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There is an identified need for fully representing groundwater-surface water transition zone (i.e., the sediment zone that connects groundwater and surface water) processes in modeling fate and transport of contaminants to assist with management of contaminated sediments. Most existing groundwater and surface water fate and transport models are not dynamically linked and do not consider transition zone processes such as bioturbation and deposition and erosion of sediments. An interface module is developed herein to holistically simulate the fate and transport by coupling two commonly used models, Environmental Fluid Dynamics Code (EFDC) and SEAWAT, to simulate surface water and groundwater hydrodynamics, while providing an enhanced representation of the processes in the transition zone. Transition zone and surface water contaminant processes were represented through an enhanced version of the EFDC model, AQFATE. AQFATE also includes SEDZLJ, a state-of-the-science surface water sediment transport model. The modeling framework was tested on a published test problem and applied to evaluate field-scale two- and three-dimensional contaminant transport. The model accurately simulated concentrations of salinity from a published test case. For the field-scale applications, the model showed excellent mass balance closure for the transition zone and provided accurate simulations of all transition zone processes represented in the modeling framework. The model predictions for the two-dimensional field case were consistent with site-specific observations of contaminant migration. This modeling framework represents advancement in the simulation of transition zone processes and can help inform risk assessment at sites where contaminant sources from upland areas have the potential to impact sediments and surface water.

Aiff°(H3+) is off by 3 kcal/mol (which is more than likely), this would bring the value up to AHf°298(H02) = 3.4 ± 2 kcal/mol, which is in good agreement with most data.A mean value °298( 02) = 3.5 kcal/mol is obtained by considering most of the data except those from Kochubei and Moin (which was ruled out) and from Khachatryan et al. (which has a large uncertainty). An upper limit of 4.5 is adopted from Foner and Hudson's measurements and Heneghan and Benson's measurements. A lower limit of 3.0 is assigned since three studies15•17•21 show that the value of AHf°(H02) has to be greater than 3.0 kcal/mol. Therefore, we recommend AHf°298(H02) = 3.5^5°kcal/mol as the best value.Acknowledgment. This work has been supported by the U.S. Army Research Office for scientific research under grant No. DAAG29-82-K-0043 and the National Science Foundation under grant No. CHE-79-26623. Registry No. Hydroperoxyl radical, 3170-83-0.

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Identifying or ruling out groundwater discharges into sediment and surface waters is often critical for evaluating impacts and for planning remedial actions. Information about subsurface structure and groundwater can be helpful, but imperfect information, heterogeneous materials, and the likelihood of preferential pathways make it difficult to locate seeps without direct seep monitoring. We present the practical application of a method that uses fiber optic temperature measurement to provide high-resolution, sensitive, and dynamic monitoring of seepage from sediments over large areas: distributed temperature sensing to identify groundwater discharge (DTSID). First, we introduce a stochastic Monte Carlo method for designing DTSID installation based on site characteristics and the required probability of detecting particular size seeps. We then present practical methods for analysing DTSID results to prioritize locations for further investigation used at three industrial locations. Summer conditions generally presented greater difficulty in the method due to stronger environmentally-driven temperature fluctuations and thermal stratification of surface water. Tidal fluctuations were shown to be helpful in seepage detection at some locations by creating a dynamic temperature pattern that likely reflects changing seepage with varying water levels. At locations with suitable conditions for the application of DTSID, it can provide unique information regarding likely seep locations, enhancing an integrated site investigation.