Acquisition and Interpretation of WaterLevel Data

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Acquisition and Interpretation of Water-Level Data

• Travis von Dessonneck

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Importance of Water-Level Data

• The acquisition and interpretation of
  ground-water data are essential for environmental
  site assesment
• Can be used to determine hydraulic head in
  formations
• Used to make 3D flow patterns

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Water level and Hydraulic-head relationships

• Hydraulic head varies spatially and temporally
• Piezometer
• Monitoring device for measuring water levels
• Hollow vertical pipe with a screen
• Elevation head
• The elevation of the bottom of the well/piezometer

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Water level and Hydraulic-head relationships

• Pressure head
• The height of the water above the bottom of the
  well
• Total hydraulic head
• Elevation head Pressure head

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Hydraulic Media and aquifer systems

• Aquifer is not a water-bearinglayer of geologic
  material, which will yield water in a usable
  quantity to a well or spring in this instance
• Aquifer is where water lies with respect to the
  top of a geologic unit

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Design features for water-level monitoring systems

• Takes into account water-level monitoring and
  sampling
• 2 phases
• Site data collection
• Monitoring for changes and proper placement of
  wells
• Can also be used to determine if monitoring
  system is not set up correctly
• Site geology must be known
• Heterogeneous sites require more monitoring than
  homogeneous sites

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Piezometers or wells

• Piezometers are generally not used to gather
  water samples
• Small diameter pipe
• Can accommodate pressure transducers
• Wells are designed for sampling
• Larger diameter

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Approach to system designs

• What to consider
• Boring and well logs
• Surficial geology
• Topographic maps
• Drainage features
• Cultural features (well fields, irrigation,
  pipes)
• Rainfall
• Recharge

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Approach to system designs

• Review the data to get
• Depth and characteristics of high and low K areas
• Depth to water, intermittent or perched zones
• Flow direction
• Vertical hydraulic gradients
• Possible causes and frequency of fluctuation
• Existing wells that may be incorporated

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Number and placement of wells

• Dependant on size and complexity of site
• Minimum to establish direction and rate of flow
• Larger sites usually have a grid of six to nine
  wells to get direction
• Take into account screen depth and length

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Water-level measurement precision and intervals

• Need to accurately located wells vertically and
  horizontally
• Survey/GPS
• Accuracy to 0.1 and 0.01 ft
• Need to know what you are looking for
• Seasonal changes
• Diurnal changes

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Reporting of data

• Monitoring installations
• Geologic sequence
• Well construction features
• Depth and elevation of well casing
• Water-level data
• Date and time of measurement
• Method used
• Other conditions that might affect the well level

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Manual measurements in nonflowing wells

• Wetted chalked tape method
• Weight attached to bottom of tape
• Coat bottom 2-3ft of tape with carpenters chalk
• Accurate to 0.01ft (USGS 1980)
• Disadvantages
• Stretching of the tape
• Need to know approximate depth to water

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Manual measurements in nonflowing wells

• Air-line submergence method
• Insert a small diameter tube below the water
  surface
• Pump the water out the bottom by hand or electric
  pump
• Ending psi 2.31 gives feet
• Subtract the calculated distance from length of
  tube

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Manual measurements in nonflowing wells

• Electrical methods
• Whistler
• Open circuit is completed when it comes in
  contact with the water and beeps at you
• Wires are at the end of a measuring tape
• Read the tape to determine depth

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Manual measurements in nonflowing wells

• Pressure transducer methods
• Measures the pressure in the well at the sensor
• Open to the atmosphere by a small capillary tube
• Usually have a sealed data logger
• Sensor is lowered a known distance into the water
  when installed

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Manual measurements in nonflowing wells

• Float method
• A float is attached to the end of a steel tape
• Read the depth off of the steel tape

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Manual measurements in nonflowing wells

• Sonic or audible methods
• The classic drop the pebble in the well
  approach only with a tape attached to the pebble
• Drop a battery powered probe down the beeps when
  it is in the water (whistler)

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Manual measurements in nonflowing wells

• Ultrasonic/radar/laser methods
• A sonar type device
• Calculates the reflection time
• Can get depth to water and total depth of the well

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Manual measurements in flowing wells

• Manometers and pressure gauges
• Well is sealed and a pressure gauge is installed
  in the top
• Mercury can be accurate to 0.005ft
• Pressure gauges can be accurate to 0.2 ft

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Methods of Continuous measurement

• Mechanical float recorder systems
• A float attached to a seismometer type drum
• Electromechanical Iterative Conductance Probes
  (dippers)
• Probe is lowered to the water surface by a
  stepping motor
• Sensor like on a whistler tells the motor to stop
• Motor reverses and repeats at set intervals
• Data loggers

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Analysis, Interpretation, and Presentation of
Water-level data

• Water-level can be effected by recharge and
  discharge conditions
• Water flows down during recharge and up during
  discharge

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Approach to Interpreting Water-level data

• Conduct a thorough site analysis
• Review monitoring wells features
• Establish groundwater flow direction and
  magnitude
• Monitor for several days to see long term
  fluctuations

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Transient Effects

• Water level can change due to many things
• Seasonal precipitation
• Irrigation
• Well pumping
• River stage
• Tidal fluctuations
• These can reverse flow direction

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Contouring water level elevation data

• Made like a topo map, only of the water table and
  not the surface elevation
• May require cross sections in areas with high
  vertical flow

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Manual measurements in nonflowing wells
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Manual measurements in nonflowing wells
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Manual measurements in nonflowing wells
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Manual measurements in nonflowing wells
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Manual measurements in nonflowing wells