Application of Visual MODFLOW to assess the Sewage Plant accident pool leakage impact on groundwater in the Guanting Reservoir area of Beijing

In this paper, Visual MODFLOW is used to simulate groundwater flow and transport within the study area based on a certain scenario, assessing the leakage impact of a Sewage Plant accidental pool on groundwater using NH3-N as the assessment factor. In the model constructed, soil absorption and degradation was taken into account; the adsorption process of NH3-N adopted the Langmuir equation and the degradation was simplified as a first-order dynamic reaction. The leakage process was defined as a recharge with contaminants in the case that where there are two accidents happening to the Sewage Plant within a one month interval. The result of the model indicated that the NH3-N concentration of groundwater increased sharply when the Sewage Plant was malfunctioning. The peak of NH3-N concentration under the accident pool was about 8.0 x 10(-5) mg/L at the first accident. When the second accident happened, the NH3-N concentration increased to a maximum of about 1.1 x 10(-4) mg/L. At a location of about 20 m from the accident pool, the concentration declined to about one sixth of the center, which demonstrated that the NH3-N concentration increase caused by leakage of the accident pool was little, and the spatial influence also was small. The paper provides a method of dealing with the transport of physically and chemically reactive substances in groundwater with Visual MODFLOW and assessing the Sewage Plant accident pool leakage impact on groundwater quantitatively.