MRD Drilled Well Technical Specifications and Drawings
Ministry of Rural Development
Drilled Well
Technical Specifications and Drawings
Grade II/III
(English Version)
Department of Rural Water Supply
Supported by UNICEF
Revised in December 2008
Table of Contents
A. Technical Requirements ......
1. Well Drilling Methods ......
2. Geological Conditions ......
3. Water Supply for Rotary Drilling ......
4. Requirements for Drilling Equipment and Workmanship
5. Requirements for Mobilization, Transport and Well Site Preparation ......
6. Well Site Environmental Impact and Protection ......
7. Well Site Access Guidelines ......
8. Sampling during Drilling ......
9. Final Depth and Borehole Diameter Requirements ......
10. Casing and Well Screen Requirements ......
11. Gravel Pack and Cement Grout Requirements ......
12. Inert Back-fill and Sanitary Seal Requirements ......
13. Well Development Procedures ......
14. Water Level Measurement & Minimum Water Yield Requirements .....
15. Water Quality Testing Requirements ......
16. Dry Hole/Unsuccessful Well Procedures ......
B. Supervision Requirements
- Technical Monitoring and Supervision Guidelines ......
- Extended Down-time ......
- Acceptance of Work ......
- Rejection of Work ......
- Secondary Work ......
- National Drilling Log Sheet & Well Identification Requirements ......
Technical Requirements
- Well Drilling Methods & Drilling Contractor Capacity Requirements
The Contractor will employ drilling methods which do not endanger the permeability of the aquifer, such as compressor driven Down The Hole (DTH) hammer or rotary systems with air, foam or clear water being preferable as a cooling, circulation and hole stabilizing medium. When applying rotary mud-flush drilling, the Contractor shall use a self destructive polymer drilling mud which has been approved by the PDRD supervisor. The use of bentonite drilling fluid is strictly forbidden.
- Geological Conditions
The MRD or the respective PDRD will make available to the drilling teams, all national drilling log sheet records for the commune/village where the Watsan activity is planned for implementation. If drilling log sheets are not available for a particular area, then a simple assessment would need to be provided by the PDRD and/or commune/village authorities based on existing water facilities in the village;
The contractor must be prepared to drill in any kind of geological setting, even if different from the one assessed by the PDRD or from national drilling log sheet records.
- Water Supply for Rotary Drilling
The Contractor will be responsible for the job site water supply requirements at their own expense. Clean water must be used for drilling, development and/or washing the wells. Clean and clear water must be checked and agreed upon by the PDRD supervisor prior to use by the Contractor in order to avoid the introduction of organic or inorganic contaminants into the borehole and water producing zone. Some treatment of the job site water supply may be required following inspection by the PDRD supervisor before use is approved. The Contractor will be responsible for examining the local conditions to identify appropriate local water supply sources and acceptable possibilities.
- Requirements for Drilling Equipment and Workmanship
All drilling machines, equipment, accessories, instruments and material supplies required for drilling, developing, installing, pumping and testing, and all other necessary operations shall be provided by the Contractor well in advance in order to avoid delays. The PDRD supervisor shall have the right to order the removal or replacement of any equipment or material that they feel is insufficient or unsatisfactory. Any equipment or material replacement requirements shall be done so at the expense of the Contractor.
The number of drilling rigs and equipment to be operated for implementation of the contract will be decided by the Contractor according to the required rate of progress and the drilling rate per rig that the Contractor anticipates. Prior to the mobilization and transport of the drilling rigs and equipment to the work site, the Contractor shall inform the PDRD supervisor of the number and type of drilling rigs and equipment that the Contractor intends to set-up in the field. The Contractor must get approval from the PDRD supervisor concerning the number and type of drilling rigs and equipment to be used. The Contractor will be responsible for providing adequate drilling rigs and equipment that should enable the Contractor to drill in both hard and soft (geologic) formations.
The Contractor is expected to carry out all works as specified in the contract and as instructed by the PDRD supervisor in a thorough and workman-like manner and in accordance with current professional standards. The Contractor will carry out all operations with due efficiency and dispatch in accordance with the terms of the contract and to the satisfaction of the PDRD supervisor. For this purpose, the Contractor will use suitable machinery and gear, and supply a sufficient number of experienced staff. The Contractor shall follow all required safety regulations and the country’s labour law to protect the workers at the job site.
- Requirements for Mobilization, Transport and Well Site Preparation
This would include all preparations and making available drilling machines, accessories, equipment and their transport to the area of work including the transportation of each drilling machine and accessories to the first drilling site, and after completion of the work from the last drilling site. The transportation under this clause comprises the transportation of all equipment and machinery for drilling, development, test pumping, water supply camp, job site workshop, vehicles, spare parts and materials necessary for the performance of the work and the travelling cost for drilling staff to and from the boreholes.
Included in well site preparation is the erection of drilling machinery and equipment at the drilling site and all ready to work installation requirements so that drilling, sampling, development, test pumping and all other operations may proceed without interruption or delay. Dismantling would include removal of all machinery, equipment, stores and other material and cleaning and restoration of the site.
- Well Site Environmental Impact and Protection
Care must be taken in the handling and storage of all drilling fluids, oils, greases and fuel at the job site in order to avoid any environmental degradation. The Contractor shall dispose of any toxic materials, drilling fluid, additives, drill cuttings and discharged water in a manner approved by the PDRD supervisor in order to limit damage to public and private property. On the completion of each borehole the site must be left clean and free from all debris, hydrocarbons and waste, and all circulation pits filled to the satisfaction of the PDRD supervisor. A site not delivered clean may result in the delay of payment until that time the Contractor re-cleans the site to the satisfaction of the PDRD supervisor.
The Contractor shall drill all boreholes at exactly the sites prescribed as indicated by the PDRD supervisor and the PDRD staff responsible for site selection. Payment shall not be made for any boreholes installed at non-prescribed locations. An improperly located borehole may be subject to abandonment procedures at the expense of the Contractor in the event the landowner requires this course of action.
- Well Site Access Requirements
Tracks required for access by the drilling machinery, equipment and accessories to the drill site shall be made by the Contractor and shall, as little as possible, interfere with existing fences and cultivated land. The cost of track installation shall be at the expense of the Contractor and would be reflected in the rate for overall drilling cost for the contracted works.
Upon completion of drilling and well installation activities, it may be necessary for the Contractor to restore the land back to its original state depending on the wishes of the land owner. The Contractor shall be responsible for discussing well site access issues with the Commune Council, Village Chief, WSUG and/or land owners prior to mobilization and transport.
- Sampling Requirements during Drilling
The Contractor shall be responsible for taking representative and continuous samples of the strata penetrated for each colour or texture change or at 2-3 meter intervals by whatever sampling method that is standard for the drilling technique in use and approved by the PDRD supervisor.
The Contractor shall take every possible precaution to guard against sample contamination. Collected samples must not be washed. The samples shall be stored in open sample box tray with depth indication and displayed near the drilling rig. The samples shall be disposed of after completion of the borehole and after recording in the national Well Log Sheet under the supervision of PDRD staff.
- Final Depth and Borehole Diameter Requirements
The expected average borehole depth will be provided for each well type (drilled and combined wells) and for each respective province. The expected average borehole depth shall be used by the Contractor for planning purposes and shall not be considered a contract specification. To be declared positive, a minimum yield of 1.0 m3/hour must be obtained. For positive boreholes, the final depth should be 10 meters below the water inflow. For negative (dry hole or unsuccessful) boreholes, the final depth shall be determined by the PDRD supervisor. The depth of the borehole shall be determined from the ground surface to the bottom of the borehole.
The borehole diameter requirements shall be as follows:
· 180 mm for drilled well in sediment
- Casing and Well Screen Requirements
Permanent casing and well screen shall only be installed upon instruction and approval from the PDRD supervisor. The permanent casing shall be of rigid PVC. The casing shall be 49 mm inside diameter and shall have a resistance to pressure of 8.5 bars for all drilled wells. The PDRD supervisor shall certify the quality of the PVC.
The PVC casing and well screen shall be joined by threads and the joints shall be watertight. Well screen shall be of rigid PVC with a horizontal slot size of between 0.3 to 1.0 mm with a minimum of six (6) slots on the circumference. Well screen shall have a minimum inside diameter of 49 mm for all drilled wells. Sections of well screen will be provided in maximum 2 meter length and joined by watertight connections. The expected average length of well screen per borehole is 4 meters. The final depth at which the screen will be installed shall be determined on the basis of the nature and thickness of the water bearing strata. The top of the screen shall be a minimum of 1.5 meters below the lowest expected dynamic water level and 1.0 meter above the water inflow. A two (2) meter sand collector pipe/casing footer shall be installed below the screened interval at the bottom of the borehole and fitted with a PVC or rubber plug.
- Gravel Pack and Cement Grout Requirements
The gravel pack material shall consist of well rounded, clean quartz gravel that is strong when wet or dry. Less than 10% shall be smaller than 2 mm diameter, less than 10% shall be larger than 4 mm diameter. When the gravel pack material is washed, the washing water must be clear after washing. The gravel pack material must not contain any organic material.
The gravel pack material shall be placed around the well screen carefully to avoid bridging or separation of the different grain sizes. The gravel pack shall rise a minimum of 5 meters above the top of the well screen. Gravel pack installation shall be carried out in a continuous feed operation. The Contractor shall make every effort to obtain a well-settled uniform gravel pack around the well screen.
When drilling in hard rock formation, PVC casing is needed to be installed to the bottom of the borehole. The final three (3) meters at the top of the borehole shall also be filled with cement grout.
In case of the many drilled boreholes have limited water yield in the area, the installation of PVC casing in hard rock formation may not be required, however, it needs to be discussed with and approved by PDRD and UNICEF.
- Inert Back-fill and Sanitary Seal Requirements
When drilling in sediment or soft rock formations, the annular space between the casing and the borehole wall 5 meters above the gravel pack shall be filled with clay pellets. After that it shall be filled with inert material (sand, gravel or drill cuttings) from the clay seal above the well screen to within three (3) meters from the surface. Surface soil shall not be used for backfilling. The final three (3) meters at the top of the borehole shall also be filled with cement grout.
- Well Development Procedures
The Contractor shall be responsible for the development and cleaning of the borehole upon completion of drilling and well installation and prior to taking water level measurements. The development process will remove native fine grained sediment, clays and drilling fluid residues deposited on the borehole wall and adjacent portions of the aquifer during drilling operations. If organic drilling fluids are used, they shall be broken down chemically according to the manufacturer’s recommendations either before or after well development. Borehole development and cleaning shall be carried out by the Contractor using compressor airlift, surging, backwashing or jetting methods as agreed by the UNICEF supervisor. The development methods proposed by the Contractor shall be submitted to the PDRD supervisor for approval.
Well development procedures should continue for a minimum of at least 4 hours. Well development shall be considered completed when the discharged water meets the following requirement: the sand content shall be based on the average of a 20 litre sample collected at the end of the development procedures. The sample will be allowed to settle not less than 5 minutes before the water is decanted after creating a whirlpool with the hand. The average volume of sand sized grains in the samples shall not exceed a spot of 5 mm diameter in the middle of the bucket.
Following well development and prior to hand pump installation and platform construction, the Contractor shall be responsible for any objectionable materials that may fall into the borehole and any effect it may have on water quality or quantity until completion of the works and acceptance of the borehole by the PDRD supervisor. In the event that a positive borehole is left unattended it must be capped with a lockable cap.
- Water Level Measurement & Minimum Water Yield Requirements
The Contractor will be responsible for making yield estimates during drilling operations every time a water bearing zone is encountered using a yield estimation technique that is approved by the PDRD supervisor. Following installation and development of the well, the contractor will measure the following parameters: