DFN-M field characterization of sandstone for a process-based site conceptual model and numerical simulations of TCE transport with degradation

Pierce, Amanda A.; Chapman, S.; Zimmerman, Laura K.; Hurley, Jennifer C.; Aravena, Ramón; Cherry, John A.; Parker, Beth L.

doi:10.1016/j.jconhyd.2018.03.001

Cited by 25 publications

(22 citation statements)

References 49 publications

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“…Groundwater flow was simulated using the discrete fracture package in HGS (Therrien et al 2010; Brunner and Simmons 2012). HGS was chosen because it is uniquely suited for simulating groundwater flow in fractured till because it can simulate coupled groundwater flow in both discrete fractures and porous media (Therrien and Sudicky 1996;Therrien et al 2010;Pierce et al 2018). HGS simulates 2-D flow in the fractures and 3-D flow in the porous media, while flow between the two domains is governed via a first-order fluid exchange term, , (Therrien et al 2010) discussed later in this section.…”

Section: Equations Of Flow In Hgsmentioning

confidence: 99%

“…As a result, characterizing fracture hydraulic properties and integrating them into numerical models should be an important component of contaminant transport investigations in fractured till. Such characterizations are not been routuinely performed, however, because explicitly simulating groundwater flow and solute transport in fractured porous media at scales larger than ~100 m 2 is exceptionally challenging (Neumann 2005, de Dreuzy et al 2012Pierce et al 2018).…”

Section: Introductionmentioning

confidence: 99%

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Estimation of the representative elementary volume of a fractured till: a field and groundwater modeling approach

et al. 2019

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Fractured till is often represented as an equivalent porous medium (EPM) in groundwater models. Knowledge of the representative elementary volume (REV) is necessary for proper application of an EPM model. While REV estimation and hydraulic conductivity tensor determinations are common in fractured rock studies, they are rarely applied to materials with a permeable matrix, such as fractured till. This study uses field fracture measurements, model simulations, and the FracKFinder toolbox to estimate the REV and determine hydraulic conductivity tensors for the fractured, late Wisconsinan till of the Dows Formation in central Iowa (USA), at depths of 1.0-1.5, 2.0-2.5, and 3.3-3.7 m. Results indicate that the REV of the till is directly related to both fracture density and transmissivity. REV size ranges from 4 to 5 m3 at depths of 1-2 m, where fractures are densest (P32 27.5 m2/m3) and most transmissive, to 2 to 3 m3 at depths of 3.3-3.7 m where fractures are least dense (P32 24.4 m2/m3) and least transmissive. Fracture hydraulic conductivity is five, four, and three orders of magnitude greater than matrix hydraulic conductivity at the shallowest to deepest depths of investigation, respectively. The results also suggest that hydraulic conductivity values estimated from permeameters and large-core laboratory experiments may not be of sufficient volume to represent the REV of fractured till.

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Section: Equations Of Flow In Hgsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Estimation of the representative elementary volume of a fractured till: a field and groundwater modeling approach

et al. 2019

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“…2). The hydrogeology of the site has been investigated intensively over the past 20 years because of the chemical contamination in groundwater (Pierce et al, 2018a;Pierce et al, 2018b;Sterling et al, 2005;MWH, 2009;Cherry J.A., 2009) and construction of a 3-D flow model (FeFlow) has been an on-going effort (AquaResource and MWH, 2007). For this model, information about the spatial distribution of recharge is needed as an upper boundary condition and to refine results of previous studies.…”

Section: Pagementioning

confidence: 99%

Spatial and temporal variability of groundwater recharge in a sandstone aquifer in a semi-arid region

Manna¹,

Murray²,

Abbey³

et al. 2018

Preprint

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Abstract. With the aim to understand the spatial and temporal variability of groundwater recharge, a high-resolution, spatially-distributed numerical model (MIKE SHE) representing surface water and groundwater was used to simulate responses to precipitation in a 2.16 km2 upland catchment on fractured sandstone near Los Angeles, California. Exceptionally high temporal and spatial resolution was used for this catchment modeling: an hourly time-step, a 20 × 20 meter grid in the horizontal plane and 240 numerical layers distributed vertically within the thick vadose zone and in the upper part of the groundwater zone. The finest-practical spatial and temporal resolution were selected to accommodate the large degree of surface and subsurface variability of catchment features. Physical property values for the different lithologies were assigned based on previous on-site investigations whereas the parameters controlling streamflow and evapotranspiration were derived from literature information. The calibration of streamflow at the outfall and of transient and average hydraulic head provided confidence in the reasonableness of these input values and in the ability of the model to reproduce observed processes. Confidence in the calibrated model was enhanced by validation through, (i) comparison of simulated average recharge to estimates based on the applications of the chloride mass-balance method from data from the groundwater and vadose zones within and beyond the catchment (Manna et al., 2016; Manna et al., 2017) and, (ii) comparison of the water isotope signature (18O and 2H) in shallow groundwater to the variability of isotope signatures for precipitation events over an annual cycle. The average simulated recharge across the catchment for the period 1995–2014 is 16 mm y−1 (4 % of the average annual precipitation), which is consistent with previous estimates obtained by using the chloride mass balance method (4.2 % of the average precipitation). However, one of the most unexpected results was that local recharge was simulated to vary from 0 to > 1000 mm y−1 due to episodic precipitation and overland runoff effects. This recharge occurs episodically with the major flux events at the bottom of the evapotranspiration zone, as simulated by MIKE SHE and confirmed by the isotope signatures, occurring only at the end of the rainy season. This is the first study that combines MIKE SHE simulations with the analysis of water isotopes in groundwater and rainfall to determine the timing of recharge processes in semi-arid regions. The study advances the understanding of recharge and unsaturated flow processes in semi-arid regions and enhances our ability to predict the effects of surface and subsurface features on recharge rates. This is crucial in highly heterogeneous contaminated sites because different contaminant source areas have widely varying recharge and, hence, groundwater fluxes impacting their mobility.

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“…1b,c). Fifth, the geologic Cl that existed when the sandstone formed has been removed by flushing during many millions of years of rainfall and groundwater flow 18 . Sixth, there is abundant information about the nature of the subsurface conditions based on studies of the vadose and groundwater zones that began in 1984, including studies of recharge 16,17,19,20 .…”

Section: Introductionmentioning

confidence: 99%

Five-century record of climate and groundwater recharge variability in southern California

Manna

Walton

Cherry

et al. 2019

Sci Rep

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Modifications to the rates of water flowing from the surface to groundwater (groundwater recharge) due to climate variability are the most difficult to assess because of the lack of direct long-term observations. Here, we analyze the chloride salt distribution below the surface soil on a plateau near Los Angeles to reconstruct the amount of recharge that occurred in the last five centuries. Over this time interval, periods of major high and low recharge with different duration follow each other and this cyclicity is consistent with long-term atmospheric forcing patterns, such as the Pacific Decadal Oscillation. This study determines the range and the natural variability of recharge to groundwater, which sustains local freshwater flow system, and helps forecast future availability of groundwater resource in southern California, where water scarcity is critical to both local and global populations.

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DFN-M field characterization of sandstone for a process-based site conceptual model and numerical simulations of TCE transport with degradation

Cited by 25 publications

References 49 publications

Estimation of the representative elementary volume of a fractured till: a field and groundwater modeling approach

Estimation of the representative elementary volume of a fractured till: a field and groundwater modeling approach

Spatial and temporal variability of groundwater recharge in a sandstone aquifer in a semi-arid region

Five-century record of climate and groundwater recharge variability in southern California

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