Water Exam (Dan's Questions from test)

Question 1

Design considerations: 120 gal/capita/day
pipe 36” in diameter and 23,000 ft long
Planned operation: 5560 gpm
12 hours per day
Calculate the contact time for the carbon feed from the low service pumps to the rapid mixer at operating conditions.

a. 14 hours 57 min
b. 3 hours 38 min
c. 2 hours 23 min
d. 6 hours 34 min

Answer 1

B. 3 hours 38 min

Question 2

Planned operation: 5560 gpm, 12 hours/day
Operating data: Ca=260 mg/L as CaCO3; Free CO2= 3mg/L as CO2; Mg=76 mg/L as CaCO3; T.Alk=170 mg/L as CaCO3; Lime is 90% pure; Lime costs $85/Ton; CaO is used
What is the cost per MG to Lime soften this water?

a. $50 / MG
b. $56 / MG
c. $62 / MG
d. $65 / MG

Answer 2

b. $56 / MG

Question 3

Design Considerations: 120 gal/capita/day
Planned operation: 5560 gpm, 12 hours per day
Operating data: Raw PA 0 TA 110
Settled PA 40 TA 70 CO2=.15 lbs/cubic foot
Carbonated PA 28 TA 60

How many pounds per million gallons CO2 are needed for recarbonation in the model plant?

a. 42.75 lbs/MG
b. 51.38 lbs/MG
c. 59.45 lbs/MG
d. 65.20 lbs/MG

Answer 3

b. 51.38 lbs/MG

Question 4

Design considerations: 120 gal/capita/day; 4 filters each 32’ by 26’ overall; half filter 14’ by 26’ sand area
Planned operation: 5560 gpm, 12 hours per day; 46 half filter washes per month; 2,511,600 gallons of filter wash water.

What is the average half filter wash time if the rate of rise is 24 inches per minute?

a. 5 min
b. 10 min
c. 15 min
d. 20 min

Answer 4

b. 10 min

Question 5

Design considerations: 4 basins, 38’ by 106’ by 11’ deep
Planned operation: 5560 gpm, 12 hours per day

What is the flow thru velocity of the sedimentation basins? (2 basins are in use)

a. 1.78 ft/min
b. .89 ft/min
c. .59 ft/min
d. .32 ft/min

Answer 5

b. .89 ft/min

Question 6

Design considerations: 120 gal/capita/day, 30 days in a month
Planned operation: 5560 gpm, 12 hours per day
Operating data: 1465 lbs Na2SiF6 per month, 61%

Calculate the applied value of fluoride ion in mg/L.

a. 0.66 mg/L
b. 0.89 mg/L
c. 0.93 mg/L
d. 0.99 mg/L

Answer 6

b. 0.89 mg/L

Question 7

Design considerations: 120 gal/capita/day; 17.1 mg/L = 1 gpg
Planned operation: 5560 gpm, 12 hours per day
Operating data: Ca=258 mg/L as CaCO3; Mg=75 mg/L as CaCO3; TA=280 mg/L as CaCO3; Free CO2=40 mg/L as CaCO3

Calculate the approximate cost of ion exchange softening of this water to a hardness of 90 mg/L, assuming a costs $35 per ton and 0.20 pounds of salt per 1,000 grains of hardness removed.

a. $35.00 MG
b. $46.23 MG
c. $49.74 MG
d. $54.78 MG

Answer 7

c. $49.74 MG