Water Resources and Environmental Engineering — Quiz 8

Questions in this quiz (10)

1. A chemical analysis of a water sample indicates $$Ca^{++}$$ is at a concentration of $$10\ \mathrm{mg/L}$$ and $$Mg^{++}$$ is at a concentration of $$25\ \mathrm{mg/L}$$. The total hardness of the water expressed as $$CaCO_3$$ is most nearly:

   • 35.0
   • 58.5
   • 102.5
   • 127.5

2. A constructed wetland is designed to reduce BOD from $$60\ \mathrm{mg/L}$$ to $$15\ \mathrm{mg/L}$$ using first-order kinetics with a rate constant of $$0.18\ \mathrm{day^{-1}}$$. If the design flow is $$650\ \mathrm{m^3/day}$$, calculate the required wetland volume.

   • 2,780 m^3
   • 4,915 m^3
   • 3,860 m^3
   • 6,250 m^3

3. A ductile iron water main has a Hazen-Williams $$C$$ value of $$135$$ when new. After years of service, the $$C$$ value decreases to $$90$$. If the original head loss in a $$250$$ m section was $$2.95$$ m, what is the head loss in the aged pipe at the same flow rate?

   • 4.10 m
   • 5.86 m
   • 6.42 m
   • 3.75 m

4. A municipal activated sludge wastewater treatment plant with primary clarification and anaerobic digestion has the following influent characteristics: Flow = $$5\ \mathrm{MGD}$$ $$BOD_5=200\ \mathrm{mg/L}$$ If the plant $$BOD_5$$ removal efficiency is $$95\%$$ and the primary clarifier removes $$35\%$$ of the influent BOD, the amount of $$BOD_5$$ removed in the biological reaction in $$\mathrm{lb/day}$$ is most nearly:

   • 2,919
   • 5,004
   • 6,592
   • 7,923

5. The depth of flow in a channel at a section varies with time. This flow type is called:

   • Steady
   • Unsteady
   • Uniform
   • Non-uniform

6. Which statement of the following is INCORRECT about the energy line?

   • It is always above grade line.
   • It is defined as an imaginary line that represents the sum of total head line above a horizontal datum.
   • It is defined as an imaginary line that represents the pressure head along the pipe length.
   • It is based on Bernoulli's equation.

7. A water tank has a capacity of $$200{,}000$$ gal. The demand for water is estimated to be $$800$$ gal/min. The inflow into the tank is $$300$$ gal/min. The time in hours needed to empty $$95\%$$ of the tank is most nearly:

   • 4
   • 5
   • 6
   • 11

8. A $$2$$-in diameter, sharp-edge, orifice discharges freely into atmosphere from a tank. The water level is maintained at $$10$$ ft above the center of orifice. The orifice discharge rate in gallon/s is most nearly:

   • 0.34
   • 2.55
   • 49
   • 366

9. A rectangular channel has a width of $$2.5$$ m, Manning's $$n$$ of $$0.022$$, and a slope of $$0.0015$$ m/m. Calculate the normal depth for a discharge of $$3.8\ \mathrm{m^3/s}$$.

   • 1.18 m
   • 0.92 m
   • 1.45 m
   • 0.76 m

10. Two pumps are connected in series. Pump A produces $$18$$ m of head and Pump B produces $$22$$ m of head at the same flow rate. What is the total head produced by the system?

    • 40 m
    • 20 m
    • 36 m
    • 44 m