Donald O. Whittemore

Groundwater chemistry and water-rock interactions at Stripa

Groundwaters from near surface to a depth of 1232 m in the Stripa granite have been sampled and analyzed for major and trace constituents. The groundwater composition consists of two general types: a typical recharge water of Ca-HCO3 type ( 700 m depth) of high pH (8–10) that reaches a maximum of 1250 mg/L in total dissolved solids (TDS). Intermediate depths show mixtures of the two types that are highly fracture-dependent rather than depth-dependent. Any borehole can vary significantly and erratically in TDS for either a horizontal or vertical direction. The general transition from Ca-HCO3 type to Na-Ca-Cl type correlates with the depth profile for hydraulic conductivity that drops from 10−8 m/s to 10−11 m/s or lower. Thermomechanical stress (from heater experiments) clearly shows an effect on the groundwater composition that could be caused by changing flow paths, leakage of fluid inclusions or both. Dissolution and precipitation of calcite, fluorite and barite, aluminosilicate hydrolysis, and addition of a saline source (possibly fluid inclusion leakage) play the major roles in defining the groundwater composition. The low permeability of the Stripa granite has produced a groundwater composition that appears intermediate between the dilute, shallow groundwaters typical of recharge in a crystalline rock terrain and the saline waters and brines typical of cratonic shield areas at depth.

Non-parametric trend analysis of water quality data of rivers in Kansas

Abstract Surface water quality data for 15 sampling stations in the Arkansas, Verdigris, Neosho, and Walnut river basins inside the state of Kansas were analyzed to detect trends (or lack of trends) in 17 major constituents by using four different non-parametric methods. The results show that concentrations of specific conductance, total dissolved solids, calcium, total hardness, sodium, potassium, alkalinity, sulfate, chloride, total phosphorus, ammonia plus organic nitrogen, and suspended sediment generally have downward trends. Some of the downward trends are related to increases in discharge, while others could be caused by decreases in pollution sources. Homogeneity tests show that both station-wide trends and basinwide trends are non-homogeneous.

Geochemistry of halogens in the Milk River aquifer, Alberta, Canada

Abstract Analytical data are presented for Cl, Br and I on a regional scale for the Milk River aquifer. The three halides show strikingly similar spatial distributions and are highly correlated. Concentrations are low in the freshwater portions of the aquifer but increase by as much as two orders of magnitude along the margins. However, halide ratios reach nearly constant values moving down-gradient, suggesting the dominance of a common subsurface source for these ions. Ratios of Cl/I and Cl/Br are less than those of seawater and fit an origin derived from the diagenesis of organic matter in the sediments. Halide ratios rule out leakage and/or diffusion from the underlying Colorado Group as a major influence on the chemistry; the favored hypothesis is altered connate seawater diffusing from low-permeability units within the Milk River Formation as the primary source of salts. This hypothesis of an internal source has important implications for solute sources in other aquifers affected by saline waters because it does not require the importation of a distant fluid. The129I/I ratio has a meteoric value in groundwater collected near the recharge area, but ratios for downflow waters are only 8–70% of this value. Due to the 16 Ma half-life of129I, these data indicate that most of the increase in dissolved I cannot derive from concentration of a meteoric source by ion filtration, but must have a subsurface origin. Concentrations of129I producedin situ by spontaneous fission of238U attain measurable levels only in the oldest waters sampled (ages≥ 105a), in which it may account for nearly 90% of the total dissolved129I concentration. Water ages based upon36Cl/Cl data range up to 2 Ma if uncorrected for any dilution by subsurface sources of dead Cl. If one assumes that the subsurface contributions of Cl contribute at least 90% of total Cl in the distal portion, then the36Cl-based ages are reduced to ∼ 1Ma, somewhat greater than those estimated by hydrodynamic modeling.

Patterns of Tamarix water use during a record drought

During a record drought (2006) in southwest Kansas, USA, we assessed groundwater dynamics in a shallow, unconfined aquifer, along with plant water sources and physiological responses of the invasive riparian shrub Tamarix ramosissima. In early May, diel water table fluctuations indicated evapotranspirative consumption of groundwater by vegetation. During the summer drought, the water table elevation dropped past the lowest position previously recorded. Concurrent with this drop, water table fluctuations abruptly diminished at all wells at which they had previously been observed despite increasing evapotranspirative demand. Following reductions in groundwater fluctuations, volumetric water content declined corresponding to the well-specific depths of the capillary fringe in early May, suggesting a switch from primary dependence on groundwater to vadose-zone water. In at least one well, the fluctuations appear to re-intensify in August, suggesting increased groundwater uptake by Tamarix or other non-senesced species from a deeper water table later in the growing season. Our data suggest that Tamarix can rapidly shift water sources in response to declines in the water table. The use of multiple water sources by Tamarix minimized leaf-level water stress during drought periods. This study illustrates the importance of the previous hydrologic conditions experienced by site vegetation for controlling root establishment at depth and demonstrates the utility of data from high-frequency hydrologic monitoring in the interpretation of plant water sources using isotopic methods.

Assessing the major drivers of water-level declines: new insights into the future of heavily stressed aquifers

ABSTRACT The major driver of water-level changes in many heavily stressed aquifers is irrigation pumping, which is primarily a function of meteorological conditions (precipitation and potential evapotranspiration). Correlations among climatic indices, water-level changes, and pumping can thus often be used to assess the impact of climatic and anthropogenic stresses. The power of this simple, first-order approach, which captures the primary excitation–response relationships driving aquifer behavior, is demonstrated for the High Plains aquifer in the central United States (Kansas). Regional correlations between water-level changes and climatic indices indicate that a repeat of the most severe drought on record would more than double water-level decline rates. More importantly, correlations between water-level changes and reported pumping reveal that practically feasible pumping reductions should stabilize water levels, at least temporarily, over much of the aquifer in Kansas. This example illustrates that when uncertainty obscures process-based modeling projections, simple approaches such as described here can often provide insights of great practical value. Editor D. Koutsoyiannis; Associate editor A. Fiori

Hydrogeochemistry and stable isotopes of ground and surface waters from two adjacent closed basins, Atacama Desert, northern Chile

The geochemistry and stable isotopes of groundwaters, surface waters, and precipitation indicate different sources of some dissolved constituents, but a common source of recharge and other constituents in two adjacent closed basins in the Atacama Desert region of northern Chile (24°15′–24°45′S). Waters from artesian wells, trenches, and ephemeral streams in the Punta Negra Basin are characterized by concentrations of Na>Ca>Mg and Cl≥SO4,with TDS Mg≥Ca and SO4 >Cl, with TDS also Mg≥Ca and SO4 >Cl, but with TDS up to 40 g/l. The deep mine waters have pH between 3.2 and 3.9, and are high in dissolved CO2 (δ13C= −4.8%PDB), indicating probable interaction with oxidizing sulfides. The deep mine waters have δ18O values of ≈−1.8%.compared with values < −3.5‰ for other Hamburgo Basin waters; thus the mine waters may represent a mixture of meteoric waters with deeper “metamorphic” waters, which had interacted with rocks and exchanged oxygen isotopes at elevated temperatures. Alternatively, the deep mine waters may represent fossil meteoric waters which evolved isotopically along an evaporative trend starting from values quite depleted in δ18O and °Dd relative to either precipitation or shallow groundwaters. High I/Br ratios in the Hamburgo Basin waters and La Escondida mine waters are consistent with regionally high I in surficial deposits in the Atacama Desert region and may represent dissolution of a wind-blown evaporite component. Rain and snow collected during June 1984, indicate systematic δ18O and δD fractionation with increasing elevation between 3150 and 4180 m a.s.l. (−0.21ℵ.δ18O and−1.7ℵ.δD per 100 m). Excluding the deep mine waters from La Escondida, the waters from the Hamburgo and Punta Negra Basins have similar δD and δ18O values and together show a distinct evaporative trend (δD = 5.0 δ18O− 20.2). Snowmelt from the central Andes Cordillera to the east is the most likely source of recharge to both basins. Some of the waters in the Hamburgo Basin may have been recharged during late Pleistocene, when the climate was wetter and a lake filled the intervening Punta Negra Basin, as suggested by recent archaeological and geomorphological studies.

Effects of variations in recharge on groundwater quality

Abstract The predominant regional effect of recharge on municipal groundwater quality in Kansas is the dilution of mineralized water in aquifers with relatively shallow water tables. The individual dissolved constituents contributing most to the water-quality variations are sulfate and chloride, and the calcium and sodium accompanying them, which are derived from the dissolution of evaporite minerals within the aquifer or from saline formation water in bedrock underlying the aquifer. The relationship between recharge and groundwater-quality variation can be quantified by associating certain climatic indices, especially the Palmer Drought Index, with quality observations. The response time of the maximum water-quality change relative to the occurrence of drought or substantial recharge ranges from a month to 3 years depending on the aquifer characteristics, and is generally proportional to the saturated thickness and specific yield. The response time is also affected by discharge to and recharge from nearby streams and by the well construction, particularly the placement of the screened interval, and pumping stress.

Interpretation of water level changes in the high plains aquifer in Western Kansas.

Water level changes in wells provide a direct measure of the impact of groundwater development at a scale of relevance for management activities. Important information about aquifer dynamics and an aquifers future is thus often embedded in hydrographs from continuously monitored wells. Interpretation of those hydrographs using methods developed for pumping-test analyses can provide insights that are difficult to obtain via other means. These insights are demonstrated at two sites in the High Plains aquifer in western Kansas. One site has thin unconfined and confined intervals separated by a thick aquitard. Pumping-induced responses in the unconfined interval indicate a closed (surrounded by units of relatively low permeability) system that is vulnerable to rapid depletion with continued development. Responses in the confined interval indicate that withdrawals are largely supported by leakage. Given the potential for rapid depletion of the unconfined interval, the probable source of that leakage, it is likely that large-scale irrigation withdrawals will not be sustainable in the confined interval beyond a decade. A second site has a relatively thick unconfined aquifer with responses that again indicate a closed system. However, unlike the first site, previously unrecognized vertical inflow can be discerned in data from the recovery periods. In years of relatively low withdrawals, this inflow can produce year-on-year increases in water levels, an unexpected occurrence in western Kansas. The prevalence of bounded-aquifer responses at both sites has important ramifications for modeling studies; transmissivity values from pumping tests, for example, must be used cautiously in regional models of such systems.

Movement and fate of atrazine and bromide in central Kansas croplands

Abstract Two flooding experiments were conducted at two sites with different soils to study the transport and fate of the commonly used herbicide atrazine and inorganic chemicals in the Great Bend Prairie croplands of south-central Kansas. The instantaneous profile method supplemented by the use of an organic (atrazine) and an inorganic (bromide) tracer chemical was used to characterize in situ the hydraulic and chemical properties of the appropriately instrumented field sites. Atrazine readily degraded to hydroxyatrazine and biodegradation by-products and was not detected deeper in the soil profile and underlying shallow aquifer. The classical processes of chemical movement based on porous media-equilibrium-diffuse flow did not fit the data well at either site. Incompletely mixed, slug flow appeared to predominate at one of the sites and preferential flow at the other. The slug movement caused ‘piston-type’ displacement of more saline solutions in the soil profile to the shallow water table. Recommendations for conducting related field studies based on our sampling experience are given.

Field Investigation of a New Recharge Approach for ASR Projects in Near-Surface Aquifers.

Aquifer storage and recovery (ASR) is the artificial recharge and temporary storage of water in an aquifer when water is abundant, and recovery of all or a portion of that water when it is needed. One key limiting factor that still hinders the effectiveness of ASR is the high costs of constructing, maintaining, and operating the artificial recharge systems. Here we investigate a new recharge method for ASR in near-surface unconsolidated aquifers that uses small-diameter, low-cost wells installed with direct-push (DP) technology. The effectiveness of a DP well for ASR recharge is compared with that of a surface infiltration basin at a field site in north-central Kansas. The performance of the surface basin was poor at the site due to the presence of a shallow continuous clay layer, identified with DP profiling methods, that constrained the downward movement of infiltrated water and significantly reduced the basin recharge capacity. The DP well penetrated through this clay layer and was able to recharge water by gravity alone at a much higher rate. Most importantly, the costs of the DP well, including both the construction and land costs, were only a small fraction of those for the infiltration basin. This low-cost approach could significantly expand the applicability of ASR as a water resources management tool to entities with limited fiscal resources, such as many small municipalities and rural communities. The results of this investigation demonstrate the great potential of DP wells as a new recharge option for ASR projects in near-surface unconsolidated aquifers.