A drinking water well is located 1.6 km downgradient from a plume containing dieldrin entering the aquifer. How long will it take before the concentration of dieldrin in the well reaches 30% of the concentration at the origin of the plume? Pore-water velocity = 0.20 m/d Dx = 0.02 m2/d n = 0.45 Organic carbon content (for the primary sorbent) = 0.1% Bulk density = 1.8 g/cm3 k = 0.00002 d-1