Jesse E. Dickinson

A New Capture Fraction Method to Map How Pumpage Affects Surface Water Flow

All groundwater pumped is balanced by removal of water somewhere, initially from storage in the aquifer and later from capture in the form of increase in recharge and decrease in discharge. Capture that results in a loss of water in streams, rivers, and wetlands now is a concern in many parts of the United States. Hydrologists commonly use analytical and numerical approaches to study temporal variations in sources of water to wells for select points of interest. Much can be learned about coupled surface/groundwater systems, however, by looking at the spatial distribution of theoretical capture for select times of interest. Development of maps of capture requires (1) a reasonably well-constructed transient or steady state model of an aquifer with head-dependent flow boundaries representing surface water features or evapotranspiration and (2) an automated procedure to run the model repeatedly and extract results, each time with a well in a different location. This paper presents new methods for simulating and mapping capture using three-dimensional groundwater flow models and presents examples from Arizona, Oregon, and Michigan.

Inference of lithologic distributions in an alluvial aquifer using airborne transient electromagnetic surveys

An airborne transient electromagnetic TEM survey was completedintheUpperSanPedroBasininsoutheasternArizona to map resistivity distributions within the alluvial aquifer. This investigation evaluated the utility of 1D vertical resistivity models of theTEM data to infer lithologic distributions in an alluvial aquifer. Comparisons of the resistivity values and layers in the 1D resistivity models of airborne TEM data to 1D resistivity models of groundTEM data, borehole resistivity logs, and lithologic descriptions in drill logs indicated that the airborne TEM identified thick conductive fine-grained sediments that result in semiconfinedgroundwaterconditions.One-dimensionalmodels of ground-based TEM surveys and subsurface lithology at three sites were used to determine starting models and constraints to invert airborne TEM data using a constrained Marquardt-style underparameterized method. A maximum structural resolution of six layers underlain by a half-space was determined from the resistivity structure of the 1D models of the ground TEM data. The 1D resistivity models of the airborne TEM data compared well with the control data to depths of approximately 100 m in areas of thick conductive silt and clay and to depths of 200 m in areasofresistivesandandgravel.Comparisonofa3Dinterpolation of the 1D resistivity models to drill logs indicated resistive mean of 65 ohm-mcoarse-grained sediments along basin margins and conductive mean of 8 ohm-m fine-grained sediments atthebasincenter.Extentsofhydrologicallysignificantthicksilt and clay were well mapped by the 1D resistivity models of airborneTEMdata.Areasofuncertainlithologyremainbelowconductivefine-grainedsedimentswherethe1Dresistivitystructure is not resolved: in areas where multiple lithologies have similar resistivityvaluesandinareasofhighsalinity.

Inhibition of Akt enhances the chemopreventive effects of topical rapamycin in mouse skin

The PI3Kinase/Akt/mTOR pathway has important roles in cancer development for multiple tumor types, including UV-induced nonmelanoma skin cancer. Immunosuppressed populations are at increased risk of aggressive cutaneous squamous cell carcinoma (SCC). Individuals who are treated with rapamycin (sirolimus, a classical mTOR inhibitor) have significantly decreased rates of developing new cutaneous SCCs compared with those that receive traditional immunosuppression. However, systemic rapamycin use can lead to significant adverse events. Here, we explored the use of topical rapamycin as a chemopreventive agent in the context of solar-simulated light (SSL)-induced skin carcinogenesis. In SKH-1 mice, topical rapamycin treatment decreased tumor yields when applied after completion of 15 weeks of SSL exposure compared with controls. However, applying rapamycin during SSL exposure for 15 weeks, and continuing for 10 weeks after UV treatment, increased tumor yields. We also examined whether a combinatorial approach might result in more significant tumor suppression by rapamycin. We validated that rapamycin causes increased Akt (S473) phosphorylation in the epidermis after SSL, and show for the first time that this dysregulation can be inhibited in vivo by a selective PDK1/Akt inhibitor, PHT-427. Combining rapamycin with PHT-427 on tumor prone skin additively caused a significant reduction of tumor multiplicity compared with vehicle controls. Our findings indicate that patients taking rapamycin should avoid sun exposure, and that combining topical mTOR inhibitors and Akt inhibitors may be a viable chemoprevention option for individuals at high risk for cutaneous SCC. Cancer Prev Res; 9(3); 215–24. ©2016 AACR.

Evaluation of the importance of clay confining units on groundwater flow in alluvial basins using solute and isotope tracers: the case of Middle San Pedro Basin in southeastern Arizona (USA)

As groundwater becomes an increasingly important water resource worldwide, it is essential to understand how local geology affects groundwater quality, flowpaths and residence times. This study utilized multiple tracers to improve conceptual and numerical models of groundwater flow in the Middle San Pedro Basin in southeastern Arizona (USA) by determining recharge areas, compartmentalization of water sources, flowpaths and residence times. Ninety-five groundwater and surface-water samples were analyzed for major ion chemistry (water type and Ca/Sr ratios) and stable (18O, 2H, 13C) and radiogenic (3H, 14C) isotopes, and resulting data were used in conjunction with hydrogeologic information (e.g. hydraulic head and hydrostratigraphy). Results show that recent recharge (<60 years) has occurred within mountain systems along the basin margins and in shallow floodplain aquifers adjacent to the San Pedro River. Groundwater in the lower basin fill aquifer (semi confined) was recharged at high elevation in the fractured bedrock and has been extensively modified by water-rock reactions (increasing F and Sr, decreasing 14C) over long timescales (up to 35,000 years BP). Distinct solute and isotope geochemistries between the lower and upper basin fill aquifers show the importance of a clay confining unit on groundwater flow in the basin, which minimizes vertical groundwater movement.RésuméL’eau souterraine devenant une ressource d’importance croissante à travers le monde, il est essentiel de comprendre comment la géologie locale affecte la qualité de l’eau souterraine, l’organisation des écoulements et les temps de séjour. Cette étude a utilisé des traceurs multiples pour améliorer les modèles d’écoulement souterrain conceptuel et numérique dans le Bassin Moyen de San Pedro, Sud-Est de l’Arizona (USA), en déterminant les aires de recharge, la compartimentation des venues d’eau, l’organisation des écoulements et les temps de séjour. Quatre-vingt quinze échantillons d’eau souterraine et d’eau de surface ont été analysés pour la chimie des ions majeurs (type d’eau et ratios Ca/Sr), isotopes stables (18O, 2H, 13C) et radiogéniques (3H, 14C), et les données résultantes utilisées en conjonction avec les données hydrogéologiques (e.g. charge hydraulique et hydro stratigraphie). Les résultats montrent que la recharge récente (<60 ans) a lieu dans les systèmes montagneux le long des marges du bassin et dans des aquifères peu profonds de plaine d’inondation le long de la rivière San Pedro. L’aquifère du bassin inférieur (semi-captif) est rechargé à une cote élevée dans le substrat fracturé et considérablement modifié par des réactions eau-roche (accroissement de F et Sr, décroissance du14C) sur de longues périodes de temps (jusqu’à 35 000 ans avant l’actuel). Les différences géochimiques des solutés et des isotopes entre le remplissage des aquifères des bassins supérieur et inférieur montrent l’importance de l’unité argileuse «confinante» sur les écoulements souterrains dans le bassin, qui minimise les mouvements verticaux de l’eau souterraine.ResumenPuesto que el agua subterránea se convierte en un recurso de agua crecientemente más importante en todo el mundo, es esencial entender como la geología local afecta la calidad del agua subterránea, las trayectorias de flujo y los tiempos de residencias. Este estudio utilizó múltiples trazadores para mejorar los modelos conceptuales y numéricos del flujo de agua subterránea en la cuenca de Middle San Pedro en el sudeste de Arizona (EEUU) determinando las área de recarga, la compartimentación de las fuentes de agua, las trayectorias de flujo y los tiempos de residencia. Se analizaron noventa y cinco muestras de agua subterránea y de agua superficial en la búsqueda de los iones químicos principales (tipo de agua y relaciones Ca/Sr) e isótopos estables (18O, 2H, 13C) y radiogénicos (3H, 14C), y los datos resultantes fueron usados en conjunción con la información hidrogeológica (por ejemplo carga hidráulica e hidroestratigrafía). Los resultados muestran que ha ocurrido una recarga reciente (<60 años) dentro de los sistemas montañosos a lo largo de los márgenes de cuenca y en los acuíferos someros de la planicie de inundación adyacente al Río San Pedro. El agua subterránea en los acuíferos de relleno (semiconfinados) de la cuenca inferior fue recargada en las altas elevaciones en las rocas fracturadas del basamento y ha sido extensamente modificada por las reacciones agua – roca (incrementándose el F y Sr, y disminuyendo el 14C) a lo largo de grandes escalas de tiempo (hasta 35,000 años antes del presente). La geoquímica de distintos solutos y los isótopos en los acuíferos de relleno en la cuenca inferior y superior muestran la importancia de una unidad arcillosa confinante sobre el flujo de agua subterránea en la cuenca, lo que minimiza el movimiento vertical del agua subterránea.ResumoÀ medida que a água subterrânea se torna progressivamente num importante recurso hídrico à escala mundial, é essencial perceber-se como a geologia local afeta a qualidade da água subterrânea, os caminhos de fluxo e os tempos de residência. Este estudo utilizou múltiplos traçadores para melhorar os modelos conceptuais e numéricos do fluxo de água subterrânea na Bacia Média de San Pedro, no sudeste do Arizona (EUA), através da determinação das áreas de recarga, da compartimentação das origens da água, dos caminhos de fluxo e dos tempos de residência. Foram analisadas noventa e cinco amostras de água subterrânea e superficial para o quimismo dos iões principais (tipos de água e rácios Ca/Sr), os isótopos estáveis (18O, 2H, 13C) e os radiogénicos (3H, 14C), tendo os dados resultantes sido usados em conjugação com informação hidrogeológica (p. ex. carga hidráulica e hidrostratigrafia). Os resultados mostram que a recarga recente (<60 anos) ocorreu nos sistemas montanhosos ao longo das margens da bacia e nas planícies de cheia baixas, adjacentes ao rio San Pedro. A água subterrânea no aquífero inferior do enchimento da bacia (semi-confinado) foi recarregada a cotas superiores no embasamento rochoso fraturado e foi extensivamente modificada por reações água-rocha (aumento de F e Sr, decréscimo de 14C) ao longo de extensas escalas temporais (até 35,000 anos antes do presente). As distintas geoquímicas dos solutos e dos isótopos entre os aquíferos superiores e inferiores no enchimento da bacia mostram a importância de uma unidade confinante de argila no fluxo de água subterrânea na bacia, a qual minimiza a movimentação vertical da água subterrânea.

Forecasting the Probability of Future Groundwater Levels Declining Below Specified Low Thresholds in the Conterminous U.S.

We present a logistic regression approach for forecasting the probability of future groundwater levels declining or maintaining below specific groundwater-level thresholds. We tested our approach on 102 groundwater wells in different climatic regions and aquifers of the United States that are part of the U.S. Geological Survey Groundwater Climate Response Network. We evaluated the importance of current groundwater levels, precipitation, streamflow, seasonal variability, Palmer Drought Severity Index, and atmosphere/ocean indices for developing the logistic regression equations. Several diagnostics of model fit were used to evaluate the regression equations, including testing of autocorrelation of residuals, goodness-of-fit metrics, and bootstrap validation testing. The probabilistic predictions were most successful at wells with high persistence (low month-to-month variability) in their groundwater records and at wells where the groundwater level remained below the defined low threshold for sustained periods (generally three months or longer). The model fit was weakest at wells with strong seasonal variability in levels and with shorter duration low-threshold events. We identified challenges in deriving probabilistic-forecasting models and possible approaches for addressing those challenges.

NEW GHOST-NODE METHOD FOR LINKING DIFFERENT MODELS WITH VARIED GRID REFINEMENT

A flexible, robust method for linking grids of locally refined models that may be constructed using different types of numerical methods is needed to address a variety of hydrologic problems. This work outlines and tests a new ghost-node model-linking method based on the iterative method of Mehl and Hill (2002, 2004). It is applicable to steady-state solutions for ground-water flow. Tests are presented for a homogeneous two-dimensional system that facilitates clear analysis of typical problems. The coupled grids are simulated using the finite-difference and finite-element models MODFLOW and FEHM. Results indicate that when the grids are matched spatially so that nodes and control volume boundaries are aligned, the new coupling technique has approximately twice the error as coupling using two MODFLOW models. When the grids are non-matching; model accuracy is slightly increased over matching grid cases. Overall, results indicate that the ghost-node technique is a viable means to accurately couple distinct models.

Advective transport observations with MODPATH-OBS--documentation of the MODPATH observation process

The MODPATH-OBS computer program described in this report is designed to calculate simulated equivalents for observations related to advective groundwater transport that can be represented in a quantitative way by using simulated particle-tracking data. The simulated equivalents supported by MODPATH-OBS are (1) distance from a source location at a defined time, or proximity to an observed location; (2) time of travel from an initial location to defined locations, areas, or volumes of the simulated system; (3) concentrations used to simulate groundwater age; and (4) percentages of water derived from contributing source areas. Although particle tracking only simulates the advective component of conservative transport, effects of non-conservative processes such as retardation can be approximated through manipulation of the effective-porosity value used to calculate velocity based on the properties of selected conservative tracers. This program can also account for simple decay or production, but it cannot account for diffusion. Dispersion can be represented through direct simulation of subsurface heterogeneity and the use of many particles. MODPATH-OBS acts as a postprocessor to MODPATH, so that the sequence of model runs generally required is MODFLOW, MODPATH, and MODPATH-OBS. The version of MODFLOW and MODPATH that support the version of MODPATH-OBS presented in this report are MODFLOW2000/2005 or MODFLOW-LGR, and MODPATH or MODPATH-LGR. MODFLOW-LGR is derived from MODFLOW-2005, MODPATH 5, and MODPATH 6 and supports local grid refinement. MODPATH-LGR is derived from MODPATH 5. It supports the forward and backward tracking of particles through locally refined grids and provides the output needed for MODPATH-OBS. MODPATH-LGR and MODPATH-OBS simulations can use nearly all of the capabilities of MODFLOW-2005 and MODFLOW-LGR; for example, simulations may be steady-state, transient, or a combination. Though the program name MODPATH-OBS specifically refers to observations, the program also can be used to calculate model prediction of observations. MODPATH-OBS is primarily intended for use with separate programs that conduct sensitivity analysis, data needs assessment, parameter estimation, and uncertainty analysis, such as UCODE_2005, and PEST. In many circumstances, refined grids in selected parts of a model are important to simulated hydraulics, detailed inflows and outflows, or other system characteristics. MODFLOW-LGR and MODPATH-LGR support accurate local grid refinement in which both mass (flows) and energy (head) are conserved across the local grid boundary. MODPATH-OBS is designed to take advantage of these capabilities. For example, particles tracked between a pumping well and a nearby stream, which are simulated poorly if a river and well are located in a single large grid cell, can be simulated with improved accuracy using a locally refined grid in MODFLOW-LGR, MODPATH-LGR, and MODPATHOBS. The locally-refined-grid approach can provide more accurate simulated equivalents to observed transport between the well and the river. The documentation presented here includes a brief discussion of previous work, description of the methods, and detailed descriptions of the required input files and how the output files are typically used.

MODPATH-LGR; documentation of a computer program for particle tracking in shared-node locally refined grids by using MODFLOW-LGR

MODPATH-LGR is a particle tracking post-processing program for computing three-dimensional flow paths for steady-state and transient groundwater flow in models with local-grid refinement (sometimes called embedded models). Locally refined grids consist of a larger regional-scale parent model and one or more smaller embedded local-scale child models. This program uses output produced by MODFLOWLGR, in which child grids in parent grids are refined by using the Shared-Node Local Grid Refinement (LGR) package of the three-dimensional finite-difference groundwater-flow model MODFLOW published by the U.S. Geological Survey (USGS). The particle tracking scheme is based on MODPATH, which uses an analytical expression for particle movement within each finite-difference cell. Particles are tracked among cells until discharged through model boundaries, weak sinks, or other designated discharge zones. MODPATHLGR tracks particles between the parent and child models by using flows calculated at the interface boundaries. Flows calculated by MODFLOW-LGR are modified to account for fractional finite-difference cells along the shared-node interface between parent and child models. Required program input includes standard MODPATH input files for the parent and child models and a MODPATH-LGR control file. This documentation describes how particles are transferred between parent and child models and demonstrates program operation with two hypothetical steady-state xsimulations.