SEEPAGE LOSSES FROM ANIMAL WASTE LAGOONS: A SUMMARY OF A FOUR–YEAR INVESTIGATION IN KANSAS

Abstract

Seepage losses from animal waste lagoons can affect groundwater quality if liquid effluent is not properly contained within the basin. Seepage rates from 20 anaerobic lagoons were measured using water balance methods. Study locations included 14 swine sites, 5 cattle feedlots, and a single dairy. Seepage results and basin geometry were used to estimate the hydraulic conductivity (Ks) of the compacted soil liner at each site. Seepage data and waste chemistry were used to calculate rates of chemical export into the vadose zone. Profiles of ammonium–nitrogen (N) and other chemicals were determined by sampling soils beneath old lagoons. Seepage rates from 20 lagoons averaged 1.1 mm/d and ranged from 0.2 to 2.4 mm/d. Fifteen of the 20 lagoons had seepage rates between 0.5 and 1.5 mm/d. The variation among locations was small despite large differences in soil types and depths to groundwater. On average, the Ks of lagoon liners was 1.8 U 10–7 cm/s. Variation in seepage rates and Ks among sites was lognormally distributed. There was evidence that seepage was moderated by the organic sludge that blankets the bottom of lagoons. Concentrations of nitrogen, phosphorus, and other waste constituents were, on average, 3 to 5 times higher in swine waste lagoons compared to cattle feedlot lagoons. Ammonium–N seepage into the subsoil ranged from 2000 to 5000 kg ha–1 yr–1 at the larger swine sites but averaged 385 kg ha–1 yr–1 at cattle feedlots. Soil cores showed that concentrations of ammonium–N, organic–N, phosphorus, and other cations were highest near the original floor of the lagoon but decreased markedly with depth. In most cases, concentrations of nutrients in the soil returned to background levels about 3 m under the lagoons. Additional research is needed on fate and transport of contaminants that accumulate beneath lagoons and best management practices for lagoon closure.