GROUND WATER -- Release of OFR 94-59, "Documentation of a Computer Program to Simulate Transient Leakage from Confining Units Using the Modular Finite-Difference Ground-Water Flow Model" by S.A. Leake, P. Patrick Leahy, and Anthony S. Navoy In Reply Refer To: July 12, 1994 Mail Stop 411 OFFICE OF GROUND WATER TECHNICAL MEMORANDUM 94.04 Subject: GROUND WATER -- Release of OFR 94-59, "Documentation of a Computer Program to Simulate Transient Leakage from Confining Units Using the Modular Finite- Difference Ground-Water Flow Model" by S.A. Leake, P. Patrick Leahy, and Anthony S. Navoy The subject report describes the addition of a Transient Leakage (TLK) Package to the U.S. Geological Survey modular model, MODFLOW. The TLK Package simulates transient leakage into or out of a compressible, fine-grained confining unit as a result of ground-water storage changes. The TLK Package works by solving equations defining the flow across the confining unit boundaries. The method generally requires considerably less computational effort and computer memory than using multiple model layers to simulate the confining unit. We recommend that this report be brought to the attention of technical and management personnel concerned with ground-water modeling studies. A version of MODFLOW has been created that incorporates the TLK Package along with most of the other published MODFLOW additions. The Hydrologic Analysis Support Section (HASS) is handling the distribution of this program within the Water Resources Division. HASS recently sent an electronic mail message to all system administrators describing how to retrieve and install a compiled version of this program for use on Data General computers. To determine if the updated version of MODFLOW has been installed on your computer, issue the following command: what /usr/opt/bin/modflow Several lines of information should appear on your computer display, and one of these lines should state that the version is 2.4. If this version of MODFLOW has not been installed on your computer, contact your system administrator. If there are problems installing the software or if you would like the source code for the program, contact HASS by electronic mail (wrdapp) or by phone (Steve Regan 703-648-5896). Additional copies of the report are available from Stan Leake in the Arizona District. Sincerely, /s/ William M. Alley Chief, Office of Ground Water Distribution: A and B (memo only) S, FO, and PO (memo and report)