Validation of an Innovative Groundwater Contaminant Flux Measurement Method

Flux measurement methods can be categorized as either point methods or integral methods. As the name suggests, point methods measure flux at a specific point or points in the subsurface. To increase confidence in the accuracy of the measurement, it is necessary to increase the number of points (and therefore, the cost) of the sampling network. Integral methods avoid this disadvantage by using pumping wells to interrogate large volumes of the subsurface. Unfortunately, integral methods are expensive because they require that large volumes of contaminated water be extracted and managed. HFTWs combine the advantages of each of the two approaches described above; that is, it s anintegral technique that samples a large volume of the subsurface while not requiring extraction of contaminated water from the subsurface. In this study, the accuracy of the HFTW flux measurement method was quantified by applying the method in an artificial aquifer, where the flux being measured was known. Two HFTW approaches, the multi-dipole approach and the tracer test approach, were compared to each other, as well as being compared to the transect method of measuring flux, which is the conventionally used point method. Results found that the transect and HFTW tracer test approaches provided reasonably accurate measures of flux (within 50% and 44% respectively) in the artificial aquifer, while the multi-dipole approach was too sensitive to small hydraulic head measurement errors to be useful. A comparison of the costs of applying the different methods at a generic site showed that the HFTW method had significant cost advantages.