Showing papers by "John A. Cherry published in 1986"
TL;DR: A large-scale field experiment on natural gradient transport of solutes in groundwater has been conducted at a site in Borden, Ontario as discussed by the authors, where over 19,900 samples have been collected over a 3-year period.
Abstract: A large-scale field experiment on natural gradient transport of solutes in groundwater has been conducted at a site in Borden, Ontario. Well-defined initial conditions were achieved by the pulse injection of 12 m3 of a uniform solution containing known masses of two inorganic tracers (chloride and bromide) and five halogenated organic chemicals (bromoform, carbon tetrachloride, tetrachloroethylene, 1,2-dichlorobenzene, and hexachloroethane). A dense, three-dimensional array of over 5000 sampling points was installed throughout the zone traversed by the solutes. Over 19,900 samples have been collected over a 3-year period. The tracers followed a linear horizontal trajectory at an approximately constant velocity, both of which compare well with expectations based on water table contours and estimates of hydraulic head gradient, porosity, and hydraulic conductivity. The vertical displacement over the duration of the experiment was small. Spreading was much more pronounced in the horizontal longitudinal than in the horizontal transverse direction; vertical spreading was very small. The organic solutes were retarded in mobility, as expected.
634 citations
TL;DR: In this article, Nitrate and a conservative tracer (bromide) were added to natural groundwater and injected at 3 m depth into a shallow, unconfined sand aquifer.
274 citations
TL;DR: In this article, the isotopic enrichment of groundwaters in the low-permeability Quaternary glacial deposits of southwestern Ontario has been investigated and the authors concluded that the isotope enrichment in 35Cl was caused by upward diffusion over a period of about 15,000 years.
170 citations
TL;DR: In this article, an unweathered glacial till was found to have a bulk permeability that exceeds its matrix permeability by two orders of magnitude and a mean specific storage of 1.3 × 10−4 m−1.
Abstract: Field and laboratory studies of a clayey unweathered glacial till have shown that its bulk permeability exceeds its matrix permeability by two orders of magnitude. Such findings are common for weathered till but are rare for unweathered till, and have important implications for groundwater recharge and contaminant transport. The till in question is 6 m thick and appears to be unweathered and unfractured. It is overlain by 12 m of weathered and highly fractured till. Results of consolidation tests on the unweathered till indicate a mean vertical hydraulic conductivity of 3.5 × 10−11 m∙s−1 and a mean specific storage of 1.3 × 10−4 m−1. Results of slug tests yield a horizontal hydraulic conductivity of about 5 × 10−9 m∙s−1. Drawdowns in the till in response to pumping from the aquifer below indicate a vertical hydraulic diffusivity of 4.5 × 10−5m2∙s−1. The slug test results combined with specific storage results from consolidation tests indicate a similar value for horizontal hydraulic diffusivity of 4 × 10−...
127 citations
TL;DR: In this article, a 22 km/sup 2/ area of the Interior Plains Region of southern Alberta, Canada consists of an upper brown gypsiferous weathered zone and a lower discontinuous grey nonweathered zone.
Abstract: Glacial till in a 22-km/sup 2/ area of the Interior Plains Region of southern Alberta, Canada consists of an upper brown gypsiferous weathered zone (up to 20 m thick) and a lower discontinuous grey nonweathered zone (up to 25 m thick). Although the total sulfur content of the two till zones is the same (0.34%), the mean total sulfate content of the weathered till (4.0 mg g/sup -1/) exceeds that the nonweathered till (0.8 mg g/sup -1/). Similarities suggest that all SO/sub 4//sup 2 -/ in the nonweathered till and 20% of the sulfate in the weathered till was derived from sulfate-rich bedrock fragments incorporated in the till during deposition. Laboratory experiments and delta/sup 18/O and delta/sup 34/S analyses of total SO/sub 4//sup 2 -/ and the sulfur forms in the two zones show that the majority of the sulfate in the weathered till was derived from the oxidation of organic S at some time after the till was deposited. Mass balance and flux calculations indicate that this oxidation occurred under partially saturated conditions. Groundwater flow simulations suggest that the water table was much lower and that a thick partially saturated zone was possible during the drier Altithermal period (11,000more » to 3000 years B.P.). The following chemical processes account for the major ions that are found in the groundwater but were generated when the partially saturated zone existed. The oxidation of reduced S produced SO/sub 4//sup 2 -/ and H/sup +/. The H/sup +/ reacted with carbonate minerals under elevated p/sub CO2/, with Ca/sup 2 +/ loss by exchange for Na/sup +/ and gypsum precipitation. Volume shrinkage in the weathered till resulting from these geochemical processes may have enhanced the development of fractures and caused the associated increased hydraulic conductivity.« less
117 citations
TL;DR: In this paper, the authors considered the system to be an equivalent porous medium (EPM) and the rapidity with which fracture/immobile-matrix equilibrium is established will be determined in part by the: fracture aperture (2b), interfracture spacing (2B); porosity in the immobile matrix (θim); and the matrix diffusion coefficient (D′).
62 citations
TL;DR: In this article, a field study demonstrated the probable presence and mechanisms of formation of siderite through indirect aqueous-based methods: pH-pe diagram, saturation indices of minerals calculated through a speciation model, availability of reactants for precipitation reactions and stoichiometry of precipitation reactions.
28 citations