Well Drilling and Inspection Techniques
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Questions and Answers

What is the maximum depth at which a drilled pipe can be utilized?

  • 50 feet
  • 130 feet
  • 4000 feet (correct)
  • 15 feet

What is the function of caissons in the context presented?

  • To collect excess water
  • To facilitate horizontal drilling
  • To support adjacent structures (correct)
  • To transport heavy machinery

What type of structure is typically jacked through the ports near the bottom of water bodies?

  • Drilled wells
  • Radial pipes (correct)
  • Concrete barriers
  • Caisson foundations

How deep can caissons reach when sunk into the aquifer?

<p>Up to 130 feet (C)</p> Signup and view all the answers

What is a useful application for bored pipes?

<p>Pumping loose sand (C)</p> Signup and view all the answers

What is the maximum size of a bored pipe mentioned?

<p>36 inches (D)</p> Signup and view all the answers

In which formation are radial pipes typically installed?

<p>In sandy formations (B)</p> Signup and view all the answers

What is a primary reason for using pumps with single metal types?

<p>To prevent corrosion (D)</p> Signup and view all the answers

What type of equipment is used for Down Hole Inspections?

<p>Special television equipment (D)</p> Signup and view all the answers

What is an essential feature of a rotating earth auger?

<p>It helps to excavate loose soil (B)</p> Signup and view all the answers

What depth can wells be inspected using special television equipment?

<p>Up to 900 m (A)</p> Signup and view all the answers

What is another term for periodic well cleaning?

<p>Well rehabilitation (C)</p> Signup and view all the answers

Why is effective sealing important after the abandonment of wells?

<p>To prevent pollution of ground water (C)</p> Signup and view all the answers

Which organization’s guidelines must be followed for the abandonment of wells?

<p>AWWA (D)</p> Signup and view all the answers

What type of data is included in pre-design checklists for well locations?

<p>Geological and groundwater resource reports (D)</p> Signup and view all the answers

What information is gathered from existing wells to assess treatment requirements?

<p>Chemical, physical, and bacteriological analyses (C)</p> Signup and view all the answers

What is the primary reason for selecting the northeast flatland site for test drilling?

<p>It has good potential for recharge from surface drainage. (D)</p> Signup and view all the answers

What is indicated by the records regarding the flooding risk at the chosen drilling site?

<p>The site has a 100-year flood level of approximately 675 feet. (C)</p> Signup and view all the answers

What is a primary characteristic of an aquifer?

<p>It yields water in sufficient quantity to be economical. (D)</p> Signup and view all the answers

What does the water table represent?

<p>The level of saturated soil below ground. (C)</p> Signup and view all the answers

Which statement about the situation of the site is accurate?

<p>The site is bordered by a large river on the west. (B)</p> Signup and view all the answers

What is the required yield for the well in gallons per minute (gpm)?

<p>350 gpm (B)</p> Signup and view all the answers

Which condition allows water in a well to rise above the top of the aquifer?

<p>The water being under artesian conditions. (D)</p> Signup and view all the answers

Which feature was not included in Figure B-1 for clarity?

<p>Vegetation (C)</p> Signup and view all the answers

What factors can cause the water table to fall?

<p>Periods of drought. (A)</p> Signup and view all the answers

Which of the following describes the surrounding land use of the site?

<p>Undeveloped land primarily. (A)</p> Signup and view all the answers

What is a characteristic of confined aquifers?

<p>They are located directly beneath an impermeable bed. (A)</p> Signup and view all the answers

What type of well was specifically mentioned in the test drilling?

<p>Pumping well. (C)</p> Signup and view all the answers

What type of materials are typically targeted for well location?

<p>Coarse sand and gravel with interconnecting pore spaces. (A)</p> Signup and view all the answers

What is the depth to the static water level as indicated by the pumping test?

<p>100 ft (B)</p> Signup and view all the answers

How is unconfined water in aquifers typically described?

<p>It is directly influenced by atmospheric conditions. (A)</p> Signup and view all the answers

What best describes groundwater infiltration?

<p>Water percolating down through soil and rock layers. (D)</p> Signup and view all the answers

What is the minimum casing diameter required for the pump specified?

<p>8 inches (A)</p> Signup and view all the answers

What is one of the main purposes of grouting in well construction?

<p>To prevent contamination from the surface (D)</p> Signup and view all the answers

What pressure must the distribution system maintain at the maximum ground elevation of 820 ft?

<p>40 psi (C)</p> Signup and view all the answers

What component is included in the calculation of Total Dynamic Head (TDH) that is NOT influenced by elevation?

<p>Friction head (A)</p> Signup and view all the answers

When should grout be completely placed in the well creation process?

<p>Before the initial set occurs (C)</p> Signup and view all the answers

What factor is considered when determining the location for well installation?

<p>Future facility expansion (B)</p> Signup and view all the answers

Where should grout ideally be introduced in the well construction process?

<p>At the bottom of the space to be grouted (A)</p> Signup and view all the answers

What standard practice is mentioned for water treatment at the well site?

<p>Chlorine disinfection (B)</p> Signup and view all the answers

What should be ensured to prevent subsurface contamination?

<p>Sealing off poor quality water formations (C)</p> Signup and view all the answers

How should the well location be selected to protect water quality?

<p>On elevated ground away from pollution sources (A)</p> Signup and view all the answers

What is the required action before selecting a pump for the system?

<p>Review manufacturer's literature (A)</p> Signup and view all the answers

What is the purpose of analyzing water samples according to Standard Methods?

<p>To ensure no treatment is necessary (B)</p> Signup and view all the answers

What additional feature is recommended to protect well water quality?

<p>Construction of a concrete slab (D)</p> Signup and view all the answers

What is the minimum spacing required for the installation of the additional well?

<p>250 ft (A)</p> Signup and view all the answers

What is the minimum thickness for the concrete slab surrounding the well casing?

<p>100 mm (4 in) (C)</p> Signup and view all the answers

How far should the top of the well casing extend above the concrete surface slab?

<p>300 mm (12 in) (B)</p> Signup and view all the answers

Flashcards

Ground water

Subsurface water filling the spaces within permeable rock, gravel, sand, etc.

Aquifer

A water-bearing layer of rock, gravel, or soil that allows significant water flow and extraction.

Unconfined Aquifer

An aquifer that is not confined by an impervious layer above it. The top of this aquifer is the water table.

Confined Aquifer

An aquifer that is confined between two impervious layers. Water pressure can cause it to rise above the top layer.

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Water Table

The level at which groundwater in an unconfined aquifer is at atmospheric pressure.

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Infiltration and Recharge Areas

Areas where groundwater is replenished by rainfall or surface water seepage.

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Discharge

When groundwater flows to the surface naturally, often through an opening like a spring.

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Artesian Conditions

Water in a confined aquifer that rises due to pressure and can flow to the surface when tapped by a well.

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Drilled Well

A method of extracting groundwater using a rotating drill bit to create a hole in the ground, into which a pipe is inserted.

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Driven Well

A well constructed by driving a prefabricated pipe into loose sand formations, often used when the ground is difficult to drill.

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Reinforced Concrete Caisson

A type of well casing (pipe) used to support surrounding soil and prevent collapse during drilling.

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Bored Well

A well that uses a rotating earth auger (drill) to excavate the borehole, suitable for softer grounds.

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Radial Well

A well where pumped water is discharged through a pipe, usually positioned horizontally, creating a radial flow pattern in the aquifer.

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Well Installation by Driving

The process of creating a well by driving a pipe into the ground, used for extracting water from loose sand formations.

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Well Installation by Drilling

The process of creating a well by drilling a hole into the ground and installing a pipe casing.

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Installation by Augering and Bracket

The process of securing a pipe or casing in place during well installation by using a bracket that adheres to surrounding soil or rock.

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Grouting: What's the key for preventing contamination from the surface?

Grouting should be done in one continuous operation to prevent contamination from the surface.

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Grouting: When should grouting be finished?

Grouting should be completely placed before the initial set occurs to prevent contamination from the surface.

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Grouting: Where does it start?

Grout is introduced at the bottom of the space to be grouted to prevent contamination from the surface.

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Grouting: How does it prevent subsurface contamination?

For well construction, formations holding poor water quality above the target aquifer can be sealed off by grouting the outer casing before installing the deeper well casing. This helps prevent subsurface contamination.

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Grouting: What to do if a confining unit is breached?

Any portion of the confining unit that is breached during drilling should be replaced with grout to prevent subsurface contamination.

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Well Location: Accessibility & Safety

The well location should be accessible for pump repair, cleaning, disinfection, testing, and inspection. The top of the well should never be below the surface grade.

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Well Location: Minimizing Surface Contamination

The well or wells should be located on the highest ground practicable, higher than nearby potential sources of surface pollution. The surface near the site should be built up, by fill if necessary, to ensure surface drainage is away from the well in all directions.

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Well Design: Surface Slab

The well casing should be surrounded at the surface by a concrete slab extending outward from the casing a minimum of 600 mm (2 ft) in all directions. This slab helps prevent surface contamination.

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Downhole Inspection

Using special television equipment to visually inspect the inside of a well, allowing for high-resolution images even underwater.

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Well Cleaning

A process of cleaning a well by removing mineral deposits or other materials that can reduce its efficiency.

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Well Abandonment

The process of permanently sealing abandoned wells, test wells, and test holes to prevent groundwater pollution.

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Confined Aquifer Well

A type of well where groundwater is trapped under pressure between two layers of rock. Water can rise above the top layer when tapped.

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Unconfined Aquifer Well

A type of well where groundwater is not trapped under pressure. The top of the aquifer is the water table.

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Safe Yield

The rate at which water can be safely withdrawn from an aquifer without lowering the water level.

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Sanitary Survey

A comprehensive review of a water supply system's health and safety, including potential sources of pollution.

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What is well yield?

The yield of a well is the amount of water it can produce over a specific period of time, often measured in gallons per minute (gpm).

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What is a pumping test?

A pumping test measures the well's ability to provide water over time. It involves pumping water from the well and observing how the water level drops and recovers.

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What is drawdown in a well?

The drawdown of a well is the difference between the static water level and the water level during pumping. It reflects the well's impact on groundwater pressure.

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What is specific capacity of a well?

The specific capacity of a well represents its efficiency in producing water. It is calculated by dividing the well yield by the drawdown.

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What is the purpose of observation wells?

Observation wells are used to monitor water levels in an aquifer. They are placed at strategic locations to assess changes in groundwater levels.

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What is the static water level?

The static water level in a well is the level at which water sits when the well is not being pumped. It represents the pressure of the surrounding groundwater.

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Why are energy conservation measures important in well design?

Energy conservation measures aim to reduce energy consumption while maintaining the efficiency of a well and its pumping system.

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How does well location affect energy consumption?

The well's location should be strategically chosen to minimize energy consumption and maximize its efficiency. This includes factors like the distance to the pumping station and the depth of the well.

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Suction Head

The vertical distance from the pump level to the water surface in the well, accounting for the screen depth and the water table.

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Discharge Head

The difference in elevation between the pump and the water level in the storage tank, factoring in the required pressure.

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Friction Head

The pressure loss due to friction within the pipe and fittings.

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Velocity Loss

The pressure loss due to the velocity of the water moving through the pipe.

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Total Dynamic Head (TDH)

The sum of suction head, discharge head, friction head, and velocity loss. This measures the total energy required to pump water.

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Grouting

The process of filling the space between the well casing and the surrounding soil with a mixture of cement and water to prevent contamination.

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Study Notes

Bong County Technical College - Course Information

  • Location: Gbarnga City, Bong County
  • Department: Engineering
  • Course Title: Water supply and environmental Engineering
  • Lecturer: Eng. Cooper B. Saysay
  • Qualifications: BSc, MSc in Civil Engineering
  • Email: [email protected]
  • Contact: +231-770-299-886/+231-880-538-294

Sources of Water

  • Rain water
  • Surface water
  • Ground water
  • Water obtained from reclamation

Water Supply Systems

  • Objective: to take water from the best available source and process to ensure good physical quality, free from unpleasant taste/odour and free from anything detrimental to health
  • Involves: additions to, subtractions from, or chemical changes in the raw water
  • Components: Collection works, Transmission works, Purification works, and Distribution works

Hydrology

  • The science dealing with the occurrence, distribution, and movement of water on Earth, including the atmosphere and below the surface.
  • Water exists in vapour form, on the surface as water, snow or ice and below the surface as ground water.

Computation of Average Rainfall

  • Arithmetic Average Method: used when rainfall is uniformly distributed, involves calculating the simple average of the recorded values
  • Thiessen Polygon Method: more common, involves weighting the rain-gauge observations according to the area they represent
  • Isohyetal Method: involves drawing lines connecting points with equal rainfall amounts

Infiltration

  • Defined as the movement of water from the soil surface into the soil
  • Infiltration capacity: maximum rate of water entry into soil
  • Infiltration rate: rate at which water enters the soil

Infiltration Index

  • Represents the average rate of loss of water
  • Two types:
    • Average infiltration rate (W-index)
    • K-index

Chapter 1 - Introduction

  • Purpose and Scope: Introduction to selecting water sources and determining water requirements for water supplies.
  • Applicability: Guidelines are applicable to selecting water sources and planning/designing water supply systems.
  • References: Many professional references are available in literature.
  • Definitions: General Definitions: Water works, supply works, supply line, treatment work, distribution system, feeder mains, distribution mains, service line. Also addresses effective population, capacity factor, and required daily demand, peak domestic demand, fire flow, and fire demand, rated capacity and cross-connections, definitions of several terms relating to wells and ground water such as specific capacity and vertical line shaft turbine pump and submersible turbine pump

Other Water Quality Considerations

  • Total Dissolved Solids (TDS): Solids should not exceed 500 or 1000 mg/L
  • Chloride and Sulphate: concentration not to exceed 250 mg/L
  • Other Constituents: Presence of toxic heavy metals, fluoride, pesticides, and radioactivity with concentrations exceeding recognized standards

Well Hydraulics

  • Definitions: Static water level, Pumping level, Drawdown, Cone of depression, Radius of influence, Permeability, Hydraulic Conductivity
  • Well Discharge Formulas: Formulas for aquifer calculations (Eq 5.1-5.3)

Water Quality Evaluation

  • Selection of well sites: criteria such as local hydrogeology, terrain, soil type, depth, thickness, water bearing zone, proximity to sewage and industrial facilities etc.
  • History of water, oil, and gas wells
  • Direction and rate of travel of groundwater
  • Minimum distances from pollution sources

Other topics

  • Capacity Factors: tables of capacity factors
  • System design capacity
  • Special design capacity
  • Expansion of existing systems
  • Use of Existing Systems
  • Other water systems( if near municipality)
  • Environmental Considerations
  • Watershed Control and Surveillance
  • Treatment Requirements (Groundwater under direct influence of surface water & not under influence)
  • Surface Water
  • Quality of Surface Waters
  • Water Laws

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Description

This quiz covers various aspects of well drilling and inspection techniques, including the use of caissons, bored pipes, and inspection equipment. Test your knowledge on the maximum depths of drilled pipes, well abandonment guidelines, and essential features of drilling equipment.

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