CE 452 – Introduction to Environmental Engineering

Second Semester 2013 Problem Set 1 Due: Thur, Feb 21

Stocks, Flows And Residence Time

1. Flaming Gorge Reservoir, was created by a large concrete arch dam at the mouth of Lodore Canyon on the Green River. The capacity of Flaming Gorge is about 1.25 million acre-ft when full. The average annual inflow to Flaming Gorge is about 3.0 million acre-ft.

a. Find the capacity of Flaming Gorge in cubic meters, and the flow through it

in cubic meters per year.

b. Determine the mean residence time of a drop of water (a molecule really) in the reservoir assuming the inflow and outflow of Flaming Gorge is at steady state. NOTE: one acre-ft = the area of one acre (43,560 sq. ft) times a one foot depth. It is a measure of volume that is commonly used in the US water resources profession

2. University Engineering Center Building has a volume of about 8000 m3. If all the air in the rooms were replaced, on average, every two hours, what would be the averaged airflow rate through the entire ventilation system?

AQUEOUS CONCENTRATIONS AND SIMPLE MASS BALANCE

3. During drinking water treatment, 17 lb of chlorine are added daily to disinfect 5 million gallons of water. What is the aqueous concentration of chlorine in mg/L? The chlorine demand is the concentration of chlorine used during disinfection. The chlorine residual is the concentration of chlorine that remains after treatment, and is used to maintain disinfecting capacity in the distribution system during the water's journey from the water treatment plant to a household. If the residual concentration is 0.20 mg/L, what is the chlorine demand?

4. Concentrations of nitrate exceeding 22.1 mg NO3-/L are a concern in drinking

water due to the infant disease, methemoglobinemia. Nitrate levels can be enhanced by improper use of synthetic and natural fertilizers, irrigation practices, livestock-handling operations, and industrial-waste handling. Due to the presence/ absence of animal wastes, fertilizer application, and groundwater recharge patterns, nitrate concentrations near three rural wells were reported as 0.01 mg NO3

- N/L, 5.3 NO3- N/L and 20 NO3

- N/L. Do any of these wells exceed the 22.1 ppm level?

5. Five million gallons per day (MGD) of a conservative substance, with concentration 10.0 mg/L, is released into a stream having an upstream flow of 10 MGD and substance concentration of 3.0 mg/L. Assume complete mixing.

a. What is the concentration in ppm just downstream? b. How many pounds of substance per day pass a given spot downstream?

6. A river with 400 ppm of salts (a conservative substance) and an up stream flow

of 25 m3/s receives an agricultural discharge of 5.0 m3/s carrying 2000 mg/L of salts. The salts quickly become uniformly distributed in the river. A municipality just downstream withdraws water and mixes it with enough pure water (no salt) from another source to deliver water having no more than 500 ppm salts to its customers. What should the mixture ratio (F) of pure water to the river water be?

APPLICATIONS OF IDEAL GAS LAWS AND UNIT DEFINITIONS

7. In a certain houses, the median indoor air concentration of Carbon Monoxide

(CO) was measured at 0.5 µg/cu. m.

a. What is the concentration of CO in ppb in the house air, assuming that T= 293 K and p= 1atm?

b. The same study that estimated the airborne concentration of CO reported

measurements of 40 µg/L in drinking water, in those same houses. What is that concentration in ppb in the drinking water?

c. A typical adult inhales about 20 cubic meters of air a day and drinks about

2L of water a day. What gives an adult occupying this house the greatest exposure? Air or water?

d. A carcinogen, carbon tetrachloride, CCl4, was found in the same houses.

The mean air concentration was 2.1 µg/cu.m, and the mean water

concentration was 0.10 µg/L