4.2 Well Construction & Groundwater Production

Well Construction & Groundwater Production

Quick Answer: A properly constructed well uses casing, screen, sanitary seal, and a correctly sized pump to deliver groundwater while excluding surface contamination. TCEQ Class C/B groundwater operators must understand construction features, wellhead protection, aquifer behavior, pumping metrics, and disinfection of new wells.

Groundwater systems look simple from the outside — a pump house and a discharge meter — but exam questions dig into how the well keeps dirty surface water out and how pumping affects the aquifer.

Essential Well Components

Sanitary seal is repeatedly tested on licensing exams because a perfect aquifer can still deliver contaminated water through a bad annular seal or an unsealed wellhead.

Wellhead Protection in Daily Operations

Wellhead protection is both a planning program and a shift checklist:

• Keep the slab or pad graded so ponded water drains away from the casing
• Maintain a watertight sanitary seal and capped unused openings
• Lock the wellhouse; restrict unauthorized access
• Keep fuel, chemicals, and spare parts stored so spills cannot drain to the well
• Know setbacks from septic systems, livestock pens, chemical storage, and wastewater lines
• Inspect after floods — submerged wellheads are high-risk events
• Sample raw water per TCEQ monitoring schedules and after construction or repair work

If coliform appears in a groundwater system that historically was clean, start at the wellhead and sample tap before blaming the aquifer geology.

Aquifer Types Operators Should Recognize

Unconfined (Water-Table) Aquifers

• Upper surface is the water table open to atmospheric pressure
• Recharge is relatively direct from infiltration
• More vulnerable to surface spills, nitrates, and septic influence
• Water levels respond faster to drought and pumping

Confined Aquifers

• Bounded above and below by low-permeability layers (aquitards/aquicludes)
• Water is under pressure; flowing artesian conditions are possible
• Generally better natural protection from surface contamination
• Still vulnerable if wells are poorly sealed through the confining layer (creating a conduit)

Other useful distinctions

• Consolidated rock aquifers (limestone, sandstone) vs unconsolidated sand/gravel
• Karst limestone (common in parts of Texas) can transmit contamination rapidly through fractures and conduits — treat "remote" surface activities as closer than they look on a map

Capacity, Drawdown, and Specific Capacity

These three terms show up constantly in groundwater NTK (need-to-know) material:

Static Water Level

Depth to water when the pump has been off long enough for recovery (no pumping influence).

Pumping Water Level

Depth to water while pumping at a steady rate.

Drawdown

[ \text{Drawdown} = \text{Pumping water level} - \text{Static water level} ] (Expressed as a length, typically feet.)

Well Capacity / Yield

The sustainable pumping rate the well can produce (often gpm) without excessive sand, cavitation, or unacceptable drawdown.

Specific Capacity

[ \text{Specific capacity} = \frac{\text{Pumping rate (gpm)}}{\text{Drawdown (ft)}} ] Units: gpm/ft.

Why it matters: Declining specific capacity over months or years signals plugging, biofouling, sanding, or pump/well deterioration. A sudden drop after construction or rehab needs investigation before you assume the aquifer "ran out."

Example: Pumping 300 gpm with 20 ft of drawdown → specific capacity = 15 gpm/ft.

Disinfection of New or Repaired Wells

Before a new well (or a well that was opened for major repair) enters potable service:

1. Clean debris and construction materials from the well
2. Disinfect with an approved chlorine solution at a concentration and contact time consistent with TCEQ/AWWA practice for well disinfection
3. Pump the well to waste until chlorine residual is purged and water quality stabilizes
4. Collect bacteriological samples as required
5. Place the well in service only after satisfactory results and authorization under the system's procedures / TCEQ approval conditions

Exam trap: Shock chlorination of a well is not the same as continuous distribution residual. Construction disinfection is a temporary, high-dose sanitation step; finished-water residual is a separate ongoing barrier.

Groundwater Production Operations (Class C/B GW NTK)

Day-to-day groundwater production includes:

• Starting/stopping pumps to meet demand without short-cycling
• Recording raw meter totals, run hours, and amperage
• Watching discharge pressure and comparing to normal baselines
• Managing multiple wells to avoid over-pumping a single zone
• Blending wells when mineral quality differs (hardness, iron, arsenic)
• Maintaining backup power readiness for outages
• Coordinating well maintenance (pulling pumps, acid/chemical rehab) with sampling and customer notification when needed

Sand production after raising pump speed or lowering the pump is a warning: you may be overpumping the formation or have a damaged screen.

Air / gas binding and cascading water in the well can reduce capacity and create noisy operation — investigate water levels and pump setting depth.

TCEQ Exam Framing

Expect scenario questions such as:

• Coliform positive at the well → inspect sanitary seal, sample tap, recent flooding, and nearby contamination sources
• Falling specific capacity → fouling or well deterioration, not automatically "more chlorine"
• New well ready for customers → disinfection + bacteriological clearance first
• Unconfined shallow aquifer near ag land → nitrate and pathogen vulnerability higher than deep confined aquifer

Know the components, the metrics, and the protection mindset — that trio covers most groundwater construction and production items on the Texas exams.