decision of who designs and installs your vapor intrusion mitigation system will have consequences for decades to come.
Our guarantee speaks to our confidence: we provide 1+ year warranties on systems we design and install, and our 500+ passive new construction designs have achieved zero failures requiring conversion to active systems. These aren’t marketing claims—they’re the results of bringing genuine expertise and professional engineering to every project.
Don’t leave indoor air quality to chance or settle for contractors learning on your project. Work with the vapor intrusion specialists who literally helped write the standards the industry follows.
Ready to discuss your vapor intrusion mitigation needs?
Email us at info@cleanvapor.com or schedule a meeting with our team. Let’s talk about designing a site-specific vapor intrusion mitigation system that protects your building occupants, satisfies regulatory requirements, and performs reliably for decades—not just months.
Clean Vapor. The Vapor Intrusion Mitigation Company™. Protecting human health through better indoor air since 1987.
