File: ABSTRACT.TXT PRZM Model System Abstract Center for Exposure Assessment Modeling (CEAM) National Exposure Research Laboratory - Ecosystems Research Division Office of Research and Development (ORD) U.S. Environmental Protection Agency (U.S. EPA) 960 College Station Road Athens, Georgia 30605-2700 706/355-8400 ----------------------------------------------------------------------------- Summary This publication contains documentation for the PRZM-3 model. PRZM-3 is the most recent version of a modeling system that links two subordinate models-- PRZM and VADOFT--in order to predict pesticide transport and transformation down through the crop root and unsaturated zone. Enhancements to Release 3.0 include algorithms that enable modeling of nitrogen cycle soil kinetic processes with the ability to track nitrogen discharges from a septic tank into the soil environment and movement to groundwater. Additional enhancements enable better simulation of physicochemical processes, increased flexibility in representing agronomic practices, and improved post-processing and data interpretation aids. PRZM is a one-dimensional, finite-difference model that accounts for pesticide and nitrogen fate in the crop root zone. PRZM-3 includes modeling capabilities for such phenomena as soil temperature simulation, volatilization and vapor phase transport in soils, irrigation simulation, microbial transformation, and a method of characteristics (MOC) algorithm to eliminate numerical dispersion. PRZM is capable of simulating transport and transformation of the parent compound and as many as two daughter species. VADOFT is a one-dimensional, finite-element code that solves the Richard's equation for flow in the unsaturated zone. The user may make use of constitutive relationships between pressure, water content, and hydraulic conductivity to solve the flow equations. VADOFT may also simulate the fate of two parent and two daughter products. The PRZM and VADOFT codes are linked together with the aid of a flexible execution supervisor that allows the user to build loading models that are tailored to site-specific situations. In order to perform probability-based exposure assessments, the code is also equipped with a Monte Carlo pre- and post-processor. Disclaimer The information in the PRZM3 User's Manual has been funded wholly or in part by the United States Environmental Protection Agency under Contract No. 68-C6-0020 to HydroGeoLogic, Inc. It has not been subject to the Agency's peer and administrative review, and therefore it has not been approved for publication as an EPA document. Certain of the model code enhancements have received preliminary evaluation by either AQUA TERRA Consultants, Waterborne Environmental, Inc. or the U.S. Environmental Protection Agency. Additional peer and administration review and testing is ongoing, but not yet completed. In no event shall AQUA TERRA Consultants or Waterborne Environmental, Inc. be liable for any loss of profit or any commercial damage, including but not limited to special, consequential, or other damages resulting from the use of this software. Mention of trade names of commercial products does not constitute endorsement or recommendation for use by the U.S. Environmental Protection Agency. Documentation The PRZM3 User's Manual is available as WordPerfect (version 6.1) documents in (binary, non-ASCII) files INTRO.WPD, CHAP1.WPD, CHAP2.WPD, CHAP3.WPD, CHPT4.WPD, CHAP5.WPD, CHPT6.WPD, CHAP7.WPD, CHAP8.WPD, CHAP9.WPD, CHAP10.WPD, and CHAP11.WPD within the DOCUMENT sub-directory. Refer to file READ.ME in the README sub-directory for further information on the storage format and hardware and/or software print/view requirement(s) of the user's manual files. -----------------------------------------------------------------------------