# Question: runoff from a highway contains initially high concentrations of metals...

###### Question details

Runoff from a highway contains initially high concentrations of metals that have accumulated on the roadway during dry periods and are released in the first impulse of rainfall runoff. An engineer proposes to build a series of four ponds to treat the runoff water rather than one large one. If the runoff flow rate is 0.56 cfs with an initial metal impulse of 226 g, plot the effluent concentrations (in m/L) from treatment system A (four ponds with a volume of 1000 ft3 each) and from treatment system B (one pond with a volume of 4000 ft3) over a 12 hr period. Assume the ponds are full initially with zero initial metal concentration and operate with completely mixed conditions. If the treatment objective is 1.8 mg/L, explain the value of the multi-pond design. Is this "treatment" truly better?