NC Well Driller flashcards
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- Minimum septic tank setback
- The well casing must be at least 50 feet horizontally from a septic tank. Distance is measured from the well head to the nearest edge of the tank.
- Minimum drainfield setback
- The well casing must be at least 100 feet horizontally from a septic absorption field or drainfield. Local rules may require a greater separation distance.
- Sewer line setback
- A well must be at least 50 feet from a sanitary sewer line. Where the line is a force main under pressure, the required separation is larger.
- Setback measurement point
- Setbacks are measured horizontally from the well casing to the nearest edge of the facility, not to a building centerline or the middle of a drainfield.
- Well head grading
- Ground around the casing must slope away from the well so surface water drains off. The well head must not sit in a swale or low spot.
- Floodway well siting
- A well should not be placed in a floodway or frequently flooded area unless the casing is extended and sealed to keep floodwater out of the well.
- Animal feedlot setback
- Barnyards, feedlots, and chemical storage areas must be at least 100 feet from a well. Fuel tanks and lines have separate required distances.
- Neat cement grout mix
- Neat cement grout uses no more than 6 gallons of clean water per 94-pound sack of cement. Excess water weakens the seal and causes shrinkage.
- Tremie grouting method
- Grout is placed from the bottom of the annular space upward through a tremie pipe using a positive displacement pump. Free-fall dumping is not acceptable.
- Bentonite grout density
- Bentonite slurry grout is mixed to the manufacturer's density, typically about 9.4 pounds per gallon or heavier, so the seal sets properly.
- Grout volume formula
- Volume equals 0.7854 times the difference of borehole diameter squared minus casing diameter squared, times length. Add margin for washouts.
- Grout seal extent
- The grout seal runs from the top of the screen or open interval to land surface or the well house floor, with no unsealed gap.
- Well abandonment sealing
- An abandoned well must be filled with grout or approved sealing material, the casing removed or perforated as specified, and the top capped.
- Granular bentonite use
- Granular bentonite may be used in a dry, stable annulus. Below the water table or in caving ground, a slurry or cement grout is required.
- Casing height above grade
- Casing must extend at least 12 inches above finished grade or above the well house floor, and be fitted with a sanitary, vermin-proof cap.
- Annular clearance minimum
- The space between borehole wall and casing should be about 2 inches nominal. Too small blocks grout; too large risks bridging.
- Casing material requirement
- New wells require new steel or NSF/ANSI 61-certified plastic casing. Used casing is generally prohibited for new potable water wells.
- Screen slot sizing
- Screen openings are chosen to retain about 90 percent or more of the formation sample, based on sieve analysis of the aquifer material.
- Rotary versus cable tool
- Rotary air or mud drilling suits unconsolidated sediments. Cable tool is preferred where boulders, hard rock, or caving formations hinder hole cleaning.
- Well log filing
- The well log records total depth, casing and grout depths, and yield. It is filed with the state and is the legal record of construction.
- Confining layer penetration
- Do not drill through a confining layer deeper than needed. Each extra aquifer tapped raises the risk of cross-contamination between water zones.
- Well development purpose
- Development removes drilling fines and mud cake to raise yield. Methods include surging, jetting, bailing, and air-lift pumping until discharge clears.
- Development stopping point
- Stop development when turbidity stabilizes at a low level. Overdevelopment can destabilize the formation or pull fines into the gravel pack.
- Pump setting depth
- The pump intake must stay above the screen and above expected drawdown, so the pump does not cavitate or run dry during normal use.
- Total dynamic head
- TDH equals static lift plus drawdown plus friction loss plus discharge pressure head. It is used to size the submersible pump.
- Specific capacity
- Specific capacity is yield divided by drawdown, in gallons per minute per foot. It indicates how productive the well is per foot of drawdown.
- Pitless adapter function
- A pitless adapter makes a below-frost, sanitary connection through the casing. The casing top is still sealed with a cap and vent.
- Pressure tank role
- The pressure tank maintains system pressure and limits pump cycling. A check valve on the discharge prevents backflow and protects the pump.
- Permit before construction
- A well permit must be obtained before construction begins. The application includes proposed location, depth, casing, and intended use.
- Certified contractor requirement
- Well construction in North Carolina requires a certified well contractor whose certification is current and in good standing when the work is done.
- Well log submission
- The completion report and well log must be filed with the state within the required time after construction, with a copy given to the owner.
- Grounds for revocation
- Certification may be suspended or revoked for violations such as building without a permit, failing to grout, or falsifying a well log.