USGS Science⌕ Search

SEARCH · USGS Science

Results for “Environmental Science and Technology - Water”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8Linked to original sources
USGS2002

Batch experiments characterizing the reduction of chromium(VI) using suboxic material from a mildly reducing sand and gravel aquifer

Batch experiments were conducted with sand collected from a shallow sand and gravel aquifer to identify the principal chemical reactions influencing the reduction of Cr(VI), so that field-observed Cr(V1) reduction could be described. The reduction appeared to be heterogeneous and occurred primarily on Fe(I1)-bearing minerals. At only 1 wt % , the fine fraction (<64 μ m diameter) of the sediments dominated the amount of aqueous Cr(V1) reduction because of its greater reactivity and surface area. Although reduction of Cr(V1) increased with decreasing pH, small variations in the abundance of fine fraction among the replicate samples obscured pH trends in the batch experiments. Consistent results could only be obtained by separating the fine material from the sand and running parallel experiments on each fraction. As pH decreased (6.4 to 4.5), Cr(V1) reduction increased from 30 to 50 nmol/m 2 for the sand fraction (64-1000 μ m) and from 130 to 200 nmol/m 2 for the fine fraction. The amount of Cr(V1) reduced in both the sand-sized and fine material increased from 35 to 80 and from 130 to 1000 nmol/m 2 , respectively, for a 10-fold increase in Cr(VI) initial . A consistent description of the rate data was achieved by assuming that intraparticle diffusion limited the observed rate of reduction.

Environmental Science & Technology↗
USGS2002

Polychlorinated biphenyl congeners in emergent mayflies from the upper Mississippi River

We determined polychlorinated biphenyls (pcbs) in emergent mayflies (hexagenia bilineata) from a 1250-km reach of the upper mississippi river (UMR). Total pcb concentrations (sum of 125 congeners) ranged from 0.21 To 4.1 Mu g/g of dry weight (1.2-29 mu g/g of lipid weight). Concentrations were highest in pools near the twin cities and the quad cities metropolitan areas. Longitudinal movement of pcbs was extensive downstream from the twin cities (175-320 km) but was not apparent downstream from the quad cities. The pcb composition of mayflies was relatively homogeneous throughout most of the river. However, the congener composition in mayflies from two distant locations differed markedly from the other samples and contained a greater abundance of lower molecular weight congeners. Recent pcb discharges from point and nonpoint sources may account for these differences. Emergent mayflies seem to be a useful indicator of pcb contamination of the UMR.

Environmental Science & Technology↗
USGS2002

Sorption of chlorobenzenes to cape cod aquifer sediments

Sorption of tetra- and pentachlorobenzene by sediment from a glacial outwash aquifer on Cape Cod, MA, was evaluated. Particle size and mineralogical fractions (separated based on paramagnetic susceptibility) were characterized with respect to sediment organic carbon (SOC), mineralogy, surface area, metal oxide coatings, and spatial variability. SOC increases by a factor of 10 as particle size decreases from 500-1000 to <63 um. Magnetic mineral abundance is a function of particle size and increases from 5 % in the 500-1000-xm fraction to > 25 % in the <63-um fraction, and SOC is preferentially associated with the magnetic minerals. Sorption increases with decreasing particle size (increasing SOC, magnetic minerals, surface area, and metal oxyhydroxides), and the magnetic mineral fraction has greater sorption than the bulk or nonmagnetic fractions. Removal of SOC decreases sorption proportional to the decrease in SOC and results in a nonlinear isotherm.

Environmental Science & Technology↗
USGS2002

Behavior of pollutant-degrading microorganisms in aquifers: Predictions for genetically engineered organisms

Bioremediation via environmental introductions of degradative microorganisms requires that the microbes survive in substantial numbers and effect an increase in the rate and extent of pollutant removal. Combined field and microcosm studies were used to assess these abilities for laboratory-grown bacteria. Following introduction into a contaminated aquifer, viable cells of Pseudomonas sp. B13 were present in the contaminant plume for 447 days; die-off was rapid in pristine areas. In aquifer microcosms, survival of B13 and FR120, a genetically engineered derivative of B13 having enhanced catabolic capabilities for substituted aromatics, was comparable to B13 field results; both bacteria degraded target pollutants in microcosms made with aquifer samples from the aerobic zone of the pollutant plume. Results suggest that field studies with nonrecombinant microorganisms may be coupled to laboratory studies with derivative strains to estimate their bioremediative efficacy. Furthermore, laboratory strains of bacteria can survive for extended periods of time in nature and thus may have important bioremediative applications.

Environmental Science & Technology↗
USGS2002

Reductive dehalogenation of hexachloroethane, carbon tetrachloride, and bromoform by anthrahydroquinone disulfonate and humic acid

The reductive dehalogenation of hexachloroethane (C2Cl6), carbon tetrachloride (CCl4), and bromoform (CHBr3) was examined at 50??C in aqueous solutions containing either (1) 500 ??M of 2,6-anthrahydroquinone disulfonate (AHQDS), (2) 250 ??M Fe2+, or (3) 250 ??M HS-. The pH ranged from 4.5 to 11.5 for AHQDS solutions and was 7.2 in the Fe2+ solutions and 7.8 in the HS- solutions. The observed disappearance of C2Cl6 in the presence of AHQDS was pseudo-first-order and fit k??ccl4 = k0[A(OH)2] + k1[A(OH)O-] + k2[A(O)22-] where A(OH)2, A(OH)O-, and A(O)22- represent the concentrations of the three forms of the AHQDS in solution. The values of k0, k1, and k2 were ???0,0.031, and 0.24 M-1 s-1, respectively. The addition of 25 mg of C/L of humic acid or organic matter extracted from Borden aquifer solids to aqueous solutions containing 250 ??M HS- or Fe2+ increased the reduction rate by factors of up to 10. The logarithms of the rate constants for the disappearance of C2Cl6 and CCl4 in seven different experimental systems were significantly correlated; log k???ccl4 = 0-64 log k??? c2cl6 - 0.83 with r2 = 0.80. The observed trend in reaction rates of C2Cl6 > CCl4 > CHBr3 is consistent with a decreasing trend in one-electron reduction potentials. ?? 1994 American Chemical Society.

Environmental Science & Technology↗
USGS2002

Differences between nipher and slter shielded rain gages at two Colorado deposition monitoring sites

In the last decade the United States and Canada have made significant progress in establishing spatial ad temporal estimates of atmospheric deposition throughout North America. Fundamental to the wet-deposition portion of these estimates is the accurate and precise measurement of precipitation amount. Goodison and others (I-3) have reported on a new type of shielded snow gage known as the Canadian MSC Nipher shielded snow gage. Because this shielded snow gage has been shown to be superior to other precipitation gages for the estimation of snowfall amount, its design was adapted to the Universal Belfort precipitation gage (4), the dominant precipitation gage used at deposition monitoring sites in the United States. Favorable results taken from monitoring sites using this modified Nipher shielded snow gage (3-6) have prompted the U.S. Environmental Protection Agency and the Electric Power Research Institute to adopt the Nipher shielded Belfort gage as a standard piece of equipment in the Acid MODES and Operational Evaluation Network (OEN) monitoring programs and to propose that is be included as a standard snow gage in other North American deposition monitoring programs. This communication details preliminary results from two of nine NADP/NTN deposition monitoring sites selected by the Environmental Protection Agency to compare Nipher shielded Belfort precipitation gage volumes to volumes obtained from the standard Belfort gage used in the NADP/NTN monitoring program.

Environmental Science & Technology↗
USGS2002

The surface area of soil organic matter

The previously reported surface area for soil organic matter (SOM) of 560-800 m2/g as determined by the ethylene glycol (EG) retention method was reexamined by the standard BET method based on nitrogen adsorption at liquid nitrogen temperature. Test samples consisted of two high organic content soils, a freeze-dried soil humic acid, and an oven-dried soil humic acid. The measured BET areas for these samples were less than 1 m2/g, except for the freeze-dried humic acid. The results suggest that surface adsorption of nonionic organic compounds by SOM is practically insignificant in comparison to uptake by partition. The discrepancy between the surface areas of SOM obtained by BET and EG methods was explained in terms of the 'free surface area' and the 'apparent surface area' associated with these measurements.The previously reported surface area for soil organic matter (SOM) of 560-800 m2/g as determined by the ethylene glycol (EG) retention method was reexamined by the standard BET method based on nitrogen adsorption at liquid nitrogen temperature. Test samples consisted of two high organic content soils, a freeze-dried soil humic acid, and an oven-dried soil humic acid. The measured BET areas for these samples were less than 1 m2/g, except for the freeze-dried humic acid. The results suggest that surface adsorption of nonionic organic compounds by SOM is practically insignificant in comparison to uptake by partition. The discrepancy between the surface areas of SOM obtained by BET and EG methods was explained in terms of the 'free surface area' and the 'apparent surface area' associated with these measurements.

Environmental Science & Technology↗