Exam G is a 50-question, one-hour, closed-book specialized drilling exam with a 70 percent minimum passing score, administered year-round at PSI test centers. To earn the Certified Well Driller designation you also need the general drilling exam, both passed within one 12-month period. Study the reverse-rotary flow path first — fluid down the annulus, cuttings up the drill pipe — then the issuer's recommended drilling texts.
What Exam G is and where it fits
Exam G: Reverse Circulation Drilling is one of NGWA's specialized drilling exams. It counts toward the Certified Well Driller designation only alongside the general drilling exam.
NGWA lists Exam G among its drilling specialty categories, alongside cable tool, air rotary, mud rotary, jetting and driving, and augering and monitoring. To earn the Certified Well Driller (CWD) designation, you must pass the general drilling exam and at least one specialized drilling exam. Both required exams must be passed within one 12-month period with scores of 70 percent or better.
That structure shapes your decision sequence. If you have not yet passed the general drilling exam, schedule both and plan to clear them inside a single 12-month window, because a pass outside the window does not count toward the designation.
Sitting the exam itself is separate from applying for certification. No NGWA approval is needed to schedule a test, and the bulletin confirms that eligibility review happens with the application, not before testing.
Official sources: Groundwater | NGWA Certification exams — Exam categories, preparation materials, fees, scheduling, and DACUM overview; Groundwater | NGWA Certification for contractors — Program overview, eligibility, and application requirements; PSI NGWA candidate information bulletin — Visually checked NGWA content tables, pages 5-7 (May 2022)
Format, scoring, and scheduling
Expect 50 questions in one hour, a 70 percent minimum score, closed-book conditions, and an immediate score report at the test center.
The PSI candidate bulletin's NGWA content tables give Exam G 50 questions, a 70 percent minimum passing score, and one hour. All NGWA examinations are closed book, so plan to reason from memory rather than reference material.
PSI administers the online exams at a nationwide network of test centers, and you can test year-round at your convenience. Scores are issued immediately when you finish; collect your score report before leaving the center, because reissued copies cost extra and scores are never given by phone.
All testing centers are ADA compliant. If you need accommodations, contact NGWA first; NGWA then sends approval to PSI and PSI contacts you to complete registration. If scheduling problems arise, NGWA's certification staff will work with PSI to resolve them.
- 50 questions, one hour, 70 percent minimum — verified from the bulletin's NGWA content table
- Closed book for all NGWA exams
- Immediate score report at the test center
- Accommodations arranged through NGWA before PSI completes your registration
Official sources: Groundwater | NGWA Certification exams — Exam categories, preparation materials, fees, scheduling, and DACUM overview; PSI NGWA candidate information bulletin — Visually checked NGWA content tables, pages 5-7 (May 2022)
What the published outline does and does not tell you
The bulletin's table lists a single 50-item domain called Reverse Circulation Drilling. No finer topic weights are published in the retrieved sources.
Unlike some NGWA exams whose tables break content into duties such as mobilizing, constructing, and developing wells, the Exam G row shows one domain carrying all 50 items. That means you cannot prioritize subtopics from the bulletin alone, and you should not treat topic lists from study sites as official weights.
The retrieved PSI bulletin is dated September 2022, with content pages marked May 2022. NGWA’s current exam page confirms Exam G’s identity, question count and time. Check the bulletin supplied for your booking for later changes.
For subject depth, NGWA recommends its Professional Designations Information and Study Guide and drilling texts. Use those references to work beyond the single-domain outline.
Official sources: Groundwater | NGWA Certification exams — Exam categories, preparation materials, fees, scheduling, and DACUM overview; PSI NGWA candidate information bulletin — Visually checked NGWA content tables, pages 5-7 (May 2022)
The method at the core of the exam: follow the fluid
In the reverse rotary method, drilling fluid is circulated down the annular space and up the drill pipe — the reverse of normal rotary, where fluid goes down the pipe and up the annulus.
USGS's Basic Ground-Water Hydrology describes the hydraulic rotary method as excavating a hole by rotating drill pipe with a drag or roller bit attached. In the normal rotary approach, water containing clay is pumped down the drill pipe and returns up the annular space, both to cool the bit and to carry rock cuttings out.
Reverse rotary reverses that circuit: fluid travels down the annular space and returns up the drill pipe. As a study exercise, draw the two routes with arrows and label the pipe and annulus.
USGS also describes cable tool percussion, jetting and augering, which NGWA lists in other specialized categories. The flow-path comparison below focuses on the distinction relevant to reverse circulation.
Practice exercise
A drilling crew switches a hole from normal rotary to the reverse rotary method mid-job. In one or two sentences, state where the drilling fluid enters the hole and how the cuttings reach the surface under the reverse circuit.
Show answer
The drilling fluid is circulated down the annular space between the borehole wall and the drill pipe, and it returns up the inside of the drill pipe, carrying the cuttings with it.
USGS defines the reverse rotary method by this exact flow reversal: in normal rotary the clay-bearing water goes down the drill pipe and up the annulus, while in reverse rotary the direction swaps. If your answer placed the fluid down the pipe, you described the normal circuit, which is the contrast the question tests.
| Circuit | Fluid path down | Fluid and cuttings path up |
|---|---|---|
| Normal rotary | Inside the drill pipe | Up the annular space |
| Reverse rotary | Down the annular space | Up the drill pipe |
Official sources: USGS Water-Supply Paper 2220, Basic Ground-Water Hydrology (1983) — Selected fundamentals: well construction methods, development, specific capacity; Groundwater | NGWA Certification exams — Exam categories, preparation materials, fees, scheduling, and DACUM overview
Development and specific capacity, with a worked exercise
Well development removes clay, silt, and fine sand near the screen or open hole so the well produces sediment-free water. Specific capacity is yield per unit of drawdown, computed from readings taken at the same time.
Development follows construction and concerns the area next to the screen or open hole. Its purpose differs from drilling the hole itself: the objective is to remove fine material so the well produces sediment-free water.
USGS also supplies the standard measure of well performance: specific capacity is the yield per unit of drawdown, found by dividing the pumping rate by the drawdown at the same time during a test. The same-time condition matters; a rate read at 60 minutes divided by a drawdown read at 30 minutes is not specific capacity.
One caution before the exercise: a specific-capacity figure describes one test point. It cannot by itself prove a well's sustainable yield or size a pump, so avoid extending the number beyond what the readings support.
Practice exercise
During a pumping test on a newly developed well, the crew records a pumping rate of 300 gpm and a drawdown of 24 feet, both read 60 minutes after the pump started. Calculate the well's specific capacity, and state in one sentence what the figure does and does not tell you.
Show answer
Specific capacity is 12.5 gpm per foot of drawdown. It describes yield per unit of drawdown at that test point, but it cannot alone prove the well's sustainable yield or serve as the basis for pump selection.
Divide the pumping rate by the drawdown measured at the same elapsed time: 300 divided by 24 equals 12.5 gpm/ft. The question states both readings were taken at the 60-minute point, so the same-time condition USGS requires is met. If the readings had come from different times, no valid specific capacity could be computed from them.
Official sources: USGS Water-Supply Paper 2220, Basic Ground-Water Hydrology (1983) — Selected fundamentals: well construction methods, development, specific capacity
After you pass: the certification application
Passing Exam G and the general drilling exam makes you eligible to apply, but certification also requires age and experience minimums, two outside references, an agreement form, and a current-year affidavit.
NGWA's voluntary certification program is national, run by and for groundwater contractors, and it dates to 1970. NGWA also notes that many state agencies use these same exams in their licensing programs — but certification and a state license are separate things, and your state's rules control any licensing requirement.
Eligibility for certification has four parts: you must be at least 20 years old, have at least 24 consecutive months of full-time drilling or pump installation experience, pass the required exam pair within one 12-month period at 70 percent or better, and submit written experience references from two professional contacts not affiliated with your current company, plus an agreement form and an affidavit for the current year.
Timing matters after your last pass: application materials must be received within 12 months of the qualifying exam session. Plan the paperwork alongside your exam scheduling so the window does not lapse.
- Age 20 or older
- 24 consecutive months of full-time relevant experience
- Both required exams passed within one 12-month period at 70 percent or better
- Two references from outside your current company, plus an agreement form and current-year affidavit
- Application materials received within 12 months of the qualifying exam session
Official sources: Groundwater | NGWA Certification for contractors — Program overview, eligibility, and application requirements
A focused preparation sequence
Anchor your study in the issuer's own materials, learn the two rotary circuits cold, and use the drilling contractor task chart to see the work the subject sits in.
Start with the sources the issuer points to. NGWA recommends the Professional Designations Information and Study Guide for all exams, and for the drilling exams it recommends Groundwater & Wells, the Manual of Water Well Construction Practices, the Water Well Driller's Beginning Training Manual, and the Procedures for Well Drilling Operations CD. NGWA University also offers self-paced online training for the general drilling exam with knowledge checks and video lectures.
A sequence that matches how the subject is built: first master the exam structure and the flow-direction contrast from the table above; second work through the reverse circulation chapter of your chosen text, tracing every circuit you meet as arrows; third study well development and its performance measures, repeating the specific-capacity exercise with your own numbers; fourth review the DACUM task chart for drilling contractors and operators to see the duties — client assessment, planning, mobilizing, constructing, developing, decommissioning, and closing out — that frame the whole program. Note that the chart's duty letters are not exam codes; its letter G is a development-wells duty, unrelated to Exam G.
This sequence is a study suggestion. Use the linked practice questions and General Drilling guide to continue preparing for the two-exam CWD route.
Official sources: Groundwater | NGWA Certification exams — Exam categories, preparation materials, fees, scheduling, and DACUM overview; PSI NGWA candidate information bulletin — Visually checked NGWA content tables, pages 5-7 (May 2022); Drilling contractors and operators (DACUM Research Chart) — Duties and tasks for drilling contractors and operators; USGS Water-Supply Paper 2220, Basic Ground-Water Hydrology (1983) — Selected fundamentals: well construction methods, development, specific capacity
Official sources
Facts checked against the PSI bulletin and NGWA certification pages, September 2026: