Modeling seepage from an unlined beef cattle feedlot runoff storage pond

A site-specific water balance model was developed to evaluate the effects o f sludge accumulation, starting stage, and annual precipitation on. seepage from an unlined beef cattle feedlot runoff storage pond. The computer mode l predicted daily inflows due to precipitation and runoff and outflows due to evaporation and seepage. The seepage component was estimated using the S WMS 2D finite element saturated/unsaturated flow model, while feedlot runof f was estimated using the Natural Resource Conservation Service runoff meth od. Evaporation, precipitation, and temperature data from a nearby weather station were used in the model. Based on results of 9,100 annual simulation s, the mean seepage volume ranged from 31 900 m(3)/y with no sludge accumul ation to 19 300 m(3)/y with 22 years of sludge accumulation (1.5 m of sludg e). The mean seepage rate ranged from 1.11 cm/day with no sludge accumulati on to 0.50 cm/day with 22 years of sludge accumulation. Sidewall seepage vo lumes ranged from 49 to 73% of the total pond seepage volume. Increasing th e pond stage from 0 to 250 cm at the beginning of the simulations caused a 200% increase in annual seepage volumes, yet only a 20% increase in annual seepage rates. Annual seepage volumes increased as much as 62% when annual precipitation increased from 44 to 96 cm/y. Average annual seepage rates va ried little with varying annual precipitation. Seepage losses were 1.5 to 3 .2 times as great as evaporation losses. This research provides information on variability in seepage rates that will be valuable to regulatory person nel when writing new environmental regulations, and to engineers when desig ning new storage ponds and lagoons.