kitui mutua hydro report

HYDROGEOLOGICAL/GEOPHYSICAL SURVEY FOR BOREHOLE SITE INVESTIGATIONS PASCAL MUTUKU MUTUA-2012

PASCAL MUTUKU MUTUA

PROPOSED BOREHOLE WATER PROJECT

DETAILED HYDROGEOLOGICAL/ GEOPHYSICAL SURVEY REPORT

FOR

BOREHOLE SITE INVESTIGATIONS

AT

MULUTU VILLAGE, MULUTU LOCATION,

KYANGWITHYA DIVISION, KITUI CENTRAL DISTRICT

OF KITUI COUNTY

OCTOBER, 2012

*** INVESTIGATING HYDROGEOLOGIST: C.N.KITHOME, MSC.(ENGINEER)

PROFESSIONAL LICENCE NO. WD/WRP/138 &NEMA 1278/2010

CONSULTANTS C.N. Kithome/E.N. Nyakoni Registered Hydrogeologists/Engineers P.o. Box 554322-00200

NAIROBI

CLIENT Mr. Pascal Mutuku Mutua P.o. Box 30-90200

KITUI


SUMMARY

This report summarizes and describes the results of groundwater potential survey carried out on a piece of land for Mr. Pascal Mutuku Mutua situated within MULUTU location, Kyangwithya Division, Kitui Central District of KITUI County and covering about 4 hectares of land. The Client intends to develop the land to enable generation of additional income. This part of Kenya is semi-arid, humid and rainfall is moderate. It is expected that water demand will increase with time due to climate change and diminishing of surface water flow due to land degradation. The Client water demand is estimated to be about 20cubic metres per day for domestic, livestock and minor irrigation purposes. The current water sources are from seasonal streams located over 2-5 kilometres range from the Client utility land. There is no surface water except during the wet season when the existing depressions collect water that flow to the nearby main tributaries. No other feasible alternative sources of water exist within the vicinity of the project area except ground water. Due to the increasing water needs and lack of reliable water supply, the Client has sought professional advice on the possibility for exploration of alternative and reliable water sources. The objective of the water investigations was to establish the optimum location for sinking of one borehole/well to provide water for domestic, livestock and minor irrigation purposes. The report concludes that the area is of moderate groundwater potential. Available data of boreholes near the surveyed area indicate moderate but varying borehole yields. Generally, the land is open grassland with thorny shrubs and is ready for development. The vegetation cover comprises of scattered Acacia trees and thick bushes. Underlying the area, are the dark-red soils or clayey soils overlying the Metamorphic Rocks, in that stratigraphic order. The main water-bearing zone is encountered within the weathered and fractured zones of metamorphic rock formations.

The rocks existing in the area are crystalline gneisses, schist, and granulites of the Archaean Basement System. During Archaean age an extensive deposit of material was laid down in a depression, most probably in a sea. East-West compression following the deposition of the Basement System sediments resulted in their subjection to intense heat, pressure and deformation, transforming the succession into a metamorphic series of crystalline schist, gneisses and granulites. The compression and folding of the Basement System rocks led to the formation of hills which, later were extremely eroded leading to the exposure of the more highly changed rocks in the centre of the hills. After the development of the sub-Miocene peneplain the Kapiti phonolite lavas covered great stretches of the area. The steady phase following the Miocene period of eruption resulted in the formation of the end-Tertiary peneplain. The rivers laid down small deposits of ill-sorted pebbles, gravels and cross- bedded sands on their floodplains, during Pleistocene times; these were however eroded leading to the present land form. . It is observed that the total drilled depths ranges between 63m and 130m below ground level, while the water struck levels are found between 35 and 52m for 1st aquifer and 65m to 130m for the main aquifer. Tested yields ranges between 2.36 and 5 M3/HR. The borehole yields ranges between 2,560 to over 5,000 litres per hour for boreholes sunk to depths of about 130 metres below ground level. The groundwater quality is expected to be better for most purposes. During the drilling exercise, there will be need to carry out water quality analysis for information and record purpose. The report recommends that a borehole should be drilled at the selected site to a maximum depth of 130metres. The drilling site is pegged on the ground and is known to the Client himself and is also marked on the enclosed map extract.


TABLE OF CONTENTS

1. INTRODUCTION ............................................................................................................................................ 9

2. TERMS OF REFERENCE ............................................................................................................................ 9

3. BACKGROUND INFORMATION ............................................................................................................... 10

3.1 General .......................................................................................................................................... 10

3.1.1 Communications, Geographical Location, Topography. .....................10

3.2 Location .......................................................................................................................................... 10

3.3 Physiography ................................................................................................................................. 10

3.4 Climate ........................................................................................................................................... 10

3.5 Current Land Use and Potential .................................................................................................. 11

3.6.1 Economic Activities Human activities and settlement ..........................12

3.6.2 Cultivation .................................................................................................13

3.6 Water Demand .............................................................................................................................. 14

4. WATER RESOURCES ................................................................................................................................. 15

4.1 Surface Water Resources ............................................................................................................ 15

4.2 Groundwater Resources .............................................................................................................. 15

5. GEOLOGY ..................................................................................................................................................... 17

5.1 Regional Geology ......................................................................................................................... 17

5.2 Geology of the Project Area ......................................................................................................... 17

5.2.1 The Basement System ............................................................................18

5.2.2 Calcareous Crystalline Limestone(Marbles) .........................................18

5.2.3 Semi Calcareous Gneisses and granulites .........................................18

5.2.4 Calc-Silicate granulites ...........................................................................18

5.2.5 Pelitic and Semi-Pelitic Kyanite,Schists,Gneisses and Granulites ..................................................................................................18

5.2.6 Psammitic Graphitic quartz-schist ........................................................18

5.2.7 Tertiary Volcanic sediments ....................................................................20

5.2.8 Superficial Deposits ................................................................................20

5.2.9 Pleistocene Gravels and Boulders .........................................................20

5.2.10 Recent Deposits ......................................................................................20

5.2.11 Structural Geology ...................................................................................20

5.2.12 Geology of the Investigated Site ...........................................................20

6. HYDROGEOLOGY ...................................................................................................................................... 22

6.2 Groundwater Occurrence. .......................................................................................................... 22

6.2.1 Shallow Groundwater confined to the alluvial deposits .....................22

6.2.2 Groundwater in the Weathered/fractured formation .........................22

6.2.3 Groundwater in the superficial deposits ..............................................23

6.3 Hydrogeology of the Project Area .............................................................................................. 24

6.4 Previous Groundwater Development ........................................................................................ 25

6.5.1 Specific Capacities (Sc) .........................................................................26

6.5.2 Transmissivity (T) ....................................................................................26

6.5.4 Porosity (n) ...............................................................................................26

6.5.5 Hydraulic conductivity (K)/Groundwater Flux .....................................28

6.5.4 Hydraulic conductivity (K)/Groundwater Flux .....................................29

6.6 Groundwater Recharge ............................................................................................................... 30

6.8 Discharge ...................................................................................................................................... 30


7. WATER QUALITY ........................................................................................................................................ 32

7.1 Evaporation and Transpiration. .................................................................................................. 32

7.2 Dissolution and Evaporates ........................................................................................................ 32

7.3 Dissolution of Host Rock ............................................................................................................. 32

8. GEOPHYSICS .............................................................................................................................................. 33

8.1 Resistivity Methods-Introduction .................................................................................................. 33

8.2 Theory-Basic Principles ................................................................................................................ 33

8.3 Apparent Resistivity ...................................................................................................................... 35

8.4 Vertical Electrical Soundings (VES)-The Schlumberger Array Configuration ........................ 37

8.5 Horizontal Electrical Profiling-The Wenner Array Configuration ............................................... 37

8.6 Fieldwork and Results .................................................................................................................. 38

8.7 Field Data and Modelled Curve. ................................................................................................ 38

8.7.1 VES 1 Field Raw Data-PASCAL DATA ...............................................38

*Drilling is thus recommended on this point as there is good fracturing and enough storage .................................................................................39

8.7.2 MULUTU_VES 1 Model curve ................................................................39

8.8 Field Data and Modelled Curve. ................................................................................................ 39

8.8.1 MULUTU_VES 2 Field Raw Data within the school Compound( 37M 323864 UTM9847134, Alt:1340m) ........................39

8.8.2 VES 2 Model Interpretation ...................................................................41

9. Impacts of the Proposed Drilling Activity .................................................................................................. 42

9.1 Impacts on Local Aquifer’s Quantity and Quality .................................................................... 42

9.2 Impacts on Existing Boreholes in the Area .............................................................................. 42

It is noteworthy that there are no many existing boreholes in the present area of investigation. Therefore we do not expect any negative impacts on any other existing borehole within the vicinity. Thus there will not be incidences of cones of depression or coalescing aquifers. ............................................................................................ 42

9.3 Regulations and Management Arrangement ........................................................................... 42

10. CONCLUSIONS AND RECOMMENDATIONS ....................................................................................... 43

1305m ...................................................................................................................43

11. REFERENCES ............................................................................................................................................. 45

12. APPENDIX .................................................................................................................................................... 46

13. ADDENDUM ................................................................................................................................................. 46

14. ADDENDUM ................................................................................................................................................. 50

xxi. Signing for final acceptance of works on behalf of the Client ................................................................ 54


Figure 1GIS-TOPO Map of the study area


ABBREVIATIONS (All S.I Units unless indicated otherwise) agl above ground level amsl above mean sea level bgl below ground level E East

EC electrical conductivity (µS/cm) hr hour m metre N North PWL pumped water level Q discharge (m3/hr) s drawdown (m) S South SWL static water level T transmissivity (m2/day) VES Vertical Electrical Sounding W West WAB Water Apportionment Board WSL water struck level

µS/cm micro-Siemens per centimetre: Unit for electrical conductivity °C degrees Celsius: Unit for temperature " Inch


GLOSSARY OF TERMS

Alluvium General term for detrital material deposited by flowing water.

Aquifer

A geological formation or structure, which stores and transmits water and which is able to

supply water to wells, boreholes or springs

Conductivity Transmissivity per unit length (m/day).

Confined aquifer A formation in which the groundwater is isolated from the atmosphere by impermeable geologic formations. Confined water is generally at greater pressure than atmospheric, and

will therefore rise above the struck level in a borehole.

Denudation Surface erosion.

Evapotranspiration Loss of water from a land area through transpiration from plants and evaporation from the

surface

Fault A larger fracture surface along which appreciable displacement has taken place.

Fluvial General term for detrital material deposited within a river environment and usually graded.

Gneiss Irregularly banded rock, with predominant quartz and feldspar over micaceous minerals. A product of regional metamorphism, especially of the higher grade.

Granitization The process by which solid rocks are converted into rocks of granitic character without melting into a magmatic stage.

Gradient The rate of change in total head per unit of distance, which causes flow in the direction of the

lowest >head.

Heterogeneous Not uniform in structure or composition throughout

Hydrogeological Those factors that deal with subsurface waters and related geological aspects of surface waters

Hydraulic head Energy contained in a water mass, produced by elevation, pressure or velocity.

Infiltration Process of water entering the soil through the ground surface.

Joint Fractures along which no significant displacement has taken place

Migmatite Rocks in which a granitic component (granite, aplite, pegmatite, etc.) is intimately mixed with a metamorphic component (schist or gneiss).

Perched aquifer Unconfined groundwater separated from an underlying main aquifer by an unsaturated zone. Downward percolation hindered by an impermeable layer.

Percolation Process of water seeping through the unsaturated zone, generally intimately mixed with a

metamorphic component (schist or gneiss).

Permeability The capacity of a porous medium for transmitting fluid.

Piezometric level An imaginary water table, representing the total head in a confined aquifer, and is defined by the level to which water would rise in a well.

Porosity The portion of bulk volume in a rock or sediment that is occupied by openings, whether isolated or connected.

Pumping test A test that is conducted to determine aquifer and/or well characteristics

Recharge General term applied to the passage of water from surface or subsurface sources (e.g. rivers,

rainfall, lateral groundwater flow) to the aquifer zones.

Regolith General term for the layer of weathered, fragmented and unconsolidated rock material that overlies the fresh bedrock.

Specific capacity The rate of discharge from a well per unit drawdown.

Static water level The level of water in a well that is not being affected by pumping. (Also known as "rest water level")

Transmissivity A measure for the capacity of an aquifer to conduct water through its saturated thickness

(m2/day).

Yield Volume of water discharged from a well.


PROJECT SUMMARY SHEET

Client MR. PASCAL MUTUKU MUTUA P.O. BOX 30-90200 KITUI

Project MR. PASCAL MUTUA’S PROPOSED BOREHOLE WATER

PROJECT

L.R. No. (Documents encls)

Locality MULUTU LOCATION

District KYANGWITHYA

County KITUI

Selected Borehole Site

Map Sheet KITUI NO. 53

Coordinates (GPS) UTM -1.341166, 37M 97879

Elevation (GPS) 1259 m asl

Projected Water Demand 20m3/day

Main Purpose of Water Use Domestic and Minor Irrigation

Investigating Hydrogeologist/Engineers Charles Kithome & Nyambane Nyakoni

Description This application is for drilling of a borehole for private water supply to be located within BOREHOLE AT MULUTU

AREA, KYANGWITHYA DIVISION, KYANGWITHYA DISTRICT

OF KITUI COUNTY It is expected that the water will be used for Medium Scale Irrigation and serve the local Client’s members.

Geology The investigated area is underlain by sediments of Precambrian era metamorphic rocks, with Basement at depth consisting of gneisses with horneblendes and schists and granulites. Outcrops of these rocks are noted within the vicinity confirming them as the host rock.

Current water source At present the water supply situation in this area is very poor with the main source being water from shallow hand dug wells and roof catchment and the mulutu and kalundu rivers. The hand dug wells are vulnerable to pollution and are also unreliable during the dry spell as most members have to walk long distances in search of clean water. The Client has also water supply connection from Kitui Water and sanitation Company which is unreliable.

Location of proposed borehole site. To be drilled within Client’s designated public utility land at VES-1 and defined by co-ordinates: UTM -1.341166, 37M 97879 at elevation of 1259 amsi.

Supervision Qualified Hydrogeologist

Recommended Drilling Method Air-Rotary

Recommended drilling depth -130mbgl at VES I-Marked and known by Client


1. INTRODUCTION This report summarizes and describes the results the results of groundwater potential survey

carried out on a piece of land for the proposed Mr. Pascal Mutuku Mutua situated within MULUTU Location, Kyangwithya Division, Kyangwithya District of KITUI County and covering about 6 hectares of land. The Client intends to develop the land to enable generation of additional income on his rain-fed cultivation farm. The water source will also be a permanent panacea to all his water-related woes and expand his fish-farming project.

In order to achieve this, the Client commissioned a consultant from East African Aquatech &

Geotechnical Consulting Ltd, to carry out a hydrogeological survey of the area and identify one suitable site to drill a production borehole. The scope of the present study is to select a suitable site for groundwater development, taking into account the prospects for sustainable abstraction, water quality parameters, and economic viability. For this purpose, the relevant geological and hydrogeological information of the area has been analyzed and evaluated.

The address of the Client is:-

Mr. Pascal Mutuku Mutua

P.o. Box 30-90200

KITUI

2. TERMS OF REFERENCE The Consultant will undertake to carry out a hydrogeological survey of the project area and its

environs (the project area) and subsequently identifies possible drilling site(s) and presents a hydrogeological report under the following terms:

� Carry out a desk study and compile all the available Hydrogeological, geological, geophysical and

hydrological data for the project area.

� Carry out fieldwork involving observation of the topography, geology, hydrogeology, drainage pattern of

the project area; carry out a geophysical survey and check on the site conditions including availability of

space for a drilling rig to access the project site.

� Analyze all the above data in order to assess the groundwater potential of the project area.

� Select the most suitable borehole sites within the project area subject to the results in i-iii above and

taking into account the water quality expected and the requirements of the Water Act.

� Compile and submit to the Client a comprehensive report which shall include all the details of the above

investigations and the Consultant’s recommendations on the proposed drilling site.

� Present, to the client, a detailed qualitatative and quantitative report of the overall findings and advice on

project investment viability and substantial groundwater abstraction feasibility

� Recommend the best method of the proposed borehole drilling

� Obtain the necessary groundwater water authorizations and permits on behalf of the client and integrate

the component of an EIA /audit report ahead of the actual drilling


BACKGROUND INFORMATION 2.1 General

Kitui district is one of the 13 districts of Eastern Province. It is located in the southern part of Kenya. It borders Machakos and Makueni districts to the west, Mwingi District to the north, Tana River district to the east and Taita Taveta district to the south. The district is located between longitudes 370 45’ and 390 0’ east and latitudes 00 3.7’ and 3o 0o south. The district covers an area of approximately 20,402 km2 including 6,90.3 km2 occupied by the uninhabited Tsavo National Park. The district is divided into 10 divisions 57 locations and 187 sub-locations. There are 4 parliamentary constituencies in the district. These are Kitui Central, Kitui West, Mutitu. The altitude of the district ranges between 400m and 1800m above sea level. The Central part of the district is characterized by hilly ridges separated by wide, low lying areas and has slightly lower elevation of between 600m and 900m above sea level. To the eastern side of the district, the main relief feature is the Yatta Plateau, which stretches from the north to the south between rivers Athi and Tana. The plateau is almost plain with wide shallow spaced valleys. The highest areas in the district are Kitui Central, Mutitu Hills and Yatta Plateau.

2.1.1 Communications, Geographical Location, Topography. The road from Kitui to Nairobi via Thika is among the better roads in Kenya. The Kitui-Kibwezi Road is a tough slog of three hours-plus, much of it rough and dusty, or muddy (but the shortest). Some 20 to 30 km at each end is reasonably graded, but the rest is mostly very poor conditions, save for the off bridge where the road builders have been at work. The road heading north to Embu is tarmacked and in good condition to Kangondi. There are some morning matatus through Embu.

2.2 Location

The project area is within topographic map sheet SA-37-15, KITUI of the survey of Kenya on a scale of 1:50,000. The proposed borehole site location is on Grid Reference:

UTM -1.341166, 37M 97879 ALT. 1259

2.3 Physiography

The altitude of the district ranges between 400m and 1800m above the sea level. The central part of the district is characterized by hilly ridges separated by wide low lying areas and has slightly low elevation of between 600m and 900m above the sea level to the eastern side of the district, the main relief feature is the Yatta plateau, which stretches from the North to the South between rivers Athi and Tana. The plateau is almost plain with wide shallow spaced valleys. The highest areas in the district are Kitui Central, Mutitu hills and Yatta plateau. Due to their high altitudes they receive more rainfall than other parts in the district and are the most productive areas

2.4 Climate

The climate of the district is arid and semi-arid with very erratic and unreliable rainfall. Most of the areas are generally hot to dry leading to high rate of evaporation. This combined with unreliable rainfall; limits intensive and meaningful land use and related development activities. The annual rainfall ranges between 500 -1050mm with 40 percent reliability. The long rains come in April/May and short rains in November/December. The short rains are more reliable while long rains are usually unreliable. The periods falling between June to September and January to March are


usually dry. The topography of the landscape influences the amount of rainfall received. The high- land areas of Central hills in Kitui and Mutitu in the Eastern parts of the district receive between 500- 760mm of rainfall per year. The Endau hills receive 500-1050mm per year while the drier eastern and southern areas receive less than 500mm. The district experiences high temperatures throughout the year, which ranges from 160c to 340c. The hot months are between June and September and January and February. The minimum mean annual temperatures are 280c in the western part and 220c in the eastern parts. Maximum mean annual temperatures on other hand are 28oC in the western part and 32o C in the eastern part.

Figure 2 Annual Evaporation

2.5 Current Land Use and Potential

The rainfall is low, bimodal and highly variable, ranging between 400 - 600 mm. This low rainfall has rendered the area to be of marginal agricultural potential and therefore, most of the area is under Irrigation and rain fed agriculture practiced in a few areas, mostly within the main rivers. much of the natural vegetation cover in Kitui has been depleted. Within Kitui town, there is a considerable natural vegetation cover in the neighbouring hills but in the outskirts much of it has been depleted. The depletion of natural vegetation cover is as result of increased population pressure and intensive human activities (construction, cultivation, livestock keeping and charcoal burning).This has led to serious soil erosion rendering the lands infertile.


Figure 3; Annual Evaporation in Kitui

3.6.1 Economic Activities Human activities and settlement

Agricultural development in Kitui just as in other marginal lands is problematic due to low rainfall and the menace of wildlife and pests. In the District crop production has been made quite unreliable and unevenly distributed in the recent years the district has been experiencing crop failure of almost 90% thus rendering the majority of people in the district destitute and in dear need of food. The people of Kitui are engaged in various economic activities for their livelihoods. Whereas the majority is engaged in agriculture, livestock keeping still remains the income earner in the district and especially in the drier area. People practice mixed farming because livestock acts as a buffer during poor rain seasons. Most of what is harvested is consumed domestically, and there is hardly any net surplus. The District is famine-prone; whatever is produced has to be upplemented with external food aid to avert starvation. Major commercial activities like wholesale, retail shop keeping process of food products, honey farming harvesting and refining are ther economic activities taking place in urban centers and market places. Not to be underrated in their capacity to absorb the labor force are the Jua-kali workshops spread out in all towns and markets centers. Cotton ginning, formerly a major commercial activity has greatly declined due to worsening climatic conditions, while charcoal burning and sales has gone up considerably. There are several financial institutions in the District, most of these Micro-enterprises make acquisition of credit to small-scale business people and farmers possible and has been a great boost to the people in the district as they strive to fight and alleviate poverty. Self-help groups have also increased in number in the district and have become a great source of income for the members. The groups, which are registered at the department of Social Services and the department of culture, are involved in many income generating activities which include Bee-keeping, poultry keeping water -kiosks, basketry, merry go round and small loans to members among other activities. Human activities recorded in this survey included livestock (sheep, goats, cattle and donkeys), human settlements, cultivation fields, charcoal production, sand harvesting activities and artificial water provisions. Human settlements included structures such as schools, churches, shopping centers and homesteads.


3.6.2 Cultivation

Due to the reduced land size (minimum of 8 acres), beans, maize and various fruits are being tried as well as goats and milk cows. Rocks in this area hold extractable water only in small cells, which generally occur in low areas near stream channels. On the central part, where the municipality is situated, have sedimentary plains which usually low in naturally fertility. This is worsened by the comparatively low rainfall in the region. These soils are rich in sodium and are considered to be best grazing grounds. 66% of the district falls under AEZ IL5 and IL6 that is classified as range lands. This is mainly in Ikutha, Mutha, Mwitika and lower Yatta. 32% of the district falls under AEZ LM4 and LM5- which is Agri-marginal areas. This covers the area of Mutomo Chuluni (Lower), upper Yatta and Mutitu division. Meanwhile 2% of the district falls under AEZ UM4 and LM3 which is regarded as suitable for agricultural production and include Central Upper Chuluni, Matinyani and Mutonguni Divisions. Although according to land suitability classification UM3 UM4, LM5 millet and cotton zone a mixture of all the above crops and livestock have been pushed in these areas including the rangeland. In this zone various crops (Maize, Sorghum, Millet Beans, Cowpeas, Pigeons peas, green grams and cotton) are mixed on the same place of land, mostly with no defined rotational pattern.

Therefore, the district as whole can be divided into the following 4 agro-ecological zones.

� Arid Agro-pastoral Areas: These areas are extensive and are generally used for grazing. However, due to population pressures the land being put into crop production.

� Semi-arid Farming Areas: This zone has good potential for agricultural development and is currently either cultivated or under woodlands.

� Semi-arid Ranching Areas: These areas are less fertile and are currently used for drought resistant crops and livestock rearing.

� Arid-pastoral Zone: There is no crop farming here. The area is mainly used for rearing livestock. The nomads shift in search of pasture and water during the dry spell.


2.6 Water Demand

The project is tailored to suffice the client’s water demand per capita consumption of 12,000litres per day. The estimated water demand is hence 20m3/day required for domestic uses. To ensure sufficient availability of water, it is envisaged that the Client will acquire additional storage facility in form of an elevated tank, from where the water will be distributed by gravity infrastructure delivery system

According to Sphere Standards however, the longest distance to a water point should be 500

meters while a single hand-pump should serve 500 people. This means that due to the scattered patterns of settlement in the area, the coverage is far from complete and more will have to be done in the way of safe water provision. It has been estimated that a demand of about 8 cubic metres of water per hour suffices the community needs. Water from the proposed borehole is to be used for domestic and micro- irrigation purposes by the Client’s. Supply from the proposed borehole source will meet the proposed daily water demand.

Domestic water demand = =12,000 Litres/day Irrigation water demand = =8,000 Litres/day TOTAL DEMAND =20,000 Litres/day


3. WATER RESOURCES 3.1 Surface Water Resources

Water sustainability resolves around quality and quantity issues. Increasing demand place an increasing

strain on natural water bodies. Water resources depletion and pollution is a threat to environmental

degradation and thus social -economic conflicts deterioration and hence poverty propagation. Due to

limited rainfall received surface water sources are very scarce. The major sources of surface water are

seasonal rivers that form during the rainy seasons and dry up immediately after the rains. River Athi is the

only perennial river in the district and flows along the border with Machakos and Makueni Districts. The

district has no lake but has several dams and pans that play a significant role in providing water. Most of

the dams dry up during the dry season due to the high evaporation rates of between1800 -2000mm/year.

Spring water is generally found in the hilly areas of the district namely Mutitu hills, Endau hills and Mutha

hills. The springs vary in their flow regimes and some dry up during extended drought period.

3.2 Groundwater Resources

In the Kitui District four main groups of aquifers are recognized (Louis Berger International Inc., 1983):

� Quaternary superficial deposits;

� Tertiary rocks;

� Paleozoic sedimentary rocks;

� Precambrium crystalline rocks.

The Quaternary superficial deposits consist of alluvium aquifers and Quarternary deposits. The Alluvium aquifers are sands and gravels along river channels. Where the river channel crosses resistant rocks, natural subsurface barriers are formed which form good shallow aquifers. The other type of Quaternary aquifers are formed by deposits of talus or loose unconsolidated materials, e.g. at the base of steep slopes. The tertiary volcanic rocks that outcrop in the plains and along the Eastern boundary of the district have a low porosity and form poor aquifers. Only when water is trapped in open joints small springs can occur. In the South-East corner of the district (mainly in Tsavo East National Park) shales, grits and sandstones of Paleozoic age form good aquifers in which large quantities of water are stored.. Most of the Kitui District is underlain by metamorphosed crystalline Precambrian rocks. In general, these rocks from poor aquifers, although locally water can be stored in fractures, faults, joints and weathered zones. The schists are on the whole unfavourable as aquifers since cracks in mica schists are often sealed by the clay resulting from their weathering. However, at some locations, especially where faults have been occupied by quartzite vein materials, these rocks may yield water supplies. The water supply at Ithookwe, which provides the water supply for Kitui town, is an example of this. The aquifer properties of the quartzite veins are completely dependent on the presence of sufficiently interconnected joints. Recharge of the groundwater comes solely from rainfall, either directly or indirectly through local areas with concentrated recharge (i.e. near stream or areas with ponds). Major groundwater recharge zones are on the hill ranges of North and Central Kitui. Places with the most favourable conditions for groundwater recharge are the Miambani and Migwani Ridges where runoff from the hills in channelled over the permeable Mui-Ikoo-Mutito fault zone with direct connection to the quaternary alluvial and Precambrian fractured rock aquifers. For details about groundwater levels and quality in the Kitui district the reader is referred to reports by Earth Water Ltd. (2003) and Wotuku (2001a and 2001b).


Figure 4 Figure 5 TopoMap: MULUTU and Surrounding.


4. GEOLOGY

The Kitui District area is largely covered by Precambrian (540 Ma BP and older) crystalline rocks, which mainly consist of gneisses, granulites, schists, migmatites, with minor intrusives. These Precambrian rocks are generally referred to as the “basement system” and generally show a regional structural North-South trend of foliation. This regional setting is in agreement with the geology of the Mozambique belt, which is of Proterozoic (2,500 Ma – 540 Ma BP) age. This geological feature is to be found in large parts of East Africa and stretches from Mozambique in the South through Kenya to Ethiopia and Sudan in the North. Since the Archaean (2,500 Ma BP and older) metamorphism the rocks have been subjected to continuous erosional processes, which led to different erosional levels. Tectonic activity and these erosional processes shaped the coarse outlines of the present morphological features, which influenced later distribution of deposits. Tertiary (65 Ma – 2 Ma BP) and Quaternary (2 Ma BP until present) deposits are present on the hillslopes and in the riverbed. In the South-eastern corner of the Kitui district Paleozoic sandstones occur. Due to complex tectonic activity most of the primary structures and textures have been lost through crystallisation and recrystallisation. However it is still recognized that the sandstones, greywackes and other sedimentary rocks were metamorphed to a.o. gneisses, which form the lithology at present. At present the land is a peneplain, in which few inselbergs are present (e.g. Nzambani Rock, Figures 2.9 and 2.10). A geological map is enclosed in Appendix B.

. 4.1 Regional Geology

The rocks existing in the area are crystalline gneisses, schist, and granulites of the Archaean Basement System. During Archaean age an extensive deposit of material was laid down in a depression, most probably in a sea. East-West compression following the deposition of the Basement System sediments resulted in their subjection to intense heat, pressure and deformation, transforming the succession into a metamorphic series of crystalline schist, gneisses and granulites. The compression and folding of the Basement System rocks led to the formation of hills which, later were extremely eroded leading to the exposure of the more highly changed rocks in the centre of the hills. After the development of the sub-Miocene peneplain the Kapiti phonolite lavas covered great stretches of the area. The steady phase following the Miocene period of eruption resulted in the formation of the end-Tertiary peneplain. The rivers laid down small deposits of ill-sorted pebbles, gravels and cross- bedded sands on their floodplains, during Pleistocene times; these were however eroded leading to the present land form..

4.2 Geology of the Project Area

The geology of the study area is based on the Geology of Kitui geological report No. 53 and the rocks of the KITUI area fall readily into nine groups In order of increasing age and formation, these are: —

re :

� The Basement System Rocks

� Calcareous Crystalline Limestone(Marbles)

� Semi-Calcareous Gneisses and Granulites

� Calc-Silicate Granulites

� Pelitic and Semi-Pelitic Kyanite Schist, Gneisses and Granulites

� Psammitic Graphitic Quartz Schist

� Tertiary Volcanic Sediments

� Superficial Deposits

� Pleistocene Gravels and Boulder Beds


� Recent Deposits

4.2.1 The Basement System

In Kyangwithya area, these are constituted by calcareous crystalline limestone, gneisses, and silicate granulites; Psammitic quartzite, graphitic quartz schist and pyroxene-quartz schist and granulites; and volcanic intrusive pegmatite and haplites. The gneisses, schist and granulites belonging to the Basement System are of sedimentary origin. Bedding of the original sediments persists in the metamorphosed rocks

4.2.2 Calcareous Crystalline Limestone(Marbles)

They occur in zones which are constant along the strike. The marbles are more resistant to erosion than the surrounding country-rocks and form ridges which are usually covered by surface limestone (Kunkar). The plentiful growth of certain small trees on the limestone areas is helpful in tracing their boundary. Limestone outcrops are usually found on top of the ridges and occasionally where streams cut across their strike. The outcrops are often interlaminated with, and sheathed by hornblendic rocks. Graphitic rocks are often allied with the main set of crystalline limestone. Marbles are also sometimes graphitic and often show green copper-staining and release a rotten odour on fracturing. Thin quartzite is also associated with marbles bands. Banding of the marbles parallel to the strike is thought to be of sedimentary origin

4.2.3 Semi Calcareous Gneisses and granulites With decline in lime content of the marbles due to the increase of silicates, the crystalline limestone grade into semi-calcareous gneisses. In some cases these rocks are thought to have developed as a result of original impurities in the sediments, with later addition of constituents by metasomatic processes. In most cases, however, metasomatic additions to the original make-up have played a major role in the formation of these rocks. The gneisses of Mutito hill have very high quartz content. The increase of mafic minerals in these rocks produces melanocratic banded gneisses or schist.

4.2.4 Calc-Silicate granulites

The calc-silicate rocks crop up as highly resistant lens-like bodies scattered over most of the area. Commonly they are dark grey to reddish, medium to fine grained, and are sometimes faintly banded due to siliceous layers. The origin of calc-silicate granulites is attributed to the regional metamorphism of partly calcareous sediments. With change in their mineral assemblages, they grade into Calcareous gneisses.

4.2.5 Pelitic and Semi-Pelitic Kyanite,Schists,Gneisses and Granulites

Kyanite-graphite schist is common in the area, occurring below the lowest member of the marble group. Lateral change in the amount of Kyanite as well as graphite is noticeable. They usually outcrop in the river beds or along the western slopes of limestone ridges. Locally kyanite and graphite occur within the marble itself. The kyanite occurs as xenoblastic crystals often enclosing rounded chadacrysts of quartz. The graphite flakes are variable in size, and always arranged parallel to the foliation planes. Usually kynite and graphite occur together. Foliation is imparted to the rocks not only by graphite but also by biotite, usually occurring related with other dark minerals in bands).

4.2.6 Psammitic Graphitic quartz-schist

Directly below the quartzite in the Mango hill, graphitic quartz schist occur and are occasionally inter-bedded with the quartzite itself. The schist is grey and fine grained, with a feeble schistosity revealed by numerous graphite flakes. An imprecise banding is imparted to the rocks by lenticular aggregates of quartz and feldspar. The rocks are highly


fissile, breaking along thin bands which are often rich in small bright green micaceous flakes.


4.2.7 Tertiary Volcanic sediments An extensive development of volcanic and sediments occur in the area west of the project area. The oldest volcanic rock in the area is the Yatta Phonolite which is believed to be of Miocene age. It was probably formed by s stream of lava passing through the area.However, this formation might not be encountered during drilling of this borehole as Yatta plateau is some kilometres away from the study area

4.2.8 Superficial Deposits

The river mulutu and Kalundu deposited pebbles, gravels, and sands on its floodplain during Pleistocene times. More recently, red brown sands were derived from the Basement System rocks. Black cotton soils occur in areas of bad drainage. Kunkar (surface limestone) is common in the area because of the abundance of calcareous rocks in the Basement System

4.2.9 Pleistocene Gravels and Boulders

Patches of ill-sorted pebble-beds and gravel occur on the end-Tertiary peneplain. The pebbles are sub-rounded and form the major constituent of the beds. The occurrence of large boulders is common. The matrix is a soft friable consolidated sandy loam. The quartzite pebbles and boulders were derived from the nearby hill and deposited in the flood valley of the River Mulutu, which has incised its course into the sediments. The beds are Possibly Mid-Pleistocene age.

4.2.10 Recent Deposits Red-brown sandy soils in the area are suggestive of underlying Basement System rocks. Such soils are prevalent over the area and their widest distribution on the sub-Miocene peneplain. They form great thicknesses around the hills, usually deeply gullied by seasonal streams running from the steep hillsides. Areas covered by black cotton soils form the seasonal swamps. Such soils are symptomatic of poor drainage and mostly overly the Basement System rocks in the area. Surface Limestone (Kunkar) often covers large areas underlain by calcareous deposits. The colour frequently indicates the nature of the covered underlying rock: Off-white indicating marble while reddish colour is imparted to the kunkar by hornblendic rocks. Many pebbles of all sizes, originating usually from pegmatite and quartzite in the Basement System, occur in the sandy riverbeds. The sands consist mostly of quartz, feldspar and micaceous flakes

4.2.11 Structural Geology

The area has not been affected by heavy tectonic movement. According to the geological map covering the area, there are no major faults within the vicinity of the project area.

4.2.12 Geology of the Investigated Site

The local geology has been delineated based on the few visible outcrops and the geological report of the area. As observed during the fieldwork, the investigated area is mostly underlain by crystalline gneisses, schist, and granulites of the Archaean age Basement System and largely covered by superficial deposits


Legend XnXnXnXn= Granitoid Gneisses XXXXa= Pelitic Schist and Gneisses XgaXgaXgaXga= Migmatite with Pelitic host rocks.

Figure 4.1: Geology of KITUI Area where the study area is premised


5. HYDROGEOLOGY

Kitui district is mainly formed of two distinct catchment areas defined by the ridges which forms part of great Mozambique belts. .The upper catchments area with altitude of 1200m a.s l forms the main water catchments to the lower area whose altitude is averagely 500m a.s.I.oduction

6.2 Groundwater Occurrence.

Based on the available data of the drilling boreholes and the resistivity values of the fore mentioned geoeletrical units, groundwater occurs in different types of lithological composition and is present under confined or unconfined conditions. The main factors that control the quality of ground-water are the permeability of the rock, the rock type and the degree of recharge from surface runoff and rainfall. Water of the poorest quality, with high total dissolved solids (TDS), is associated with the poorly drained recent Deposits; intermediate quality water is associated with Psammitic Graphitic quartz-schist; while the best quality is associated with unconsolidated sands, gravels and Tertiary volcanics that receive efficient recharge due to their high infiltration capacities.The aquifers are discussed as follows: -

6.2.1 Shallow Groundwater confined to the alluvial deposits During periods of flood, water percolates down into the sandy riverbeds of the laggas.

Additional recharge of these bodies may take place by lateral flow from the alluvial deposits along the river. This seepage is usually indicated by the occurrence of secondary limestone along the edges of the alluvial deposits.

The Client depends on water supplies from various wells and water holes, in natural

subsurface reservoirs in dry riverbeds. A problem occurring where calcrete is formed is that a large quantity of the water

evaporates, causing an increased salinity of the remaining water. Water with a high salinity can be found in these riverbed deposits where the groundwater becomes stagnant or where it is forced to rise to shallower depths by a natural subsurface dam.

Further, due to leaching from the volcanic material through which the water flows and the

slightly elevated temperature observed in some of them flowing for long distances at shall depth under a lava plain devoid of vegetation cover.

6.2.2 Groundwater in the Weathered/fractured formation The gneisses, granites, if deeply weathered/fractured, may contain water in sufficient

amounts. This is not always the case, however, as granitic rocks usually have intercalations of clays, which form thick, impermeable layers that obstruct re-charge and limit the potential for abstraction.

The coarse sands of the riverbeds along the river and its tributaries form considerable water

reservoirs during the wet season. Many laggas on the lower reaches in these areas have also been reported to have a perennial sub-surface flow. This means that during the greater part of the year water can be found in the riverbed deposits.


6.2.3 Groundwater in the superficial deposits Groundwater in these lithological units is shallow and superficial as well as intermittent and

may dry with time depending on the fluctuations of the recharge conditions. These fracture systems may store groundwater in reasonable quantities and enhance the sub-surface recharge. These aquifers are not deeply seated and may be encountered during drilling works.

Figure 4.5 Groundwater flow Direction and Piezometric Levels in the study area, KITUI


6.3 Hydrogeology of the Project Area

Virtually all of Kitui District’s total area belongs to the Tana River drainage basin. Only a narrow strip along the south and southwest border drains to the Athi River. These two rivers form the northern, western and southern boundaries of the district. The Tana river is Kenya’s largest river and drains the Eastern flank of the Aberdares and the Southern slopes of Mount Kenya. Both of the rivers discharge to the Indian Ocean. Figure 2.14 False colour composite satellite image of the Southern part of Kenya (source: USGS and NASA)There are no perennial rivers in the District except the Tana River. In spite of perennial headwaters, the Athi often runs dry due to evaporation and infiltration losses. All of Kitui’s rivers, including the Tana River, are strongly characterized with high flows in April-May and November-December and very low (or nil) flows in the intervening dry periods. Most of the ephemeral streams that drain into the Tana River generally become dry within one month after the rainy season.

:

Direct primary recharge as rain: Unconfined recharge to phreatic or water table aquifers as a result of river Mulutu. This is most significant on the intermediate zones, where rainwater percolates freely into the sandy soil. Direct recharge will be relatively low over the clayey lower plains. However, because of the limited lateral extent and the wide coverage of the permeable sands the total volume of recharge may still be considerable.

• Direct secondary recharge from river; this recharge may occur via big rivers.

When a river changers its course, the buried old river course retain underground connectivity with the main river. The fluvial materials under the old channel have high transmissivity allowing water from the river to permeate. Once underground, water will move in response to gravity: its velocity and direction is determined by the gradient and the material through which the water drains.

• Indirect recharge # (1): Rainwater infiltrating directly into the surface on relatively high ground flows under gravity towards the lower plains. The rate of flow is determined by both gradient and geological material. Gradients are gentle throughout the area, and flow rates will be low. Due to the limited storage volume, water levels may nevertheless be variable and seasonally controlled. This recharge mechanism (sub-surface flow) occurs along the wide river basins and the intermediate zone. It is responsible for the formation and replenishment of aquifers along the boundary of the intermediate lands. Sub-surface flow eventually reaches the vast plains, where it indirectly replenishes the various types of aquifers underlying the plains. The bulk of recharge into the intermediate lands may be derived through this mechanism. Indirect recharge # (2): Where hydraulic continuity exists between the alluvial topsoil and the deeply seated weathered or fractured Basement aquifers, there will be recharge from infiltrating surface water (streams and swamps). The magnitude of this mechanism will vary very much at the local level, depending on the nature of the alluvium. Where this is clayey, the volume of leakage may be much less than expected at first sight.The relatively high rainfall and the imperfectly developed surface drainage of the project area should be factors that promote aquifer replenishment. However, due to the some sandy clay regolith, the percentage that actually goes to recharge (i.e. effective precipitation) must be quite small, and thus much of the rainfall may be lost through evapotranspiration


Watershed Area

6.4 Previous Groundwater Development

There have been a few number of boreholes drilled in the study area over the years with a high success rate. Table 5.2 below indicates some of these boreholes and their hydrogeological data. There have also been some studies carried out in the area in the past that included drilling of exploration boreholes. A study carried out by MW&I revealed considerable ground water potential around the study area. The sites selected for the exploration boreholes are near but outside the project area.

Table 5.2: Boreholes Close To The MULUTU Area

B/HOLE No OWNER Depth

(m) Wsl (m) WRL (M) Yield m3/hr DRAWDOWN

(M)

C-425 DWD 122 9 5 0.36

C-1738 63 35 35 11.3

C-3326 62 5 5 0.24

C-3795 60 48 44 4.56 6

C-4136 94 50 40 20.5 9.1

C-4299 DWD

C-7730 MALOMBE, DANIEL 66 43; 57; 64 8.6 4.38 21.2

C-7844 NDOTTO J.K. 58 32; 42 27.8 3.6

C-10198 MATINYANI CLIENT 100 18; 56 11.6 8.28 46.1

C-10929 KENYA FORESTRY 250 34; 48; 56 4 4.8 87

C-11043 MULANGO BIBLE INST. 70 29; 59 24.7 1.44 16.7

C-13259 DWD (MULANGO G. H. SCH) 160 87; 128; 154 18.9 1.2 124

NOTES:


It is observed that the total drilled depths ranges between 81m and 150m below ground level, while the water struck levels are found between between 39 and 58m m for 1st aquifer and 61m to 130m for the main aquifer. Tested yields ranges between 0.8 and 11.6 M3/HR

6.5 Aquifer Parameters 6.5.1 Specific Capacities (Sc) The boreholes specific capacities have been calculated based on the formula Sc= Q/s

(Driscoll, 1986), where Q is the yield during the pump test and s is the drawdown i.e. PWL-WRL. Transmissivity on the other hand is calculated using the formula T=0.183 Q/s. This formula is applicable where well test data is available in log scale.

6.5.2 Transmissivity (T)

However, the available data from the Ministry of Water and Irrigation only provides data in summary of form, and thus the above formula is of little use. It is however possible to estimate the transmissivity using the Logan’s formula (Logan, 1964) i.e. T=1.22Q/s, or (Driscroll, 1986) T=1.385Q/s. A drawback of this estimate is that it may lead to overestimation of the Transmissivity; nevertheless it gives a fair indication of the same.

The Modified Non-Steady State flow equation relies in a change in drawdown on a laminar scale with the log cycle of time and is independent of the magnitude of the drawdown. Thus, T=2.3Q/(4∏∆s), where T=Transmissivity, ∆s=Drawdown per log cycle. Reliable data was not available from nearby boreholes for proper analysis of the test pumping parameters within the surveyed area.

6.5.3 Specific Yield (S)

Specific retention (Sr), specific yield (Sy) and total porosity (n) (from Heath 1983).Specific yield is defined as the volume of water released from storage by an unconfined aquifer per unit surface area of aquifer per unit decline of the water table.Bear (1979) relates specific yield to total porosity as follows:

n = Sy + Sr

where n is total porosity [dimensionless], Sy is specific yield [dimensionless] and Sr is specific retention [dimensionless], the amount of water retained by capillary forces during gravity drainage of an unconfined aquifer. Thus, specific yield, which is sometimes called effective porosity, is less than the total porosity of an unconfined aquifer (Bear 1979).Heath (1983) reports the following values (in percent by volume) for porosity, specific yield and specific retention:

6.5.4 Porosity (n)

Porosity is defined as the void space of a rock or unconsolidated material:

n = Vv/VT

where n is porosity [dimensionless], Vv is void volume [L3] and VT is total volume [L3].The following tables show representative porosity values for various unconsolidated sedimentary materials, sedimentary rocks The main aquifer of target in the study area consists of lava,


mainly pyroclastics in the older olivine basaltic zones. The specific yield of these aquifer materials according to table III above lies within 8- 38% and the porosity within 3-35% range.


6.5.5 Hydraulic conductivity (K)/Groundwater Flux Up to now, hydraulic conductivity and groundwater flux can only be accurately determined by

time-consuming and expensive methods like pumping tests or sampling, isotope methods and laboratory investigations. The results are confined to few locations, and they depend on the scale of the investigation method. Measurements on rock samples in the laboratory can differ significantly from well test result. However, a simple estimation of hydraulic conductivity can be derived from the formula T= kD which can be rearranged to k=T/D, where k is the hydraulic conductivity, T is the transmissivity, and D is the aquifer thickness. A drawback to this estimation in this case however is the cumulative aquifer thickness which is recorded at the strike point rather than as an interval.

6.5.6 Storativity

The Storativity of a confined aquifer (or aquitard) is defined as the volume of water released from storage per unit surface area of a confined aquifer (or aquitard) per unit decline in hydraulic head. Storativity is also known by the terms coefficient of storage and storage coefficient.

In a confined aquifer (or aquitard), storativity is defined as

S = Ssb

where S is storativity [dimensionless], Ss is specific storage [L-1] and b is aquifer (or aquitard) thickness [L]. Specific storage is the volume of water that a unit volume of aquifer (or aquitard) releases from storage under a unit decline in head by the expansion of water and compression of the soil or rock skeleton.

Specific storage is related to the compressibility’s of the aquifer (or aquitard) and water as follows:

Ss = ρg(α + neβ)

where ρ is mass density of water [M/L3], g is gravitational acceleration (= 9.8 m/sec2) [L/T2], α is aquifer (or aquitard) compressibility [T2L/M], ne is effective porosity [dimensionless], and β is compressibility of water (= 4.4x10-10 m sec2/kg or Pa-1) [T2L/M].

Storativity of an unconfined (water-table) aquifer (from Ferris et al. 1962).In an unconfined aquifer (or aquitard), storativity is given by


S = Sy + Ssb

where Sy is specific yield. Because Ssb is typically small in comparison to Sy, storativity in an unconfined aquifer is often simply equated with specific yield.The storativity of a confined aquifer, which varies with specific storage and aquifer thickness, typically ranges from 5x10-5 to 5x10-3 (Todd 1980); in unconfined aquifers, storativity ranges from 0.1 to 0.3 (Lohman 1972).

The following table provides representative values of specific storage for various geologic materials (Domenico and Mifflin 1965 as reported in Batu 1998):

Material Ss (ft-1)

Plastic clay 7.8x10-4 to 6.2x10-3 Stiff clay 3.9x10-4 to 7.8x10-4 Medium hard clay 2.8x10-4 to 3.9x10-4 Loose sand 1.5x10-4 to 3.1x10-4 Dense sand 3.9x10-5 to 6.2x10-5 Dense sandy gravel 1.5x10-5 to 3.1x10-5 Rock, fissured 1x10-6 to 2.1x10-5 Rock, sound < 1x10-6

To Convert Divide By To Obtainft-1 0.3048 m-1

Freeze and Cherry (1979) provided the following compressibility values for various aquifer materials:

Material Compressibility, α (m2/N or Pa-1)

Clay 10-8 to 10-6 Sand 10-9 to 10-7 Gravel 10-10 to 10-8 Jointed rock 10-10 to 10-8 Sound rock 10-11 to 10-9

Pa-1 = m2/N = m sec2/kg Table.1: Hydraulic conductivities of typical geologic material (Bear, 1972).

Borehole no. C Specific capacity(m2/hr) Transmissivity (m²/day)

C-7730 0.04 1.17

C-7844 0.04179 1.1224

C-10198 0.041 1.2

C-10929 0.0378 1.1078

C-11043 0.1028 3.009

C-13259 0.1376 4.031

The Specific capacity ranges from 0.04 to 0.1376m²/hr while the transmissivity range from 1.1224 to 4.031m²/day.

The main aquifer of target in the study area consists of fractured granitic- gneisses and pelitic schists The specific yield of these aquifer materials according to table III above lies within 34 - 57% range.

6.5.4 Hydraulic conductivity (K)/Groundwater Flux


Up to now, hydraulic conductivity and groundwater flux can only be accurately determined by time-consuming and expensive methods like pumping tests or sampling, isotope methods and laboratory investigations. The results are confined to few locations, and they depend on the scale of the investigation method. Measurements on rock samples in the laboratory can differ significantly from well test result. However, a simple estimation of hydraulic conductivity can be derived from the formula T= kD which can be rearranged to k=T/D, where k is the hydraulic conductivity, T is the transmissivity, and D is the aquifer thickness. A drawback to this estimation in this case however is the cumulative aquifer thickness which is recorded at the strike point rather than as an interval.

Boreholes number

C.

Hydraulic conductivity Ground water flux

m3/day

C-7730 0.1952 7.32

C-7844 0.2039 7.648

C-10198 0.2 7.503

C-10929 0.1846 6.923

C-11043 0.2508 9.404

C-13259 0.224 8.399

The hydraulic conductivity ranges from 0.1846 to 0.2508m/day and ground water flux ranges from 6.923 to 9.404m3/day.

6.6 Groundwater Recharge

6.6.7 Estimating the Mean Annual Recharge

Although rainfall within the study area is medium, regional recharge is of great essence in this area. Much of regional recharge occurs within the flanks of the Sokoke forest. However, this recharge mechanism is mainly important for the replenishment of (regional) sandstone aquifers and is what has been used to estimate the Mean Annul Recharge.

At the present location, water also percolates directly into the faults, fractures, local rivers and streams (via fractures) thus deeper and adjacent units are recharged over time.

Mean Annual Recharge has therefore been estimated as follows: The Recharge is estimated as 5% of the Mean Annual Rainfall of the recharge area 600mm x 5% Mean Annual Recharge = 30mm However, this recharge amount is probably estimation due to the possibility of influent of local recharge through local rivers and rainwater percolation through faults into the weathered/fractured sandstone suite. The selected drilling locations combine good geological and recharge conditions.

6.8 Discharge

Discharge from aquifers is either through natural processes as groundwater base flow to streams and springs or artificial discharge through human activities. The total effective discharge from the underlying aquifers via the above means is not known.


Figure 5 An Isopach Map showing the Piezometric heights of the existing boreholes and the yield expectations of the new borehole


6. WATER QUALITY

Significant peak concentrations of chlorides, sulphate, sodium and potassium ions can occur in KITUI, especially where groundwater is shallow, groundwater flow is low or absent and evapo-transpiration rate is high. The factors that determine the degree of salinity are as follows:

6.1 Evaporation and Transpiration.

Direct evaporation by the heat of the sun and preferential uptake of certain mineral ions by plants can, in certain environments, lead to salinisation.

6.2 Dissolution and Evaporates

The process of evapo-transpiration may, in arid conditions lead to the precipitation of salts in the unsaturated zone (soil). These salts may then be carried down to the groundwater store during periods of rain, thus leading to ion concentrations in space and time. This process is exacerbated in an intensely seasonal climatic regime, such as is in the study area.

6.3 Dissolution of Host Rock

Given relatively long residence times and fairly ambient temperatures in groundwater system, progressive salinity of groundwater can be expected via the rock host. This will vary according to local geology, local structures (which may speed the passage of water through an aquifer by means of faults, etc, and so limit retention time), and local climate and so on.

Nonetheless, it is advisable that samples of water obtained from the proposed borehole be

submitted for full chemical, physical and bacteriological analysis before it is made available for use.

Water quality standards vary from country to country and are determined by the intended use of

water. Drinking water standards are based on the toxicity of certain elements such as lead, Arsenic, Nickel or Selenium, while Nitrate levels are set by the tolerance levels of infants as it causes conditions known as baby syndrome at levels exceeding 10mg/l.


7. GEOPHYSICS 7.1 Resistivity Methods-Introduction

Surface electrical resistivity surveying is based on the principle that the distribution of electrical potential in the ground around a current-carrying electrode depends on the electrical resistivities and distribution of the surrounding soils and rocks. The usual practice in the field is to apply an electrical direct current (DC) between two electrodes implanted in the ground and to measure the difference of potential between two additional electrodes that do not carry current. Usually, the potential electrodes are in line between the current electrodes, but in principle, they can be located anywhere. The current used is either direct current, commutated direct current (i.e., a square-wave alternating current), or AC of low frequency (typically about 20 Hz). All analysis and interpretation are done on the basis of direct currents. The distribution of potential can be related theoretically to ground resistivities and their distribution for some simple cases, notably, the case of a horizontally stratified ground and the case of homogeneous masses separated by vertical planes (e.g., a vertical fault with a large throw or a vertical dike). For other kinds of resistivity distributions, interpretation is usually done by qualitative comparison of observed response with that of idealized hypothetical models or on the basis of empirical methods.

. The main emphasis of the geophysical survey undertaken by the Consultant was to determine the nature of the underlying strata, the presence of faults and to trace water-bearing zones.

This information is obtained in the field using resistivity method: mainly Horizontal electric

profiling [HEP] and the Vertical Electrical Sounding (VES): The resistivity profiling method is used to trace lateral variation in resistivity to locate fractured and fault zones while, the VES probes the resistivity layering below the site of measurement.

7.2 Theory-Basic Principles

Data from resistivity surveys are customarily presented and interpreted in the form of values of apparent resistivity ρa. Apparent resistivity is defined as the resistivity of an electrically


homogeneous and isotropic half-space that would yield the measured relationship between the applied current and the potential difference for a particular arrangement and spacing of electrodes. An equation giving the apparent resistivity in terms of applied current, distribution of potential, and arrangement of electrodes can be arrived at through an examination of the potential distribution due to a single current electrode. The effect of an electrode pair (or any other combination) can be found by superposition. Consider a single point electrode, located on the boundary of a semi-infinite, electrically homogeneous medium, which represents a fictitious homogeneous earth. If the electrode carries a current I, measured in amperes (a), the potential at any point in the medium or on the boundary is given by:

(1)

where

U = potential, in V,

ρ = resistivity of the medium,

r = distance from the electrode.

The mathematical demonstration for the derivation of the equation may be found in textbooks on geophysics, such as Keller and Frischknecht (1966).

For an electrode pair with current I at electrode A, and -I at electrode B (figure 1), the potential at a point is given by the algebraic sum of the individual contributions:

(2)

where

rA and rB = distances from the point to electrodes A and B

Figure 1 illustrates the electric field around the two electrodes in terms of equipotentials and current lines. The equipotentials represent imagery shells, or bowls, surrounding the current electrodes, and on any one of which the electrical potential is everywhere equal. The current lines represent a sampling of the infinitely many paths followed by the current, paths that are defined by the condition that they must be everywhere normal to the equipotential surfaces.


Figure 1. Equipotentials and current lines for a pair of current electrodes A and B on a homogeneous half-space.

In addition to current electrodes A and B, figure 1 shows a pair of electrodes M and N, which carry no current, but between which the potential difference V may be measured. Following the previous equation, the potential difference V may be written

(3)

where

UM and UN = potentials at M and N,

AM = distance between electrodes A and M, etc.

These distances are always the actual distances between the respective electrodes, whether or not they lie on a line. The quantity inside the brackets is a function only of the various electrode spacings. The quantity is denoted 1/K, which allows rewriting the equation as:

(4)

where

K = array geometric factor.

Equation 58 can be solved for ρ to obtain:

(5) The resistivity of the medium can be found from measured values of V, I, and K, the geometric factor. K is a function only of the geometry of the electrode arrangement

7.3 Apparent Resistivity

Wherever these measurements are made over a real heterogeneous earth, as distinguished from the fictitious homogeneous half-space, the symbol ρ is replaced by ρa for apparent resistivity. The resistivity surveying problem is, reduced to its essence, the use of


apparent resistivity values from field observations at various locations and with various electrode configurations to estimate the true resistivities of the several earth materials present at a site and to locate their boundaries spatially below the surface of the site. An electrode array with constant spacing is used to investigate lateral changes in apparent resistivity reflecting lateral geologic variability or localized anomalous features. To investigate changes in resistivity with depth, the size of the electrode array is varied. The apparent resistivity is affected by material at increasingly greater depths (hence larger volume) as the electrode spacing is increased. Because of this effect, a plot of apparent resistivity against electrode spacing can be used to indicate vertical variations in resistivity. The types of electrode arrays that are most commonly used (Schlumberger, Wenner, and dipole-dipole) are illustrated in figure 2. There are other electrode configurations that are used experimentally or for non-geotechnical problems or are not in wide popularity today. Some of these include the Lee, half-Schlumberger, polar dipole, bipole dipole, and gradient arrays. In any case, the geometric factor for any four-electrode system can be found from equation 3 and can be developed for more complicated systems by using the rule illustrated by equation 2. It can also be seen from equation 58 that the current and potential electrodes can be interchanged without affecting the results; this property is called reciprocity.


7.4 Vertical Electrical Soundings (VES)-The Schlumberger Array Configuration

For this array (figure 2a), in the limit as a approaches zero, the quantity V/a approaches the value of the potential gradient at the midpoint of the array. In practice, the sensitivity of the instruments limits the ratio of s to a and usually keeps it within the limits of about 3 to 30. Therefore, it is typical practice to use a finite electrode spacing and equation 2 to compute the geometric factor (Keller and Frischknecht, 1966). The apparent resistivity (r) is:

(6)

In usual field operations, the inner (potential) electrodes remain fixed, while the outer (current) electrodes are adjusted to vary the distance s. The spacing a is adjusted when it is needed because of decreasing sensitivity of measurement. The spacing a must never be larger than 0.4s or the potential gradient assumption is no longer valid. Also, the a spacing may sometimes be adjusted with s held constant in order to detect the presence of local inhomogeneities or lateral changes in the neighbourhood of the potential electrodes.

This graph can be interpreted in the field by an experienced geophysicist. Final interpretation is

done with the aid of a computer. The actual resistivity layering of the subsoil is obtained. The depths by resistivity values provide the hydrogeologist with information on the geological layering and thus the occurrence of groundwater.The method is otherwise called Electric drilling.

7.5 Horizontal Electrical Profiling-The Wenner Array Configuration

This array (figure 2b) consists of four electrodes in line, separated by equal intervals, denoted a. Applying equation 2, the user will find that the geometric factor K is equal to a , so the apparent resistivity is given by:

(7)

Although the Schlumberger array has always been the favored array in Europe, until recently, the Wenner array was used more extensively than the Schlumberger array in the United States. In a survey with varying electrode spacing, field operations with the Schlumberger array are faster, because all four electrodes of the Wenner array are moved between successive observations, but with the Schlumberger array, only the outer ones need to be moved. The Schlumberger array also is said to be superior in distinguishing lateral from vertical variations in resistivity. On the other hand, the Wenner array demands less instrument sensitivity, and reduction of data is marginally easier.


7.6 Fieldwork and Results

The fieldwork was carried out on October, 2012. An initial meeting with the Client was held. Discussions held with Mr. Mutua, the Client came up with a priority area that the consultant would carry out surveys.

The surveys comprised visual observation, geology and topography at the proposed site with a

view of checking its accessibility by a drilling rig. The drainage and recharge of the area, and distances to the neighbouring boreholes were also observed.

Two (2 nr.) Vertical Electrical Soundings (VES) were thereafter conducted at the sites that

indicated presence of anomalous zones (potential sites). The interpreted results of the VES are shown here below:

7.7 Field Data and Modelled Curve.

7.7.1 VES 1 Field Raw Data-PASCAL DATA

Point AB/2 MN

True

Resistivity Point AB/2 MN

True

Resistivity

1 1.60

0.5 258.00

13 25.00

0.5 42.00

2 2.00

0.5 181.00 14

32.00

10 76.00

3 2.50

0.5 164.00 15

40.00

10 78.00

4 3.20

0.5 156.00 16

50.00

10 86.00

5 4.00

0.5 132.00 17

63.00

10 111.00

6 5.00

0.5 119.00 18

80.00

10 128.00

7 6.30

0.5 108.00 19

100.00

10 161.00

8 8.00

0.5 99.00 20

130.00

10 211.00

9 10.00

0.5 94.00 21

160.00

10 320.00

10 13.00

0.5 81.00 22

200.00

10 401.00

11 16.00

0.5 72.00 23

250.00

25 00.00

12 20.00

0.5 55.00 24

320.00

25 0.0

VES 1 Model Interpretation

No Depth (m) bgl Resistivity (Omh-m)

Expected Lithology Aquiferous(??)

Layer From To

1 00 2.5572 452 Brownish sandy soil

No

2 3.5452 11.161 119 Lateritic material tending compact

No

3 10.185 11.844 144 compact micaceous gneiss.

No

4 13.466 13.371 14 Differentiated micaceous

gneiss

Formation Sitting on Main aquifer

5 58.6637 124 401 Fractured gneisses Water-bearing

6 >150 ∞ 12038 Fresh basement Impervious


*Drilling is thus recommended on this point as there is good fracturing and enough storage 7.7.2 MULUTU_VES 1 Model curve

7.8 Field Data and Modelled Curve.

7.8.1 MULUTU_VES 2 Field Raw Data within the school Compound( 37M 323864 UTM9847134, Alt:1340m)

Point AB/2 MN

True

Resistivity Point AB/3 MN

True

Resistivity

1 1.60

0.5 158.00

13 25.00

25.00

51.00

2 2.00

0.5 102.00 14

32.00

32.00

74.00

3 2.50

0.5 82.00 15

40.00

40.00

80.00

4 3.20

0.5 57.00 16

50.00

50.00

87.00

5 4.00

0.5 50.00 17

63.00

63.00

88.00

6 5.00

0.5 43.00 18

80.00

80.00

105.00

7 6.30

0.5 41.00 19

100.00

100.00

140.00

8 8.00

0.5 39.00 20

130.00

130.00

181.00

9 10.00

0.5 38.00 21

160.00

160.00

169.00

10 13.00

0.5 38.00 22

200.00

200.00

219.00

11 16.00

0.5 46.00 23

250.00

250.00

00.00


12 20.00

0.5 50.00 24

320.00

320.00

00.00


7.8.2 VES 2 Model Interpretation No Depth (m) bgl Resistivity

(Omh-m) Expected Lithology Aquiferous(??)

Layer From To

1 1 1 259 Brownish sandy soil

No

2 10 11 36 LOOSE Lateritic sediments

No

3 2 13 81 Slightly Compact gneiss.

No

4 3 16 40 Differentiated micaceous gneiss Formation Sitting on Main aquifer

5 98 114 182 Slightly fractured gneisses Water-bearing but poor storage

6 >130.00 ∞∞∞∞ 7483 Fresh basement Impervious

*Drilling is NOT recommended on this point as there is NO good fracturing and enough storage

VES 2 Model curve


8. Impacts of the Proposed Drilling Activity In project’s study area, the rock formations are metamorphic basement in nature. Basement aquifers are localized, therefore drilling activity within the study area shall have no impact on the aquifers, water quality, and the abstractors and neither shall there be a likelihood of coalescing cones of depression. It shall have no negative implications for other ground water users.

8.1 Impacts on Local Aquifer’s Quantity and Quality

The sustainability of water quality depends on the level of abstraction and recharge rate. If ground water is abstracted at a rate greater than its natural replenishment rate, then the water table lowers and the project will not be sustainable. Based on the yields of the boreholes in the area, the proposed abstraction of 20m3/day based on a 10 hour pumping regime is not expected to have any major impact on the aquifers, as the aquifer is expected to be quit productive

8.2 Impacts on Existing Boreholes in the Area

It is noteworthy that there are no many existing boreholes in the present area of investigation. Therefore we do not expect any negative impacts on any other existing borehole within the vicinity. Thus there will not be incidences of cones of depression or coalescing aquifers.

8.3 Regulations and Management Arrangement

.The Water Act provides for the management, conservation, use and control of water resources and for the acquisition and regulation of rights to use water. The Act is provided by the following responsibilities: -

� Development principles, guidelines and procedures for the allocation of water resources;

� Monitor, and reassess the national water management strategy;

� Receive and determine applications for permits for water use, and monitor and enforce

conditions attached to water permits for use;

� Regulate and protect water resources and quality for adverse impacts;

� Management and protect water catchment and liaise with other bodies for better regulation and

management of water resources;

� To gather and maintain information on water resources and regularly publish forecasts,

projections and information on water resources.


9. CONCLUSIONS AND RECOMMENDATIONS From a Hydrogeological point of view and based on the foregoing study, the following conclusions were made:-

� The geological and hydrogeological conditions at the project sites indicate good prospects for striking groundwater and are therefore suitable for drilling a borehole.

� The aquifer systems in the area have moderate to high productivity as reflected in the data of boreholes located in the project area.

� Borehole yields in the area are generally variable, indicating slight variance in the local hydro-geologic conditions in the subsurface geological formations. It is observed that the total drilled depths ranges between 77m and 153m below ground level, while the water struck levels are found between 39 and 48m m for 1st aquifer and 61m to 130m for the main aquifer. Tested yields ranges between 2.36 and 5 M3/HR.

� The water to be used from the proposed boreholes will be mainly for domestic purposes and minor irrigation.

The following recommendations are proposed: From the foregoing conclusions, it is recommended as follows; -

� The report therefore recommends that the borehole be drilled at site MULUTU_VES I, to a maximum depth of 130m below the ground level..

� The borehole shall be drilled to a finished internal cased diameter of 152mm (6inch).

� A valid Authorization to sink a borehole must be obtained from the Water Resources Management Authority (WRMA) as per the requirement of Water Act 2002.

� The completed borehole is required to be test-pumped for a minimum period of 24hours. The purpose of this test is to determine the actual quantity of groundwater that can be abstracted from the borehole, the abstraction capacity of the pump to be installed and the depth at which the pump (submersible) can be installed,

� A sufficient quantity of the water is to be submitted to the nearest competent water testing laboratory to determine the physical, chemical and bacteriological parameters the groundwater.

� Upon completion of the borehole, a water meter and an airline are required in order to facilitate monitoring of groundwater abstraction and the static water level measurements, especially for the maintenance respectively,

� The whole drilling process, especially the boreholes, construction and test pumping are very crucial to the success of the borehole and therefore supervision of the work by an independent and qualified Hydrogeologist is highly recommended.

� That an Environmental Impact Assessment (EIA) be carried out according to section58 of the Environmental Management and Coordination Act (EMCA) of 1999.

� The proposed borehole, drilling site is known to the client himself Mr. Pascal Mutuku and the Consultant did accurately mark on the ground and on the sketch location and topographical maps attached and positioned by GPS system.

Table 8.1: Recommended Drilling Sites Site No.

Name of Site Location Geo-Reference (By GPS)

Altitude (m )

Recommended Drilling Depth (m)

1. PASCAL MUTUA’S BH WATER PROJECT

MULUTU UTM -1.341166, 37M 97879 1259m

130


Legal Requirements

It is a legal requirement, stipulated in the Kenyan Water Act, that the Client applies for an authorization to drill a borehole from the Water Resources Management Authority(WRMA), Tana Catchment, Embu. For this purpose, three signed copies of the present report must be submitted to the Authority through its sub-regional offices in Kitui for examination. An Environmental Impact Assessment (EIA) should be conducted and accompany the hydrogeological report. For this purpose ten (10) copies of the EIA report should be signed by the Lead expert and submitted to NEMA for approval.


10. REFERENCES

Biodiversity Conservation Programme (BCP) for south Kitui National reserve.

Demonstration Guide ISFP Technical series No.1.

DEO. (2005). Draft NEAP/DEAP Manual (November 2005). Nairobi: GoK.

Environmental Impact Assessment Report - Nyumbani village Home Kitui.

GoK. Annual reports from the following Departments of: Agriculture, Forestry, Water, Lands,

Fisheries,Livestock, Energy, Health, education. Nairobi: GoK.

GoK. (2005). Environmental Management Plan (DASS 2005-2010). Nairobi: GoK.

GoK. (2002). KITUI District Development Plan (2002-2008). Nairobi: GoK.

GOK. ( 2000). KITUI District Forestry Master Plan (draft report may 2000). Nairobi: GOK.

GOK. ((2001-2004)). KITUI District PRSP consultation Report. Nairobi: GOK.

GoK. (2004). KITUI District State of Environment Reports for the years 2003& 2004. Nairobi:

GoK.

GoK. (2003). KITUI District State of Environment Reports for the years 2003& 2004, 2004)TIVA Forests

. Nairobi: GoK.

GoK. (2005). KITUI District Vision and Strategy: Natural Resources Management 2005-2015. Nairobi:

GoK.

GoK. (2005). KITUI District Vision and Strategy: Natural Resources Management 2005-2015, 2005).

Nairobi: GoK.

KITUI District Drought Contingency Plan.

NEMA. (2005). National Environment Management Authority (strategic plan 2005-2010). Nairobi:

GoK. Registry, MoWR, (on-going)

Ministry of Water Resources (MoWR), Borehole Completion Records.

Saggerson E P, (1971)

Geological Survey of Kenya, Geological Map of the Kangundo Area, Scale 1: 50,000.

Sombroek W.G; Braun H.M.H; and van der Pouw B.J.A, (1982)

Exploratory Soil Map and Agroclimatic Zone map of Kenya, 1980, Kenya Soil Survey.

Tippetts-Abbett-McCarthy-Stratton (TAMS, 1980)

Ministry of Water Development, National Master Water Plan, Stage 1.

Whitten D G A & Brooks J R V, (1972)

Penguin Books, The Penguin Dictionary of Geology.


11. APPENDIX

• Field survey data

• Topographical map extract [Mapsheet, 1:50,000]

• Sketch Map of the project area Showing Selected Drilling Site

• Schematic Design of the Borehole

12. ADDENDUM

• Borehole drilling procedures

• References

• Bore Drilling agreement


Sketch Map and direction to the project site.

Pascal Mutua’s Proposed BH site


Figure 5: DIGITAL Terrain Extract Map of the Project Site

Proposed Pascal mutua’s BH


EXPECTED FORMATION FOR PASCAL MUTUA BOREHOLE


13. ADDENDUM DRILLING, CONSTRUCTION AND DEVELOPMENT PROCEDURES 1. Drilling Drilling should be carried out with an appropriate tool - either percussion or rotary machines will

be suitable, though the latter are considerably faster and have a low noise level. Geological rock samples should be collected at 2 metre intervals. Struck and rest water levels and if possible, estimates of the yield of individual aquifers encountered, should also be noted.

2. Well Design The design of the well should ensure that screens are placed opposite the optimum aquifer

zones. The final design should be left in the hands of an experienced driller or hydrogeologist. 3. Casing and Screens The well should be cased and screened with appropriate steel casings and screens as per the

design given above. In comparatively shallow wells, uPVC casing and screens of 5" or 6" diameter may be adequate. Slots should be 1 mm in size.

4. Gravel Pack The use of gravel pack is recommended within the aquifer zone, because the aquifer could

contain sands or silts which are finer than the screen slot size. An 8" diameter borehole screened at 6" will leave an annular space of approximately 1", which should be sufficient. Should the slot size chosen be too large, the well will `pump sand', thus damaging pumping plant, and leading to gradual `siltation' of the well. The grain size of the gravel pack should be an average 2 - 4 mm.

5. Well Construction Once the design has been agreed upon, construction can proceed. In installing screen and

casing, centralizers at 6 metre intervals should be used to ensure centrality within the borehole.

This is particularly important if an artificial gravel pack is to be installed as it ensures an

approximately even annular space. If installed, gravel packed sections should be sealed off top and bottom with clay. It is normal practice nowadays to gravel pack nearly the total length of the borehole but seal off the weathered/topsoil zone at the top. The remaining annular space should be backfilled with an inert material, and the top five metres grouted with cement to ensure that no surface water at the well head can enter the well bore.

6. Well Development Once the screen, gravel pack, seals and backfill have been installed, the well should be

developed. Development has two broad aims: a) It repairs the damage done to the aquifer during the course of drilling by removing

clays and other additives from the borehole walls, and


b) It alters the physical characteristics of the aquifer around the screen and removes fine particles.

We would not advocate the use of overpumping as a means of development since it only

increases permeability in zones which are already permeable. Instead, we would recommend the use of air or water jetting, which physically agitates the gravel pack and adjacent aquifer material. This is an extremely efficient method of developing and cleaning wells.

Well development is an expensive element in the completion of a well but it is usually justified

in longer well life, greater efficiencies, lower operational and maintenance costs and a more constant yield.

7. Well Testing After development and preliminary tests, a long-duration well test should be carried out. Well

tests have to be carried out on all newly completed wells, because not only does this give an indication of the success of the drilling, design and development, but it also yields information on aquifer parameters which are vital to hydrogeologists.

A well test consists of pumping a well from a measured start level (SWL) at a known or

measured yield, and recording the rate and pattern by which the water level within the well changes. Once a dynamic water level is reached, the rate of inflow to the well equals to the rate of pumping. Towards the end of the test a water sample of at least two litres should be collected for chemical analysis.

The duration of the test should be 24 hours, with a further 24 hours for a recovery test (during

which the rate of recovery to SWL is recorded). The results of the test will enable a hydrogeologist to calculate the best pumping rate, the pump installation depth, and the drawdown for a given discharge rate.

8. Well Maintenance Once the well has been commissioned and a pump installed at the correct depth, the

maintenance schedule should be established. Checks on discharge (m3/day), pumping water level (metres below a leveled and immovable bench mark), and static water level (if for any reason the well is not used for a 24-hour period) should be taken as part of a regular, routing process. This will enable the evaluation of all known conditions should reduction in the yield or other problems occur in the future, and recommend the most appropriate action.


APPENDIX V: DRILLING SUPERVISION

This Appendix discusses technical aspects of drilling supervision, and is presented for the Client's information should he wish to either deploy one of his own personnel, or appoint a drilling hydrogeologist to supervise drilling works.

Drilling Supervision: Introduction

The Supervisor's responsibility in the first place is to advise the Client and act as his faithful representative on site, and furthermore to ensure that all works are carried out according to the Contract and the Technical Specifications. He/she should carry out supervision in conformity with sound professional practices and standards.

It is absolutely essential that the Client makes clear to the Drilling Contractor the precise role of the Supervisor, and that the Supervisor and Contractor clearly understand that they are working together to produce the best borehole possible in the circumstances. Too often the Supervisor's role is seen as an antagonistic one, when the precise reverse should be the case.

It is therefore essential when selecting the Supervisor that an individual with suitable experience and credentials is appointed.

Drilling Supervision: Tasks of the Drilling Supervisor

The tasks of the Supervisor include, but are not necessarily limited to, the following. The final selection of duties should arise out of discussion between the Supervisor and the Client, bearing in mind the specific needs of the Client and the precise nature of the drilling to be supervised.

The comment made above, that the Supervisor is on site to ensure the construction of the best hole possible, must be borne in mind at all times.

i. Site selection: verify that drilling is carried out at the exact spot selected by the survey team.

ii. Inspection and verification of drilling equipment (physical plant and consumables), and borehole materials (casing, screen, gravel pack etc.), on site; ensure that suitable equipment and sufficient materials are on site before drilling commences.

iii. Selection, in consultation with the Contractor, Client and any pertinent Local Authorities, of a suitable site or sites for the drilling team temporary camp should this be necessary; inspection of the camp for environmental and hygiene standards.

iv. Assist as appropriate in the selection of a source of drilling make-up water, and liase with relevant authorities or utilities in ensuring that the source is made available throughout the drilling operations. Waters of high total dissolved solids, or of very low or very high pH, may denature drilling additives and can, in certain circumstances, lead to the loss of the hole through collapse or "heave" when an additive "breaks".

v. Monitor the Contractor's daily progress and keep a detailed record (all activities relevant to the construction of the borehole and associated works); this record should be independent of the record kept by the Contractor, and will be used to verify quantities, overworks or standby time claimed by the Contractor.

The drilling process should accord with good working practices.

vi. Sampling and geological logging of drill cuttings; ensuring that the Contractor collects, dries, bags and labels samples in accordance with the Contract. Analyses and interprets the geological logs in accordance with accepted or agreed methods, or in conjunction with geophysical logging data (§x).

vii. Monitor the outflow of water or drilling fluid during the drilling process, using a V-notch weir or other


suitable volumetric flow measuring method; noting changes in outflow volume: and monitor changes in the crude chemical characteristics of drill fluid or returns by means of a suitable instrument such as an electrical conductivity meter.

viii. Monitor drilling penetration rate; this should consider bit diameter and other drilling criteria such as pulldown or holdback, loss of circulation and any other relevant variable; rate of penetration may be expressed in terms of time to drill a single length of drill-pipe or measured part thereof for direct rotary plant: or time per unit length for percussion plant.

Of particular importance is any sudden change in the rate of penetration; penetration rates should be correlated with observed drill cuttings and interpreted geology and hydrogeology.

ix. On the basis of observed outflow (§vii), penetration rate (§viii), geological samples (§vi) and any other pertinent information, decide when sufficient depth has been reached and so terminate drilling.

x. In the event that downhole geophysical logs are deployed, the Supervisor will oversee the entire operation, and undertake the interpretation in conjunction with the geological logs already collected.

If downhole logs are to be deployed, the basic minimum suite should comprise the following:

Ø Long- (64") and short-normal (16") resistivity

Ø Self potential

Ø Caliper

Ø Temperature and conductivity.

A natural gamma log will indicate clay horizons, and other logs may be deployed as appropriate to specific ground conditions. The selection of downhole logs should be the responsibility of the Supervisor.

xi. Advise the Driller on matters of drilling, casing installation, development or testing, as circumstances dictate.

xii. In conjunction with the Driller, draw up a permanent design for casing, screen, gravel pack, grout and sanitary seals, on the basis of observed outflow, penetration rate, geological samples and other pertinent variables. The design philosophy should be explained to the Client.

xiii. Supervise the installation of materials installed in the borehole and keep a tally of quantities used. Ensure that installation proceeds according to design (§xii), or justify changes in installation in the light of actual downhole conditions.

xiv. Draw up and supervise a suitable well development programme, either in accordance with observed conditions or the Technical Specifications; and terminate the development process when appropriate, or after consultation with the Client.

xv. Undertake or supervise the pumping tests stipulated in the Contract and Technical Specifications; check and analyse the data collected: these must include elapsed time, discharge and water level data; and may include water quality parameters such as electrical conductivity or total dissolved solids, temperature, pH, total alkalinity, dissolved oxygen and redox potential.

xvi. Collect water samples according to the Contract and Technical Specifications; undertake the wellhead analysis of electrical conductivity, temperature, pH, total alkalinity, pH, dissolved oxygen and redox potential, or any other parameter agreed in the Contract and Technical Specifications, as appropriate.

xvii. Ensure that water samples are analysed for biological and chemical activity as agreed in the Contract and Technical Specifications, or as otherwise appropriate.

xviii. On the basis of test data interpretation, recommend safe discharge and pump installation depth to the Client. The safe intake depth must take into account the likely variations in "natural" water levels, brought about by seasonal influences.


xix. Ensure drilling and campsite restitution in accordance with the Contract and Technical Specifications, or as otherwise necessary.

xx. Certify invoices submitted by the Contractor to the Client, checking quantities and times against his/her own records.

xxi. Signing for final acceptance of works on behalf of the Client


SCHEMATIC BOREHOLE DESIGN