Glossary
Comprehensive definitions of water drilling terminology.
AquiferA saturated geological formation capable of yielding significant quantities of water to wells or springs.
AquitardA low-permeability formation that retards (but does not prevent) groundwater flow. Examples: clay, shale.
ArtesianCondition where groundwater under pressure rises above the top of the aquifer. Flowing artesian = water rises above ground surface.
BailerA hollow tube with a check valve used to remove cuttings and water from the borehole during cable tool drilling.
BentoniteSodium montmorillonite clay that swells 10-20× in water. Used in drilling mud and well grouting.
CasingA permanent liner (steel or PVC) installed in a borehole to prevent collapse and seal out contaminated water.
Cone of depressionThe drawdown surface around a pumping well, shaped like an inverted cone.
Darcy's LawQ = K × A × (dh/dL) — fundamental equation relating flow rate to hydraulic conductivity, area, and gradient.
DevelopmentPost-construction process of removing fine materials and drilling fluids from around the well screen to maximize yield.
DrawdownThe vertical distance the water level drops in a well during pumping, measured from the static water level.
DTH (Down-the-Hole)A pneumatic hammer that strikes the drill bit at high frequency, driven by compressed air.
Filter cakeA thin, impermeable layer of clay deposited on the borehole wall by drilling mud, preventing fluid loss.
Gravel packFiltered gravel placed between the well screen and borehole wall to improve filtration and yield.
Hydraulic conductivity (K)A measure of how easily water flows through a material. Units: m/s. Depends on both the fluid and the porous medium.
Hydraulic gradientThe slope of the water table or potentiometric surface — the driving force for groundwater flow.
Marshall funnelA simple device for measuring drilling mud viscosity — time for 1 quart to drain through the funnel.
Porosity (n)The percentage of rock volume occupied by void spaces. Determines water storage capacity.
Potentiometric surfaceThe imaginary surface to which water would rise in a well penetrating a confined aquifer.
RechargeWater entering an aquifer from the surface — through infiltration, stream leakage, or artificial injection.
Safe yieldThe maximum extraction rate that can be maintained indefinitely without unacceptable consequences.
ScreenA perforated section at the bottom of the casing that allows water to enter while keeping formation material out.
Specific capacityWell yield divided by drawdown (Q/s). An indicator of well efficiency — declining trends indicate deterioration.
Static water levelThe natural water level in a well when no pumping is occurring.
Storage coefficient (S)Volume of water released from storage per unit area per unit decline in head. Also called storativity.
Transmissivity (T)The water-transmitting capacity of the full aquifer thickness: T = K × b. Units: m²/day.
Unconfined aquiferAn aquifer whose upper boundary is the water table — free to rise and fall with recharge and discharge.
Water tableThe upper surface of the saturated zone in an unconfined aquifer — the level where pore water pressure equals atmospheric pressure.
YieldThe rate at which a well produces water. Typically measured in L/s, m³/h, or gallons per minute (GPM).
Formulas & Equations
Essential equations for hydrogeology and well design.
Groundwater Flow
Darcy's Law:
Q = K × A × (dh/dL)
Darcy Velocity:
v = Q / A = K × (dh/dL)
Transmissivity:
T = K × b
Storage Coefficient (confined):
S = Ss × b
Q = K × A × (dh/dL)
Darcy Velocity:
v = Q / A = K × (dh/dL)
Transmissivity:
T = K × b
Storage Coefficient (confined):
S = Ss × b
Pumping Test Analysis
Theis Equation (confined):
s = (Q / 4πT) × W(u)
u = r²S / (4Tt)
Cooper-Jacob Approximation:
s = (2.3Q / 4πT) × log₁₀(2.25Tt / r²S)
Hantush (leaky aquifer):
s = (Q / 4πT) × W(u, r/B)
B = √(Tb'/K') — leakage factor
s = (Q / 4πT) × W(u)
u = r²S / (4Tt)
Cooper-Jacob Approximation:
s = (2.3Q / 4πT) × log₁₀(2.25Tt / r²S)
Hantush (leaky aquifer):
s = (Q / 4πT) × W(u, r/B)
B = √(Tb'/K') — leakage factor
Well Design
Total Dynamic Head:
TDH = Hstatic + Hdrawdown + Hfriction + Hdischarge
Pump Power Required:
P(kW) = Q(m³/s) × TDH(m) × ρ × g / η
Specific Capacity:
SC = Q / s
Well Efficiency:
ηwell = stheoretical / sactual × 100%
Step-Drawdown Test:
s = BQ + CQ²
TDH = Hstatic + Hdrawdown + Hfriction + Hdischarge
Pump Power Required:
P(kW) = Q(m³/s) × TDH(m) × ρ × g / η
Specific Capacity:
SC = Q / s
Well Efficiency:
ηwell = stheoretical / sactual × 100%
Step-Drawdown Test:
s = BQ + CQ²
Hydraulic Conductivity Ranges
| Material | K (m/s) | K (m/day) | Aquifer Rating |
|---|---|---|---|
| Gravel | 10⁻² to 10⁻¹ | 1000-10,000 | Excellent |
| Coarse sand | 10⁻⁵ to 10⁻² | 1-100 | Good |
| Fine sand | 10⁻⁷ to 10⁻⁵ | 0.01-1 | Moderate |
| Silt | 10⁻⁹ to 10⁻⁷ | 0.0001-0.01 | Poor |
| Clay | <10⁻⁹ | <0.0001 | Aquitard |
| Sandstone | 10⁻⁸ to 10⁻³ | 0.001-100 | Variable |
| Limestone (karst) | 10⁻⁵ to 10⁻¹ | 1-10,000 | Excellent |
| Fractured granite | 10⁻⁸ to 10⁻⁴ | 0.001-10 | Variable |
Unit Conversions
| From | To | Multiply By |
|---|---|---|
| L/s | m³/day | 86.4 |
| GPM | L/s | 0.0631 |
| m³/day | GPM | 18.46 |
| ft | m | 0.3048 |
| m | ft | 3.281 |
| psi | bar | 0.0689 |
| bar | psi | 14.50 |
| °F | °C | (°F-32)/1.8 |
Resources & Links
Essential references, standards, and organizations for water well professionals.
Professional Organizations
- National Ground Water Association (NGWA) — ngwa.org — US professional association for groundwater industry
- American Water Works Association (AWWA) — awwa.org — Water industry standards and best practices
- International Association of Hydrogeologists (IAH) — iah.org — Global groundwater science organization
- Water Well Journal — WaterWellJournal.com — Technical publication for well drillers
- American Institute of Hydrology (AIH) — aih.org — Professional hydrologist certification
Standards & Specifications
- AWWA A100 — Water Wells standard (design, construction, testing)
- API 5CT — Casing and Tubing specifications (steel casing)
- ASTM D596 — Standard guide for test hole drilling
- NSF/ANSI 61 — Drinking water system components (materials safety)
- State Well Construction Codes — Vary by jurisdiction — check your state/province
Key Publications
- "Groundwater Hydrology" by Todd & Mays — Comprehensive textbook on groundwater science
- "Water Well Technology" by Sterrett — Professional reference for well design and construction
- "Groundwater" by Freeze & Cherry — Foundational hydrogeology text
- "Theis Memorial Volume" (AWRA) — Collection of seminal papers in groundwater hydrology
- USGS Water Supply Papers — Free technical reports on aquifer characteristics worldwide
Government Resources
- USGS Groundwater — usgs.gov/mission-areas/water-science — Data, tools, and research
- EPA Underground Injection Control — epa.gov/uic — Well classification and regulations
- State geological surveys — Aquifer maps, well databases, geological reports
- GRACE-FO satellite data — grace.jpl.nasa.gov — Global water storage monitoring
Continue Learning
This knowledgebase is a living resource. New topics, case studies, and technological updates are added regularly. For the latest information, check the reference links above and join professional organizations to stay connected with the groundwater community.