Borewell - Performance monitoring

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Borewell - Performance monitoring

The Community Engineer
Administrator
There have been many questions raised in many forums regarding borewell performance, monitoring and maintenance/rehabilitation.

This post shall be dedicated to discussions on these aspects. Here I have discussed the performance aspect of borewells.
                                       
Monitoring Boreholes
                                       
        Processes Affecting Performance
        1 Physical Process
                        Clogging
                                drilling fluid invasion damage at the time of construction
                                inter-mixing of aquifer horizons as a result of wash-out and caving during drilling and development
                                inter-mixing of aquifer and gravel pack material due to poor installation procedure or overaggressive development
                                migration of fines from the formation into the gravel pack material due to high flows during operation
                                migration of aquifer material and infilling of the borehole and pumping system
                                       
                        Abrasion
                                high velocity particle laden water
        2 Chemical Process
                        Clogging
                                chemical precipitation
                                        iron oxyhydroxide
                                        iron sulphide
                                        calcium carbonate
                        Electro-chemical corrosion
                                coupling of dissimilar metals
                                impurities in the composition of metals
                                degree of surface protection
                                exposure to different conditions
                                differrence in metal treatment
        3 Microbial Process
                        Clogging
                                biofouling
                        Microbially induced corrosion
                                sulphate reducing bacteria
        4 Operational Factors
                        Inappropriate operating schedules
                                intermittent pumping
                                high pumping rate
                        Aquifer over abstraction
        5 Structural and Mechanical Factors
                        Poor design and construction
                                flow velocity
                                poor installation of screen and casing
                                inappropriate use and placement of grouting materials
                                poor selection and installation of gravel pack
                                poor drilling technique
                        Inappropriate selection of borehole component materials
                                use of mild steel materials
                                        corrosion
                                                sand pumping due to enlarged screen
                                                pump failure due to corrosion
                                                clogging by increased iron concentration and hence iron fouling
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Re: Borewell - Performance monitoring

The Community Engineer
Administrator
Water quality parameters and indicators



pH
  corrosion and iron incrustation potential
  calcium carbonate incrustation
  treatment requirement
       
Eh  
  corrosion and iron incrustation potential (used in conjunction with pH)
       
Temperature  
  corrosion

Conductivity
  aquifer contamination
      - saline intrusion
      - waste leachate
  corrosion
       
Alkalinity  
  calcium carbonate incrustation
  corrosion resistance (in conjunction with chloride)
       
Chloride
  corrosion
  aquifer contamination and potability
       
Hydrogen Sulphide  
  corrosion
  treatment requirement
  iron sulphide formation"
       
Carbon dioxide
  corrosion
  calcium carbonate incrustation
  treatment requirement
  microbial activity

Suspended solids
  fines pumping
  biofouling
  treatment requirement
       
Turbidity and colour
  iron and manganese content
  dissolved carbon dioxide
  clay/colloidal matter in suspension
       
Iron and manganese
  corrosion
   incrustation and biofouling
  treatment requirement

Dissolved oxygen
  iron incrustation and biofouling
  corrosion

Sulphate  biocorrosion
       
Nitrate
  aquifer contamination
  treatment requirement
       
Total organic carbon  
  microbial activity (see nutrients)

Bacteria
  biofouling (eg Gallionella)
  biocorrosion (eg Desulphovibrians)
  contamination (eg.Pseudomonas)
  treatment requirement (total coliforms, E coli)
       
Nutrients
  microbial activity
  contamination
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Borewell Diagnosing and Maintenance/Rehabilitation

The Community Engineer
Administrator
Borewell Diagnosing has been methodically arranged in this spreadsheet. It also lists maintenance actions and methods.Borehole.xls
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Hydraulic design for a borewell

The Community Engineer
Administrator
Hydraulic design is very important for sustainable borewell performance. It decides the screen enterance velocity and the vertical velocity inside the borewell. Commonly recommended value for enterance velocity is 0.03 m/s.

The velocity can be calculated using the following formula.

Ve =Q/(pi)DLpb

Ve - Enterance velocity
Q -  Discharge in m/s
D - Diameter of screen in m.
L - Net length of screen in m.
p - Proportion of open area in screen
b - blocking factor (take a value of 0.5)

It is recommended to take a design value of 0.02 m/s for borewells with problems of incrustation and biofouling. In fissured aquifers the velocity need to be calculated emperically. (compare with existing borewells in same formation; carry out a trial and error to reduce sand ingress)

Reducing enterance velocity / design discharge have many benefits.

  Sand ingress is reduced
  Erosion of screen slots are reduced
  Supply of nutrients are reduced
  Loss of kinetic energy is reduced

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Re: Borewell Diagnosing and Maintenance/Rehabilitation

Ajin P Tomy
In reply to this post by The Community Engineer
Hello,  I'd like to seek your guidance on th geological aspects on the design of Borewell on an artificial island. For de watering an area for construction, I'd like to use borewell pumps adjacent to the said site which has a water column height of 9.5 m from the bottom and short of 2. 5 meters from above (the ground level). The area is 4 m in length and 6 meter in breadth. The total volume of water at any point of time is presumably 228 m3 (4x6x9.5). I was thinking of putting 4 borewell pumps of 6 "casing size with 29 m3/hr and suitable head, around the periphery of the site. I'd appreciate your guidance on any precaution to be taken for the job.

Thanks and Regards,
Ajin