title: Screening-level estimates of mass discharge uncertainty from point measurement methods.
abstract: The uncertainty of mass discharge measurements associated with point-scale measurement techniques was investigated by deriving analytical solutions for the mass discharge coefficient of variation for two simplified, conceptual models. In the first case, a depth-averaged domain was assumed, consisting of one-dimensional groundwater flow perpendicular to a one-dimensional control plane of uniformly spaced sampling points. The contaminant flux along the control plane was assumed to be normally distributed. The second case consisted of one-dimensional groundwater flow perpendicular to a two-dimensional control plane of uniformly spaced sampling points. The contaminant flux in this case was assumed to be distributed according to a bivariate normal distribution. The center point for the flux distributions in both cases was allowed to vary in the domain of the control plane as a uniform random variable. Simplified equations for the uncertainty were investigated to facilitate screening-level evaluations of uncertainty as a function of sampling network design. Results were used to express uncertainty as a function of the length of the control plane and number of wells, or alternatively as a function of the sample spacing. Uncertainty was also expressed as a function of a new dimensionless parameter, Ω, defined as the ratio of the maximum local flux to the product of mass discharge and sample density. Expressing uncertainty as a function of Ω provided a convenient means to demonstrate the relationship between uncertainty, the magnitude of a local hot spot, magnitude of mass discharge, distribution of the contaminant across the control plane, and the sampling density.
authors.affiliation: National Risk Management Research Laboratory, US Environmental Protection Agency, Ada, OK 74820, United States. Electronic address: brooks.michael@epa.gov.
authors.forename: Michael C
authors.initials: MC
authors.lastname: Brooks
authors.affiliation: National Research Council Post-Doctoral Associate, US Environmental Protection Agency, Ada, OK 74820, United States.
authors.forename: Ki Young
authors.initials: KY
authors.lastname: Cha
authors.affiliation: National Risk Management Research Laboratory, US Environmental Protection Agency, Ada, OK 74820, United States.
authors.forename: A Lynn
authors.initials: AL
authors.lastname: Wood
authors.affiliation: Interdisciplinary Program in Hydrologic Sciences, Department of Environmental Engineering Sciences, University of Florida, Gainesville, FL 32611, United States.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Annable
mesh_terms: D004784:Environmental Monitoring / Q000379:methods*; D060587:Groundwater; D008962:Models, Theoretical; D035501:Uncertainty; D014874:Water Pollutants, Chemical / Q000032:analysis; D014876:Water Pollution / Q000032:analysis*; D060986:Water Wells
chemical_list: D014874:Water Pollutants, Chemical
keywords: Mass discharge; Mass flux; Uncertainty