# Principles of Hydrogeology ( GHT 405) – 2013

Department of Geology

University of Dhaka

Fourth -Year B.S. Honor’s Course -Final Examination 2013

Subject: Geology

Course: GHT 405. Course Name: Principles of Hydrogeology

Subjective Part

Full marks 25 Time 2 Hours

*The figure at the right margin indicates full marks. Answer any five of the following questions. Draw suitable sketches and diagrams wherever necessary*

1.

a) Which physical properties of rocks do control occurrence of groundwater? Differentiate between primary and secondary porosity. 4

b) List the various laboratory and field methods for measuring hydraulic conductivity. 1

c) Briefly discuss various geological formations forming aquifers. 3

2.

a) What is meant by groundwater exploration? Mention the various stages of exploration. 1

b) Distinguish between percussion and rotary drilling methods. 1

c) List the common logs used in groundwater exploration. Briefly discuss log interpretation techniques. 3

3.

a) Why do we conduct pumping tests? Name the various types of pumping tests. 1

b) List the various methods for measuring discharge during pumping test. 1

c) Briefly discuss the test procure for long term constant discharge pumping test. 3

4.

a) What is non -equilibrium well equation? Who did develop it? 1

b) Enumerate the assumptions made in the derivation of the equation. 2

c) Explain how Jacob modified the non -equilibrium well equation. 2

5.

a) Derive an equation for steady-state flow of a pumped unconfined aquifer. Show how this –r equation can be re -arranged to express it in terms of corrected drawdown. 2

b) Mention the assumption for the above equation. 1

c) Explain the differences between the processes by which water is released from storage when groundwater is abstracted from a confined aquifer and an unconfined aquifer. 2

6.

a) A well in an unconfined aquifer is pumped over a long period at a rate of 0.05 m3/s until approximate steady-state conditions are achieved. Two observation wells at distances of 25m and 50m from the abstraction well give observed drawdowns below the initial water table level of 15.3m and 9.5m respectively. If the saturated thickness of the aquifer prior to pumping is 80m determine the hydraulic conductivity of the aquifer material.,2

b) Calculate sly steady-state drawdown at the pumping well which fully penetrates a confined aquifer if the pumping well is 65 in from a river which is in full hydraulic connection with the aquifer. The following useful data mobs used in calculating: (i) Diameter of pumping well -0.2 m, (ii) Pumping rate .4000 m3 /day. and (iii)Transmissivity 470m2 /day. 2

c) What would be the drawdown in a piezometer 100m from the well and 25m from the river? 1