The filing of an amended consent decree to an old Superfund site recently caught the attention of environmental lawyers around the country because it added a vapor intrusion remedy to a decades-old site.  See Joint Stipulation to Amend Consent Decree (Dkt. 74), United States v. Intel Corp. and Raytheon Co., 91-CV-20275 (N.D.Calif. Filed Dec. 21, 2011).  

The site at issue is the Middlefield-Ellis Whisman (MEW) Superfund Study Area in Mountain View and Moffett Field, California, which was the subject of a 1992 consent decree.  During the 1960s and 1970s, several industrial companies manufacturing semiconductors, electronics, and other products released volatile organic compounds (VOCs) into the environment, primarily trichloroethylene (TCE), which later mixed with similar releases from nearby U.S. Navy and NASA contaminant sources.  

The initial soil cleanup included excavation, with treatment by aeration, and vapor extraction, with treatment by vapor phase granular activated carbon.  The groundwater cleanup, which is expected to continue into the future for “many decades,” has included slurry walls to contain contaminant sources and extraction and treatment systems using granular activated carbon and/or air strippers.  

Following EPA’s certification of the completion of the initial work at the site in 2001, EPA was advised that the remedy was not protective of human health and the environment because it failed to address potential health concerns arising through the vapor intrusion pathway.  In 2002, the parties implementing the cleanup and EPA began evaluating the vapor intrusion pathway, which culminated in the proposed vapor intrusion work plan.  

EPA’s 2010 Record of Decision Amendment is especially interesting to environmental professionals because it sheds light on the type of circumstances that caused EPA to address the vapor intrusion pathway, the contaminant levels at issue, the types of engineering and institutional controls to address vapor intrusion, the cleanup goals, and ultimate costs of the remedy.  

The elevated TCE impacts to shallow groundwater triggered the vapor intrusion study.  The maximum TCE concentrations found in shallow groundwater (approximately 5 to 10 feet below the surface) were 40,000 micrograms per liter (ug/L) in the MEW Area.  Between 2003 and 2008, approximately 3,000 air samples were collected from 47 commercial buildings and 20 residences at the site.  The maximum TCE indoor air concentrations found in existing residential and commercial buildings overlying the shallow groundwater contamination within the study area were 490 micrograms per cubic meter (ug/m3) in the MEW Area, with the highest concentration coming from the indoor air of a building that had a basement.  

EPA later determined that the outdoor concentrations of TCE at the site typically ranged from below laboratory detection limits to 0.4 ug/m3, and set a TCE indoor air cleanup level of 5 ug/m3 for commercial buildings and 1 ug/m3 for residential buildings.  

The engineering and institutional controls are many.  For existing buildings, the remedies include installation, operation, maintenance, and monitoring of appropriate-sized sub-slab/sub-membrane ventilation systems, where determined as necessary through indoor air and other evidence.  In fact, there is an interesting section on the use and development of pilot studies. 

Existing non-residential buildings can utilize the building’s indoor air mechanical ventilation systems as the remedy if the property/building owner agrees to use, operate, and allow for monitoring of the system.  For future buildings, the remedies include installation of vapor barriers and passive sub-slab ventilation systems with the ability to make such systems active, except where the evidence shows there is no potential for vapor intrusion above the appropriate site indoor air cleanup levels.  

The institutional controls include city planning and permitting requirements to require the appropriate vapor intrusion control measures in new building construction at the site and to require that EPA approve any new construction plans.  The controls also include recording of covenants with owners to provide notice to future building/property owners of the vapor intrusion remedy and requirements; access for sampling, remedy operation and maintenance, and monitoring; and notice to EPA and the parties implementing the remedy when there are changes in ownership.  

Finally, EPA estimated that the 30-year present worth site-wide costs of the vapor intrusion remedy based on the building tiering system described in the work plan and associated response actions, including capital costs, operation and maintenance costs, institutional controls, and actions conducted to date, is between $14 million to $24 million, based on a 7% discount rate.  EPA described the estimate as “an order-of-magnitude engineering cost estimate that is expected to be within +50 to -30 percent of the actual project cost.”