PE Civil: Water Resources & Environmental practice set
40 exam-style problems with fully worked solutions, by Michael Flynn, PE. Every wrong answer choice is the number you get from one specific, common mistake, and the solutions explain each one, so you learn the traps as well as the method.
40 problems · 23 pages · answer key · full worked solutions · why each wrong answer is wrong
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What's in it
| Topic | Problems |
|---|---|
| Closed-conduit hydraulics | 6 |
| Open-channel hydraulics | 7 |
| Hydrology | 7 |
| Groundwater and wells | 4 |
| Water treatment | 6 |
| Wastewater treatment | 6 |
| Water distribution | 4 |
- Each problem lists the search terms that find the right equation in the NCEES handbook. The exam is computer-based and you search the handbook on screen, so finding things fast matters.
- Every number was computed by script from the stated equations, and no two answer choices are within 4% of each other.
- Where a free pe-calc calculator covers the topic, the solution links to it so you can try your own variations.
Try five problems free
Water at 60°F (ν = 1.217 × 10⁻⁵ ft²/s) flows at 2.5 cfs through 1,500 ft of 8-in new commercial steel pipe (ε = 0.00015 ft). Using the Swamee-Jain friction factor, the head loss (ft) is most nearly:
Show answer and worked solution
- A = πD²/4 = π(0.6667 ft)²/4 = 0.3491 ft²; V = Q/A = 7.162 ft/s
- Re = VD/ν = (7.162)(0.6667)/(1.217 × 10⁻⁵) = 392,329 (turbulent)
- ε/D = 2.25 × 10⁻⁴; f = 0.25/[log₁₀(ε/3.7D + 5.74/Re⁰·⁹)]² = 0.0161
- h_f = f(L/D)V²/2g = 0.0161(2,250)(7.162)²/(2 × 32.2) = 28.81 ft
Why the other choices are wrong
- (A) 1.920: reported the loss per 100 ft of pipe
- (B) 2.401: used D = 8 (inches) in L/D
- (C) 4.022: used V instead of V² in the velocity head
Check it with the free calculator: pe-calc.com/tools/darcy-weisbach.html
A pond outlet is a 4 ft × 4 ft riser box (crest perimeter 16 ft, Cw = 3.0; open top 16 ft², Cd = 0.6) draining through a 24-in barrel. With the pond 1.5 ft above the riser crest, the barrel can pass 32 cfs at that pond stage. The pond outflow (cfs) is most nearly:
Show answer and worked solution
- Crest as a weir: Q = 3.0(16)(1.5)¹·⁵ = 88.18 cfs; top as an orifice: Q = 0.6(16)√(2g × 1.5) = 94.35 cfs
- The riser passes the lesser: 88.18 cfs
- The riser drains INTO the barrel, so the two act in series: the pond passes the lesser of riser and barrel
- Q = min(88.18, 32) = 32.00 cfs (barrel control)
Why the other choices are wrong
- (B) 88.18: ignored the barrel (riser capacity only)
- (C) 94.35: used orifice flow on the riser top only
- (D) 120.2: added riser and barrel as if in parallel
Check it with the free calculator: pe-calc.com/tools/culvert.html
A watershed with CN = 78 receives 5.0 in of rain. Using Ia = 0.2S, the runoff depth (in) is most nearly:
Show answer and worked solution
- S = 1,000/CN − 10 = 2.821 in; Ia = 0.2S = 0.5641 in
- Q = (P − Ia)²/(P − Ia + S) = (4.436)²/(7.256) = 2.712 in
Why the other choices are wrong
- (A) 0.3889: used S = 1,000/CN (forgot the −10)
- (C) 3.197: left out initial abstraction (Ia = 0)
- (D) 4.436: took runoff as P − Ia (no retention term)
Check it with the free calculator: pe-calc.com/tools/scs-runoff.html
A 0.5-MG clearwell (baffling factor 0.3) receives a peak-hour flow of 3.0 MGD. The free chlorine residual at the outlet is 1.2 mg/L. The CT provided (mg·min/L) is most nearly:
Show answer and worked solution
- HDT = V/Q = 0.5/3.0 × 1,440 = 240.0 min
- T₁₀ = BF × HDT = 0.3 × 240.0 = 72.00 min
- CT = C × T₁₀ = 1.2 × 72.00 = 86.40 mg·min/L
Why the other choices are wrong
- (A) 1.440: left T₁₀ in hours
- (C) 288.0: used the full detention time (no baffling factor)
- (D) 960.0: divided by the baffling factor
Check it with the free calculator: pe-calc.com/tools/chlorine-disinfection.html
A 1.2-MG aeration basin holds MLSS of 3,000 mg/L. Waste sludge is 0.040 MGD at 10,000 mg/L, and the 4.96-MGD effluent carries 15 mg/L TSS. The SRT (days) is most nearly:
Show answer and worked solution
- SRT = VX/(Q_wX_w + Q_eX_e) = (1.2 × 3,000)/(0.040 × 10,000 + 4.96 × 15)
- = 3,600/(400 + 74.4) = 7.589 days
Why the other choices are wrong
- (A) 0.2400: computed hydraulic detention time (days)
- (B) 3.510: applied 8.34 to one term only
- (D) 9.000: ignored solids lost in the effluent
Check it with the free calculator: pe-calc.com/tools/mlss-fm-ratio.html
40 problems · 23 pages · answer key · full worked solutions · why each wrong answer is wrong
Secure checkout by Stripe. You get the download page right after paying, and the link by email.
Questions, or found an error? Email hello@hydrocomplete.com. Not affiliated with or endorsed by NCEES. The problems are original practice problems, not past exam questions. Sold by HydroComplete LLC.