Life Cycle of Methyl <i>tert</i>-Butyl Ether in California Public Water Supply Wells

We have utilized the California Department of Public Health Water Quality Analyses database, with approximately 250000 results for methyl <i>tert</i>-butyl ether (MTBE), to evaluate the extent of MTBE in public water supply wells in California and how these impacts have changed over time. These data show that MTBE has never been detected in >98% of 13183 public water supply wells that have been tested for MTBE. The number of wells with first-time detections of MTBE peaked in 2000 and has decreased by 80% since that time. For the 188 wells in which MTBE has been detected at least once, MTBE was not detected in the most recent analysis of 142 of these wells. Tetrachloroethene, another common groundwater contaminant, has been detected more commonly, and new detections are declining more slowly. These results indicate that the impact of MTBE on public water supply wells has peaked and is declining

Evaluation of Vapor Intrusion Using Controlled Building Pressure

The use of measured volatile organic chemical (VOC) concentrations in indoor air to evaluate vapor intrusion is complicated by (i) indoor sources of the same VOCs and (ii) temporal variability in vapor intrusion. This study evaluated the efficacy of utilizing induced negative and positive building pressure conditions during a vapor intrusion investigation program to provide an improved understanding of the potential for vapor intrusion. Pressure control was achieved in five of six buildings where the investigation program was tested. For these five buildings, the induced pressure differences were sufficient to control the flow of soil gas through the building foundation. A comparison of VOC concentrations in indoor air measured during the negative and positive pressure test conditions was sufficient to determine whether vapor intrusion was the primary source of VOCs in indoor air at these buildings. The study results indicate that sampling under controlled building pressure can help minimize ambiguity caused by both indoor sources of VOCs and temporal variability in vapor intrusion