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A. L. Baehr

Publications and source records attributed to A. L. Baehr.

10 recordsLinked to original sources
USGS2009

Effect of grain-coating mineralogy on nitrate and sulfate storage in the unsaturated zone

Unsaturated-zone sediments and the chemistry of shallow groundwater underlying a small (∼8-km 2 ) watershed were studied to identify the mechanisms responsible for anion storage within the Miocene Bridgeton Formation and weathered Coastal Plain deposits in southern New Jersey. Lower unsaturated-zone sediments and shallow groundwater samples were collected and concentrations of selected ions (including NO 3 − and SO 4 2− ) from 11 locations were determined. Grain size, sorting, and color of the lower unsaturated-zone sediments were determined and the mineralogy of these grains and the composition of coatings were analyzed by petrographic examination, scanning electron microscopy and energy dispersive analysis of x-rays, and quantitative whole-rock x-ray diffraction. The sediment grains, largely quartz and chert (80–94% w/w), are coated with a very fine-grained (<20 μm), complex mixture of kaolinite, halloysite, goethite, and possibly gibbsite and lepidocrocite. The mineral coatings are present as an open fabric, resulting in a large surface area in contact with pore water. Significant correlations between the amount of goethite in the grain coatings and the concentration of sediment-bound SO 4 2− were observed, indicative of anion sorption. Other mineral–chemical relations indicate that negatively charged surfaces and competition with SO 4 2− results in exclusion of NO 3 − from inner sphere exchange sites. The observed NO 3 − storage may be a result of matrix forces within the grain coatings and outer sphere complexation. The results of this study indicate that the mineralogy of grain coatings can have demonstrable effects on the storage of NO 3 − and SO 4 2− in the unsaturated zone.

Vadose Zone Journal↗
USGS2007

Used motor oil as a source of MTBE, TAME, and BTEX to ground water

Methyl tert-butyl ether (MTBE), the widely used gasoline oxygenate, has been identified as a common ground water contaminant, and BTEX compounds (benzene, toluene, ethylbenzene, and xylenes) have long been associated with gasoline spills. Because not all instances of ground water contamination by MTBE and BTEX can be attributed to spills or leaking storage tanks, other potential sources need to be considered. In this study, used motor oil was investigated as a potential source of these contaminants. MTBE in oil was measured directly by methanol extraction and gas chromatography using a flame ionization detector (GC/FID). Water was equilibrated with oil samples and analyzed for MTBE, BTEX, and the oxygenate tert-amyl methyl ether (TAME) by purge-and-trap concentration followed by GC/FID analysis. Raoult's law was used to calculate oil-phase concentrations of MTBE, BTEX, and TAME from aqueous-phase concentrations. MTBE, TAME, and BTEX were not detected in any of five new motor oil samples, whereas these compounds were found at significant concentrations in all six samples of the used motor oil tested for MTBE and all four samples tested for TAME and BTEX. MTBE concentrations in used motor oil were on the order of 100 mg/L. TAME concentrations ranged from 2.2 to 87 mg/L. Concentrations of benzene were 29 to 66 mg/L, but those of other BTEX compounds were higher, typically 500 to 2000 mg/L.

Ground Water Monitoring and Remediation↗
USGS2005

Type curves to determine the relative importance of advection and dispersion for solute and vapor transport

The relative importance of advection and dispersion for both solute and vapor transport can be determined from type curves or concentration, flux, or cumulative flux. The dimensionless form of the type curves provides a means to directly evaluate the importance of mass transport by advection relative to that of mass transport by diffusion and dispersion. Type curves based on an analytical solution to the advection-dispersion equation are plotted in terms of dimensionless time and Peclet number. Flux and cumulative flux type curves provide additional rationale for transport regime determination in addition to the traditional concentration type curves. The extension of type curves to include vapor transport with phase partitioning in the unsaturated zone is a new development. Type curves for negative Peclet numbers also are presented. A negative Peclet number characterizes a problem in which one direction of flow is toward the contamination source, and thereby diffusion and advection can act in opposite directions. Examples are the diffusion of solutes away from the downgradient edge of a pump-and-treat capture zone, the upward diffusion of vapors through the unsaturated zone with recharge, and the diffusion of solutes through a low hydraulic conductivity cutoff wall with an inward advective gradient.

Ground Water↗
USGS2005

A direct immunoassay for detecting diatoms in groundwater as an indicator of the direct influence of surface water

Groundwater under the direct influence of surface water (GWUDISW) is of concern in communities where growing public demand on groundwater resources has resulted in increased withdrawals and hydraulic stress near surface water bodies. Under these conditions, contaminants such as methyl-tert butyl ether (MTBE) and biological materials have been detected in domestic wells. Other contaminants and pathogens associated with surface water are not routinely tested for in groundwater-supplied systems. To address the need for methods to easily identify potentially vulnerable supplies, a direct immunoassay for the quantitative detection of diatoms in raw water samples was developed as a measure of surface water influence on groundwater. Cell wall preparations from Nitzschia palea Kützing, a freshwater diatom found throughout North America, were used to produce a polyclonal antibody that was applied in a direct enzyme-linked immunosorbent assay (ELISA) developed to detect the presence of N. palea cell wall components. The direct immunoassay allows detection at 500 cells L −1 , a level similar to diatom concentrations observed in samples of groundwater collected near the test site. This investigation was the first attempt to utilize an ELISA as an indicator of surface water influence on groundwater. Further research is needed to develop more specific diatom-based monoclonal antibodies, determine cross-reactivity, and optimize sample processing and ELISA procedures for development of a standardized method.

Journal of Applied Phycology↗
USGS2000

Comparison of nitrate, pesticides, and volatile organic compounds in samples from monitoring and public-supply wells, Kirkwood-Cohansey aquifer system, southern New Jersey

The number and total concentration of volatile organic compounds (VOCs) per sample were significantly greater in water from public-supply wells than in water from shallow and moderate-depth monitoring wells in the surficial Kirkwood-Cohansey aquifer system in the Glassboro area of southern New Jersey. In contrast, concentrations of nitrate (as nitrogen) and the number and total concentration of pesticides per sample were statistically similar in samples from shallow and moderate-depth monitoring wells and those from public-supply wells. VOCs in ground water typically are derived from point sources, which commonly exist in urban areas and which result in spatially variable contaminant concentrations near the water table. Because larger volumes of water are withdrawn from public-supply wells than from monitoring wells, their contributing areas are larger and, therefore, they are more likely to intercept water flowing from VOC point sources. Additionally, public-supply wells intercept flow paths that span a large temporal interval. Public-supply wells in the Glassboro study area withdraw water flowing along short paths, which contains VOCs that recently entered the aquifer system, and water flowing along relatively long paths, which contains VOCs that originated from the degradation of parent compounds or that are associated with past land uses. Because the volume of water withdrawn from monitoring wells is small and because shallow monitoring wells are screened near the water table, they generally intercept only relatively short flow paths. Therefore, samples from these wells represent relatively recent, discrete time intervals and contain both fewer VOCs and a lower total VOC concentration than samples from public-supply wells. Nitrate and pesticides in ground water typically are derived from nonpoint sources, which commonly are found in both agricultural and urban areas and typically result in lowlevel, relatively uniform concentrations near the water table. Because nonpoint sources are diffuse and because processes such as degradation or sorption/dispersion do not occur at rates sufficient to prevent detection of these constituents in parts of the aquifer used for domestic and public supply in the study area, concentrations of nitrate and pesticides and numbers of pesticide compounds are likely to be similar in samples from shallow monitoring wells and samples from public-supply wells. Results of a comparison of (1) the general characteristics of, and water-quality data from, public-supply wells in the Glassboro study area to available data from public-supply wells screened in the Kirkwood-Cohansey aquifer system outside the study area, and (2) land-use settings, soil characteristics, and aquifer properties in and outside the study area indicate that the findings of this study likely are applicable to the entire extent of the Kirkwood- Cohansey aquifer system in southern New Jersey.

New Jersey↗
USGS1989

Removing volatile contaminants from the unsaturated zone by inducing advective air-phase transport

Organic liquids inadvertently spilled and then distributed in the unsaturated zone can pose a long-term threat to ground water. Many of these substances have significant volatility, and thereby establish a premise for contaminant removal from the unsaturated zone by inducing advective air-phase transport with wells screened in the unsaturated zone. In order to focus attention on the rates of mass transfer from liquid to vapour phases, sand columns were partially saturated with gasoline and vented under steady air-flow conditions. The ability of an equilibrium-based transport model to predict the hydrocarbon vapor flux from the columns implies an efficient rate of local phase transfer for reasonably high air-phase velocities. Thus the success of venting remediations will depend primarily on the ability to induce an air-flow field in a heterogeneous unsaturated zone that will intersect the distributed contaminant. To analyze this aspect of the technique, a mathematical model was developed to predict radially symmetric air flow induced by venting from a single well. This model allows for in-situ determinations of air-phase permeability, which is the fundamental design parameter, and for the analysis of the limitations of a single well design. A successful application of the technique at a site once contaminated by gasoline supports the optimism derived from the experimental and modeliing phases of this study, and illustrates the well construction and field methods used to document the volatile contaminant recovery.

Journal of Contaminant Hydrology↗