The Deep Tubewell Drilling Site was located at Lamjung. The GPS Coordinate of the well drilling site is 28°09’41.06″N, 84°14’46.03″E about 70 m arial distance from Midim khola .
After Site Mobilization, the drilling work on the site at Vorletar work was started on 2080/02/13. The drilling work was continued smoothly and achieved 132 m of penetration. After this depth, the drilling work was stopped as the well has penetrated sufficient depth. During the drilling operation; the cutting samples were collected. Representative sample of each layer were collected. The driller has also prepared litholog on the basis of cuttings, nature of progress of the well penetration .According to driller’s lithological log & well penetration rate, the well was designed. The whole drilling work was carried in the direction and close supervised of office representative. The lithological log of the Tube well is presented. After the completion of the drilling work on the basis of aquifer layer presence of the well the screen pipe and casing pipe were lowered.
Drilling works at a Vorletar
Pipe Lowering at site
Figure 4 Well design along with assembly and Litholog
Total length of casing and screen used
250 mm MS Casing Pipe- 42 m
250 mm Perforated Screen- 30m
200 mm MS Casing Pipe- 12 m
200 mm Perforated Screen – 18 m
Total length – 102 m
Note: +0.5 m above the ground level.
The well development by air compressor and pump test work was done after installation of Tube well. Compressor was used during drilling lme and Development of tube well by pump has been carried out immediately after installation of the pipe assembly. The well development has broad objectives:
• To repair damage done to the formation (aquifer) by the drilling operation so that the natural hydraulic properties are restored
• To alter the basic physical characteristics of the aquifer near the borehole so that the water will flow more freely to the well.
Pumping Test
After the water we ll was developed, pumping test of the well shall be conducted to determine the performance characteristics of a well and hydraulic parameters of the aquifer. From the pumping test data, the principle factors of aquifer performance like Transmissivity and storage coefficient can be calculated. Measurements taken in this pump test were:
• Static Water Level just before the start of pump test
• time since pump started
• pumping rate
• pumping or dynamic water level at various interval during the pumping period
• time of any changes in discharge
• time at which pumping stopped
• water level after the pumping is stopped (recovery) at various interval
The pumping test was carried out by Constant-Rate Test. From the constant rate we obtain value of Transmissivity using semi-log graph (time-drawdown graphs) and Cooper-Jacob method.
Continuous Pumping Test
The continuous test was conducted by using submersible pump. In this test, the well was pumped at constant rate for 15 hrs. The pumping test data and measurement taken during the pumping test are shown in Annex A. The static water level was 3.2 m. The dynamic water level after 15 hr. was 45.0 m at 8 lit/sec discharges. And the Transmissivity is:
Transmissivity (T) = 2.44*10-3 m2/sec Hydraulic Conductivity (K) = 3.05*10-5 m/sec
3.2 Recovery Test
After 15 hrs. of pump operation, constant rate pumping test was stopped. Recovery test was conducted immediately after pump had stopped. It took 2 hrs. 45 minutes to recover water level to initial level.
conclusion
The well was drilled up to the depth 102 meters below the ground surface. The perforated screen pipes were installed on the basis of aquifer presence of the well. Perforated screen of 3.2 mm screen opening size were used in well. Well was developed by air compressor for 4 hrs and 15 HP submersible pumps was installed in tube well. The discharge of tube well was satisfactory having discharge not less than 8 l/s. A tube well’s performance was satisfactory and was successful.