Water Supply - Questions

1. Lab analysis of a water sample is as follows:

Ca++ = 75.0 mg/L
Mg++ = 18 mg/L
Na+ = 28 mg/L
K+ = 39 mg/L
pH = 7.7
HCO3- = 275 mg/L
SO4-- = 72 mg/ L
Cl- = 50 mg/L

a) What is the hardness in terms of calcium carbonate equivalent?
b) Assume compounds are formed proportionally to the relative concentrations of ions. What is the concentrations of calcium bicarbonate?
c) What is the concentrations of magnesium bicarbonate?
d) What is the concentrations of magnesium sulfate?
e) What is the amount of lime (CaO) needed to remove calcium carbonate hardness?

2. A spherical sand particle has an SG of 2.5 and a diameter of 1.1 mm. Determine the settling velocity.

3. Water supply for a town of 14,000 people is taken from a river. Average consumption is 115 gpcd and the water has the following attributes:

turbidity = 25 to 95 NTU (varies)
total hardness = less than 60 mg/L as CaCO3
coliform count = 250 to 950 for 100 mL (varies)

a) what capacity should the distribution and treatment system have?
b) If application rate is 4 gal/min, what total filter area is required?
c) If a Chlorine dose of 2.5 mg/L is required for desired residual, how much Cholrine is required every 24 hours?