The Experts below are selected from a list of 96 Experts worldwide ranked by ideXlab platform
Lynn Michael - One of the best experts on this subject based on the ideXlab platform.
-
Restaurant Tips and Service Quality: A Commentary on Bodvarsson, Luksetich and McDermott
The Scholarly Commons, 2003Co-Authors: Lynn MichaelAbstract:Bodvarsson, et. al. (2003) argue that a non-recursive relationship between service and tipping has lead researchers to under-estimate the strength of the causal impact of service on tipping. In this paper, I criticize their arguments, analyses, and conclusions. Then, I reanalyze their data to draw more appropriate conclusions about what the data say concerning the effects of service on tipping
-
Restaurant Tips and Service Quality: A Commentary on Bodvarsson, Luksetich and McDermott
'Informa UK Limited', 2003Co-Authors: Lynn MichaelAbstract:Bodvarsson, et. al. (2003) argue that a non-recursive relationship between service and tipping has lead researchers to under-estimate the strength of the causal impact of service on tipping. In this paper, I criticize their arguments, analyses, and conclusions. Then, I reanalyze their data to draw more appropriate conclusions about what the data say concerning the effects of service on tipping.Lynn26_Restaurant_Tips_and_Service_Quality.pdf: 367 downloads, before Aug. 1, 2020
-
The Relationship between Tipping and Service Quality: A Comment on Bodvarsson and Gibson’s Article
The Scholarly Commons, 2000Co-Authors: Lynn MichaelAbstract:Numerous studies have found that tip size is only weakly related to service quality. Bodvarsson and Gibson recently challenged this finding—criticizing previous research and reporting that consumers say they would tip substantially different amounts with different levels of service quality. This paper presents a critical response to Bodvarsson and Gibson’s article. Contrary to Bodvarsson and Gibson’s claims, the weakness of the tipping–service relationship in the existing literature is not just a reflection of restricted variability in service ratings. Nor is it attributable to other methodological problems with service ratings. Furthermore, the data from Bodvarsson and Gibson’s role-playing survey is suspect, because what people say they would do in a given situation is often different from what they actually do in that situation
-
The Relationship between Tipping and Service Quality: A Comment on Bodvarsson and Gibson’s Article
'Elsevier BV', 2000Co-Authors: Lynn MichaelAbstract:Numerous studies have found that tip size is only weakly related to service quality. Bodvarsson and Gibson recently challenged this finding—criticizing previous research and reporting that consumers say they would tip substantially different amounts with different levels of service quality. This paper presents a critical response to Bodvarsson and Gibson’s article. Contrary to Bodvarsson and Gibson’s claims, the weakness of the tipping–service relationship in the existing literature is not just a reflection of restricted variability in service ratings. Nor is it attributable to other methodological problems with service ratings. Furthermore, the data from Bodvarsson and Gibson’s role-playing survey is suspect, because what people say they would do in a given situation is often different from what they actually do in that situation.Lynn39_The_relationship_between_tipping_and_service_quality.pdf: 9954 downloads, before Aug. 1, 2020
June Fabrykamartin - One of the best experts on this subject based on the ideXlab platform.
-
evolution of the conceptual model of unsaturated zone hydrology at yucca mountain nevada
Journal of Hydrology, 2001Co-Authors: Alan L Flint, G S Bodvarsson, Lorraine E Flint, Edward M Kwicklis, June FabrykamartinAbstract:Abstract Yucca Mountain is an arid site proposed for consideration as the United States’ first underground high-level radioactive waste repository. Low rainfall (approximately 170 mm/yr) and a thick unsaturated zone (500–1000 m) are important physical attributes of the site because the quantity of water likely to reach the waste and the paths and rates of movement of the water to the saturated zone under future climates would be major factors in controlling the concentrations and times of arrival of radionuclides at the surrounding accessible environment. The framework for understanding the hydrologic processes that occur at this site and that control how quickly water will penetrate through the unsaturated zone to the water table has evolved during the past 15 yr. Early conceptual models assumed that very small volumes of water infiltrated into the bedrock (0.5–4.5 mm/yr, or 2–3 percent of rainfall), that much of the infiltrated water flowed laterally within the upper nonwelded units because of capillary barrier effects, and that the remaining water flowed down faults with a small amount flowing through the matrix of the lower welded, fractured rocks. It was believed that the matrix had to be saturated for fractures to flow. However, accumulating evidence indicated that infiltration rates were higher than initially estimated, such as infiltration modeling based on neutron borehole data, bomb-pulse isotopes deep in the mountain, perched water analyses and thermal analyses. Mechanisms supporting lateral diversion did not apply at these higher fluxes, and the flux calculated in the lower welded unit exceeded the conductivity of the matrix, implying vertical flow of water in the high permeability fractures of the potential repository host rock, and disequilibrium between matrix and fracture water potentials. The development of numerical modeling methods and parameter values evolved concurrently with the conceptual model in order to account for the observed field data, particularly fracture flow deep in the unsaturated zone. This paper presents the history of the evolution of conceptual models of hydrology and numerical models of unsaturated zone flow at Yucca Mountain, Nevada ( Flint, A.L., Flint, L.E., Kwicklis, E.M., Bodvarsson, G.S., Fabryka-Martin, J.M., 2001. Hydrology of Yucca Mountain. Reviews of Geophysics in press ). This retrospective is the basis for recommendations for optimizing the efficiency with which a viable and robust conceptual model can be developed for a complex site.
G S Bodvarsson - One of the best experts on this subject based on the ideXlab platform.
-
Analyzing Flow Patterns in Unsaturated Fractured Rock of Yucca Mountain Using an Integrated Modeling Approach
2020Co-Authors: Keni Zhang, L Pan, G S BodvarssonAbstract:Abstract This paper presents a series of modeling investigations to characterize percolation patterns in the unsaturated zone of Yucca Mountain, Nevada, a proposed underground repository site for storing high-level radioactive waste. The investigations are conducted using a modeling approach that integrates a wide variety of moisture, pneumatic, thermal, and isotopic geochemical field data into a comprehensive three-dimensional numerical model through model calibration. This integrated modeling approach, based on a dualcontinuum formulation, takes into account the coupled processes of fluid and heat flow and chemical isotopic transport in Yucca Mountain's highly heterogeneous, unsaturated fractured tuffs. In particular, the model results are examined against different types of field-measured data and used to evaluate different hydrogeological conceptual models and their effects on flow patterns in the unsaturated zone. The objective of this work to provide understanding of percolation patterns and flow behavior through the unsaturated zone, which is a crucial issue in assessing repository performance. Introduction Since the 1980s, the unsaturated zone (UZ) of the highly heterogeneous, fractured tuff at Yucca Mountain, Nevada, has been investigated by the U.S. Department of Energy as a possible repository site for storing high-level radioactive waste. Characterization of flow and transport processes in fractured rock of the Yucca Mountain UZ has received significant attention and generated tremendous interest in scientific communities over the last two decades. During this long and extensive study, many types of data have been collected from the Yucca Mountain UZ, and these data have helped to develop a conceptual understanding of various physical processes within the UZ system. The complexity of geological conditions and physical processes within the Yucca Mountain has posed a tremendous challenge for site-characterization effort, while quantitative evaluation of fluid flow, chemical transport, and heat transfer has proven to be essential. The need for quantitative investigations of flow and transport at the Yucca Mountain site has motivated a continual effort in developing and applying large, mountain-scale flow and transport models [e.g., Wu et al., 1999a and The site characterization studies of the unsaturated tuff at the Nevada Test Site and at Yucca Mountain began in the late 1970s and early 1980s. Those early hydrological, geological, and geophysical investigations of Yucca Mountain and the surrounding region were conducted to assess the feasibility of the site as a geological repository for storing high-level radioactive waste and to provide conceptual understanding of UZ flow processes In the early 1990s, more progress was made in UZ model development. Wittwer et al. [1992, 1995] developed a three-dimensional (3-D) site-scale model that incorporated several geological and hydrological complexities, such as geological layering, degree of welding, fault offsets, and different matrix and fracture properties. The 3-D model handled fracture-matrix flow using an effective continuum method (ECM) and was applied to evaluate various assumptions concerning faults and infiltration patterns. Using the ECM concept, Ahlers et al. [1995a, 1995b] continued development of the UZ site-scale model with increased numerical and spatial resolution. Their studies considered more processes, such as gas and heat flow analyses, and introduced an inverse modeling approach for estimating model-input properties. However, more comprehensive UZ models were not developed until a couple of years later, when the UZ models were developed for total system performance assessment-viability assessment (TSPA-VA) [e.g., Wu et al., 1999a and The next generation of UZ models included those primarily developed for the TSPA-site recommendation (SR) calculations [e.g., Wu et al., 2002a; Moridis et al., 2003; Robinson et al., 2003]. These TSPA-SR models were enhanced from the TSPA-VA model. More 4 importantly, the newer models took into account the coupled processes of flow and transport in highly heterogeneous, unsaturated fractured porous rock, and were applied to analyzing the effect of current and future climates on radionuclide transport through the UZ system. The site-scale UZ flow and transport models developed during the site characterization of Yucca Mountain have built upon the past research as well as the above-referenced work and many other studies [e.g., McLaren et al., 2000; Robinson et al., 1996 and 1997; This paper presents the results of our continuing effort to develop a realistic and representative UZ flow model to characterize the Yucca Mountain UZ system. More specifically, we focus on analyzing unsaturated flow patterns in the Yucca Mountain UZ under various climates and different hydrogeological conceptual models using an integrated modeling approach. This effort integrates different field-observed data, such as water potential, liquid saturation, perched water, gas pressure, chloride, and temperature logs into one single 3-D UZ flow and transport model. Using the dual-permeability modeling approach, the integrated modeling effort provides consistent model predictions for different, but inter-related hydrological, pneumatical, geochemical, and geothermal processes in the UZ. More importantly, such an integrated modeling exercise will improve the model's capability and credibility in describing and predicting current and future conditions and processes of the UZ system. At the same time, the combined model calibration will present a consistent check on modeled percolation fluxes and reveal better insight into the UZ flow patterns. The modeling study of this work consists of (1) UZ model description; (2) model development and calibration using liquid saturation, water potential, perched water, and pneumatic data; (3) assessing percolation patterns and flow behavior using thermal and geochemical data; and (4) simulated percolation pattern analysis. Conceptual Model of UZ Flow Over the past two decades, extensive scientific investigations have been conducted for the site characterization of Yucca Mountain, including data collection from surface mapping, sampling from many deep and shallow boreholes, constructing underground tunnels, and field testing [e.g., Rousseau, 1998]. of faults and perched water on the UZ system. As illustrated in In fact, the PTn's capability of attenuating episodic percolation fluxes has been observed in field tests of water release into the PTn matrix In addition, the possibility for capillary barriers exists at both upper and lower PTn contacts, as well as within the PTn layers PTn layers. However, the extent of lateral flow diversion within the PTn remains a topic of debate. For example, a recent study using a conceptual model with transitional changes in rock properties argues that lateral diversion may be small Perched Water Perched water has been encountered in a number of boreholes at Yucca Mountain, including UZ-14, SD-7, SD-9, SD-12, NRG-7a, G-2, and WT-24 ( Perched water may occur where percolation flux exceeds the capacity of the geological media to transmit vertical flux in the UZ [Rousseau et al., 1998]. Several conceptual models have been investigated for explaining the genesis of perched water at Yucca Mountain [e.g., Wu et al., 1999b and Faults In addition to possible capillary and permeability barriers, major faults in the UZ are also expected to play an important role in controlling percolation flux. Permeability within faults is much higher than that in the surrounding tuff Pneumatic permeability measurements taken along portions of faults revealed low airentry pressures, indicating that large fracture apertures are present in the fault zones. Highly brecciated fault zones may act as vertical capillary barriers to lateral flow. Once water is diverted into a fault zone, however, its high permeability could facilitate rapid vertical flow through the unsaturated system Heterogeneity A considerable amount of field data, obtained from tens of boreholes, two underground tunnels, and hundreds of outcrop samples at the site, constrains the distribution of rock properties within different units. In general, field data indicate that the Yucca Mountain formation is more heterogeneous vertically than horizontally, such that layer-wise representations are found to provide reasonable approximations of the complex geological system. This is because many model calibration results using this approximation are able to match different types of observation data obtained from different locations and depths [e.g., Bandurraga and Bodvarsson, 1999; 8 In summary, as shown in Ambient water flow in the UZ system is at a quasi-steady state condition, subject to spatially varying net infiltration on the ground surface. Hydrogeological units/layers are internally homogeneous, unless interrupted by faults or altered. There may exist capillary barriers in the PTn unit, causing lateral flow. Perched water results from permeability barrier effects. Major faults serve as fast vertical flow pathways for laterally diverted flow. Numerical Modeling Approach and Model Description Because of the complexity of the UZ geological system and the highly nonlinear nature of governing equations for UZ flow and transport, numerical modeling approaches were used in this study. Numerical simulations were carried out using the TOUGH2 and T2R3D codes [Pruess, 1991; Wu et al., 1996]. Most UZ flow simulations in this study were performed using an unsaturated flow module of the TOUGH2 code, which solves Richards' equation. Two active phases (liquid and gas) and heat flow was simulated using a two-phase fluid and heat flow module. Tracer and geochemical transport runs were carried out with the T2R3D code. Numerical Model Grids There are two 3-D numerical model grids used in this study, as shown in plan view in consists of 980 mesh columns of fracture and matrix continua, 86,440 gridblocks, and 350,000 connections in a dual-permeability grid. Vertically, the thermal grid has an average of 45 computational grid layers. Modeling Fracture-Matrix Interaction Modeling fracture and matrix flow and interaction under multiphase, multicomponent, isothermal or nonisothermal conditions has been a key issue for simulating fluid and heat flow in the Yucca Mountain UZ. Different modeling approaches have been tested for handling fracture-matrix interaction at Yucca Mountain The dual-permeability methodology considers global flow and transport occurring not only between fractures but also between matrix gridblocks. In this approach, the rockvolume domain is represented by two overlapping (yet interacting) fracture and matrix 10 continua, and local fracture-matrix flow and transport is approximated as a quasi-steady state. When applied in this work, however, the traditional dual-permeability concept is first modified by using an active fracture model Model Input Parameters Since the Richards' and two-active-phases flow equations are used in modeling unsaturated flow of water and air through fracture and matrix, relative permeability and capillary pressure curves are needed for the two media. In addition, other intrinsic fracture and matrix properties are also needed, such as porosity, permeability, density, and fracture geometric parameters, as well as rock thermal properties. In our modeling study, the van Genuchten models of relative permeability and capillary pressure functions The model input parameters of fractured and matrix rock were determined by two steps: (1) using field and laboratory measurements Model Boundary Conditions The ground surface of the mountain (or the tuff-alluvium contact in the area of significant alluvial cover) is taken as the top model boundary, while the water table is treated as the bottom model boundary. For flow simulations, net infiltration is applied to fractures along the top boundary using a source term. The bottom boundary at the water table is treated as a Dirichlet-type boundary. All the lateral boundaries, as shown in Net infiltration of water, resulting from precipitation that penetrates the top-soil layer of the mountain, is the most important factor affecting the overall hydrological, geochemical and thermal-hydrological behavior of the UZ. Net infiltration is the ultimate source of groundwater recharge and deep-zone percolation through the UZ, and provides a vehicle for transporting radionuclides from the repository to the water table. To cover the various possible scenarios and uncertainties of current and future climates at Yucca Mountain, we have incorporated a total of nine net infiltration maps, provided by US Geological Survey (USGS) scientists [Hevesi and Flint, 2000; As shown in Model Calibration The complexities of the heterogeneous geological formation at the Yucca Mountain UZ, A total of 18 flow simulation scenarios are studied in this work, as listed in In these calibrations, the gas flow model uses the UZ thermal model grid Comparison of model simulation results and field-measured pneumatic data for boreholes UZ-7a is shown in Flow Patterns and Analyses The primary objective of modeling UZ flow at Yucca Mountain is to estimate percolation flux through the UZ system. This is because percolation is the most critical factor that affects overall repository performance under current and future climates. However, in situ Past studies [e.g., Wu et al., 2002a] have shown that it is very difficult even to quantify the range of percolation fluxed by using hydrological data alone. Percolation patterns inside the UZ strongly depend on infiltration rates and their spatial distribution, among other factors. Therefore, over the past two decades, significant research effort has been devoted to estimating the infiltration rates [e.g., Flint et al., 1996; Hevesi and Flint, 2000; 17 Simulated Percolation Fluxes Percolation Patterns at Repository: Percolation fluxes at the repository horizon, as predicted using 18 3-D UZ flow simulation results of Flow Pattern Analyses Simulated In this study, heat flow simulations use the 3-D thermal model grid Temperature distributions at the bottom boundary of the thermal model are taken from deep-borehole-measured temperature profiles All Cl transport simulations were run using the T2R3D code for 100,000 years to approximate the current, steady-state condition under the infiltration scenarios considered. Chloride is treated as a conservative component transported through the UZ, subject to advection, diffusion, and first-order delay. The mechanical dispersion effect through the fracture-matrix system was ignored. A constant molecular diffusion coefficient of 2.032 × 10 -9 m 2 /s is used for matrix diffusion for Cl and the half-life for radioactive decay is 301,000 years. Concluding Remarks This paper presents a large-scale modeling study to characterize percolation patterns in the unsaturated zone of Yucca Mountain, Nevada, a proposed underground repository site for storing high-level radioactive waste. The modeling studies are conducted using an integrated modeling approach, which incorporates a wide variety of field data into a This study summarizes our current research effort to characterize UZ flow patterns at Yucca Mountain. Even with the significant progress made in quantitative evaluation of UZ flow and transport processes at the site using numerical models over the last two decades, there still exist a number of limitations and shortcomings with these models and their results. In general, accuracy and reliability of UZ site-scale models and simulation results are critically dependent on the accuracy of estimated model-related properties and other types of input parameters as well as hydrogeological conceptual models. The main limitations and uncertainties with the current UZ site-scale models are (1) the lack of indepth knowledge of the mountain system (including the geological and conceptual models and the availability of field and laboratory data), and (2) the approximations of a large volume-averaged modeling approach. As a result, continual research effort is still 26 needed toward a better understanding of the Yucca Mountain UZ system
-
evolution of the conceptual model of unsaturated zone hydrology at yucca mountain nevada
Journal of Hydrology, 2001Co-Authors: Alan L Flint, G S Bodvarsson, Lorraine E Flint, Edward M Kwicklis, June FabrykamartinAbstract:Abstract Yucca Mountain is an arid site proposed for consideration as the United States’ first underground high-level radioactive waste repository. Low rainfall (approximately 170 mm/yr) and a thick unsaturated zone (500–1000 m) are important physical attributes of the site because the quantity of water likely to reach the waste and the paths and rates of movement of the water to the saturated zone under future climates would be major factors in controlling the concentrations and times of arrival of radionuclides at the surrounding accessible environment. The framework for understanding the hydrologic processes that occur at this site and that control how quickly water will penetrate through the unsaturated zone to the water table has evolved during the past 15 yr. Early conceptual models assumed that very small volumes of water infiltrated into the bedrock (0.5–4.5 mm/yr, or 2–3 percent of rainfall), that much of the infiltrated water flowed laterally within the upper nonwelded units because of capillary barrier effects, and that the remaining water flowed down faults with a small amount flowing through the matrix of the lower welded, fractured rocks. It was believed that the matrix had to be saturated for fractures to flow. However, accumulating evidence indicated that infiltration rates were higher than initially estimated, such as infiltration modeling based on neutron borehole data, bomb-pulse isotopes deep in the mountain, perched water analyses and thermal analyses. Mechanisms supporting lateral diversion did not apply at these higher fluxes, and the flux calculated in the lower welded unit exceeded the conductivity of the matrix, implying vertical flow of water in the high permeability fractures of the potential repository host rock, and disequilibrium between matrix and fracture water potentials. The development of numerical modeling methods and parameter values evolved concurrently with the conceptual model in order to account for the observed field data, particularly fracture flow deep in the unsaturated zone. This paper presents the history of the evolution of conceptual models of hydrology and numerical models of unsaturated zone flow at Yucca Mountain, Nevada ( Flint, A.L., Flint, L.E., Kwicklis, E.M., Bodvarsson, G.S., Fabryka-Martin, J.M., 2001. Hydrology of Yucca Mountain. Reviews of Geophysics in press ). This retrospective is the basis for recommendations for optimizing the efficiency with which a viable and robust conceptual model can be developed for a complex site.
Law Ryan - One of the best experts on this subject based on the ideXlab platform.
-
Geothermal systems in the Chalk of the south east of England : methods of predicting thermal transport in a fractured aquifer
2010Co-Authors: Law RyanAbstract:There has recently been a steady increase in the number of licenses granted for the abstraction of water from the Chalk aquifer beneath London to supply "open loop" geothermal systems (Environment Agency, 2007). However, there has been little research conducted on how the water re-injected by these systems, which often differs in temperature by as much as 10°C, will interact with the fractured Chalk aquifer in both the short and long term. An analytical solution developed by Bodvarsson (1989) was used to show that, for most configurations of a geothermal system, thermal transport would be governed by fractures. It was then proved that the United States Geological Survey SUTRA code could be used to construct a more detailed model of the aquifer. A thermal test was devised to collect hydrogeological and thermal data. This test, along with conventional site investigation techniques, was used at a site in central London. A detailed numerical model of the geothermal system and the aquifer was then constructed in SUTRA. The results showed that the fracture zones found during testing would affect the system performance. Building on these results a procedure was developed for designers, to ensure such systems function in an appropriate way.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
-
Geothermal systems in the Chalk of the south east of England: methods of predicting thermal transport in a fractured aquifer
2010Co-Authors: Law RyanAbstract:There has recently been a steady increase in the number of licenses granted for the abstraction of water from the Chalk aquifer beneath London to supply "open loop" geothermal systems (Environment Agency, 2007). However, there has been little research conducted on how the water re-injected by these systems, which often differs in temperature by as much as 10°C, will interact with the fractured Chalk aquifer in both the short and long term. An analytical solution developed by Bodvarsson (1989) was used to show that, for most configurations of a geothermal system, thermal transport would be governed by fractures. It was then proved that the United States Geological Survey SUTRA code could be used to construct a more detailed model of the aquifer. A thermal test was devised to collect hydrogeological and thermal data. This test, along with conventional site investigation techniques, was used at a site in central London. A detailed numerical model of the geothermal system and the aquifer was then constructed in SUTRA. The results showed that the fracture zones found during testing would affect the system performance. Building on these results a procedure was developed for designers, to ensure such systems function in an appropriate way
Alan L Flint - One of the best experts on this subject based on the ideXlab platform.
-
evolution of the conceptual model of unsaturated zone hydrology at yucca mountain nevada
Journal of Hydrology, 2001Co-Authors: Alan L Flint, G S Bodvarsson, Lorraine E Flint, Edward M Kwicklis, June FabrykamartinAbstract:Abstract Yucca Mountain is an arid site proposed for consideration as the United States’ first underground high-level radioactive waste repository. Low rainfall (approximately 170 mm/yr) and a thick unsaturated zone (500–1000 m) are important physical attributes of the site because the quantity of water likely to reach the waste and the paths and rates of movement of the water to the saturated zone under future climates would be major factors in controlling the concentrations and times of arrival of radionuclides at the surrounding accessible environment. The framework for understanding the hydrologic processes that occur at this site and that control how quickly water will penetrate through the unsaturated zone to the water table has evolved during the past 15 yr. Early conceptual models assumed that very small volumes of water infiltrated into the bedrock (0.5–4.5 mm/yr, or 2–3 percent of rainfall), that much of the infiltrated water flowed laterally within the upper nonwelded units because of capillary barrier effects, and that the remaining water flowed down faults with a small amount flowing through the matrix of the lower welded, fractured rocks. It was believed that the matrix had to be saturated for fractures to flow. However, accumulating evidence indicated that infiltration rates were higher than initially estimated, such as infiltration modeling based on neutron borehole data, bomb-pulse isotopes deep in the mountain, perched water analyses and thermal analyses. Mechanisms supporting lateral diversion did not apply at these higher fluxes, and the flux calculated in the lower welded unit exceeded the conductivity of the matrix, implying vertical flow of water in the high permeability fractures of the potential repository host rock, and disequilibrium between matrix and fracture water potentials. The development of numerical modeling methods and parameter values evolved concurrently with the conceptual model in order to account for the observed field data, particularly fracture flow deep in the unsaturated zone. This paper presents the history of the evolution of conceptual models of hydrology and numerical models of unsaturated zone flow at Yucca Mountain, Nevada ( Flint, A.L., Flint, L.E., Kwicklis, E.M., Bodvarsson, G.S., Fabryka-Martin, J.M., 2001. Hydrology of Yucca Mountain. Reviews of Geophysics in press ). This retrospective is the basis for recommendations for optimizing the efficiency with which a viable and robust conceptual model can be developed for a complex site.