What is the New Guidance on Vapor Intrusion and How Will It Affect Residential Redevelopment in California?

Residential brownfield development is a significant route to address housing shortages in California. However, such redevelopment needs to be approached with caution.

In California, about 200,000 properties have environmental impacts from past use. These uses range from manufacturing to old gas stations, and they are often the most valuable sites…in urban areas and close to public transportation.

This means that safety and development needs need to be balanced.

What is Vapor Intrusion?

A significant issue for these sites is vapor intrusion. This happens when chemical vapors in the soil or subsurface enter the building above. This can result in poor indoor air quality and even levels of toxicity. The vapors enter through any gaps and cracks in the foundation and also through sewer lines.

The kind of chemicals that are of concern here are those which volatilize easily, which include trichloroethylene, perchloroethylene, gasoline and diesel, paints, paint thinners, and mercury.

Remediation is necessary to prevent vapor intrusion, but it can be expensive, and it’s vital to find a balance between protecting future residents and allowing for redevelopment in California.

Why Are There New Guidelines in California?

CalEPA is putting together new draft guidelines that will make the requirements for mitigating vapor intrusion amongst the most stringent in the country.

The primary reason for these guidelines is to improve consistency. The draft, entitled “Supplemental Guidance: Screening and Evaluating Vapor Intrusion” was released in 2020 for public comment. It provides a solid framework and approach for screening and evaluating vapor intrusion.

In the past, there have been a variety of approaches taken in different parts of the state, and these are admittedly confusing and even contradictory. However, developers are concerned about certain aspects. The specific concern is attenuation factors.

These are how you estimate how much vapor concentration reduces as the chemicals are released into the indoor environment. These factors are combined with subsurface data to evaluate the safety of the site for occupation.

In the past, the U.S. EPA generated mathematical models which were based on theoretical behavior, but these are now considered outdated and unreliable. Unfortunately, the proposed replacement is generic attenuation factors, which while empirical are also unpredictable. They require site-specific information which may not be fully available at design, making it hard to create mitigation systems.

The new guidance presents a four-step process, although this is primarily designed to be used after a spill. For new construction, sampling buildings is not possible, but vapor intrusion must be evaluated using soil gas data. This is done using probes close to building sites and then conducting multiple rounds in different seasons. This alone could delay construction. Then the likely vapor intrusion has to be estimated.

The “Cost” of the Problem

The ultimate issue here is that the EPA has developed these generic attenuation factors based on sites that are, for the most part, not in California. This means they don’t take into account California’s climate and geology, especially as it varies through the state. The public comment period drew outrage from developers, some of whom believed it might overestimate the potential by as much as 95%.

The issue is a simple one. Expense. It is much more expensive for developers to meet these standards, and while we don’t want to compromise health and safety, the fact is that the increased expense and complexity might lead to the much-needed housing not being built. The sites most affected by vapor intrusion are those on the outskirts of cities, right where affordable housing is most needed.

The Impact on Redevelopment

The proposed guidelines are, in fact, considered non-binding. For now. Developers, however, must plan for the assumption that it will be implemented as a requirement, to assist regional and local agencies.

There is absolutely no question that this will stall development. Developers are hoping for revision or finalization, and that their concerns will be taken into account. However, until that is the case, the guidance is being implemented as written. This is forcing developers to choose between preemptively installing expensive mitigation systems that might prove unnecessary, or taking the risk of continuing construction in the hope that the rules will change or that things will turn out not to be as bad. The latter runs the risk of having to retrofit to add mitigation barriers to combat vapor intrusion later, which inevitably costs more and delays occupation.

This makes residential redevelopment in California on these sites difficult and expensive. Many developers feel that this guidance will essentially prohibit brownfield development for residential purposes. At the very least, the cost will end up being passed on to eventual residents, pricing the new buildings out of affordability and only exacerbating the situation. Unfortunately, this is a critical need given the housing shortage. There is also the issue of continued urban blight from abandoned sites. Failed strip malls and abandoned gas stations are eyesores and present problems of their own.

What Happens Next?

Nobody here is thinking that people should have unsafe homes, or that affordable housing should be built without regard to safety standards. However, new development must be built to address the housing crisis.

The CalEPA working group still has time to fix this. They can revisit the practical implications and, ideally, wait until attenuation factors designed specifically for California can be presented. Likely this would involve several standards due to the size of the state and its highly varied geology.

The guidance needs to allow development to move forward. They also need to protect human health and the environment. Unsurprisingly, CalEPA has chosen to err in favor of the latter; after all, lives are worth more than money. However, to address the housing crisis, a middle ground needs to be found.

As a side note, the new rules will also increase the expense of investigation after a spill, although this does not directly affect developers. However, this might be necessary. Developers have legitimate concerns about the added cost of vapor mitigation. Residents need to be safe. Everyone involved needs to work together to ensure that the guidelines meet everyone’s needs without lurching from too conservative to too liberal. This is being implemented now in a form that will increase housing costs and stall redevelopment in California.