Toward site-specific design standards for animal-waste lagoons: Protectingground water quality

Seepage losses from animal-waste lagoons can affect ground water quality, i f facilities are not properly sited, designed, and constructed. Most states in the Great Plains stipulate that earthen lagoons cannot seep more than s ome specified rate (mm d(-1)). These criteria often apply to the entire sta te and all livestock species, although ground water vulnerability and waste characteristics are highly variable from site to site. Because of this var iability, statewide;ide "blanket" regulations may overregulate some produce rs and underregulate others. Furthermore, wide disparity exists in seepage allowances among neighboring states, and regulations often are influenced b y public opinion rather than scientific findings. This paper argues that la goon design should be site specific and presents a logical framework to det ermine the maximum allowable seepage rate for a gi,:en location and type of operation (e.g., dairy, swine, cattle feedlot). Site-specific factors, suc h as soil properties, depth to water table, and chemistry of the waste, are used to arrive at lagoon performance standards that minimize long-term ris k. The decision process within the framework is presented as a conceptual m odel for lagoon permitting and may need to be customized to meet the requir ements of each state. Nevertheless, use of site-specific design criteria wi ll ensure that manure storages are adequate (e.g., plastic-lined lagoons) i n regions with vulnerable ground water, while providing reduced lagoon cons truction costs (lower cost of soil-lined lagoons) for producers who site th eir operations in areas of low risk. To complement the site-specific approa ch, the whole-lagoon seepage rate should be measured after construction to verify that the prescribed performance criteria have been met.