Kenneth Belitz

Bio: Kenneth Belitz is an academic researcher from United States Geological Survey. The author has contributed to research in topics: Groundwater & Aquifer. The author has an hindex of 30, co-authored 183 publications receiving 5731 citations. Previous affiliations of Kenneth Belitz include Queens College & Dartmouth College.

Verification, Validation, and Confirmation of Numerical Models in the Earth Sciences

Abstract: Verification and validation of numerical models of natural systems is impossible. This is because natural systems are never closed and because model results are always nonunique. Models can be confirmed by the demonstration of agreement between observation and prediction, but confirmation is inherently partial. Complete confirmation is logically precluded by the fallacy of affirming the consequent and by incomplete access to natural phenomena. Models can only be evaluated in relative terms, and their predictive value is always open to question. The primary value of models is heuristic.

Hormones and Pharmaceuticals in Groundwater Used As a Source of Drinking Water Across the United States

Abstract: This is the first large-scale, systematic assessment of hormone and pharmaceutical occurrence in groundwater used for drinking across the United States. Samples from 1091 sites in Principal Aquifers representing 60% of the volume pumped for drinking-water supply had final data for 21 hormones and 103 pharmaceuticals. At least one compound was detected at 5.9% of 844 sites representing the resource used for public supply across the entirety of 15 Principal Aquifers, and at 11.3% of 247 sites representing the resource used for domestic supply over subareas of nine Principal Aquifers. Of 34 compounds detected, one plastics component (bisphenol A), three pharmaceuticals (carbamazepine, sulfamethoxazole, and meprobamate), and the caffeine degradate 1,7-dimethylxanthine were detected in more than 0.5% of samples. Hydrocortisone had a concentration greater than a human-health benchmark at 1 site. Compounds with high solubility and low Koc were most likely to be detected. Detections were most common in shallow wells with a component of recent recharge, particularly in crystalline-rock and mixed land-use settings. Results indicate vulnerability of groundwater used for drinking water in the U.S. to contamination by these compounds is generally limited, and exposure to these compounds at detected concentrations is unlikely to have adverse effects on human health.

Hydrodynamics of Denver Basin: Explanation of Subnormal Fluid Pressures

Abstract: Anomalously low fluid potential (and hence subnormal fluid pressure) is found in Mesozoic and Paleozoic rocks of the Denver basin. The potentiometric surface for the Dakota and basal Cretaceous sandstones is 2,000-3,000 ft (600-900 m) beneath the land surface in parts of the Denver basin in Colorado and Nebraska. The potentiometric surface for pre-Pennsylvanian carbonate rocks is 1,500 ft (450 m) lower than the potentiometric surface for the Dakota Sandstone in southeastern Colorado and western Kansas. The low fluid potential seems especially anomalous considering the high elevation of the outcrops along the Laramie and Front Ranges and the Black Hills. A quasi-three-dimensional numerical flow model is used to investigate the regional flow system in the Denver basin and adjacent Mid-Continent. The model simulates flow through the entire Phanerozoic sedimentary column and indicates that subnormal pressures are a consequence of hydraulic insulation of the strata within the basin from their recharge zones as compared to their discharge zones. The Dakota Sandstone and underlying hydrostratigraphic units are insulated from the overlying water table by low-permeability shales of Cretaceous age, and from their own high-elevation outcrops by a zone of low permeability coincident with the basin deep. Subnormal pressures in the area of Denver, Colorado, and southward are further enhanced by faulting along the Front Range that isolates the stra a within the basin from their outcrops. The results of this study show that (1) subnormal fluid pressures can be explained as a consequence of steady-state regional ground-water flow, (2) shale is an important factor in the regional flow system, and (3) depth is an important control on the distribution of hydraulic conductivity.

Factors controlling the regional distribution of vanadium in groundwater.

Abstract: Although the ingestion of vanadium (V) in drinking water may have possible adverse health effects, there have been relatively few studies of V in groundwater. Given the importance of groundwater as a source of drinking water in many areas of the world, this study examines the potential sources and geochemical processes that control the distribution of V in groundwater on a regional scale. Potential sources of V to groundwater include dissolution of V rich rocks, and waste streams from industrial processes. Geochemical processes such as adsorption/desorption, precipitation/dissolution, and chemical transformations control V concentrations in groundwater. Based on thermodynamic data and laboratory studies, V concentrations are expected to be highest in samples collected from oxic and alkaline groundwater. However, the extent to which thermodynamic data and laboratory results apply to the actual distribution of V in groundwater is not well understood. More than 8400 groundwater samples collected in California were used in this study. Of these samples, high (> or =50 microg/L) and moderate (25 to 49 microg/L) V concentrations were most frequently detected in regions where both source rock and favorable geochemical conditions occurred. The distribution of V concentrations in groundwater samples suggests that significant sources of V are mafic and andesitic rock. Anthropogenic activities do not appear to be a significant contributor of V to groundwater in this study. High V concentrations in groundwater samples analyzed in this study were almost always associated with oxic and alkaline groundwater conditions, which is consistent with predictions based on thermodynamic data.

AUC: a misleading measure of the performance of predictive distribution models

Abstract: The area under the receiver operating characteristic (ROC) curve, known as the AUC, is currently considered to be the standard method to assess the accuracy of predictive distribution models. It avoids the supposed subjectivity in the threshold selection process, when continuous probability derived scores are converted to a binary presence‐absence variable, by summarizing overall model performance over all possible thresholds. In this manuscript we review some of the features of this measure and bring into question its reliability as a comparative measure of accuracy between model results. We do not recommend using AUC for five reasons: (1) it ignores the predicted probability values and the goodness-of-fit of the model; (2) it summarises the test performance over regions of the ROC space in which one would rarely operate; (3) it weights omission and commission errors equally; (4) it does not give information about the spatial distribution of model errors; and, most importantly, (5) the total extent to which models are carried out highly influences the rate of well-predicted absences and the AUC scores.