Horizontal drilling and hydraulic fracturing are transforming energy production, but their potential environmental effects remain controversial. We analyzed 141 drinking water wells across the Appalachian Plateaus physiographic province of northeastern Pennsylvania, examining natural gas concentrations and isotopic signatures with proximity to shale gas wells. Methane was detected in 82% of drinking water samples, with average concentrations six times higher for homes <1 km from natural gas wells (P = 0.0006). Ethane was 23 times higher in homes <1 km from gas wells (P = 0.0013); propane was detected in 10 water wells, all within approximately 1 km distance (P = 0.01). Of three factors previously proposed to influence gas concentrations in shallow groundwater (distances to gas wells, valley bottoms, and the Appalachian Structural Front, a proxy for tectonic deformation), distance to gas wells was highly significant for methane concentrations (P = 0.007; multiple regression), whereas distances to valley bottoms and the Appalachian Structural Front were not significant (P = 0.27 and P = 0.11, respectively). Distance to gas wells was also the most significant factor for Pearson and Spearman correlation analyses (P < 0.01). For ethane concentrations, distance to gas wells was the only statistically significant factor (P < 0.005). Isotopic signatures (δ 13 C-CH 4 , δ 13 C-C 2 H 6 , and δ 2 H-CH 4 ), hydrocarbon ratios (methane to ethane and propane), and the ratio of the noble gas 4 He to CH 4 in groundwater were characteristic of a thermally postmature Marcellus-like source in some cases. Overall, our data suggest that some homeowners living <1 km from gas wells have drinking water contaminated with stray gases.carbon, hydrogen, and helium isotopes | groundwater contamination | geochemical fingerprinting | fracking | hydrology and ecology
Natural-abundance delta15N showed that nitrate generated from commercial land application of swine (Sus scrofa domesticus) waste within a North Carolina Coastal Plain catchment was being discharged to surface waters by ground water passing beneath the sprayfields and adjacent riparian buffers. This was significant because intensive swine farms in North Carolina are considered non-discharge operations, and riparian buffers with minimum widths of 7.6 m (25 ft) are the primary regulatory control on ground water export of nitrate from these operations. This study shows that such buffers are not always adequate to prevent discharge of concentrated nitrate in ground water from commercial swine farms in the Mid-Atlantic Coastal Plain, and that additional measures are required to ensure non-discharge conditions. The median delta15N-total N of liquids in site swine waste lagoons was +15.4 +/- 0.2% vs. atmospheric nitrogen. The median delta15N-NO3 values of shallow ground water beneath and adjacent to site sprayfields, a stream draining sprayfields, and waters up to 1.5 km downstream were + 15.3 +/- 0.2 to + 15.4 +/- 0.2%. Seasonal and spatial isotopic variations in lagoons and well waters were greatly homogenized during ground water transport and discharge to streams. Neither denitrification nor losses of ammonia during spraying significantly altered the bulk ground water delta15N signal being delivered to streams. The lagoons were sources of chloride and potassium enrichment, and shallow ground water showed strong correlation between nitrate N, potassium, and chloride. The 15N-enriched nitrate in ground water beneath swine waste sprayfields can thus be successfully traced during transport and discharge into nearby surface waters.
The most common currency for estimating N(2) fixation is acetylene reduction to ethylene. Real-time estimates of nitrogen fixation are needed to close the global nitrogen budget and these remain a critical gap in both laboratory and field experiments. We present a new method for continuous real-time measurements of ethylene production: Acetylene Reduction Assays by Cavity ring-down laser Absorption Spectroscopy (ARACAS). In ARACAS, air in the headspace of an incubation chamber is circulated with a diaphragm pump through a cavity ring-down ethylene spectrometer and back to the incubation chamber. This paper describes the new approach and its benefits compared to the conventional detection of ethylene by flame ionization detector gas chromatography. First, the detection of acetylene reduction to ethylene is non-intrusive and chemically non-destructive, allowing for real-time measurements of nitrogenase activity. Second, the measurements are made instantaneously and continuously at ppb levels, allowing for observation of real-time kinetics on time intervals as short as a few seconds. Third, the instrument can be automated for long time periods of measurement. Finally, the technique will be widely accessible by the research community as it can be readily adapted to most existing acetylene reduction protocols and is based on a modestly priced, commercially available instrument. We illustrate its use for measuring N(2) fixation using two species, the diazotrophic bacterium Azotobacter vinelandii and the lichen Peltigera praetextata. We also discuss potential limitations of the approach, primarily the implications of leaks in the analyzer, as well as future improvements.
Hexavalent
chromium [Cr(VI)] is a known pulmonary carcinogen. Recent
detection of Cr(VI) in drinking water wells in North Carolina has
raised public concern about contamination of drinking water wells
by nearby coal ash ponds. Here we report, for the first time, the
prevalence of Cr and Cr(VI) in drinking water wells from the Piedmont
region of central North Carolina, combined with a geochemical analysis
to determine the source of the elevated Cr(VI) levels. We show that
Cr(VI) is the predominant species of dissolved Cr in groundwater and
elevated levels of Cr and Cr(VI) are found in wells located both near
and far (>30 km) from coal ash ponds. The geochemical characteristics,
including the overall chemistry, boron to chromium ratios, and strontium
isotope (87Sr/86Sr) variations in groundwater
with elevated Cr(IV) levels, are different from those of coal ash
leachates. Alternatively, the groundwater chemistry and Sr isotope
variations are consistent with water–rock interactions as the
major source for Cr(VI) in groundwater. Our results indicate that
Cr(VI) is most likely naturally occurring and ubiquitous in groundwater
from the Piedmont region in the eastern United States, which could
pose health risks to residents in the region who consume well water
as a major drinking water source.
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