An aeated clarifier-type unit for grit removal and preaeration is 12 ft by 12 ft with an 8-ft liquid depth. The wastewater flow is 0.8 MGD with an estimated grit volume of 3 ft cubed/mil gal. A separate hopper-bottomed grit storage tank has a usable volume of 3 cubic yards. Compute the detention time in the aerated unit and the estimated length of time required to fill the storage tank with grit.