|Nienaber, John - Jack|
Submitted to: American Society of Agri Engineers Special Meetings and Conferences Papers
Publication Type: Other
Publication Acceptance Date: 7/7/1995
Publication Date: N/A
Citation: N/A Interpretive Summary: A beef cattle feedlot runoff detention pond that had been used for 22 years without sludge removal was investigated for possible seepage. Soil cores were taken at several locations along the sides, along the side slopes and across the bottom of the pond to give a profile of seepage from the pond. From the measured levels of various compounds it was clear that some seepage had occurred and that the side slopes and not the bottom were the most probable sites of seepage. This seepage pattern, while supporting the action of sludge as a sealant in the bottom of detention ponds, nevertheless indicates seepage from the pond sidewalls needs further consideration and research. No definite conclusions were reached since the full extent of the seepage was not found within the depths sampled in this study. However, the information collected in this study provides a base for testing a model for pollutant movement in the soil. This is valuable for risk assessment.
Technical Abstract: Water and chemical transport were investigated beneath a 22-year-old beef feedlot runoff storage pond from which sludge had never been removed. Soil samples were collected from 6.1 m deep borings in a cross-section across the pond. The soils consisted of silty loam and clay loam. Soil samples were analyzed for various chemical compounds and organic matter. Soil water extracts were analyzed for pH, electrical conductivity, and dissolve organic matter. Analytical results indicated that seepage from the sidewalls was greater than from the bottom of the pond. Chloride concentrations in the background boring ranged from 1-6 mg/kg, while at the 6.1 m depth beneath the pond they approached 160-180 mg/kg. Phosphorus concentrations were similar in the background boring and beneath the pond. Ammonium concentrations ranged from 4-8 mg/kg in the background boring, and 8-83 mg/kg at the 6.1 m depth beneath the pond. Organic nitrogen concentrations ranged from 100-700 mg/kg in the background boring, and 750 1,600 mg/kg at the 6.1 m depth beneath the pond. Nitrate was not found beneath the pond bottom, but isolated occurrences were found beneath the pond sidewalls, with a maximum concentration of 55 mg/kg. A seepage rate of 0.87 cm/day was measured after a large rainfall event, following a period when the pond was near empty. This one-time measure exceeds the allowable seepage rate in several states. We believe that seepage decreases with time following saturation of the sidewalls. This project has shown that, even in low permeability soils, water and chemical movement does occur in the unsaturated zone beneath feedlot runoff storage ponds. The data provides a basis for initiation of modeling flow in unsaturated zones for risk assessment.