Geology topics

Christopher L. Shope

Publications and source records attributed to Christopher L. Shope.

8 recordsLinked to original sources

USGS2020

Environmental tracer evidence for connection between shallow and bedrock aquifers and high intrinsic susceptibility to contamination of the conterminous U.S. glacial aquifer

Covering a large portion of the northern conterminous United States (1.87 x 106 km2), the glacial aquifer serves as the primary water supply for 39 million public and domestic water users. Mean groundwater age, groundwater age distribution, and susceptibility to land surface contamination, using a new metric (Susceptibility Index; SI) based on the full age distribution and less prone to bias than estimated mean age, is reported for 168 public and domestic wells across the aquifer. Comparison of groundwater age metrics between well networks of varying spatial scale suggest an extensive sample network of equally spaced, long screened interval wells can be used to characterize aquifer wide groundwater age. Estimated mean age ranges from 1 to 50,000 years and, according to the composite age distribution, approximately 63 percent of all sampled water recharged after 1950 (i.e., modern) and 18 percent of the sampled water was recharged greater than 10,000 years ago. The later finding strongly suggests a connection between the glacial aquifer and underlying bedrock aquifers. Statistical analysis of glacial aquifer hydrogeology and age metrics show groundwater ages are young (less than few 100 years) and more susceptible to land surface contamination (larger SI) in unconfined and shallow portions of the aquifer. Old groundwater (greater than 1000 years) is more often associated with thicker sequences of fine grain sediments and/or shallow bedrock. Calculated SI is shown to be more strongly related to the number of land surface contaminants detected than mean age or fraction modern. Statistical analysis of SI and hydrogeology indicates SI is largely dictated by well depth and confinement. This study demonstrates how sample network design can be used to characterize groundwater age of large aquifers with a limited number of samples and how interpretation of environmental tracers can be used to improve conceptual models of groundwater aquifers and identify groundwater susceptible to contamination.

Glacial aquifer↗

USGS2018

Regional variability of nitrate fluxes in the unsaturated zone and groundwater, Wisconsin, USA

Process-based modeling of regional NO3− fluxes to groundwater is critical for understanding and managing water quality, but the complexity of NO3− reactive transport processes make implementation a challenge. This study introduces a regional vertical flux method (VFM) for efficient estimation of reactive transport of NO3− in the vadose zone and groundwater. The regional VFM was applied to 443 well samples in central-eastern Wisconsin. Chemical measurements included O2, NO3−, N2 from denitrification, and atmospheric tracers of groundwater age including carbon-14, chlorofluorocarbons, tritium, and tritiogenic helium. VFM results were consistent with observed chemistry, and calibrated parameters were in-line with estimates from previous studies. Results indicated that (1) unsaturated zone travel times were a substantial portion of the transit time to wells and streams (2) since 1945 fractions of applied N leached to groundwater have increased for manure-N, possibly due to increased injection of liquid manure, and decreased for fertilizer-N, and (3) under current practices and conditions, approximately 60% of the shallow aquifer will eventually be affected by downward migration of NO3−, with denitrification protecting the remaining 40%. Recharge variability strongly affected the unsaturated zone lag times and the eventual depth of the NO3− front. Principal components regression demonstrated that VFM parameters and predictions were significantly correlated with hydrogeochemical landscape features. The diverse and sometimes conflicting aspects of N management (e.g. limiting N volatilization versus limiting N losses to groundwater) warrant continued development of large-scale holistic strategies to manage water quality and quantity.

Wisconsin↗

USGS2015

Calculating salt loads to Great Salt Lake and the associated uncertainties for water year 2013; updating a 48 year old standard

Effective management of surface waters requires a robust understanding of spatiotemporal constituent loadings from upstream sources and the uncertainty associated with these estimates. We compared the total dissolved solids loading into the Great Salt Lake (GSL) for water year 2013 with estimates of previously sampled periods in the early 1960s.We also provide updated results on GSL loading, quantitatively bounded by sampling uncertainties, which are useful for current and future management efforts. Our statistical loading results were more accurate than those from simple regression models. Our results indicate that TDS loading to the GSL in water year 2013 was 14.6 million metric tons with uncertainty ranging from 2.8 to 46.3 million metric tons, which varies greatly from previous regression estimates for water year 1964 of 2.7 million metric tons. Results also indicate that locations with increased sampling frequency are correlated with decreasing confidence intervals. Because time is incorporated into the LOADEST models, discrepancies are largely expected to be a function of temporally lagged salt storage delivery to the GSL associated with terrestrial and in-stream processes. By incorporating temporally variable estimates and statistically derived uncertainty of these estimates,we have provided quantifiable variability in the annual estimates of dissolved solids loading into the GSL. Further, our results support the need for increased monitoring of dissolved solids loading into saline lakes like the GSL by demonstrating the uncertainty associated with different levels of sampling frequency.

Utah↗

USGS2014

Continuous estimation of baseflow in snowmelt-dominated streams and rivers in the Upper Colorado River Basin: A chemical hydrograph separation approach

Effective science-based management of water resources in large basins requires a qualitative understanding of hydrologic conditions and quantitative measures of the various components of the water budget, including difficult to measure components such as baseflow discharge to streams. Using widely available discharge and continuously collected specific conductance (SC) data, we adapted and applied a long established chemical hydrograph separation approach to quantify daily and representative annual baseflow discharge at fourteen streams and rivers at large spatial (> 1,000 km 2 watersheds) and temporal (up to 37 years) scales in the Upper Colorado River Basin. On average, annual baseflow was 21-58% of annual stream discharge, 13-45% of discharge during snowmelt, and 40-86% of discharge during low-flow conditions. Results suggest that reservoirs may act to store baseflow discharged to the stream during snowmelt and release that baseflow during low-flow conditions, and that irrigation return flows may contribute to increases in fall baseflow in heavily irrigated watersheds. The chemical hydrograph separation approach, and associated conceptual model defined here provide a basis for the identification of land use, management, and climate effects on baseflow.

Colorado, Utah↗

USGS2014

Groundwater and surface-water resources in the Bureau of Land Management Moab Master Leasing Plan area and adjacent areas, Grand and San Juan Counties, Utah, and Mesa and Montrose Counties, Colorado

The Bureau of Land Management (BLM) Canyon Country District Office is preparing a leasing plan known as the Moab Master Leasing Plan (Moab MLP) for oil, gas, and potash mineral rights in an area encompassing 946,469 acres in southeastern Utah. The BLM has identified water resources as being potentially affected by oil, gas, and potash development and has requested that the U.S. Geological Survey prepare a summary of existing water-resources information for the Moab MLP area. This report includes a summary and synthesis of previous and ongoing investigations conducted in the Moab MLP and adjacent areas in Utah and Colorado from the early 1930s through the late 2000s. Eight principal aquifers and six confining units were identified within the study area. Permeability is a function of both the primary permeability from interstitial pore connectivity and secondary permeability created by karst features or faults and fractures. Vertical hydraulic connection generally is restricted to strongly folded and fractured zones, which are concentrated along steeply dipping monoclines and in narrow regions encompassing igneous and salt intrusive masses. Several studies have identified both an upper and lower aquifer system separated by the Pennsylvanian age Paradox Member of the Hermosa Formation evaporite, which is considered a confining unit and is present throughout large parts of the study area. Surface-water resources of the study area are dominated by the Colorado River. Several perennial and ephemeral or intermittent tributaries join the Colorado River as it flows from northeast to southwest across the study area. An annual spring snowmelt and runoff event dominates the hydrology of streams draining mountainous parts of the study area, and most perennial streams in the study area are snowmelt-dominated. A bimodal distribution is observed in hydrographs from some sites with a late-spring snowmelt-runoff peak followed by smaller peaks of shorter duration during the late summer. The large regional streams (Colorado, Green, and Dolores Rivers) integrate the regional hydrologic partitioning of a very large contributing area and, therefore, the hydrographs for these streams are much more smooth and consistent. Several streams throughout the study area are considered impaired and do not meet the standards set by the Environmental Protection Agency for specific designated-use classifications. Limited data are available to quantitatively estimate the large-scale regional groundwater budget for the study area. Previous studies have estimated groundwater budgets for areas in and adjacent to the current study area, namely Moab-Spanish Valley and parts of the Paradox Basin. Most groundwater recharge to the study area originates as infiltration of precipitation from upland areas and is further enhanced in areas covered with sandy soils or in areas where the bedrock is highly fractured. Additional groundwater recharge occurs as seepage from streams and irrigation water, and as subsurface inflow, both vertically between aquifers and as lateral movement into the study area. Groundwater discharge occurs as seepage to streams, evapotranspiration, to springs and seeps, well withdrawals; and as subsurface outflow, both vertically between aquifers and as lateral movement out of the study area across its defined boundaries. Groundwater use in the study area was determined using data from the Utah Division of Water Rights. Most wells in the study area are categorized as having multiple uses. Mean specific-conductance values for groundwater from wells and springs in the study area range from 101 to 220,000 microsiemens per centimeter at 25° C (μS/cm); most of the wells or springs have mean specific-conductance values of less than or equal to 1,000 μS/cm. Previously reported total dissolved-solids concentrations, specific conductances, and other groundwater-quality data for each of the principal aquifers indicate relative freshwater throughout the study area, except within the lower aquifer system and areas in contact with the Paradox Member of the Hermosa Formation evaporites. There is limited information on the resource availability of brines and saline groundwater in the study area. Total dissolved-solids concentrations typically are high (greater than 35,000 milligrams per liter) in groundwater from, or in contact with, the Paradox Member of the Hermosa Formation. Total dissolved-solids concentrations also are high in groundwater samples collected from the lower aquifer system. Because the Paradox Member of the Hermosa Formation is considered a barrier to vertical groundwater flow, most of the brine and saline groundwater resources are restricted to the lower aquifer system.

Colorado, Utah↗

USGS2014

Assessment of dissolved-solids loading to the Colorado River in the Paradox Basin between the Dolores River and Gypsum Canyon, Utah

Salinity loads throughout the Colorado River Basin have been a concern over recent decades due to adverse impacts on population, natural resources, and regional economics. With substantial financial resources and various reclamation projects, the salt loading to Lake Powell and associated total dissolved-solids concentrations in the Lower Colorado River Basin have been substantially reduced. The Colorado River between its confluence with the Dolores River and Lake Powell traverses a physiographic area where saline sedimentary formations and evaporite deposits are prevalent. However, the dissolved-solids loading in this area is poorly understood due to the paucity of water-quality data. From 2003 to 2011, the U.S. Geological Survey in cooperation with the U.S. Bureau of Reclamation conducted four synoptic sampling events to quantify the salinity loading throughout the study reach and evaluate the occurrence and impacts of both natural and anthropogenic sources. The results from this study indicate that under late-summer base-flow conditions, dissolved-solids loading in the reach is negligible with the exception of the Green River, and that variations in calculated loads between synoptic sampling events are within measurement and analytical uncertainties. The Green River contributed approximately 22 percent of the Colorado River dissolved-solids load, based on samples collected at the lower end of the study reach. These conclusions are supported by water-quality analyses for chloride and bromide, and the results of analyses for the stable isotopes of oxygen and deuterium. Overall, no significant sources of dissolved-solids loading from tributaries or directly by groundwater discharge, with the exception of the Green River, were identified in the study area.

Utah↗

USGS2006

The influence of hydrous Mn–Zn oxides on diel cycling of Zn in an alkaline stream draining abandoned mine lands

Many mining-impacted streams in western Montana with pH near or above neutrality display large (up to 500%) diel cycles in dissolved Zn concentrations. The streams in question typically contain boulders coated with a thin biofilm, as well as black mineral crusts composed of hydrous Mn–Zn oxides. Laboratory mesocosm experiments simulating diel behavior in High Ore Creek (one of the Montana streams with particularly high Zn concentrations) show that the Zn cycles are not caused by 24-h changes in streamflow or hyporheic exchange, but rather to reversible in-stream processes that are driven by the solar cycle and its attendant influence on pH and water temperature ( T ). Laboratory experiments using natural Mn–Zn precipitates from the creek show that the mobilities of Zn and Mn increase nearly an order of magnitude for each unit decrease in pH, and decrease 2.4-fold for an increase in T from 5 to 20 °C. The response of dissolved metal concentration to small changes in either pH or T was rapid and reversible, and dissolved Zn concentrations were roughly an order of magnitude higher than Mn. These observations are best explained by sorption of Zn 2+ and Mn 2+ onto the secondary Mn–Zn oxide surfaces. From the T -dependence of residual metal concentrations in solution, approximate adsorption enthalpies of +50 kJ/mol (Zn) and +46 kJ/mol (Mn) were obtained, which are within the range of enthalpy values reported in the literature for sorption of divalent metal cations onto hydrous metal oxides. Using the derived pH- and T -dependencies from the experiments, good agreement is shown between predicted and observed diel Zn cycles for several historical data sets collected from High Ore Creek.

Applied Geochemistry↗

USGS2005

A 24 h investigation of the hydrogeochemistry of baseflow and stormwater in an urban area impacted by mining: Butte, Montana

Changes in water quality during a storm event were continuously monitored over a 24 h period at a single location along an urban stormwater drain in Butte, Montana. The Butte Metro Storm Drain (MSD) collects groundwater baseflow and stormwater draining Butte Hill, a densely populated site that has been severely impacted by 130 years of mining, milling, and smelting of copper-rich, polymetallic mineral deposits. On the afternoon of 26 June 2002, a heavy thunderstorm caused streamflow in the MSD to increase 100-fold, from 0·2 ft 3 s −1 to more than 20 ft 3 s −1 . Hourly discharge and water quality data were collected before, during, and following the storm. The most significant finding was that the calculated loads (grams per hour) of both dissolved and particulate copper passing down the MSD increased more than 100-fold in the first hour following the storm, and remained elevated over baseline conditions for the remainder of the study period. Other metals, such as zinc, cadmium, and manganese, showed a decrease in load from pre-storm to post-storm conditions. In addition to the large flush of copper, loads of soluble phosphorus increased during the storm, whereas dissolved oxygen dropped to low levels (<2 mg l −1 ). These results show that infrequent storm events in Butte have the potential to generate large volumes of runoff that exceed Montana water quality standards for acute exposure of aquatic life to copper, as well as depressed levels of dissolved oxygen. This study has important implications to ongoing reclamation activities in the upper Clark Fork Superfund site, particularly with respect to management of storm flow, and may be applicable to other watersheds impacted by mining activities.

Montana↗