ARCHIVED REPORTS XR0008945 - Laserfiche WebLink

Home Browse Search

Other possible sources of measured TBA in groundwater, including abiotic transformation in the environment, or presence of TBA as an artifact of chemical analysis methods, for the conditions investigated, are likely insignificant contributors for the levels of TBA observed at the investigated sites Microcosm analyses conducted on soils (collected below the water table) as part of this work showed degradation of MTBE and TBA in both aerobic and anaerobic conditions Investigation of co-metabolism of TBA or MTBE in the presence of propane was inconclusive, since degradation had been observed without the presence of the selected (propane) co-metabolic substrate In further conclusion, the identified prevalence of observed biodegradation of MTBE and TBA at the investigated sites is encouraging evidence for either a monitored natural attenuation or enhanced natural attenuation solution for these sites, as well as other similar underground storage tank remediation project sites Either existing natural attenuation guidance (ASTM E1943-98, Wiedemeier et al 1995, 1997) or a modified guidance to-be-developed would aid in this application As a preliminary proposal, along the lines of evidence commonly used in natural attenuation studies • To establish plume stability Continued groundwater monitoring of MTBE, TBA, and other chemicals of concern in quarterly monitoring events Evaluation of trends in data using statistical or other methods to establish that concentrations in the groundwater plume are stable or decreasing in time and extent Geochemical indicators Monitoring of relevant electron acceptors, primarily dissolved oxygen, sulfate, and nitrate, as well as methane, as evidence of biological activity • Biological indicators In selected cases, laboratory microcosm studies of site media samples to establish the level and type of biological transformation occurring at a site Finally, we note that the selected sites exhibited low groundwater gradients and inferred low groundwater seepage velocities We would expect the effects of biological degradation to be more significant and observable at these types of sites, than at sites with higher groundwater flow rates (high permeability/high recharge sites) This is especially true if degradation in anaerobic conditions is the significant transformation and removal mechanism 9. References ASTM 1998 Standard Guide for Remediation of Ground Water by Natural Attenuation at Petroleum Release Sites,E1943-98, American Society for Testing Materials West Conshohocken,PA 23