Search

The χMD matrix solver package is incorporated into USGS groundwater modeling software, such as MODFLOW-NWT, MODFLOW-USG, and MT3D. The solver is used to solve matrices assembled through numerical discretization of the groundwater flow equation, and solute transport equations. χMD has demonstrated its higher robustness, faster execution speed, and more efficient memory usage compared to the existing solvers for many types of groundwater flow problems. χMD uses preconditioned iterative Krylov-subspace methods and consists of preconditioning and acceleration modules. Because the solver package uses a variety of preconditioning features including level-based incomplete lower-upper (ILU) factorization method with a drop tolerance scheme, users must choose optimal preconditioning parameters to improve execution speed and robustness. In order to examine how the preconditioning parameters, ILU factorization level, and drop tolerance values affect the overall performance of the matrix solver, we evaluated five different groundwater model applications using MODFLOW-USG that include different numerical complexities. For those five cases, the number of discretization nodes varied from 10,000 cells to 730,300 cells. From the analysis, we found that the preconditioning parameters greatly affect execution times and memory usage of the preconditioning and acceleration procedures. In addition, a combination of the ILU level between five to seven and the drop tolerance value between 10 -2 and 10 -3 usually resulted in shorter overall execution time. Our study suggests that the users can elicit higher performance and robustness of the χMD matrix solver using this combination of the parameters and enhance computational efficiency of solving groundwater and solute transport problems., (© 2021 National Ground Water Association.)

This paper shows how important the historical contaminant boom, 1975 to 2005, has been to hydrogeology. Its role in this respect has never been well documented or appreciated. We use text mining and machine learning to extract information describing research trends in subsurface hydrology (SH), groundwater plus the vadose zone. The analysis, using articles from Water Resources Research (WRR) and Environmental Science and Technology, shows how SH grew from a small niche area within broader hydrologic sciences in the 1960s to become the dominant area of research by 1995. Subsequently, the performance of SH has declined, as other areas of hydrologic sciences have emerged. These patterns reflect the growth and decline of research related to contaminant topics in SH. Thus, the decline is economic-less money leads to less research. The boom in contaminant hydrogeology was effectively a 1000-year flood of money for SH. It let us outcompete the non-SH areas for a while. From 1991 to 2000, SH research in WRR was dominated by papers on contaminant-related themes. More recently, these themes and all other areas of SH except one have declined significantly in WRR. All major topics related to non-SH areas are growing except one. This evidence points to a continuing decline in competitiveness of basic research in SH. The fact that critical problems or social needs for research still exist has not changed this basic trend. The focus of research has clearly shifted away from SH to areas of hydrology associated with climate change, water cycle modeling and similar themes., (© 2018, National Ground Water Association.)

The academic world is driven by scholarly research and publications. Yet, for many fields, the volume of published research and the associated knowledge base have been expanding exponentially for decades. The result is that scientists are literally drowning in data and information. There are strategies and approaches that could help with this problem. The goal of this paper is to demonstrate the power of computer-based approaches such as data mining and machine learning to evaluate large collections of papers. The objective is to conduct a systematic analysis of research related to the emerging area of groundwater-related diseases. More specifically, the analysis of information from the database of papers will examine systematics in the research topics, the inter-relationships among multiple diseases, contaminants, and groundwater, and discover styles of research associated with groundwater and disease. The analysis uses 426 papers (1971 to 2017) retrieved from a MEDLINE bibliographic database, PubMed, given the search terms "groundwater" and "disease." We developed tools that take care of necessary text processing steps, which lead naturally to clustering and visualization techniques that demonstrate published research. The resulting 2D article map shows how the collection of papers is subdivided into 11 article clusters. The cluster topics were determined by analyzing keywords or common words contained in the articles' titles, abstracts, and key words. We found that research on water-related disease in groundwater primarily focuses on two types of contaminants-chemical compounds and pathogens. Cancer and diarrhea are two major diseases associated with groundwater contamination. According to the systematic analysis, the study of this area is still growing., (© 2018, National Ground Water Association.)

Several technologies for cleaning up DNAPLs in source zones rely on solubilizing contaminants or destroying them in situ. Typically, these approaches employ an injection/withdrawal system to recirculate this treatment fluids. Our interest is in examining factors that influence delivery efficiency. Although many factors can affect this efficiency, this study looks at the combined influence of density-driven flow and porous media heterogeneities. The analysis is based on a series of numerical simulations of hypothetical chemical floods (e.g., potassium permanganate), which are highly resolved in space and time with a scale that is typical of field installations. Results indicate that the characteristics of convective mixing, i.e., natural, forced, and mixed convection, greatly affect delivery efficiency and patterns of mass transport. The ratio of the Grashof number (Gr) and Reynolds number (Re) proved useful in interpreting the patterns of flooding in a homogeneous porous medium. When higher-permeability layers are included in the domain, they act as conduits, effectively expediting the transport of treatment chemicals from injection to recovery wells. These large fluxes of chemicals in the high-permeability layers produce significant flooding inefficiencies. The problem is less severe in heterogeneous medium where the connectivity through the treatment zone is less well developed. Overall, this paper illustrates that density effects and high-permeability pathways need to be considered in designing chemical floods.

This paper uses citation data to assess whether articles published in key ground water journals such as Ground Water (GW) and Water Resources Research (WRR) are impacting research. Citation information was obtained from SCI Journal Citation Reports and The Web of Science--databases maintained by the Institute for Scientific Information (ISI). Information extracted from The Web of Science was processed further to remove corrections to papers, discussion/replies, and book reviews. Generally, there are many ground water papers published, but citations of these papers are limited. Approximately 10% to 15% of WRR articles, and 2% to 3% of GW articles attract more than 50 citations in their lifetimes. In both GW and WRR, the top 10% of papers eventually will contribute nearly half of the total yearly citations. Another emerging trend is a diminishing emphasis on citations to new work as compared to work more than 10 years in age. When articles in Ground Water or Journal of Hydrology cite papers in Water Resources Research, those papers cite work 10 or more years old half of the time. If one believes that citations are a measure of science impact, then there is cause for concern. Research is inefficient with much produced for little gain. On a typical industrial life-cycle curve, ground water research is likely ranked as mature and close to aging. At this stage, much work will have been completed and the number of truly impactful problems will have dwindled to just a few.