*5.5. Data Analysis*

The hydrogeochemical and isotopic data of each unit were statistically analyzed and are listed in Table 1.


**Table 1.** Hydrochemical properties and isotopes of all units.

Notes: (1) Concentrations are in meq/L unless otherwise indicated, such as deuterium and oxygen 18O in ‰, and (2) "-" means that there is only one sampling point and the square error cannot be determined.

In the studied area, the drainage methods of the confined aquifer were mainly lateral runoff discharging and artificial well-group pumping. Artificial exploitation was 27.95 × 106 <sup>m</sup>3/a and the mining volume of each unit was calculated according to the proportion of the unit area. The mining volume of each unit is shown in Table 2. The lateral discharging volumes were 8.57 × <sup>10</sup><sup>6</sup> m3/a and 7.10 × <sup>10</sup><sup>6</sup> <sup>m</sup>3/a, as shown in Table 3.




#### *5.6. Results and Analysis*

The results showed (Figure 12) that units a and b in the studied area were singlestructure unconfined aquifers as the main recharge resources of the downstream confined aquifer. Unit C accepted the lateral recharge from unit a and the leakage recharge from Unit c, which were 9.77 × <sup>10</sup><sup>6</sup> <sup>m</sup>3/a and 0.64 × 106 m3/a, respectively. Unit E received the lateral recharge from unit C and the overflow recharge from unit e, which were 4.67 × 106 <sup>m</sup>3/a and 2.80 × 106 <sup>m</sup>3/a, respectively. The unit F received the lateral recharge from the unit E and the overflow recharge from the f unit, which were 6.10 × 106 <sup>m</sup>3/a and 0.90 × <sup>10</sup><sup>6</sup> <sup>m</sup>3/a, respectively. Unit D received the lateral recharge from unit b and the overflow recharge from unit d, which were 1.71 × <sup>10</sup><sup>6</sup> <sup>m</sup>3/a and 5.66 × <sup>10</sup><sup>6</sup> <sup>m</sup>3/a, respectively. The unit G received the lateral recharge from the unit D, and the recharging was 5.90 × <sup>10</sup><sup>6</sup> m3/a. This recharge relationship and degree were consistent with results from hydrochemistry and isotope.

**Figure 12.** Quantitative water circulation model of the unconfined aquifer and the confined aquifer in the studied area.

The total groundwater recharge volume from the confined aquifer in the studied area was 21.48 × 106 <sup>m</sup>3/a, of which the lateral recharge was 11.48 × <sup>10</sup><sup>6</sup> m3/a, accounting for 53.45% of the total, and the vertical leakage recharge was 10.00 × 106 m3/a, accounting for 46.55% of the total. The vertical leakage recharge in the southeast was very small and negligible. The total discharging volume from the confined aquifer was 36.87 × <sup>10</sup><sup>6</sup> m3/a, of which the lateral discharging volume was 15.67 × 106 m3/a, accounting for 42.5%, and artificial exploitation was 21.2 × 106 <sup>m</sup>3/a, accounting for 57.5%. These results showed that the confined aquifer was in an accumulation and superposition state of negative balance along the direction of the underground water flow.
