Biomedical subjects

Michael C Brooks

Publications and source records attributed to Michael C Brooks.

7 recordsLinked to original sources

PubMed2005

Field demonstration of surfactant-enhanced solubilization of DNAPL at Dover Air Force Base, Delaware.

This study reports on a surfactant-based flood for tetrachloroethylene (PCE) removal from a control test cell at the Dover National Test Site. The surfactant formulation (sodium dihexyl sulfosuccinate (Aerosol-MA or AMA), isopropanol and calcium chloride) was able to achieve a high concentration of PCE in swollen micelles (supersolubilization) without vertical PCE migration. The hydraulic system included eight screened wells that were operated in both vertical circulation and line drive configurations. After 10 pore volumes of flushing, the overall PCE removal was 68% (65% of which corresponded to the surfactant flooding alone). In addition, the residual PCE saturation was reduced from 0.7% to 0.2%, and the concentration of PCE in the groundwater was reduced from 37-190 mg/L before the flushing to 7.3 mg/L after flooding. Recycling the surfactant solution reduced the required surfactant mass (and thus cost, and waste) by 90%. Close to 80% of the total PCE removal was obtained during the first five pore volumes which were operated in an upward vertical circulation flow scheme. No free oil phase was observed during the test. Further analysis of multilevel sampler data suggests that most of the trapped oil remaining in the cell was likely localized in secluded regions of the aquifer, which helps explain the lower PCE groundwater concentration after remedial activities. In summary, this field study demonstrated the feasibility of surfactant-enhanced remediation to reduce the mass in the source zone and significantly reduce the PCE aqueous concentration and therefore the risk associated with the contaminant plume.

2-Propanol↗

PubMed2005

Design of aquifer remediation systems: (1) describing hydraulic structure and NAPL architecture using tracers.

Aquifer heterogeneity (structure) and NAPL distribution (architecture) are described based on tracer data. An inverse modelling approach that estimates the hydraulic structure and NAPL architecture based on a Lagrangian stochastic model where the hydraulic structure is described by one or more populations of lognormally distributed travel times and the NAPL architecture is selected from eight possible assumed distributions. Optimization of the model parameters for each tested realization is based on the minimization of the sum of the square residuals between the log of measured tracer data and model predictions for the same temporal observation. For a given NAPL architecture the error is reduced with each added population. Model selection was based on a fitness which penalized models for increasing complexity. The technique is demonstrated under a range of hydrologic and contaminant settings using data from three small field-scale tracer tests: the first implementation at an LNAPL site using a line-drive flow pattern, the second at a DNAPL site with an inverted five-spot flow pattern, and the third at the same DNAPL site using a vertical circulation flow pattern. The Lagrangian model was capable of accurately duplicating experimentally derived tracer breakthrough curves, with a correlation coefficient of 0.97 or better. Furthermore, the model estimate of the NAPL volume is similar to the estimates based on moment analysis of field data.

Computer Simulation↗

PubMed2005

Design of aquifer remediation systems: (2) estimating site-specific performance and benefits of partial source removal.

A Lagrangian stochastic model is proposed as a tool that can be utilized in forecasting remedial performance and estimating the benefits (in terms of flux and mass reduction) derived from a source zone remedial effort. The stochastic functional relationships that describe the hydraulic "structure" and non-aqueous phase liquid (NAPL) "architecture" have been described in a companion paper (Enfield, C.G., Wood, A.L., Espinoza, F.P., Brooks, M.C., Annable, M., Rao, P.S.C., this issue. Design of aquifer remediation systems: (1) describing hydraulic structure and NAPL architecture using tracers. J. Contam. Hydrol.). The previously defined functions were used along with the properties of the remedial fluids to describe remedial performance. There are two objectives for this paper. First, is to show that a simple analytic element model can be used to give a reasonable estimate of system performance. This is accomplished by comparing forecast performance to observed performance. The second objective is to display the model output in terms of change in mass flux and mass removal as a function of pore volumes of remedial fluid injected. The modelling results suggest that short term benefits are obtained and related to mass reduction at the sites where the model was tested.

Fresh Water↗

PubMed2005

Uncertainty in NAPL volume estimates due to random measurement errors during partitioning tracer tests.

The uncertainty in NAPL volume estimates obtained through partitioning tracers can be quantified as a function of random errors in volume and concentration measurements when moments are calculated from experimentally measured breakthrough curves using the trapezoidal rule for numerical integration. The methodology is based upon standard stochastic methods for random error propagation. Monte Carlo simulations using a synthetic data set derived from the one-dimensional solution of the advective-dispersive equation serve to verify the process. It is shown that the uncertainty in NAPL volume predictions nonlinearly increases as the retardation factor decreases. An important result of this observation is that there is a large degree of uncertainty in using partitioning tracers to conclude NAPL is absent from the swept zone. Under the conditions investigated, random errors in concentration measurements are shown to have a greater impact on NAPL volume uncertainty than random errors in volume measurements, and it is also shown that uncertainty in NAPL volume decreases as the resolution of the breakthrough curves increases. The impact of uncertainty in background retardation (i.e., sorption of partitioning tracers in the absence of NAPL) was also investigated, and it likewise indicated that the relative uncertainty in NAPL volume estimates increases as the retardation factor decreases.

Computer Simulation↗

PubMed2005

Errors in NAPL volume estimates due to systematic measurement errors during partitioning tracer tests.

During moment-based analyses of partitioning tracer tests, systematic errors in volume and concentration measurements propagate to yield errors in the saturation and volume estimates for nonaqueous phase liquid (NAPL). Derived expressions could be applied to help practitioners bracket their estimates of NAPL saturation and volume obtained from such tests. In practice, many of these effects may be overshadowed by other complications experienced in the field. Errors are propagated for systematic constant (offset) volume, proportional volume, and constant (offset) concentration errors. Previous efforts to quantify the impact of these errors were predicated upon the specific assumption that nonpartitioning and partitioning masses were equal. The current work relaxes that assumption and is therefore more general in scope. Through the use of nondimensional concentration, systematic proportional concentration errors do not affect the accuracy of the method. Specific consideration needs to be given to accurate flow measurements and minimizing baseline concentration errors when performing partitioning tracer tests in order to prevent the propagation of systematic errors.

Environmental Monitoring↗

PubMed2004

Controlled release, blind test of DNAPL remediation by ethanol flushing.

A dense nonaqueous phase liquid (DNAPL) source zone was established within a sheet-pile isolated cell through a controlled release of perchloroethylene (PCE) to evaluate DNAPL remediation by in-situ cosolvent flushing. Ethanol was used as the cosolvent, and the main remedial mechanism was enhanced dissolution based on the phase behavior of the water-ethanol-PCE system. Based on the knowledge of the actual PCE volume introduced into the cell, it was estimated that 83 L of PCE were present at the start of the test. Over a 40-day period, 64% of the PCE was removed by flushing the cell with an alcohol solution of approximately 70% ethanol and 30% water. High removal efficiencies at the end of the test indicated that more PCE could have been removed had it been possible to continue the demonstration. The ethanol solution extracted from the cell was recycled during the test using activated carbon and air stripping treatment. Both of these treatment processes were successful in removing PCE for recycling purposes, with minimal impact on the ethanol content in the treated fluids. Results from pre- and post-flushing partitioning tracer tests overestimated the treatment performance. However, both of these tracer tests missed significant amounts of the PCE present, likely due to inaccessibility of the PCE. The tracer results suggest that some PCE was inaccessible to the ethanol solution which led to the inefficient PCE removal rates observed. The flux-averaged aqueous PCE concentrations measured in the post-flushing tracer test were reduced by a factor of 3 to 4 in the extraction wells that showed the highest PCE removal compared to those concentrations in the pre-flushing tracer test.

Environmental Pollutants↗

PubMed2002

Controlled release, blind tests of DNAPL characterization using partitioning tracers.

The partitioning tracer technique for dense nonaqueous phase liquid (DNAPL) characterization was evaluated in an isolated test cell, in which controlled releases of perchloroethylene (PCE) had occurred. Four partitioning tracer tests were conducted, two using an inverted, double five-spot pumping pattern, and two using vertical circulation wells. Two of the four tests were conducted prior to remedial activities, and two were conducted after. Each test was conducted as a "blind test" where researchers conducting the partitioning tracer tests had no knowledge of the volume, method of release, nor resulting spatial distribution of DNAPL. Multiple partitioning tracers were used in each test, and the DNAPL volume estimates varied significantly within each test based on the different partitioning tracers. The tracers with large partitioning coefficients generally predicted a smaller volume of PCE than that expected based on the actual release volume. However, these predictions were made for low DNAPL saturations (average saturation was approximately 0.003), under conditions near the limits of the method's application. Furthermore, there were several factors that may have hindered prediction accuracy, including tracer degradation and remedial fluid interference.

Alcohols↗