*4.2. Hydrochemical Characteristics of Shallow High As Groundwater*

In this part, 462 sets of shallow high-As groundwater samples are discussed, including 242 from the HT Plain, 29 from the SHH plain, 107 from the HB Plain, and 87 from the SBYR Plain. The groundwater was weakly alkaline, achieving a pH value of 7.15–9.26. The pH value of the HT plain approached that of the SBYR Plain, with levels of 7.15–9.26 and 7.37–9.25, respectively. The pH value of the SHH Plain approached that of the HB Plain, with levels of 7.44–8.65 and 7.26–8.76, respectively.
