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use of image wells to analytically model groundwater divides

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  • Mark Eisner
    I am seeking professional or scholarly citations (textbooks, USGS references, etc.) providing guidelines for handling groundwater divides in an analytical
    Message 1 of 8 , Mar 1, 2007
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      I am seeking professional or scholarly citations (textbooks, USGS references, etc.) providing guidelines for handling groundwater divides in an analytical groundwater flow model (yes, I know this is yesteryear).

      Consider the circumstance of two interfering municipal production wells separated by (say) five miles in a highly transmissive, confined aquifer. The Theis assumptions are reasonably met other than with respect to a pumping-induced groundwater divide that exists between the two users. One well pumps four times the rate of the other. The aforementioned groundwater divide now exists between the two. The larger use remains fixed, but the other withdrawal will increase if a permit is issued.

      The regulatory agency requires an evaluation of the increased drawdown associated specifically with the projected increase of the smaller well. The projected increase will bring the use of the smaller well from 20% to 25% of the total combined. I have contended that in such a scenario, (1) the location of the groundwater divide will remain essentially unchanged; (2) one cannot reasonably expect the smaller withdrawal to capture groundwater from the far side of the divide; (3) that modeling the divide as an essentially impermeable boundary (with an image well) is reasonable and appropriate to evaluate the additional drawdown arising from the increase if such an evaluation is restricted to the vicinity of the smaller well.

      I have been challenged (in court, sadly, yes) in the use of an image well and thus, for the underlying assumption that the groundwater divide essentially acts as a no-flow boundary. I seek scholarly or governmental citation(s) supporting (or I suppose, refuting) what to be seemed (1) reasonable and (2) the only way analytically I know to segregate the effect of the 5% withdrawal increase from the 800 lb gorilla in my hydrogeologic closet with me (the larger user). Remember, numerical modeling is judged overkill by the agency for permitting evaluations of this nature.

      Thoughts? Comments? Am I off the wacko deep end of indefensibility? Thanks.
    • Richard B. Winston
      You should check out Analytic Element Modeling of Groundwater Flow by H. M. Haitjema and an earlier book by Strack. You should find plenty of support for the
      Message 2 of 8 , Mar 2, 2007
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        You should check out Analytic Element Modeling of Groundwater Flow by
        H. M. Haitjema and an earlier book by Strack. You should find plenty of
        support for the use of analytic methods in them although they may go
        further with them than you want to go.

        Mark Eisner wrote:
        >
        > I am seeking professional or scholarly citations (textbooks, USGS
        > references, etc.) providing guidelines for handling groundwater
        > divides in an analytical groundwater flow model (yes, I know this is
        > yesteryear).
        >
        > Consider the circumstance of two interfering municipal production
        > wells separated by (say) five miles in a highly transmissive, confined
        > aquifer. The Theis assumptions are reasonably met other than with
        > respect to a pumping-induced groundwater divide that exists between
        > the two users. One well pumps four times the rate of the other. The
        > aforementioned groundwater divide now exists between the two. The
        > larger use remains fixed, but the other withdrawal will increase if a
        > permit is issued.
        >
        > The regulatory agency requires an evaluation of the increased drawdown
        > associated specifically with the projected increase of the smaller
        > well. The projected increase will bring the use of the smaller well
        > from 20% to 25% of the total combined. I have contended that in such a
        > scenario, (1) the location of the groundwater divide will remain
        > essentially unchanged; (2) one cannot reasonably expect the smaller
        > withdrawal to capture groundwater from the far side of the divide; (3)
        > that modeling the divide as an essentially impermeable boundary (with
        > an image well) is reasonable and appropriate to evaluate the
        > additional drawdown arising from the increase if such an evaluation is
        > restricted to the vicinity of the smaller well.
        >
        > I have been challenged (in court, sadly, yes) in the use of an image
        > well and thus, for the underlying assumption that the groundwater
        > divide essentially acts as a no-flow boundary. I seek scholarly or
        > governmental citation(s) supporting (or I suppose, refuting) what to
        > be seemed (1) reasonable and (2) the only way analytically I know to
        > segregate the effect of the 5% withdrawal increase from the 800 lb
        > gorilla in my hydrogeologic closet with me (the larger user).
        > Remember, numerical modeling is judged overkill by the agency for
        > permitting evaluations of this nature.
        >
        > Thoughts? Comments? Am I off the wacko deep end of indefensibility?
        > Thanks.
        >
        >
        > Messages in this topic
        > <http://groups.yahoo.com/group/gwmodel/message/2459;_ylc=X3oDMTM0MTdwa2loBF9TAzk3MzU5NzE0BGdycElkAzM5NjEzOTYEZ3Jwc3BJZAMxNzA1MDgzMjM1BG1zZ0lkAzI0NTkEc2VjA2Z0cgRzbGsDdnRwYwRzdGltZQMxMTcyODA2NjU4BHRwY0lkAzI0NTk->
        > (1)
        > <http://groups.yahoo.com/group/gwmodel/post;_ylc=X3oDMTJwZ3RubnZwBF9TAzk3MzU5NzE0BGdycElkAzM5NjEzOTYEZ3Jwc3BJZAMxNzA1MDgzMjM1BG1zZ0lkAzI0NTkEc2VjA2Z0cgRzbGsDcnBseQRzdGltZQMxMTcyODA2NjU4?act=reply&messageNum=2459>
      • Wilsnack, Mark
        Dear Sir: No, you are not off base. The use of image wells may be legitimate. Have a look at Strack (1989) and Haitjema (1995) to see how this approach is
        Message 3 of 8 , Mar 2, 2007
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          Dear Sir:

          No, you are not off base. The use of image wells may be legitimate. Have
          a look at Strack (1989) and Haitjema (1995) to see how this approach is
          used. Also, I once saw the legendary Jay Lehr demonstrate its use in a
          training session about 15 years ago.

          Best Wishes,

          Mark
          SFWMD
          ========================================================================
          =

          -----Original Message-----
          From: gwmodel@yahoogroups.com [mailto:gwmodel@yahoogroups.com] On Behalf
          Of Mark Eisner
          Sent: Thursday, March 01, 2007 10:21 AM
          To: gwmodel@yahoogroups.com
          Subject: [gwmodel] use of image wells to analytically model groundwater
          divides

          I am seeking professional or scholarly citations (textbooks, USGS
          references, etc.) providing guidelines for handling groundwater divides
          in an analytical groundwater flow model (yes, I know this is
          yesteryear).

          Consider the circumstance of two interfering municipal production wells
          separated by (say) five miles in a highly transmissive, confined
          aquifer. The Theis assumptions are reasonably met other than with
          respect to a pumping-induced groundwater divide that exists between the
          two users. One well pumps four times the rate of the other. The
          aforementioned groundwater divide now exists between the two. The larger
          use remains fixed, but the other withdrawal will increase if a permit is
          issued.

          The regulatory agency requires an evaluation of the increased drawdown
          associated specifically with the projected increase of the smaller well.
          The projected increase will bring the use of the smaller well from 20%
          to 25% of the total combined. I have contended that in such a scenario,
          (1) the location of the groundwater divide will remain essentially
          unchanged; (2) one cannot reasonably expect the smaller withdrawal to
          capture groundwater from the far side of the divide; (3) that modeling
          the divide as an essentially impermeable boundary (with an image well)
          is reasonable and appropriate to evaluate the additional drawdown
          arising from the increase if such an evaluation is restricted to the
          vicinity of the smaller well.

          I have been challenged (in court, sadly, yes) in the use of an image
          well and thus, for the underlying assumption that the groundwater divide
          essentially acts as a no-flow boundary. I seek scholarly or governmental
          citation(s) supporting (or I suppose, refuting) what to be seemed (1)
          reasonable and (2) the only way analytically I know to segregate the
          effect of the 5% withdrawal increase from the 800 lb gorilla in my
          hydrogeologic closet with me (the larger user). Remember, numerical
          modeling is judged overkill by the agency for permitting evaluations of
          this nature.

          Thoughts? Comments? Am I off the wacko deep end of indefensibility?
          Thanks.
        • Jonathan Welch
          Mark The answer appears to be in the question. A pumping induced groundwater divide will be affected by a change in the ratio of pumping rates between
          Message 4 of 8 , Mar 3, 2007
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            Mark

            The answer appears to be in the question. A pumping induced groundwater divide will be affected by a change in the ratio of pumping rates between interfering wells. The principle is one of superposition of drawdown which occurs linearly for confined conditions. Analytical or numerical solutions will demonstrate this phenomenon.

            Analytical methods could be used to test whether the movement in groundwater divide is significant for steady state. For highly stressed water resources it could be necessary to consider transient conditions leading up to periods of drought in order to assess the impact of a change to the groundwater divide.

            Perhaps you need to find out if the groundwater divide is really pumping induced. This could be done with a sophisticated analytic elements program, or by numerical methods. However you will need detailed knowledge of leakage into the aquifer and a fully calibrated and verifiable model to predict future conditions.

            Regards,
            Jonathan

            ----- Original Message -----
            From: Mark Eisner
            To: gwmodel@yahoogroups.com
            Sent: Thursday, March 01, 2007 3:21 PM
            Subject: [gwmodel] use of image wells to analytically model groundwater divides


            I am seeking professional or scholarly citations (textbooks, USGS references, etc.) providing guidelines for handling groundwater divides in an analytical groundwater flow model (yes, I know this is yesteryear).

            Consider the circumstance of two interfering municipal production wells separated by (say) five miles in a highly transmissive, confined aquifer. The Theis assumptions are reasonably met other than with respect to a pumping-induced groundwater divide that exists between the two users. One well pumps four times the rate of the other. The aforementioned groundwater divide now exists between the two. The larger use remains fixed, but the other withdrawal will increase if a permit is issued.

            The regulatory agency requires an evaluation of the increased drawdown associated specifically with the projected increase of the smaller well. The projected increase will bring the use of the smaller well from 20% to 25% of the total combined. I have contended that in such a scenario, (1) the location of the groundwater divide will remain essentially unchanged; (2) one cannot reasonably expect the smaller withdrawal to capture groundwater from the far side of the divide; (3) that modeling the divide as an essentially impermeable boundary (with an image well) is reasonable and appropriate to evaluate the additional drawdown arising from the increase if such an evaluation is restricted to the vicinity of the smaller well.

            I have been challenged (in court, sadly, yes) in the use of an image well and thus, for the underlying assumption that the groundwater divide essentially acts as a no-flow boundary. I seek scholarly or governmental citation(s) supporting (or I suppose, refuting) what to be seemed (1) reasonable and (2) the only way analytically I know to segregate the effect of the 5% withdrawal increase from the 800 lb gorilla in my hydrogeologic closet with me (the larger user). Remember, numerical modeling is judged overkill by the agency for permitting evaluations of this nature.

            Thoughts? Comments? Am I off the wacko deep end of indefensibility? Thanks.
          • hydrosolve
            Mark, You may find the following publication useful in regard to image well theory: Theory of Aquifer Tests by Ferris et al. (1962) You can download a PDF
            Message 5 of 8 , Mar 3, 2007
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              Mark,

              You may find the following publication useful in regard to image well
              theory:

              "Theory of Aquifer Tests" by Ferris et al. (1962)

              You can download a PDF version of this report at:

              http://pubs.usgs.gov/wsp/wsp1536-E/

              You will find more free publications relating to aquifer testing at
              the AQTESOLV Users Group:

              http://tech.groups.yahoo.com/group/AQTESOLV/

              Just join the group to access the links.

              Kind regards,
              Glenn

              Glenn M. Duffield
              HydroSOLVE, Inc.
              AQTESOLV: http://www.aqtesolv.com/
              HydroSOLVE, Inc.: http://www.hydrosolveinc.com/hydrosolve/
              Aquifer Test Forum: http://www.aquifertest.com/forum/
              Blog: http://aqtesolv.blogspot.com/
            • Pradeep Raj
              Dear Sir, I think this is very interesting. One of the finest treatment of the topic is in 2nd edition of that fantastic book by Driscol (what was earlier
              Message 6 of 8 , Mar 3, 2007
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                Dear Sir,

                I think this is very interesting. One of the finest treatment of the topic is in 2nd edition of that fantastic book by Driscol (what was earlier known as JOHNSON'S GROUNDWATER AND WELLS).

                He has given some examples that are directly related to Municipal supplies.

                I hope this is useful.

                Regards
                Pradeep


                "Wilsnack, Mark" <mwilsnac@...> wrote:
                Dear Sir:

                No, you are not off base. The use of image wells may be legitimate. Have
                a look at Strack (1989) and Haitjema (1995) to see how this approach is
                used. Also, I once saw the legendary Jay Lehr demonstrate its use in a
                training session about 15 years ago.

                Best Wishes,

                Mark
                SFWMD
                ========================================================================
                =

                -----Original Message-----
                From: gwmodel@yahoogroups.com [mailto:gwmodel@yahoogroups.com] On Behalf
                Of Mark Eisner
                Sent: Thursday, March 01, 2007 10:21 AM
                To: gwmodel@yahoogroups.com
                Subject: [gwmodel] use of image wells to analytically model groundwater
                divides

                I am seeking professional or scholarly citations (textbooks, USGS
                references, etc.) providing guidelines for handling groundwater divides
                in an analytical groundwater flow model (yes, I know this is
                yesteryear).

                Consider the circumstance of two interfering municipal production wells
                separated by (say) five miles in a highly transmissive, confined
                aquifer. The Theis assumptions are reasonably met other than with
                respect to a pumping-induced groundwater divide that exists between the
                two users. One well pumps four times the rate of the other. The
                aforementioned groundwater divide now exists between the two. The larger
                use remains fixed, but the other withdrawal will increase if a permit is
                issued.

                The regulatory agency requires an evaluation of the increased drawdown
                associated specifically with the projected increase of the smaller well.
                The projected increase will bring the use of the smaller well from 20%
                to 25% of the total combined. I have contended that in such a scenario,
                (1) the location of the groundwater divide will remain essentially
                unchanged; (2) one cannot reasonably expect the smaller withdrawal to
                capture groundwater from the far side of the divide; (3) that modeling
                the divide as an essentially impermeable boundary (with an image well)
                is reasonable and appropriate to evaluate the additional drawdown
                arising from the increase if such an evaluation is restricted to the
                vicinity of the smaller well.

                I have been challenged (in court, sadly, yes) in the use of an image
                well and thus, for the underlying assumption that the groundwater divide
                essentially acts as a no-flow boundary. I seek scholarly or governmental
                citation(s) supporting (or I suppose, refuting) what to be seemed (1)
                reasonable and (2) the only way analytically I know to segregate the
                effect of the 5% withdrawal increase from the 800 lb gorilla in my
                hydrogeologic closet with me (the larger user). Remember, numerical
                modeling is judged overkill by the agency for permitting evaluations of
                this nature.

                Thoughts? Comments? Am I off the wacko deep end of indefensibility?
                Thanks.
              • syed hashmath
                Hi all, Is there any option of exporting top, bottom, K, S, Rch etc in VMOD. I wish to export them in ascii (x,y,z) or in grid format. Regards, Hash
                Message 7 of 8 , Mar 10, 2007
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                  Hi all,

                  Is there any option of exporting top, bottom, K, S, Rch etc in VMOD. I wish to export them in ascii (x,y,z) or in grid format.

                  Regards,
                  Hash
                • Patrick Delaney
                  Hello Syed, In order to export the data in xyz grid format you need to have that data as active in Visual MODFLOW. For example, if you wanted to export the K
                  Message 8 of 8 , Mar 11, 2007
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                    Hello Syed,

                    In order to export the data in xyz grid format you need to have that data as
                    active in Visual MODFLOW. For example, if you wanted to export the K values,
                    you need to go to the Input mode and open the Conductivity Input screen.
                    Then select File/Export Data and you will be able to choose from a variety
                    of export formats.

                    Hope this helps.

                    Patrick Delaney


                    >From: syed hashmath <hashmath01@...>
                    >Reply-To: gwmodel@yahoogroups.com
                    >To: gwmodel@yahoogroups.com
                    >CC: visual-modflow@...
                    >Subject: [gwmodel] Exporting in VMOD
                    >Date: Sat, 10 Mar 2007 19:52:36 -0800 (PST)
                    >
                    >Hi all,
                    >
                    > Is there any option of exporting top, bottom, K, S, Rch etc in VMOD. I
                    >wish to export them in ascii (x,y,z) or in grid format.
                    >
                    > Regards,
                    > Hash
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