Well Drilling and Construction Practices
What this domain tests
Construction questions on the California exam ask you to take a site from permit to a completed, sanitary well without creating a pathway for contamination. Expect siting and clearances, drilling method selection, borehole and casing geometry, screen and filter-pack design, and the driller's duty to keep aquifers from intermingling.
Siting and site preparation
- Maintain separation from contamination sources. Typical county minimums run 50 feet from septic tanks and leach lines and 50 feet from sewers, with 100 feet or more from sewage ponds, manure piles, and solid-waste areas. Local ordinances govern and are often stricter than DWR Bulletin 74-90.
- Grade the site so surface water drains away from the casing; in flood-prone areas the casing must terminate above expected flood level.
- Confirm the local permit, call 811 for utility locates, and plan rig access plus room for grout and gravel equipment before the rig arrives.
Hole geometry and drilling method
- Cable-tool rigs handle boulders and cobbles and give clean, straight holes; direct rotary with mud is fast in sand and clay; air rotary with a hammer is standard in hard rock; hollow-stem augers suit shallow monitoring wells but not gravel or deep holes.
- Leave an annulus that can actually be grouted, about 2 inches per side as a practical minimum; gravel-packed wells need more. A hole that will not pass the casing must be reamed, not forced.
- Match screen to filter pack and pack to formation: slot openings smaller than the pack, pack graded to the aquifer, pack thickness commonly 3 inches or more.
Protecting water quality during construction
Casing, grout, and the surface completion all exist to stop water of one quality from moving into another zone. Drill cuttings are never acceptable annular backfill, and an unsealed annulus is a failed well regardless of how well it produces.
Worked example
A driller proposes a 6-inch borehole with 4-inch casing for a 60-foot domestic well 40 feet from a septic tank. Two problems stand out. First, the annulus is only 1 inch per side, too narrow to place grout reliably with a tremie pipe. Second, 40 feet is closer than the setback most county ordinances require. The fix is an 8-inch hole giving a 2-inch annulus, a relocated or confirmed setback per the local ordinance, and a seal designed for the required depth.
Traps that cost marks
- Treating Bulletin 74-90 as the only rule; county ordinances control and add requirements.
- Confusing borehole diameter with casing diameter when computing annulus.
- Forgetting that a dry hole still triggers reporting obligations.