airslug(1) U.S. Geological Survey (wrdapp) airslug(1) NAME airslug - A Fortran program to generate type curves to interpret the recovery data from prematurely terminated air-pressurized slug tests ABSTRACT 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). METHOD 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 storativity. HISTORY Version 1.1 1996/03/12 - First UNIX release Version 1.0 1996/02/01 - Original release DATA REQUIREMENTS 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 7 Jul 1998 1 airslug(1) U.S. Geological Survey (wrdapp) airslug(1) 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 alpha. OUTPUT OPTIONS 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. SYSTEM REQUIREMENTS 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. APPLICATIONS 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. DOCUMENTATION 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. RELATED DOCUMENTATION 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. CONTACTS Operation: U.S. Geological Survey Branch of Regional Research Earl A. Greene 7 Jul 1998 2 airslug(1) U.S. Geological Survey (wrdapp) airslug(1) 431 National Center Reston, VA 20192 eagreene@usgs.gov U.S. Geological Survey Office of Hydrologic Research Allen M. Shapiro 431 National Center Reston, VA 20192 ashapiro@usgs.gov Distribution: U.S. Geological Survey Hydrologic Analysis Software Support Program 437 National Center Reston, VA 20192 h2osoft@usgs.gov Official versions of U.S. Geological Survey water-resources analysis software are available for electronic retrieval via the World Wide Web (WWW) at: http://water.usgs.gov/software/ and via anonymous File Transfer Protocol (FTP) from: water.usgs.gov (path: /pub/software). The WWW page and anonymous FTP directory from which the AIRSLUG software can be retrieved are, respectively: http://water.usgs.gov/software/airslug.html --and-- /pub/software/ground_water/airslug 7 Jul 1998 3