PCE Vapor Intrusion in Multifamily Development: The Issue That Quietly Controls Your Project

Multifamily development in California increasingly takes place on urban infill sites—properties that often come with a prior life as retail, commercial, or light industrial uses.

Many of these sites carry a condition that does not show up in a title report or early financial model but can ultimately determine whether a project moves forward at all: vapor intrusion associated with Perchloroethylene (PCE).

For developers and investors, this is not an edge-case environmental issue. It is a recurring, predictable risk that directly affects feasibility, design, and long-term ownership obligations.

Why Dry Cleaner Contamination Still Matters

PCE was widely used in dry cleaning for decades, and its behavior in the environment makes it particularly difficult to deal with long after operations have ended. It does not simply dissipate or degrade quickly. Instead, it moves downward through soil, settles into groundwater, and can remain in place for decades.

Over time, PCE transitions into a vapor form and begins moving upward. When that vapor reaches the surface, it can enter buildings through foundation cracks, joints, and utility penetrations. This process—vapor intrusion—creates a direct pathway from historical contamination to present-day indoor air.

That is the key issue for residential development. Regulators are not focused on what happened historically; they are focused on whether people living in the building will be exposed to unsafe indoor air today and in the future.

How Regulators Approach Vapor Intrusion

In California, agencies such as the California Department of Toxic Substances Control (“DTSC”) and the Regional Water Quality Control Boards take a structured but cautious approach to vapor intrusion. Their authority comes from statutes including the Hazardous Substance Account Act (“HSAA”) and the Porter-Cologne Water Quality Control Act, and their guidance documents set conservative screening levels for residential exposure.

Once a potential vapor pathway exists—or cannot be ruled out—agencies typically expect a thorough evaluation of subsurface conditions. That process often starts with soil gas sampling and can expand into sub-slab or indoor air testing depending on the results. It is not a one-step exercise. The investigation tends to evolve as data comes in, and agencies often request additional rounds of sampling before they are comfortable with the conclusions.

This can feel like an entry into “upside down world.” We’re used to an “innocent until proven guilty” system, but when environmental concerns arise, parties have to prove themselves innocent. From a developer’s perspective, this is where expectations and reality often diverge. What appears to be a manageable issue at acquisition can become a multi-phase investigation that directly affects the project schedule, cost, and use.

Why Vapor Intrusion Drives Design and Timeline

Vapor intrusion tends to move from an abstract environmental concern to a very concrete design problem the moment regulators conclude that a pathway may exist. At that point, the issue no longer lives in a report—it shows up in the plans.

Addressing it usually requires more than a simple adjustment. Mitigation systems such as vapor barriers or sub-slab depressurization have to be integrated into the building from the ground up, not added later. That integration affects how the slab is designed, how utilities are routed, and how the building interfaces with the subsurface. It also requires coordination across disciplines—environmental consultants, geotechnical engineers, architects, and mechanical engineers all need to align on a solution that regulators will accept.

That process takes time, and it rarely unfolds in a straight line. Regulators often review mitigation approaches iteratively, asking for revisions or additional data before approving a final design. While that is happening, the rest of the project cannot fully advance. In some cases, developers also have to plan for the reality that these systems will remain in place after construction, which introduces ongoing monitoring requirements or land use restrictions that follow the property.

What makes this particularly challenging is that it is not just a question of whether contamination exists. The real issue is whether the building, as designed, can safely occupy the site. Until that question is resolved, it is difficult to lock down schedules, cost, or even a final design with confidence.

CEQA Streamlining Does Not Solve This Problem

There is no question that recent CEQA reforms improved the entitlement landscape for multifamily housing. Statutory exemptions under provisions like Public Resources Code sections 21080.27 and 21080.66 will reduce the time and uncertainty associated with environmental review, particularly in urban infill settings where delay has historically been a major barrier.

But those changes operate in a different lane from environmental cleanup and risk management. Agencies like DTSC and the Regional Water Quality Control Boards continue to evaluate contamination under their own statutory authority, and they do not adjust their requirements based on whether a project qualifies for CEQA streamlining.

This is where expectations often get out of sync with reality. A project may move efficiently through planning approvals and appear ready to break ground, only to slow down when subsurface conditions require further investigation or a more robust mitigation strategy. From the outside, it can feel like the project is “approved but not buildable,” which is often exactly what has happened.

The underlying issue is not a conflict between agencies, but a misunderstanding of sequencing. CEQA reform addresses procedural delay, not physical site conditions. When those conditions are not fully understood early, they tend to reassert themselves later—at a point when redesign is more disruptive and more expensive.

Liability Still Follows the Property

One of the more difficult realities for developers and investors is that vapor intrusion risk often originates from activities that have nothing to do with the current project. A dry cleaner that operated decades ago—sometimes even on a neighboring parcel—can leave behind contamination that migrates and persists long after the original business is gone.

That history does not stay neatly in the past. Under statutes such as the Comprehensive Environmental Response, Compensation, and Liability Act (“CERCLA”), the Porter-Cologne Act, and the HSAA, regulatory agencies can require current owners and operators to investigate and address those conditions regardless of who caused them. The legal structure prioritizes cleanup and risk reduction, which means liability tends to attach to the parties with the ability to take action.

There are, of course, defenses and risk allocation tools available, but they require careful planning and strict compliance. More importantly, they do not eliminate the practical need to resolve vapor intrusion as part of development. Even where liability protections exist, regulators will still expect the site to meet standards that are protective of residential use.

From an investment perspective, this shifts the focus away from fault and toward control. The key question is not who caused the problem, but who will have to deal with it—and how that obligation affects the project’s economics and timeline.

What This Means for Multifamily Developers and Investors

None of this suggests that savvy investors or buyers should always avoid sites with a history of dry cleaning or similar uses. In many urban markets, those sites represent some of the most viable opportunities for multifamily development precisely because they have not yet been fully repositioned.

The difference between a project that moves forward and one that struggles usually comes down to timing and clarity. When developers identify potential environmental concerns early—before acquisition closes or design is finalized—they have options. They can scope the investigation appropriately, engage with regulators in a more deliberate way, and incorporate mitigation strategies into the project in a way that feels intentional rather than reactive.

When that work gets deferred, the same issues tend to surface later, but with far less flexibility. At that point, the project team may already have committed to a design, secured financing, and set construction timelines. Adjusting course becomes more complicated, and the costs—both financial and operational—become more pronounced.

In that sense, vapor intrusion functions less like an unexpected problem and more like a known variable to account for. In California’s development environment, particularly for multifamily housing, it often plays a decisive role in shaping how a project is built and how it performs over time.

Frequently Asked Questions

What is PCE vapor intrusion in simple terms?
It is the movement of chemical vapors from contaminated soil or groundwater into indoor air. In multifamily housing, that means a building could sit over contamination that affects the air residents breathe.

Why is this such a big issue for residential projects?
Because regulators evaluate risk based on long-term human exposure. Residential use triggers stricter standards than commercial or industrial uses, which makes vapor intrusion a more sensitive and closely regulated issue.

Can this risk be managed, or does it stop development entirely?
It can often be managed, but it requires investigation, design changes, and regulatory approval. In some cases, mitigation systems become part of the building and must be maintained over time.

Does a CEQA exemption mean environmental issues are resolved?
No. CEQA exemptions address the environmental review process, not the underlying condition of the property. Agencies can still require full investigation and cleanup.

When should vapor intrusion be evaluated?
Ideally during early due diligence, before acquisition or final pricing. Waiting until later in the project increases the risk of delays, redesign, and unexpected costs.

Are neighboring properties a concern, or just the site itself?
Neighboring properties can be a major factor. PCE contamination often migrates in groundwater or soil gas, so a project can be affected by a dry cleaner that operated off-site years ago.

About Us

The Law Office of Jennifer F. Novak offers smart legal support for property owners and businesses. We focus on environmental court cases and rule compliance. Our team handles soil and groundwater cleanup, Clean Water Act citizen suits, and Water Board orders. We guide you through complex rules and fight for fair treatment. Contact us today for dedicated environmental legal help.