Poor Interconnectivity Research Articles

Creation of an Artificially Produced Fracture Zone to Prevent Contaminated Ground‐Water Migration

ABSTRACTRecovery of contaminated ground water in a fractured bedrock system presents some unique problems. Typically, the most common problem occurs from the inability to adequately characterize the discrete fractures through which contaminants may be migrating. Without adequate characterization, difficulties arise in properly positioning recovery wells and verifying the performance of the system. To overcome these difficulties at a site in Upstate New York, an innovative approach was developed involving the creation of an artificial fracture zone through controlled blasting to intercept contaminated ground‐water flow.Site investigations delineated the extent of a ground‐ water contamination plume migrating within a fractured bedrock aquifer (Medina sandstone) which underlies approximately 15 ft of glacial till. A 72‐hr aquifer test involving one recovery well resulted in a low yield (3.5 gpm with 20 ft of drawdown). Data collected from adjacent observation wells indicated poor interconnection among the naturally occurring fractures. Although the response of some observation wells mirrored that of the recovery well, others showed little or no response to pumping. Therefore, achieving the corrective action objectives (i.e., preventing further contaminant migration and removing and treating contaminated ground water) would be difficult using a “traditional” multiple recovery well system. It was decided that controlled linear blasting could provide the enhanced fracture interconnection necessary to successfully intercept the contaminated ground‐water plume, which would then be captured and removed by judicious placement of recovery well(s) installed within the fracture zone.Using a carefully controlled single line pattern blasting technique, a 6‐ft wide, 300‐ft long fracture zone was created in the upper 25 ft of the bedrock aquifer perpendicular to the centerline of the plume. Following fracturing, a second 72‐hr aquifer test was conducted at the same location and under conditions similar to the first test. The second test indicated that the single recovery well located in the newly created fracture zone should be fully capable of recovering contaminated ground water and preventing further migration of the plume. The recovery well produced a substantially higher yeild of 18.5 gpm with only 11.2 ft of drawdown. Futhermore, all of the nearby observation wells showed significant response to pumping.Success at this site is promising, and the approach may prove useful at other sites involving contaminated bedrock aquifers.

Frequency analysis of the EEG under different behavioral states : D. Giannitrapam (Chicago, Ill., U.S.A.)

Multichannel EEG recordings from 18 healthy subjects were used to investigate brain activity in four delta subbands during two mental arithmetic tasks (number comparison and two-digit multiplication) and a control condition. The spatial redistribution of signal-power (SP) was explored based on four consecutives subbands of the delta rhythm. Additionally, network analysis was performed, independently for each subband, and the related graphs reflecting functional connectivity were characterized in terms of local structure (i.e. the clustering coefficient), overall integration (i.e. the path length) and the optimality of network organization (i.e. the “small-worldness”). EEG delta activity showed a widespread increase in all subbands during the performance of both arithmetic tasks. The inter-task comparison of the two arithmetic tasks revealed significant differences, in terms of signal-power, for the two subbands of higher frequency over left hemisphere (frontal, temporal, parietal and occipital) regions. The estimated brain networks exhibited small-world characteristics in the case of all subbands. On the contrary, lower frequency subbands were found to operate differently than the higher frequency subbands, with the latter featuring nodal organization and poor remote interconnectivity. These findings possibly reflect the deactivation of default mode network and could be attributed to inhibitory mechanisms activated during mental tasks.