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Identifying the spatial distribution and magnitude of seepage flux across the groundwater-surface water (GW-SW) interface is critical for assessing potential impairments and restoration alternatives for water bodies adjacent to sites with groundwater contamination. Measurement of the vertical distribution and time-varying characteristics of temperature in sediments provides an indirect way to map out spatial and temporal patterns of seepage flux into surface water. Two spreadsheet-based calculation tools are introduced that implement four one-dimensional analytical solutions to calculate the magnitude and direction of seepage flux based on measurement of steady-state vertical temperature profiles or transient diel temperature signals at two depths within sediment. Performance of these calculation tools is demonstrated for a pond receiving contaminated groundwater discharge from an adjacent landfill. Transient versus steady-state model performance is compared, and limitations of transient modelsare illustrated for a situation with unfavorable sediment characteristics and inadequate sensor spacing. The availability of a range of analytical solutions implemented within Microsoft Excel® is intended to encourage practitioners to explore use of this seepage flux characterization method and develop greater insight into best practices for model selection and use., Plain Language Summary Open-access spreadsheet-based calculation tools are provided to make use of sediment temperature for estimating the magnitude and direction of seepage flux between groundwater and surface water. The performance of the different models coded in these tools is illustrated for a study site influenced by varying weather conditions.

Discharge of contaminated ground water may serve as a primary and on-going source of contamination to surface water. A field investigation was conducted at a Superfund site in Massachusetts, USA to define the locus of contaminant flux and support source identification for arsenic contamination in a pond abutting a closed landfill. Subsurface hydrology and ground-water chemistry were evaluated in the aquifer between the landfill and the pond during the period 2005–2009 employing a network of wells to delineate the spatial and temporal variability in subsurface conditions. These observations were compared with concurrent measures of ground-water seepage and surface water chemistry within a shallow cove that had a historical visual record of hydrous ferric oxide precipitation along with elevated arsenic concentrations in shallow sediments. Barium, presumably derived from materials disposed in the landfill, served as an indicator of leachate-impacted ground water discharging into the cove. Evaluation of the spatial distributions of seepage flux and the concentrations of barium, calcium, and ammonium-nitrogen indicated that the identified plume primarily discharged into the central portion of the cove. Comparison of the spatial distribution of chemical signatures at depth within the water column demonstrated that direct discharge of leachate-impacted ground water was the source of highest arsenic concentrations observed within the cove. These observations demonstrate that restoration of the impacted surface water body will necessitate control of leachate-impacted ground water that continues to discharge into the cove.

A laser-induced fluorescence system for in situ detection of soil contamination with cone penetrometer technology, capable of collecting three-dimensional fluorescence fingerprints (excitation–emission matrices, or EEMs) as the probe is advanced vertically, has been developed. In this report, we describe a recent field test at Hanscom Air Force Base, Massachusetts, in which we demonstrated successful operation of the system. The system uses a pair of silica-clad-silica optical fibers for each of its channels (eight of which were used in the work described), one to deliver excitation light from the multiwavelength laser excitation source to the sample, and the other to conduct contaminant fluorescence to a grating spectrograph that utilizes a charge-coupled-device detector to record fluorescence intensity as a function of both excitation and emission wavelength. The matrix-formatted field data are displayed as three-dimensional fingerprints of contamination at given push locations and depths; they are also reduced in dimension by summing over one or both wavelength axes and plotting summed fluorescence versus depth to facilitate visualization of the approximate extent of the contaminant plume. Selected EEMs from each push location are examined for characteristic patterns and compared to standard EEMs of pure compounds and fuels. © 1997 John Wiley & Sons, Inc. Field Analyt Chem Technol 1: 343–355, 1997

In this paper, a screening model for flow of a nonaqueous phase liquid (NAPL) and associated chemical transport in the vadose zone is developed. The model is based on kinematic approximation of the governing equations for both the NAPL and a partitionable chemical constituent. The resulting governing equation is a first-order, quasi-linear hyperbolic equation to which the generalized method of characteristics can be applied. This approach generally neglects the contribution to the NAPL flux from capillary pressure gradients. During infiltration under ponded conditions, or when the NAPL flux exceeds the maximum effective conductivity of the soil, the effect of capillary suction is included in the model through the usage of the Green-Ampt model. All of the resulting model equations are in the form of ordinary differential equations which are solved numerically by a variable time step Runge-Kutta technique. Results from a simple column experiment were used to evaluate the vadose zone flow model assumptions. Independently measured parameters allow simulation without calibration of the model results. The match of the model to the data suggests that the model captures the qualitative behavior of the experimental system and is capable of an acceptable degree of quantitative agreement.

Fiber optic probes employing single channel laser excitation and fluorescence collection have been seeing increasing use for remote sensing applications. However, multi-channel systems offer enhanced capacity for qualitative and quantitative determination of analytes. We describe a system which employs simultaneous delivery of laser excitation wavelengths arising from stimulated Raman scattering. Separate fluorescence responses for each excitation channel are imaged through a spectrograph onto a CCD array detector. Each channel has a dedicated fiber optic pair to deliver and collect light. REsults will be presented which evaluate the capabilities of this type of spectrometer for determination of organic contaminant mixtures in various sample matrices.