CWD Well Construction & Casing Design 2 — Questions and Answers
Question 1: What is the primary purpose of casing centralizers used during well construction?
- To keep the casing centered in the borehole for uniform annular grout placement (Correct answer)
- To increase the weight of the casing string for easier installation
- To prevent groundwater from entering the borehole during drilling
- To measure the true diameter of the completed borehole
Correct answer: To keep the casing centered in the borehole for uniform annular grout placement
Centralizers maintain uniform annular space around the casing so that grout fills completely without channeling, ensuring a continuous sanitary seal.
Question 2: Which well screen type provides the most precise slot sizing and is best suited for fine sand formations?
- Torch-cut slotted pipe
- Wire-wound continuous slot screen (Correct answer)
- Machine-slotted perforated pipe
- Bridge-slotted casing
Correct answer: Wire-wound continuous slot screen
Wire-wound continuous slot screens offer precise, consistent slot openings and maximum open area per unit length, making them optimal for fine-grained aquifer materials.
Question 3: What AWWA standard primarily governs the construction of drilled water wells in the United States?
- AWWA A200
- AWWA A100 (Correct answer)
- AWWA C900
- AWWA B300
Correct answer: AWWA A100
AWWA A100 is the standard for water wells, establishing design, construction, development, and testing requirements for drilled groundwater supply wells.
Question 4: What is a pitless adapter, and what problem does it solve in well construction?
- A fitting that allows the water line to exit the casing below the frost line while maintaining a sanitary seal (Correct answer)
- A tool used to retrieve debris from the bottom of a completed well
- A type of submersible pump designed for shallow pitless installations
- A grout injection device for sealing the lower annular space
Correct answer: A fitting that allows the water line to exit the casing below the frost line while maintaining a sanitary seal
A pitless adapter is a manufactured, NSF-approved fitting that creates a watertight, sanitary penetration through the casing wall below frost depth, eliminating the need for an open well pit.
Question 5: Which material is most commonly approved for sealing the annular space around a well casing?
- Bentonite clay or neat cement grout (Correct answer)
- Sand and gravel mixture
- Crushed limestone aggregate
- Epoxy resin compound
Correct answer: Bentonite clay or neat cement grout
Bentonite and neat cement are standard-approved annular sealants because both achieve very low hydraulic conductivity, creating an effective barrier against contaminant migration.
Question 6: What is the purpose of a conductor casing in a well construction program?
- To guide drilling, prevent near-surface formation collapse, and enable drilling fluid circulation (Correct answer)
- To carry electrical conduit safely from the surface to the pump
- To measure electrical conductivity of the groundwater column
- To transfer structural casing loads through soft overburden to bedrock
Correct answer: To guide drilling, prevent near-surface formation collapse, and enable drilling fluid circulation
Conductor casing is the first, largest-diameter casing set to stabilize shallow unconsolidated formations, guide the drill string, and establish a fluid-circulation pathway.
Question 7: When placing annular grout using the tremie method, in which direction should grout be pumped to ensure a void-free seal?
- From the surface downward through the annular space
- From the bottom of the annular space upward, displacing drilling fluids (Correct answer)
- Horizontally through ports drilled in the casing at multiple depths
- In alternating directions to achieve even distribution
Correct answer: From the bottom of the annular space upward, displacing drilling fluids
Pumping grout from the bottom upward displaces drilling fluids without trapping them, ensuring a continuous, void-free annular seal from the bottom of the grouted interval to the surface.
CWD Well Construction & Casing Design 2
What is the primary purpose of casing centralizers used during well construction?