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Quantifying Seepage Flux using Sediment Temperatures
Citation:
Lien, B. AND R. Ford. Quantifying Seepage Flux using Sediment Temperatures. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-14/454, 2014.
Impact/Purpose:
The report provides an overview of the use of temperature-based methods to determine groundwater seepage flux into surface water. Strengths, limitations and data requirements for each of the models are discussed to provide guidance for method implementation. Illustration of model use and verification is provided through examples of site characterization work conducted with a pond and a river receiving groundwater discharge.
Description:
This report provides a demonstration of different modeling approaches that use sediment temperatures to estimate the magnitude and direction of water flux across the groundwater-surface water transition zone. Analytical models based on steady-state or transient temperature solutions are reviewed and demonstrated. Case study applications of these modeling approaches are illustrated for two different field settings with quiescent and flowing surface water systems. For the quiescent system, application of two different steady-state models to evaluate temperature records from three depths is illustrated for estimating groundwater seepage into a pond. For the flowing water system, application of two different transient models is illustrated for estimating water exchange across a granular cap placed on top of sediments in a small river. The transient models use amplitude ratio or phase shift of diurnal temperature records from two depths to estimate seepage flux. These models require isolation of a diurnal signal component from the raw temperature time-series. Two diurnal signal extraction techniques of harmonic regression and bandpass filtering were implemented and compared. The results indicate that average calculated fluxes were indistinguishable for both signal isolation techniques. However, it was demonstrated that the harmonic regression technique provided greater detail in the temporal fluctuations in calculated seepage. Application of forward modeling using 1DTempPro with the VS2DH flow and heat-transport model to assess the reliability of calculated seepage from steady-state and transient models is also demonstrated. This report covers a period from 31 July 2011 to 31 July 2012 and work was completed as of 3 August 2012.