Date of this Version
Water and chemical transport were investigated beneath a 22-year-old beef feedlot runoff storage pond. Soil and sludge samples were collected from 14 borings to 6.1-m depths in a cross-section across the pond. The soils consisted of silt loam and clay loam, and the groundwater level was about 30 m beneath the land surface. Soil samples were analyzed for pH, NO3-N, NH4-N, Cl, P, K, SO4-S, TKN, and organic matter. Physical and hydraulic properties were measured on undisturbed samples of soil and sludge to compare saturated hydraulic conductivity, moisture release characteristics, and bulk density. Saturated hydraulic conductivity measured in the laboratory ranged from 0.005 to 0.044 cm/day for the sludge and from 0.008 to 31.4 cm/day for the sidewall soil. The mean hydraulic conductivity values for the sludge and sidewall soil were not significantly different. Mean bulk densities were significantly different. The sludge exhibited high shrinkage when dried, and did not swell to its original volume when rewetted. Moisture content and chemical concentrations were higher beneath the sidewalls than beneath the pond bottom. A seepage rate of 0.87 cm/day was measured after a 7.6-cm rainfall event, following an extended dry period when the pond was empty. This short-term measurement exceeded the allowable seepage rate in Nebraska, however, seepage decreased with time following recharge of the sidewalls. Results have shown that water and chemical movement has occurred beneath the unlined feedlot runoff storage pond and that the plumes have traveled further than the maximum sampled depth of 6.1 m after 22 years of operation.