WASH Cluster – Emergency Training GWD GWD1 1 Groundwater Development and Drilling Session 1 Occurrence of Groundwater

WASH Cluster – Emergency Training GWD GWD1 Session Objectives 2 Provide an understanding of how groundwater occurs in nature Examine how this can influence: the location of potential groundwater sources, and the means of developing the source

WASH Cluster – Emergency Training GWD GWD1 3

WASH Cluster – Emergency Training GWD GWD1 What is Groundwater? 4 After: US Geological Survey website:

WASH Cluster – Emergency Training GWD GWD1 Three broad groups of rocks are: –igneous rocks - formed by heat crystallized below the surface of the earth (plutonic rocks) erupted at the surface through volcanoes (volcanic rocks) –sedimentary rocks deposited in layers in rivers, lakes, the sea or by wind –metamorphic rocks – transformed from sedimentary or igneous rocks under heat and/or pressure. Types of rocks 5

WASH Cluster – Emergency Training GWD GWD1 Rocks are aggregates of mineral particles 6 From Longwell, Flint, Sanders 1969, Wiley International interlocking crystalline rock (A) cemented particulate rock (B)

WASH Cluster – Emergency Training GWD GWD1 Typical crystalline rocks 7 Slate (black) invaded by quartz veins Gneiss Granitic rocks

WASH Cluster – Emergency Training GWD GWD1 Crystalline rocks 8 Groundwater is stored in fractures in crystalline rocks - therefore sporadic in extent and volume.

WASH Cluster – Emergency Training GWD GWD1 Basalt Variety of different cracks – water is stored in the cracks, and also flows through the cracks in the subsurface 9

WASH Cluster – Emergency Training GWD GWD1 10 Vesicles in basalt – the vesicles are generally not interconnected. the porosity in basalts is largely through cracks and fractures Drill core covering a vertical profile of basalt

WASH Cluster – Emergency Training GWD GWD1 hard, consolidated OR unconsolidated Sedimentary Deposits 11

WASH Cluster – Emergency Training GWD GWD1 12 sandstone with sand grains strongly cemented and no porosity finely layered cemented fine sandstone

WASH Cluster – Emergency Training GWD GWD1 13 Coarse river gravel with large open pore spaces. Thick layers of this material store large volumes of water Coarse pebbles cemented together to form conglomerate – these rocks have low porosity and generally only hold water in fractures

WASH Cluster – Emergency Training GWD GWD1 Consolidated Sedimentary Rocks 14 Continuous layering (bedding) in flat-lying sediments, Grand Canyon USA. On RHS vertical cracks show how these consolidated rocks fracture Strongly tilted layers of fine grained siltstone, with very few visible open cracks

WASH Cluster – Emergency Training GWD GWD1 Unconsolidated sediments 15 Sand and Gravel forms porous aquifers

WASH Cluster – Emergency Training GWD GWD1 Can be very hard OR Relatively unconsolidated Can have high porosity because of cavities and caves Limestone 16

WASH Cluster – Emergency Training GWD GWD1 17 Limestone showing fossil fragments as well as cavities formed by solution of particles

WASH Cluster – Emergency Training GWD GWD1 18 Limestone caves and cavities provide huge porosity and massive flows of groundwater

WASH Cluster – Emergency Training GWD GWD1 Fractured rock aquifers: –no primary porosity in crystalline rocks and consolidated sedimentary rocks –Porosity due to fractures Porous media –unconsolidated granular material with open pore spaces (unconsolidated sediments) “Karst” –associated with limestone deposits and cave systems. Aquifer types and porosity 19

WASH Cluster – Emergency Training GWD GWD1 How Aquifers occur 20

WASH Cluster – Emergency Training GWD GWD1 Knowing the rock type helps work out : –Where to search –The extent and depth of the aquifer –How to develop the groundwater source (eg drilling method) –The volume available Why is this useful 21

WASH Cluster – Emergency Training GWD GWD1 22 CASE STUDY 1: APPLICATION OF GEOLOGY IN IDENTIFYING GROUNDWATER SOURCES IN CHAD

WASH Cluster – Emergency Training GWD GWD1 23 EXERCISE 1: WHAT CAN WE FIND FROM A GEOLOGICAL MAP