*1.2.5 Analyzing and evaluating pumping test data*

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 part of the hydrogeologist.

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 respect to the above mean sea level).

#### *1.2.6 Pumping tests and methods of analysis*

Among the main techniques are analytical/conventional methods and numerical methods. Analytical/conventional methods involve one of the curve matching, finding inflection points, or for special cases and fitting straight lines to the pumping test data [4].

does not drop significantly. Late-time response is a function of transmissivity and specific yield (drainable porosity). Release of water is due to drainage from formation over large area water table decline slows and flow is essentially horizontal. At intermediate time, the response is controlled by the aquifer's vertical hydraulic conductivity. The release of water is from gravity drainage and slope of time-

After comparative analysis of various methods for determination of specific yield, the author in [8] concluded that the water table response to pumping is a much faster phenomenon than drainage in the unsaturated zone above it.

hydrogeologists in analysis of pumping tests conducted in water table (unconfined aquifers). One of the primary features of the model is that it allows drawdown to vary continuously in the vertical as well as the horizontal directions, thus retaining the full three-dimensional, axisymmetric character of the flow regime. Another feature is that the model accounts for aquifer compressibility. However, the use of Neuman type curve fitting for unconfined aquifer conditions has sometimes led to values of specific yield that are unrealistically low (plus sometime too high) com-

Moreover, although both the Boulton and Neuman models could account for the compressive characteristics of an aquifer by assuming the pumped well is infinitesimal in diameter, it becomes impossible to account for effects of well bore storage, thereby limiting the usefulness of the models for accurate evaluation of specific storage. This assumption necessitates that observation wells be located at large distances from the pumped well to reduce the influence of well bore storage. Unfortunately, this last requirement makes it difficult to record accurate early-time

The study by Neuman [7] attributed the inability of Neuman's models to give reasonable estimates of specific yield (Sy) and capture this observed behavior near the water table due to the disregard of "gradual drainage." To resolve this problem, the instantaneous moving water table boundary condition used by Neuman was replaced with one containing a Boulton [13] delayed yield convolution integral. The study by Neuman [7] recommended the composite analysis of pumping test data and grouping of corresponding time drawdown data for parameterization as

The Moench solution, presented in AquiferTest V. 2.55, is an extension of the

unconfined aquifer with fully or partially penetrating pumping and multiple observation wells. The Moench solution also allows for water in the overlying unsaturated zone to be released either instantaneously in response to a declining water

There are a number of software programs that can be used to complete the data

In the analysis of a multiple pumping test conducted in a layered unconfined aquifer (harbor area of Antwerp, Belgium), the use of two computer programs was presented: AquiferTest and WTAQ to investigate and compare previous results obtained for transmissivity, hydraulic conductivity specific yield, and storage

Neuman solution for drawdown in a homogeneous anisotropic confined or

analysis of aquifer test drawdown data that include, but are not limited to,

table or gradually as approximated by Boulton's convolution integral.

*1.2.7 AquiferTest software application for pumping test data analysis*

in the assumption, the Neuman model has been used successfully by many

The analytical model developed by Moench [14] combines and extends the work of Boulton [13] and of Neuman [7, 8] to account for the release of water from the unsaturated zone above the water table. In spite of the possible limitations inherent

drawdown curve relative to Theis curve decreases.

*Aquifer Characterization: The Case of Hawassa City Aquifer*

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

pared to volume-based calculations.

measurements due to small drawdowns at large distances.

opposed to the analyses of individual drawdown curves.

AQTESOLV, AquiferTest, WTAQ, and AquiferWin32.

**39**

Models for the interpretation of pumping test data were initiated under constant pumping test rate and equilibrium conditions for confined and unconfined aquifers. Since then, different methods have been designed for pumping test analysis. Reliable estimates of the hydraulic parameters controlling an unconfined aquifer's capacity to store and transmit water are generally obtained by pumping test analysis with one or more analytical models, of which authors [5, 7–14] are the most popular. Nowadays, the entire computation procedures and hydrological equations are typically written into computer programs.

However, each of the methods is based on basic assumptions relating to geologic formation, the basic types of well, such as well diameter, dug well and bore well. Therefore, it is important to choose the right method of interpretation based on the field conditions [3].

The study by Mishra and Kuhlman [6] discussed concisely the issue of which model for which well conditions. According to this study, analytic and semi-analytic solutions are often used by researchers and practitioners to estimate aquifer parameters from unconfined aquifer pumping tests. The nonlinearity associated with unconfined (i.e., water table) aquifer tests make their analysis more complex than confined tests.

As the method by Cooper and Jacob [5] is a simplification of the Theis method solution, the pumping well should fully penetrate a confined, homogeneous, and isotropic aquifer. Single well tests from partially penetrating wells in unconfined aquifers depart greatly from the Theis model. Moreover, unconfined aquifer tests are affected by vertical anisotropy and specific yield in addition to transmissivity and storage coefficient. These additional parameters control vertical gradients that are created by partial penetration and drainage from the water table. Likewise, leakage from adjacent confining beds also could affect transmissivity estimates, which likely will be overestimated by the Cooper-Jacob method [15].

The study in Neuman [7] presented a physically based mathematical model that treated the unconfined aquifer as compressible and the water table as a moving material boundary. Newman's approach describes the aquifer delayed response was caused by physical water table movement; therefore, it was proposed to replace the phrase "delayed yield" by "delayed water table response." Besides this, the model exhibits three distinct drawdown segments as shown in **Figure 1**.

Early-time response is controlled by the transmissivity and elastic storage coefficient and is analogous to the response of a confined aquifer, and the water table

**Figure 1.** *The three distinct drawdown segments in an unconfined aquifer (from [16]).*

### *Aquifer Characterization: The Case of Hawassa City Aquifer DOI: http://dx.doi.org/10.5772/intechopen.91211*

*1.2.6 Pumping tests and methods of analysis*

typically written into computer programs.

pumping test data [4].

*Resources of Water*

field conditions [3].

**Figure 1.**

**38**

Among the main techniques are analytical/conventional methods and numerical

Models for the interpretation of pumping test data were initiated under constant pumping test rate and equilibrium conditions for confined and unconfined aquifers. Since then, different methods have been designed for pumping test analysis. Reliable estimates of the hydraulic parameters controlling an unconfined aquifer's capacity to store and transmit water are generally obtained by pumping test analysis with one or more analytical models, of which authors [5, 7–14] are the most popular. Nowadays, the entire computation procedures and hydrological equations are

However, each of the methods is based on basic assumptions relating to geologic formation, the basic types of well, such as well diameter, dug well and bore well. Therefore, it is important to choose the right method of interpretation based on the

The study by Mishra and Kuhlman [6] discussed concisely the issue of which model for which well conditions. According to this study, analytic and semi-analytic solutions are often used by researchers and practitioners to estimate aquifer parameters from unconfined aquifer pumping tests. The nonlinearity associated with unconfined (i.e., water table) aquifer tests make their analysis more complex than confined tests.

As the method by Cooper and Jacob [5] is a simplification of the Theis method solution, the pumping well should fully penetrate a confined, homogeneous, and isotropic aquifer. Single well tests from partially penetrating wells in unconfined aquifers depart greatly from the Theis model. Moreover, unconfined aquifer tests are affected by vertical anisotropy and specific yield in addition to transmissivity and storage coefficient. These additional parameters control vertical gradients that are created by partial penetration and drainage from the water table. Likewise, leakage from adjacent confining beds also could affect transmissivity estimates,

The study in Neuman [7] presented a physically based mathematical model that treated the unconfined aquifer as compressible and the water table as a moving material boundary. Newman's approach describes the aquifer delayed response was caused by physical water table movement; therefore, it was proposed to replace the phrase "delayed yield" by "delayed water table response." Besides this, the model

Early-time response is controlled by the transmissivity and elastic storage coefficient and is analogous to the response of a confined aquifer, and the water table

which likely will be overestimated by the Cooper-Jacob method [15].

exhibits three distinct drawdown segments as shown in **Figure 1**.

*The three distinct drawdown segments in an unconfined aquifer (from [16]).*

methods. Analytical/conventional methods involve one of the curve matching, finding inflection points, or for special cases and fitting straight lines to the

does not drop significantly. Late-time response is a function of transmissivity and specific yield (drainable porosity). Release of water is due to drainage from formation over large area water table decline slows and flow is essentially horizontal. At intermediate time, the response is controlled by the aquifer's vertical hydraulic conductivity. The release of water is from gravity drainage and slope of timedrawdown curve relative to Theis curve decreases.

After comparative analysis of various methods for determination of specific yield, the author in [8] concluded that the water table response to pumping is a much faster phenomenon than drainage in the unsaturated zone above it.

The analytical model developed by Moench [14] combines and extends the work of Boulton [13] and of Neuman [7, 8] to account for the release of water from the unsaturated zone above the water table. In spite of the possible limitations inherent in the assumption, the Neuman model has been used successfully by many hydrogeologists in analysis of pumping tests conducted in water table (unconfined aquifers). One of the primary features of the model is that it allows drawdown to vary continuously in the vertical as well as the horizontal directions, thus retaining the full three-dimensional, axisymmetric character of the flow regime. Another feature is that the model accounts for aquifer compressibility. However, the use of Neuman type curve fitting for unconfined aquifer conditions has sometimes led to values of specific yield that are unrealistically low (plus sometime too high) compared to volume-based calculations.

Moreover, although both the Boulton and Neuman models could account for the compressive characteristics of an aquifer by assuming the pumped well is infinitesimal in diameter, it becomes impossible to account for effects of well bore storage, thereby limiting the usefulness of the models for accurate evaluation of specific storage. This assumption necessitates that observation wells be located at large distances from the pumped well to reduce the influence of well bore storage. Unfortunately, this last requirement makes it difficult to record accurate early-time measurements due to small drawdowns at large distances.

The study by Neuman [7] attributed the inability of Neuman's models to give reasonable estimates of specific yield (Sy) and capture this observed behavior near the water table due to the disregard of "gradual drainage." To resolve this problem, the instantaneous moving water table boundary condition used by Neuman was replaced with one containing a Boulton [13] delayed yield convolution integral. The study by Neuman [7] recommended the composite analysis of pumping test data and grouping of corresponding time drawdown data for parameterization as opposed to the analyses of individual drawdown curves.

The Moench solution, presented in AquiferTest V. 2.55, is an extension of the Neuman solution for drawdown in a homogeneous anisotropic confined or unconfined aquifer with fully or partially penetrating pumping and multiple observation wells. The Moench solution also allows for water in the overlying unsaturated zone to be released either instantaneously in response to a declining water table or gradually as approximated by Boulton's convolution integral.

#### *1.2.7 AquiferTest software application for pumping test data analysis*

There are a number of software programs that can be used to complete the data analysis of aquifer test drawdown data that include, but are not limited to, AQTESOLV, AquiferTest, WTAQ, and AquiferWin32.

In the analysis of a multiple pumping test conducted in a layered unconfined aquifer (harbor area of Antwerp, Belgium), the use of two computer programs was presented: AquiferTest and WTAQ to investigate and compare previous results obtained for transmissivity, hydraulic conductivity specific yield, and storage

coefficient. The study made use of the Theis-type [14] curve method in AquiferTest applicable to both partially and fully penetrating wells. This was used to calculate dimensional drawdowns that are compared with time-drawdown data from 23 observation points to estimate the hydraulic properties of a finite, layered unconfined aquifer situated in the harbor area of Antwerp. The study concluded that AquiferTest and WTAQ form an excellent pair for the analyses of single or multiple pumping tests in unconfined aquifers.

Around the western part of the city (the industry zone), the water striking point is the deepest of the study area. Highly fractured and weathered scoriaceous formation dominates the water-bearing strata (52–84 m). The central areas generally fractured basalt (12–21.5 m), sand and ignimbrite (22.64–33.54 m), scoria and pumice (27.38–38.20 m), and highly weathered ignimbrite (39.27–45 m).

About 30–60 m ignimbrites and pumice are dominant in large area of the central part. These ignimbrite and pumice of the rift floor are well jointed while in some cases, it is massive and pumiceous. Where it is well jointed, it has a high or moder-

The relationship between lithology and aquifer characteristics is used to understand the qualitative and quantitative aspects of the hydrogeology in these areas. The study by Glenn and Duffield [17] established the estimate of the representative range of hydraulic properties (horizontal and vertical hydraulic conductivity, storativity, specific yield, and porosity) of aquifers and aquitards in relation to the formation type using values reported in different literatures. These tabulated values

Therefore, the dominant water-bearing formations (weathered pumice, scoria, fractured basalt, and sand of different types) possess large pores. Pumice and fractured basalts strata, which are common relatively in the shallower formations, are devoid of primary openings but possess secondary openings in the form of fractures and joints. These features aid in the infiltration of surface water. Besides, pores and fractures in

Highly fractured and weathered scoriaceous formation dominates the waterbearing strata (52–84 m), and the fine-to-course-grained sand is the main water source in depth beyond 100 m. Furthermore, lack of confining rocks like clay in the area studied indicates that groundwater occurs in phreatic, unconfined conditions

Looking into representative values, aquifers in the area are high hydraulic conductivity units and large porosity which will produce higher and more sustained well yields than an aquifer where the clean sands and gravels are compartmentalized by interbedding with clay and other low hydraulic conductivity units.

The results show (**Table 1**) the depth ranges from 25 m to 200 m below the surface. The pumping phase of the tests had a duration of 1440 min; the recovery phase of the tests had a duration of 45–240 min. Constant rate of discharge was applied for each of the wells. These constant discharge rates are from 3.0 l/s (for Gara Riqita 6) to 66 l/s (for Gara Riqita 1). Total drawdown varied from 0.03 m (for

The specific capacity of the wells as the ratio of the yield to the total drawdown is determined using Eq. (1). These two parameters (TDDw and Sc) along with the discharge rate are calculated and tabulated for 29 wells as shown in **Table 1**.

As per **Table 1**, values of specific capacity range from 0.54 l/s/m to 2200 l/s/m. Maximum values are toward the southwest part of the city (at Hawassa University Referral Hospital) and tend to decline toward the central and then to the northern corner. A decline in specific capacity may indicate declining S or T values due to declining water levels or piezometric surfaces, thus large water level drawdown for the specified discharge rate. It can also be used to determine the distribution of transmissivity in the aquifer. The spatial distribution of specific capacity reveals

Zewdu Village) to 12.36 m (for HU Techno Village) and average of 2.53 m.

ate permeability, but in the other part, it has low permeability.

*Aquifer Characterization: The Case of Hawassa City Aquifer*

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

are used to understand the hydraulic properties of the study area.

in the weathered basalts that outcrop at the surface.

**2.1 Aquifer physical properties of Hawassa City**

*2.1.1 Specific capacity*

**41**

laterites and fractures and joints in basalts act as reservoirs of groundwater.

An assessment was made for the hydraulic properties of the Ethiopian Ashange formations applying AquiferTest software. In the study, a total of 70 wells raw pumping test data were analyzed and used besides their respective lithological log to determine hydraulic property of Ashange formation. This study has done identification, analysis, and interpretation of aquifer system hydraulic properties of the geologic formation using the secondary well pump test data, lithological log, and data of hydro geological field observations. Among the different stages of pumping tests, constant rate pumping tests lasting between 5 and 72 h and recovery tests were used to determine transmissivity, hydraulic conductivity, and storativity values. The study analyzed single pumping test data mainly using Theis time-drawdown graphic method by which aquifer properties have been calculated. The pump test data including measured and calculated ones have been organized and processed using the Aquifer test software version 3.5. Arc GIS 9.2 and Global mapper 11 were also used for mapping in that study. As a result, the study finally identified the aquifer characteristics of the Ashange formation with respect to depth of the boreholes, age, and variation of its spatial distribution and groundwater potential.
