Distribution and Origins of Hardness in Shallow and Deep Groundwaters of the Hebei Plain, China

Abstract

Elevated hardness concentrations in groundwater have become a noteworthy concern in recent decades because long-term drinking of groundwater with high levels of hardness is an important factor resulting in chronic kidney diseases. In this study, the distribution and origins of groundwater total hardness (TH) in various sub-plains and different land-use areas of the Hebei Plain (HBP) were investigated. A total of 445 groundwater samples in the HBP were collected once in 2021, and twelve chemical parameters, including TH in groundwater, were analyzed. Results showed that TH-rich (>450 mg/L) shallow groundwater in both the central and littoral plains was more than twice that in the Piedmont plain. Similarly, TH-rich deep groundwater accounted for about 18% in the central plain but was negligible in the Piedmont plain. In the Piedmont plain, TH-rich shallow groundwater in urban areas was twice or more than in other land use types. By contrast, both TH-rich shallow and deep groundwaters in agricultural areas in the central plain were higher than those in rural areas. This was opposite to TH-rich shallow groundwater in the littoral plain. In the Piedmont plain, TH-rich shallow groundwater was mainly attributed to water-rock interaction, groundwater over-extraction, and the infiltration of domestic sewage and animal waste. In the central plain, both TH-rich shallow and deep groundwaters likely ascribed to the evaporite dissolution and seawater intrusion. By contrast, the leaching of agricultural fertilizers resulting in the dissolution of Ca-rich and Mg-rich minerals in the vadose zone was mainly responsible for the occurrence of TH-rich shallow groundwater in the littoral plain. Therefore, in order to limit elevated hardness concentrations in groundwater in the HBP, limiting shallow groundwater extraction and strengthening the supervision of the domestic sewage and animal waste in the Piedmont plain are recommended. Besides, restricting the use of nitrogenous fertilizers in the littoral plain is also recommended.