A multistage multicriteria spatial sampling strategy for estimating contaminant mass discharge and its uncertainty

Li, K. Betty; Abriola, Linda M.

doi:10.1029/2008wr007362

Cited by 13 publications

(13 citation statements)

References 57 publications

(85 reference statements)

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“…As illustrated in frame (f), for a sparse transect in such a setting it is not necessary to monitor the highest concentration portion of each of the sub‐plumes. In practice, of course, it is not possible to know what portion of the plume concentration distribution has been captured by a sparse transect unless: (1) detailed characterization has been conducted, ideally before transect installation, as suggested by others (Cai et al 2011; Li and Abriola 2009), and (2) it is known or reasonably assumed that the plume location does not shift laterally at the transect over time.…”

Section: Resultsmentioning

confidence: 99%

Mass Discharge in a Tracer Plume: Evaluation of the Theissen Polygon Method

et al. 2012

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A tracer plume was created within a thin aquifer by injection for 299 days of two adjacent “sub-plumes” to represent one type of plume heterogeneity encountered in practice. The plume was monitored by snapshot sampling of transects of fully screened wells. The mass injection rate and total mass injected were known. Using all wells in each transect (0.77 m well spacing, 1.4 points/m2 sampling density), the Theissen Polygon Method (TPM) yielded apparently accurate mass discharge (Md) estimates at 3 transects for 12 snapshots. When applied to hypothetical sparser transects using subsets of the wells with average spacing and sampling density from 1.55 to 5.39 m and 0.70 to 0.20 points/m2, respectively, the TPM accuracy depended on well spacing and location of the wells in the hypothesized transect with respect to the sub-plumes. Potential error was relatively low when the well spacing was less than the widths of the sub-plumes (> 0.35 points/m2). Potential error increased for well spacing similar to or greater than the sub-plume widths, or when less than 1% of the plume area was sampled. For low density sampling of laterally heterogeneous plumes, small changes in groundwater flow direction can lead to wide fluctuations in Md estimates by the TPM. However, sampling conducted when flow is known or likely to be in a preferred direction can potentially allow more useful comparisons of Md over multiyear time frames, such as required for performance evaluation of natural attenuation or engineered remediation systems.

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Section: Resultsmentioning

confidence: 99%

Mass Discharge in a Tracer Plume: Evaluation of the Theissen Polygon Method

et al. 2012

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“…Selecting a sampling network with a larger sampling density would have to weigh the likelihood of this particular case against the cost of over design. Or, consideration could be given to a staged sampling approach (e.g., Li and Abriola, 2009), so that the risk this particular case represents is addressed through additional measurements if needed. We emphasize that defining CV ṁ[2] b 0.3 as acceptable and CV ṁ[2] = 0.8 as questionable levels of uncertainty was done here for illustration purposes only.…”

Section: Comparisons To Other Uncertainty Studiesmentioning

confidence: 99%

“…A screening level assessment could be used to help guide preliminary field plans for mass discharge measurements. For example, such guidance could be used to help select sample spacing in the initial round of regularly-spaced sampling activities in the multi-staged sampling strategy of Li and Abriola (2009). Moreover, such an analysis is needed to help guide decisions about method selection when considering pumping-measurement versus point-measurement methods.…”

Section: Introductionmentioning

confidence: 97%

“…A number of studies have been completed on pointmeasurement method uncertainty (Béland-Pelletier et al, 2011;Cai et al, 2011Cai et al, , 2012Chen et al, 2014;Klammler et al, 2012;Kübert and Finkel, 2006;Li and Abriola, 2009;Li et al, 2007;MacKay et al, 2012;Schwede and Cirpka, 2010;Troldborg et al, 2010Troldborg et al, , 2012. Two of these studies were based on field trials (Béland-Pelletier et al, 2011;MacKay et al, 2012), two of the studies used flow and transport simulations within Monte Carlo frameworks (Chen et al, 2014;Kübert and Finkel, 2006); two more studies likewise used flow and transport simulations within Monte Carlo frameworks, but simulations were conditioned to field data (Schwede and Cirpka, 2010;Troldborg et al, 2010); and the remaining studies employed various conditional, geostatistical techniques, wherein one or more parameters across the control plane were treated as spatial random variables.…”

Section: Introductionmentioning

confidence: 99%

“…To achieve a~20% mean relative error for ṁ = 15 g/d, their results indicated a S D of~3 pt/m 2 would be needed. This work was extended by Li and Abriola (2009) who presented a staged sampling strategy, where optimal sample locations were identified by evaluating initial sampling results from mean C, local random variable entropy, and C conditional variance criterion. Compared to sampling densities based on a single sampling event with a regularly spaced grid, a sampling density of half or less was needed based on their staged approach.…”

Section: Introductionmentioning

confidence: 99%

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Screening-level estimates of mass discharge uncertainty from point measurement methods

Brooks

Young

Wood

et al. 2015

Journal of Contaminant Hydrology

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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.

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Comparison of upscaled models for multistage mass discharge from DNAPL source zones

Kokkinaki

Werth

Sleep

2014

Water Resources Research

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Analytical upscaled models that can describe the depletion of dense nonaqueous phase liquids (DNAPLs) and the associated mass discharge are a practical alternative to computationally demanding and data-intensive multiphase numerical simulators. A major shortcoming of most existing upscaled models is that they cannot reproduce the nonmonotonic, multistage effluent concentrations often observed in experiments and numerical simulations. Upscaled models that can produce multistage concentrations either require calibration, which increases the cost of applying them in the field, or use dual-domain conceptual models that may not apply for spatially complex source zones. In this study, a new upscaled model is presented that can describe the nonmonotonic, multistage average concentrations emanating from complex DNAPL source zones. This is achieved by explicitly considering the temporal evolution of three source zone parameters, namely source zone projected area, the average of local-scale DNAPL saturations, and the average of local-scale aqueous relative permeability, without using empirical parameters. The model is evaluated for two real and twelve hypothetical centimeter-scale complex source zones. The proposed model captures the temporal variations in concentrations better than an empirical model and a dual-domain ganglia-to-pool ratio model. The results provide evidence that effluent concentrations downgradient of DNAPL source zones are controlled by the evolution of the aforementioned macroscopic parameters. This knowledge can be useful for the interpretation of field observations of effluent concentrations downstream of DNAPL source zones, and for the development of predictive upscaled models. Advances in DNAPL characterization techniques are needed to quantify these macroscopic parameters that can be used to guide DNAPL remediation efforts.

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A multistage multicriteria spatial sampling strategy for estimating contaminant mass discharge and its uncertainty

Cited by 13 publications

References 57 publications

Mass Discharge in a Tracer Plume: Evaluation of the Theissen Polygon Method

Mass Discharge in a Tracer Plume: Evaluation of the Theissen Polygon Method

Screening-level estimates of mass discharge uncertainty from point measurement methods

Comparison of upscaled models for multistage mass discharge from DNAPL source zones

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