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2.35 The Department of Environmental Quality determined that toxaphene concentrations in soil
exceeding 60 µg/kg (regulatory action level) can pose a threat to underlying groundwater. (a) If a
100 g sample of soil contains 10-5 g of toxaphene, what are the (a) toxaphene soil and (b)
regulatory action level concentrations reported in units of ppbm?
Solution:
2.36 Polycyclic aromatic hydrocarbons (PAHs) are a class of organic chemicals associated with
the combustion of fossil fuels. Undeveloped areas may have total PAH soil concentrations of 5
µg/kg, while urban areas may have soil concentrations that range from 600 µg/kg to 3,000 µg/
kg. What is the concentration of PAHs in undeveloped areas in units of ppmm?
Solution:
2.37 The concentration of toluene (C7H8) in subsurface soil samples collected after an
underground storage tank was removed indicated the toluene concentration was 5 mg/kg. What is
the toluene concentration in ppmm?
Solution:
2.38 While visiting Zagreb, Croatia, Mr. Arthur Van de Lay visits the Mimara Art Museum and
then takes in the great architecture of the city. He stops at a café in the old town and orders a
bottle of mineral water. The reported chemical concentration of this water is: [Na+] = 0.65 mg/L,
[K+] = 0.4 mg/L, [Mg2+] = 19 mg/L, [Ca2+] = 35 mg/L, [Cl-] = 0.8 mg/L, [SO42-] = 14.3 mg/L,
[HCO3-] = 189 mg/L, [NO3-] = 3.8 mg/L. The pH of the water is 7.3. (a) What is the hardness of
the water in mg/L CaCO3? (b) Is the chemical analysis correct?
Solution:
2.39 The city of Melbourne, Florida has a surface water treatment plant that produces 20 MGD
of potable drinking water. The water source has hardness measured as 94 mg/L as CaCO3 and
after treatment, the hardness is reduced to 85 mg/L as CaCO3. (a) Is the treated water, soft,
moderately hard, or hard? (b) Assuming all the hardness is derived from calcium ion, what
would the concentration of calcium be in the treated water (mg Ca2+/L). (c) Assuming all the
hardness is derived from magnesium ion, what would the concentration of magnesium be in the
treated water (mg Mg2+/L).
1 𝑒𝑞𝑣 ) = 𝟐𝟎.𝟒 𝒎𝒈 𝐌𝐠𝟐+
2.40 A laboratory provides the following analysis obtained from a 50-ml sample of water. [Ca2+]
= 60 mg/L, [Mg2+] = 10 mg/L, [Fe2+] = 5 mg/L, [Fe3+] = 10 mg/L, Total solids = 200 mg/L,
suspended solids = 160 mg/L, fixed suspended solids = 40 mg/L, and volatile suspended solids =
120 mg/L. (a) What is the hardness of this water sample in units of mg/L as CaCO3? (b) What
is the concentration of total dissolved solids of this sample? (c) If this sample was filtered
through a glass-fiber filter, then the filter was placed in a muffle furnace at 550oC overnight,
what would be the weight of the solids (in mg) remaining on the filter after the night in the
furnace?
Solution:
2.41 In 2010 landfills in the U.S. produced approximately 107.8 Tg CO2e of methane emissions.
Wastewater treatment plants emitted 16.3 Tg CO2e of methane. (a) How many pounds and
metric tons of methane (reported as CO2 equivalents) did landfills and wastewater plants emit in
2010? (b) What percent of the total 2010 methane emissions (and greenhouse gas emissions) do
these two sources contribute (total methane emissions in 2010 were 666.5 Tg CO2e and total
greenhouse gas emissions in 2010 were 6,821.8 CO2e).
Solution:
2.42 Mobile combustion of N2O in 2010 emitted 20.6 Tg CO2e. How many Gg of N2O was this?
Solution:
2.43 Reverse osmosis is used to treat brackish groundwater water and requires 1 kWh of energy
per 1 m3 of treated water. In comparison, reverse osmosis of seawater requires 4 kWh of energy
per 1 m3 of treated water (this difference is because of the higher TDS concentration of
seawater). According to eGRID, the carbon dioxide equivalent emission rate is 1,324.79 lb
CO2e/MWh in Florida and 727.26 lb CO2e/MWh in California. Estimate the carbon footprint of
using reverse osmosis to desalinate 1 m3 brackish groundwater and 1 m3 sea water in Florida and
California. Ignore line losses in your estimate.
Solution:
2.44 Your home in Texas averages 24 kwh/day of electricity use. (a) what is your annual
estimate of individual greenhouse gas emissions of CO2, CH4, and N2O for operating the home?
(b) What is the carbon footprint (in lb CO2e) for living in the home for one year with and without
line losses included in the estimate?
Solution:
2.45 You are considering installing a 10kW solar system that will provide 14,000 kW-hr of
electricity per year (assume you live in the E-Grid subregion, SERC Midwest). Assuming your
electricity consumption remains the same, how much is your carbon footprint reduced every year
(in pounds of CO2) if you install the solar panels?
Solution:
2.46 You are considering purchasing a new television set and wish to factor in the energy
consequences of your purchase. You are considering a 55-inch screen model (screen is 49.75
inches high and 29.75 inches wide) and a 32-inch screen model (screen is 29.1 inches wide and
17.5 inches high). Research shows that for these particular models, the 55-inch screen consumes
0.10 Watts/in2 and the 32-inch screen consumes 0.17 Watts/in2. (a) Compare the two televisions
by determining the power rating (number of Watts) associated with each television size. Report
your answer in Watts, N-m/sec, and joules/sec. (b) How many kW-hr of energy are consumed
by each screen if you operate the television for 3 hours per day (? (c) Assuming that operating
the television for 1kW-hr produces 0.5453 kg of CO2, compare the two screen sizes in terms of
their carbon footprint calculated over a 365-day year (assume you operate the television 3 hours
per day).
Solution:
2.47 A laboratory provides the following solids analysis for a wastewater sample: TS = 200
mg/L; TDS = 30 mg/L; FSS = 30 mg/L. (a) What is the total suspended solids concentration of
this sample? (b) Does this sample have appreciable organic matter? Why or why not?
Solution:
2.48 A 100-mL water sample is collected from the activated sludge process of municipal
wastewater treatment. The sample is placed in a drying dish (weight = 0.5000 g before the
sample is added), and then placed in an oven at 104°C until all the moisture is evaporated. The
weight of the dried dish is recorded as 0.5625 g. A similar 100-mL sample is filtered and the
100-mL liquid sample that passes through the filter is collected and placed in another drying dish
(weight of dish before sample is added is also 0.5000 g). This sample is dried at 104°C and the
dried dish’s weight is recorded as 0.5325 g. Determine the concentration (in mg/L) of (a) total
solids, (b) total dissolved solids, (c) total suspended solids, and (d) volatile suspended solids,
(Assume that VSS = 0.7 x TSS.)
Solution:
