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

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  • subrata halder
    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
    Message 1 of 10 , Nov 11, 2012
      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 11) 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 2Put �T, Q, �Sw�values in Huntley's Equation (for fissured rocks) andfind 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)/2πStep3�Find rad of Influence 'R' from�� � � � � � � � � A = (2.3*log R/rw)/2π� � � � � � � � � � � � � � � � � � � � � � � � � � � �
      � � � � � � � � � � � � � � � � rw - radious of bore holeStep 4Calculate 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
    • 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 2 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 3 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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