acquisition and interpretation of water level data
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Acquisition and Interpretation of Water-Level Data. Travis von Dessonneck. 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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Presentation Transcript
importance of water level data
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
water level and hydraulic head relationships
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
water level and hydraulic head relationships1
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
hydraulic media and aquifer systems
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
design features for water level monitoring systems
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
piezometers or wells
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
approach to system designs
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
approach to system designs1
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
number and placement of wells
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
water level measurement precision and intervals
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
reporting of data
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
manual measurements in nonflowing wells
Manual measurements in nonflowing wells
  • Wetted chalked tape method
    • Weight attached to bottom of tape
    • Coat bottom 2-3ft of tape with carpenter’s chalk
    • Accurate to 0.01ft (USGS 1980)
    • Disadvantages
      • Stretching of the tape
      • Need to know approximate depth to water
manual measurements in nonflowing wells1
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
manual measurements in nonflowing wells2
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
manual measurements in nonflowing wells3
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
manual measurements in nonflowing wells4
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
manual measurements in nonflowing wells5
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)
manual measurements in nonflowing wells6
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
manual measurements in flowing wells
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
methods of continuous measurement
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
analysis interpretation and presentation of water level data
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
approach to interpreting water level data
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
transient effects
Transient Effects
  • Water level can change due to many things
    • Seasonal precipitation
    • Irrigation
    • Well pumping
    • River stage
    • Tidal fluctuations
  • These can reverse flow direction
contouring water level elevation data
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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