400-Foot Well Drilling Cost

The hard-rock residential depth

Four hundred feet is the depth at which the granite-belt economics of well drilling become unavoidable. In southern New England the bedrock fracture zone that produces residential water typically sits at 250 to 450 feet; in northern New England the productive zone is deeper still and 400 feet is the median completion depth in NH Department of Environmental Services well-log records. The same pattern holds across the Blue Ridge of Virginia and North Carolina, the Adirondacks, the Cascades and the Sierra foothills.

What changes at 400 feet relative to 300 feet is the relative weight of each cost category. Drilling becomes 65 to 70 percent of the total bill (vs 60 percent at 200 feet). The casing fraction drops because hard rock is almost entirely uncased open bore, so only 30 to 60 feet of casing through the upper weathered zone is required. The pump-and-electrical share rises because the bigger HP rating and longer drop pipe push the equipment cost up by $1,500 to $2,500 over the 300-foot configuration.

The 400-foot bracket is also where contingency clauses in the bid become genuinely important. Drilling 400 feet in granite at $58 per foot is a $23,200 commitment before casing, pump or contingency. A 10 percent overrun (homeowner finds out at 380 feet that the bore is producing 1.5 gpm and needs another 50 feet or hydrofracturing) costs $2,500 to $3,000. Build that into the budget from the start; it is the norm at this depth, not an exception.

Cost breakdown for a representative bid

Take a 400-foot well in northern New Hampshire, drilled through 60 feet of glacial till into 340 feet of granite. Six-inch steel casing is set 60 feet. The remaining 340 feet is open bore through the bedrock. A 1.5 HP submersible pump is set at 380 feet on galvanized drop pipe. A 60-gallon pressure tank is plumbed in the basement.

Line items at 2026 rates. Mobilisation $1,000. Drilling 60 feet through glacial till at $40 per foot ($2,400). Drilling 340 feet through granite at $58 per foot ($19,720). Six-inch steel casing 60 feet at $16 per foot ($960). Grouting 40 feet, $600. Well cap with pitless adapter, $300. Development 6 hours, $720. Submersible pump 1.5 HP with control box, $2,200. Galvanized drop pipe 380 feet at $5 per foot ($1,900). Electrical cable 380 feet, $700. Pressure tank 60 gallon, $900. Trench from well to house 175 feet, $700. Permit and water test $300. Subtotal: $32,400. With 10 percent contingency, $35,640. That is a typical upper bid for granite-belt NH in 2026.

Drilling alone ($22,120) is 68 percent of the subtotal. Pump-and-electrical package ($5,700) is 18 percent. Casing-grouting-cap ($1,860) is 6 percent. Everything else (mobilisation, development, trench, permit) is 8 percent. The proportions are heavily weighted toward drilling because hard-rock per-foot rates dominate the bill.

Why DTH-hammer rigs dominate this depth in hard rock

A down-the-hole hammer (sometimes "down-hole hammer") is a pneumatic percussion bit that sits at the bottom of the drill string. Compressed air from a surface compressor (typically 750 to 1,200 cfm at 250 to 350 psi) powers the hammer, which strikes the rock at 600 to 1,000 blows per minute while the drill string slowly rotates. The combination of percussion and rotation is much faster than rotary drilling alone in hard rock: 20 to 40 feet per hour in granite vs 8 to 15 feet per hour with a tricone bit.

At 400 feet in granite, the speed advantage saves a full day of drilling time, which more than pays for the higher fuel and equipment cost of running a DTH rig. The downside is the compressor, which is loud (often 100+ dB at 50 feet) and uses 150 to 250 gallons of diesel per day. Residential drillers running DTH usually arrive with a sound-attenuated compressor and dust-collection equipment to comply with local noise and air-quality rules.

On a 400-foot bid in hard-rock country, the DTH-rig premium over a mud-rotary rig is typically $5 to $10 per foot ($2,000 to $4,000 on the bore). For most homeowners, the time savings (one day vs three) and the cleaner production water (no mud invasion of fractures) make the DTH bid the better value.

Yield expectations and the hydrofracture decision

Bedrock wells at 400 feet have wide yield variance. Excellent wells produce 15 to 25 gpm sustained; poor wells produce less than 2 gpm. The geology determines this within a county, but the specific bore location on a property can vary by an order of magnitude over 100 yards. There is no reliable way to predict yield before drilling; it is the genuinely random component of the project.

A 400-foot bedrock well that comes in below 3 gpm sustained is a candidate for hydrofracturing. The success rate is higher in this depth bracket than at any other (700-foot wells are deeper than most hydrofracture rigs can effectively reach; 200-foot wells often have not crossed enough fracture zones to give the fracture process material to work with). NGWA case studies typically show 70 to 85 percent of 400-foot bedrock wells in the 1 to 3 gpm range will improve to 4 to 8 gpm after a single hydrofracture treatment.

The economics: $1,500 to $4,500 for hydrofracture vs $4,000 to $6,000 for an additional 100 feet of bore that may or may not improve yield. The hydrofracture math wins in most cases. See well hydrofracturing for the full process.

Drop pipe and pump-pulling at 400 feet

Drop pipe at 400 feet is its own engineering problem. The column of water inside the pipe weighs about 180 lb (a column of water 380 feet x 0.43 psi per foot of head x pipe cross-section). The pipe itself adds 50 to 200 lb depending on material. The pump motor adds another 25 to 75 lb. The pitless adapter at the surface must support that entire dead-load plus the dynamic loads of pump starts and stops over the life of the system.

Plastic drop pipe (schedule-80 PVC or polyethylene rated for submersible service) works at 400 feet but is close to its safety margin. Most drillers spec galvanized steel or stainless-steel drop pipe at this depth for the longer service life and the easier handling during pump replacement. Galvanized adds about $4 per foot over schedule-80 PVC ($1,500 on a 380-foot drop). Worth the cost over the well's 30+ year life.

When the pump fails (after 10 to 20 years), pulling it from 400 feet is a day-long job for two workers with a small crane truck. Labour alone runs $1,200 to $2,400. A replacement pump installed is $4,000 to $7,000. This is one reason to budget the bigger pump and bigger pressure tank at install time: less cycling, longer pump life, fewer of these expensive pulls over the well's life.

Cross-references and adjacent depths

For the per-foot rate breakdown, well drilling cost per foot 2026. For the shallower bracket, 300-foot well drilling cost. Next depth up, 500-foot well drilling cost. For the geology that dominates 400-foot drilling, bedrock well drilling cost. For the pump and drop-pipe details, pump installation costs.