Repository for Oil and Gas Energy Research (ROGER)

Abstract:
The potential contamination of shallow groundwater with inorganic constituents is a major environmental concern associated with shale gas extraction through hydraulic fracturing. However, the impact of shale gas development on groundwater quality is a highly controversial issue. The only way to reliably assess whether groundwater quality has been impacted by shale gas development is to collect pre-development baseline data against which subsequent changes in groundwater quality can be compared. The objective of this paper is to provide a conceptual and methodological framework for establishing a baseline of inorganic groundwater quality in shale gas areas, which is becoming standard practice as a prerequisite for evaluating shale gas development impacts on shallow aquifers. For this purpose, this paper first reviews the potential sources of inorganic contaminants in shallow groundwater from shale gas areas. Then, it reviews the previous baseline studies of groundwater geochemistry in shale gas areas, showing that a comprehensive baseline assessment includes documenting the natural sources of salinity, potential geogenic contamination, and potential anthropogenic influences from legacy contamination and surface land use activities that are not related to shale gas development. Based on this knowledge, best practices are identified in terms of baseline sampling, selection of inorganic baseline parameters, and definition of threshold levels.

Abstract:
Elevated dissolved methane (CH4) concentrations in groundwater are an environmental concern associated with hydraulic fracturing for shale gas. Therefore, determining dissolved CH4 baselines is important for detecting and understanding any potential environmental impacts. Such baselines should change in time and space to reflect ongoing environmental change and should be able to predict the probability that a change in dissolved CH4 concentration has occurred. We considered four dissolved CH4 concentration datasets of English groundwater using a Bayesian approach: two national datasets and two local datasets from shale gas exploration sites. The most sensitive national dataset (the previously published British Geological Survey CH4 baseline) was used as a strong prior for a larger (2153 measurements compared to 439) but less sensitive (detection limit 1000 times higher) Environment Agency dataset. The use of the strong prior over a weak prior improved the precision of the Environment Agency dataset by 75%. The expected mean dissolved CH4 concentration in English groundwater based on the Bayesian approach is 0.24 mg/l, with a 95% credible interval of 0.11 to 0.45 mg/l, and a Weibull distribution of W(0.35±0.01, 0.34±0.16). This indicates the amount of CH4 degassing from English groundwater to the atmosphere equates to between 0.7 to 3.1 kt CH4/year, with an expected value of 1.65 kt CH4/year and a greenhouse gas warming potential of 40.3 kt CO2eq/year. The two local monitoring datasets from shale gas exploration sites, in combination with the national datasets, show that dissolved CH4 concentrations in English groundwater are generally low, but locations with concentrations greater than or equal to the widely used risk action level of 10.0 mg/l do exist. Statistical analyses of groundwater redox conditions at these locations suggest that it may be possible to identify other locations with dissolved CH4 concentrations ≥10.0 mg/l using redox parameters such as Fe concentration.

Abstract:
The prospect of unconventional shale gas development in the semi-arid Karoo Basin (South Africa) has created the prerequisite to temporally characterise the natural radioactivity in associated groundwater which is solely depended on for drinking and agriculture purposes. Radon (222Rn) was the primary natural radionuclide of interest in this study; however, supplementary radium (226Ra and 228Ra) in-water measurements were also conducted. A total of 53 aquifers spanning three provinces were studied during three separate measurement campaigns from 2014 to 2016. The Karoo Basin's natural radon-in-water levels can be characterised by a minimum of 1 ± 1 Bq/L (consistent with zero or below LLD), a maximum of 183 ± 18 Bq/L and mean of 41 ± 5 Bq/L. The mean radon-in-water levels for shallow aquifers were systematically higher (55 ± 10 Bq/L) compared to deep (14 ± 3 Bq/L) or mixed aquifers (20 ± 6 Bq/L). Radon-in-water activity concentration fluctuations were predominantly observed from shallow aquifers compared to the generally steady levels of deep aquifers. A collective seasonal mean radon-in-water levels increase from the winter of 2014 (44 ± 8 Bq/L) to winter of 2016 (61 ± 16 Bq/L) was noticed which could be related to the extreme national drought experienced in 2015. Radium-in-water (228Ra and 226Ra) levels ranged from below detection level to a maximum of 0.008 Bq/L (226Ra) and 0.015 Bq/L (228Ra). The 228Ra/226Ra ratio was characterized by a minimum of 0.93, a maximum of 6.5 and a mean value of 3.3 ± 1.3. Developing and improving baseline naturally occurring radionuclide groundwater databases is vital to study potential radiological environmental impacts attributed to industrial processes such as hydraulic fracturing or mining.

Abstract:
Skip to Next Section The Eastern Cape Karoo region is water stressed and will become increasingly so with further climate change. Effective and reliable groundwater management is crucial for a development such as the proposed hydraulic fracturing for shale gas. This is especially critical across this region of agriculture and protected ecosystem services. The research, as part of baseline data gathering, aims to characterize the hydrochemistry for both the shallow groundwater (<500 m) and saline groundwater closer to the c. 2–5 km deep shale gas. The classification will be used to determine possible vertical hydraulic connectivity between the shallow and deep aquifers, prior to anticipated hydraulic fracturing. This paper reports on the baseline framework that includes the sampling design and a hydrocensus with field-recorded parameters shown as interpolated maps. This includes electrical conductivity, groundwater level and borehole yield. Together with completed sampling results, these data provide a record against which the environmental impact of hydraulic fracturing and the reinjection of production water can be determined. The research is a critical first step towards the successful governance of groundwater in light of proposed shale gas development in the Karoo. In its absence, effective regulation of the sector will not be effective.

Abstract:
Bacterial communities in groundwater are very important as they maintain a balanced biogeochemical environment. When subjected to stressful environments, for example, due to anthropogenic contamination, bacterial communities and their dynamics change. Studying the responses of the groundwater microbiome in the face of environmental changes can add to our growing knowledge of microbial ecology, which can be utilized for the development of novel bioremediation strategies. High-throughput and simpler techniques that allow the real-time study of different microbiomes and their dynamics are necessary, especially when examining larger data sets. Matrix-assisted laser desorption-ionization (MALDI) time-of-flight mass spectrometry (TOF-MS) is a workhorse for the high-throughput identification of bacteria. In this work, groundwater samples were collected from a rural area in southern Texas, where agricultural activities and unconventional oil and gas development are the most prevalent anthropogenic activities. Bacterial communities were assessed using MALDI-TOF MS, with bacterial diversity and abundance being analyzed with the contexts of numerous organic and inorganic groundwater constituents. Mainly denitrifying and heterotrophic bacteria from the Phylum Proteobacteria were isolated. These microorganisms are able to either transform nitrate into gaseous forms of nitrogen or degrade organic compounds such as hydrocarbons. Overall, the bacterial communities varied significantly with respect to the compositional differences that were observed from the collected groundwater samples. Collectively, these data provide a baseline measurement of bacterial diversity in groundwater located near anthropogenic surface and subsurface activities.

Abstract:
To assess radium (226Ra) as a potential indicator of impact in well waters, we investigated its behavior under natural conditions using a case study approach. 226Ra geochemistry was investigated in 67 private wells of southeastern New Brunswick, Canada, a region targeted for potential shale gas exploitation. Objectives were to i) establish 226Ra baseline in groundwater; ii) characterize 226Ra spatial distribution and temporal variability; iii) characterize 226Ra partitioning between dissolved phase and particulate forms in well waters; and iv) understand the mechanisms controlling 226Ra mobility under natural environmental settings. 226Ra levels were generally low (median = 0.061 pg L−1, or 2.2 mBq L−1), stable over time, and randomly distributed. A principal component analysis revealed that concentrations of 226Ra were controlled by key water geochemistry factors: the highest levels were observed in waters with high hardness, and/or high concentrations of individual alkaline earth elements (i.e. Mg, Ca, Sr, Ba), high concentrations of Mn and Fe, and low pH. As for partitioning, 226Ra was essentially observed in the dissolved phase (106 ± 19%) suggesting that the geochemical conditions of groundwater in the studied regions are prone to limit 226Ra sorption, enhancing its mobility. Overall, this study provided comprehensive knowledge on 226Ra background distribution at local and regional scales. Moreover, it provided a framework to establish 226Ra baselines and determine which geochemical conditions to monitor in well waters in order to use this radionuclide as an indicator of environmental impact caused by anthropogenic activities (e.g. unconventional shale gas exploitation, uranium mining, or nuclear generating power plants).

Abstract:
Interest in dissolved methane (CH4) concentrations in aquifers in England, Scotland and Wales ('Great Britain' or GB) has grown concurrently with interest in the exploitation of unconventional gas sources (UGS). Experience, mainly from North America, has shown the importance of a pre-production baseline against which changes possibly due to UGS extraction can be compared. The British Geological Survey, aided by water utilities, private users and regulators, has compiled a unique dataset for CH4 in groundwaters of GB. This focuses principally on areas where UGS exploration is considered more likely, as indicated by the underlying geology. All the main water supply aquifers (Principal aquifers) were targeted, plus Secondary aquifers where locally important. The average dissolved CH4 concentration across GB in the aquifers sampled was 45 mu g/l. Out of a total of 343 sites, 96% showed dissolved CH4 concentrations <100 mu g/l, 80% <10 mu g/l, and 43% < 1 mu g/l. No site had a CH4 concentration above the US Department of the Interior suggested risk action level of 10,000 mu g/l. While most sites were sampled only once, a subset was monitored quarterly to determine the magnitude of seasonal or other variations. Generally these variations were minor, with 84% of sites showing variations within the range 0.5-37 mu g/l, but some aquifers where the porosity was primarily fracture-related showed larger changes (0.5-264 mu g/l). This may have been due to the nature of sampling at these sites which, unlike the others, did not have installed pumps. Since the regulatory compliance monitoring attending UGS operations will include the measurement of parameters such as dissolved CH4, it is essential that sampling methods are tested to ensure that reliable and comparable datasets can be obtained. (C) 2017 BGS ? NERC, British Geological Survey, a component Institute of NERC. Published by Elsevier B.V.

Abstract:
Exploitation of shale gas by hydraulic fracturing (fracking) is highly controversial and concerns have been raised regarding induced risks from this technique. As part of the EU-funded SHEER Project, a shallow aquifer used for drinking water, overlying a zone of active shale-gas fracking, has been monitored for more than a year. Early results reveal the functioning of the shallow aquifer and hydrochemistry, focusing on the identification of potential impacts from the shale gas operation. This stage is an essential precursor to modeling impact scenarios of contamination and to predict changes in the aquifer.

Abstract:
Some of the most important issues surrounding unconventional oil and gas (UOG) extraction are the possible impacts of this activity on potable groundwater resources and how to minimise and mitigate such impacts. A groundwater vulnerability map for UOG extraction has been developed as part of an interactive vulnerability map for South Africa in an effort to address such concerns and minimize possible future impacts linked to UOG extraction. This article describes the development of the groundwater theme of the interactive vulnerability map and highlights important aspects that were considered during the development of this map, which would also be of concern to other countries that may plan to embark on UOG extraction. The policy implications of the groundwater vulnerability map for managing UOG extraction impacts is also highlighted in this article.

Abstract:
The expanding use of horizontal drilling and hydraulic fracturing technology to produce oil and gas from tight rock formations has increased public concern about potential impacts on the environment, especially on shallow drinking water aquifers. In eastern Kentucky, horizontal drilling and hydraulic fracturing have been used to develop the Berea Sandstone and the Rogersville Shale. To assess baseline groundwater chemistry and evaluate methane detected in groundwater overlying the Berea and Rogersville plays, we sampled 51 water wells and analyzed the samples for concentrations of major cations and anions, metals, dissolved methane, and other light hydrocarbon gases. In addition, the stable carbon and hydrogen isotopic composition of methane (δ13C-CH4 and δ2H-CH4) was analyzed for samples with methane concentration exceeding 1 mg/L. Our study indicates that methane is a relatively common constituent in shallow groundwater in eastern Kentucky, where methane was detected in 78% of the sampled wells (40 of 51 wells) with 51% of wells (26 of 51 wells) exhibiting methane concentrations above 1 mg/L. The δ13C-CH4 and δ2H-CH4 ranged from −84.0‰ to −58.3‰ and from −246.5‰ to −146.0‰, respectively. Isotopic analysis indicated that dissolved methane was primarily microbial in origin formed through CO2 reduction pathway. Results from this study provide a first assessment of methane in the shallow aquifers in the Berea and Rogersville play areas and can be used as a reference to evaluate potential impacts of future horizontal drilling and hydraulic fracturing activities on groundwater quality in the region.

Abstract:
The proposed drilling for shale gas resources in the Eastern Cape Karoo region of South Africa has triggered much debate over the potential effects of hydraulic fracturing on water resources. Herein we present results on some limnological aspects of surface waterbodies in this water-scarce region before shale gas exploration. Thirty-three waterbodies (nine dams, 13 depression wetlands and 11 rivers) were sampled in November 2014 and April 2015. Principal component analysis revealed that depression wetlands and rivers had distinct physicochemical signatures, whereas dams were highly variable in their physicochemical attributes and exhibited characteristics similar to those of either rivers or depression wetlands. Non-parametric multivariate regressions and permutational multivariate analysis of variance (MANOVA) indicated that landscape variables such as underlying geology, altitude and land use poorly explained the physicochemical characteristics of the sampled waterbodies. Waterbody type was the only factor that explained a significant amount of the variation in physicochemistry during both sampling events. These data need to be supplemented by water quality information from additional sites and over longer time periods, as well as supporting data relating to other aspects, such as algae and invertebrates, before they can be used as a baseline for the long-term monitoring of freshwater ecosystems in the region.

Abstract:
Hydraulic fracturing for shale gas exploration is not free from environmental risk. The environmental concerns related to hydraulic fracturing has been greatly attracted. One of most important environmental concerns is regional water quality which may be contaminated by produced waters through induced and natural fractures and wastewater discharge. At present, the baseline water quality must be firstly obtained to identify potential pollution of the activity and monitoring indicators should be studied for better environmental monitoring. We sampled shallow groundwater, produced waters, shale rock and soil in the Jiaoshiba shale-gas region, SW China and measurements have included water chemistry and isotopes. Preliminary results show that the present shallow karst groundwater quality is pretty good with the total dissolved solids (TDS) ranging from 129 to 343mg/L and with water chemistry type of HCO3-Ca, However, some groundwaters have been polluted by agricultural activities. Produced waters have relatively high salinity with TDS ranging from 2 to 14g/L. Laboratory experiment of fracturing liquid and shale rock interaction at simulated reservoir conditions shows that TDS in the flowback fluid increases 10 times and Ca2+, Na+, Cl− and SO42− make dominant contributions. The main geochemical reactions are inferred to be pyrite oxidation and the dissolution of calcite, dolomite and plagioclase, resulting in increases of major ions in the flowback fluid. The inorganic geochemical monitoring indicators for shale gas exploration of the Silurian Longmaxi formation has been determined.

Abstract:
Water-quality and isotopic data were collected in central Nevada, USA in an exploration hydraulic fracturing area with no previous oil or gas production. The target shales of the Elko Formation are unique fresh-water hydrocarbon reservoirs with relatively dilute source water (8.5 g/L total dissolved solids [TDS]). Additionally, the Elko Formation is underlain by a fresh-water carbonate aquifer (0.2-0.3 g/L TDS) that outcrops downgradient of the exploration area. The water quality and isotopic data were used to evaluate pre-hydraulic fracturing conditions in this undeveloped area. The same data were also collected for groundwater and surface-water sites about two months and one year after exploration hydraulic fracturing. No systematic differences in water chemistry were observed between pre- and post-hydraulic fracturing samples. Based on water chemistry of shallow groundwater, surface water, and from the production zone, the most useful constituents identified for monitoring for potential future incursion of reservoir-associated fluids into the near-surface environment are TDS (or electrical conductivity), chloride, propane, methanol, ethanol, and 2-butoxyethanol. Groundwater flow and transport models were developed to evaluate the potential movement of hydrocarbons and hydraulic fracturing fluids from the targeted zones, which are about 1800 to 3600 m beneath the land surface, to shallow groundwater (<300 m below land surface). Model simulations indicate that hydraulic fracturing fluid remains contained within the target shales for at least 1,000 years for most development scenarios.

Abstract:
The baseline chemistry of groundwater from two aquifers in the Vale of Pickering, North Yorkshire, has been investigated ahead of a proposal to explore for shale gas, planning permission for which has recently been granted. Groundwater in a shallow aquifer including Quaternary and/or Jurassic Kimmeridge Clay deposits shows compositions distinct from a Corallian (Jurassic) Limestone aquifer, reflecting different lithologies and hydrogeological conditions. Corallian groundwaters along the margins of the vale are controlled by reaction with carbonate, with redox conditions varying according to degree of aquifer confinement. Superficial aquifer groundwaters are confined and strongly reducing, with some observed high concentrations of dissolved CH4 (up to 37 mg/L; Feb 2016 data). This appears to be of mixed biogenic-thermogenic origin but further work is needed to determine whether the source includes a deeper hydrocarbon reservoir contributing via fractures, or a shallower source in the Quaternary or Kimmeridge sediments. The data show a shallow aquifer with a high-CH4 baseline which pre-dates any shale-gas activity.

Abstract:
The geochemical characteristics of shallow groundwater are essential for environmental impact studies in the shale gas production area. Jiaoshiba in the Sichuan basin is the first commercial-scale shale gas production area in China. This paper studied the geochemical and isotopic characteristics of the shallow groundwater of the area for future environmental concerns. Results show that the average pH of the shallow groundwater is 7.5 and the total dissolved solids (TDS) vary from 150 mg/L to 350 mg/L. The main water types are HCO3-Ca and HCO3-Ca·Mg due to the carbonates dissolution equilibrium in karst aquifers. The concentrations of major ions and typical toxic elements including Mn, Cr, Cu, Zn, Ba, and Pb are below the drinking water standard of China and are safe for use as drinking water. The high nitrate content is inferred to be caused by agricultural pollution. The shallow groundwater is recharged by local precipitation and flows in the vertical circulation zone. Evidences from low TDS, water isotopes, and high 3H and 14C indicate that the circulation rate of shallow groundwater is rapid, and the lateral groundwater has strong renewability. Once groundwater pollution from deep shale gas production occurs, it will be recovered soon by enough precipitation.

Abstract:
Shale gas exploration in the St. Lawrence Platform of southern Quebec (eastern Canada) focussed on the Upper Ordovician Utica Shale from 2006 to 2010 during which 28 wells were drilled, 18 of which were fracked. The St. Lawrence Platform is thus considered as a pristine geological domain where potential environmental effects of fracking can be evaluated relative to the natural baseline conditions of the shallow aquifers. In the Saint-Édouard area southwest of Quebec City, it has been shown that groundwater carries variable and locally high levels of naturally occurring dissolved hydrocarbons in which thermogenic ethane and propane can be found. Fifteen shallow (30–147 m) wells were drilled into bedrock and sampled (cores and cuttings) with the purpose of characterizing the shallow bedrock in a shale gas pre-development context. The shallow bedrock geology is made of three Upper Ordovician clastic formations. The Lotbinière and Les Fonds formations are time- and facies-correlative with the Utica Shale present at a depth of 1.5 to 2 km in this area. They are dominated by calcareous black shales with minor siltstone and micrite beds. The Nicolet Formation is the youngest unit of the area and consists of gray to dark gray shales with locally abundant thick siltstone and fine-grained sandstone beds. The organic matter in the Lotbinière and Les Fonds formations is represented by solid bitumen with subordinate liptinite algae, graptolites and chitinozoans representing normal marine Type II kerogen. Both formations are at the post-peak hydrocarbon generation as indicated by the equivalent random vitrinite reflectance of 0.94 to 1.04%. Rock Eval data support the Type II nature of the kerogen and the late oil window maturation level. Hydrocarbon extracts from the three formations have yielded high to low concentrations of C1 to C6. For all units, an upward decrease in total volatiles (C1 + C2 + C3) together with an increase in the gas dryness ratio (C1/C2 + C3) is recorded, the transitions occurring at depths shallower than 50 m where the shales are more fractured. The upward increase in the gas dryness ratio results from the more significant reduction of ethane and propane concentrations compared to that of methane. Consistent with the dryness ratio trend, the δ13CVPDB values of methane change from thermogenic values (≈− 50‰) for deeper samples, to more biogenic (negative) values (<− 60‰) at shallow depths. A similar δ2HVSMOW trend of more negative values at shallower depths is noted. The δ13CVPDB and δ2HVSMOW values of rock-hosted methane indicate that samples at shallow depth recorded a microbial influence. It is proposed that diffusion and some microbial degradation of hydrocarbons are responsible for the decrease of rock volatiles and the in situ generation of biogenic methane in the shales at shallow depths to mix with the in situ thermogenic methane. The Utica Shale is a very good source rock with high generation potential. However, thermogenic volatiles can also originate from shallower units with much shorter migration pathways. The mixed thermogenic and biogenic methane in the groundwater results from fracture-enhanced diffusion and biodegradation of volatiles at shallow depths.

Abstract:

Abstract:
Unconventional natural gas production in the Marcellus and Utica formations of the Northeastern United States raises concerns about potential impacts to shallow groundwater. We examined and interpreted 13,040 analyses from pre-drilling groundwater samples from domestic water wells in northeastern (NE) Pennsylvania and 8004 samples from water wells in the “Western Area” which includes southwest Pennsylvania, eastern Ohio, and north-central West Virginia. These samples were acquired on behalf of Chesapeake Energy Corporation as part of its local pre-drilling water supply monitoring program. We evaluated concentrations of major ions and metals relative to federal drinking-water-quality standards upon which regulatory decisions are often based. Chesapeake’s dataset, the most comprehensive for these areas, shows that exceedance of at least one water-quality standard occurs in 63% of water well samples in NE Pennsylvania and 87% in the Western Area. In NE Pennsylvania, 10% of the samples exceeded one or more of the United States Environmental Protection Agency’s (USEPA) primary maximum contaminant levels (MCLs) for drinking-water supplies, 46.1% of the samples exceeded one or more of USEPA secondary maximum contaminant levels (SMCLs), and another 7% exceeded one or more of USEPA health advisory or regional screening levels for tap water. In the Western Area 8% of samples exceeded one or more MCLs, 65% exceeded one or more SMCLs, and 15% exceeded one or more health advisory or regional screening levels for tap water. Chesapeake’s dataset, orders of magnitude larger than any in previously published literature, shows that water-quality exceedances relate to factors such: as where the sample occurs within the groundwater flow system, the natural groundwater chemical type (hydrochemical facies), the geologic unit producing the water, and/or the topographic position (valley versus upland). Our comparison of these results to historical groundwater data from NE Pennsylvania, which pre-dates most unconventional shale gas development, shows that the recent pre-drilling geochemical data is similar to historical data. We see no broad changes in variability of chemical quality in this large dataset to suggest any unusual salinization caused by possible release of produced waters from oil and gas operations, even after thousands of gas wells have been drilled among tens of thousands of domestic wells within the two areas studied. Our evaluation also agrees with early researchers such as Piper (1933) and Lohman (1939, 1937) who found that the saline waters in both areas underlie fresher groundwater. The saline water is naturally-occurring connate brine or salt water which has not been flushed by circulating meteoric water; rather than vertical migration of salt water from deep strata such as the Marcellus shale as suggested by Warner et al. (2012). Elevated metals concentrations, particularly iron and manganese, partly relate to sample turbidity; dissolved metals would provide a more accurate measurement of metals in shallow groundwater than does the total metals analysis typically required by regulations.

Abstract:
Flowback fluids associated with hydraulic fracturing shale gas extraction are a potential source of contamination for shallow aquifers. In the Marcellus Shale region of northeastern Pennsylvania, certified water tests have been used to establish baseline water chemistry of private drinking water wells. This study investigates whether a single, certified multiparameter water test is sufficient for establishing baseline water chemistry from which possible future contamination by flowback waters could be reliably recognized. We analyzed the water chemistry (major and minor inorganic elements and stable isotopic composition) of multiple samples collected from lake, spring, and well water from 35 houses around Fiddle Lake, Susquehanna County, PA that were collected over approximately a two-year period. Statistical models estimated variance of results within and between households and tested for significant differences between means of our repeated measurements and prior certified water tests. Overall, groundwater chemistry varies more spatially due to heterogeneity of minerals within the bedrock aquifer and due to varying inputs of road salt runoff from paved roads than it does temporally at a single location. For wells located within road salt-runoff zones, Na+ and Cl− concentrations, although elevated, are generally consistent through repeated measurements. High acid neutralizing capacity (ANC) and base cation concentrations in well water sourced from mineral weathering reactions, and a uniform stable isotopic composition for well water, suggests long flowpaths for groundwater that dampen seasonal variability of most elements. Exceptions occur for two wells within road salt runoff zones that show the greatest range of concentrations for Na+ and Cl−, suggesting that these wells have a faster pathway to surficial recharge. Additionally, sampling protocols can induce variability for Fe, Mn, and Pb, making other elements identified in flowback fluids (Ba, Br, Ca, Cl, Mg, Na, Sr) more dependable indicators of contamination. Although there is general concordance between our repeated measurements and the certified test results, characterizing baseline chemistry is strengthened when results from multiple households are combined to establish regional upper baseline limits that will have a low probability of being exceeded by future samples unless conditions have changed.

Abstract:
Public and regulatory agencies are concerned over the potential for drinking water contamination related to high-volume hydraulic fracturing (hydrofracking) of the Marcellus shale in Pennsylvania and in New York State (NYS), where exploitation of Marcellus gas has not yet begun. Unique natural tracers are helpful for distinguishing the influence of formation water and/or flow-back water. Here we use halogen concentrations, particularly bromine and iodine, to characterize natural variability of baseline water chemistry in the southern tier of NYS. Majority of streams and drinking water wells have Br and I concentrations below 1 and 0.1 μM, respectively, a range typical for relatively pristine surface water and shallow groundwater. Wells that have higher Br and I concentrations are likely affected by formation waters. Br/I ratios indicate two different sources of formation waters in these wells, possibly controlled by geologic settings. Our results suggest that iodine, combined with other halogens, may be a novel and sensitive tool for fingerprinting trace levels of formation water signal in drinking water sources.

Abstract:
Unconventional natural gas development via horizontal drilling and hydraulic fracturing has greatly increased the supply of natural gas in the United States. However, the practice presents concerns about the possibility for impacts on shallow groundwater aquifers. The Deep River Triassic Basin in central North Carolina is likely to contain natural gas that could be extracted via hydraulic fracturing in the future. Unlike other states where hydraulic fracturing has been employed, North Carolina has no history of commercial oil and gas extraction. In this study, we measured water chemistry, dissolved gases, and volatile organic compounds in 51 private drinking water well samples over the Deep River Triassic Basin. Our data document the background water quality of shallow aquifers in the Deep River Basin, which could provide an important baseline dataset if hydraulic fracturing occurs here in the future. We found only two of the 51 water wells sampled had dissolved CH4 concentrations >0.1 mg/L, and no well had a methane concentration >0.5 mg/L. The δ 13C–CH4 of the two highest CH4 concentration water wells (−69.5‰ and −61‰) suggest a biogenic CH4 source and are distinct from the δ 13C–CH4 of two test gas wells drilled in the area (−54.41‰ and −45.11‰). Unlike other basins overlying shale gas formations in the US, we find no evidence for CH4 migration into shallow groundwater in the Triassic basin. In addition, we found only seven VOCs in five water samples, with all levels below the US EPA’s maximum contaminant levels. Ion and trace metal concentrations in most samples were also below US EPA primary drinking water standards, with the exception of two samples that exceed the standards for As. We modeled the depth of the upper surface of the Cumnock Shale formation in the Deep River Basin using a kriging algorithm and found that its depth below the surface is shallow (0–∼1500 m) relative to other shale formations that have been drilled commercially in the US, including the Marcellus in Pennsylvania and the Fayetteville in Arkansas. The relatively shallow shale, combined with the presence of multiple faults and diabase intrusions that characterize the geology of the area, may make the Deep River Triassic Basin more vulnerable to deep fluid connectivity to shallow aquifers.

Abstract:
Hydraulic fracturing is becoming an important technique worldwide to recover hydrocarbons from unconventional sources such as shale gas. In Quebec (Canada), the Utica Shale has been identified as having unconventional gas production potential. However, there has been a moratorium on shale gas exploration since 2010. The work reported here was aimed at defining baseline concentrations of methane in shallow aquifers of the St. Lawrence Lowlands and its sources using δ13C methane signatures. Since this study was performed prior to large-scale fracturing activities, it provides background data prior to the eventual exploitation of shale gas through hydraulic fracturing. Groundwater was sampled from private (n=81), municipal (n=34) and observation (n=15) wells between August 2012 and May 2013. Methane was detected in 80% of the wells with an average concentration of 3.8 ± 8.8 mg/L, and a range of < 0.0006 to 45.9 mg/L. Methane concentrations were linked to groundwater chemistry and distance to the major faults in the studied area. The methane δ13C signature of 19 samples was > -50‰, indicating a potential thermogenic source. Localized areas of high methane concentrations from predominantly biogenic sources were found throughout the study area. In several samples, mixing, migration and oxidation processes likely affected the chemical and isotopic composition of the gases, making it difficult to pinpoint their origin. Energy companies should respect a safe distance from major natural faults in the bedrock when planning the localization of hydraulic fracturation activities to minimize the risk of contaminating the surrounding groundwater since natural faults are likely to be a preferential migration pathway for methane.

Abstract:
High-volume hydraulic fracturing (HVHF) gas-drilling operations in the Marcellus Play have raised environmental concerns, including the risk of groundwater contamination. Fingerprinting water impacted by gas-drilling operations is not trivial given other potential sources of contamination. We present a multivariate statistical modeling framework for developing a quantitative, geochemical fingerprinting tool to distinguish sources of high salinity in shallow groundwater. The model was developed using new geochemical data for 204 wells in New York State (NYS), which has a HVHF moratorium and published data for additional wells in NYS and several salinity sources (Appalachian Basin brines, road salt, septic effluent, and animal waste). The model incorporates a stochastic simulation to predict the geochemistry of high salinity (>20 mg/L Cl) groundwater impacted by different salinity sources and then employs linear discriminant analysis to classify samples from different populations. Model results indicate Appalachian Basin brines are the primary source of salinity in 35% of sampled NYS groundwater wells with >20 mg/L Cl. The model provides an effective means for differentiating groundwater impacted by basin brines versus other contaminants. Using this framework, similar discriminatory tools can be derived for other regions from background water quality data.

Abstract:
As the pace of drilling activity in the Marcellus Formation in the northern Appalachian Basin has increased, so has the number of alleged incidents of stray natural gas migration to shallow aquifer systems. For this study, more than 2300 gas and water samples were analyzed for molecular composition and stable isotope compositions of methane and ethane. The samples are from Neogene- to Middle Devonian-age strata in a five-county study area in northeastern Pennsylvania. Samples were collected from the vertical and lateral sections of 234 gas wells during mud gas logging (MGL) programs and 67 private groundwater-supply wells during baseline groundwater-quality testing programs. Evaluation of this geochemical database reveals that microbial, mixed microbial and thermogenic, and thermogenic gases of different thermal maturities occur in some shallow aquifer systems and throughout the stratigraphy above the Marcellus Formation. The gas occurrences predate Marcellus Formation drilling activity. Isotope data reveal that thermogenic gases are predominant in the regional Neogene and Upper Devonian rocks that comprise the potable aquifer system in the upper 305 m (1000 ft) (average delta13C1 = minus43.53permil; average delta13C2 = minus40.95permil; average deltaDC1 = minus232.50permil) and typically are distinct from gases in the Middle Devonian Marcellus Formation (average delta13C1 = minus32.37permil; average delta13C2 = minus38.48permil; average deltaDC1 = minus162.34permil ). Additionally, isotope geochemistry at the site-specific level reveals a complex thermal and migration history with gas mixtures and partial isotope reversals (delta13C1 gt delta13C2) in the units overlying the Marcellus Formation. Identifying a source for stray natural gas requires the synthesis of multiple data types at the site-specific level. Molecular and isotope geochemistry provide evidence of gas origin and secondary processes that may have affected the gases during migration. Such data provide focus for investigations where the potential sources for stray gas include multiple, naturally occurring, and anthropogenic gases.

Abstract:
Reliably identifying the effects of energy development on groundwater quality can be difficult because baseline assessments of water quality completed before the onset of energy development are rare and because interactions between hydrocarbon reservoirs and aquifers can be complex, involving both natural and human processes. Groundwater age and mixing data can strengthen interpretations of monitoring data from those areas by providing better understanding of the groundwater flow systems. Chemical, isotopic, and age tracers were used to characterize groundwater ages and mixing with deeper saline water in three areas of the Piceance Basin natural gas province. The data revealed a complex array of groundwater ages (<10 to >50,000 years) and mixing patterns in the basin that helped explain concentrations and sources of methane in groundwater. Age and mixing data also can strengthen the design of monitoring programs by providing information on time scales at which water quality changes in aquifers might be expected to occur. This information could be used to establish maximum allowable distances of monitoring wells from energy development activity and the appropriate duration of monitoring.