Short definition
A borehole is the small-diameter hole a driller bores into the ground to reach an aquifer. The casing, screen, pump, and drop pipe go inside the borehole; together they make a finished well. In US homeowner usage, “well” usually wins — but you’ll see “borehole” on quotes, well logs, and trade conversation.
What it is
A licensed driller advances a rotary or percussion rig downward, setting steel or PVC casing as the hole deepens. Residential boreholes are typically 4 to 6 inches in diameter. Depth depends on where the producing aquifer is — shallow drilled wells in parts of Western Washington land at 30 to 80 feet; deeper aquifers in Eastern Washington or hard-rock terrain can run 200 to 600 feet or more.
Construction sequence: drill the borehole → set casing and seal the annular space with bentonite or grout to keep surface water out → place a well screen at the producing zone → install pitless adapter, drop pipe, and submersible pump → cap and connect to the pressure tank.
Why it matters to a homeowner
The borehole is what you pay for by the foot. In Washington, drilling quotes are usually structured as a per-foot price plus per-foot casing and grouting charges. Knowing the realistic depth range for your aquifer prevents a sticker shock when the rig keeps going past 200 feet without a producing zone.
You’ll also encounter the term in three failure conversations:
- Old well no longer producing. The driller may recommend deepening the existing borehole or abandoning it and drilling a new one. Decommissioning the old hole is required under WA Department of Ecology rules.
- Casing corroded out. The original 1960s steel casing has failed; the borehole itself may still be usable with a re-line, or it may need to be replaced.
- Real-estate listing. “Drilled borehole” in the description is the same as “drilled well” — both mean a modern rotary-drilled installation.
Washington note
Washington wells are constructed under WAC 173-160, the Department of Ecology’s well construction standards, by drillers licensed under RCW 18.104. Every new borehole gets a well log filed with Ecology — the homeowner can request a copy from Ecology’s well log database to learn casing depth, static water level, yield test, and aquifer description. Decommissioning an unused borehole is also a regulated process; you can’t simply leave an old hole open.