File: ABSTRACT.TXT

                      3DFEMWATER/3DLEWASTE
    Numerical Codes for Delineating Wellhead Protection Areas
                     in Agricultural Regions
          Based on the Assimilative Capacity Criterion
                          Version 1.00

                            July 1993


         Center for Exposure Assessment Modeling (CEAM)
              U.S. Environmental Protection Agency
               Office of Research and Development
                Environmental Research Laboratory
                    960 College Station Road
                   Athens, Georgia  30605-2720

                          706/355-8420



_________________________________________________________________

Summary

The 1986 Amendments to the Safe Drinking Water Act require each
State to develop and submit to the U.S. EPA a wellhead protection
program.  As part of the program, States must establish
procedures for delineating wellhead protection areas around each
water well or well field which supplies a public water system.
Of the five criteria that have been suggested by the U.S. EPA for
delineating wellhead protection areas, the assimilative capacity
criterion is potentially the most accurate.  It takes into
account the reduction in concentration of contaminants being
transported toward a well caused by chemical and environmental
processes at the land surface and in the vadose and saturated
zones.  

Nationwide, agricultural areas are located in many diverse
hydrogeologic environments.  Recharge and pumping rates can vary
widely within an area because of irrigation practices and/or
climate.  In addition, contamination scenarios must consider
multiple point and nonpoint source loadings of pesticides which
vary both spatially and temporally.  In order to delineate
wellhead protection areas in agricultural regions using the
assimilative capacity criterion, the use of a numerical model
which accounts for 1) flow and transport in three-dimensional
variably-saturated porous media under transient conditions, 2)
multiple distributed and point sources/sinks, and 3) processes
which retard the transport of contaminants, is needed.  

This document describes two related numerical codes, 3DFEMWATER
and 3DLEWASTE, which can be used to delineate wellhead protection
areas in agricultural regions using the assimilative capacity
criterion.  3DFEMWATER (A Three-dimensional Finite Element Model
of WATER Flow through Saturated-Unsaturated Media) simulates
subsurface flows, whereas 3DLEWASTE (A Hybrid Three-Dimensional
Lagrangian-Eulerian Finite Element Model of WASTE Transport
through Saturated-Unsaturated Media) models contaminant
transport.  Both codes 1) treat heterogeneous and anisotropic
media consisting of as many geologic formations as desired, 2)
consider both distributed and point sources/sinks that are
spatially and temporally dependent, and 3) accept four types of
boundary conditions (i.e., Dirichlet (fixed-head or
concentration), specified-flux, Neumann (specified-pressure-head
gradient or specified-dispersive flux), and variable).  The
variable boundary condition in 3DFEMWATER simulates
evaporation/infiltration/ seepage on the soil-air interface and
in 3DLEWASTE, simulates mass infiltration into or advection out
of the system.  3DLEWASTE contains options to model adsorption
using a linear, Freundlich, or Langmuir isotherm, dispersion, and
first-order decay.

This report was submitted in partial fulfillment of Work
Assignment Number 1, Contract Number 68-CO-0019 by AQUA TERRA
Consultants, under the sponsorship of the U.S. Environmental
Protection Agency.  This report covers the period May 1991 to
July 1992, and work was completed as of August 1992.