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Home > Fate and Transport Factors |
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*Source Water Protection |
FATE AND TRANSPORT OF AFO-DERIVED CONTAMINANTS IN THE ENVIRONMENT An understanding of the principles of the fate and transport of animal waste contaminants in the environment is important for water utilities to be able to more accurately assess potential impacts on source water quality from releases of these wastes. Wastes can be released to the environment during any of the animal waste generation and handling steps, including the animal confinement areas, treatment and storage lagoons, manure stockpiles, and land where manure is applied. The main transport pathways include surface runoff and erosion, overflows from lagoons, spills and other dry-weather discharges, leaching into soil and ground water, and volatilization of compounds (e.g., ammonia) and subsequent redeposition on land or surface water (USEPA, 2003a). Various factors affect the fate and transport of contaminants from waste sources to the subsurface or into surface water sources. Fate and transport mechanisms include: 1. water transport related processes: a) advection (including preferential flow), b) dispersion, c) diffusion; 2. phase transfer processes: a) immobilization, b) sorption, c) ion exchange, d) volatilization, e) dissolution/precipitation; 3. species transformation processes: a) reduction/oxidation reactions, b) acid-base reactions, c) hydrolysis/substitution, d) complexation, e) biological degradation, f) photochemical degradation, and g) radioactive decay. Runoff of animal wastes applied to land is more likely when precipitation occurs shortly after application. This is especially true if the manure is overapplied, misapplied, or is not injected or incorporated into the land. Furthermore, erosion of soil that has contaminants (e.g., phosphorus, pathogens) bound to it can also occur during rain events. More direct pollution of surface waters occurs when animals are allowed direct access to waterbodies (e.g., cows allowed to drink in streams); or when manure storage areas leak, overflow, or their containment system is breached; or when manure or other piping systems leak or break. Flooding from severe precipitation events can result in substantial release of wastes from a variety of areas. Animal wastes can of course also reach groundwater or surface water during dry periods, including overflow of manure storage areas, spills when containment systems fail, or through intentional releases. Contamination of groundwater can occur through many of the same sources, and is especially predominant when manure or other pollutants are applied to land and then rainfall carries the contaminants into the subsurface (e.g., nitrate from animal wastes). Contamination of air is also a possibility through release of volatile compounds from waste or byproducts of animal waste decomposition such as ammonia, hydrogen sulfide and methane. Spray irrigation systems and wind-blown dust particles also are a source of atmospheric contamination. Any chemical that becomes airborne may then later be redeposited on surface waters or soils (USEPA, 2003a). The factors affecting the transport of select groups of contaminants can be found in the links below: Pathogens Nutrients Pharmaceuticals (antibiotics and hormones) Heavy metals and trace elements |
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