Geochemical & Descriptive Data for Sedimentary Aquifer Materials, Southwestern Idaho
Data
Sampling
HydroLogic, Inc., Scanlan Engineering, and the Bureau of Reclamation provided drill cuttings from wells located in or near the Lake Lowell area in southwestern Idaho (Fig. 1). In total, samples of cuttings from 12 drill holes from 10 locations were obtained. Quality and extent of documentation varied from well to well, ranging from basic drillers' logs to complete lithologic and geophysical logs. Location, depth, well construction information, and other data for sampled wells. Excel Format (19K)
Drill cuttings were composite samples that previously had been collected at the drill site at 5-ft intervals and placed in recloseable plastic bags. Because in some cases the plastic bags had been stored in nearly airtight plastic buckets for up to 4 years, many of the samples were still wet when this study was undertaken. Samples from a few wells had been previously dried, and small representative samples had been reserved in a white cloth bag for reference purposes. In these cases, limited amounts of sample were available, but amounts were still sufficient for geochemical analysis. Because study focus was primarily on the presence and quantity of total arsenic in the solid phases, not its current oxidation state (speciation), the stored material, dry or wet, was useful for geochemical analysis.
For this study, grab samples of representative material were taken from selected intervals for each well. Lithology (a variety of sands, silts, and clays), location of screened intervals (water-producing sands and impermeable clays), and depth were considered in selecting intervals to sample. The grab samples were air dried and their lithology was briefly described. Drill cuttings from 7 of the 12 wells (107 samples in all) were selected and 50 to 100-gram splits were taken for geochemical analysis. All but one sample consisted of unconsolidated sediment. Fifty-nine of the samples were classified as "clay" and 47 were classified as "sand". Samples ranged in grain size from clay to coarse sand. One sample was basalt, which was included to determine "background" concentrations of arsenic and other elements in basalt. Samples selected for geochemical analysis were inspected using a binocular microscope and descriptions, including mineral identification, were made. Descriptive data for drill cutting samples analyzed by inductively coupled plasma-mass spectrometry. Excel (53K)
Analytical
Samples were prepared and geochemical analyses were performed at the U.S. Geological Survey Central Mineral Resources Team analytical chemistry facility in Denver, CO. Thirty-seven elements were determined by inductively coupled plasma-mass spectrometry (ICP-MS). Analytical methods, including sample digestion and quality control procedures, are summarized in a report by Briggs and Meier (2002). Samples were digested by use of a multi-acid technique that results in complete dissolution in most cases, with the exception of refractory or resistant minerals and some secondary minerals (for example, Cr in chromite, Ti in rutile, and Ba in barite). Analytical results for inductively coupled plasma-mass spectrometry analyses of selected drill cuttings (37 elements). Excel (55K)
As an additional quality control measure, 10 samples were also analyzed by use of the hydride-generation atomic absorption spectrophotometry (HGAA) method (Hageman and others, 2002) The sample digestion procedure is slightly different than for ICP-MS (Hageman and others, 2002), but complete sample digestion is achieved in most cases, except for certain refractory minerals. Arsenic concentrations in 10 selected drill cutting samples determined by hydride generation atomic absorption spectrometry and by inductively coupled plasma mass spectrometry. Excel (15K)
