HR: 17:45h
AN: H34C-08    [Abstracts]
TI: An Integrated Modeling Approach for Numerical Simulations of Long-Term Groundwater Contaminant Loading Into Streams in Agricultural Watersheds
AU: * Wang, M
EM: wang.mingyu@epa.gov
AF: Center for Subsurface Modeling Support, Robert S. Kerr Environmental Research Center, 919 Kerr Research Drive P.O. Box 1198, Ada, OK 74820 United States
AU: * Wang, M
EM: wang.mingyu@epa.gov
AF: Shaw Environmental, Inc., 919 Kerr Research Drive, Ada, OK 74820 United States
AB: Groundwater contamination due to infiltration of various contaminants such as nitrate from agricultural practices may be degrading water quality and aquatic habitats. Numerical simulations are especially helpful for investigations of the impact of this contamination while it is challenging to practically model long-term groundwater contaminant loading into streams in agricultural watersheds as a result of limited field data availability, complexity of groundwater systems, uncertainty from different model parameters, and difficulty of boundary approximation. In this study, a number of general system features of watersheds and aquifers are first identified and discussed such as relatively independent water flow systems with certain hydraulic impact from adjacent watersheds, hydraulic and chemical interactions between groundwater and surface water, spatially and temporally varied groundwater recharge rates from precipitation, and seasonal changes of contaminant loading into streams. A comprehensive modeling approach integrating different attributes, including model components, pertinent factors, system statuses, and useful methods and tools, is then proposed to achieve a practical numerical model. A case study is presented in which groundwater flow and nitrate transport and fate are modeled, using the comprehensive GMS modeling package, in the regional aquifers beneath two adjacent agricultural watersheds of the Chester River Basin, Maryland. This was a part of efforts to investigate the eutrophication and water quality of Chesapeake Bay. This model was calibrated, including estimations of variable groundwater recharge rates from rainfall in different zones for different seasons, and validated successfully by implementing the integrated approach in which different types of the field data such as water head and nitrate concentrations, stream fluxes, geographic and geologic data, and precipitation were utilized adequately and integrally. Model simulations predict a long-term groundwater nitrate loading into the streams and Chesapeake Bay from the two watersheds with different patterns of agricultural nitrate applications, considering significant denitrification in aquifer sediments and other riparian-instream nitrate removal processes. It is observed that the integrated modeling approach has capability of accomplishing a valuable complex numerical model for investigations of long-term groundwater contaminant loading into streams in agricultural watersheds for different agricultural contaminant disturbances. As a result, an optimal and integrated ecosystem management pertaining to the concerned watersheds may be facilitated by implementing the established numerical model which accounts for the hydraulic and chemical interactions between groundwater and surface water.
DE: 1800 HYDROLOGY
DE: 1830 Groundwater/surface water interaction
DE: 1847 Modeling
DE: 1860 Streamflow
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: Fall Meeting 2005