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Title: IMPROVED TENSION INFILTROMETER FOR MEASURING LOW FLUID FLOW RATES IN FRACTURED ROCK

Author
item CASTIGLIONE, PAOLO - LRES, MONTANA ST UNIV
item Shouse, Peter
item MOHANTY, BINAYAK - TEXAS A&M UNIV., TEXAS
item HUDSON, DAVID - USGS, LAS VEGAS, NV
item Van Genuchten, Martinus

Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2004
Publication Date: 8/16/2005
Citation: Castiglione, P., Shouse, P.J., Mohanty, B., Hudson, D., Van Genuchten, M.T. 2004. Improved tension infiltrometer for measuring low fluid flow rates in fractured rock. Vadose Zone Journal. 4:885-890.

Interpretive Summary: Tension infiltrometers are used to characterize water flow through soils and fractured rock. Most commercially available tension infiltrometers were developed to measure moderately fast flow rates. Slow flow rate characteristic of geologic deposits (rock) require a modified infiltrometer. We designed and built an infiltrometer system to accurately measure infiltration into rock formations and other low flow applications (clay soils). Our results showed that our improved design reduces temperature effects, allowed for longer periods of unattended operation (auto-refill), and nearly eliminated evaporation from the infiltrometer. We were able to make measurements of fluid fluxes as low as 10 mm/yr.

Technical Abstract: The search for a permanent storage facility for the geological disposal of high-level nuclear waste has motivated extensive research during the past several decades to characterize and predict fluid flow into and through unsaturated fractured rock. Tension infiltrometer experiments are extremely useful to investigate infiltration into fracture networks, but are most difficult to perform using commercially available equipment developed for mostly for soils. Our objective was to develop a tension infiltrometer suited for accurate measurements of infiltration into fractured rock for very low flow rates and long equilibration times. We constructed several prototype instruments from porous stainless steel membrane, stainless steel, acrylic tubing, several pressure transducers, solenoid valves, and a data logger for automated control and data acquisition. Design criteria were examined that minimize the influence of temperature fluctuations on flux measurements. An automated refill system was additional developed to facilitate long unattended equilibration periods typical for infiltration experiments on fractured rock. Results show that the improved design reduces temperature effects on the infiltration rate, allow for much longer periods of unattended operation (auto-refill), and reduces evaporation from the infiltrometer. We were able to make measurements of the fluid flux of as low as 10 mm/yr at a pressure heads of about -120 cm.