MTBE CONTAMINATION OF GROUNDWATER IN THE LAHONTAN REGION OF CALIFORNIA

Groundwater contaminated by methyl tertiary butyl ether (MTBE) via leaking underground gasoline storage tanks continues to remain a serious threat to California's potable and non-potable groundwater sources. MTBE's adverse qualities include its carcinogenic and neurotoxic potential, and its unpleasant turpentine-like taste in drinking water. Adding to MTBE's potential as a contaminant is its low solubility in groundwater, thus preventing timely degradation. Our overall goal is to better understand the dynamics of MTBE plume migration and behavior in differing geologic settings. Our area of interest here is the Lahontan Regional Water Quality Control Board (Region 6V) of California.

Data was obtained from quarterly reports collected from on-site sampling wells, including the source well (greatest MTBE concentration) and one to three down-gradient wells that fall within the scope of an adjusted straight line. Forty contaminated sites were reviewed with eighteen fitting our chosen analytical model, an adaptation of Domenico (1987). To facilitate ease of use, model parameters were integrated into an Excel program. The horizontal MTBE plume length (maximum distance between source well and plume edge) was predicted after model calibration via adjustments in longitudinal dispersivity, groundwater velocity and degradation rate constant. MTBE levels in our study area ranged from a minimum of 130 parts per billion (ppb) to a maximum of 16500 ppb. For reference, the acceptable secondary level for MTBE in the state of California is 5 ppb. MTBE plume lengths in the study area ranged from 127 to 790 feet. These results will be used to compare with data from other regions of California to predict MTBE plume configurations and dynamics in various geologic settings.