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Case Study

Addressing the Vapor Intrusion Pathway at Middlefield‐Ellis‐Whisman Superfund Study Area

By Susan B. Welt, MPH, P.E., Principal, Engineering


One of Integral’s core values is collaboration. Many of our projects, including this one, involve working with other consultants, multiple parties, and agencies. For this project, Integral’s challenge is to address the vapor intrusion (VI) pathway within the Middlefield‐Ellis‐Whisman Superfund Study Area in Mountain View, California, which includes multiple sites at former semiconductor manufacturing facilities and the former Naval Air Station Moffett Field. The footprint of the Study Area is approximately 1 square mile and consists of areas of facility‐specific and regional responsibility. Eight parties are performing activities within the Study Area to address U.S. Environmental Protection Agency (EPA) Region 9 enforcement instruments.

Our primary concern within the VI is the potential for trichloroethylene (and related volatile compounds) detected in shallow groundwater impact the indoor air quality of current or future buildings.


This strategy includes using a multiple-lines-of-evidence approach to assess the potential for VI to impact the indoor air quality of existing and future structures overlying contaminated shallow groundwater.

A comprehensive, integrated approach that considers all environmental media (e.g., air, water, soil, and soil vapor) is used to develop an appropriate strategy for each parcel that facilitates social and economic advancement. Integral works with developers, property owners, the responding parties, legal and technical consultants, architects, the City of Mountain View permitting departments, EPA, and the Bay Area Air Quality Management District to collect and assess the necessary environmental data to design and construct the VI mitigation measures needed, if any, for each building while meeting permitting requirements. These measures have included heating, ventilation, and air conditioning modification; soil-vapor extraction systems; active subslab venting systems; and passive subslab venting systems using innovative, green, and sustainable technologies, such as aerated floors and wind turbines.


Working closely with EPA and other stakeholders, Integral has developed a proactive approach to assess and address the potential for VI in existing or planned residential and commercial buildings and modified existing treatment system components to facilitate development.  Our approach saves stakeholders time and money because we are able to develop and design VI control measures during the planning phase of construction or tenant improvements; obtain access and support; and implement the appropriate vapor intrusion remedy required by the “Record of Decision” for each building in a manner that does not impact those specific occupants. Integral has used this approach successfully in implementing the vapor intrusion remedy at more than 90 buildings located within this Study Area, including new construction.

Key Contact

Ms. Susan Welt is a Registered Professional Engineer with more than 20 years of experience in environmental consulting and regulatory... Full bio

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