Permeability index (PI)
PI is also one of the important indices to evaluate the fitness of
groundwater for irrigation purposes. Continuous usage of rich minerals
such as calcium, magnesium, sodium, and bicarbonate ions in groundwater
causes the low permeability of the soil and reduces the crop yield
(Rufino et al., 2019). According to PI classification, classes I and II
are suitable, and class III is unsuitable for irrigation. The PI varied
from 13.11 to 70.33 %, with a mean of 36.87% in the study area
(Table.4). About 76.67 % of groundwater samples fall under class II,
and 23.33 % of groundwater found to be class III (Table.6). The spatial
distribution of PI observed that 642.02 sq.km areas are suitable, and
24.93 sq.km is unsuitable for irrigation purposes (Fig.11h). Excess
value of PI is associated to sodium and bicarbonate ions, which may be
due to the ion exchange, calcite and dolomite dissolution.