The Qujiang River Basin is a significant water system located in Zhejiang Province, China, that serves as a primary water source for Quzhou City. For this research, we collected and examined water samples from the Qujiang River Basin. In this study, we collected and analyzed water samples from the Qujiang River Basin and employed a combination of methods, including water balance analysis; Piper trilinear diagram; Gibbs diagram; and environmental tracer techniques, such as hydrochemical and isotopic analysis. These techniques helped us to analyze the spatial distribution patterns and evolutionary trends of surface water and groundwater hydrochemistry, along with the stable isotopes of hydrogen and oxygen, as well as to determine the sources of surface water and groundwater by calculating the conversion ratio between surface water and groundwater. (1) The findings of our study indicate that the primary hydrochemical types in the study area are Ca-HCO₃ and Ca-HCO₃·Cl, with the ion composition of water primarily influenced by rock weathering and precipitation. (2) Similar spatial variations in hydrochemical indicators were observed between surface water and groundwater in the study area, with frequent transitions between the two. (3) The hydrogen and oxygen isotope content increases downstream, signifying that both groundwater and surface water in the study area are replenished by atmospheric precipitation, as supported by the relationship between hydrogen and oxygen isotopes and the meteoric water line. (4) We determined that groundwater predominantly replenishes surface water in the upstream area. The average contribution rate of groundwater to surface water is 19.67%, with an annual average recharge volume of 1.23 × 10⁶ m³. Midstream and downstream, surface water mainly recharges groundwater, with an average contribution rate of 22.77% and an annual average recharge volume of 1.59 × 10⁶ m³.

Benzene and toluene contamination of groundwater can pose a serious threat to human health. Although extraction-treatment and other ex-situ remediation technologies can be used to rapidly reduce the concentration of pollutants at the initial stage of remediation, the inevitable tailing and rebound effects make it a research hotspot to explore more efficient in-situ remediation technologies. Groundwater circulating well is a kind of in-situ remediation technology for groundwater that is more and more widely used. This paper improves the removal efficiency of benzene and toluene by adding zero-valent iron reaction materials to the well structure, through the comparative experiment of homogeneous and heterogeneous aquifers, it is concluded that the remediation efficiency of pollutants in homogeneous aquifers is higher than that in heterogeneous aquifers. This paper provides a theoretical basis for the engineering practice of zero-valent iron reactive groundwater circulation well.

In order to improve the remediation efficiency of the groundwater circulation well (GCW) on toluene-contaminated soil, we used a combination of GCW and Fenton reagent for remediation. Taking a toluene-contaminated site in Suzhou City, Jiangsu Province, China, as an example, Fenton reagent with a molar ratio of H2O2/contaminant = 10:1 and H2O2/Fe2+ = 2:1 was added to GCW at an aeration rate of 0.005 m3/s. After 216 h of remediation, the toluene concentrations at the site were reduced to the remediation target values. In this study, the Fenton reagent was rapidly delivered to the influence radius of GCW, which reduced the time required for remediation and provided a new model for the application of GCW.

A static batch test was used to determine the optimal ratio of Fenton’s reagent for removing benzene and toluene from contaminated subsurface at a site, followed by a two-dimensional simulation tank experiment, where benzene and toluene were distributed throughout the tank, and then in the groundwater circulation wells. The Fenton’s reagent of 0.05 L of 3% H₂O₂ and 6.12 g of FeSO₄·7H₂O was added in the ratio of 0.05 L of 3% H₂O₂ and 6.12 g of FeSO₄·7H₂O, and the reactive circulation wells were initiated at an aeration rate of 15 L/min.The results show:The groundwater circulation close to the circulation wells is highly disturbed, the mass transfer between the gas and water phases is strong, benzene and toluene are preferentially removed, and a remediation area centered on the circulation wells is gradually formed; after 12 h of cumulative aeration, contaminants within a 50 cm radius from the circulation well were below the detection limit. Residual benzene and toluene were concentrated in the area on both sides of the simulation tank, away from the circulation well. The contaminant removal efficiency within the 50-cm radius of influence of the circulation wells was high, and the enhanced remediation of benzene- and toluene-contaminated groundwater by reactive circulation wells using Fenton’s reagent as the remediation agent was more effective.

This study is based on 63 sets of groundwater samples from the Qian’an Basin to calculate the environmental background values of groundwater, focusing on total dissolved solids (TDS), total hardness, and NO3 ⁻. Mathematical statistical methods were employed to identify and remove outliers. Ion correlation analysis and ratio plots were also used to investigate the chemical composition, formation mechanisms, and background values of the groundwater while analyzing the spatial distribution characteristics of these background values. The research results showed that the dominant cations in the groundwater were Ca²⁺, followed by Mg²⁺, while the main anions were HCO₃-and SO₄²⁻. The hydrochemical types were classified as HCO₃-Ca·Mg and HCO₃SO₄-Ca·Mg, indicating that the dissolution of carbonate rocks played a dominant role in controlling the groundwater chemistry. The background value thresholds of total dissolved solids (TDS), total hardness, and NO3- were calculated to be 162-729.95 mg/L, 122.05-508.55 mg/L, and 0.002-32.62 mg/L. The background values of TDS and total hardness showed no significant spatial variation overall. In contrast, the background values for NO3- were higher and exhibited clear spatial variability, indicating that human activities influenced the groundwater. The study identified the hydrochemical and environmental background characteristics of shallow groundwater in the Qian’an Basin, deepening the understanding of the groundwater quality formation and evolution mechanisms in the region compared to previous studies and providing important support for the sustainable development of regional groundwater.