Abstract

A review of studies conducted in the past decades on nutrient and pathogen contributions to surface and subsurface waters is presented. Factors such as soil structure, water table levels, dissolved oxygen, organic matter content, and cation content in soils determine the movement of nutrient and pathogens in soils. Monitoring studies agree, in general, on the influence that these factors have on nutrient and pathogen movement in soils. Generally, data collected from monitoring wells show that nutrients and pathogens decrease in concentration for wells located farther away from the drainfield. Similar trends are found for wells placed deeper in the soil. Several studies that monitored nitrogen (N) removal from On-Site Wastewater Systems (OSWS) explained that N adsorption onto soils, dilution in the groundwater, and denitrification act as the main paths of N removal. Some studies found that little nitrification took place in nearly saturated soils. On the other hand, significant nitrate (NO₃^-) movement away from the drainfield was observed from OSWS placed in unsaturated soils with low organic matter content. However, NO₃^- moving over long distances towards surface water was observed to decrease when the plume encountered sediments with high organic matter content. Studies that monitored phosphorus (P) removal from OSWS documented high P removal in close distance from the drainfield. Precipitation of phosphorus with aluminum (Al³⁺), iron (Fe³⁺) and calcium (Ca²⁺) is the main path for P removal. However, dissolution of acid soil P precipitates is likely when saturated conditions are present. Nevertheless, P was not found in high concentrations in soils. Several studies concluded the filtration, adsorption, and die-off mechanisms are the main removal path of pathogens in soils. While large pathogens are removed mainly through filtration bacteria and viruses are removed through adsorption and die-off. High saturation levels, low cation content in soils, and rainfall may hinder bacterial and viral adsorption. Differences in behavior were documented between bacteria and viruses. Furthermore, viral survival was lower than bacterial survival under summer temperature conditions. In addition, removal of both viruses and bacteria was more efficient under lower loading rates and unsaturated conditions. Several studies that monitored bacterial movement away from the drainfield confirmed that bacterial survival is enhanced by saturated conditions, rainfall events, high saturated conductivity, and low temperatures. However, for longer distances away from the drainfield relationships of viral survival with rainfall, low temperatures, and bacterial survival were not well established.

Please address any questions to Dr. David Lindbo.

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Vera MacConnell, Research Technician, I on February 23, 1999.
Last Updated on 6/27/00 by Roland O. Coburn, Research Tech. I.