HR: 1340h
AN: H13A-1318    [Abstracts]
TI: Assessment of Alternative Conceptual Models Using Reactive Transport Modeling with Monitoring Data
AU: Dai, Z
EM: zdai@alltel.net
AF: Advanced Environmental Solutions, LLC, 407 West Main St., Lexington, SC 29072 United States
AU: * Price, V
EM: vprice@alltel.net
AF: Advanced Environmental Solutions, LLC, 407 West Main St., Lexington, SC 29072 United States
AU: Heffner, D
EM: dheffner@advenvsoln.com
AF: Advanced Environmental Solutions, LLC, 407 West Main St., Lexington, SC 29072 United States
AU: Hodges, R
EM: rhodges@alltel.net
AF: Advanced Environmental Solutions, LLC, 407 West Main St., Lexington, SC 29072 United States
AU: Temples, T
EM: ttemples@sc.edu
AF: Center for Water Research and Policy, University of South Carolina, 901 Sumter St., Columbia, SC 29208 United States
AU: Nicholson, T
EM: tjn@nrc.gov
AF: U.S. Nuclear Regulatory Commission, 11545 Rockville Pike, Rockville, MD 20852 United States
AB: Monitoring data proved very useful in evaluating alternative conceptual models, simulating contaminant transport behavior, and reducing uncertainty. A graded approach using three alternative conceptual site models was formulated to simulate a field case of tetrachloroethene (PCE) transport and biodegradation. These models ranged from simple to complex in their representation of subsurface heterogeneities. The simplest model was a single-layer homogeneous aquifer that employed an analytical reactive transport code, BIOCHLOR (Aziz et al., 1999). Due to over-simplification of the aquifer structure, this simulation could not reproduce the monitoring data. The second model consisted of a multi-layer conceptual model, in combination with numerical modules, MODFLOW and RT3D within GMS, to simulate flow and reactive transport. Although the simulation results from the second model were comparatively better than those from the simple model, they still did not adequately reproduce the monitoring well concentrations because the geological structures were still inadequately defined. Finally, a more realistic conceptual model was formulated that incorporated heterogeneities and geologic structures identified from well logs and seismic survey data using the Petra and PetraSeis software. This conceptual model included both a major channel and a younger channel that were detected in the PCE source area. In this model, these channels control the local ground-water flow direction and provide a preferential chemical transport pathway. Simulation results using this conceptual site model proved compatible with the monitoring concentration data. This study demonstrates that the bias and uncertainty from inadequate conceptual models are much larger than those introduced from an inadequate choice of model parameter values (Neuman and Wierenga, 2003; Meyer et al., 2004; Ye et al., 2004). This case study integrated conceptual and numerical models, based on interpreted local hydrogeologic and geochemical data, with detailed monitoring plume data. It provided key insights for confirming alternative conceptual site models and assessing the performance of monitoring networks. A monitoring strategy based on this graded approach for assessing alternative conceptual models can provide the technical bases for identifying critical monitoring locations, adequate monitoring frequency, and performance indicator parameters for performance monitoring involving ground-water levels and PCE concentrations.
DE: 1800 HYDROLOGY
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: Fall Meeting 2005