**1. Introduction**

#### **1.1 Aquifer characterization**

Characterization of hydraulic properties of an aquifer involves the use of existing pumping test data, hydrogeological map, geologic map, soil map, lithology obtained from well logs, aquifer thickness, water table depth, structures and surface water features, etc., so as to analyze the lateral distribution and nature of the aquifer.

Pumping test analysis and well logs were used to identify the aquifer system of Tarmaber formation by the author [1]. Accordingly, the formation is categorized as fractured aquifer where the dominant aquifer types are confined-double porosity and single plane vertical aquifer. The double porosity aquifers are related to deeply drilled wells reflecting presence of large and narrow fracture systems with high permeability but with lower storage capacity. Transmissivity varies between 0.5 and 1400 m<sup>2</sup> /day.

### **1.2 Pumping test, slug test, and recovery measurement**

#### *1.2.1 Pumping test*

Aquifer pumping test involves posing artificial stress on the hydrogeological system by pumping water from a well and measuring the changes in water levels in the pumped well and nearby observation wells. The response of the hydraulic head in the aquifer can be used to estimate transmissivity or hydraulic conductivity in the particular aquifer. The data from the pumping tests are used to calculate the specific capacity (specific capacity = Q/s, where Q = yield and s = drawdown) of the well.

The total drawdown is the algebraic sum of the individual drawdowns during the constant rate of pumping. The total drawdown can be estimated as:

$$\text{TDD}\_{\text{W}} = \text{DWL} - \text{SWL} \tag{1}$$

*1.2.3 Recovery measurement*

*Aquifer Characterization: The Case of Hawassa City Aquifer*

*DOI: http://dx.doi.org/10.5772/intechopen.91211*

following relationship:

*1.2.4 Specific capacity*

After a pump test is performed for the specified time period, the well is shut off and recovered data (heads in the observation well at times after the pump is shut off) are collected. The recovery is the rate at which water in the well returns to its static water level after the pumping is turned off. The recovery measure is another estimate of the well yield. Percentage of recovery can be estimated by the

where PR is percentage recovery, DWL is dynamic water level, MRWL is the

Specific capacity is known as well performance test estimated by assuming the well is pumped at a constant rate long enough to establish the equilibrium drawdown; within the well, there is a combination of the decrease in hydraulic head (pressure) and a pressure loss due to well loss. Specific capacity is defined as:

where Sc is specific capacity, Q is the pumping rate, and TDDw is the total

Well loss is created by the turbulent flow of water through the well screen and into the pump intake. Specific capacity is estimated by discharge on a linear x-axis and drawdown on a linear y-axis and measuring the slope of the straight line fit.

Different hydrogeologists [2, 3] suggested very similar procedures for analyzing and evaluating pumping test data. In general, it is as much an art as a science. It is a science because it is based on theoretical models that the hydrogeologist must understand and thorough investigations must be conducted into the geological formations in the area of the test. It is an art because different types of aquifers can exhibit similar drawdown behaviors, which demand interpretational skills on the

During an aquifer test, the hydraulic head in the aquifer declines as the time of pumping increases. Analysis of hydraulic head decline, or drawdown, allows for the estimation of aquifer hydraulic properties. For instance, authors [4] in the study of aquifer parameters estimation in basaltic terrain and the application of wireless sensor networks at Chikhaldara region, India; identified a pumping test as the best available method to evaluate aquifer parameters. The tests were performed at 20 locations using the local farmers' well pumps. The pumping phase of the tests had a short duration of 60–210 min; the recovery phase of the tests had a longer duration of 90–300 min. Three methods were adapted to estimate the aquifer parameters in a basaltic terrain. Out of the three methods, two were conventional or analytical curve matching techniques (the study is found in [5, 6]). The other technique was a numerical method. Moreover, this study determined the flow direction of sub-surface water using static groundwater level data within a basin from the past 20 years (1972–1992); an annual average water level map was constructed (with

maximum recovery of water level, and TDDW is total drawdown.

drawdown in the well due to both aquifer drawdown and well loss.

*1.2.5 Analyzing and evaluating pumping test data*

part of the hydrogeologist.

respect to the above mean sea level).

**37**

PR ¼ 100 � ð Þ DWL � MRWL *=*TDDW (2)

Sc ¼ Q *=*TDDw (3)

where TDDW is total drawdown, DWL is dynamic water level, and SWL is static water level.

In addition to estimating hydraulic properties of an aquifer system such as transmissivity and hydraulic conductivity, a step-drawdown test is made to evaluate well performance criteria such as well loss and well efficiency. All conventional well hydraulic theories are based on the assumption that laminar flow conditions prevail in the aquifer during pumping.

In our study area Lake Hawassa catchment, pumping tests are most commonly conducted following the development works usually for 24 h. The objective of the pumping test is to evaluate the production capacity of the well and the aquifers and to decide on the capacity and the position of the production well. Moreover, the results of the pumping test are of great value to be used in the well operation and maintenance apart from being used for future ground water study and research purposes. A pumping well with a pump that allows to control the pumping rate, one or more observation wells close enough to see the influence of the pumping well (mostly in the pumped well or control well itself), some means of measuring water levels in the observation wells at specific times throughout the course of the test; using automatic pressure transducers or manually using depth meters.

#### *1.2.2 Slug tests*

Multiple well pump tests are not always feasible—there may not be any observation wells, and it may cost too much to put new wells in or it could be that we are dealing with a contaminated system, and everything we pump out of the well have to be hauled away and treated, which need more investment. There are alternative methods that involve piezometers and a general set of tests called "slug" tests. These tests involve introducing or removing a known quantity of water (a "slug" of water) from a piezometer and measuring the time it takes to recover to the initial static water level [2].

## *1.2.3 Recovery measurement*

Pumping test analysis and well logs were used to identify the aquifer system of Tarmaber formation by the author [1]. Accordingly, the formation is categorized as fractured aquifer where the dominant aquifer types are confined-double porosity and single plane vertical aquifer. The double porosity aquifers are related to deeply drilled wells reflecting presence of large and narrow fracture systems with high permeability but with lower storage capacity. Transmissivity varies between

Aquifer pumping test involves posing artificial stress on the hydrogeological system by pumping water from a well and measuring the changes in water levels in the pumped well and nearby observation wells. The response of the hydraulic head in the aquifer can be used to estimate transmissivity or hydraulic conductivity in the particular aquifer. The data from the pumping tests are used to calculate the specific capacity (specific capacity = Q/s, where Q = yield and s = drawdown) of the well. The total drawdown is the algebraic sum of the individual drawdowns during

where TDDW is total drawdown, DWL is dynamic water level, and SWL is static

In our study area Lake Hawassa catchment, pumping tests are most commonly conducted following the development works usually for 24 h. The objective of the pumping test is to evaluate the production capacity of the well and the aquifers and to decide on the capacity and the position of the production well. Moreover, the results of the pumping test are of great value to be used in the well operation and maintenance apart from being used for future ground water study and research purposes. A pumping well with a pump that allows to control the pumping rate, one or more observation wells close enough to see the influence of the pumping well (mostly in the pumped well or control well itself), some means of measuring water levels in the observation wells at specific times throughout the course of the test;

Multiple well pump tests are not always feasible—there may not be any observation wells, and it may cost too much to put new wells in or it could be that we are dealing with a contaminated system, and everything we pump out of the well have to be hauled away and treated, which need more investment. There are alternative methods that involve piezometers and a general set of tests called "slug" tests. These tests involve introducing or removing a known quantity of water (a "slug" of water) from a piezometer and measuring the time it takes to recover to the initial static

In addition to estimating hydraulic properties of an aquifer system such as transmissivity and hydraulic conductivity, a step-drawdown test is made to evaluate well performance criteria such as well loss and well efficiency. All conventional well hydraulic theories are based on the assumption that laminar flow conditions

TDDW ¼ DWL � SWL (1)

the constant rate of pumping. The total drawdown can be estimated as:

using automatic pressure transducers or manually using depth meters.

0.5 and 1400 m<sup>2</sup>

*Resources of Water*

*1.2.1 Pumping test*

water level.

*1.2.2 Slug tests*

water level [2].

**36**

/day.

prevail in the aquifer during pumping.

**1.2 Pumping test, slug test, and recovery measurement**

After a pump test is performed for the specified time period, the well is shut off and recovered data (heads in the observation well at times after the pump is shut off) are collected. The recovery is the rate at which water in the well returns to its static water level after the pumping is turned off. The recovery measure is another estimate of the well yield. Percentage of recovery can be estimated by the following relationship:

$$\text{PR} = \text{100} \times (\text{DWL} - \text{MRWL}) / \text{TDD}\_{\text{W}} \tag{2}$$

where PR is percentage recovery, DWL is dynamic water level, MRWL is the maximum recovery of water level, and TDDW is total drawdown.
