LNAPL Recovery Endpoints: Lessons Learnt Through Modeling,Experiments, and Field Trials     

Kaveh Sookhak Lari  John L. Rayner  Greg B. Davis  Colin D. Johnston 《Ground Water Monitoring & Remediation》2020,40(3):21-29

It is important to estimate what light nonaqueous phase liquid (LNAPL) recovery can be practicably achieved from subsurface environments. Over the last decade, research to address this included a broad field program, laboratory measurements and experimentation, and modeling approaches. Here, we consolidate key findings from the research in the context of current literature and understanding, with a focus on a well-validated, multiphase multicomponent modeling approach to achieve estimates of reasonable endpoints for LNAPL recovery. Simple analytical models can provide approximate saturation distributions and estimates of LNAPL recoverability via transmissivity approximation, but are insufficient to predict LNAPL saturation- and composition-based recovery endpoints for various recovery technologies. This is because they cannot account for multiphase, multicomponent fate and transport and key processes such as hysteresis. Recent advances to improve estimates of the fraction of recoverable LNAPL and its transmissivity are summarized. These advances include further development and application of a well-validated model to characterize active LNAPL recovery endpoints. We present key factors that affect the determination of LNAPL recovery endpoints, and outline how recovery endpoints are affected by natural source zone depletion (NSZD—currently gaining acceptance as a LNAPL remediation option). Major factors include geo-physical characteristics of the formation, magnitude of an LNAPL release and partitioning properties of the key LNAPL constituents of concern. Based on the capabilities of the validated model, the paper also provides a basis to optimize LNAPL recovery efforts.  相似文献   

Evaluation of Bias Associated with Capture Maps Derived from Nonlinear Groundwater Flow Models          下载免费PDF全文

Cara Nadler  Kip Allander  Greg Pohll  Eric Morway  Ramon Naranjo  Justin Huntington 《Ground water》2018,56(3):458-469

The impact of groundwater withdrawal on surface water is a concern of water users and water managers, particularly in the arid western United States. Capture maps are useful tools to spatially assess the impact of groundwater pumping on water sources (e.g., streamflow depletion) and are being used more frequently for conjunctive management of surface water and groundwater. Capture maps have been derived using linear groundwater flow models and rely on the principle of superposition to demonstrate the effects of pumping in various locations on resources of interest. However, nonlinear models are often necessary to simulate head‐dependent boundary conditions and unconfined aquifers. Capture maps developed using nonlinear models with the principle of superposition may over‐ or underestimate capture magnitude and spatial extent. This paper presents new methods for generating capture difference maps, which assess spatial effects of model nonlinearity on capture fraction sensitivity to pumping rate, and for calculating the bias associated with capture maps. The sensitivity of capture map bias to selected parameters related to model design and conceptualization for the arid western United States is explored. This study finds that the simulation of stream continuity, pumping rates, stream incision, well proximity to capture sources, aquifer hydraulic conductivity, and groundwater evapotranspiration extinction depth substantially affect capture map bias. Capture difference maps demonstrate that regions with large capture fraction differences are indicative of greater potential capture map bias. Understanding both spatial and temporal bias in capture maps derived from nonlinear groundwater flow models improves their utility and defensibility as conjunctive‐use management tools.  相似文献   

A simple algorithm for generating streamflow networks for grid‐based,macroscale hydrological models     

Greg O'Donnell  Bart Nijssen  Dennis P. Lettenmaier 《水文研究》1999,13(8):1269-1275

A simple algorithm for generating streamflow networks for macroscale hydrological models (MHMs) from digital elevation models (DEMs) is presented. Typically these hydrological models are grid based, with the simulated runoff produced within each cell routed through a stream network which connects the centers of cells in the direction of the major streams. Construction of such stream networks is a time consuming task, which has generally been done by hand with the aid of maps. Results indicate that the algorithm works satisfactorily in areas of both high and low relief, and for a wide range of model cell resolutions, although some manual adjustments may be necessary. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Defrocking the false father of the ‘Driftless Area’, USA     

Greg Brick 《Geology Today》2023,39(2):62-66

The Driftless Area is a designation popular in American promotional tourist literature for an area in four contiguous American states, Minnesota, Wisconsin, Iowa and Illinois, that were not glaciated during the latest ice advance. Geographer Lawrence Martin published several articles asserting that geologist William H. Keating first discovered this area in 1823, an error that has crept into subsequent accounts. But historical evidence goes to show that three geologists, Roland D. Irving, Newton H. Winchell and Thomas C. Chamberlin, were simultaneous originators of the concept as we understand it today, about the year 1877.  相似文献