Frank W. Schwartz

Oxidative degradation and kinetics of chlorinated ethylenes by potassium permanganate

The oxidative treatment of chlorinated ethylenes in ground water using permanganate was investigated in a series of batch kinetic tests. Five chlorinated ethylenes including tetrachloroethylene (PCE), trichloroethylene (TCE), and three isomers of dichloroethylenes (DCEs) were examined. The degradation process was rapid with pseudo-first-order rate constants ranging from 4.5×10−5 to 0.03 s−1 at MnO4−=1 mM. The rate increased with a decreasing number of chlorine substituents on the ethylene. The higher reactivity of trans-DCE (kobs=30×10−3 s−1 at MnO4−=1 mM) as compared to cis-DCE (kobs=0.9×10−3 s−1 at MnO4−=1 mM) is thought to be caused by a significant steric effect due to the formation of a large cyclic activated complex. TCE oxidation as a second-order reaction was confirmed and the rate constant, k=0.67±0.03 M−1 s−1, is independent of pH over the range of 4–8. The activity of both Cl− and hydrogen ions was monitored over time and suggests essentially complete dechlorination, making the degradation products less harmful than the parent compounds. Competition for MnO4− from other organic compounds in ground water or highly contaminated ground water was also evaluated in experiments. A simple and quick approach was demonstrated to estimate permanganate consumption by other organic compounds for field applications and to predict the TCE degradation rate in a system involving multiple contaminants. The modeling results suggest that the effect of autocatalysis by MnO2 on TCE degradation is significant when the system contains high concentration levels of MnO4− and TOC.

Verification of the Vertical Error in C-Band SRTM DEM Using ICESat and Landsat-7, Otter Tail County, MN

The Shuttle Radar Topography Mission (SRTM) provided scientists with digital elevation data on a nearly global scale and with highly consistent accuracy. This paper compares elevation values of the C-band SRTM 30-m digital elevation model (DEM) with pointwise elevations from the Ice, Cloud, and land-Elevation Satellite (ICESat) laser altimetry for Otter Tail County, Minnesota. The accuracy of SRTM DEM is measured as a function of land covers and geomorphologic characteristics. The typical mean vertical difference between the SRTM DEM and ICESat elevations in this paper was determined in each classified land-use type and is approximately 1.5 m over bare ground, with the SRTM measuring lower elevations. Significant changes in the SRTM DEM uncertainties have been identified over different surface types classified from Landsat-7 imagery, e.g., bare ground, urban, and forested areas. Based on this result, the difference of the SRTM 30-m DEM and ICESat elevations has been removed from the DEM and made available for improved hydrological applications

A Review of In Situ Chemical Oxidation and Heterogeneity

Chemical oxidants are increasingly being used for the in situ destruction of organic contaminants in groundwater. The most common implementation involves using an injection/withdrawal system to circulate oxidants (e.g., potassium permanganate, hydrogen peroxide, and Fentons reagent) through a source zone containing a dense non-aqueous phase liquid (DNAPL). Because the efficiency of chemical oxidation is highly dependent on geological heterogeneities, effective delivery schemes are essential for successful remediation. This article reviews the impact of heterogeneities on the success of in situ chemical oxidation. Physical heterogeneities are primarily concerned with the permeable pathways along which oxidants are transported to the zone of contamination. Chemical heterogeneities refer generally to variability in geochemical properties that also bear on the efficiency of oxidant flooding. Both types of heterogeneities work against bringing the oxidant to zones of high contaminant saturations. The highly heterogeneous distribution of contaminants and difficulties in characterization make it difficult to target specific zones for treatment. As a result, large volumes of sediments could be treated whether they are contaminated or not. Heterogeneities in hydraulic conductivity at most sites provide an intensive dose of chemical reagents along permeable pathways and little treatment of low-conductivity zones. Large quantities of oxidizable materials in geologic units are capable of consuming the oxidant during delivery. Reaction products [e.g., CO2, MnO2, and Fe(OH)3] tend to plug the porous medium, especially in zones with large contaminant saturations. The oxidant flood is diverted away from these zones, making the flooding inefficient.

Simulation of variable-density flow and transport of reactive and nonreactive solutes during a tracer test at Cape Cod, Massachusetts

A multispecies numerical code was developed to simulate flow and mass transport with kinetic adsorption in variable-density flow systems. The two-dimensional code simulated the transport of bromide (Br−), a nonreactive tracer, and lithium (Li+), a reactive tracer, in a large-scale tracer test performed in a sand-and-gravel aquifer at Cape Cod, Massachusetts. A two-fraction kinetic adsorption model was implemented to simulate the interaction of Li+ with the aquifer solids. Initial estimates for some of the transport parameters were obtained from a nonlinear least squares curve-fitting procedure, where the breakthrough curves from column experiments were matched with one-dimensional theoretical models. The numerical code successfully simulated the basic characteristics of the two plumes in the tracer test. At early times the centers of mass of Br− and Li+ sank because the two plumes were closely coupled to the density-driven velocity field. At later times the rate of downward movement in the Br− plume due to gravity slowed significantly because of dilution by dispersion. The downward movement of the Li+ plume was negligible because the two plumes moved in locally different velocity regimes, where Li+ transport was retarded relative to Br−. The maximum extent of downward transport of the Li+ plume was less than that of the Br− plume. This study also found that at early times the downward movement of a plume created by a three-dimensional source could be much more extensive than the case with a two-dimensional source having the same cross-sectional area. The observed shape of the Br− plume at Cape Cod was simulated by adding two layers with different hydraulic conductivities at shallow depth across the region. The large dispersion and asymmetrical shape of the Li+ plume were simulated by including kinetic adsorption-desorption reactions.

Climate forcing of wetland landscape connectivity in the Great Plains

Habitat connectivity is a landscape attribute critical to the long-term viability of many wildlife species, including migratory birds. Climate change has the potential to affect habitat connectivity within and across the three main wetland complexes in the Great Plains of North America: the prairie potholes of the northern plains, the Rainwater Basin of Nebraska, and the playas of the southern plains. Here, we use these wetlands as model systems in a graph-theory-based approach to establish links between climatic drivers and habitat connectivity for wildlife in current and projected wetland landscapes and to discern how that capacity can vary as a function of climatic forcing. We also provide a case study of macrosystems ecology to examine how the patterns and processes that determine habitat connectivity fluctuate across landscapes, regions, and continents.

Application of retracked satellite altimetry for inland hydrologic studies

We explored the application of satellite radar altimetry for the monitoring of small inland bodies of water and hydrologic studies using a water-detection algorithm, optimally retracked TOPEX/POSEIDON data at 10-Hz sampling, and investigated the use of radar backscatter to improve land cover classification. The procedure was demonstrated over Manitoba and south-western (SW) Ontario, and the Amazon River Basin study regions. Compared with an L-band synthetic aperture radar data generated water-land cover mask, the water-detection algorithm detected more water points over the Amazon basin. High correlation of 0.98 between the retracked 10-Hz altimetry and the gauge measurements in Manitoba confirmed that the retracked TOPEX data are more accurate than the non-retracked data, and with higher along-track spatial resolution by virtue of its higher sampling at 10 Hz.

Limitations in the Hydrologic Applications of C-Band SRTM DEMs in Low-Relief Settings

The shuttle radar topography mission (SRTM) data represent a major breakthrough in terms of providing accurate and consistent elevation data on a worldwide basis. These data are being used in many scientific applications, hydrology in particular. This letter examines the feasibility of using SRTM data for hydrologic characterizations, particularly in a region of low relief exemplified by the Otter Tail basin in Minnesota. The Version 2 SRTM data product provides a useful starting place for estimating the stage for larger lakes. Indications for Minnesota are that these estimates are accurate to several meters but are biased toward underestimation. Over land, the inherent noise in the data makes watershed boundary and stream network extraction problematic. We found large errors in estimated basin shape and area, and in the geometry of extracted stream networks, as compared to more traditional U.S. Geological Survey data products.

Citation data analysis on hydrogeology

This article explores the status of research in hydrogeology using data mining techniques. First we try to explain what citation analysis is and review some of the previous work on citation analysis. The main idea in this article is to address some common issues about citation numbers and the use of these data. To validate the use of citation numbers, we compare the citation patterns for Water Resources Research papers in the 1980s with those in the 1990s. The citation growths for highly cited authors from the 1980s are used to examine whether it is possible to predict the citation patterns for highly-cited authors in the 1990s. If the citation data prove to be steady and stable, these numbers then can be used to explore the evolution of science in hydrogeology. The famous quotation, “If you are not the lead dog, the scenery never changes,” attributed to Lee Iacocca, points to the importance of an entrepreneurial spirit in all forms of endeavor. In the case of hydrogeological research, impact analysis makes it clear how important it is to be a pioneer. Statistical correlation coefficients are used to retrieve papers among a collection of 2,847 papers before and after 1991 sharing the same topics with 273 papers in 1991 in Water Resources Research. The numbers of papers before and after 1991 are then plotted against various levels of citations for papers in 1991 to compare the distributions of paper population before and after that year. The similarity metrics based on word counts can ensure that the “before” papers are like ancestors and “after” papers are descendants in the same type of research. This exercise gives us an idea of how many papers are populated before and after 1991 (1991 is chosen based on balanced numbers of papers before and after that year). In addition, the impact of papers is measured in terms of citation presented as “percentile,” a relative measure based on rankings in one year, in order to minimize the effect of time.

Description and verification of a novel flow and transport model for silicate-gel emplacement

We present a novel approach for the numerical simulation of the gelation of silicate solutions under density-dependent flow conditions. The method utilizes an auxiliary, not density-dependent solute that is subject to a linear decay function to provide temporal information that is used to describe the viscosity change of the fluid. By comparing the modeling results to experimental data, we are able to simulate the behavior and the gelation process of the injected solute for three different compositions, including long-term stability of the gelated area, and non-gelation of low concentrations due to hydro-dynamic dispersion. This approach can also be used for other types of solutes with this gelling property and is useful in a variety of applications in geological, civil and environmental engineering.

Frog in a Well

or a country like Australia that makes its living on exporting agricultural products and natural resources in a climate decidedly hostile to such activities. Yet, a research community growing up without big problems runs a risk of being parochial and inwardly looking—frogs in a well. For example, my look at the papers in Grundwasser discovered a broad swath of researchers working with a decidedly German focus on classical problems, e.g., karst, aquifer testing, brown-coal geochemistry, and technical problems related to energy in the subsurface. There are of course larger Helmholtz and EU-wide programs looking at broad issues, like Water Resources Management. That strong research consistently produces papers for top tier journals. Yet, coming with these large programs is the difficult problem of organizing for innovation. From what I see, Germany and the EU follow the usual funding model for large projects, chopping the budget into “bitesized pieces” to let groundwater people do their small pieces, the ecologists study their frogs and bugs, and the French do pieces as well. These funding models typically produce good groundwater science; but absent significant integration the hydrogeologists remain frogs in a well. Fundamentally, groundwater is a relatively small field that has largely run out of foundational science. It stays alive mostly by sorting out complexities in systems and parameters, or by solving problems relevant to local issues. Leading journals like Water Resources Research, once so groundwater focused, have moved away to surface water, watersheds and global ecology. Journals with groundwater as their name and major focus (Groundwater, Hydrogeology Journal, Grundwasser) have become the newest frogs in a well. These journals will survive and serve some useful purpose—yet, it is difficult to envision pathways for growth and diversification when stuck in a well. Asian cultures usually have some version of the story about the frog in a well. In China, the story revolves around a sea turtle that visits a frog living in a shallow well. The frog proudly shows his lovely home, the circular view of the sky, and his happiness in being the lord of the well. He is shocked and surprised when the turtle describes the oceanic world—immense and complicated—a different place. Reflecting on my wonderful experiences at the 2014 FHDGG meeting and other travels to Germany, I thought about the frog in the well on several different levels. In Germany, rainfall averages ~ 780 mm per year and well able to take care of all of the water needs for a stable population of about 80 million people. Indeed, the science that is reported in Grundwasser and elsewhere reflects a research community that has been largely insulated from the massive groundwater problems of other countries. Germany’s total annual groundwater production of 5.8 km3 is miniscule compared to other countries that count on irrigated agriculture for food production. For the United States, groundwater withdrawals total about 112 km3/yr with production from just one aquifer—the High Plains system about 10 km3/yr. The over-production of groundwater worldwide has created enormous local impacts causing a loss of surface waters, destruction of riparian ecosystems, and land subsidence. The coming shortages have the potential to change societies in unimaginable ways. From a social perspective, Germany is wonderfully placed, without the burden of groundwater problems of for example, a populated Southeast Asia, a dry Middle East,