# Groundwater Mixing Process Identification in Deep Mines Based on Hydrogeochemical Property Analysis
## 4 Results and Discussion  
Specific chemical properties of each groundwater sample are shown in Table 2. All the component concentrations of each groundwater sample in Carboniferous Taiyuan limestone karst-fissure aquifer are quite different (K\({}^{+}\) + Na\({}^{+}\) of 202.68-1030.31 mg/L, Ca\({}^{2+}\) of 58.9-144.53 mg/L, Mg\({}^{2+}\) of 24.62-83.50 mg/L, HCO\({}_{3}\)\({}^{-}\) of 268.24-573.03 mg/L, SO\({}_{4}\)\({}^{2-}\) of 206.16-1903.19 mg/L, Cl\({}^{-}\) of 97.97-268.16 mg/L, alkalinity of 4.396-9.391 mg/L, pH of 7.8-8.4, total dissolved solid (TDS) of 1206-3693 mg/L, hardness of 14.58-39.48 \({}^{\circ}\)H), which means that the groundwater in the Carboniferous Taiyuan limestone karst-fissure aquifers have encountered external disturbance. Meanwhile, the component concentrations of the groundwater sample in Ordovician limestone karst-fissure aquifer (K\({}^{+}\) + Na\({}^{+}\) of 193.3 mg/L, Ca\({}^{2+}\) of 10.63 mg/L, Mg\({}^{2+}\) of 27.01 mg/L, HCO\({}_{3}\)\({}^{-}\) of 314.81 mg/L, SO\({}_{4}\)\({}^{2-}\) of 83.19 mg/L, Cl\({}^{-}\) of 82.37 mg/L, alkalinity of 353.81 mg/L, pH of 9.4, TDS of 1180 mg/L, hardness of 137.8 \({}^{\circ}\)H) are different from that in Carboniferous Taiyuan limestone karst-fissure aquifers. The chemical properties of groundwater samples indicate the hydraulic connection occurred between the two aquifer systems through one or more karst collapse columns in the study area. According to the concentrations of cations and anions, the piper diagram of all groundwater samples was plotted in Figure 5 and the hydrochemical types [36; 37] of all groundwater samples were analyzed in Table 3. In the piper diagram, most groundwater samples (except of C12 and O1) were located in the seventh district of the diamond field, and the hydrochemical type of groundwater [38; 39] is SO\({}_{4}\)-K + Na. This kind of groundwater is typically connate water which is highly mineralized, the primarily conventional groundwater chemical ions [40] are SO\({}_{4}\)\({}^{2-}\) and K\({}^{+}\) + Na\({}^{+}\) with a content percentage of greater than 50%, and the TDS value is usually high. Groundwater samples of C12 and O1 were located in the ninth district of the diamond field, and the hydrochemical type of groundwater is HCO\({}_{3}\)-K + Na. This kind of groundwater is typically geothermal water in the deep stratum, and there were no primary cations and anions with a percentage content greater than 50%. \begin{table}
\begin{tabular}{c c} \hline Reaction Term & Dissolution Reaction Equation \\ \hline CO\({}_{2}\) (g) & CO\({}_{2}\) + H\({}_{2}\)O \(\rightleftharpoons\) H\({}^{+}\) + HCO\({}_{3}\)\({}^{-}\) \\ Gypsum & CaSO\({}_{4}\)\({}^{2}\)H\({}_{2}\)O = Ca\({}^{2+}\) + SO\({}_{4}\)\({}^{2-}\) + 2H\({}_{2}\)O \\ Anhydrite & CaSO\({}_{4}\) = Ca\({}^{2+}\) + SO\({}_{4}\)\({}^{2-}\) \\ Halite & NaCl \(\rightleftharpoons\) Na\({}^{+}\) + Cl\({}^{-}\) \\ Calcite & CaCO\({}_{3}\) \(\rightleftharpoons\) Ca\({}^{2+}\) + CO\({}_{3}\)\({}^{2-}\) \\ Dolomite & CaMg(CO\({}_{3}\))\({}_{2}\)\(\rightleftharpoons\) Ca\({}^{2+}\) + Mg\({}^{2+}\) + 2 CO\({}_{3}\)\({}^{2-}\) \\ Cation Exchange & 2 NaX + Ca\({}^{2+}\)\(\rightleftharpoons\) 2 Na\({}^{+}\) + CaX\({}_{2}\) \\ \hline \end{tabular}
\end{table} 
Table 1: Chemical reaction considering in PHREEQC model. Sample C1, representing original groundwater in a Carboniferous Taiyuan limestone karst-fissure aquifer, was located in the far right of the seventh district, while Sample O1, representing groundwater in the Ordovician limestone karst-fissure aquifer, was located in the ninth district. As shown in Figure 4, the locations of the other groundwater samples in Carboniferous Taiyuan limestone karst-fissure aquifers gradually transformed from the seventh district to the ninth district, especially for Sample C12, which was only located in the ninth district next to the Sample O1. Therefore, it is confirmed that the groundwater in the Taiyuan aquifer has been mixed with the groundwater from the Ordovician aquifer, and the passage lies on the point of Sample C12.