Alandfill is leaking an effluent with a concentration of chromium of 150 |mg/l. it seeps into an aquifer with a hydraulic conductivity of 7.5 m/day, a gradient of 0.0035, and an effective porosity of 0.15. a down-gradient monitoring well is located 75 m from the landfill. a) what would the sodium concentration be in this monitoring well 365 days after the leak begins? note: in this problem you will need to find erfc(-x), which is equal to 1+ erf(x)