Unsaturated Hydraulic Characterization of Carbonatic Rock in the Laboratory

1. Geoscience Horizons November 2-5 Unsaturated Hydraulic Characterization of Carbonatic Rock in the Laboratory M.C. Caputo, Water Research Institute – IRSA–CNR, Bari, Italy J.R. Nimmo, US Geological Survey, Menlo Park, CA, USA A. Basile, ISAFOM–CNR, Napoli, Italy N. Walsh , Department of Geology and Geophysics - University of Bari, Italy

2. Geoscience Horizons November 2-5 Objective We measured in the laboratory the unsaturated hydraulic conductivity K(q) and water retention q(h) of several lithotypes of calcarenite using two methods: • a modification of Wind’s (1968) evaporation method for soils • a new quasi-steady centrifuge (QSC) method

3. Geoscience Horizons November 2-5 Materials • Calcarenite • Sedimentary rock • Marine origin • Widely found in the Mediterranean basin • Often constitutes a thick layer of the vadose zone Lithotypes tested • From Apulia in Southern Italy • Lithotypes A and B from same quarry, different depths • Lithotype M from a quarry in another area

4. Geoscience Horizons November 2-5 • Lithotype A • medium-fine grains • “grainstone” type • “grain-sustained” texture(*) • Lithotype B • biocalcarenite • medium-coarse grains • “packestone” type • “grain-sustained” texture(*) • Lithotype M • fine grains • “wackestone” type • “mud-sustained” texture(*) Materials The lithotypes tested vary in their proportions of lithoclasts, bioclasts, matrix, and cement. Thin sections photographed using an optical microscope (*) Dunham, 1962

5. Geoscience Horizons November 2-5 Methods Wind’s evaporation methodallows the simultaneous determination of q(h) and K(q). Required Assumptions • Homogeneous with respect to the property measured • Water flow obeys Darcy’s law [q= -K(h)dh/dz] • Potentials other than matric are neglegible • Sample is conceptually divided into compartments • Water content varies linearly within each compartment

6. Geoscience Horizons November 2-5 fan tensiometers sample load cell Methods • Wind’s method • The measured data include: • matric potential with depth and time, h(z,t) • average water content of the whole sample, qavg(t)

7. Geoscience Horizons November 2-5 Methods Wind’s method Convert matric potential values to water content using estimated water retention curve. Compare with the measured qavg(t). If differences are significant, estimate a new retention curve, iterate until discrepancies are tolerable. Use measured h(z,t) and calculated qe(z,t) to calculate the hydraulic conductivity, K(q).

8. Geoscience Horizons November 2-5 Methods Thequasi-steady centrifuge (QSC) method is based on the steady-state centrifuge (SSC) method, which has a steady flow of water within a sample in a centrifuge, applied by either a constant head (Nimmo et al., 1987) or a metering pump (Conca and Wright, 1998). If suitable conditions develop within the sample, hydraulic conductivitycan be computed using the centrifugal form of Darcy’s law. The QSC method somewhat relaxes the criterion for steadiness. This entails a slight increase in measurement uncertainty, but affords advantages including simpler apparatus, larger sample capacity, and adaptability to various machines and operating conditions. Thequasi-steady centrifuge (QSC) method: The steady-state centrifuge (SSC) method, which the QSC method derives from has a steady flow of water within a sample in a centrifuge, applied by either a constant head (Nimmo et al., 1987) or a metering pump (Conca and Wright, 1998). If suitable conditions develop within the sample, K(q) can be computed using the centrifugal form of Darcy’s law. The QSC method somewhat relaxes the criterion for steadiness. This entails a slight increase in measurement uncertainty, but affords advantages including simpler apparatus, larger sample capacity, and adaptability to various machines and operating conditions. Thequasi-steady centrifuge (QSC) method: The steady-state centrifuge (SSC) method, which the QSC method derives from has a steady flow of water within a sample in a centrifuge, applied by either a constant head (Nimmo et al., 1987) or a metering pump (Conca and Wright, 1998). If suitable conditions develop within the sample, K(q) can be computed using the centrifugal form of Darcy’s law. The QSC method somewhat relaxes the criterion for steadiness. This entails a slight increase in measurement uncertainty, but affords advantages including simpler apparatus, larger sample capacity, and adaptability to various machines and operating conditions.