HYDROGEOLOGICAL ASSESSMENT REPORT Wambandu Primary School L/R No. East Bunyore/Ebunangwe /912 Echichibulu Location, Emuhaya Division, Emuhaya District VIHIGA COUNTY *********** October, 2012 CONSULTANT: Sebastian Namwamba EARTHS SCOPE GEO- HYDRO SERVICES Water, Sanitation and Environmental Engineering P. O. Box 55127-00200 NAIROBI Cell-phone: 0720-438377 Signed: Date Hydrogeological & Geophysical Investigations Wambandu Primary School, Emuhaya District, Vihiga County, Kenya. SUMMARY Introduction This report presents the results of hydrogeological and geophysical investigations to evaluate groundwater resources for Wambandu Primary School - Wambandu in Emuhaya district, Vihiga County, Kenya. The borehole will be used to supply water to the School and surrounding community, thus supplementing water from springs and roof catchment in the area. Climate The climate in the area is mainly humid type, with a bi-modal rainfall pattern. Long rains are experienced in March to July while short rains occur in August to October. The main source of rainfall over Wambandu region is the Lake Victoria. It occurs in form of either convectional or frontal rainfall. The mean annual rainfall ranges between 1100 and 2700 mm. The mean maximum and minimum temperatures in the area are given as 27oC and 15oC respectively. Evaporation is relatively low and increases from less than 1400 mm to 1800 mm per year. Geology The regional geology of the investigated area is dominated by the Basement System Complex which can be divided into two groups: - (a) The Basement Complex rocks, (sedimentary in origin) and the (b) The undeformed post- Basement formations. The geology of the investigated site include, the recent deposits which include lateric iron stone resulting to production of thick red soils. These are underlain by the Kavirondian series rocks consisting of feldspathic grits, conglomerates, shale and siltstones. Granites are the major intrusives in the area. Geophysical Fieldwork Geophysical fieldwork was executed on 27th September 2012. The resistivity method was used for the present investigations. Geophysical measurements were used to determine the thickness of the underlying layers, their potential as aquifers, and the expected quality of groundwater in these formations .One vertical electrical soundings were executed on selected points. Conclusions From the present study it is concluded that the prospects for sufficient groundwater for use in the station are good, based on the geological and hydrogeological evidence gathered. Recommendations for Drilling Drilling of a Borehole to a minimum of 130 m bgl and a maximum of 150m bgl is recommended at the location of the VES. The recommended drilling site is known to Mr. Isaac Kisambo (Head teacher) – 0720984101. The borehole should be drilled at 8‟‟ diameter and installed with 6" diameter uPVC casings and screens with high % open surface area. Recommendations are given for borehole construction and completion methods.The importance of correct and comprehensive techniques in this particular aspect cannot be over-emphasized. Generally, the water quality is expected to be good. Earths Scope Geo - Hydro Services October 2012, Page i Hydrogeological & Geophysical Investigations Wambandu Primary School, Emuhaya District, Vihiga County, Kenya. Monitoring Regular monitoring should be instituted and maintained in the borehole in order to keep track of groundwater levels. A piezometer should be installed in the borehole to be able to monitor the water level in the well. Drilling Before drilling starts, a groundwater permit should be applied for from the Water Resources Management Authority (WRMA), Lake Victoria North Drainage Basin –Regional Office in Kakamega. Additional recommendations for borehole drilling, installation, development and are given in Appendix 1 Earths Scope Geo - Hydro Services October 2012, Page ii Hydrogeological & Geophysical Investigations Wambandu Primary School, Emuhaya District, Vihiga County, Kenya. TABLE OF CONTENTS 1. INTRODUCTION ............................................................................................................................................... 1 2. BACKGROUND INFORMATION ................................................................................................................... 2 2.1. LOCATION ................................................................................................................................................... 2 2.2. VEGETATION AND CLIMATE ........................................................................................................................ 2 2.3. TOPOGRAPHY AND DRAINAGE .................................................................................................................... 2 2.4. EXISTING WATER SUPPLY AND DEMAND .................................................................................................... 2 3. GEOLOGY .......................................................................................................................................................... 4 3.1. REGIONAL GEOLOGY .................................................................................................................................. 4 3.1.1. Precambrian .......................................................................................................................................... 4 3.1.2. Cretaceous ............................................................................................................................................. 4 3.1.3. Tertiary .................................................................................................................................................. 4 3.1.4. Pleistocene to Recent............................................................................................................................. 5 3.2. GEOLOGICAL ROCK FORMATIONS ............................................................................................................... 5 3.2.1. Pleistocene and Recent Deposits ........................................................................................................... 5 3.2.2. Older Rocks ........................................................................................................................................... 5 3.2.3. Kavirondian System ............................................................................................................................... 5 3.2.4. Nyanzian System .................................................................................................................................... 6 3.2.5. Basement System ................................................................................................................................... 6 3.3. GEOLOGY OF THE INVESTIGATED SITE ........................................................................................................ 6 4. HYDROGEOLOGY ........................................................................................................................................... 8 4.1. GROUNDWATER OCCURRENCE ................................................................................................................... 8 4.2. BASEMENT AQUIFER OCCURRENCE ............................................................................................................ 8 4.3. WEATHERING AND ITS SIGNIFICANCE IN AQUIFER OCCURRENCE ................................................................ 9 4.3.1. The Collapsed Zone ............................................................................................................................... 9 4.3.2. Saprolite ................................................................................................................................................ 9 4.3.3. Saprock .................................................................................................................................................. 9 4.3.4. Bedrock ................................................................................................................................................. 9 4.3.5. Regolith ............................................................................................................................................... 10 4.4. HYDROGEOLOGY OF THE WAMBANDU AREA ............................................................................................ 10 4.5. HYDRAULIC CHARACTERISTICS OF THE AQUIFER ...................................................................................... 11 4.5.1. Specific Capacity ................................................................................................................................. 11 4.5.2. Transmissivities ................................................................................................................................... 11 4.5.3. The Storage Coefficient ....................................................................................................................... 11 4.5.4. Recharge Mechanisim ......................................................................................................................... 11 4.5.5. Groundwater Movement ...................................................................................................................... 12 4.6. GROUNDWATER QUALITY ......................................................................................................................... 12 5. GEOPHYSICAL INVESTIGATION METHODS ........................................................................................