Fig. 3.

Composition of groundwater with three distinct vertical redox zonations flowinginto the model at the upland boundary (left), the simulation result of As plume migration and Fe oxide precipitation using SCM based PHT3D after 80 years of model run (middle), and the comparison of simulated groundwater As over 80 years between parametric Kd based model (dashed lines) and SCM based model (solid lines) (right). Arrows indicate variable recharge rates parameterized to simulate nearshore circulation due to tides and waves, and the white box (right corner, middle panel) on the bay side indicates a 2-m river boundary. In the middle reducing layer (2-4 m), the model has 4 zones to capture the geochemical gradient with increasing surface site density and Kd values towards the bay. Contour interval for As is 3 μg/L. Observed total dissolved As at PZ10 (circle), PZ6 (square), and PZ3 (triangle) compare well with SCM based model. Simulated Fe oxide ranging from 3 to 15 mg/kg has the contour intervalof 3 mg/kg.