A review of physical, chemical, and hydrogeologic characteristics of stray gas migration: Implications for investigation and remediation.

Releases of natural gas into groundwater from oil and gas exploration, production, or storage (i.e., "stray gas") can pose a risk to groundwater users and landowners in the form of a fire or explosive hazard.

Purging and other sampling variables affecting dissolved methane concentration in water supply wells.

Determining whether changes in groundwater methane concentration are naturally occurring or related to oil and gas operations can be complicated by numerous sources of variability. This study of 10 residential water supply wells in Northeastern Pennsylvania evaluates how i) sampling from different points within the water well system, ii) purging different water volumes prior to sampling, and ii) natural variation over time, affects concentrations of naturally occurring dissolved methane and other water quality parameters. Among the population of wells, all had dissolved methane concentrations >1mg/L.

A Tiered Approach to Evaluating Salinity Sources in Water at Oil and Gas Production Sites.

A suspected increase in the salinity of fresh water resources can trigger a site investigation to identify the source(s) of salinity and the extent of any impacts. These investigations can be complicated by the presence of naturally elevated total dissolved solids or chlorides concentrations, multiple potential sources of salinity, and incomplete data and information on both naturally occurring conditions and the characteristics of potential sources. As a result, data evaluation techniques that are effective at one site may not be effective at another.

1,4-Dioxane drinking water occurrence data from the third unregulated contaminant monitoring rule.

This study examined data collected from U.S. public drinking water supplies in support of the recently-completed third round of the Unregulated Contaminant Monitoring Rule (UCMR3) to better understand the nature and occurrence of 1,4-dioxane and the basis for establishing drinking water standards.

Application of natural resource valuation concepts for development of sustainable remediation plans for groundwater.

This paper explores the application of natural resource assessment and valuation procedures as a tool for developing groundwater remediation strategies that achieve the objectives for health and environmental protection, in balance with considerations of economic viability and conservation of natural resources. The natural resource assessment process, as applied under U.S.

Effect of Different Sampling Methodologies on Measured Methane Concentrations in Groundwater Samples.

Analysis of dissolved light hydrocarbon gas concentrations (primarily methane and ethane) in water supply wells is commonly used to establish conditions before and after drilling in areas of shale gas and oil extraction. Several methods are currently used to collect samples for dissolved gas analysis from water supply wells; however, the reliability of results obtained from these methods has not been quantified. This study compares dissolved methane and ethane concentrations measured in groundwater samples collected using three sampling methods employed in pre- and post-drill sampling programs in the Appalachian Basin.

Environmental Factors Associated With Natural Methane Occurrence in the Appalachian Basin.

The recent boom in shale gas development in the Marcellus Shale has increased interest in the methods to distinguish between naturally occurring methane in groundwater and stray methane associated with drilling and production operations. This study evaluates the relationship between natural methane occurrence and three principal environmental factors (groundwater redox state, water type, and topography) using two pre-drill datasets of 132 samples from western Pennsylvania, Ohio, and West Virginia and 1417 samples from northeastern Pennsylvania. Higher natural methane concentrations in residential wells are strongly associated with reducing conditions characterized by low nitrate and low sulfate ([NO ] < 0.

Exceptionally Long MTBE Plumes of the Past Have Greatly Diminished.

Studies published in the late 1990s and early 2000s identified the presence of exceptionally long methyl tert-butyl ether (MTBE) plumes (more than 600 m or 2000 feet) in groundwater and have been cited in technical literature as characteristic of MTBE plumes. However, the scientific literature is incomplete in regard to the subsequent behavior and fate of these MTBE plumes over the past decade. To address this gap, this issue paper compiles recent groundwater monitoring records for nine exceptional plumes that were identified in prior studies.

Review of quantitative surveys of the length and stability of MTBE, TBA, and benzene plumes in groundwater at UST sites.

Quantitative information regarding the length and stability condition of groundwater plumes of benzene, methyl tert-butyl ether (MTBE), and tert-butyl alcohol (TBA) has been compiled from thousands of underground storage tank (UST) sites in the United States where gasoline fuel releases have occurred. This paper presents a review and summary of 13 published scientific surveys, of which 10 address benzene and/or MTBE plumes only, and 3 address benzene, MTBE, and TBA plumes. These data show the observed lengths of benzene and MTBE plumes to be relatively consistent among various regions and hydrogeologic settings, with median lengths at a delineation limit of 10 µg/L falling into relatively narrow ranges from 101 to 185 feet for benzene and 110 to 178 feet for MTBE.

Progress in remediation of groundwater at petroleum sites in California.

Quantifying the overall progress in remediation of contaminated groundwater has been a significant challenge. We utilized the GeoTracker database to evaluate the progress in groundwater remediation from 2001 to 2011 at over 12,000 sites in California with contaminated groundwater. This paper presents an analysis of analytical results from over 2.

Evaluation of methane sources in groundwater in northeastern Pennsylvania.

Testing of 1701 water wells in northeastern Pennsylvania shows that methane is ubiquitous in groundwater, with higher concentrations observed in valleys vs. upland areas and in association with calcium-sodium-bicarbonate, sodium-bicarbonate, and sodium-chloride rich waters--indicating that, on a regional scale, methane concentrations are best correlated to topographic and hydrogeologic features, rather than shale-gas extraction. In addition, our assessment of isotopic and molecular analyses of hydrocarbon gases in the Dimock Township suggest that gases present in local water wells are most consistent with Middle and Upper Devonian gases sampled in the annular spaces of local gas wells, as opposed to Marcellus Production gas.

Astrocyte activation and wound healing in intact-skull mouse after focal brain injury.

Localised brain tissue damage activates surrounding astrocytes, which significantly influences subsequent long-term pathological processes. Most existing focal brain injury models in rodents employ craniotomy to localise mechanical insults. However, the craniotomy procedure itself induces gliosis.

NR2B-NMDA receptor-mediated increases in intracellular Ca2+ concentration regulate the tyrosine phosphatase, STEP, and ERK MAP kinase signaling.

NMDA receptors regulate both the activation and inactivation of the extracellular signal-regulated kinase (ERK) signaling cascade, a key pathway involved in neuronal plasticity and survival. This bi-directional regulation of ERK activity by NMDA receptors has been attributed to opposing actions of NR2A- versus NR2B-containing NMDA receptors, but how this is implemented is not understood. Here, we show that glutamate-mediated intracellular Ca(2+) increases occur in two phases, a rapid initial increase followed by a delayed larger increase.

Differential changes of glutathione levels in astrocytes and neurons in ischemic brains by two-photon imaging.

Using two-photon imaging techniques with monochlorobimane as a glutathione (GSH) probe, we investigated GSH levels in both core and penumbra regions of an ischemic brain after middle cerebral artery occlusion. We found that the GSH level significantly decreased in the ischemic core, but increased significantly in the penumbra. Furthermore, we observed a differential change of the GSH levels in neurons and astrocytes in the penumbra.

Development of epileptiform excitability in the deep entorhinal cortex after status epilepticus.

Epileptiform neuronal activity during seizures is observed in many brain areas, but its origins following status epilepticus (SE) are unclear. We have used the Li low-dose pilocarpine rat model of temporal lobe epilepsy to examine early development of epileptiform activity in the deep entorhinal cortex (EC). We show that during the 3-week latent period that follows SE, an increasing percentage of neurons in EC layer 5 respond to a single synaptic stimulus with polysynaptic burst depolarizations.

Localized loss of Ca2+ homeostasis in neuronal dendrites is a downstream consequence of metabolic compromise during extended NMDA exposures.

Excessive Ca(2+) loading is central to most hypotheses of excitotoxic neuronal damage. We examined dendritic Ca(2+) signals in single CA1 neurons, injected with fluorescent indicators, after extended exposures to a low concentration of NMDA (5 microM). As shown previously, NMDA produces an initial transient Ca(2+) elevation of several micromolar, followed by recovery to submicromolar levels.

An epigenetic induction of a right-shift in hippocampal asymmetry: selectivity for short- and long-term potentiation but not post-tetanic potentiation.

In humans, it is well established that major psychological functions are asymmetrically represented between the left and right cerebral cortices. The developmental origin of such functional lateralization remains unknown. Using the rat as a model system, we examined whether exposing neonates briefly to a novel environment can differentially affect synaptic plasticity in the left and right hippocampi during adulthood.

Emergence of a spermine-sensitive, non-inactivating conductance in mature hippocampal CA1 pyramidal neurons upon reduction of extracellular Ca2+: dependence on intracellular Mg2+ and ATP.

Large and protracted elevations of intracellular [Ca(2+)] and [Na(+)] play a crucial role in neuronal injury in ischemic conditions. In addition to excessive glutamate receptor activation, other ion channels may contribute to disruption of intracellular ionic homeostasis. During episodes of ischemia, extracellular [Ca(2+)] falls significantly.

Early life modulators and predictors of adult synaptic plasticity.

Early life experience can induce long-lasting changes in brain and behaviour that are opposite in direction, such as enhancement or impairment in regulation of stress response, structural and functional integrity of the hippocampus, and learning and memory. To explore how multiple early life events jointly determine developmental outcome, we investigated the combined effects of neonatal trauma (anoxia on postnatal day 1, P1) and neonatal novelty exposure (P2-21) on adult social recognition memory (3 months of age) and synaptic plasticity in the CA1 of the rat hippocampus (4.5-8 months of age).

GABAergic protection of hippocampal pyramidal neurons against glutamate insult: deficit in young animals compared to adults.

Hypoxia-ischemia (HI) injury in neonatal animals leads to selective regional loss of neurons including CA1 and CA3 pyramidal neurons of the hippocampus as well as nonlethal pathologies. Glutamate-receptor over-activation and Ca2+ influx are involved in these neonatal changes. We examined glutamate-evoked Ca2+ responses in neonatal (PN 7-13) and young adult (PN 21-27) CA1 pyramidal neurons in acute slices from rats.

NAD(P)H fluorescence transients after synaptic activity in brain slices: predominant role of mitochondrial function.

Excitatory stimulation in hippocampal slices results in biphasic NAD(P)H fluorescence transients. Previous studies using differing stimulus protocols agreed that the oxidation phase is a consequence of mitochondrial metabolism, but the reduction phase has been attributed to (1) mitochondrial nicotinamide adenine dinucleotide (NADH) generation or (2) astrocytic glycolysis triggered by glutamate uptake. In an attempt to reconcile these two views, the present study examined NAD(P)H signals evoked by a wide range of stimulus durations (40 ms to 20 secs).

Caffeine releasable stores of Ca2+ show depletion prior to the final steps in delayed CA1 neuronal death.

In addition to their role in signaling, Ca2+ ions in the endoplasmic reticulum also regulate important steps in protein processing and trafficking that are critical for normal cell function. Chronic depletion of Ca2+ in the endoplasmic reticulum has been shown to lead to cell degeneration and has been proposed as a mechanism underlying delayed neuronal death following ischemic insults to the CNS. Experiments here have assessed the relative content of ryanodine receptor-gated stores in CA1 neurons by measuring cytoplasmic Ca2+ increases induced by caffeine.