After years in the making behind closed doors, on February 14, 2020, the California Department of Toxic Substances Control (DTSC), the San Francisco Bay Regional Water Quality Control Board and the California State Water Resources Control Board released their draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion (VI Guidance). Despite extending the public comment period due to COVID-19, on June 1, 2020, the state closed the opportunity for the public to comment on the VI Guidance, but not without skeptics expressing concern over the validity of its technical and legal footing.
As explained by the VI Guidance, vapor intrusion is the migration of chemical vapors from subsurface soils and groundwater into buildings. Chemical vapors can be a problem at contaminated sites, that, if uncontrolled, can migrate into buildings and pose a risk to human health. Vapor migration in the subsurface, through building foundations and within buildings is influenced by natural factors such as climate; the condition and structure of buildings; and the operation of the heating, ventilation and air-conditioning systems. To address the variability of vapor intrusion conditions, the state has proposed its VI Guidance to provide a consistent and proactive approach to evaluating buildings that may be at risk from vapor intrusion and a framework to decide when such risk should be managed.
Few dispute that the risk of vapor intrusion at commercial and residential sites is a critical concern that should be addressed to protect human health and public safety. Yet, while perhaps well-intended, the proposed VI Guidance has garnered scrutiny over its technical and legal footing and its implications of unnecessarily delaying and increasing the cost of developing needed urban infill projects in the state of California.
Draft Guidance Recommendations
The draft VI Guidance recommends four steps for determining whether there is vapor intrusion that could pose a risk to the health of people inside buildings:
Step 1 – Decide which buildings should be tested first and how, starting with those that are occupied and closest to the contamination, such as a building above or close to the spill, and evaluate whether the sewer could bring toxic vapors inside.
Step 2 – Screen buildings from outside by measuring vapor-forming chemicals underground.
Step 3 – Test indoor air by measuring vapor-forming chemicals in the indoor air, beneath the building’s foundation and in the outdoor air at the same time.
Step 4 – Act to protect public health, including protecting current occupants, by taking action based on the amount of vapor-forming chemicals in the indoor air; protect future occupants by taking action based on the amount of vapor-forming chemicals underground.
The VI Guidance advises that a soil vapor attenuation factor (AF) of 0.03, recommended by the U.S. Environmental Protection Agency (U.S. EPA), should be used to estimate the amount of the vapors underground or in groundwater that could end up in the indoor air. The attenuation factor was calculated by the U.S. EPA based on a study of buildings at contaminated sites. The VI Guidance advises that the best response is to clean up the contamination at the spill (remediation) and to use protective technologies when remediation is not feasible or until the spill is cleaned up. In extreme cases, occupants may need to be temporarily relocated.
Criticisms of the Proposed VI Guidance
Although the proposed guidance is replete with statements that it is not intended as regulation or policy, is not binding on California Environmental Protection Agencies or staff or on members of the public, and does not have the force or effect of law, there is significant apprehension from the regulated community otherwise. At odds with its admonishments, the VI Guidance also clearly states that its purpose is to create a “statewide standard practice” that is “to be used by practitioners and regulatory when screening buildings for the subsurface vapor risk to building occupants.” Instances have already been experienced where agency staff have insisted on following the guidance in draft form and even prior to its release.
Given the breadth and use of the proposed VI Guidance, a coalition of stakeholders has expressed that the guidance does not satisfy California’s Administrative Procedures Act (APA) requirements for rule makings and likely constitutes an “underground regulation.” The coalition advocates for the VI Guidance to be revised and then for the formal process for adopting a regulation pursuant to the California APA to proceed.
Outside Technical and Peer Review Requested
The five-year process that led to the development of the draft VI Guidance was mostly behind closed doors, as it was primarily internal to the Water Boards and DTSC. It is not apparent that the draft VI Guidance has been subject to external scientific peer review during its development. Although the state was approached by stakeholders offering input by subject matter experts, the state did not afford an opportunity for public collaboration, except for periodic meetings to discuss conceptual elements. While the state’s interagency team had contemplated the formation of a technical advisory group to assist with developing the guidance, it never came to fruition. The state has not indicated what steps it will take to address public comments and finalize the guidance document.
Default Attenuation Factor
Commenters have also raised reservations regarding the fit and implications of the use of the U.S. EPA soil vapor attenuation factor. The draft VI Guidance proposes to rely on the U.S. EPA’s default soil vapor attenuation factor of 0.03 for risk management decisions relative to soil vapor intrusion, all the while acknowledging the shortcomings of the conservative default factor. For instance, despite recognition that attenuation of soil vapor is highly variable over time, climate, substance and site conditions, the draft VI Guidance proposes using the one-size-fits-all default attenuation factor, which is based on data primarily from Colorado and New York—not California. Using the highly conservative 0.03 attenuation factor could vastly increase the number of locations in California considered at risk for vapor intrusion, thereby requiring expensive mitigation measures or the expense of additional testing and site-specific risk assessment to demonstrate the lack of an actual risk. However, it has also been pointed out that the draft VI Guidance fails to provide guidance on conducting such site-specific risk analysis. Concern has also been raised that the draft VI Guidance and the one-size-fits-all attenuation factor do not differentiate between residential and commercial buildings, even though such structures present significantly different potential vapor intrusion risks given use patterns and structural and operational differences. Treating commercial buildings in the same manner as residential buildings could create unnecessary new impediments to local economic development.
Implications on Development
The draft VI Guidance document could create a new barrier to affordable urban infill development projects in California. By most accounts, such urban infill projects, such as those near public transit systems, are effective and efficient means of meeting California energy and greenhouse gas reduction goals. Notably, essential businesses and activities exempted from COVID-19 “shelter in place” orders have included construction of affordable housing. However, the success of infill housing and complementary commercial development depends on avoiding the imposition of unnecessary costs.