FIELD METHODS IN ENVIRONMENTAL GEOLOGYFIELD METHODS IN ENVIRONMENTAL GEOLOGYGEOS 3110GEOS 3110
GROUNDWATER CHARACTERIZATIONGROUNDWATER CHARACTERIZATION
Groundwater Characterization
- Introduction
- Parameters to be measured
- Methodology
Introduction
WHAT IS A SLUG TEST
In a slug test, an instantaneous change in water level is causedin a well, and then the rate at which water level returns to the initiallevel is measured.
TYPES:- falling-head tests- rising-head tests
Slug Test Types
- Introduction
- Parameters to be measured
- Methodology
Groundwater Characterization
- Depth-to-water surface
Parameters
Depth-to-water Surface
Electric Cable Water-Level Indicator
Depth-to-water Surface
- Depth-to-water surface
- Hydraulic conductivity
Parameters
Hydraulic conductivity ( K ) is a measure of the ease with which a porous medium can transmit a fluid (such as water).
The term hydraulic conductivity is sometimes used interchangeblywith the term permeability.
Permeability is a characteristic only of the porous medium Hydraulic conductivity is a characteristic of both the porous mediumand the fluid.
Hydraulic Conductivity
Hydraulic Conductivity Computation
Hydraulic Conductivity Computation
K = r ln(L/R)2
2LT0
K - hydraulic conductivity ( m/sec)r - radius of the well (m)L - length of the saturation portion of the screen (m)R - radius of the screen (m)T - basic time lag which is read from the graph (sec)
For our case: r = 5 cm R = 5 cm L = 30.48 m
0
- Depth-to-water surface
- Hydraulic conductivity
- Chemical data
Parameters
See lab.3 - Water Quality Measurements
Perform the same analysis following the same procedures
Chemical Data
- Introduction
- Parameters to be measured
- Methodology
Groundwater Characterization
1. SLUG TEST
2. CHEMICAL ANALYSIS
Methodology
Slug Test Methodology- Before beginning the test, measure the depth-to-water level in well
- Measure depth to the bottom of the well to be sure that the well can accommodate the slug and water-level measuring device.
- Remove 4 liters of water using the bailer ( 1bailer = 1 liter )
- Begin measuring and recording the water level immediately after withdrawing the slug. The first object is to measure the lowest water level, which will occur within the first second after the slug is removed.
- Read and record the water level as it returns to normal, along with time of the measurements. Change the reading interval after every 5-10% changes in the readings. Reading interval: 15 sec, 30 sec, 1 min, 5 min.
- Stop the test after 60 % to 80% of the initial head has been recovered.
Slug Test Methodology
Slug Test Methodology1. Determine the Ho - the maximum level below the initial level to which the water falls immediately after the slug has been removed. Find Ho from subtracting the depth to water before the test from the depth to water immediately after the slug has been removed.
2. Compute H-Ho and devide the result to Ho. (drawdown)
3. Construct the graph Time vs. Drawdown. The Y axis have to be a logarithmic scale.
4. Define the best linear fit of these points.
5. Determine the To value from the graph. This value correspond to a drawdown equal with 0.37.
6. Use the formula to compute the hydraulic conductivity.