Baseline Groundwater Quality before Shale Gas Development in Xishui, Southwest China: Analyses of Hydrochemistry and Multiple Environmental Isotopes (2H, 18O, 13C, 87Sr/86Sr, 11B, and Noble Gas Isotopes)

Abstract

The baseline quality of pre-drilling shallow groundwater is essential for the evaluation of potential environmental impacts of shale gas development. The Xishui region in the northern Guizhou Province of Southwest China has the potential for shale gas development but there is a lack of commercial production. As for the future environmental concerns in this undeveloped area, this study presented the hydrochemical and isotopic characteristics of shallow groundwater and its dissolved gas before shale gas development and determined the sensitive monitoring indicators. Results showed that shallow groundwater with an average pH of 7.73 had low total dissolved solids (TDS) ranging between 102 and 397 mg/L, with the main water chemistry types of HCO3-Ca and HCO3-Ca·Mg. The quality of most groundwater samples satisfied the drinking water standards of China. The mass concentration of dissolved methane in groundwater was below the detection limit (<0.01 mg/L), suggesting the low baseline value of hydrocarbon. The shallow groundwater was mainly recharged by local precipitation based on water isotopes. Water chemistry was modified by the dominant dissolution of carbonate rocks and partial dissolution of clastic rocks, as indicated by δ13C-DIC, 87Sr/86Sr, and δ11B. Evidence from carbon isotopes of dissolved methane and CO2 (δ13C-CH4 and δ13C-CO2) and noble gas isotopes (3He/4He and 4He/20Ne) demonstrated that the biogenic methane mainly originated from acetate fermentation and the dissolved noble gas was a result of the dissolution of air. Based on the geochemical and isotopic differences between shallow groundwater and flowback and produced water (including shale gas) from the Weiyuan and Fuling shale gas fields as well as shale gas from Xishui, this study has provided the sensitive monitoring indicators and methods for identifying potential pollution of regional shallow groundwater related to shale gas development in the future.

Multidisciplinary Research of Thermal Springs Area in Topusko (Croatia)

“…The major anion and cation composition of thermal water is graphically presented in the Piper diagram (Figure 3) [51]. All samples show Ca-HCO 3 hydrochemical facies [79], with a dominance of Ca 2+ cation followed by Mg 2+ , which is a characteristic of groundwater in carbonate aquifers [80][81][82]. The ion composition is almost constant over time, which indicates a large and stable hydrothermal system.…”

“…Instead, the samples showed an equivalent ratio of 2.1, suggesting that the excess of Ca 2+ comes from carbonate dissolution, and the origin of the sulphate anion remains undetermined. The dissolution resulting from silicate weathering may have contributed to the groundwater chemistry, providing the additional source of Ca 2+ and Mg 2+ balanced by sulphate anions [80,86,87]. Figures 3 and 4 point to (i) carbonate dissolution as the primary process driving the solute content in the thermal waters of Topusko, (ii) the interaction of the waters with Mesozoic carbonates that represent the main aquifer of THS, and (iii) the presence of limestone and dolomite rock in the system.…”

Sensitivity Assessment of Boron Isotope as Indicator of Contaminated Groundwater for Hydraulic Fracturing Flowback Fluids Produced from the Dameigou Shale of the Northern Qaidam Basin

“…Warner et al [23] stated that δ 11 B values for HFFF from the Marcellus and Fayetteville Formations (marine shales) fall within a narrow range (25 to 31‰) with high B/Cl ratios (>0.1 × 10 −1 ), and were distinct from major river systems (δ 11 B = 3 to 14‰, B/Cl = 0.2 × 10 −4 -0.1 × 10 −1 ) and shallow groundwater (δ 11 B = 34 to 54‰, B/Cl < 0.3 × 10 −4 ) in shale gas fields. Ni et al [24] reported that the HFFF from the Permian Longmaxi Formation in the Sichuan Basin (δ 11 B = 22.5 to 31.6‰) had similar δ 11 B values to those of HFFF from the Marcellus Formation and were different from shallow groundwater (δ 11 B = −7.8 to 6.4‰) [25]. Additionally, Cui et al [16] proposed that extensive dissolution of feldspars occurring during hydraulic fracturing can impart a unique δ 11 B fingerprint from continental shale (−30.1 to 10.2‰) to HFFF.…”