TABLE OF CONTENTS... 1 LIST OF TABLES... 2 INTRODUCTION... 3 ACKNOWLEDGEMENT Geology of the Area... 5

Transcription

1 TABLE OF CONTENTS TABLE OF CONTENTS... 1 LIST OF TABLES... 2 INTRODUCTION ACKNOWLEDGEMENT Geology of the Area... 5 BOREHOLEDRILLING ACTIVITIES AND RESULTS Borehole Design and Casings Surface Casing... 5 Plain and Screen Casings... 6 Gravel Pack and Backfilling Sanitary Seal Well Development BOREHOLE DRILLING RESULTS/SAMPLE ANALYSIS Ilagala-Rusesa... 7 TEST PUMPING RESULTS... 9 CONSTANT-REOVERY RESULTS Test Pump results and Suggestions APPENDIX 1 AND

2 LIST OF TABLES TABLE 1; ILAGALA-RUSESA DRILLED SAMPLE ANALYSIS.. 8 2

3 INTRODUCTION. Water has always been an important for the existence of human life from time immemorial. Water affects all sectors of the economy including domestic, agriculture, livestock, and industries e.t.c. However the shortage of good quality water from surface source has made groundwater to be important in common places. Shortage of sufficient water together with the rapid water quality deterioration brings a challenge to the people internationally. To minimize the problem in Kigoma District Council, specifically Ilagala village where Environmental protection seems to failure due to small palm industries continuing their palm oil processing on the river bank of Malagarasi; The Lake Tanganyika Integrated Management Project under Vice President s office sponsored one Borehole for small palm oil processors. The borehole is drilled 78m away from the edge of the river bank of Malagarasi to protect river sedimentation and to conserve the environmental at large. 3

4 ACKNOWLEDGEMENT. Inevitably numerous persons have contributed to this borehole drilling since its inception. Each contribution enriched the process and facilitated my ability to bring it to successful conclusion. A grateful appreciation and acknowledgement goes to Lake Tanganyika Integrated Management (UNDP/GEF) Project for commissioning the task of drilling one borehole for purpose of environmental conservation. Special mention and sincere appreciation is to the project coordinator Mrs. Hawa Mshamu, Mr. Seleboni J. Mushi the assistant Project coordinator for their significant guidelines and helpful suggestions resulting to the accomplishment of this task. Words of thanks also go to Mr. Chobaliko Lubabwa the Basin Water Board Officer for having permitted me to supervise this task. Words are inadequate in offering my thanks to village leaders who participated fully during the process starting from the commencement of drilling to the process of pumping test of the borehole. Finally, yet importantly, I would like to express my heartfelt thanks to Mr. K.J Babu and his team from Ardhi Water Wells Ltd/ Aqua Well Drilling Company for the successful completion of this task. 4

5 Geology of the Area. The village is covered by the oldest rocks mainly gneisses and schists of exactly similar type of Ubendian system. The rocks are often veined with acidic injection material and represent an ancient series of sediments probably shales, sandstones and greywacke which were altered by regional metamorphism and migmatization. Overlying with unconformity are Kigoma Quartzite of white and occasionally cream or maove color, pure quartzite and sandstones. There is a thin development of Ilagala Dolomitic limestones in the area with an occasional stromatolithic structures. The structural feature of interest of the village is the Lake Tanganyika Rift into which the Rift faulting dominates the area. There is a tectonically unstable trough towards the North of Kigoma where the rift faulting appears to take form of series of faults trending North-South (NS) BOREHOLEDRILLING ACTIVITIES AND RESULTS. Borehole Design and Casings. After a well has been drilled to terminal depth and confirmed that the water has satisfactory quality and quantity, the well was reamed and completed by placing working casings to the bottom of the loam, consolidated layer, placement of casings (Bentonite and Sanitary seals), as well as well as gravel packing. Surface Casing Placement of well working/surface casing was usually from ground surface through the unconsolidated soils into a base of that particular stratum or into stable strata. In this case surface casing served in supporting unstable materials during drilling. Some other advantages of surface casing includes; facilitation of installation and removing of other casing i.e. screens and plain casings, aided in placing gravel pack and sanitary seals. It also served as a structural support against surface water and any other undesirable water to pollute the ground water. Surface casing were usually smaller than the drilled hole and hence, could allow casing to be lowered into place. Surface casing used were of plastic made with diameter of 250mm (upvc). Understandably, due to the smaller thickness of loose formation-clay and sand. Inside the working casing, the 152mm bit and drilling pipe was driven to the determined depth. Later on the borehole was reamed by 205mm bit. 5

6 Plain and Screen Casings. Following drilling operation for the productive well, 165mm-casings were lowered into the hole with perforated sections (screens) inserted or created opposite water strikes noted during pilot drilling phase. At the places where no water was encounted, plain casings were placed. The design was in such way that plain casing was bottom most pipe plugged with wooden plug, followed by one pipe of screen to collect water from the bottom most aquifer. On top of this screen a plain casing was connected. This plain casing is considered as a pump house, of which even during the pump test exercise the pump will be placed at this level. From this section upward the arrangement of screen and plain casings depended on water strikes and potential aquifers. The topmost plain casing was capped with wooden cap. The principle behind of placing casings is to stabilize the sides of the hole, to prevent loose material movement into the well as well as to allow a maximum amount of water to inter into the well with a minimum hydraulic resistance. Gravel Pack and Backfilling. The gravel pack was designed in such a way that small particles from the aquifer can pass freely through the pores of the gravel. When these particles have been removed during development, the effective porosity and permeability are increased and as a result higher yield and no finer particles movement may occur to the well. Gravel pack was poured through annular space, immediately after screen and plain Casings are placed to the terminal depth (Designed by site geologist). Gravel pack was Placed to few metres above the uppermost screen casing. Above the gravel pack, backfilling of impermeable material i.e. clay was placed. Between gravel pack and backfill material levels, a bentonite seal was designed in order to prevent unnecessary seepage into productive aquifers below. Gravel pack used were quartz and feldspar gravels collected from the shores of Lake Tanganyika of which it is transported to the shore by waves of the Lake. The grain sizes varies from 2mm to 4mm, normally gravels were thoroughly sieved and washed to make sure the sizes are attained and to remove clay contents respectively and then poured into the well through annular space, i.e. between casings and the borehole walls. Gravel packs volume were determined in terms of number of bags as well as the length of column below the ground level. 6

7 Sanitary Seal. Whenever groundwater pumped from a well is intended for human consumptions, proper Sanitary precautions must be taken to protect the water quality especially the on-surface Pollution. It is due to this reason, in the project, a mixture of cement, gravel and sand at a ratio of 1: 4: 6 respectively were used to protect a well as a sanitary seal for every productive borehole. A column of 2.5m inside annular space was poured with sanitary seal concrete/bentonite in order to prevent deep groundwater be contaminated by any pollution from the surface. Well Development. Following the borehole construction above the borehole was cleaned. The borehole was developed in order to increase its specific capacity, prevent sanding and obtain maximum economic well life. These results were accomplished by removing the finer particles from the natural formation surrounding, perforated sections of the casings. The importance of this exercise cannot underestimated as it improves the opening of pore Spaces and make direct connection between borehole and natural formations/aquifers and Hence improves maximum yield of the borehole. BOREHOLE DRILLING RESULTS/SAMPLE ANALYSIS. Ilagala-Rusesa. The borehole is located at S, E 75m from the edge of Malagarasi River, with the total depth of 60m. Three aquifers were encounted during drilling at the depth ranges of 17-24m, 32-38m and 46-50m with estimate discharge of 10.5m 3 /hr, 15.5m 3/ hr, 18.7m 3 /hr respectively. During well development the well shows an estimate yield of 20m 3 /hr in which the actual yield after pump test is 30m 3 /hr. At first the borehole was drilled using Air Rotary up to a depth of 24m where Mud drill starts to drill up to a terminal depth of 60m. The PAT-DRILL machine was deployed at this site to secure collapsing of borehole. 7

8 Tables below show sample analysis of the borehole and Test Pumping results. Table 1; Ilagala-Rusesa Drilled sample analysis. Depth Range (m). Formation Details. Borehole diameter Sand, clay, silt medium 8 inches grained Mudstones-dark black 8 inches colored Mudstones-dark black 8 inches colored Clay, sand, mud. 8 inches Basalt, shales, sand medium 8 inches to coarse grains Clayey sand, medium to 8 inches coarse grains, brownish in color Highly weathered basaltic rock, dark colored. 8 inches Clayey sand, fine to 8 inches medium grains Clayey sand, mud dark 8 inches brown in color Sand, mud, shales. 8 inches Shales, basalts and mud, dark colored. 8 inches 8

9 TEST PUMPING RESULTS. CONSTANT RATE PUMPING TEST RESULTS. Village: Ilagala Depth pump inlet: 58m Sub-Village: Rusesa Static water level: 4.02m District: Kigoma District Council Coordinates: S, E Total depth: 60m Time Elapsed time(min) Water level(m) Draw-down(m) Discharge Q(m 3 /hr) 08:00am

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11 CONSTANT-REOVERY RESULTS. Time Elapsed time(min) Water level(m) Residual Drawdown(m) 08:00am Calculated Recovery. 11

12 :00am Test Pump results and Suggestions. 1. The pump type used is Submersible of size 7.5Kw. 2. The pumping test took 24 hours for constant pumping and 2 hours for Recovery, of which the total of 26 hours were used to complete the task. 3. The calculated recovery for 2 hours is 40.59m; hence the well has good recovery. 4. The well yield is 30m 3 /hr (30000lts/hr). For details see Appendix 1. Suggestions. 1. To ensure the well life a Submersible pump of size 10Kw to 13Kw must be installed depending on the head (height at which water is raised). 2. Source of power to pump water from a borehole can be Power Generator, Wind or installation of Solar Panel. Among the three sources, installation of Solar Panel is the best because the running cost of Power Generator is ambiguous to villagers and for the case of Windmill, the area has no enough wind blowing throughout a day. 3. The choice of the size of Solar Panel will depend on the size of submersible pump and water head. NB. The Results of Water quality and Testing is attached in Appendix 2 as analyzed by Ingenieria Sin Fronteras (ISF)-Kigoma office. 12

13 APPENDIX 1 AND 2 13