2.3.3. Experimental Test Instrument

According to the groundwater quality standard (GB/T 14848-2017) and other standards, the Pb concentrations for the sample solution and sample sand were detected by a flame atomic adsorption spectrophotometer (FAAS, Manufacturer: Beijing Ruili Analytical Instrument Co. Ltd., Beijing, China). The pH of the solution was detected using the glass electrode method (Micro600, Manufacturer: Palintest Co. Ltd., Newcastle, UK). The medium sample was digested under microwave irradiation. The Pb contents were determined by FAAS.

**Figure 2.** Water table fluctuations process.
