Water quality adjacent to swine slurry holding ponds associated with a concentrated animal feeding operation

Environmental concerns exist over extended storage of liquid animal waste in outdoor holding ponds before land application, particularly in regions with underlying karst geology. To determine the effects of holding ponds on water quality, belowground interceptor trenches, groundwater (well), and a downslope ephemeral stream were monitored for water quality parameters. Nitrate-nitrogen concentrations increased (p < .0001) in well and ephemeral stream samples but decreased in trench samples (Trench 1 with a p < .0001) near the swine production facility and holding ponds over a 5-yr monitoring period (April 2014-June 2019). In contrast, chloride, which is a conservative element that can move freely through the soil without chemical, physical, or biological modification, and electrical conductivity decreased (p < .0001 to .0203) over the monitoring period in well and Trench 1 samples. Flow in the interceptor trenches was highly responsive to rainfall, suggesting the trenches were mainly capturing shallow subsurface flows initiated by rainfall. A lack of any increasing trend in chloride and electrical conductivity for ephemeral stream, well, or trench samples suggests that elevated nitrate-nitrogen concentrations in well and ephemeral stream samples may have been influenced by sources other than the liquid manure holding ponds (i.e., sources that have low chloride and electrical conductivity values). In regions with underlying karst geology, surface and subsurface water resources may require more expansive monitoring to demonstrate liquid manure holding ponds effects on nearby water quality.