Ariver with a discharge of 10 m3/s carries a concentration of 10 ppb of benzene and discharges into a 5,000,000 mº lake. at time zero, a plant begins discharging 1 m3/s with 20 ppb of benzene. what is the concentration of benzene leaving the lake 7 days after the plant begins discharging? the benzene decay coefficient for the lake is 0.001mg/l-day. a. 5.0 ppb b. 5.1 ppb c. 5.2 ppb d. 5.3 ppb e. 5.4 ppb f. 5.5 ppb g. 5.6 ppb h. 5.7 ppb