1.2 Reference Handbook and Units

Treat References as Test Tools

The PE Civil WRE exam is closed book with electronic references. Under the active April 2024 specification, NCEES supplies the PE Civil Reference Handbook plus two design standards: the Recommended Standards for Wastewater Facilities (2014) and the Recommended Standards for Water Works (2018) — both published by the Great Lakes—Upper Mississippi River Board (often abbreviated TSS for the "Ten States Standards" / Ten-State Standards lineage). Personal copies, printed binders, handwritten notes, and outside PDFs are not allowed in the testing room.

That policy reshapes how you study. Your goal is not to memorize every equation in hydrology, pipe flow, open-channel flow, treatment, groundwater, or sitework. Your goal is to know which reference family controls the problem, navigate to it fast, and confirm the variables and units match the item.

Memorize the handbook's table of contents structure, not its contents. Knowing that, for example, open-channel relations and Manning's equation live in the water-resources section saves a minute per lookup across 80 items.

A common trap is assuming the handbook contains everything. It does not contain the design criteria that the two standards carry — clarifier surface overflow rates, filtration loading limits, minimum detention times, recommended distribution storage. Those are scored against the Recommended Standards documents, so a candidate who only practices from the handbook will fail to recognize when a question is really a standards-lookup. Train yourself to ask, on every wastewater or drinking-water item, "is this a handbook equation or a standards criterion?" before searching.

How Electronic Search Changes the Work

The handbook and both standards are searchable electronic PDFs available the entire exam, but the standards are split into individual chapters, and only one chapter can be opened and searched at a time so the software handles the large files efficiently. That means you cannot keyword-search across an entire standard at once; you must first guess the correct chapter, then search within it. During preparation, never build habits around browser tabs, sticky notes, or a giant personal equation sheet you will not have.

A high-value reference drill: solve each practice problem twice. First, solve it normally. Second, write the exact navigation path you used — reference (handbook or which standard), chapter, search term, equation label or table number, and the unit trap. Over weeks this builds navigation muscle memory that survives the one-chapter-at-a-time constraint.

Units Are a First-Pass Decision

The WRE specification uses both the International System of Units (SI) and the U.S. Customary System (USCS). A large share of misses occur before any engineering begins: gallons per minute mixed with cubic feet per second, million gallons per day (MGD) converted too late, milligrams per liter (mg/L) treated as a mass instead of a concentration, or head and pressure dropped into one equation without conversion (1 psi ≈ 2.31 ft of water head).

Apply this unit process to every quantitative item:

1. Restate the target unit before opening any reference.
2. Convert flow, area, and time units before substituting into an equation.
3. Keep concentration-load problems dimensional end to end (the load equation lb/day = flow MGD × concentration mg/L × 8.34 is a top-five WRE workhorse).
4. Use the handbook conversion factor that matches the requested unit system, not a remembered approximation.
5. Sanity-check the magnitude against the facility or watershed scale.

High-frequency WRE unit contexts include MGD, gpm, cfs, acre-feet, ft of head, psi, mg/L, lb/day, ft², acres, and cubic yards. Recurring conceptual traps: flow versus load, peak rate versus runoff volume, energy grade line (EGL) versus hydraulic grade line (HGL), and open-channel versus pressurized-flow assumptions.

Standard-Year Discipline

When a question references a design standard, NCEES scores only against the standards and revision years listed in the active specification — solutions based on other standards or editions receive no credit. For pre-April-2027 exams that means the 2014 Wastewater and 2018 Water Works editions specifically. The April 2027 specification revises this list, so candidates testing after the transition must not assume the same references or revision years.

A Worked Reference-and-Unit Example

Consider a circulating-water item: a pump delivers 700 gpm through a pipe and you must report flow in cfs to use a handbook headloss chart. Apply the unit process first. The conversion 1 cfs = 448.8 gpm lives in the handbook's conversion tables, so 700 gpm / 448.8 = 1.56 cfs. Only now open the headloss reference, because the chart's axis is in cfs. A candidate who skips the conversion and reads the chart at "700" lands three orders of magnitude off and wastes the item.

Now extend it to load: if that same flow is 1.0 MGD of secondary effluent at 30 mg/L total suspended solids, the daily solids load is 1.0 × 30 × 8.34 = 250 lb/day. The dimensional discipline — pairing MGD with mg/L and the 8.34 factor — is what makes the answer trustworthy, and it is the same pattern the practice and flashcard sets drill repeatedly. Keep the workflow consistent: target unit first, conversion factor from the supplied reference, substitution last, magnitude check at the end.