Impact of wastewater from pig farm lagoons on the quality of local groundwater

• Significant natural purification of farm wastewaters takes place in the lagoons.
• The major portion of metals from wastewater is concentrated in the solid manure.
• Positive statistical correlation shows that shallow groundwaters on the farms are contaminated.
• Shallow groundwater contains elevated amounts of organic matter and ammonia.
• No deterioration of the quality of drinking water was detected in the deeper wells on the farms.

The objective of this study was to determine the degree of contamination of the shallow groundwater and the quality of drinking water, on the locations of three pig farms employing liquid manure cleaning systems, in lagoons without hydroisolation for storing wastewaters.For the purpose of monitoring the quality of shallow groundwater and its level, ten piezometers were installed on three pig farms, whereas the quality of drinking water was followed using samples from the local wells.The minimum fluctuations of shallow groundwater level were measured in the reference piezometers, whereas the highest variations (up to 4.19 m) were detected in the piezometers drilled near the lagoons, indicating the infiltration of water from the lagoon. A significant correlation (P < 0.001) between the amount of rainfall and the level of water in the piezometers, indicates the possible penetration of the pollutants from the earth surface to the groundwater. The measurements encompassed the physico-chemical parameters that characterize pig farm wastewater, viz. organic and suspended matter and dry matter. The results of measuring the parameters of wastewater, solid manure, and lagoon sediment indicate that efficient water purification occurred in the lagoons under natural conditions. The organic matter content in the lagoons was reduced by 85–90%, dry matter by 56–69%, suspended matter by 94–96%, total P by 31–50%, total N by 39–55%, Cu by 69–85%, and Zn by 83–89%. The results also show that most of the metals settled on the bed of the lagoon, reducing thus the risk of contamination of surface water and groundwater.The investigation showed large variations in the parameters of shallow groundwater on the locations of the farms. The concentrations of NH4+-N in water of the reference piezometers ranged between 0.02 and 1.52 mg/L, while in the piezometers close to the lagoons they were up to 52.6 mg/L. The content of total N in the reference piezometers was between 0.14 and 22.4 mg/L, while in the piezometers close to the source of contamination it reached 90.4 mg/L. Also, at one of the farms the amounts of P and Cl− measured in the piezometers close to the lagoon were up to 7 and 5 times higher than in the reference piezometer. The correlations between electrical conductivity (EC) and Cl−, SO42−, Na+, K+, between total N and NH4+-N, NO3−-N and organic N by Kjeldahl (ONK) and various metals in the shallow groundwater, indicate their common origin from farm wastewaters.On the other hand, the results clearly indicate that there was no degradation of the quality of the drinking water in the deeper layers, and none of the drinking water quality parameters showed significant variation during the investigation period. This is explained by the presence of 4–6 m thick clay layer between the lagoon and the drinking water aquifer.Overall, this study clearly shows that the pollution of shallow groundwater on the farms is of a local character, and that here is no significant pollution of groundwater sources, despite the fact that farms employing liquid manure cleaning systems have been in operation for many decades.