CIVE 2334 HOMEWORK PROBLEMS FALL 2021
HOMEWORK #1 (Air Pollution, Water Pollution)
1. The National Ambient Air Quality Standard (NAAQS) for sulfur dioxide (SO2) is 0.144 ppmv (24-hr average). What is the concentration in ug/m3 assuming an air temperature of 25 degrees C?
2. A water sample contains 10 mg NO3-/L. What is the concentration in (a) ppmm, (b) moles/L, (c) mg NO3 as N/L (this is mass of N per L), and (d) ppbm?
3. Formaldehyde (CH2O) is commonly found in the indoor air of improperly designed and constructed buildings. If the concentration of formaldehyde in a home is 0.7 ppm, and the inside volume is 800 cubic meters, what mass (in grams) of formaldehyde vapor is inside the home? Assume T=298K, P=1 atm.
4. A water quality analysis of a well water used for drinking water in a rural home found an arsenic concentration of 0.5 micromolar. This value seems very small to you. But you need to see if it still exceeds the drinking water standard of 10 ppbm. Is the well water violating the standard (and therefore the water would require treatment)?
5. Find out what air or water pollutants are being released in your hometown. Go to the EPA’s Toxics Release Inventory website, https:
www.epa.gov/toxics-release-inventory-tri-program
a. Go to the search engine at the bottom of the webpage, “Learn More About TRI in Your Community: Get Location-Based Factsheets and Information on Specific Facilities”. Search the zip code of your hometown (or cu
ent residence if there are no hits for your hometown). Browse the site—lots of interesting facts on who is releasing what chemicals to the environment. If there are not companies listed at this zip code, either try another zip code or instead search by metropolitan area and enter in the name of any city.
. Go to the section “Top five facilities by total disposal or other releases”. Click on one of the company names.
c. Review this TRI Facility Report for this company.
d. Report, in a list or table, the company name, what toxic chemicals are used/treated
eleased there, and what lbs of what chemical(s) was released in the most recent year for data, if these chemicals were air or water releases. Much of this information can be found under the “chemicals” or “releases” tabs.
HOMEWORK (Risk Assessment)
1. Consider a carcinogenic VOC with the dose-response curve shown in Figure P4.1 in the Masters & Ela textbook.
If 70-kg people
eathe 20 m3/day of air containing 10-3 mg/m3 of this VOC throughout their entire 70-year lifetime, find the cancer risk (you first need to find the potency). You may assume typical exposure values for air inhalation.
2. Suppose a city’s water supply has 0.2 ppb (1ppb=10-3 mg/L) of polychlorinated biphenyls (PCBs) in it. Using the PCB oral slope factor (7.7 (mg/kg-d)-1 and the EPA recommended exposure factors given in Table 6.14 below,
(a) What would be the individual lifetime cancer risk for an adult male residential consumer?
(b) In a city of 1 million people, use this risk assessment to estimate the number of extra cancers per year caused by the PCBs in the water supply. “Extra” cancers refers to cancers caused by PCBs (as opposed to other causes such as smoking, etc.)
(c) Assume the average cancer death rate in the United States in 193 per 100,000 per year. How many cancer deaths would be expected in a city of 1 million? Do you think the incremental cancers caused by PCBs in the drinking water would be detectable?
3. It has been estimated that about 75 million people in the Ukraine and Byelorussia were exposed to an average of 0.4 rem of radiation as a result of the Chernobyl nuclear accident. Human exposure to radiation is often measured in rems (roentgen-quivalent man) or millirems (mrem). The cancer risk caused by exposure to radiation is thought to be approximately 1 fatal cancer per 8,000 person-rems of exposure (for example, this is like saying when 8000 people are exposed to 1 rem each, one person will die of cancer caused by this exposure).
(a) How many extra cancer deaths might eventually be expected from this exposure?
(b) If the normal probability of dying of cancer from all causes is 0.22 (that is, 22% of any population of people will die of cancer), how many cancer deaths would you normally expect among those 75 million people?
4. A man works in an aluminum smelter for 10 years. The drinking water in the smelter contains 0.070 mg/L arsenic and 0.560 mg/L methylene chloride. His only exposure to these chemicals in water is at work. Recall the total HI (i.e. the total overall risk) is the sum of individual HI values.
(a) What is the hazard index (HI) associated with this exposure?
(b) Does the HI indicate this is a safe level of exposure?
(c) What is the incremental lifetime cancer risk for the man due solely to the water he drinks at work and does it seem to be an acceptable risk according to the EPA’s standard of acceptable risk?
5. Calculate a risk-based groundwater standard (in ppb) for the chemical 1,2-dichloroethane for a residential homeowner where the person’s well used for drinking water is contaminated with 1,2-dichloroethane. Assume the risk is for an average adult who weighs 70 kg. The state where you work has determined that an acceptable risk is one cancer occu
ence per 106 people. Use the values for route of intake, exposure frequency, exposure duration, and averaging time provided for residential use in the following table XXXXXXXXXXAssume an oral slope factor for 1,2-dichloroethane of 9.2x10-2 per (mg/kg)/day.
HOMEWORK (Environmental Chemistry)
1. Consider the following reaction representing the combustion of propane:
(a) Balance the equation.
(b) How many moles of oxygen are required to burn 1 mol of propane?
(c) How many grams of oxygen are required to burn 100 g of propane?
(d) At standard temperature (0 degrees C) and pressure, what volume of oxygen (in cubic meters) would be required to burn 100 g of propane? If air is 21 percent oxygen, what volume of air at STP would be required?
(e) At STP, what volume of CO2 (in cubic meters) would be produced when 100 g of propane are burned?
2. Suppose totally world energy consumption of fossil fuels, equal to 3 × 1017 kJ/yr, were to be obtained entirely by combustion of petroleum with the approximate chemical formula C2H3. Combustion of petroleum (with O2) releases an amount of energy about 43 × 103 kJ/kg (seems like a lot of moles of C2H3). Estimate the emissions of CO2 per year in units of kg CO2, assuming complete conversion of all C in petroleum to CO2.
3. Hydrochloric acid, HCl, completely ionizes to H+ and Cl- when dissolved in water. Calculate the pH of a solution after 25 mg/L of HCl is added to water.
4. Hydrogen sulfide (H2S) is an odorous gas that can be stripped from solution by bu
ling air through the solution. H2S when dissolved in water is also a weak acid that can deprotonate to bisulfide ions which are not removed by air stripping. That reaction is
With equili
ium constant Ka=0.86x10-7.
Find the fraction of hydrogen sulfide in the H2S form at pH 6 and pH 8. At which pH would you expect to have an easier time to strip away H2S gas?
5. Determine the equili
ium pH of aqueous solutions of the following strong acids or bases. Remember, strong acids and bases completely dissociate. (a) 15 mg/L of HSO4-, (b) 10 mM NaOH, (c) 2,500 ug/L of HNO3.
6. The chemical 1,4-dichlorobenzene (1,4-DCB) is sometimes used as a disinfectant in public lavatories. Its odor could be particularly annoying. At 20°C (68°F) the vapor pressure is 5.3 × 10-4 atm. What would be the concentration in the air in units of g/m3? The molecular weight of l,4-DCB is 147 g/mole.
7. Pure toluene comes into contact with groundwater. (a) What is the concentration of toluene in the water at equili
ium? (b) This groundwater flows slowly through the soil that has a foc value of 9%. Estimate the concentration (in mg/kg) of toluene in the soil at equili
ium.
HOMEWORK (Mass Balances, Reactors)
1. Five million gallons per day (MGD) of wastewater, with a concentration of 10.0 mg/L of a conservative pollutant, is released into a stream having an upstream flow of 10 MGD and pollutant concentration of 3.0 mg/L.
(a) What is the concentration in ppm just downstream?
(b) How many pounds of substance per day pass a given spot downstream?
2. A lake with constant volume 10 × 106 m3 is fed by a pollution-free stream with flow rate 50 m3/s. A factory dumps 5 m3/s of a nonconservative waste with concentration 100 mg/L into the lake. There is one outflow from the lake. The pollutant decays and has a first order reaction rate coefficient k of 0.25/day. Assuming the pollutant is well mixed in the lake, find the steady-state concentration of pollutant in the lake.
3. A lagoon is to be designed to accommodate an input flow of 0.10 m3/s of nonconservative pollutant with concentration 30.0 mg/L and reaction rate constant 0.20/day. The effluent from the lagoon must have pollutant concentration of less than 10.0 mg/L. Assuming complete mixing, how large must the lagoon be?
4. A lagoon with volume 1,200 m3 has been receiving a steady flow of conservative waste at a rate of 100 m3/day for a long enough time to assume that steady-state conditions apply. The waste entering the lagoon has a concentration of 10 mg/L. Assuming completely mixed conditions, what would be the concentration of pollutant in the effluent leaving the lagoon?
5. Repeat problem 4 for a nonconservative pollutant with rate constant k=0.20/d.
6. A mixture of two gas flows is used to cali
ate an air pollution measurement instrument. The cali
ation system is shown below. If the cali
ation gas concentration Ccal is 4.9 ppmv, the cali
ation gas flow rate Qcal is 0.010 L/min, and the total gas flow rate Qtotal is 1.000 L/min, what is the concentration of cali
ation gas after mixing (Cd)? Assume that the