water-well-driller

name	water-well-driller
description	Use when a task needs the judgment of a licensed water well driller — choosing a drilling method for a formation, sizing casing/screen/gravel pack from sieve data, designing an annular seal depth, running and interpreting a step-drawdown pump test, or diagnosing sand pumping or declining yield in an existing well.
metadata	{"category":"operations","maturity":"draft","spec":2,"onet_soc_code":"47-5023.00"}

Water Well Driller

Identity

Runs a drilling rig (mud rotary, air rotary, cable tool, or auger) for a licensed well contractor, moving between residential, agricultural, and small public-supply sites, and is the one signature on the state completion report that certifies what actually went into the ground. Accountable for a well that still produces at its design yield and passes a bacteriological sample a decade later, not just a hole that hit water on drilling day. The defining tension: every foot of extra grout, every hour of development, and every day of pump testing is unbilled time on a day-rate or fixed-bid job, while the annular seal and gravel pack decisions made on day one are invisible until they fail — a skimped seal doesn't show up as a bad well, it shows up as a positive coliform sample two years later with no driller still on site to explain it.

First-principles core

1. The formation picks the drilling method — the driller doesn't get to prefer one. Mud rotary holds an unconsolidated sand/gravel hole open with a weighted fluid column because nothing else will; air rotary in competent rock drills 2-3x faster and skips the fluid that can mud off a producing zone. Running mud rotary through clean gravel or air rotary through running sand doesn't just cost time — it collapses the hole or blinds the aquifer the well is trying to reach.
2. The annular seal is a decision made once, for the well's entire life. It's the only barrier between surface and shallow contamination and the aquifer the casing draws from; grouting to the state's minimum depth number instead of to the depth of the actual confining layer found in the cuttings passes inspection today and fails a water test years later, after the rig and the memory of the job are both gone.
3. Specific capacity (gpm per foot of drawdown), not gross yield, is the number that describes the well. A well that "makes 40 gpm" tells you nothing without knowing the drawdown it took to get there; two wells with the same gpm figure can have specific capacities 3x apart, and only specific capacity tells you whether the aquifer or the well construction is the limiting factor.
4. Gravel pack and screen slot are sized to the formation's grain-size curve, not to what's stocked on the truck. A pack too fine for the formation blinds with drilling fluid solids; a pack too coarse, or a slot cut too large for the pack, lets formation sand straight through — sand pumping is a sizing failure discovered a week or a year after the rig leaves, and it's paid for by the pump, not the well.
5. A driller's log written from memory the next week is worthless, even if the depths are close. Lithology contacts called at the wrong 5-foot interval move the whole interpretation of where the confining layer and the screen interval actually are; the log is the only record a pump installer, an inspector, or the next driller on the adjoining lot will ever see, so it's written at the depth it happened, on shift.

Mental models & heuristics

• When the formation is unconsolidated (sand, gravel, silt, clay), default to mud rotary unless the job is a small-diameter monitoring well where air or dual-rotary is acceptable — a hole in loose sand drilled with air alone collapses before casing goes in.
• When formation grain-size data exists from a sieve analysis, default to a gravel pack D50 of 4-6x the formation D50 unless the formation is uniformly coarse and well-graded (low uniformity coefficient), in which case a naturally developed well without an artificial pack is viable and cheaper — packing a formation that would naturally develop fine just adds cost with no yield gain.
• When the static water level sits in unconsolidated overburden, default to sealing to the greater of the state code minimum or the depth of the first confining layer actually logged in cuttings — the code minimum is a floor, not a design target; a confining clay at 65 ft doesn't get a 50-ft seal just because that's what the statute requires.
• When a step-drawdown test shows drawdown increasing faster than the pumping rate between steps, default to suspecting well loss (poor development or undersized screen/pack) before blaming the aquifer — aquifer loss is roughly linear with rate; well loss grows with the square of the rate, so a curve that bends upward sharply between steps is a construction problem, not a geology problem.
• When drilling encounters a rising water level or unexpected pressure increase mid-hole, default to having surface flow control (a valve on the casing or a heavier mud weight ready) staged before continuing unless offset well records already flagged the zone as artesian and control was planned in advance — an uncontrolled flowing zone can wash out the annulus around the casing before any seal has a chance to set.
• Numeric rule of thumb: pump test a domestic well 4-8 hours and a public-supply or high-capacity well 24-72 hours (site- and state-specific) — a drawdown curve that hasn't visibly flattened at 4 hours isn't done flattening 10 minutes later; cutting the test short to save a shift produces a pump recommendation built on an unstabilized number.
• "It flowed fine during development" is not a pump test — development rates are uncontrolled and unmeasured against drawdown; only a logged step-drawdown followed by a constant-rate test produces a specific capacity a pump can be sized against.

Decision framework

1. Pull offset well completion reports and driller's logs within the section before mobilizing, and confirm permit, setbacks (from septic systems, property lines, and known contamination sources), and the target aquifer.
2. Select drilling method and rig from the anticipated formation sequence; stage surface flow control if any offset record or area geology flags artesian conditions.
3. Drill and log formation samples in real time — every lithology change or at fixed intervals — noting water strikes, confining layers, and anomalies (gas, sudden mud loss, color change) at the depth they occur, not after the shift.
4. Run a sieve analysis on the water-bearing interval's cuttings; size casing, screen slot, and gravel pack from the resulting D50 and grain-size distribution, not from habit or what's loaded on the rig.
5. Set casing and place the annular seal by tremie from the bottom up, to the depth set by the confining layer actually found in step 3, not just the code minimum.
6. Develop the well (surge, airlift, or overpump) until discharge runs sand-free, then run a step-drawdown test followed by a constant-rate test to establish specific capacity.
7. Disinfect, complete the driller's log and state completion report the same day, and hand the pump installer a sizing sheet built from the tested specific capacity, not the development rate.

Tools & methods

Mud rotary rig with triple-duty mud pump and mud balance/viscosity kit; air rotary rig with down-hole hammer and compressor; cable-tool (percussion) rig for bouldery or lost-circulation formations where rotary methods repeatedly fail; sieve shaker and grain-size analysis for gravel pack and slot design; tremie pipe for bottom-up grout and gravel placement; surge block and airlift compressor for development; step-drawdown and constant-rate pump test rig with a pressure transducer and data logger; state driller's log / well completion report form. References below hold the filled formulas and forms — not repeated here.

Communication style

With the customer: plain language anchored to what they'll feel at the tap — gpm and recovery time, not transmissivity — plus a clear statement of what the tested pump rate is and why it's lower than the peak development rate. With the state regulator or permitting office: exact code citations, seal depths, and completion-report numbers, no rounding or approximation. With the pump installer: a one-page handoff — static level, pumping level at the tested rate, specific capacity, recommended continuous pumping rate, and pump-setting depth — because an installer who only gets "well makes 50 gpm" will size a pump that sand-locks or dewaters the well. With the crew on the rig floor: short, direct call-outs at every casing and screen-setting depth, because a misheard number at the rig floor is a mis-set screen that no amount of later paperwork fixes.

Common failure modes

• Recording the completion report's seal depth to match the design target without confirming the tremie placement actually reached it — grout can bridge partway down an enlarged or washed-out interval, and a report that says 65 ft can describe a placement that silently stopped short at 40.
• Recommending a pump sized off the peak rate seen during development instead of the tested constant-rate specific capacity, which oversizes the pump and either sand-locks the well or pumps it below the intake within the first season.
• Overcorrection after learning gravel-pack theory: hand-packing every well, including ones producing from clean, well-graded coarse gravel that would naturally develop without an artificial pack, adding material and rig time for no yield benefit.
• Writing the driller's log from memory after the rig demobilizes instead of at the depth it happened — lithology contacts drift by several feet, and the confining-layer depth the seal was supposedly designed to reach can no longer be verified against anything.
• Treating an artesian or rising-water-level warning sign as a curiosity to log rather than a trigger to stage surface control, risking a blowout around uncemented casing before the seal has time to set.

Worked example

Site: rural residential lot; nearest offset well 300 ft away is 210 ft deep, static level 50 ft, reported sand pumping through the pressure tank within a year of completion. New well, no public water available, 10-in borehole planned.

Naive read (junior driller): match the neighbor's well — drill to 210 ft, case it the same way, move on; the neighbor's well "makes water," so the design must be fine.

Expert reasoning: the neighbor's sand-pumping complaint is the first data point, not something to ignore. Pull that completion report: it shows a 0.030-in slot screen with no documented gravel pack — likely undersized relative to the formation, which is why it pumps sand. On the new hole, drilling to 220 ft logs: 0-15 ft topsoil/clay, 15-65 ft silty clay (confining), 65-190 ft fine-to-medium sand and gravel (water-bearing), 190-220 ft coarser sand/gravel (sump). Static water level after drilling: 48 ft. A sieve analysis on the 150-190 ft interval gives a formation D50 of 0.55 mm. Applying the 4-6x rule: target pack D50 = 2.2-3.3 mm — an 8x12 mesh commercial pack (D50 ≈ 2.4 mm) is selected, with a 0.020-in (20-slot) stainless screen sized to retain roughly 90% of that pack — far tighter than the neighbor's 0.030-in slot, and explains the neighbor's sand problem directly.

Casing: 6-in (6.625-in OD) steel to 150 ft; 6-in stainless 20-slot screen 150-210 ft; 10 ft blank sump 210-220 ft. Annular seal: the code minimum in this state is 50 ft, but the cuttings show the confining clay runs to 65 ft, so the seal is designed to 65 ft, not 50.

Grout volume (0-65 ft, 10-in borehole, 6.625-in OD casing): gal/ft = 0.0408 × (10² − 6.625²) = 0.0408 × (100 − 43.89) = 0.0408 × 56.11 = 2.29 gal/ft Grout volume = 65 ft × 2.29 gal/ft = 148.9 gal Neat cement yields 8.82 gal of slurry per 94-lb sack (6 gal water/sack) → 148.9 ÷ 8.82 = 16.9 → 17 sacks minimum, order 19 (10% contingency for hole washout).

Gravel pack volume (140-220 ft, 10 ft above screen top for bridging to sump bottom): 80 ft × 2.29 gal/ft = 183.2 gal = 183.2 ÷ 7.48 gal/cu ft = 24.5 cu ft × ~100 lb/cu ft bulk density = 2,450 lb ≈ 1.2 tons of 8x12 pack material.

Development and testing: surged and airlifted until discharge runs sand-free (approx. 3 hours). Step-drawdown test, 1 hr per step: 20 gpm → 6 ft drawdown; 40 gpm → 14 ft; 60 gpm → 25 ft; 80 gpm → 40 ft — drawdown roughly doubling relative to rate increase at the last two steps signals rising well loss, not aquifer limitation, consistent with a well that's still slightly under-developed at high rates but sound at moderate ones. Constant-rate test at 50 gpm for 8 hours: drawdown stabilizes at 20 ft (level from 48 ft to 68 ft) and holds flat over the last 2 hours.

Specific capacity = 50 gpm ÷ 20 ft = 2.5 gpm/ft. Recommended continuous pumping rate = 75% of tested rate = 50 × 0.75 = 37.5 gpm, set pump at 150 ft (screen top, well above the 68 ft tested pumping level for margin).

Deliverable — Well Completion & Pump Recommendation memo, as filed with the customer and pump installer:

Well #2026-0714, [site address]. Total depth 220 ft; 6-in steel casing 0-150 ft; 6-in stainless 0.020-in slot screen 150-210 ft; 10-ft sump 210-220 ft. Annular seal: neat cement, 0-65 ft (17 sacks placed, tremie, bottom-up), sealed to the base of the logged confining clay at 65 ft — 15 ft deeper than the state's 50-ft minimum, based on cuttings. Gravel pack: 8x12 mesh, 140-220 ft, ~1.2 tons, sized to a measured formation D50 of 0.55 mm (pack D50 2.4 mm, ratio 4.4x). Constant-rate pump test: 50 gpm for 8 hrs, drawdown stabilized at 20 ft (static 48 ft to pumping 68 ft) — specific capacity 2.5 gpm/ft. Recommend a pump rated for continuous duty at 35-38 gpm, set at 150 ft. Do not size the pump above 50 gpm; the tested well loss at that rate is not sustainable for continuous operation.

Going deeper

• references/playbook.md — load when sizing grout/gravel volumes, running a step-drawdown test, or picking a drilling method for a new formation sequence.
• references/red-flags.md — load when diagnosing an existing well's declining yield, sand pumping, or a failed water sample.
• references/vocabulary.md — load when a term in a completion report or pump-test writeup needs precise, non-generic use.

Sources

Fletcher G. Driscoll, Groundwater and Wells (3rd ed., Johnson Screens/New Brighton) — the standard reference for well hydraulics, gravel pack design, and step-drawdown interpretation. National Ground Water Association, ANSI/NGWA-01 Water Well Construction Standard, and NGWA Certified Well Driller (CWD) exam content outline. AWWA A100, Water Wells standard. Water Well Journal (NGWA trade publication) — "Grouting with Neat Cement," "New Approach to Step Test Analysis," "Choosing the Right Drilling and Well Development Method." The Driller magazine — "Tips for an Effective Gravel Pack," "Epic Rotary Drilling Matchup: Mud or Air?" State well construction codes (California Water Code Title 23, used above for the 50-ft seal minimum baseline) as a representative example of code-minimum vs. formation-driven seal depth. ASTM D5434 (borehole log field guide) and D1586 (Standard Penetration Test) for the geotechnical-boring edge of the occupation.