Well Construction and Design
What the exam tests
Well construction and design covers casing, screen, gravel pack, grout, wellhead, and how those choices protect water quality and well life. New Jersey reviews design against N.J.A.C. 7:9D, not just manufacturer tables.
Core rules
- Casing must be continuous, watertight, and grouted to the surface; the annular seal prevents surface water and shallow contamination from moving down the borehole.
- NJ wells commonly carry a minimum 40-foot casing length; bedrock wells must seat casing into competent rock. Check the current rule for the specific well type and any local health department add-ons.
- Screen slot size is matched to the formation gradation; the gravel pack is sized to the sand, and the screen slot is sized to the gravel. A slot that passes too much sand causes pumping sand and pump wear.
- The wellhead must be above grade, capped with a sanitary seal, and fitted with a pitless adapter or equivalent. A pit that can flood is a direct contamination pathway.
- Centralizers keep casing centered so grout forms a continuous annulus.
Worked example
Design a 6-inch well in a Coastal Plain sand at 120 feet. Set 6-inch steel casing to 60 feet, then 6-inch PVC screen from 60 to 100 feet with a 10-foot sump. Sieve analysis shows 90% of sand finer than 0.5 mm; choose a 0.020-inch slot with a 10-20 gravel pack. Grout the casing annulus from 60 feet to surface with bentonite-cement, and leave the screen interval open to the formation. The design protects the upper aquifer while producing from the target sand.
Traps
Do not grout only the top 20 feet - voids below allow cross-connection. Do not set screen across a confining layer. Do not choose slot size only by what the supply house stocks. Do not leave casing short of the confining unit just to save steel; the exam treats that as a water-quality failure.