AL Well Driller cheat sheet

Cable-tool drilling breaks rock by percussion and removes cuttings with a bailer; rotary drilling cuts with a rotating bit and lifts cuttings with circulating fluid.

Rotary mud drilling relies on bentonite or polymer slurry to cool the bit, stabilize the borehole wall, and carry cuttings to the surface.

Air rotary drilling is preferred where the hole must be kept open in hard rock and the formation produces little water; foam or water injection controls dust.

Reverse circulation pumps drilling fluid down the annulus and up through the drill pipe, giving faster cuttings removal in large-diameter holes.

Bit types: tricone roller bits for hard rock, drag or blade bits for soft formations, and down-the-hole hammers for hard, fractured rock.

Penetration rate depends on weight on bit, rotational speed, bit condition, and circulation rate; excessive weight on bit can bend drill pipe.

A driven well uses a hardened point and screen pushed or driven into unconsolidated sand; it is limited to shallow depths and fine-grained formations.

Jetted wells use a high-velocity water jet to wash a hole into sand and gravel, then casing is set as the jet advances.

Lost circulation occurs when fluid escapes into fractures or caverns; remedies include reducing fluid weight, adding lost-circulation material, or using air.

Annular space is the volume between the borehole wall and the outside of the casing, and is the target for grout or filter pack.

Filter pack (gravel pack) is sized to the formation: typically the pack is 4 to 5 times the 50-percent retained size of the aquifer material.

Well screen slot size is selected so roughly 40 to 50 percent of the filter pack material passes through the slots.

A sanitary seal of grout must extend from land surface to a minimum depth specified by rule, sealing off surface water and shallow contamination.

The pump setting depth must keep the pump intake above the bottom of the well and below the pumping water level to avoid cavitation.

Well development removes drilling mud and fines from the filter pack and screen, increasing specific capacity and reducing sand production.

Artesian (flowing) wells occur where the potentiometric surface of a confined aquifer stands above land surface.

Static water level is the non-pumping water level; pumping water level is the stabilized level during pumping, and their difference is drawdown.

Casing must be centered with centralizers so the annular space is uniform and grout can fully surround the casing.

Grout is typically neat cement, cement-sand, or bentonite slurry; neat cement gives the highest strength and lowest permeability.

Grout volume for an annular space equals pi times the difference of the squares of the borehole and casing radii, times the length, plus a lost-circulation allowance.

Grouting is placed from the bottom up, usually by tremie pipe, to displace water and avoid voids and bridging.

Casing wall thickness is specified by weight per foot and schedule; thicker wall resists collapse and corrosion but reduces inside diameter.

Casing must extend above land surface or above the well pad so that surface water cannot enter the annulus.

Thermoplastic (PVC) casing is joined by solvent cement or threaded couplings; steel casing is joined by welding or threaded couplings.

A drive shoe is a hardened ring on the bottom of casing that protects the casing and cuts a seat into bedrock during driving.

Alabama well construction is governed by the State of Alabama Water Well Standards, administered through ADEM and the Alabama Department of Public Health.

A water well driller must hold a valid Alabama well driller license issued by the state before drilling or constructing wells.

A well permit or notification must be obtained before construction, and the driller must file a well log or completion report after construction.

Well logs record location, depth, diameter, casing and screen intervals, grout intervals, water levels, and formation descriptions.

Abandoned or unusable wells must be properly sealed with grout or approved material to prevent cross-contamination between aquifers.

Setback distances from sources of contamination (such as septic systems or animal lots) must be met when siting a new well.

Disinfection after construction typically uses a chlorine solution (commonly 50 to 200 ppm) held in the well for a contact period before pumping to waste.

Inspection and enforcement authority rests with the state agency; violations can result in permit denial, fines, or license action.

Porosity is the fraction of rock or sediment volume that is void space; specific yield is the drainable porosity.

Hydraulic conductivity describes a formation's ability to transmit water; transmissivity equals hydraulic conductivity times saturated thickness.

Darcy's law: Q = K i A, where Q is discharge, K is hydraulic conductivity, i is hydraulic gradient, and A is cross-sectional area.

The water table is the upper surface of the saturated zone in an unconfined aquifer; the potentiometric surface is the equivalent for a confined aquifer.

Specific capacity equals pumping rate divided by drawdown and is a common measure of well performance.

Hardness in groundwater is mainly caused by dissolved calcium and magnesium; iron and manganese cause staining and taste problems.

Common contaminants include nitrate from fertilizers and septic systems, bacteria, arsenic, and volatile organic compounds from industrial sources.

A cone of depression forms around a pumping well and can capture nearby contamination or cause interference between neighboring wells.

Groundwater flows from areas of higher hydraulic head to lower head, generally perpendicular to equipotential lines.

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