Geology topics

D. Kip Solomon

Publications and source records attributed to D. Kip Solomon.

12 recordsLinked to original sources

USGS2025

Groundwater dominates snowmelt runoff and controls streamflow efficiency in the western United States

Climate change in seasonally snow-covered mountain catchments is reducing water supply and decreasing streamflow predictability. Here, we use tritium age dating to show that contrary to the common assumption that snowmelt quickly contributes to runoff, streamflow during snowmelt in western US catchments is dominated by older groundwater. The average age of streamwater during snowmelt runoff (5.7 ± 4.3 years) was intermediate to the average age of groundwater (10.4 ± 4.5 years) and recent precipitation, indicating that 58% (±34%) of snowmelt runoff was derived from groundwater. Water ages, streamflow, and groundwater storage were mediated by bedrock geology: low-permeability hard rock/shale catchments exhibited younger ages, less storage, and more efficient streamflow generation than high-permeability sandstone/clastic catchments. Our results demonstrate that snowmelt runoff is the result of multiple prior years of climate mediated by groundwater storage. Including these interactions will be crucial for predicting water resources as climate and landscape changes accelerate.

western united States↗

USGS2023

Quantifying stream-loss recovery in a spring using dual-tracer injections in the Snake Creek drainage, Great Basin National Park, Nevada, USA

Simultaneous short-pulse injections of two tracers (sodium bromide [Br – ] and fluorescein dye) were made in a losing reach of Snake Creek in Great Basin National Park, Nevada, USA, to evaluate the quantity of stream loss through permeable carbonates that resurfaces at a spring approximately 10 km down drainage. A revised hydrogeologic cross section for a possible flow path of the infiltrated Snake Creek water is presented, and the results may inform water management in the region. First arrival and peak concentration of the two tracers occurred at 9.5 and 12.7 days after injection, respectively. Fracture transport simulations indicate that Br – preferentially diffuses into immobile regions of the aquifer, and this diffusive flux is likely responsible for the major differences in the breakthrough curves. When considering the diffusive tracer flux, total apparent Br – and fluorescein dye recoveries were 16.9–22.1% and 21.7–24.3%, respectively. These findings imply that consideration of diffusive flux and long-term monitoring in fracture-dominated flow may support accurate quantification of tracer recovery. In addition, the apparent power law slopes of the breakthrough tails for both tracers were steeper at early times than have been attributed to heterogeneous advection or channeling in meter-scale tests, but the late-time Br – power law slope becomes less steep than has been attributed to diffusive exchange. These deviations may reflect fracture transport patterns that occur at larger scales.

Nevada↗

USGS2022

Hydrologic modeling of a perennial firn aquifer in southeast Greenland

A conceptual model, based on field observations and assumed physics of a perennial firn aquifer near Helheim Glacier (southeast Greenland), is evaluated via steady-state 2-D simulation of liquid water flow and energy transport with phase change. The simulation approach allows natural representation of flow and energy advection and conduction that occur in vertical meltwater recharge through the unsaturated zone and in lateral flow within the saturated aquifer. Agreement between measured and simulated aquifer geometry, temperature, and recharge and discharge rates confirms that the conceptual field-data-based description of the aquifer is consistent with the primary physical processes of groundwater flow, energy transport and phase change. Factors that are found to control simulated aquifer configuration include surface temperature, meltwater recharge rate, residual total-water saturation and capillary fringe thickness. Simulation analyses indicate that the size of perennial firn aquifers depends primarily on recharge rates from surface snowmelt. Results also imply that the recent aquifer expansion, likely due to a warming climate, may eventually produce lakes on the ice-sheet surface that would affect the surface energy balance.

Journal of Glaciology↗

USGS2019

Evaluation of groundwater resources in the Spanish Valley Watershed, Grand and San Juan Counties, Utah

Groundwater resources in the Spanish Valley watershed in southern Utah were quantified for the first time since the early 1970s. The primary objectives of this study were (1) to better understand sources of recharge to, groundwater flow directions within, and discharge points for both the valley-fill and Glen Canyon Group aquifers (VFA and GCGA), and (2) to quantify groundwater budget components of the combined VFA and GCGA, including both recharge and discharge. Based on both groundwater chemistry (stable isotopes, major ions, and noble gases) and environmental tracers in vadose-zone pore water of the Navajo Sandstone outcrop along Sand Flats Road, most recharge to the GCGA occurs high in the La Sal Mountains, and not on the sandstone outcrop area. The same groundwater chemistry and environmental tracer evidence from the saturated zone indicates that Pack Creek, rather than GCGA groundwater, is the primary source of recharge to the VFA. Groundwater recharge in the study area occurs mostly from infiltration of precipitation (in the form of snowmelt) at high altitudes. Additional recharge occurs from the infiltration of runoff along losing reaches of stream channels, or as unconsumed surface-water and groundwater irrigation. Average annual recharge to the Moab-Spanish Valley watershed part of the Spanish Valley study area was estimated to be between 9,550 and 30,000 acre-feet. Based on water-levels collected in the current study, groundwater in both the GCGA and the VFA generally moves downgradient parallel to the topographic slope of the watershed towards the Colorado River. Groundwater discharge measurements, and hydraulic-flux estimates at the lower end of Spanish Valley, provide a more robust estimate of the groundwater budget than evaluating recharge. The primary base-flow discharge components in the study area include groundwater discharge to gaining reaches of streams, groundwater discharge to springs, and well withdrawals. Based on 3 years of measurements (2014–16) and hydraulic-flux calculations at the lower end of Spanish Valley, total groundwater discharge was estimated to be 14,000 to 16,000 acre-feet per year (acre-ft/yr) for the entire watershed, or 13,000 to 15,000 acre-ft/yr, excluding the watershed areas of Grandstaff (formerly Negro Bill) and Ice Box Canyons (compared to the 1971 Sumsion estimate of 22,000 acre-ft/yr). The primary difference is this study’s estimate of subsurface outflow to the Colorado River of only 300 to 1,000 acre-ft/yr, compared to 11,000 acre-ft/yr estimated by Sumsion. Because the study period (2014–16) experienced above average precipitation for 2 of the 3 years, the discharge estimates may be slightly higher than long-term average annual discharge from the groundwater system.

Utah↗

USGS2019

Wetland-scale mapping of preferential fresh groundwater discharge to the Colorado River

Quantitative evaluation of groundwater/surface water exchange dynamics is universally challenging in large river systems, because existing methodology often does not yield spatially‐distributed data and is difficult to apply in deeper water. Here we apply a combined near‐surface geophysical and direct groundwater chemical toolkit to refine fresh groundwater discharge estimates to the Colorado River through a 4‐km 2 wetland that borders the town of Moab, Utah, USA. Preliminary characterization of raw electromagnetic imaging (EMI) data, collected by kayak and by walking, was used to guide additional direct‐contact electrical measurements and installation of new monitoring wells. Chemical data from the wells strongly supported the EMI spatial characterization of preferential fresh groundwater discharge embedded in natural brine groundwaters and weighted to the southern wetland section. Inversion of the EMI data revealed sub‐meter scale detail regarding bulk electrical conductivity zonation across approximately 15.5 km of transects, collected in only 3 days. This electrical detail indicates processes such as salinization of the unsaturated zone and direct discharge through the Colorado River sediments and a tributary creek bed. Overall, the study contributed to a substantial reduction in fresh groundwater discharge estimates previously made using sparse existing well data and a simplified assumption of diffuse fresh groundwater discharge below the entire wetland. EMI will likely become a widely used tool in systems with natural electrical contrast as groundwater/surface water hydrogeologists continue to recognize the prevalence of preferential groundwater discharge processes.

Groundwater↗

USGS2016

A gas-tracer injection for evaluating the fate of methane in a coastal plain stream: Degassing versus in-stream oxidation

Methane emissions from streams and rivers have recently been recognized as an important component of global greenhouse budgets. Stream methane is lost as evasion to the atmosphere or in-stream methane oxidation. Previous studies have quantified evasion and oxidation with point-scale measurements. In this study, dissolved gases (methane, krypton) were injected into a coastal plain stream in North Carolina to quantify stream CH 4 losses at the watershed scale. Stream-reach modeling yielded gas transfer and oxidation rate constants of 3.2 ± 0.5 and 0.5 ± 1.5 d –1 , respectively, indicating a ratio of about 6:1. The resulting evasion and oxidation rates of 2.9 mmol m –2 d –1 and 1,140 nmol L –1 d –1 , respectively, lie within ranges of published values. Similarly, the gas transfer velocity ( K 600 ) of 2.1 m d –1 is consistent with other gas tracer studies. This study illustrates the utility of dissolved-gas tracers for evaluating stream methane fluxes. In contrast to point measurements, this approach provides a larger watershed-scale perspective. Further work is needed to quantify the magnitude of these fluxes under varying conditions (e.g., stream temperature, nutrient load, gradient, flow rate) at regional and global scales before reliable bottom-up estimates of methane evasion can be determined at global scales.

Environmental Science & Technology↗

USGS2015

A tube seepage meter for in situ measurement of seepage rate and groundwater sampling

We designed and evaluated a “tube seepage meter” for point measurements of vertical seepage rates ( q ), collecting groundwater samples, and estimating vertical hydraulic conductivity ( K ) in streambeds. Laboratory testing in artificial streambeds show that seepage rates from the tube seepage meter agreed well with expected values. Results of field testing of the tube seepage meter in a sandy-bottom stream with a mean seepage rate of about 0.5 m/day agreed well with Darcian estimates (vertical hydraulic conductivity times head gradient) when averaged over multiple measurements. The uncertainties in q and K were evaluated with a Monte Carlo method and are typically 20% and 60%, respectively, for field data, and depend on the magnitude of the hydraulic gradient and the uncertainty in head measurements. The primary advantages of the tube seepage meter are its small footprint, concurrent and colocated assessments of q and K , and that it can also be configured as a self-purging groundwater-sampling device.

Groundwater↗

USGS2010

Testing mixing models of old and young groundwater in a tropical lowland rain forest with environmental tracers

We tested three models of mixing between old interbasin groundwater flow (IGF) and young, locally derived groundwater in a lowland rain forest in Costa Rica using a large suite of environmental tracers. We focus on the young fraction of water using the transient tracers CFC‐11, CFC‐12, CFC‐113, SF 6 , 3 H, and bomb 14 C. We measured 3 He, but 3 H/ 3 He dating is generally problematic due to the presence of mantle 3 He. Because of their unique concentration histories in the atmosphere, combinations of transient tracers are sensitive not only to subsurface travel times but also to mixing between waters having different travel times. Samples fall into three distinct categories: (1) young waters that plot along a piston flow line, (2) old samples that have near‐zero concentrations of the transient tracers, and (3) mixtures of 1 and 2. We have modeled the concentrations of the transient tracers using (1) a binary mixing model (BMM) of old and young water with the young fraction transported via piston flow, (2) an exponential mixing model (EMM) with a distribution of groundwater travel times characterized by a mean value, and (3) an exponential mixing model for the young fraction followed by binary mixing with an old fraction (EMM/BMM). In spite of the mathematical differences in the mixing models, they all lead to a similar conceptual model of young (0 to 10 year) groundwater that is locally derived mixing with old (>1000 years) groundwater that is recharged beyond the surface water boundary of the system.

Water Resources Research↗

USGS2007

Infiltration and recharge at Sand Hollow, an upland bedrock basin in southwestern Utah

Permeable bedrock aquifers in arid regions of the southwestern United States are being used increasingly as a source of water for rapidly growing populations, yet in many areas little is known about recharge processes and amounts available for sustainable development. Environmental tracers were used in this study to investigate infiltration and recharge to the Navajo Sandstone at Sand Hollow in the eastern Mojave Desert of southwestern Utah. Average annual precipitation is about 210 millimeters per year. Tracers included bromide, chloride, deuterium, oxygen-18, and tritium. The basin-wide average recharge rate, based on ground-water chloride mass balance, is about 8 millimeters per year, or 4 percent of precipitation. However, infiltration and recharge are highly variable spatially within Sand Hollow. Recharge primarily occurs both as focused infiltration of runoff from areas of outcropping bedrock and as direct infiltration beneath coarse surficial soils. Locations with higher rates generally have lower vadose-zone and ground-water chloride concentrations, smaller vadose-zone oxygen-18 evaporative shifts, and higher ground-water tritium concentrations. Infiltration rates estimated from vadose-zone tritium concentrations at borehole sites within Sand Hollow range from 1 to more than 57 millimeters per year; rates calculated from average vadose-zone chloride concentrations between land surface and the bottom of the chloride bulge range from 0 to 9 millimeters per year; rates calculated from average vadose-zone chloride concentrations below the chloride bulge range from 0.5 to 15 millimeters per year; and rates calculated from ground-water chloride concentrations range from 3 to 60 millimeters per year. A two-end-member deuterium-mixing model indicates that about 85 percent of ground-water recharge in Sand Hollow occurs in the 50 percent of the basin covered by coarser soils and bedrock. Vadose-zone chloride concentrations at individual boreholes represent as much as 12,000 years of accumulation, whereas vadose-zone tritium has only been accumulating during the past 50 years. Environmental tracers at Sand Hollow indicate the possibility of a cyclical recharge pattern from higher infiltration rates earlier in the Holocene to lower rates later in the Holocene, back again to higher infiltration rates during the past 50 years.

Utah↗

USGS2005

An integrated environmental tracer approach to characterizing groundwater circulation in a mountain block

The subsurface transfer of water from a mountain block to an adjacent basin (mountain block recharge (MBR)) is a commonly invoked mechanism of recharge to intermountain basins. However, MBR estimates are highly uncertain. We present an approach to characterize bulk fluid circulation in a mountain block and thus MBR that utilizes environmental tracers from the basin aquifer. Noble gas recharge temperatures, groundwater ages, and temperature data combined with heat and fluid flow modeling are used to identify clearly improbable flow regimes in the southeastern Salt Lake Valley, Utah, and adjacent Wasatch Mountains. The range of possible MBR rates is reduced by 70%. Derived MBR rates (5.5–12.6 × 10 4 m 3 d −1 ) are on the same order of magnitude as previous large estimates, indicating that significant MBR to intermountain basins is plausible. However, derived rates are 50–100% of the lowest previous estimate, meaning total recharge is probably less than previously thought.

Water Resources Research↗

USGS2005

3H/3He age data in assessing the susceptibility of wells to contamination

Regulatory agencies are becoming increasingly interested in using young–ground water dating techniques, such as the 3 H/ 3 He method, in assessing the susceptibility of public supply wells (PSWs) to contamination. However, recent studies emphasize that ground water samples of mixed age may be the norm, particularly from long-screened PSWs, and tracer-based “apparent” ages can differ substantially from actual mean ages for mixed-age samples. We present age and contaminant data from PSWs in Salt Lake Valley, Utah, that demonstrate the utility of 3 H and 3 He measurements in evaluating well susceptibility, despite potential age mixing. Initial 3 H concentrations (measured 3 H + measured tritiogenic 3 He) are compared to those expected based on the apparent 3 H/ 3 He age and the local precipitation 3 H record. This comparison is used to determine the amount of modern water (recharged after ∼1950) vs. prebomb water (recharged before ∼1950) samples might contain. Concentrations of common contaminants were also measured using detection limits generally lower than those used for regulatory purposes. A clear correlation exists between the potential magnitude of the modern water fraction and both the occurrence and concentration of contaminants. For samples containing dominantly modern water based on their initial 3 H concentrations, potential discrepancies between apparent 3 H/ 3 He ages and mean ages are explored using synthetic samples that are random mixtures of different modern waters. Apparent ages can exceed mean ages by up to 13 years for these samples, with an exponential age distribution resulting in the greatest discrepancies.

Ground Water↗

USGS2003

Radiogenic helium in shallow groundwater within a clay till, southwestern Ontario

Profiles of 4 He in pore water were measured in clay aquitards in SW Ontario. The 4 He distributions are consistent with groundwater velocities that are <6 mm yr −1 , and thus diffusion is the dominant transport mechanism for 4 He. Modeling indicates that the effective diffusion coefficient for 4 He is 6.3 ± 1.6 × 10 −6 cm 2 s −1 . Furthermore, the profiles are consistent with the internal release of 4 He from aquitard sediments at a rate of 0.03–0.13 μcc(STP) kg −1 yr −1 . These rates are also consistent with laboratory release experiments and, on average, are 600 times greater than the production of 4 He from U/Th decay. Modeling and the ratio of 21 Ne to 4 He within the sediments indicate that although the aquitards were deposited about 13 kA BP, the sediments released >70% of initial 4 He for 50 to 60 kA prior to incorporation into the till.

Water Resources Research↗