An industry is illegally dischargingbenzeneinto a river. The concentration in the river atthe point of discharge is 0.2mg/L. A drinking water treatment plant (DWTP) is located 1.5km downstream. The watervelocity in the riveris 0.35km/day.
A. What is the hydraulic residence time of the river between the discharge point and the DWTP?
B.If benzene degrades with a first-order rate constantk= 0.75d-1, what is the benzene concentration at the DWTPat steady state?
C.The oral potency factor for benzene is2.9×10-2(mg/kg-d)-1(text,Table 4.9). If a 70 kg person drinks 2 L of the water from the DWTP every day, is the lifetime cancer risk greater than 1 in one million? Assume no removal in drinking water treatment.