Title: Western Region Hazardous Substance Research Center Project 1-SU-01
Strategies for Cost-Effective In Situ Mixing of Contaminants and Additives in Bioremediation

Investigators: Peter Kitanidis, Stanford University; Craig Criddle, Stanford University

Institution: Oregon State University

Research Category: Groundwater, treatment, bioremediation

Project Period: 2001-2003

Goals: (1) To develop and critically evaluate principles and strategies for mixing, using recirculation units, pairs of extraction-injection wells, sparging, biocurtains, combined systems and operations that are sequenced in time and space. (2) To develop methods for cost-effective chemical delivery and mixing, prevention of clogging, and hydraulic control. (3) To define the range of application of these methods and compare them on the same basis in terms of effectiveness and cost. (4) To synthesize available knowledge and previous experience on flow, transport, and biochemical reactions using results from field-scale studies. (5) To advance and test theories for subsurface mixing at field scales through hydrodynamic dispersion, partitioning, fingering, etc. (6) To develop a set of tools and guidelines for the design of cost-effective in situ delivery and mixing systems.

Rationale: Effective mixing and chemical delivery schemes is essential in the success of in situ remediation methods. This is because these methods usually require the injection of growth promoters (in situ bioremediation), chemical additives (e.g., surfactant-enhanced remediation), or cells (bioaugmentation). To achieve successful mixing and chemical delivery at the field-scale, we needed to (1) create a sufficiently large in situ reactor, and (2) regulate residence times.

Approach: In this research, principles of mixing and the performance of mixing schemes were studied, and a broad range of existing and new full-scale mixing and chemical delivery schemes were evaluated through comprehensive mathematical, technical, and economic analysis. Research was guided by case studies.

Summary of Findings The design of an effective chemical delivery and mixing scheme for in situ bioremediation of Uranium (VI) at Oak Ridge National Laboratory (ORNL) was the focus. This was a challenging site, characterized by complex hydrogeology and biogeochemistry. The subsurface material was highly weathered saprolite. In addition to high uranium concentration, the pH was exceptionally low, at about 3.5, and nitrates were exceptionally high, at about 10 g/L. Nitrate needed to be removed and the pH needed to be raised in a controlled fashion, e.g., to prevent clogging of the porous medium from precipitation of aluminum. The speciation of U(VI), and thus its mobility, was controlled strongly by the pH. An elaborate on-site treatment plant was designed and combined with a multi-step in situ treatment experiment. We developed mathematical models of flow, transport and biogeochemistry and are comparing predictions with the results of experiments and field tests. We developed software for the delineation of injection, extraction, and recirculation zones; the efficient determination of breakthrough curves; the application of travel-time methods of modeling transport; and biogeochemical modeling using PHREEQC in conjunction with hydrogeological modeling within the MATLAB computational environment. These modeling tools were implemented at the ORNL site to extract information from data and assist in the design of new experiments.

Publications:

Journal Articles

Fienen, M. N., Luo, J., Kitanidis, P. K. (2005).Semi-Analytical, Homogeneous, Anisotropic Capture Zone Delineation. Journal of Hydrology. 312(1-4): 39-50. doi:10.1016/j.jhydrol.2005.02.008.

Fienen, M.N., J. Luo, P. K. Kitanidis (2006).A Bayesian Geostatistical Transfer Function Approach to Tracer Test Analysis. Water Resources Research, 42, doi:10.1029/2005WR004576.

Luo, J. and Kitanidis, P. K. (2004). Fluid residence times within a recirculation zone created by an extraction-injection well pair. J. of Hydrology, 295(1-4): 149-162.

Luo, J., Cirpka, O.A., Kitanidis, P.K. (2006). Temporal-moment matching for truncated breakthrough curves for step or step-pulse injection. Adv. Water Resour.,, 29(9), 1306-1313.

Luo, J., Wu, W-M., Fienen, M.N., Jardine, P.M., Mehlhorn, T.L., Watson, D.B., Cirpka, O.A., Criddle, C.S., Kitanidis, P.K. (2006). A nested-cell approach for in situ remediation. Ground Water, 44(2), 266-274.

 

Conferences Proceedings and Presentations

Luo, J., Fienen, M. N. and Kitanidis, P. K. (2002). 3-D Groundwater Flow Modeling for the Oak Ridge Reservation (ORR): Finite-Volume Method on An Unstructured Grid System. Proceeding of the International Groundwater Symposium, Berkeley, California, (March 25-28).

 

Theses

Fienen, M. N. (2006). Inverse Methods for Near-field Hydrogeologic Characterization. PhD, Stanford University.

Luo, J. (2005). Hydraulic Control and Reactive Transport Modeling for In-Situ Bioremediation of Uranium Contaminated Groundwater. PhD, Stanford University.

 

Software

Fienen, M. N., Luo, J., Kitanidis, P. K. (2005). ComCZAR:Complex Capture Zone Analysis Routine. http://www.talulat.com/mike/software/.

Fienen, M. N., J. Luo, P. K. Kitanidis (2006).A Bayesian Geostatistical Transfer Function Approach to Tracer Test Analysis - Implementation and Examples. http://www.talulat.com/mike/software/lstran.html.

 

Supplemental Keywords: In situ, remediation, groundwater, technology transfer