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AUTOMATED LONG-TERM REMOTE MONITORING OF SEDIMENT-WATER INTERFACIAL FLUX
Citation:
LIEN, B. K. AND C. G. Enfield. AUTOMATED LONG-TERM REMOTE MONITORING OF SEDIMENT-WATER INTERFACIAL FLUX. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-10/110, 2011.
Impact/Purpose:
To develop a ruggedized advective flux meter capable of unattended long-term remote monitoring of the sediment-water interfacial flux.
Description:
Advective flux across the sediment-water interface is temporally and spatially heterogeneous in nature. For contaminated sediment sites, monitoring spatial as well as temporal variation of advective flux is of importance to proper risk management. This project was conducted to develop a ruggedized advection flux meter capable of unattended long-term remote monitoring of the sediment-water interfacial flux. The flux meter, based on the heat-pulse technique, is capable of quantitatively measuring bi-directional seepage flux from 0 to 8 cm/day with the current configuration. The system has automatic data acquisition, real time data display, and signal display/analysis capability. A remotely controlled monitoring module was included to permit system monitoring and modification over the internet. The instrument has undergone several calibrations to establish relations between the flow rate and the heat-pulse travel time. For very low flow rates, an alternate approach was adopted based on the ratio of temperature rises. Using this approach, it is possible to accurately interpret flow rates down to zero flow conditions. Depending on the magnitude, flow rate can be derived as a function of peak temperature arrival time or as a ratio of rise in temperature on both sides of the heater. Using these two methods, reliable measurements can be made over a wide bi-directional range of flows. In the field operation, the flow across the sediment-water interface is isolated by a dome chamber and funneled through a flow sensor where the flow rate is measured. The advective flux through the sediment-water interface, in terms of the vertical Darcy velocity, is calculated by dividing the flow rate through the flow sensor by the cross-section area of the dome. The flux meter underwent a continuous long-term field test from June 2008 to April 2009 in the Red Cove area of Plow Shop Pond, Ford Devens, Massachusetts. Two flux meters were placed side by side; the unattended operation ran automatically with a self-sufficient power supply system. The measurement frequency was changeable through the wireless network. Seepage flux data was available for download after each measurement cycle. All of the data suggest very low flow and the majority of the data suggest an upward flow direction from the groundwater to the surface water. The average advective flux, in terms of Darcy velocity, for flux meter unit SN300 and SN303 was 0.44 ± 0.33 mm/day, respectively. Calculated seepage flux based on hydraulic conductivity and gradient data suggests the average flux was 1.12 ± 0.71 mm/day. During the winter months when the surface water was frozen, the data superficially suggests there was significant rapid oscillatory pumping of the ice-covered water during this period of time.
URLs/Downloads:
AUTOMATED LONG-TERM REMOTE MONITORING OF SEDIMENT-WATER INTERFACIAL FLUXAbstract
NRMRL Pubs Website