|Nienaber, John - Jack|
Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/1998
Publication Date: N/A
Citation: N/A Interpretive Summary: A study was done on a 22-year-old pond used to store rainfall runoff from a beef feedlot. The goal of the study was to estimate the seepage from the pond. Soil and sludge cores were taken from the bottom of the pond and deep soil samples were taken from the sides and beneath the pond. All holes were backfilled. The rate that water moved through the cores was measured in the laboratory. When wet, water movement through the cores wa low but as the cores were dried, the measured water flow increased through both the sludge and soil cores. Analyses of soil samples collected beneath and around the pond confirmed that chemical compounds found in the runoff had seeped to greater depths than we had cored. Therefore, we could not estimate total seepage. During the study, the pond was empty and the side slopes were dry and covered with weeds. Following a large rainfall, the pond was filled. The rate of seepage was measured and was found to be high hat first but then slowed down. It was believed that cracks and weed root holes were primary contributions to the seepage that had occurred then and over the 22-year-life of the pond.
Technical Abstract: 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, nitrate, ammonia, chloride, phosphorus, potassium, sulfate, total nitrogen,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 ranged from 0.005 to 0.444 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 of this project 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.