This study examines the feasibility of using earth-banked tanks (EBT’s) as an alternative and economical means of winter storage for animal and other farmyard wastes. The study contains a detailed literature review on the subject, the results of a series of laboratory-scale experiments, field studies and a predictive model of the transport process through the soil liner of an earth-banked tank.For the laboratory studies, soils were sampled at four different locations throughout Ireland. These soils were subjected to soil classification and hydraulic conductivity tests. Since this series of experiments had been conducted using water as the permeating fluid, further investigation was undertaken to examine the effect of animal slurry flowing through a soil liner. It was concluded that the presence of suspended solids in the slurry had a pronounced sealing effect on the soil liner, significantly reducing the effective permeability of the soil due to the deposition of solids on the soil surface and within the pores of the soil.An investigation of a full-scale earth-banked tank at the Teagasc Grange Beef Research Centre at Dunsany, Co. Meath was undertaken. Groundwater quality, groundwater level and slurry infiltration rates were monitored after the tank was filled with animal slurry. As a result of the monitoring programme, it was concluded that well-constructed earth-banked tanks could successfully store animal slurry and that the quality of the groundwater around the tanks was well within permissible limits post filling and compared favourably with the groundwater quality prior to the installation of the tanks. A novel methodology for measuring infiltration rates through a subsoil liner and sampling groundwater quality from directly beneath the subsoil liner of an earth-banked tank was developed. A pilot-scale tank was constructed which enabled direct sampling of the quality and measurement of the quantity of the permeate from the tank. The slurry infiltration rate was significantly below acceptable limits and declined with time, indicative of a sealing of the pores of the soil due to the deposition of bio-solids. Examination of groundwater quality data in the vicinity of the pilot-scale earth-banked tank showed no discernible deterioration in quality.A mathematical model of the soil sealing due to the physical transport of suspended solids contained in the animal slurry through the soil liner is presented. The model describes the following hydraulic conditions: falling head, constant head and rising head. The model was validated for the falling head case using suspensions of cattle slurry at three different total solids concentrations. The proposed model may be useful to regulatory authorities, enabling an estimate of the likely soil sealing by suspensions flowing through soil liners to be made.The overall conclusion of the study is that well-constructed earth-banked tanks using suitable soil that is adequately compacted can be successfully used to temporarily store highly polluting liquids such as animal slurries. The enhanced slurry-storage capacity resulting from the use of earth-banked tanks should reduce the pressure on farmers to spread slurry on land at inappropriate times, thereby contributing to an improvement in the quality of watercourses adjacent to agricultural activities.
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