MTBE in Elementary School Drinking Water

Client: Loma Prieta Joint Union School District

Location: Loma Prieta, CA

Summary: Following the Loma Prieta earthquake, groundwater wells were installed to provide drinking water for the elementary and middle school in the Loma Prieta Joint Union School District (LPJUSD). During a survey of private drinking water wells 10 years later, detectable but very low levels of MTBE were found in the water associated with LPJUSD supply wells. Cardno ENTRIX was contacted on an emergency basis to assist the school superintendent in communicating the findings to teachers and parents at a "Back-to-School Night" meeting. Cardno ENTRIX evaluated the existing data, determined that the levels were below the California Public Health goals, and assisted in developing a letter to be sent to parents. The Cardno ENTRIX Human Health toxicologist also attended the Back-to-School Night and held discussions with parents and teachers regarding the findings. Bottled water was supplied as an alternative to the school drinking fountains. Further evaluation showed that a former gasoline tank used to fuel school buses had been removed in the late 1980s, but additional soil sampling was needed to determine if a subsurface source of MTBE existed. Fractured bedrock at the site, located near the peak of the mountain area, contributes to anomalous groundwater flow. Data from onsite and nearby private groundwater wells did not indicate a clear source relationship.

Cardno ENTRIX developed soil criteria for leachability of gasoline mixtures and MTBE that would be protective of groundwater quality. Additional soil was removed at the former tank location.

Cardno ENTRIX helped the School Board develop a strategy to utilize their groundwater resources to provide a drinking water supply to the school. Two of the three wells did not contain MTBE. The supply from the contaminated well was redirected as irrigation for new ball fields, and the uncontaminated wells provide potable water for the school. Once this strategy was implemented, Cardno ENTRIX assisted the school superintendent in preparing a letter to the parents to convey this resolution, and the removal of bottled water in the school. The County also issued a site closure letter for the tank removal.

Highlights: Cardno ENTRIX integrated risk communication and human health toxicology to assist in preventing widespread fear among students, parents, and teachers regarding the quality of drinking water from groundwater wells. In addition, Cardno ENTRIX facilitated site closure and resource management for state budget and resource needs were integrated with the best interest of the students.