Results are presented for a large-scale natural gradient tracer experiment conducted in a heterogeneous alluvial aquifer at a site near Columbus, Mississippi. The study was initiated with a 48-hour pulse injection of 10 m 3 of groundwater containing bromide and three organic tracers (pentaftourobenzoic acid, o-trifiuoromethylbenzoic acid, and 2,6-diflourobenzoic acid). Over a 20-month period, seven comprehensive samplings of the tracer plume were performed at approximately 1-to 4-month intervals using an extensive three-dimensional sampling well network. The dominant feature of the tracer plume that evolved during the study was the highly asymmetric concentration distribution in the longitudinal direction. This asymmetry was produced by accelerating groundwater flow along the plume travel path that, in turn, resulted from an approximate 2-order-of-magnitude increase in the mean hydraulic conductivity between the near-field and far-field regions of the site. The Columbus study is distinct from previous natural gradient experiments because of the extreme heterogeneity of the aquifer, the large-scale spatial variations in groundwater velocity, and the extensive set of hydraulic conductivity measurements for the aquifer.

This paper discusses the latest developments in wide-area frequency-based event location using FNET. FNET, meaning "Internet Based Frequency Monitoring Network," is a low cost and quickly deployable wide-area frequency measurement system with high dynamic accuracy. This project demonstrated the feasibility of using information from FNET to estimate the location of events in the electric grid. An on-line real time event detection tool using least squares methods was developed and tested on data from FNET. This paper outlines the methods used along with an examination of implementation feasibility.

This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination.

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