Water Resources Applications Software

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Summary of AIRSLUG

       airslug - A Fortran program to generate type curves to interpret the
                 recovery data from prematurely terminated air-pressurized
                 slug tests

       Air-pressurized slug tests offer an efficient means of estimating
       the transmissivity (T) and storativity (S) of aquifers.  Air-
       pressurized slug tests are conducted by pressurizing the air in the
       casing above the column of water in a well, monitoring the declining
       water level and then releasing the air pressure and monitoring the
       rising water level.  The equipment needed to conduct an air-
       pressurized slug test is easily constructed and assembled at the top
       of the well.  The only equipment in contact with the water is a
       down-hole sensor to monitor water levels.  During the pressurized
       part of the test, fluctuations in the applied air pressure result in
       water-level fluctuations, making it difficult to estimate T and S
       from the declining water-level data.  However, if the applied air
       pressure is maintained until a new equilibrium-water level is
       achieved and then the air pressure in the well is released
       instantaneously, the slug test solution developed by Cooper and
       others (1967) can be used to estimate T and S from the rising water-
       level data.  In low-permeability formations, it may take an extended
       period of time to achieve the new equilibrium-water level for the
       applied air pressure.  The total time to conduct the test can be
       reduced, however, if the pressurized part of the test is terminated
       prior to achieving the new equilibrium-water level.  This is
       referred to as a prematurely terminated air-pressurized slug test.
       Type curves generated from the solution of Shapiro and Greene (1995)
       can be used to estimate T and S from the rising water-level data
       (recovery) from prematurely terminated air-pressurized slug tests.
       The Fortran code AIRSLUG, is used to generate the type curves from
       the solution of Shapiro and Greene (1995).

       In conducting the prematurely terminated air-pressurized slug test,
       the column of air in the well is subject to a constant applied air
       pressure (pressurized part of test) and then instantaneously reduced
       to atmospheric pressure (recovery part of test).  The drawdown data
       during the recovery part of the test are interpreted with the type
       curves generated in this program to estimate transmissivity and

       Version 1.1 1996/03/12 - First UNIX release

       Version 1.0 1996/02/01 - Original release

       The code is completely interactive and requires no data sets.  The
       program prompts the user for the needed data input.  The user will
       need to supply input in response to prompts for: (1)  DRDELT, which
       is the fraction of the maximum water-level change for the applied
       air-pressure, (2) an output file name, and (3) the number of type
       curves desired.  If all nine type curves are selected, the program
       generates type curves for all nine values of alpha.  If the user
       selects one type curve, then the user must enter their own value of

       The output is stored in the file named by the user.  The user can
       then generate plots of the type curves using external software
       plotting packages.  The values defining the type curves are in 10
       columns.  The first column contains dimensionless times, at which
       the dimensionless drawdowns are evaluated.  Columns 2 through 10
       contain dimensionless drawdowns for the dimensionless times given in
       the first column; each column corresponds to a type curve for a
       different value of alpha, alpha = 1.0E-1, 1.0E-2, ... 1.0E-9.  The
       user of AIRSLUG alternatively can specify that a single type curve
       be generated for a specific value of alpha.  In this case, the
       program will generate values for only one type curve and store them
       in a file prescribed by the user.  The values defining the type
       curve will be stored in 2 columns; the first column contains the
       dimensionless time and the second column contains the dimensionless
       water levels for the specified value of alpha.

       AIRSLUG is written in Fortran 77 with the following extensions:  use
       of COMPLEX*16 variables and functions.  Generally, the program is
       easily installed on most computer systems.  The code has been used
       on UNIX-based computers and DOS-based 386 or greater computers
       having a math coprocessor and 4 mb of memory.

       AIRSLUG is used to generate type curves needed to estimate
       transmissivity and storativity from water level data collected
       during the recovery part of an air-pressurized slug test.

       Greene, E.A., and Shapiro, A.M., 1995, Methods of conducting air-
          pressurized slug tests and computation of type curves for
          estimating transmissivity and storativity: U.S. Geological Survey
          Open-File Report 95-424, 43 p.

       Shapiro, A.M., and Greene, E.A., 1995, Interpretation of prematurely
          terminated air-pressurized slug tests: Ground Water, v. 33, no.
          4, p.  539-546.

       Cooper, H.H., Jr., Bredehoeft, J.D., and Papadopulos, I.S., 1967,
          Response of a finite-diameter well to an instantaneous charge of
          water: Water Resources Research, v. 3, no. 1, p. 263-269.

          U.S. Geological Survey
          Branch of Regional Research
          Earl A. Greene
          431 National Center
          Reston, VA 20192

          U.S. Geological Survey
          Office of Hydrologic Research
          Allen M. Shapiro
          431 National Center
          Reston, VA 20192

          U.S. Geological Survey
          Hydrologic Analysis Software Support Program
          437 National Center
          Reston, VA 20192

       Official versions of U.S. Geological Survey water-resources analysis
       software are available for electronic retrieval via the World Wide
       Web (WWW) at:


       and via anonymous File Transfer Protocol (FTP) from:

         (path: /pub/software).

       The WWW page and anonymous FTP directory from which the AIRSLUG
       software can be retrieved are, respectively:


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