Journal article
Estimating a Representative Value and Proportion of True Zeros for Censored Analytical Data with Applications to Contaminated Site Assessment
Environmental science & technology, Vol.51(13), pp.7502-7510
07/05/2017
DOI: 10.1021/acs.est.6b05385
PMID: 28613841
Abstract
This paper demonstrates a maximum likelihood (ML)-based approach to derive representative ("best guess") contaminant concentrations from data with censored values (e.g., less than the detection limit). The method represents an advancement over existing techniques because it is capable of estimating the proportion of measurements that are true zeros and incorporating varying levels of censorship (e.g., sample specific detection limits, changes through time in method detection). The ability of the method to estimate the proportion of true zeros is validated using precipitation data. The stability and flexibility of the method are demonstrated with stochastic simulation, a sensitivity analysis, and unbiasedness analysis including varying numbers of significant digits. A key aspect of this paper is the application of the statistical analysis to real site rock core contaminant concentration data collected within a plume at two locations using high resolution depth-discrete sampling. Comparison of the representative values for concentrations at each location along the plume center-line shows a larger number of true zeros and generally lower concentrations at the downgradient location according to the conceptual site model, leading to improved estimates of attenuation with distance and/or time and associated confidence; this is not achievable using deterministic methods. The practical relevance of the proposed method is that it provides an improved basis for evaluating change (spatial, temporal, or both) in environmental systems.
Details
- Title: Subtitle
- Estimating a Representative Value and Proportion of True Zeros for Censored Analytical Data with Applications to Contaminated Site Assessment
- Creators
- Claus P Haslauer - University of Tübingen , Center for Applied Geoscience, Hölderlinstrasse 12, 72074 Tübingen, GermanyJessica R Meyer - University of Guelph , G360 Institute for Groundwater Research, Guelph, Ontario N1G 2W1, CanadaAndrás Bárdossy - University of Stuttgart , Institute for Modelling Hydraulic and Environmental Systems, 70569, Stuttgart, GermanyBeth L Parker - University of Guelph , G360 Institute for Groundwater Research, Guelph, Ontario N1G 2W1, Canada
- Resource Type
- Journal article
- Publication Details
- Environmental science & technology, Vol.51(13), pp.7502-7510
- Publisher
- United States
- DOI
- 10.1021/acs.est.6b05385
- PMID
- 28613841
- ISSN
- 0013-936X
- eISSN
- 1520-5851
- Grant note
- DOI: 10.13039/501100001659, name: Deutsche Forschungsgemeinschaft, award: GRK 1829/1, HA 7339/2-1
- Language
- English
- Date published
- 07/05/2017
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9983984540402771
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