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Mackay's group addresses many aspects of groundwater contamination and decontamination, often utilizing highly detailed field studies of existing groundwater contamination and/or highly controlled field experiments. Both are conducted with resolution approaching that of laboratory studies but at scales and often including processes impossible to represent in laboratory studies. Contaminants investigated to date include:
From 1999 through 2009, both types of field research were conducted at a site at Vandenberg Air Force Base (VAFB) addressing: 1) in situ aerobic biodegradation of methyl tert-butyl ether (MTBE) and tert butyl alcohol (TBA), 2) methods to engineer in situ aerobic biotreatment of MTBE and/or TBA plumes, 3) impact of ethanol on natural attenuation (anaerobic biodegradation) of model components of gasoline (benzene, toluene, and o-xylene), 4) impact of ethanol on anaerobic biotransformation of MTBE to TBA), 5) natural biodegradation of TBA under sulfate-reducing conditions, 6) role of diffusion in controlling the flushing of contaminants from aquifers bounded with low permeability aquitards, 7) methods for estimating the total mass flux (mass discharge) of contaminants carried by groundwater flow through aquifers, and 8) methods for assessing bioremediation performance (including bio-traps, molecular methods applied to water or sediment samples, and compound-specific isotope analyses). In 2009-2010, we have applied molecular methods to characterize the microbial populations in an aquifer at a former refinery site. Our specific goals have been to determine if the monitoring tools can confirm the presence and activity of microbes capable of benzene degradation under sulfate-reducing conditions. In 2011 we have initiated new field studies at petroleum-impacted sites with sulfate-dominated aquifers to explore the feasibility of what we are calling Accelerated Natural Sulfate Reduction (ANSR) for enhancing the rate of in situ biodegradation of contaminants. This method may involve mixing of contaminated groundwater depleted in sulfate with adjacent or underlying groundwater with naturally elevated concentrations of sulfate, if we determine sulfate is the key limitation. On the other hand, we will be examining various types of monitoring data to determine if there are other limitations on biodegradation at the sites that may require attention before adding sulfate would be useful. We are also collaborating with Prof. Uli Mayer, U. British Columbia, and others to study flux of gases at ground surface arising from in situ biodegradation of biofuels in the vadose or saturated zones (see Recent News for more detail). Other topics that Mackay's groups have addressed via field research in the past include: 1) transport, sorption and degradation of various organic contaminants in sandy aquifers, 2) factors limiting pump & treat remediation of contaminated groundwater, 3) comparison of pulsed and continuous pumping for groundwater remediation by pump & treat technologies, 4) pesticide transport and sorption in groundwater, 5) remediation of groundwater via various configurations of permeable reactive biobarriers (e.g., aerobic PRBs using diffusive oxygen releasers or solid oxygen sources; anaerobic PRBs using diffusive hydrogen release or zero valent iron), 6) flushing of a high-concentration, multi-component organic/inorganic contaminant plume from a granular aquifer overlying a fractured aquitard, 7) vulnerability of Mexico City's aquifer to contamination.
Douglas M. Mackay Adjunct Professor, Department of Land, Air & Water Resources http://lawr.ucdavis.edu/ |
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