A small lake with volume of 160,000 m^3 receives agricultural drainage waters that contain 150 mg / L total dissolved solids (TDS). The drainage waters are the only source of water into the pond and evaporation is the only loss of water from the pond. Fluxes of water due to both evaporation and drainage water are 60,000 m^3 / year (the volume of the water in the lake will not change with time). If the lake is initially filled with water with 100 mg / L TDS, after how many years will the lake no longer be considered to contain freshwater?