Computer program for ground-water systems: "Documentation of finite-difference model for simulation of three-dimensional ground-water flow," UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY RESTON, VIRGINIA 22092 GW Branch November 7, 1975 4351 5016 GROUND WATER BRANCH TECHNICAL MEMORANDUM NO. 76.05 Subject: GROUND WATER - Computer program for ground-water systems: "Documentation of finite- difference model for simulation of three-dimensional ground-water flow," by Peter C. Trescott. The attached open-filed report by Peter Trescott, presently available only in limited quantity, provides documentation for a computer program that extends our simulation capability of ground- water systems, from two specialists concerned with aquifer modeling studies. Because some aquifer systems can not be represented adequately by two-dimensional approximations, this program overcomes one of the important limitations associated with two-dimensional models. Trescott's program permits consideration of an aquifer system that is heterogeneous, anisotropic, and irregularly bounded. Stresses on the system may be in the form of well discharge, well recharge, and recharge from precipitation. The program can be used to simulate three-dimensional aquifer systems, and can simulate efficiently quasi-three-dimensional systems consisting of two- dimensional aquifers separated by intervening confining layers. The upper aquifer can occur under water-table conditions and the model can handle multiple pumping periods. Requests for additional copies of this documentation or for copies of the card deck should be directed to: Mr. Ralph N. Eicher, Chief Office of Teleprocessing, MS 805 U.S. Geological Survey Reston, Virginia 22092 This report, and an updated version of Trescott's 2-D aquifer model, are being readied for publication as TWRI's. (s) Charles A. Appel for Chief, Ground Water Branch Water Resources Division Enclosure WRD DISTRIBUTION: A, FO-L(w/attach), S(w/o attach), SL (w/o attach) Subdistrict Offices