For the particle-settling data shown in Question 9, plot the removal efficiency as function of overflow rate for overflow rates ranging from 0.5 to 4 m/h. Determine the overflow rate required to achieve 60 percent removal.

QUESTION 1 (25 marks) Part A A lake is being reclaimed by lowering the water table below the bottom of the lake. The lakebed consists of 10 meters of homogeneous clay, having a saturated volumetric weight of 18 kN/m². Below the clay, the soil is sand having a saturated volumetric weight of 20 kN/m². Initially, the water level is 2 m above the soil surface, after the reclamation the groundwater level is 2 m below the soil surface, and it is assumed that the soil remains saturated. Construct graphs of total stresses, effective stresses and pore pressures before and after the reclamation to a depth up to 15m from the surface. The density of water is 10 kN/m³ (10 marks) Part B A sand sample of 25 cm in length was subjected to a constant head permeability in a permeameter having an area of 30 cm². A volume of 180 cm³ was obtained in 1 minute under a head of 39 cm. The mass of dry sand in the sample was 1,350 g. The specific gravity of the sand particles was 2.67. Darcy's equation can be…

A constant velocity grit chamber is used in a small coastal community as a form of pre- treatment to incoming wastewater flows. The town regularly experiences a number of visitors during school holiday periods. If the usual wastewater flow is 10 ML per day, and the usual holiday period flow is 18 ML per day, design an appropriately sized grit chamber arrangement if the target grit has a diameter of 0.16 mm with a specific gravity of 2.75. Show your solutions for the following (but not necessarily in this order): 1. Determine the settling velocity for the target particle 2. Assuming a horizontal flow velocity of 0.32 m/s determine an appropriate overflow rate for the grit chamber 3. Determine an appropriate chamber length and cross sectional area and draw figures 4. Comment on how you could accommodate for the seasonal fluctuations in flows.

A rectangular settling tank is to treat 3.6MLD of raw water. The sedimentation period is to be 3 hours; the velocity of flow is 10 cm/min. The cross sectional area of the basin (in m², round off to the nearest integer) is