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Radon-222 as a Tracer for Nonaqueous Phase Liquid in the Vadose Zone

Experiments and Analytical Model

^a Swiss Federal Institute of Technology (EPFL), ENAC-ISTE-LPE, CH-1015 Lausanne, Switzerland
^b University of Neuchâtel, Center for Hydrogeology (CHYN), Rue Emile Argand 11, CH-2007 Neuchâtel, Switzerland

View larger version (15K): [in a new window]   Fig. 1. Measured 222Rn activities in the batch experiments as a function of volumetric NAPL content n (black diamonds, two to three repeated measurements, counting errors of 10%), and predicted 222Rn activities (solid line), using Eq. [4]. Broken lines represent errors of 10% in the air–NAPL partitioning coefficient.

View larger version (31K): [in a new window]   Fig. 2. Modeled 222Rn activities in a homogeneous sandy vadose zone: (A) influence of volumetric NAPL content n and (B) influence of volumetric water content w.

View larger version (29K): [in a new window]   Fig. 3. Modeled 222Rn activities in a heterogeneous sandy vadose zone with two layers of equal thickness having different volumetric NAPL contents n: (A) NAPL contamination in upper layer and (B) NAPL contamination in lower layer.

View larger version (59K): [in a new window]   Fig. 4. Modeled 222Rn activities in a heterogeneous sandy vadose zone with a impermeable surface cover. The upper layer is contaminated with NAPL, similarly as in Fig. 3A.

View larger version (21K): [in a new window]   Fig. 5. Modeled 222Rn activities in a heterogeneous sandy vadose zone with three vadose zone layers. (A) Only an intermediate layer from the 1- to 1.2-m depth is contaminated with different volumetric NAPL contents n (corresponding to Fig. 6). (B) A 0.2-m-thick intermediate layer with n = 0.08 (16 L NAPL m–2) is placed at different depths, with L1 being the depth to contamination.

View larger version (30K): [in a new window]   Fig. 6. Measured 222Rn activities in lysimeter experiment. NAPL content n were 0.01 (Day 10), 0.003 (Day 28), and <0.001 on Day 287 in the intermediate layer between 1 and 1.2 m depth. Error bars represent 5% for the activity measurements, and ±0.1 m for depth (accounting for the reach of sampling tubes).