Methane and Benzene in Drinking-Water Wells Overlying the Eagle Ford, Fayetteville, and Haynesville Shale Hydrocarbon Production Areas

Abstract

Water wells (n = 116) overlying the Eagle Ford, Fayetteville, and Haynesville Shale hydrocarbon production areas were sampled for chemical, isotopic, and groundwater-age tracers to investigate the occurrence and sources of selected hydrocarbons in groundwater. Methane isotopes and hydrocarbon gas compositions indicate most of the methane in the wells was biogenic and produced by the CO reduction pathway, not from thermogenic shale gas. Two samples contained methane from the fermentation pathway that could be associated with hydrocarbon degradation based on their co-occurrence with hydrocarbons such as ethylbenzene and butane. Benzene was detected at low concentrations (<0.15 μg/L), but relatively high frequencies (2.4-13.3% of samples), in the study areas. Eight of nine samples containing benzene had groundwater ages >2500 years, indicating the benzene was from subsurface sources such as natural hydrocarbon migration or leaking hydrocarbon wells. One sample contained benzene that could be from a surface release associated with hydrocarbon production activities based on its age (10 ± 2.4 years) and proximity to hydrocarbon wells. Groundwater travel times inferred from the age-data indicate decades or longer may be needed to fully assess the effects of potential subsurface and surface releases of hydrocarbons on the wells.

Origin of Methane and Sources of High Concentrations in Los Angeles Groundwater

“…Comparison of the δ 2 H of methane and δ 13 C of methane has been used to represent distinct methane formation pathways and processes in groundwater, including CO 2 reduction and fermentation pathways and mixing and oxidation processes (Jenden & Kaplan, ; Schoell, , ; Whiticar et al, ). Nearly all of the LAB groundwater samples plot within the region indicating CO 2 reduction as the primary formation pathway for methane (Figure ), similar to results of other studies near oil and gas fields (Humez, Mayer, Ing, et al, ; McMahon et al, ). This indicates that methane in the LAB is not originating from the fermentation of organic material in recent sediments but rather methane formation by CO 2 reduction.…”

Methane emissions from groundwater pumping in the USA

“…2 High methane concentrations, those in excess of values expected from water equilibrating with the atmospheric (~5 × 10 −5 mg/L at 1 atm and 10°C), have been identified in many aquifers in hydrocarbon-producing regions across the USA and the world e.g. [24][25][26][27] The average methane concentration of 1701 Pennsylvania groundwater samples overlying the Marcellus is 0.7 mg/L 24 (less than detection-level values were assigned a value of zero, so this is a lower limit), the average concentration in aquifers overlying the Bakken shale is 2.8 mg/L, 28 Eagle Ford shale is 1.3 mg/L, Haynesville-Bossier shale is 2.6 mg/L, Fayetteville shale is 1.9 mg/L, 29 and in the entire UK is 0.045 mg/L. 30 The annual emissions of methane from the Pennsylvania groundwater overlying the Marcellus is 3.0 × 10 −6 Tg/a, calculated using the average methane concentration (0.7 mg/L), and average annual withdrawal of 4.27 × 10 9 L/a in Susquehanna County https://water.…”

“…However, if studies do not collect enough samples to be representative, or their selection is not randomized, then the uncertainty could be up to 500% based on averaging sample concentrations in an aquifer. For the USGS Principal aquifer data, 29 a randomization process was applied to available public-supply wells in the aquifers, and the uncertainty on the average methane concentrations in the public-supply aquifers was reduced to~25%. The overall uncertainty on emissions estimates, based largely on possible temporal variability of methane is~80%.…”

Attitudes, Perceptions, and Geospatial Analysis of Water Quality and Individual Health Status in a High-Fracking Region

“…Samples collected for organic ion analysis were preserved with chromatography grade chloroform to prevent microbial degradation. Samples collected for the analysis of volatile organic and semi-volatile organic compounds, total organic carbon (TOC), and total nitrogen were untreated [10,11,27,29]. Select samples for dissolved hydrocarbons gases (methane, ethane, and propane) were collected using Isoflask containers as per Molofsky et al [30].…”

“…The oil and gas industry exercises a number of precautionary measures to ensure that groundwater quality is not impacted by nature. Multiple reconnaissance efforts have recently evaluated groundwater quality throughout the Western Gulf Basin revealing elevated levels of biogenic and thermogenic natural gas [25,26]; benzene, toluene, ethylbenzene and xylene (BTEX) compounds [27]; and total organic carbon, and various organic solvents [24] in private and public water supply wells. However, these data are the first to evaluate the prevalence of organic and inorganic groundwater constituents within the context of community members' perceptions, providing unique insight into the relationship between residents and the UD industry operations.…”