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VO/VO/Vu UV:47 X731U �379 5LLU 11' U)KF MAKfINEZ LFJVU3/Uva 1. Dn RODUCTION VLEACH, A One-Dimensional Finite Difference Vadvse Zone Leaching Model, is a computer code for estimating the impact due to the mobilization and migration of a sorbed organic contaminant located in the vadose zone on the underlying groundwater resource. The model was initially developed by CHzM Hill for the U.S.Environmental protection Agency.Region IX in 1990. In particular,the model was designod specifically on the Phoenix-C3oodyear Airport Supcxfund site where it was used successfully to evaluate groundwaterimpacts and volatilization of volatile organic contaminants(Rosenbloom et al.,1993). Since that time the code has been utilizedatnumerous sites to assess the potential groundwater impacts from existing soil contaminants and in soil vapor projects.Due to the increasing use of VLEACH,work was conducted to develop a more user-friendly version of the software along with a more comprehensive user's guide. In particular,version 2.0 incorporates the following changes from version 1.1: 1) the addition of an user interface menu; 2) the user can specify any input file name rather than always having to define the file as"BATCH.1Np"; ' 3) the development of two plot files: (i)groundwater impact as a function of time and(ii) soil concentration versus depth at a user-specified time; 4) units for C.,were added to the output file printout; and 5) a common statement,"COMMON/BDRY/CINF,CATM,COW',which defines the boundary condition parameter was added to the MQUIL subroutine. Although VLEACH employs a number of major assumptions, it can be useful in making preliminary assessments of the potential impacts of contaminants within the vadose zone. Hence, it is the principle objective of the User's Guide to provide essential information on such important ' aspects as model conceptualization,model theory, assumptions and limitations, determination of input parameters,analysis of results and sensitivity analysis(parameter studies). itis anticipated that the information presented in this manual will aid the model user in making the best possible application of VLEACH.