Design, Construction & Completion

This is half the exam — about 35 of 70 questions. It covers siting the well, building it so it produces clean water, and sealing or plugging it so it never becomes a contamination pathway.

1. Siting the well (§76.100)

Before anything is drilled, the location has to satisfy minimum distances from pollution sources. These numbers are heavily tested.

Minimum distance	From
150 feet	Livestock or poultry yards, cemeteries, pesticide mixing/loading facilities, privies
100 feet	Septic-system absorption field or spray area
50 feet	Watertight sewage/liquid-waste collection facility; property line

Reductions (§76.100(b)): the 150-ft and 100-ft distances may be reduced to 50 feet where proper cementing techniques are used, and the property-line setback may be reduced to 5 feet with enhanced sealing.

Also consider: drainage away from the wellhead, flood-prone ground, access for the rig, and whether the site sits above a usable aquifer.

2. Choosing the drilling method

Match the method to the formation:

• Unconsolidated / caving (sand, gravel) → mud rotary or casing-advancement, which support the hole while drilling.
• Hard consolidated rock → air rotary or a downhole percussion hammer.
• Boulders / difficult ground → cable tool still works well.
• Clean formation samples needed → reverse circulation or dual-wall, where cuttings return up the inside of the drill pipe.

2a. Keeping the hole open and clean

In unconsolidated ground the borehole stays open because of two things working together: the hydrostatic pressure of the drilling fluid pushing outward, and the filter cake sealing the wall. Lose either one and a caving formation collapses.

Filter cake is the thin, low-permeability layer of clay the drilling fluid deposits on the borehole wall. It limits fluid loss into the formation and helps stabilize the hole. It needs to form quickly, and it should be thin and tough — a sandy, thick cake is a weak one.

The catch: the same layer that holds the hole open will choke off inflow once the well is in service. Breaking down and removing the filter cake is a primary objective of well development (see §6 below). A well that was never properly developed produces a fraction of what it should.

Lost circulation happens when the hydrostatic pressure of the fluid column exceeds the formation pressure — the formation absorbs your fluid and returns slow or stop. Expect it in gravel, fractured rock, and cavernous limestone. Drilling fluid that is too thick or too dense raises the equivalent circulating density and can cause lost circulation.

Borehole cleaning depends on uphole (annular) velocity. Too slow, and cuttings settle, regrind, and load the annulus — which leads to packing off, stuck pipe, and a poor penetration rate. How fast cuttings come out depends on the fluid's viscosity, density, and uphole velocity together.

Sand content in the fluid is worth watching: abrasive solids wear out pumps and bits and degrade the filter cake. That is what settling pits and solids-control equipment are for.

3. Casing

Casing holds the hole open, keeps unwanted water out, and carries the pump.

• Materials: steel (strength, high collapse resistance) and thermoplastic / PVC (corrosion resistance, light, lower strength). Match the material to water chemistry, depth, and expected loads.
• Wall thickness is expressed as a schedule — Schedule 40 has a thicker wall than Schedule 10; higher schedule = thicker wall, smaller inside diameter, greater collapse resistance. Deeper settings and caving ground need more collapse strength.
• Diameter must accommodate the pump plus clearance, and allow enough annular space for a proper grout seal.
• Casing must be plumb and aligned or the pump will not hang or run properly.
• Follow the manufacturer's recommendations for materials and joints (§76.78).

4. The well intake: screens and filter pack

Well screen lets water in while holding formation material out.

• Slot size is selected from a sieve (grain-size) analysis of the formation. A common production-well rule: choose a slot that retains roughly 40–60 percent of the formation material — retain nearer 60 percent where the material above the screen is readily caving, and nearer 40 percent where it is stable.
• Where layers differ in size, size the slot on the finest layer, or screen the zones separately.
• Screen length and open area control how much water can enter without excessive entrance velocity. Too little open area means high velocity, which drives incrustation and sand pumping.

Filter pack (sand/gravel pack) — clean, graded sand placed in the annulus around the screen.

• Purpose: filter fine material out of the formation, stabilize the borehole, and let the well yield sediment-free water at maximum capacity.
• Naturally developed wells rely on developing a graded envelope of coarse material out of the formation itself — suitable when the borehole diameter closely matches the screen and the formation is coarse and poorly sorted.
• Artificially filter-packed wells have graded sand introduced from the surface — needed for fine or uniform formations and for oversized boreholes.
• The pack must be clean, well-rounded, well-sorted silica sand, sized against the formation's grain-size distribution.

5. Grouting and sealing the annular space

The annular space — the gap between the borehole wall and the casing — is the most likely contamination pathway into the aquifer. Sealing it is the single most important groundwater-protection step in construction.

Acceptable grout: neat cement, cement-based grouts, and bentonite grouts (granular, pellets, chips, or high-solids slurry).

NOT grout: bentonite drilling fluid (drilling mud) and reintroduced drill cuttings. Neither can be relied on to seal a borehole.

A proper grout must:

1. have low permeability once placed,
2. bond to both the casing and the formation,
3. penetrate the surrounding formation minimally,
4. develop strength quickly enough to finish the well without excessive delay.

Placement:

• Place grout as a continuous seal from the bottom up, normally through a tremie pipe, so each interval is verified before the next is placed.
• Centralizers keep the casing centered so grout surrounds it evenly.
• Where a filter pack is installed, grout from the top of the pack (after development) upward; where a screen only is installed, grout from about 5 feet above the screen to land surface.
• Cement generates heat of hydration and needs curing time (commonly ~12–48 hours depending on type and additives) before drilling resumes. Bentonite grout needs minimal curing, stays flexible, and is self-healing.

6. Development

Development removes drilling fluid and fine material from the borehole wall and the filter pack so the well yields clean water at full capacity.

Common methods: surging (surge block), bailing, overpumping / backwashing, jetting (high-velocity water), and air lift. Development continues until the water runs clear and sand-free and yield stabilizes.

7. Completion at the surface

• The well must be completed so surface water cannot enter — a properly sealed and sloped surface completion.
• An uncovered or unattended well must be capped: the cover must prevent pollutants entering, sustain at least 400 pounds, and not be removable by hand (§76.104).
• Disinfect the well after construction before it is put into service.

8. Plugging and abandonment (§76.104)

A well no longer in use is a direct conduit to the aquifer and must be sealed.

• Who: a licensee or the well owner may plug a well.
• Cement method: pressure-place cement through a tremie from the bottom up to land surface.
• Bentonite method: clean bentonite grout of at least 9.1 pounds per gallon, tremie-placed, followed by a cement plug.
• Never fill an abandoned well with cuttings, trash, or loose soil.
• Artesian/flowing wells need special care — the flow must be controlled (for example with packers or by extending casing) before the seal will hold.
• Wells penetrating injurious-water zones get special plugging so the bad zone stays isolated (§76.101–§76.102).

Statutory deadlines: the landowner must have an abandoned or deteriorated well plugged or capped within 180 days of learning of its condition (Occ. Code §1901.255(c)), and a plugging report is due within 30 days after plugging (§1901.255(d)).

Sources: 16 TAC §§76.100, 76.101–76.102, 76.104, 76.78; Tex. Occ. Code §1901.255; EPA Handbook of Suggested Practices for the Design and Installation of Ground-Water Monitoring Wells (1991); Manual of Water Well Construction Practices, 3rd Ed., Sections 4 and 11; Groundwater and Wells, 3rd Ed. Verify all rule figures against the current official text.