Donald D. Runnells

Geochemical heterogeneity in a sand and gravel aquifer: Effect of sediment mineralogy and particle size on the sorption of chlorobenzenes

The effect of particle size, mineralogy and sediment organic carbon (SOC) on sorption of tetrachlorobenzene and pentachlorobenzene was evaluated using batch-isotherm experiments on sediment particle-size and mineralogical fractions from a sand and gravel aquifer, Cape Cod, Massachusetts. Concentration of SOC and sorption of chlorobenzenes increase with decreasing particle size. For a given particle size, the magnetic fraction has a higher SOC content and sorption capacity than the bulk or non-magnetic fractions. Sorption appears to be controlled by the magnetic minerals, which comprise only 5–25% of the bulk sediment. Although SOC content of the bulk sediment is <0.1%, the observed sorption of chlorobenzenes is consistent with a partition mechanism and is adequately predicted by models relating sorption to the octanol/water partition coefficient of the solute and SOC content. A conceptual model based on preferential association of dissolved organic matter with positively-charged mineral surfaces is proposed to describe micro-scale, intergranular variability in sorption properties of the aquifer sediments.

Geochemical controls on ground water composition at the Cripple Creek Mining District, Cripple Creek, Colorado

Abstract A combined approach involving evaluations of historical information, compositional trends, site mineralogy, and forward and inverse geochemical modeling was used to assess the effects of Au mining on ground water quality at the Cripple Creek Mining District. The District is located in a Tertiary volcanic diatreme complex surrounded by Precambrian granite. Historically, mining activity was underground whereas present-day mining occurs in surface mines. Between 1896 and 1941, a series of tunnels was excavated to drain the underground mining areas. The Carlton Tunnel, located about 900–950 m below the surface, is the primary ground water drain for the mining areas. Ground water flowing from the Carlton Tunnel has historically been of good quality. The geochemical processes controlling the quality of the Carlton Tunnel water were the focus of this study. Mineralogical and acid/base accounting data indicate that the diatreme is zoned vertically from an oxidized condition with acidic paste-pH, acidic ground water, and elevated metal concentrations near the surface to an alkaline condition with high pH, elevated SO4, and low metal concentrations at depth. The average travel time of water from the surface to the Carlton Tunnel is estimated to be at least 25a based on 3H determinations. Forward geochemical modeling results indicate that this travel time is sufficient for ground water to reach equilibrium with calcite, gypsum, and fluorite by the time it exits through the Carlton Tunnel. Equilibrium processes have effectively fixed the pH, alkalinity, and SO4 in the Carlton Tunnel water to near-constant levels for at least 24–70a based on comparisons to historically reported water compositions. Inverse geochemical modeling results indicate that there is sufficient neutralization capacity at depth in the diatreme to maintain the current good quality of the ground water flowing from the Carlton Tunnel for the forseeable future, assuming no significant changes in hydrogeochemical conditions.

Contamination of water and sediment in a desert stream by metals from an abandoned gold mine and mill, Eureka District, Arizona, U.S.A.

Abstract Boulder Creek comprises one of the major watercourses in an otherwise arid region of western Arizona, supporting a rich diversity of wildlife. The abandoned Hillside mine and mill complex, on the banks of Boulder Creek, consists of a series of tailings and waste piles, collapsed adits and shafts, and a dismantled mill. The Hillside mine extracted chiefly Au and Ag, but the mill also processed a variety of base and precious metals from other mines in the region. The non-polluted stream water above the Hillside complex is alkaline, predominantly Na Ca HCO3 in composition, and well buffered. Polluted water enters the creek from two point sources, a tailings pile and a collapsed adit. The tailings seep has a ph of 2.4 and concentration (in mg/l) up to 5240 SO4, 260 Al, 34 As, 100 Cu, 610 Fe, 52 Mn, and 500 Zn. Water from the collapsed adit has a ph of 5.4 and contains (in mg/l) upt to 1480 SO4, 21 As, 68 Fe, 45 Mn, and 9.5 Zn, but low concentrations of Al and Cu. Mixing of these waters with the oxygenated, alkaline stream water causes a rapid downstream precipitation and sedimentation of the dissolved metals. The reactions in the stream are the natural equivalents of the processes of aeration and liming which are used in water-treatment.

Geochemistry of molybdenum in some stream sediments and waters

Elevated concentrations of Mo are present in both the waters and sediments of Tenmile Creek, downstream from the large Mo deposit at Climax. Colorado. Concentrations of Mo reach a maximum of 10mg/1 in the water and 384μ/g in the (−) 80 mesh fraction of the sediment. The Mo anomaly extends for more than 80 km downstream from Climax, and results from the mining and milling at Climax. Background Mo concentrations in the nearby mountainous area are < 10μg/l (water) and < 5μg/g (sediment). Immediately below three small unmined Mo-rich orebodies elsewhere in Colorado < 3μg/l Mo are present in the waters and 20–30μg/g Mo in the fine fraction of the sediments. The Mo in the sediment of Tenmile Creek is chiefly adsorbed on coatings of amorphous Fe oxyhydroxide. and is similar to its form below two small, unmined Mo deposits. Mining has not changed the character of the chemical processes responsible for Mo dispersion from the Climax site. A modified version of the WATEQF computer program (Plummeret al., 1976) predicts that Tenmile Creek is undersaturated with respect to ferrimolybdite. molybdenite, powellite, and ilsemannite. The Mo in the stream water occurs as the molybdate ion which can be adsorbed on amorphous Fe oxyhydroxides. These predictions are supported by the absence of Mo minerals in the sediment of Tenmile Creek.

Hydrogeochemical Exploration for Uranium Ore Deposits: Use of the Computer Model Wateqfc

ABSTRACT Runnells, D.D. and Lindberg, R.D., 1981. Hydrogeochemical exploration for uranium ore deposits: use of the computer model WATEQFC. In: A.W. Rose and H. Gundlach (Editors), Geochemical Exploration 1980. J. Geochem. Explor., 15: 37–50. Groundwaters in contact with hidden ore deposits may acquire chemical compositions that offer a guide for exploration, if the chemistry of the waters can be properly interpreted. Hydrogeochemical computer models allow significant progress to be made in the interpretation of the chemistry of all types of natural waters. The computer program, WATEQFC, an expansion and restructuring of WATEQF, is directed toward geochemical exploration for uranium and base metals. The expanded program can now solve the simultaneous equilibria involved in the aqueous geochemistry of 47 chemical elements, represented by approximately 540 minerals and solid compounds and 650 aqueous species. Calibration of the model with groundwaters from known deposits of uranium ore suggests that hidden ore bodies may be revealed by the state of saturation of the waters with respect to a suite of potential ore and gangue minerals. The saturation index (SI) is a reliable predictor of the presence of uranium ore from known deposits in Texas, Wyoming, and Czechoslovakia. The use of groundwater for regional reconnaissance strongly suggests that uranium mineralization is present in the subsurface near Colorado City, Colorado, whereas a similar modeling of groundwaters from a large area of Triassic sandstones in England virtually eliminates that area from consideration as a host for hidden uranium ore.

Selenium in aqueous solutions: The impossibility of obtaining a meaningful Eh using a platinum electrode, with implications for modeling of natural waters

Oxidation-reduction reactions are clearly one of the major controlling factors in the geochemical and environmental behavior of Se. Predictions of its solubility and aqueous speciation must include some measure of the redox status (Eh or pH) of the system. However, laboratory experiments show that even at high concentrations of Se, and over a wide range of pH, the Pt electrode is completely insensitive to the relative abundances of dissolved Se (VI) and Se (IV). For Se, as for many other multivalent elements, predictions concerning aqueous speciation cannot be based on a measured Eh and equilibrium geochemical calculations; instead, chemical analyses must be used to measure the abundances of the predominant dissolved species.

Predicting the environmental stability of treated copper smelter flue dust

Abstract Column tests were conducted to determine the leachability of As, Cd, Cu, Fe and Pb from copper smelter flue dust that had been treated by the Cashman Process in an effort to recover metals while rendering the residue inert. Between 100 and 300 μg/l As [predominantly As (V)] leached from the residue from a batch-reactor test, while between 1000 and 1400 μg/l As leached from residue from a continuous-reactor test. Electron microprobe analyses of the two materials identified scorodite (FeAsO 4 ·2H 2 O) as the principal As-bearing phase. The pHs of leachate from the batch-and continuous-reactor residues were approximately 5.0 and 4.0, respectively. Cadmium and Cu leachate concentrations decreased through the tests, while Pb equilibrated at approximately 200 and 1300 μg/l for the batch and continuous residues, respectively. The measured Eh did not agree with the Eh calculated from either the As(III)/As(V) or Fe(II)/Fe(III) couple. Modeling of system chemistry using MINTEQA2 indicated that scorodite controlled the As concentration of the leachate. The variability of leachate As and metal concentrations between the batch-and continuous-reactor residues indicates that the process conditions failed to produce residues of satisfactory stability.

Comments on “directed panspermia”

Abstract In a recent paper Crick and Orgel (1973) asserted that the anomalous abundance of molybdenum in living organisms is evidence that life may have originated somewhere else in the Universe and was transported to Earth. Their argument concerned a comparison of the relative abundances and biological importance of chromium, nickel, and molybdenum. We point out that a more careful consideration of these elements does not support their conclusion.

Fluorine: its mineralogical residence in the oil shale of the Mahogany Zone of the Green River Formation, Piceance Creek Basin, Colorado, U.S.A.☆

Abstract The Eocene oil shales of northwestern Colorado comprise one of the major resources of hydrocarbon fuels in the U.S.A. Oil shales of the Mahogany Zone (Parachute Creek Member, Green River Formation) contain up to 2100 mg/kg fluorine. The content of fluorine changes rapidly within short stratigraphic intervals, and, although not organically bound, correlates positively with the organic content of the rock. Studies of the mineralogical residence of fluorine in oil shale were made possible by combining the methods of low-temperature ashing, high-speed centrifugation in a liquid with a density gradient, X-ray diffraction, X-ray fluorescence, nuclear inelastic scattering, and electron microscopy. A major portion of the fluorine in the Mahogany Zone appears to be associated with the ubiquitous micaceous clay minerals, especially illite. Other fluorine-bearing minerals, such as fluorite (CaF 2 ), cryolite (Na 3 AlF 6 ), and fluorapatite [Ca 5 (PO 4 ) 3 F] were not detected in the eleven samples studied. However, this does not exclude the possible presence of discrete crystals or crystal aggregates of these minerals in other portions of the Mahogany Zone.

Geochemical interactions between acidic tailings fluid and bedrock: use of the computer model MINTEQ

Abstract Contamination of ground water in domestic water wells has been documented in the vicinity of a uranium mill near Canon City, south-central Colorado, U.S.A. Acidic tailings fluid (raffinate) was passed through a core collected from the subjacent calcite-bearing sandstone to evaluate the effect of interactions between the raffinate and bedrock on the fluid pH, and on the mobility of Al, Ca, Cl, Fe, Mn, SO4, and Zn. In the experiment, the pH initially increased from 2.3 to 8.0 as calcite in the core dissolved and neutralized the raffinate. Concurrently, amorphous ferric hydroxide precipitated in the micro-environment surrounding the reacting carbonate grains. This led to a gradual decrease in pH to 3.4 due to the armoring of the remnant calcite cement by amorphous ferric hydroxide. The results were modeled using the mass transfer computer program, MINTEQ. The pH was modeled by simulating the dissolution of calcite in the raffinate, while the Eh was set at the values measured in the experiment. The behavior of Mn was described by the dissolution of manganocalcite, but an adequate model for dissolved Ca required both calcite dissolution and ion exchange of Ca for Na. Aluminum behavior was simulated by assuming a hydroxide solubility constraint above pH 5.7 and by AlOHSO4 in more acidic regimes. Iron was modeled by the precipitation of an amorphous ferric hydroxide. From chemical analyses, measurements of Eh and pH, and MINTEQ calculations, the log Ksp of the amorphous ferric hydroxide in the experiment was determined to be from −33.5 to −37.6. Zinc was modeled by means of the triple-layer sorption algorithm in MINTEQ, assuming the amorphous ferric hydroxide phase to be the sorbent. Comparison between the experimental effluent and ground-water metal concentrations downgradient from the site are in general agreement. Specifically, SO4 appears to be the best indicator of the encroaching front of acidic contaminants in the subsurface. The general concurrence between the observed experimental results, the computed model predictions, and the downgradient ground-water metal concentrations indicate that mass transfer models such as MINTEQ are useful in predicting the interaction between bedrock and acidic tailings fluid.