Well Field Sizes for Municipalities

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A beginner question: how many wells does a typical municipality have based on their size (PE equivalent, and if the given water source is groundwater)?

Is there any statistics on this that the network can point me to? Any input would be of help!

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5 Answers

  1. This number of it depend on the size of population served and the legislation of the country where you are staying. In South Africa the person allowed for 25litre of water per day. If community is 700 population meaning we multiple the number of population with litre served per day.  Then it will gives you the correct number of wells required as per pumping rate according to population served.

  2. In Poland, it depends on a water permit issued by a public office.   

    The same principle as it writes by Kevin Linton

  3. Dear Mr. Jensen,

    As previous comments have already mentioned: it is depending on the hydro- and geographical situation.

    But let me go a bit more in detail, because I think your question is based on a special reason: 

    in fact, water supply for municipalities is depending and based on the clients demand, the request with min. standards (i.ex. UN, WHO, etc.) and there are always more water wells to be built then exactly calculated, mostly for back-up reasons (increasing population, environmentally or industrial increasements)impacts . Less important, unfortunately,  are "maintenance" reasons, which are depending on the water quantity (drw down), its quality (Fe, Mn Ca etc.) and therefor depending rising costs after certain calculable periods of production. Water production wells are having a clear defined usage cycle and it's not solved only by particular from time-to-time "flushing" the wells with compressed air, which is still  wrongly accepted by the general civil engineering's public ! 

    Another thing in Mauritania is, for example, the location of the aquifer, the water supply field of Noukachott is 80km (ca. 150 boreholes, 30% in production, 70% abandoned) in the East in te desert, away from any kind of population and those wells need to be more observed than others, due to the long transport pipeline...in Segou, Mali, the river infiltration water wells, everywhere along the Niger river are not in a remote region and can be observed in a day-to-day period. In general, water wells for municipal water supply are drilled with a 6" - 9.5/8" pilot hole (depending on the geolog. formation), accompaigned by an accurate drilling report (sampling each meter, which can easily replace time/cost-intensive borehole logging procedures !!) and than followed with "opening" drilling by a larger diameter (i.genreal 12.1/4" -17.1/2"). It  will end, wether in a monolothic well-design (today very common and safe) or with a separate "pump-chamber" (max.12.1/4" casing), where the submersible pump will be later, after the completion, being  installed. The separate "pump-chamber" construction is in some regions (i.ex. Africa) extremely difficult (annular space, verticality, cementing, L/R connection and many others) and a lot of drilling companies are facing serious problems (more detailed after request, I've had a couple of short time contracts, where I was urgently called for project start-up after failing drilling, keeping the borehole open, installation of casings, accurate cementing job etc. ) 

    Other common options of well completion are the direct casing liner, where the sizes of filter screen pipes (PVC or Stainless steel) are having the same sizes than the plein casing, till the ground level.

    The annular space, a part from the filter-screen section, (min. 10m "over-filling"), is mandatory to be "re-filled" in respect to the penetrated formations and layers, like clay, silt and other impermeable rock strucutres. Special products, like extra drougth clay pellets; cement & bentonite mixture; just cement/water, are having proven their satisfying reactions,

    but ATTENTION:    commonly and again and again copy/pasted techical descriptions in the tender documents are talking about "backfilling" with "drilling material" or "cuttings" are absoltely wrong and not acceptable, especially if it is planned to prevent hydrological shortcuts in the borehole's annular space between different aquifers. Serious damages and chemical contaminations of the production-aquifer from the surface water and other foramtions are the result and thoses are difficult to repair. Not impossible, but varying from case to case.              

    The downhole equipment is in common built from the bottom to top:

    1. sump (decantation) pipe:  
      1. length (1,0 - 6,0 m)
      2. Material: PVC; Stainless steel, GFK, PE (rare and only chemical resistance)
      3. sizes from 3" - 8"
        1. 3" is moreless for production wells up to 20m3/hr
        2. 4"; 4.1/2" 5" & 6" are very common sizes
        3. 8" is also very common, but extremely useless
    2. filter screens:  ​​​​​​​
      1. section length (6,0m - 60,0 m)
      2. Material is PVC, Stainless Steel, coated steel, wire-meshes and others. PE is, except for  chemical resistance material not suitable.  
      3. sizes are from 3" - 10"
        1. 3" is moreless for production wells up to 20m3/hr
          1. wire wrapped screens, normally made of  stainless steel, today also in PVC available, are having large water influx  capcities   
        2. 6" is very common and reasonable, especially for production rates to 150m3/hr
        3. 8"  for higher pumping rates​​​​​
          1.  ​​​
    3. Risers & pump chamber:  ​​​​​​​
      1. length (10 - 6,0 m)
      2. sizes from 3" - 18"
        1. 3" is moreless for production wells up to 10 m3/hr
        2. "; 4.1/2" 5" & 6" are very common sizes for submersible pumps (4" and 6")
        3. 8" is very vcommon, but extremely useless for 4" pumps!
        4. 10" is good for 8" subm. pumps
        5. 12" is good for 10" subm. pumps 
        6. 13.3/8" - 18" are also a common parts in the TOR's, suitable till 12" subm. pumps, but all sizes above 14.3/4" are, a part from being extremely expensive, difficult handling, corrosion issues and also a handicap for subm. pump motor cooling,      

    It is important to take into consideration, that the well-head, where the subm. pump's riser pipe is being connected to, shouldn't be connected directly with the pump-chamber's casing. This means i other words, that the "well-head" for exaple a 6" subm. pump with 3" riser pipes, hanged in a 8" pump-chamber casing, should be manufacured on a 10.3/4" bottom (with flange on top) and "slipped-over", centralized of course, the well's casing size.

    Questions?

    Do not hesitate to conatct me at any time.


    Kind regards

    Ulf Mischke
    Sr. Consultant Water Well Engineering
    Sr. Water Source Expert (Gov. nom.)   

    WEWACO
    Well and Water Consultants
    Germany

    Mobile:    +49 152 1470 6394

    ulf.mischke@wewaco.com
    www.wewaco.com

     

  4. Ninety to 95% of this question and therefore the answer is dependant upon, 'the capacity  of the groundwater to 'yield' in the form of 'production' and the aquifers capacity to 'recover'.  These are key characteristics of a production aquifer and you will need a qualified hydrogeologist to test these for you.  Please note that pump tests and recoveries, cannot be undertaken with first drilling the bore field.  I am Lippy.  Hear me roar.