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Re:[gwmodel] Minimum permissible distance between bore holes in hard rock aquifers

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  • asokg@tce.co.in
    Dear Subrata, Thank you for clarifying Hard Rock aquifer system so clearly. Do you have the details of reference UNESCO 1972. Was ir developed through
    Message 1 of 10 , Nov 11, 2012
      Dear Subrata,

      Thank you for clarifying Hard Rock aquifer system so clearly. Do you
      have the details of reference UNESCO 1972. Was ir developed through
      observation or through some theoretical analysis?. If the original paper
      is available in soft I will like to have a copy of the same.Most of the
      equations in Step 1 are developed for Homogeneous isotropic aquifer. For
      double porosity I will like to know for what value(range) of porosity
      these equations are valid and what is the range of Reynold number for
      these porosity values. Huntleys equation is an Empirical Equation based
      on observation from field data. However, Huntley takes care of the
      turbulent flow part by introducing Specific Capacity ( S = AQ + BQ^n).
      Again in Step 3 we are using an Equation which is developed for Laminar
      Flow. Dr. Singhal has written a book of Hydrogeology of Fractured Rocks .
      I have not seen that book. I am sure you have gone through the book. I
      will like to know whether Dr. Singhal has included study of Anisotropic
      Aquifer Heterogeneous Aquifer with partial laminar flow and partial
      turbulent flow .



      subrata halder <shalder_2007@...>
      11/11/2012 11:56 PM

      To
      gwmodel@yahoogroups.com
      Subject
      Re: Fw: RE: [gwmodel] Minimum permissible distance between bore holes in
      hard rock aquifers

      Dear Mr. Veranis,

      Radius of Influence (R) in fissured Granite/gneisses rocks (UNESCO, 1972):

      1000-1500 m (in confined aquifer)
      500-1000 m (in unconfined aquifer)

      Therefore, safe spacing of bore holes in interconnected fissured
      Granite/gneisses rocks may be maintained as follows-

      Safe Spacing (Ss) >= 2 x R >= 2000-3000 m (in confined aquifer)
      >= 1000-2000 m (in
      unconfined aquifer)

      If u want to calculate safe spacing precisely u have to do pumping test in
      bore hole intercepted interconnected fissured Granite/gneisses rocks
      aquifer and then

      Step 1
      1) For unconfined aquifer match Field Data Curve with Boulton's type
      curves
      2)For leaky aquifer match Field Data Curve with Hantush type curve
      3) For double porosity leaky confined aquifer (involved delayed yield from
      block to fissures)) match Field Data Curve with Streltsova-Adams Type
      curve.
      4) For double porosity matrix confined aquifer (involved delayed yield
      from block to fissures)) match Field Data Curve with Bourdet-Gringarten's
      Type curve.
      Find out Transmissivity (T) value.

      Step 2
      Put T, Q, Sw values in Huntley's Equation (for fissured rocks) and
      find coefficient 'A' :
      T=A(Q/Sw)1.18
      T- Transmissivity (m2/day)
      Q- Discharge (m3/day)
      Sw- Drawdown (m)
      A- Coefficient = (2.3*log R/rw)/2π
      Step3
      Find rad of Influence 'R' from
      A = (2.3*log R/rw)/2π
      rw - radious of bore hole
      Step 4
      Calculate Safe Spacing (Ss) >= 2 x R

      Thanks

      Subrata Halder
      Executive Engineer (Agri-Irrigation)
      State Water Investigation Directorate
      Department of Water Resources Investigation & Development
      Govt. of West Bengal
    • subrata halder
      To Dr. A.K. Ghosh Dear Sir, 1) Dr. BBS Singhal has used the ref of UNESCO 1972 for rad of Influence in fissured rocks.  2) In double porosity model, best
      Message 2 of 10 , Nov 12, 2012
        To Dr. A.K. Ghosh

        Dear Sir,

        1) Dr. BBS Singhal has used the ref of UNESCO 1972 for rad of Influence in fissured rocks. 
        2) In double porosity model, best match with type curve has been achieved with porosity=10 %. Double porosity model is more representative of uniformly fractured aquifer. 
        3) Equations in connection with pumping Test are developed based on the assumptions of homogeneous & isotropic aquifers with laminar flow during pumping...well is 100% efficient and effective diameter is the same as the diameter of the well. But in reality aquifers are heterogeneous, anisotropic with non-laminar flow during pumping...pumping well is not 100% efficient and effective dia is usually more than dia. of screen mainly, in case of unconsolidated sediments. Considering the above reality, pumping well & observation wells are installed into closely spaced & inter-connected fractures and also, nested observation wells at different depth horizon in different direction are installed to get reading of water level at different depth & in different direction and an av. T value is computed. With a view to get  as much as radial,horizontal & laminar flow pattern, pumping well should be put in lower  1/2 or 1/3 rd of aquifer thickness and Observation
        wells should be located at dist. 1.5 times the saturated thickness of interconnected fractured aquifer. Considering the above reality, Huntley used the Specific Capacity(Q/Sw) as (Q/Sw)1.18and he modifed Thiem's Eq for fractured aquifer as T=A(Q/Sw)1.18   using the coefficient A=(2.3*log R/rw)/2π  (as in Thiem's Eq.) Thus Huntley's Eq holds good for  i) small dia 100% efficient pumping well and ii) nested observation wells in different & different direction installed in closely spaced interconnected fracture zone.  Therefore, I think earlier steps may be quite O.K. for finding out Rad of Influence (R).  
        4) Dr. BBS Singhal has not included the study of Anisotropic Aquifer Heterogeneous Aquifer with partial laminar flow and partial turbulent flow in his book. 
        Thanks
        Regards
        Subrata HalderExecutive Engineer (Agri-Irrigation)
        State Water Investigation Directorate
        Department of Water Resources Investigation & Development
        Govt. of West Bengal



        --- On Mon, 12/11/12, asokg@... <asokg@...> wrote:

        From: asokg@... <asokg@...>
        Subject: Re:[gwmodel] Minimum permissible distance between bore holes in hard rock aquifers
        To: "subrata halder" <shalder_2007@...>
        Date: Monday, 12 November, 2012, 9:54 AM

        Dear Subrata,


        Thank you for clarifying Hard Rock aquifer system so clearly. Do you

        have the details of reference UNESCO 1972. Was ir developed through

        observation or through some theoretical analysis?. If the original paper

        is available in soft I will like to have a copy of the same.Most of the

        equations in Step 1 are developed for Homogeneous isotropic aquifer. For

        double porosity I will like to know for what value(range) of porosity

        these equations are valid and what is the range of Reynold number for

        these porosity values. Huntleys equation is an Empirical Equation based

        on observation from field data. However, Huntley takes care of the

        turbulent flow part by introducing Specific Capacity ( S = AQ + BQ^n).

        Again in Step 3 we are using an Equation which is developed for Laminar

        Flow. Dr. Singhal has written a book of Hydrogeology of Fractured Rocks .

        I have not seen that book. I am sure you have gone through the book. I

        will like to know whether Dr. Singhal has included study of Anisotropic

        Aquifer Heterogeneous Aquifer with partial laminar flow and partial

        turbulent flow .
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