Testing and Standards: Water, Wastewater, Air and Noise (FE Civil)

NCEES FE Civil spec: Water Resources and Environmental Engineering, J. Testing and standards (e.g., water, wastewater, air, noise). FE Reference Handbook: Environmental Engineering chapter (Sampling and Monitoring, BOD test) and Safety chapter (Noise Pollution).

What the FE Civil Spec Covers

Section J covers testing and standards for water, wastewater, air and noise. Expect the BOD dilution test, suspended and volatile solids, what drinking water standards mean, the EPA criteria air pollutants, unit conversion for gas concentrations, and decibel arithmetic including the OSHA noise dose. The calculations are short; most of the difficulty is knowing which definition to use.

Key Concepts

BOD test. A diluted sample is incubated 5 days at 20°C in a 300 mL bottle and the DO drop is measured. Dilution keeps the final DO above zero; seed is added when the sample lacks microorganisms.
Solids. Total suspended solids (TSS) are retained on a filter and dried at 103 to 105°C. Volatile suspended solids (VSS) are the part lost on ignition at 550°C, a rough measure of organic (biological) solids.
Microbial indicators. Total and fecal coliforms (or E. coli) indicate possible contamination by pathogens; they are tested instead of each pathogen.
Drinking water standards. Under the Safe Drinking Water Act, primary standards set enforceable maximum contaminant levels (MCLs) for health. Secondary standards cover taste, odor and appearance and are not federally enforced. Examples: nitrate 10 mg/L as N, arsenic 0.010 mg/L, fluoride 4.0 mg/L; secondary pH range 6.5 to 8.5.
Air quality. The National Ambient Air Quality Standards cover six criteria pollutants: carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter (PM₁₀ and PM_2.5) and sulfur dioxide.
Noise. Sound pressure level is in decibels relative to 20 μPa. Levels add logarithmically, and a point source drops about 6 dB per doubling of distance.

Core Formulas

BOD from a dilution test, unseeded and seeded (P = sample volume / bottle volume, f = seed ratio):

B O D_{5} = \frac{D _{1} - D _{2}}{P} B O D_{5} = \frac{( D _{1} - D _{2} ) - ( B _{1} - B _{2} ) f}{P}

Total suspended solids from filter masses:

T S S = \frac{( m _{f i l t er + r es i d u e} - m _{f i l t er} )}{V _{s am pl e}}

Gas concentration conversion at 25°C and 1 atm (molar volume 24.45 L):

μ g/m^{3} = ppm \times \frac{M W \times 1000}{24.45}

Sound pressure level, adding sources, and point source attenuation:

S P L = 20 lo g_{10} \frac{P}{P _{0}} L_{t o t} = 10 lo g_{10} \sum 1 0^{L_{i} /10} Δ L = 20 lo g_{10} \frac{r _{2}}{r _{1}}

OSHA noise dose (C = hours exposed, T = hours allowed at that level):

D = 100% \times \sum \frac{C _{i}}{T _{i}}

Where It Is in the FE Reference Handbook

The BOD test solution and seeding procedure, plus sampling guidance, are in the Environmental Engineering chapter (Sampling and Monitoring and the wastewater treatment pages). Air pollution formulas are in the same chapter. Noise pollution and the OSHA permissible exposure table are in the Safety chapter.

Worked Example: BOD Test and Noise Exposure

Part 1. A 6 mL wastewater sample is diluted to 300 mL with unseeded dilution water. Initial DO is 8.8 mg/L and the 5-day DO is 4.3 mg/L. Find BOD₅.

P = \frac{6}{300} = 0.02 B O D_{5} = \frac{8.8 - 4.3}{0.02} = 225 mg/L

The DO dropped 4.5 mg/L and left a residual of 4.3 mg/L, so the test is valid (a common rule is a drop of at least 2 mg/L and a residual of at least 1 mg/L).

Part 2. Two machines produce 85 dB and 88 dB at a work station. A worker spends 4 h at 90 dBA, 2 h at 95 dBA and 2 h at 85 dBA. Find the combined level and the daily dose.

L_{t o t} = 10 lo g_{10} (1 0^{8.5} + 1 0^{8.8}) = 89.8 dB

Allowed times are 8 h at 90 dBA, 4 h at 95 dBA and 16 h at 85 dBA:

D = 100% (\frac{4}{8} + \frac{2}{4} + \frac{2}{16}) = 112.5%

The dose exceeds 100 percent, so the exposure is over the OSHA limit and must be reduced.

Common Mistakes

Dividing the DO drop by the sample volume in mL instead of the decimal fraction P.
Adding decibels arithmetically. 85 dB plus 88 dB is about 89.8 dB, not 173 dB.
Using 10 log for pressure ratios. SPL uses 20 log of pressure (or 10 log of pressure squared).
Treating secondary drinking water standards as enforceable MCLs.
Forgetting that a lead action level (treatment technique) is not the same as an MCL.

Practice Problems

Try these from the free PolyCalc FE Civil problem bank. Each one has a full worked solution.

A 10 mL sample of wastewater is diluted to 300 mL in a BOD bottle. The dissolved oxygen falls from 9.0 mg/L to 3.2 mg/L over 5 days, and the reaction rate constant is k = 0.23 day⁻¹ (base e). The ultimate BOD is most nearly: See the worked solution or practice the Environmental & Water Quality deck
Domestic wastewater is generated at roughly 0.30 kg BOD per person per day. An industrial discharge contributes 450 kg BOD per day. Its population equivalent is most nearly: See the worked solution or practice the Environmental & Water Quality deck
A treatment process decreases BOD from 200 mg/L to 20 mg/L. What is the BOD removal efficiency? See the worked solution or practice the Environmental & Water Quality deck
For a dilute aqueous solution, water with pH = 6 has an approximate hydrogen-ion concentration [H⁺] of: See the worked solution or practice the Environmental & Water Quality deck

Related Calculators and Examples

Frequently Asked Questions

How is BOD5 calculated from a dilution test?

For an unseeded sample, BOD5 equals the initial dissolved oxygen minus the dissolved oxygen after 5 days, divided by the decimal fraction of sample in the bottle. A 6 mL sample in a 300 mL bottle is a fraction of 0.02.

How do you add two noise levels in decibels?

Decibels are logarithmic, so convert each level to 10 raised to the level divided by 10, add those, then take 10 times the log of the sum. Two equal sources add 3 dB; for example two 85 dB machines give about 88 dB.

What is the OSHA permissible noise exposure?

OSHA allows 90 dBA for 8 hours, with the allowed time halving for every 5 dBA increase. The daily noise dose is the sum of actual time divided by allowed time at each level, and a dose above 100 percent exceeds the limit.

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