GA Well Driller cheat sheet

Georgia Piedmont: productive yield comes from fractures and faults in crystalline bedrock, not from intergranular porosity; a dry hole is common where no fracture is intersected.

Coastal Plain: sediments young seaward; the Floridan aquifer system is the principal supply, and the Upper Floridan is confined beneath the Dublin-Metter and other confining units.

Drawdown cone of influence radius in a confined aquifer: r = sqrt(2.25Tt/S) (Theis approximation), where T is transmissivity, S storativity, t pumping time.

Specific capacity = pumping rate / drawdown (gpm/ft); a falling specific capacity over time signals well inefficiency, not necessarily aquifer decline.

Georgia requires a 50-ft minimum separation between a well and a source of contamination such as a septic tank or animal lot; greater setbacks apply to land-application sites.

Topographic lows and drainageways concentrate recharge; siting on a ridge or steep slope reduces the catchment and increases the chance of a low-yield well.

Static water level is measured before pumping; pumping water level is measured during pumping. Difference = drawdown, used to compute specific capacity.

Confined aquifer potentiometric surface can stand above the top of the aquifer; an flowing (artesian) well results where it stands above land surface.

Casing must extend at least 20 ft into competent, unweathered bedrock where bedrock is encountered, and the annular space above the seal must be grouted to land surface.

In unconsolidated Coastal Plain sediments, casing is set through the upper confining unit and the screen is placed in the target aquifer; the annular seal must extend from the bottom of the casing to land surface.

Screen slot size is selected to retain 90-100% of the formation sand; slot openings are typically 0.010-0.040 in for Coastal Plain sands and larger for gravel-pack wells.

Gravel pack envelope thickness is normally 3-5 in around the screen; the pack must extend above the screen and be topped with a bentonite seal before grouting.

Well diameter must accommodate the pump: allow at least 2 in of clearance between pump outside diameter and casing inside diameter for motor cooling and setting depth.

Conductor casing is used to seal off unconsolidated surface material and shallow water; it is set first and the inner casing is telescoped through it.

A wellhead must be at least 12 in above finished grade, with a watertight, vermin-proof cap and a sanitary seal around the pump drop pipe.

Pitless adapters allow the discharge line to exit below frost line through the casing wall while keeping the wellhead watertight.

Mud rotary: circulation of bentonite-based fluid removes cuttings and stabilizes the borehole wall; cuttings return velocity must exceed the slip velocity of the largest cuttings.

Air rotary with a hammer is preferred in hard crystalline bedrock; foam or water injection controls dust and stabilizes the hole in wet zones.

Cable tool drilling: a heavy bit is lifted and dropped; cuttings are removed with a bailer. Formation water is not contaminated by drilling fluid, so it is useful for water-quality sampling.

Reverse circulation uses a dual-wall pipe; cuttings travel up the inner pipe and the sample is less contaminated by wall caved material.

Annular velocity for direct circulation: v = 24.5*Q/(D_h^2 - D_p^2) in ft/min with Q in gpm and diameters in inches; keep above 100-120 ft/min in large holes.

Lost circulation in fractured bedrock is treated with lost-circulation material, cement, or by switching to air; continuing to pump fluid wastes water and can wash out the formation.

Hole deviation is checked with a plumb-bob or downhole survey; excessive deviation prevents casing from seating and makes pump setting difficult.

Drilling-fluid weight must be kept low enough to avoid fracturing the formation; hydrostatic pressure = 0.433 psi/ft times mud weight in lb/gal divided by 8.34.

Neat cement grout is mixed at no more than 6 gal of water per 94-lb sack (about 15.6 lb/gal); extra water causes shrinkage, cracking, and loss of seal.

Bentonite may be added at up to 5% by weight of cement to reduce shrinkage and improve pumpability; more than that weakens the set grout.

Grout is placed from the bottom up through a tremie pipe; free-fall placement from the top causes bridging and voids.

The annular seal must be continuous from the bottom of the casing (or screen) to land surface; a shallow seal that stops below grade leaves a direct pathway for surface contamination.

Bentonite grout (high-solids sodium bentonite) is acceptable in some settings but is not a substitute for cement where the rule requires cement.

Grout volume for an annulus: V (ft^3) = 0.00545*(D_hole^2 - D_casing^2)*L, with diameters in inches and L in feet; add 10-20% for loss.

Casing centralizers keep the casing centered so the grout envelope is uniform; without them the casing can lie against the wall and leave an unsealed channel.

A grout seal must be allowed to set at least 24 hours before drilling out or pressure-testing, and the well should not be developed until the cement has reached initial set.

Development removes drilling fluid, fines, and filter cake; methods include surging, jetting, bailing, and air-lifting, continued until discharge is clear of sediment.

Specific capacity test: pump at a steady rate until drawdown stabilizes, record pumping and static levels, then compute gpm per foot of drawdown.

Constant-rate pumping test of 24 hours or more with recovery monitoring is used to estimate transmissivity and storativity for larger or public-supply wells.

Step-drawdown test (three or more steps) separates well loss from aquifer loss; well efficiency = aquifer loss / total drawdown.

Disinfection: a chlorine solution of 50-100 mg/L in the well, contact time of at least 12 hours (24 hours is common), then pump to waste until chlorine odor is gone.

Chlorine demand of the water and casing must be satisfied before a residual can be measured; test residual with a DPD kit and record the result.

Bacteriological sampling follows disinfection and a stabilization period; a total coliform-positive result requires investigation and re-disinfection, not automatic abandonment.

Water-level measurements are referenced to a marked measuring point on the casing top; record the height of that point above land surface so depths are reproducible.

Submersible pump setting depth must leave the pump above the well bottom and below the pumping water level so the motor stays submerged and cooled.

Pump capacity curve and system head curve intersect at the operating point; a pump operating far to the right of its curve can overload the motor.

Pressure tank precharge is set 2 psi below the pump cut-in pressure; a waterlogged tank (precharge lost) causes rapid cycling and motor failure.

Pressure switch settings are typically 30/50 or 40/60 psi; the gap between cut-in and cut-out determines the drawdown volume the tank must supply.

Drawdown volume of a bladder tank is roughly 25% of nominal tank volume; size the tank so the pump runs at least one minute per cycle.

Jet pumps are limited to about 25 ft of suction lift; deeper settings require a two-pipe deep-well jet or a submersible.

Pump motor voltage drop should not exceed 3% on the feeder and 5% total; undersized wire causes overheating and shortened motor life.

Backflow prevention and a check valve on the discharge protect the pump and prevent contamination of the aquifer from the distribution system.

Abandonment requires filling the entire borehole with an approved material, usually neat cement or bentonite grout, from bottom to land surface.

The uppermost 20 ft of a abandoned well must be sealed with cement grout and the casing cut off at least 12 in below grade or removed.

Bridge plugs or bentonite chips may be used to support grout in a cased or screened well, but the seal above them must still be continuous to land surface.

A well that is temporarily out of service must still be capped watertight and marked; it may not be left open or unmarked.

Abandonment records (location, depth, method, materials, and volume) must be filed with the Georgia EPD within the required reporting period.

Flowing artesian wells must be controlled during abandonment; grout is placed against the flow and the well is not left flowing between aquifers.

Abandoned well casings that are cut off must be capped or sealed so that surface water cannot enter the remaining borehole.

An abandoned well is a potential direct conduit between surface contamination and the aquifer; improper abandonment is a common cause of aquifer contamination.

Georgia Water Well Standards are administered by the Georgia Department of Natural Resources, Environmental Protection Division; the rules are in Ga. Comp. R. & Regs. 391-3-2.

A water well contractor must be licensed by the Georgia EPD; the license is required before constructing, repairing, or abandoning a well.

A well permit or notification is required before drilling in most Georgia counties; the local health department or EPD issues the permit and inspects the well.

Well logs must be filed with the EPD within 30 days of completion and must include depth, casing, screen, grout, and water-level data.

Casing must be new pipe meeting specified standards; used pipe may not be used for water well casing in Georgia.

The minimum distance from a well to a septic tank or sewage disposal area is 50 ft; greater distances apply to land application systems and other sources.

Public-supply wells are subject to additional requirements under the Safe Drinking Water Act and Georgia's public water system rules, including monitoring and operator certification.

A variance from a specific rule may be requested from the EPD in writing; the well may not be constructed until the variance is granted.

Before drilling, call 811 to have underground utilities located; drilling into a gas or electric line is a leading cause of serious injury on well sites.

Confined-space entry into a pit or vault requires atmospheric testing for oxygen, hydrogen sulfide, and combustible gas, plus a rescue plan and attendant.

Hydrogen sulfide is lethal above about 100 ppm and deadens the sense of smell; never rely on odor to judge safety.

Drilling fluid and cuttings must be contained in a pit or tank and disposed of properly; do not discharge to streams or wetlands without a permit.

Fuel and oil storage on site must be bermed or double-contained; a spill kit must be on site and spills reported to the EPD.

Rotating shafts, belts, and augers must be guarded; loose clothing and jewelry are prohibited near the drill string.

Hearing protection and a hard hat are required on active drill sites; rig mast raising and lowering is done only with the area cleared.

Site restoration includes removing cuttings, grading, reseeding, and restoring drainage so that surface water does not pond around the wellhead.