HR: 0830h
AN: H41F-1053    [PDF]
TI: Stochastic Assessment of Regional Groundwater Nonpoint Source Pollution with Spatially Variable, Transient Forcing: Conceptual Framework and Nitrate Case Study
AU: * Harter, T
EM: ThHarter@ucdavis.edu
AF: University of California, Dept. Land, Air, and Water Resources, Davis, CA 95616-8628 United States
AU: Van der Schans, M L
EM: Martin.vanderSchans@wur.nl
AF: Wageningen University, Subdepartment of Water Resources; Nieuwekanaal 11, Wageningen, 6709 PA Netherlands
AU: Leijnse, A
EM: A.Leijnse@nitg.tno.nl
AF: Wageningen University, Subdepartment of Water Resources; Nieuwekanaal 11, Wageningen, 6709 PA Netherlands
AB: We introduce a general stochastic concept of regional groundwater nonpoint source pollution in production wells or other groundwater discharge areas; present an efficient numerical procedure for its implementation; and validate the approach using a case study. Our principal hypothesis is that regional variability of and uncertainty about well pollution from nonpoint sources is primarily caused by the spatio-temporal variability of the nonpoint source strength (recharge rate and recharge pollutant concentration) and the variable spatial distribution of pumping wells, pumping rates, and other groundwater discharge relative to the location of the nonpoint sources. We describe a conceptual model of random space functions (RSFs) for nonpoint sources and wells. The resulting stochastic flow and transport equations are subject to random forcing in the nonpoint source and pumping boundary conditions (external variability). The stochastic forcing analysis yields a transient probability distribution function of water quality (water quality pdf) in a regional set of randomly distributed, discrete production wells and other groundwater discharge areas. We introduce a novel three-step numerical approach for the stochastic forcing analysis and apply the method to determine the 150-year (1910-2060) nitrate pdf for an irrigated, semi-arid region with a history of high groundwater nitrate. Comparison of the simulated nitrate pdfs with results from regional and domestic well water surveys in 1970, 1986 and 2001 shows that stochastic forcing indeed accounts for the observed temporal nitrate dynamics (mean concentration) and for 70% of the spatial variability observed in domestic well water nitrate in that region.
UR: http://groundwater.ucdavis.edu
DE: 1803 Anthropogenic effects
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
DE: 1842 Irrigation
DE: 1869 Stochastic processes
SC: Hydrology [H]
MN: 2003 Fall Meeting