Contamination of Groundwater in California by MTBE: How Do We Constrain the Problem?

The purpose of this project is to characterize and assess the contamination of groundwater in California by methyl tertiary-butyl ether (MTBE). Field data were collected by reviewing 85 leaking underground storage tank cases in Orange County, California in the Santa Ana Regional Quality Control Board Region 8. Our analytical study shows that the concentration of MTBE ranged from a minimum of 370 ppb to a maximum of 1,200,000 ppb contamination levels. The state of California considers levels >5 ppb of MTBE to be a concern. In order to estimate the length of the MTBE plumes, MTBE concentrations from the source well and one or more down-gradient monitoring wells were integrated into an Excel program based on the Domenico analytical model (1987). After the calibrations were estimated by adjusting values in longitudinal dispersivity, groundwater velocity and degradation rate constant, the horizontal MTBE plume length (maximum distance between source well and plume edge with a MCL <5pbb) was predicted. The data collected produced plume lengths ranging from 69 feet to 2790 feet. The mean calculated plume length was 760 feet. The future objective of the project is to present a comparative analysis of MTBE groundwater contamination between different hydrogeologic settings (e.g., fractured-controlled vs. alluvial-controlled) by reviewing underground storage tank cases in several regions across the state (e.g., California State Water Resources Control Regional Boards 1 (North Coast), 2 (San Francisco Bay), 5 (Central Valley), 6 (Lahontan), 8 (Santa Ana), and 9 (San Diego). The results from this project will (1) further characterize the nature of MTBE plumes, (2) provide data that can be used in future investigation, remediation and monitoring of MTBE plume sites, and (3) lead to refinement of groundwater transport models for MTBE plumes.