CWD Well Construction & Casing Design 1 — Questions and Answers
Question 1: What is the primary purpose of well casing in a drilled water well?
- To prevent borehole collapse and protect the water supply from contamination (Correct answer)
- To increase water flow rates by compressing surrounding formations
- To reduce construction costs by minimizing excavation volume
- To provide a pathway for monitoring groundwater temperature
Correct answer: To prevent borehole collapse and protect the water supply from contamination
Well casing maintains borehole integrity, prevents collapse, and seals out surface water and contaminants from reaching the aquifer.
Question 2: Which casing material is most appropriate for deep, high-pressure water wells where significant structural loads are anticipated?
- Schedule 40 PVC
- Carbon steel (Correct answer)
- Fiberglass-reinforced plastic
- Copper alloy
Correct answer: Carbon steel
Carbon steel casing is used for deep or high-pressure wells because its tensile and compressive strength far exceeds that of thermoplastic materials.
Question 3: According to AWWA A100, what is the minimum recommended thickness for an annular grout seal around well casing?
- 1 inch
- 1.5 inches
- 2 inches (Correct answer)
- 3 inches
Correct answer: 2 inches
AWWA A100 specifies a minimum 2-inch annular grout thickness to ensure a complete, void-free seal that prevents contaminant migration along the borehole wall.
Question 4: What is the primary purpose of a sanitary well seal installed at the top of a well casing?
- To prevent insects, rodents, and surface water from entering the well (Correct answer)
- To increase well yield by maintaining positive casing pressure
- To allow air circulation and prevent pressure buildup inside the casing
- To serve as a measurement port for water level monitoring
Correct answer: To prevent insects, rodents, and surface water from entering the well
The sanitary well seal creates a watertight, vermin-proof closure at the casing top, preventing biological and physical contaminants from entering the well.
Question 5: What is the primary function of a gravel pack (filter pack) installed around a well screen?
- To stabilize the borehole formation and filter fine particles from entering the well (Correct answer)
- To increase hydrostatic pressure in the aquifer zone
- To prevent chemical contamination migrating from the surface
- To reduce overall well construction costs
Correct answer: To stabilize the borehole formation and filter fine particles from entering the well
A gravel pack stabilizes fine aquifer materials around the screen and acts as a granular filter that passes water while blocking sand and silt.
Question 6: What is the minimum recommended height for well casing above finished ground surface as specified by most well construction standards?
- 4 inches
- 8 inches
- 12 inches (Correct answer)
- 18 inches
Correct answer: 12 inches
A minimum of 12 inches above finished grade is required to prevent surface water and debris from flowing directly into or over the well casing top.
Question 7: What factor primarily determines the appropriate inside diameter of a production well casing?
- The total depth of the well
- The pump size and required yield capacity (Correct answer)
- The type of aquifer material encountered
- The geographic location and state jurisdiction
Correct answer: The pump size and required yield capacity
Casing diameter must accommodate the pump bowl assembly and intake pipe while providing sufficient annular clearance for installation and the required flow velocity.
CWD Well Construction & Casing Design 1
What is the primary purpose of well casing in a drilled water well?