NETPATH is an interactive Fortran 77 computer program used to interpret net geo^hemical mass-balance reactions between an initial and final water along a hydrologic flow path. Alternatively, NETPATH computes the mixing proportions of two to five initial waters and net geo^hemical reactions that can account for the observed composition of a final water. The program utilizes previously defined chemical and isotopic data for waters from a hydrochemical system. For a set of mineral and (or) gas phases hypothesized to be the reactive phases in the system, NETPATH calculates the mass transfers in every possible combination of the selected phases that accounts for the observed changes in the selected chemical and (or) isotopic compositions observed £,long the flow path. The calculations are of use in interpreting geochemical reactions, mixing prooortions, evaporation and (or) dilution of waters, and mineral mass transfer in the chemical and isotopic evolution of natural and environmental waters. Rayleigh distillation calculations are applied to each mass-balance model that satisfies the constraints to predict carbon, sulfur, nitrogen, and strontium isotopic compositions at the end point, including radiocarbon dating. DB is an interactive Fortran 77 computer program used to enter analytical data into NETPATH, and calculate the distribution of species in aqueous solution. This report describes the types of problems that can be soVed, the methods used to solve problems, and the features available in the program to facilitate these solutions. Examples are presented to demonstrate most of the applications and features of NETPATH. The codes DB and NETPATH can be executed in the UNIX or DOS 1 environment. This report replaces U.S. Geological Survey Water-Resources Investigations Report 91-4078, by Plurrmer and others, which described the original release of NETPATH, version 1.0 (dated December, 1P91), and documents revisions and enhancements that are included in version 2.0. The use of trade, brand or product names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey. DB.FOR: This is the Fortran 77 source code of the database editing program, DB. The hydrochemical data and field information are entered and saved in the .LON file for later manipulation. DB.FOR also includes the program WATEQFP which is a generalized aqueous ion-arsociation model. WATEQFP is based on WATEQ (Truesdell and Jones, 1974), and WATEQF (Plummer and others, 1976), but is coded generally, with the data base of ion-association equilibria defined in an external data file, DB.DAT. Thermodynamic data in DB.DAT are consistent with current versions of WATEQ4F (Ball and Nordstrom, 1991) and PHREEQE (Parkl urst and others, 1980), and may be edited as needed. Current thermodynamic data used in the WATEQgeneration ion-association models are described by Nordstrom and others (1990). WATEQFP is used to calculate the distribution of aqueous species and mineral saturation indices, and to construct the inp...
