FIELD METHODS IN ENVIRONMENTAL GEOLOGY GEOS 3110

GROUNDWATER 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 caused in a well, and then the rate at which water level returns to the initial level 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 interchangebly with the term permeability. Permeability is a characteristic only of the porous medium Hydraulic conductivity is a characteristic of both the porous medium and the fluid. Hydraulic Conductivity

Hydraulic Conductivity Computation

K = r ln(L/R) 2 2LT 0 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 = 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

1. 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 Use the formula to compute the hydraulic conductivity.