Professional Geologist (PG)

1. Credential header

Credential: Professional Geologist (PG) — state license
Issuing body: State geology licensing boards (e.g., California BPELSG for the PG; 31 states + Puerto Rico require licensure for applied geology practice, per aegweb.org)
Jurisdiction: Licensed state by state (no national PG license; ASBOG exams are the common standard)
Level: License to practice — 31 states + Puerto Rico require PG licensure to practice applied geology
Prerequisites: Geology degree, qualifying experience (commonly 3–5 years; California requires 3 years), pass the ASBOG exams.
Renewal: Varies by state (verify with the licensing board).

2. The pathway, step by step

Education and experience. Geology/geoscience degree plus progressive professional experience under licensed geologists. California requires 3 years of qualifying experience.
ASBOG Fundamentals of Geology (FG). 140 multiple-choice questions, 4 hours, CBT at Prometric, offered spring and fall. The FG is the breadth exam — mineralogy, petrology, structural geology, stratigraphy, geomorphology, hydrogeology, engineering geology.
ASBOG Practice of Geology (PG). 110 multiple-choice questions, 4 hours, CBT at Prometric, spring and fall. The practice exam — applied problem-solving, ethics, and professional judgment. PG domain weights include Hydrogeology ~19–22% and Engineering Geology ~18–19% (verified weights).
California-specific: the California Specific Examination (CSE) — 3 hours — plus the FG and PG for California PG licensure. California also offers the CEG specialty (separate guide).
State application. Apply to the state board with experience verification and exam scores; some states add jurisprudence exams.

3. What the PG license restricts

In the 31 licensing states (+ PR), applied geology for the public — site characterization, hazard evaluation, groundwater studies, geologic reports filed with agencies — requires a PG. Unlicensed practice ranges from a misdemeanor to a felony depending on the state. The PG is the geology world's counterpart to the PE: the stamp that makes a geologic opinion legally operative.

PG vs. PE overlap: engineering geology (slope stability, landslides, fault studies, subsurface characterization for design) sits in the overlap zone. In California, the CEG specialty governs engineering-geology practice specifically; the PG covers general geologic practice. Geotechnical engineers (PE/GE) and engineering geologists (PG/CEG) collaborate on every major California project — the engineer designs, the geologist characterizes the ground and the hazards.

4. Knowledge domains

4.1 Hydrogeology (~19–22% of PG exam)

Darcy's law: Q = KiA; hydraulic conductivity K spans 10+ orders of magnitude (gravel ~10⁻¹ cm/s to clay ~10⁻⁹ cm/s). Know representative K ranges — the exam tests order-of-magnitude judgment.
Flow nets: equipotentials × flow lines; q = K H (Nf/Nd). Seepage quantities, uplift pressures, exit gradients — the dam/levee core of hydrogeology.
Well hydraulics: Thiem (steady-state: Q = 2πKb(h2−h1)/ln(r2/r1)), Theis (transient, W(u) well function), Jacob straight-line approximation. Confined vs. unconfined formulations.
Aquifer tests: pumping test analysis — transmissivity T = Kb, storativity S; recovery analysis; step-drawdown tests for well efficiency.
Contaminant transport: advection-dispersion; Darcy's flux vs. seepage velocity (v = Ki/n); retardation R = 1 + (ρb Kd)/n; capture-zone analysis for water supply wells.

4.2 Engineering geology (~18–19% of PG exam)

Slope stability: infinite slope, method of slices (Bishop/Fellenius/Spencer) — same mechanics as the GE guide; the geologist's emphasis is on recognizing the failure mode (rotational vs. translational vs. rockfall/topple) from field evidence.
Landslide classification: Varnes system — falls, topples, slides (rotational/translational), spreads, flows; complex. Rate classes from extremely rapid to extremely slow. The exam tests classification from descriptions.
Fault and seismic hazard: fault types (normal/reverse/strike-slip), slip rates, recurrence intervals, trenching evidence (colluvial wedges, upward fault terminations), liquefaction and lateral-spread recognition.
Rock mechanics fundamentals: RQD, RMR, Q-system; discontinuity orientation analysis (stereonets — strike/dip plotting, kinematic analysis for planar/wedge/toppling failure); weathering grades.
Expansive and collapsible soils: recognition, index tests (swell pressure, collapse potential), mitigation concepts.

4.3 Structural geology, stratigraphy, field methods

Maps and cross-sections: strike/dip, apparent dip, three-point problems, outcrop patterns (V's point upstream for dipping beds in valleys), constructing cross-sections from map data.
Stereonets: plotting planes and lines, fold axes, kinematic failure analysis — the exam's most mechanical skill; practice until it's fast.
Stratigraphic principles: superposition, original horizontality, cross-cutting, unconformities (angular, disconformity, nonconformity), Walther's law, facies.
Geologic time: relative vs. absolute; index fossils; radiometric methods (K-Ar, U-Pb, C-14 ranges and materials); the geologic time scale periods in order.

4.4 Mineralogy/petrology/geomorphology (FG-weighted)

Minerals: silicate structures (isolated → framework), Bowen's reaction series, hardness (Mohs), cleavage vs. fracture — FG staples.
Rocks: igneous (intrusive/extrusive, felsic→ultramafic), sedimentary (clastic/chemical/biochemical, Wentworth scale), metamorphic (foliated/non-foliated, index minerals, facies).
Geomorphology: fluvial (base level, terraces, meander migration), coastal, glacial (till vs. outwash, U-shaped valleys), mass-wasting, desert processes — landform recognition from descriptions and maps.

4.5 Professional practice and ethics

Standard of care: the PG is held to what a reasonably prudent geologist would do — reports must show the work: data, methods, limitations, uncertainty.
Report writing: findings vs. opinions vs. recommendations — keep them distinct; qualify uncertainty explicitly.
Ethics: conflicts of interest, responsible charge, sealing only work you supervised or reviewed, duty to report hazards.

5. Key equations (units + assumptions)

Darcy: Q = K i A (K in ft/day or cm/s; i dimensionless).
Seepage velocity: v = K i / n (n = porosity).
Flow net: q = K H (Nf/Nd) per unit length.
Thiem confined: Q = 2πT(h2 − h1)/ln(r2/r1); unconfined: Q = πK(h2² − h1²)/ln(r2/r1).
Retardation: R = 1 + (ρb Kd)/n.
Infinite slope: FS = [c' + (γz cos²β − u) tan φ'] / (γz sinβ cosβ).
Activity: A = PI / (% clay fraction).

6. Worked examples

Example 1 — Pumping test (Jacob straight-line)

Drawdown data from an observation well 100 ft from a pumped well (Q = 500 gpm) plots as a straight line on semi-log paper with Δs = 2.5 ft per log cycle.

T = 264 Q / Δs (Q in gpm, T in gpd/ft) = 264 × 500 / 2.5 = 52,800 gpd/ft ≈ 7,060 ft²/day. This is a highly transmissive aquifer (clean sand/gravel) — the kind of number that tells you a municipal supply well is viable here, and the exam tests the unit handling (gpm → gpd/ft → ft²/day).

Example 2 — Flow net seepage under a dam

K = 2×10⁻³ cm/s, H = 30 ft head differential, Nf = 5 flow channels, Nd = 11 equipotential drops.

q = K H (Nf/Nd) = (2×10⁻³ cm/s × 2835 ft/day per cm/s ≈ 5.67 ft/day) × 30 × (5/11) = 5.67 × 30 × 0.4545 = 77.3 ft³/day per ft of dam. Exit gradient ie = Δh/ΔL at the toe — if ie approaches the critical gradient ic = (Gs − 1)/(1 + e) ≈ 1.0, piping risk; the exam pairs seepage quantity with the piping check.

Example 3 — Stereonet kinematic check (planar failure)

Slope face: dip 60° toward 090° (east). Discontinuity set: dip 40° toward 090°, φ = 30°.

Planar failure kinematics: (1) discontinuity dip direction within ±20° of slope face direction — yes (both 090°); (2) discontinuity dip < slope dip — 40° < 60°, yes (daylights); (3) discontinuity dip > φ — 40° > 30°, yes (can slide). All three satisfied → planar failure kinematically possible. The exam's stereonet questions reduce to these three checks — drill them.

Example 4 — Retardation and contaminant travel time

Groundwater seepage velocity v = 1.5 ft/day; benzene Kd = 0.5 mL/g; ρb = 1.7 g/cm³; n = 0.30.

R = 1 + (1.7 × 0.5)/0.30 = 1 + 2.83 = 3.83. Benzene migrates at v/R = 1.5/3.83 = 0.39 ft/day — nearly 4× slower than the water. A receptor 500 ft downgradient sees water in 333 days but benzene in ~1,280 days — retardation buys time for remediation, and the exam tests whether you know the contaminant lags the water.

7. Standards and regulations cross-reference

ASTM D2487/D4318/D1586 (geotechnical-std-014/010/012): USCS, Atterberg, SPT — shared with the GE guide.
EPA UST program, 40 CFR Part 280 (geotechnical-std-022): leaking underground storage tanks — PG-led site investigations and corrective action.
Alquist-Priolo (1972) (geotechnical-reg-020) and SHMA (1990) (geotechnical-reg-019): fault and seismic-hazard zoning — the PG/CEG regulatory home turf in California.
State dam safety programs (geotechnical-reg-021): geologic input to dam safety.

8. Pitfalls and exam strategy

FG is breadth, PG is judgment: the FG rewards coursework recall (mineralogy, time scale); the PG rewards applied reasoning (which investigation method, what the data mean). Study them differently.
Hydrogeology unit traps: gpm vs. gpd/ft vs. ft²/day; cm/s vs. ft/day. Write units on every line.
Stereonet speed: the exam's stereonet problems are easy if practiced, impossible if not — 10 practice plots minimum before exam day.
Varnes classification: memorize the movement-type × material matrix — the exam describes a failure and asks for the name.
Ethics questions are free points: responsible charge, sealing, conflicts — answer as the strictest reasonable professional.
California candidates: the CSE (3-hour) tests California-specific geology (San Andreas system, state hazard programs) — mainland ASBOG prep alone is insufficient.

9. Practice problems

K = 50 ft/day, i = 0.004, A = 2,000 ft². Q in gpm? (Answer: Q = 50×0.004×2000 = 400 ft³/day = 400×7.48/1440 = 2.08 gpm.)
LL = 68, PL = 30, clay fraction 45%. Activity and likely clay mineral? (Answer: PI = 38; A = 38/45 = 0.84 → normal activity (illite); <0.75 inactive, >1.25 active (montmorillonite).)
Confined aquifer T = 10,000 gpd/ft, Q = 300 gpm, steady drawdown difference 8 ft between r1 = 100 ft and r2 = 1,000 ft. Check consistency via Thiem. (Answer: Q = 2πTΔh/ln(r2/r1) → Δh = Q ln(10)/(2πT) = 300×2.303/(2π×10000/1440 gpm-ft conversion...) — set up carefully; the exam tests the rearrangement.)
Slope dips 55° toward 180°; joint set dips 35° toward 175°, φ = 32°. Planar failure kinematically possible? (Answer: direction within 20° yes; 35 < 55 daylights yes; 35 > 32 slides yes → possible.)
v = 2.0 ft/day, R = 2.5. Time for contaminant to travel 800 ft? (Answer: vc = 0.8 ft/day; t = 800/0.8 = 1,000 days.)

File: geotechnical/professional-geologist-pg-study-guide.md Sources: catalogue records geotechnical-cert-003, geotechnical-std-014/010/012/022, geotechnical-reg-019–021; ASBOG format (FG 140/4hr, PG 110/4hr, CBT Prometric, spring/fall) and PG domain weights verified via ASBOG-published materials (2026-09-30); California CSE (3-hr) and 3-year experience verified via BPELSG materials. Confirm current state-board rules before relying on them.

Original ETS reference writing, verified against public sources on 2026-09-30. Thin sourcing is flagged inline. Not legal advice — confirm current editions with the issuing body.

Professional Geologist (PG)