RESOLUTION OF A COMINGLED LNAPL PLUME TO ADDRESS POTENTI^ MTBE RELEASE(S)

摘要

At an active refinery located on the US West Coast, neat Methyl Tert-Butyl Ether (MTBE) was historically released and dispersed into an existing comingled light, non-aqueous phase liquids (LNAPL) plume. Currently the MTBE in the LNAPL, and in the dissolved phase, is being delineated under a remediation program. As MTBE was phased out by regulation, there was no more use or operation associated with MTBE at the refinery; however, because the oversight agency experienced MTBE issues associated with improperly abandoned; pipelines at similar facilities in the area and the fact that the LNAPL MTBE concentration in-one of the monitoring wells substantially increased as compared with previous years, the oversight agency expressed concern on potential on-going releases of MTBE associated with an abandoned pipeline. Accordingly, a request was made to the client to address the issue under their Product Release Detection Program. Interviews with refinery staff and extensive review of operational history suggested that the on-going release scenario postulated by the agency is unlikely. A review of histoncal groundwater levels did not indicate any correlation with MTBE concentrations. Based on the information on the location of historical MTBE storage, LNAPL distribution in the are recovery well operation, and site hydrogeology, it appears that the fluctuation of MTBE concentrations in LNAPL is related to various degree of subsurface mixing of the released] refinery intermediate stream products due to dynamics of recovery well operation (e g., pumps on and off; pumping rate high or low, etc). To substantiate the suggestion, a forensic, study was conducted to provide additional evidence. The approach for the study was to resolve the comingled MTBE-containing LNAPL plume so that a correlation can be made between change of relative percentages of the "endi member" products of the comingled LNAPL plume and LNAPL MTBE concentrations over time. This paper presents the methodology to resolve the comingled LNAPL plume and, findings based on the correlation.