Multi-tracer study reveals groundwater pollution from urban waste water in rivers

​During my visit at the Center for Agricultural Resources Research in Shijiazhuang, Hebei last summer, I got involved in the work by master student, Meijia Zhu, who gathered an impressive hydrochemical data set in the Xiong’an New Area. I learned that this area will provide new housing for the ever growing region around the Chinese capital. However, the North China Plain, where these developments take place is characterized by a dramatic drop in the groundwater levels over the last decades due to its over consumption; mainly for agricultural use. Due to the water scarcity related to the groundwater mining, rivers, are running dry. To counter this development water gets regularly transferred from other basins (see Figure 4). Though, often, the river flow is dominated by sewage water from urban areas.

Figure 6. Spatial interpolation of groundwater depth (a), electrical conductivity (EC) (b), Cl− (c) and δ18O (d) of groundwater along the Fu River.

The work lead by Meijia Zhu now shows that this sewage water is not only affecting the water quality of Lake Baiyangdian, largest freshwater lake, but it also aggravates the underlaying groundwater body. We see, that the Chloride and electrical conductivity increases along the groundwater underlying studied river that flows into the Lake Baiyangdian (see Figure 6). We used end-member mixing analysis to show the ratio groundwater recharge sourced from either rainfall, lake water, or river water (see Figure 9).
The study shows clearly how the groundwater body is not only threatened by depletion, but that the combination of over use and sewage disposal into rivers affects the groundwater challenging the water supply of the new developing Xiong’an New Area.

Figure 9. d18O values versus Cl- concentrations of the groundwater and end-members. The mean values of Cl□ concentration and stable isotopes of the Fu River water in seasons without the influence of the precipitation and transferred water (samples collected in January 2018 and March 2018) were taken as values of one end-member that reflects sewage influence.

The manuscript to this study is openly available here.
Zhu M, Wang S, Kong X, Zheng W, Feng W, Zhang X, Yuan R, Song X, Sprenger M (2019): Interaction of Surface Water and Groundwater Influenced by Groundwater Over-Extraction, Waste Water Discharge and Water Transfer in Xiong'an New Area, China, Water, 11(3), 539, doi: 10.3390/w11030539.